Imaging Technology

MEDICAL IMAGING

Medical imaging is the technique and process used to create images of the human body (or parts and function thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology).

Medical imaging is often perceived to designate the set of techniques that noninvasively produce images of the internal aspect of the body. In this restricted sense, medical imaging can be seen as the solution of mathematical inverse problems. This means that cause (the properties of living tissue) is inferred from effect (the observed signal). In the case of ultrasonography the probe consists of ultrasonic pressure waves and echoes inside the tissue show the internal structure. In the case of projection radiography, the probe is X-ray radiation which is absorbed at different rates in different tissue types such as bone, muscle and fat.

Imaging technology Page 1

Medical radiography

X-radiation is a form of electromagnetic radiation. These 2D techniques are still in wide use despite the advance of 3D tomography due to the low cost, high resolution, and depending on application, lower radiation dosages. This imaging modality utilizes a wide beam of x rays for image acquisition and is the first imaging technique available in modern medicine.

History

Wilhelm Conrad Röntgen is usually credited as the discoverer of X-rays because he was the first to systematically study them, though he is not the first to have observed their effects. He is also the one who gave them the name "X-rays", though many referred to these as "Röntgen rays" for several decades after their discovery.

X-rays were found emanating from Crookes tubes, experimental discharge tubes invented around 1875, by scientists investigating the cathode rays, that is energetic electron beams, that were first created in the tubes. Crookes tubes created free electrons by ionization of the residual air in the tube by a high DC voltage of anywhere between a few kilovolts and 100 kV. This voltage


accelerated the electrons coming from the cathode to a high enough velocity that they created X-rays when they struck the anode or the glass wall of the tube. Many of the early Crookes tubes undoubtedly radiated X-rays, because early researchers noticed effects that were attributable to them, as detailed below. Wilhelm Röntgen was the first to systematically study them, in 1895.

Among the important early researchers in X-rays were Ivan Pulyui, William Crookes, Johann Wilhelm Hittorf, Eugen Goldstein, Heinrich Hertz, Philipp Lenard, Hermann von Helmholtz, Nikola Tesla, Thomas Edison, Charles Glover Barkla, Max von Laue, and Wilhelm Conrad Röntgen.

Johann Hittorf

German physicist Johann Hittorf (1824–1914), a coinventor and early researcher of the Crookes tube, found when he placed unexposed photographic plates near the tube, that some of them were flawed by shadows, though he did not investigate this effect.

In 1877 Ukranian-born Pulyui, a lecturer in experimental physics at the University of Vienna, constructed various designs of vacuum discharge tube to investigate their properties. He continued his investigations when appointed professor at the Prague Polytechnic and in 1886 he found that that sealed photographic plates became dark when exposed to the emanations from the tubes. Early in 1896, just a few weeks after Röntgen published his first X-ray photograph, Pulyui published high-quality X-ray images in journals in Paris and London. Although Pulyui had studied with Röntgen at the University of Strasbourg in the years 1873–75, his biographer Gaida (1997) asserts that his subsequent research was conducted independently.

Nikola Tesla

In April 1887, Nikola Tesla began to investigate X-rays using high voltages and tubes of his own design, as well as Crookes tubes. From his technical publications, it is indicated that he invented and developed a special single-electrode X-ray tube, which differed from other X-ray tubes in having no target electrode. The principle behind Tesla's device is called the Bremsstrahlung process, in which a high-energy secondary X-ray emission is produced when charged particles (such as electrons) pass through matter. By 1892, Tesla performed several such experiments, but he did not categorize the emissions


as what were later called X-rays. Tesla generalized the phenomenon as radiant energy of "invisible" kinds. Tesla stated the facts of his methods concerning various experiments in his 1897 X-ray lecture before the New York Academy of Sciences. Also in this lecture, Tesla stated the method of construction and safe operation of X-ray equipment. His X-ray experimentation by vacuum high field emissions also led him to alert the scientific community to the biological hazards associated with X-ray exposure.

Fernando Sanford

X-rays were generated and detected by Fernando Sanford (1854–1948), the foundation Professor of Physics at Stanford University, in 1891. From 1886 to 1888 he had studied in the Hermann Helmholtz laboratory in Berlin, where he became familiar with the cathode rays generated in vacuum tubes when a voltage was applied across separate electrodes, as previously studied by Heinrich Hertz and Philipp Lenard. His letter of January 6, 1893 (describing his discovery as "electric photography") to The Physical Review was duly published and an article entitled Without Lens or Light, Photographs Taken With Plate and Object in Darkness appeared in the San Francisco Examiner. Philipp Lenard

Philipp Lenard, a student of Heinrich Hertz, wanted to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube (later called a "Lenard tube") with a "window" in the end made of thin aluminum, facing the cathode so the cathode rays would strike it. He found that something came through, that would expose photographic plates and cause fluorescence. He measured the penetrating power of these rays through various materials. It has been suggested that at least some of these "Lenard rays" were actually X-rays. Hermann von Helmholtz formulated mathematical equations for X-rays. He postulated a dispersion theory before Röntgen made his discovery and announcement. It was formed on the basis of the electromagnetic theory of light. However, he did not work with actual X-rays.

Wilhelm Röntgen

On November 8, 1895, German physics professor Wilhelm Conrad Röntgen stumbled on X-rays while experimenting with Lenard and Crookes tubes and began studying them. He wrote an initial report "On a new kind of ray: A preliminary communication" and on December 28, 1895 submitted it to the Würzburg's Physical-Medical Society journal. This was the first paper written


on X-rays. Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation. The name stuck, although (over Röntgen's great objections) many of his colleagues suggested calling them Röntgen rays. They are still referred to as such in many languages, including German. Röntgen received the first Nobel Prize in Physics for his discovery.

There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: Röntgen was investigating cathode rays with a fluorescent screen painted with barium platinocyanide and a Crookes tube which he had wrapped in black cardboard so the visible light from the tube wouldn't interfere. He noticed a faint green glow from the screen, about 1 meter away. He realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow. He found they could also pass through books and papers on his desk. Röntgen threw himself into investigating these unknown rays systematically. Two months after his initial discovery, he published his paper.

Röntgen discovered its medical use when he saw a picture of his wife's hand on a photographic plate formed due to X-rays. His wife's hand's photograph was the first ever photograph of a human body part using X-rays.

Thomas Edison

In 1895, Thomas Edison investigated materials' ability to fluoresce when exposed to X-rays, and found that calcium tungstate was the most effective substance. Around March 1896, the fluoroscope he developed became the standard for medical X-ray examinations. Nevertheless, Edison dropped X-ray research around 1903 after the death of Clarence Madison Dally, one of his glassblowers. Dally had a habit of testing X-ray tubes on his hands, and acquired a cancer in them so tenacious that both arms were amputated in a


futile attempt to save his life. At the 1901 Pan-American Exposition in Buffalo, New York, an assassin shot President William McKinley twice at close range with a .32 caliber revolver. The first bullet was removed but the second remained lodged somewhere in his stomach. McKinley survived for some time and requested that Thomas Edison "rush an X-ray machine to Buffalo to find the stray bullet. It arrived but wasn't used . . . . McKinley died of septic shock due to bacterial infection."

Frank Austin and the Frost brothers

The first medical X-ray made in the United States was obtained using a discharge tube of Pulyui's design. In January 1896, on reading of Röntgen's discovery, Frank Austin of Dartmouth College tested all of the discharge tubes in the physics laboratory and found that only the Pulyui tube produced X-rays. This was a result of Pulyui's inclusion of an oblique "target" of mica, used for holding samples of fluorescent material, within the tube. On 3 February 1896 Gilman Frost, professor of medicine at the college, and his brother Edwin Frost, professor of physics, exposed the wrist of Eddie McCarthy, whom Edwin had treated some weeks earlier for a fracture, to the X-rays and collected the resulting image of the broken bone on gelatin photographic plates obtained from Howard Langill, a local photographer also interested in Röntgen's work.

The 20th century and beyond

A male technician taking a x-ray of a female patient in 1940. This image was used to argue that exposure to radiation during the x-ray procedure would be a myth.

The many applications of X-rays immediately generated enormous interest. Workshops began making specialized versions of Crookes tubes for generating X-rays, and these first generation cold cathode or Crookes X-ray tubes were used until about 1920.

Crookes tubes were unreliable. They had to contain a small quantity of gas (invariably air) as a current will not flow in such a tube if they are fully evacuated. However as time passed the X-rays caused the glass to absorb the gas, causing the tube to generate "harder" X-rays until it soon stopped operating. Larger and more frequently used tubes were provided with devices for restoring the air, known as "softeners". These often took the form of a small side tube which contained a small piece of mica: a substance that traps


comparatively large quantities of air within its structure. A small electrical heater heated the mica and caused it to release a small amount of air, thus restoring the tube's efficiency. However the mica had a limited life and the restore process was consequently difficult to control.

In 1904, John Ambrose Fleming invented the thermionic diode valve (vacuum tube). This used a hot cathode which permitted current to flow in a vacuum. This idea was quickly applied to X-ray tubes, and heated cathode X-ray tubes, called Coolidge tubes, replaced the troublesome cold cathode tubes by about 1920.

Two years later, physicist Charles Barkla discovered that X-rays could be scattered by gases, and that each element had a characteristic X-ray. He won the 1917 Nobel Prize in Physics for this discovery. Max von Laue, Paul Knipping and Walter Friedrich observed for the first time the diffraction of X-rays by crystals in 1912. This discovery, along with the early works of Paul Peter Ewald, William Henry Bragg and William Lawrence Bragg gave birth to the field of X-ray crystallography. The Coolidge tube was invented the following year by William D. Coolidge which permitted continuous production of X-rays; this type of tube is still in use today.ROSAT image of X-ray fluorescence of, and occultation of the X-ray background by, the Moon

The use of X-rays for medical purposes (to develop into the field of radiation therapy) was pioneered by Major John Hall-Edwards in Birmingham, England. In 1908, he had to have his left arm amputated owing to the spread of X-ray dermatitis. The X-ray microscope was invented in the 1950s.

The Chandra X-ray Observatory, launched on July 23, 1999, has been allowing the exploration of the very violent processes in the universe which produce X-rays. Unlike visible light, which is a relatively stable view of the universe, the X-ray universe is unstable, it features stars being torn apart by black holes, galactic collisions, and novas, neutron stars that build up layers of plasma that then explode into space.

An X-ray laser device was proposed as part of the Reagan Administration's Strategic Defense Initiative in the 1980s, but the first and only test of the device (a sort of laser "blaster", or death ray, powered by a thermonuclear explosion) gave inconclusive results. For technical and political reasons, the overall project (including the X-ray laser) was de-funded (though was later


revived by the second Bush Administration as National Missile Defense using different technologies).

Technology

X-rays are generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target, the anode, creating the X-rays.

To make an X-ray image of human or animal bones, short X-ray pulses illuminate the body or limb, with radiographic film placed behind it. Any bones that are present absorb most of the X-ray photons by photoelectric processes. This is because bones have a higher electron density than soft tissues. Bones contain a high percentage of calcium (20 electrons per atom), potassium (19 electrons per atom) magnesium (12 electrons per atom), and phosphorus (15 electrons per atom). The X-rays that pass through the flesh leave a latent image in the photographic film. When the film is developed, the parts of the image corresponding to higher X-ray exposure are dark, leaving a white shadow of bones on the film.

To generate an image of the cardiovascular system, including the arteries and veins (angiography) an initial image is taken of the anatomical region of interest. A second image is then taken of the same region after iodinated contrast material has been injected into the blood vessels within this area. These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels. The radiologist or surgeon then compares the image obtained to normal anatomical images to determine if there is any damage or blockage of the vessel.

Variations

Two forms of radiographic images are in use in medical imaging; projection radiography and fluoroscopy, with latter useful for intraoperative and catheter guidance

* Fluoroscopy produces real-time images of internal structures of the body in a similar fashion to radiography, but employs a constant input of x-rays, at a lower dose rate. Contrast media, such as barium, iodine, and air are used to


visualize internal organs as they work. Fluoroscopy is also used in image-guided procedures when constant feedback during a procedure is required. An image receptor is required to convert the radiation into an image after it has passed through the area of interest. Early on this was a fluorescing screen, which gave way to an Image Amplifier (IA) which was a large vacuum tube that had the receiving end coated with cesium iodide, and a mirror at the opposite end. Eventually the mirror was replaced with a TV camera.

* Projectional radiographs, more commonly known as x-rays, are often used to determine the type and extent of a fracture as well as for detecting pathological changes in the lungs. With the use of radio-opaque contrast media, such as barium, they can also be used to visualize the structure of the stomach and intestines - this can help diagnose ulcers or certain types of colon cancer.

Contrast studies: When the density of adjacent tissues is similar, a radiopaque contrast agent is often added to one tissue or structure to differentiate it from its surroundings. Structures typically requiring a contrast agent include blood vessels (for angiography) and the lumina of the GI, biliary, and GU tracts. Gas may be used to distend the lower GI tract and make it visible. Other imaging tests (eg, CT, MRI) have largely replaced contrast studies as their tomographic images provide better anatomic localization of an abnormality.

Disadvantages Diagnostic accuracy is limited in many situations. Other imaging tests may provide better image detail, be safer or faster, or have other advantages.

Contrast agents such as barium and gastrografin, if used, have disadvantages, and IV contrast agents have risks Fluoroscopy may involve high doses of radiation.


Images

Pulmonary fibrosis may have many appearance. In this case, it is curvi-linear and runs parallel to the dome of the right hemi-diaphragm.

2) Colle’s fracture


3) Pneumonia

4)Degenerative knee jt.


Dual-Energy X-Ray Absorptiometry (DEXA)DEXA stands for 'dual energy X-ray Absorptiometry'. It is a test that measures the density of bones. Density means how much of something there is in a certain amount of space. The denser the tissues, the less X-rays pass through. Air and water are less dense than solid things such as bone. This is because the particles which make air and water are not held closely together. In general, the more dense the bone, the stronger it is, and the less likely it is to break.

There are two different types of DEXA scanning devices:

Central DEXA devices are large machines that can measure bone density in the centre of your skeleton, such as your hip and spine.

Peripheral DEXA devices are smaller, portable machines that are used to measure bone density on the periphery of your skeleton, such as your wrist, heel or finger

Technology

A DEXA scan uses low energy X-rays. A machine sends X-rays from two different sources through the bone being tested. Bone blocks a certain amount of the X-rays. The more dense the bone is, the fewer X-rays get through to the detector. By using two different X-ray sources rather than one it greatly improves the accuracy in measuring the bone density.

The amount of X-rays that comes through the bone from each of the two X-ray sources is measured by a detector. This information is sent to a computer which calculates a score of the average density of the bone. A low score indicates that the bone is less dense than it should be, some material of the bone has been lost, and is more prone to fracture.


Indication

A fracture following a minor fall or injury.

Loss of height due to fracture of a vertebra (back bone).

Taken steroid tablets for three months or more.

An early menopause (aged less than 45).

A history of periods stopping (amenorrhoea) for more than one year before the menopause.

Other disorders associated with osteoporosis such as rheumatoid arthritis or coeliac disease.

A family history of hip fracture on your mother's side.

A body mass index of less than 19. (That is, if you are very underweight.)

Digital radiography

Digital radiography is a form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.

Digital Radiography (DR) or (DX) is essentially filmless X-ray image capture. In place of X-ray film, a digital image capture device is used to record the X-ray image and make it available as a digital file that can be presented for interpretation and saved as part of the patient’s medical record. The advantages of DR over film include immediate image preview and availability, a wider dynamic range which makes it more forgiving for over- and under-exposure as well as the ability to apply special image processing techniques that enhance overall display of the image. The largest motivator for healthcare facilities to adopt DR is its potential to reduce costs associated with processing, managing and storing films. Typically there are two variants of digital image capture devices. These devices include Flat Panel detectors (FPDs), and High Density Line Scan Solid State detectors.


Historical milestones for Digital Panoramic Systems

1995 - DXIS, the world wide first dental digital panoramic X-rays system available on the market, introduced by Signet (France). DXIS targets to retrofit all the panoramic models.

1997 - SIDEXIS, of Siemens (currently Sirona, Germany) offered for Ortophos Plus panoramic unit, DigiPan of Trophy Radiology (France) offered for the OP100 panoramic made by Instrumentarium (Finland).

1998-2004 - many panoramic manufacturers offered their own digital system.

2005 - SCAN300FP, of Ajat (Finland) is the last one offered. It shows the feature to acquire many hundreds of mega bytes of image information at high frame rate and to reconstruct the panoramic layer by intensive post acquisition computing like a computed tomography. The main advantage is the ability to reconstruct focused differently. The drawback is the low signal/noise ratio of primary information which involves much software work for correction. Also the ability to reconstruct various layers raises the importance of the geometrical distortions already high in dental panoramic radiography.

Currently there are several digital systems for panoramic digital radiology. Some of them are rebranded. Examples: SCAN300FP of Ajat was or is sold as SuniPan or RetroPan or Panoramic Corporation pan, DXIS of Signet was or is sold also as of LightYear, Sigma Biomedics, Panoramic Corporation, AFP Digital or Bluex, iPan of Schick was or is sold as of Bluex or Panoramic Corporation, I-MAX of Owandy sold as of Villa, etc.


Magnetic resonance imaging

Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging (NMRI), is primarily a medical imaging technique most commonly used in radiology to visualize detailed internal structure and limited function of the body. MRI provides much greater contrast between the different soft tissues of the body than computed tomography (CT) does, making it especially useful in neurological (brain), musculoskeletal, cardiovascular, and oncological (cancer) imaging.

History

Magnetic resonance imaging is a relatively new technology. The first MR image was published in 1973 and the first cross-sectional image of a living mouse was published in January 1974. The first studies performed on humans were published in 1977. By comparison, the first human X-ray image was taken in 1895.

Technology

Unlike CT, it uses no ionizing radiation, but uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water in the body. Radio frequency (RF) fields are used to systematically alter the alignment of this magnetization, causing the hydrogen nuclei to produce a rotating magnetic field detectable by the scanner. This signal can be manipulated by additional magnetic fields to build up enough information to construct an image of the body.

The body is largely composed of water molecules which each contain two hydrogen nuclei or protons. When a person goes inside the powerful magnetic field of the scanner, the magnetic moments of these protons align with the direction of the field.

A radio frequency electromagnetic field is then briefly turned on, causing the protons to alter their alignment relative to the field. When this field is turned


off the protons return to the original magnetization alignment. These alignment changes create a signal which can be detected by the scanner. The frequency at which the protons resonate depends on the strength of the magnetic field. The position of protons in the body can be determined by applying additional magnetic fields during the scan which allows an image of the body to be built up. These are created by turning gradient coils on and off which creates the knocking sounds heard during an MR scan.

Diseased tissue, such as tumors, can be detected because the protons in different tissues return to their equilibrium state at different rates. By changing the parameters on the scanner this effect is used to create contrast between different types of body tissue.

Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumors or inflammation. Contrast agents may also be directly injected into a joint in the case of arthrograms, MR images of joints. Unlike CT, MRI uses no ionizing radiation and is generally a very safe procedure. Patients with some metal implants, cochlear implants, and cardiac pacemakers are prevented from having an MRI scan due to effects of the strong magnetic field and powerful radio frequency pulses.

Uses

MRI is preferred to CT when soft-tissue contrast resolution must be highly detailed (eg, to evaluate intracranial or spinal cord abnormalities, inflammation, trauma, suspected musculoskeletal tumors, internal joint derangement). MRI is also useful for evaluating the following:

Vascular imaging: Magnetic resonance angiography (MRA) is used to image arteries with good accuracy and is less invasive than conventional angiography. Gadolinium contrast is sometimes used. MRA can be used to image the thoracic and abdominal aorta and arteries of the brain, neck, kidney, and lower extremities. Venous imaging (magnetic resonance venography) can also be done.


Hepatic and biliary tract abnormalities: Magnetic resonance cholangiopancreatography (MRCP) is particularly valuable as a noninvasive, highly accurate method of imaging the biliary and pancreatic duct systems.

Masses in the female reproductive organs: MRI is used to characterize adnexal masses and to stage uterine tumors.

Certain fractures: For example, MRI can provide accurate images of hip fractures in patients with osteopenia.

Lytic bone metastases

MRI can also be substituted for CT with contrast in patients with a high risk of contrast reactions.

Contrast: With MRI, contrast agents may be used to highlight vascular structures (for magnetic resonance angiography) and to help characterize inflammation and tumors. The most commonly used agents are gadolinium derivatives, which have magnetic properties that affect proton relaxation times. MRI of intra-articular structures may include injection of a gadolinium derivative into a joint.

Variations

Diffusion (diffusion-weighted) MRI: Signal intensities are related to diffusion of water molecules in tissue. This type of MRI can be used to detect early cerebral ischemia and infarction and to differentiate intracranial cysts from solid masses.

Echo planar imaging: This ultrafast technique (images obtained in > 1 sec) is used for diffusion, perfusion, and functional imaging of the brain and heart. Its potential advantages include showing brain and heart activity and reducing motion artifacts. However, its use is limited because it requires special technical hardware and it is susceptible to other artifacts.

Functional MRI: Functional MRI is an imaging technique that assesses brain activity by location. In the most common type, the brain is scanned at low resolution very frequently (eg, every 2 to 3 sec). The change in oxygenated Hb can be discerned, which estimates metabolic activity. Mechanisms of various neural mechanisms can be studied in research settings.


Gradient echo imaging: Gradient echo is a pulse sequence that can be used for fast imaging of moving blood and CSF (eg, in magnetic resonance angiography). Because this technique is fast, it can reduce motion artifacts (eg, blurring) during imaging that requires patients to hold their breath (eg, during imaging of cardiac and abdominal structures).

Magnetic resonance spectroscopy (MRS): MRS combines the information obtained by MRI (mainly based on water and fat content of tissues) with that of nuclear magnetic resonance, or NMR; NMR provides information about tissue metabolites. Information on metabolites can help differentiate certain abnormalities (eg, certain types of tumors).

Perfusion MRI: Perfusion MRI is a method of assessing relative cerebral blood flow. It can be used to detect an area of ischemia during imaging for stroke.

Disadvantages

MRI is relatively expensive and may not be available or available immediately.

Magnetic field: MRI is relatively contraindicated in patients with implanted materials that can be affected by powerful magnetic fields. These materials include ferromagnetic metal (containing iron), magnetically activated or electronically controlled medical devices (eg, pacemakers, implantable cardioverter defibrillators, cochlear implants), and nonferromagnetic metal electronically conductive wires or materials (eg, pacemaker wires, certain pulmonary artery catheters). Ferromagnetic material may be moved by the strong magnetic field and injure a nearby organ; movement is more likely if the material has been in place < 6 wk (before scar tissue forms). Ferromagnetic material can also cause imaging artifacts. Magnetically activated medical devices may malfunction when exposed to magnetic fields. Magnetic fields may induce current in conductive materials; this current may produce enough heat to burn tissues. Whether a specific device is compatible with MRI depends on the type of device, its components, and its manufacturer. Also, MRI machines with different magnetic field strengths have different effects on materials, so safety in one machine does not ensure safety in another. The MRI magnetic field is very strong and always on. Thus, a ferromagnetic object (eg, an O2 tank, a metal pole) at the entrance of the scanning room may be pulled into the magnet bore at high velocity and injure anyone in its path. The only way to separate the object from the magnet may be to turn off the magnetic field.


Claustrophobia: The imaging tube of an MRI machine is a tight, enclosed space that can trigger claustrophobia even in patients without preexisting phobias or anxiety. Also, some obese patients do not fit on the table or within the machine. Premedication with an anxiolytic (eg, alprazolam or lorazepam 1 to 2 mg po) 15 to 30 min before scanning is effective for most anxious patients. MRI scanners with an open side can be used. Its images may be inferior to those of enclosed scanners depending on the field strength of the magnet, but they are usually sufficient for making a diagnosis. Patients should be warned that the MRI machine makes loud, banging noises.

Contrast reactions: Gadolinium derivatives, if used, can cause headache, nausea, and pain, as well as sensation of cold at the injection site. However, serious contrast reactions are rare and much less common than with iodinated contrast agents. However, in patients with impaired renal function, nephrogenic systemic fibrosis is a risk. Nephrogenic systemic fibrosis is a rare but life-threatening disorder that involves the skin and probably internal organs, resulting in severe disability or death. For patients with impaired renal function, the following is recommended:

Gadolinium should be used only when necessary.

Before this agent is used, renal function should be checked (eg, based on patient history or laboratory tests such as GFR).

The dose should be as small as possible, and the number of tests done should be limited if possible. If a second test is required, it should be delayed about 1 wk.


Images

Normal Anatomy


]


Magnetic resonance cholangiopancreatography (MRCP) image showing a dilated duct upstream to an intraductal stone (arrow

Herniated disc


Medical ultrasonography

Introduction

Diagnostic sonography (ultrasonography) is an ultrasound-based diagnostic imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. There is a plethora of diagnostic and therapeutic applications practiced in medicine.

History

United States

Ultrasonic energy was first applied to the human body for medical purposes by Dr. George Ludwig at the Naval Medical Research Institute, Bethesda, Maryland in the late 1940s. English born and educated John Wild (1914-2009) first used ultrasound to assess the thickness of bowel tissue as early as 1949: for his early work he has been described as the "father of medical ultrasound".

In 1962, after about two years of work, Joseph Holmes, William Wright, and Ralph Meyerdirk developed the first compound contact B-mode scanner. Their work had been supported by U.S. Public Health Services and the University of Colorado. Wright and Meyerdirk left the University to form Physionic Engineering Inc., which launched the first commercial hand-held articulated arm compound contact B-mode scanner in 1963. This was the start of the most popular design in the history of ultrasound scanners.

The first demonstration of color Doppler was by Geoff Stevenson, who was involved in the early developments and medical use of Doppler shifted ultrasonic energy.


Sweden

Medical ultrasonography was used 1953 at Lund University by cardiologist Inge Edler and Carl Hellmuth Hertz, the son of Gustav Ludwig Hertz, who was a graduate student at the department of nuclear physics.

Edler had asked Hertz if it was possible to use radar to look into the body, but Hertz said this was impossible. However, he said, it might be possible to use ultrasonography. Hertz was familiar with using ultrasonic reflectoscopes for nondestructive materials testing, and together they developed the idea of using this method in medicine.

The first successful measurement of heart activity was made on October 29, 1953 using a device borrowed from the ship construction company Kockums in Malmö. On December 16 the same year, the method was used to generate an echo-encephalogram (ultrasonic probe of the brain). Edler and Hertz published their findings in 1954.

Scotland

Parallel developments in Glasgow, Scotland by Professor Ian Donald and colleagues at the Glasgow Royal Maternity Hospital (GRMH) led to the first diagnostic applications of the technique. Donald was an obstetrician with a self-confessed "childish interest in machines, electronic and otherwise", who, having treated the wife of one of the company's directors, was invited to visit the Research Department of boilermakers Babcock & Wilcox at Renfrew, where he used their industrial ultrasound equipment to conduct experiments on various morbid anatomical specimens and assess their ultrasonic characteristics. Together with the medical physicist Tom Brown and fellow obstetrician Dr John MacVicar, Donald refined the equipment to enable differentiation of pathology in live volunteer patients. These findings were reported in The Lancet on 7 June 1958[23] as "Investigation of Abdominal Masses by Pulsed Ultrasound" - possibly one of the most important papers ever published in the field of diagnostic medical imaging.

At GRMH, Professor Donald and Dr James Willocks then refined their techniques to obstetric applications including foetal head measurement to


assess the size and growth of the foetus. With the opening of the new Queen Mother's Hospital in Yorkhill in 1964, it became possible to improve these methods even further. Dr Stuart Campbell's pioneering work on foetal cephalometry led to it acquiring long-term status as the definitive method of study of foetal growth. As the technical quality of the scans was further developed, it soon became possible to study pregnancy from start to finish and diagnose its many complications such as multiple pregnancy, foetal abnormality and placenta praevia. Diagnostic ultrasound has since been imported into practically every other area of medicine.

Medical ultrasonography uses high frequency broadband sound waves in the megahertz range that are reflected by tissue to varying degrees to produce (up to 3D) images. This is commonly associated with imaging the fetus in pregnant women. Uses of ultrasound are much broader, however. Other important uses include imaging the abdominal organs, heart, breast, muscles, tendons, arteries and veins.

While it may provide less anatomical detail than techniques such as CT or MRI, it has several advantages which make it ideal in numerous situations, in particular that it studies the function of moving structures in real-time, emits no ionizing radiation, and contains speckle that can be used in elastography. It is very safe to use and does not appear to cause any adverse effects, although information on this is not well documented. It is also relatively inexpensive and quick to perform. Ultrasound scanners can be taken to critically ill patients in intensive care units, avoiding the danger caused while moving the patient to the radiology department. The real time moving image obtained can be used to guide drainage and biopsy procedures. Doppler capabilities on modern scanners allow the blood flow in arteries and veins to be assessed.

Technology

1. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.

2. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).


3. Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.

4. The reflected waves are picked up by the probe and relayed to the machine.

5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).

6. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.

In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.

Uses

Medical sonography is used in the study of many different systems:

Cardiology

Echocardiography is an essential tool in cardiology, to diagnose e.g. dilatation of parts of the heart and function of heart ventricles and valves

Emergency Medicine

Point of care ultrasound has many applications in the Emergency Department, including the Focused Assessment with Sonography for Trauma (FAST) exam for assessing significant hemoperitoneum or pericardial tamponade after trauma. Ultrasound is routinely used in the Emergency Department to expedite the care of patients with right upper quadrant abdominal pain who may have gallstones or cholecystitis.

Gastroenterology

In abdominal sonography, the solid organs of the abdomen such as the pancreas, aorta, inferior vena cava, liver, gall bladder, bile ducts, kidneys, and spleen are imaged. Sound waves are blocked by gas in the bowel; therefore


there are limited diagnostic capabilities in this area. The appendix can sometimes be seen when inflamed eg: appendicitis.

Neurology

For assessing blood flow and stenosis in the carotid arteries (Carotid ultrasonography) and the big intracerebral arteries

Obstetrics

Obstetrical ultrasound is commonly used during pregnancy to check on the development of the foetus.

Ophthalmology

A-scan ultrasonography, B-scan ultrasonography

Urology

To determine, for example, the amount of fluid retained in a patient's bladder. In a pelvic sonogram, organs of the pelvic region are imaged. This includes the uterus and ovaries or urinary bladder. Men are sometimes given a pelvic sonogram to check on the health of their bladder and prostate. There are two methods of performing a pelvic sonography - externally or internally. The internal pelvic sonogram is performed either transvaginally (in a woman) or transrectally (in a man). Sonographic imaging of the pelvic floor can produce important diagnostic information regarding the precise relationship of abnormal structures with other pelvic organs and it represents a useful hint to treat patients with symptoms related to pelvic prolapse, double incontinence and obstructed defecation.

Musculoskeletal

Tendons, muscles, nerves, and bone surfaces

Cardiovascular system

To assess patency and possible obstruction of arteries Arterial sonography, diagnose DVT (Thrombosonography) and determine extent and severity of venous insufficiency (venosonography) Intravascular ultrasound


Other types of uses include:

* Intervenional; biopsy, emptying fluids, intrauterine transfusion [disambiguation needed] (Hemolytic disease of the newborn)

* Contrast-enhanced ultrasound

A general-purpose sonographic machine may be able to be used for most imaging purposes. Usually specialty applications may be served only by use of a specialty transducer. Most ultrasound procedures are done using a transducer on the surface of the body, but improved diagnostic confidence is often possible if a transducer can be placed inside the body. For this purpose, specialty transducers, including endovaginal, endorectal, and transesophageal transducers are commonly employed. At the extreme of this, very small transducers can be mounted on small diameter catheters and placed into blood vessels to image the walls and disease of those vessels.

Therapeutic applications

Therapeutic applications use ultrasound to bring heat or agitation into the body. Therefore much higher energies are used than in diagnostic ultrasound. In many cases the range of frequencies used are also very different.

* Ultrasound may be used to clean teeth in dental hygiene.

* Ultrasound sources may be used to generate regional heating and mechanical changes in biological tissue, e.g. in occupational therapy, physical therapy and cancer treatment. However the use of ultrasound in the treatment of musculoskeletal conditions has fallen out of favor.

* Focused ultrasound may be used to generate highly localized heating to treat cysts and tumors (benign or malignant), This is known as Focused Ultrasound Surgery (FUS) or High Intensity Focused Ultrasound (HIFU). These procedures generally use lower frequencies than medical diagnostic ultrasound (from 250 kHz to 2000 kHz), but significantly higher energies. HIFU treatment is often guided by MRI.

* Focused ultrasound may be used to break up kidney stones by lithotripsy.

* Ultrasound may be used for cataract treatment by phacoemulsification.


* Additional physiological effects of low-intensity ultrasound have recently been discovered, e.g. its ability to stimulate bone-growth and its potential to disrupt the blood-brain barrier for drug delivery.

* Procoagulant at 5-12 MHz

Variations

A-mode: This display mode is the simplest; signals are recorded as spikes on a graph. The vertical (Y) axis of the display shows the echo amplitude, and the horizontal (X) axis shows depth or distance into the patient. This type of ultrasonography is used for ophthalmologic scanning.

B-mode (gray-scale): This mode is most often used in diagnostic imaging; signals are displayed as a 2-dimensional anatomic image. B-mode is commonly used to evaluate the developing fetus and to evaluate organs, including the liver, spleen, kidneys, thyroid gland, testes, breasts, and prostate gland. B-mode ultrasonography is fast enough to show real-time motion, such as the motion of the beating heart or pulsating blood vessels. Real-time imaging provides anatomic and functional information.

M-mode: This mode is used to image moving structures; signals reflected by the moving structures are converted into waves that are displayed continuously across a vertical axis. M-mode is used primarily for assessment of fetal heartbeat and in cardiac imaging, most notably to evaluate valvular disorders.

Doppler: This type of ultrasonography is used to assess blood flow. Doppler ultrasonography uses the Doppler effect (alteration of sound frequency by reflection off a moving object). The moving objects are RBCs in blood.

Direction and velocity of blood flow can be determined by analyzing changes in the frequency of sound waves:

If a reflected sound wave is lower in frequency than the transmitted sound wave, blood flow is away from the transducer.

If a reflected sound wave is higher in frequency than the transmitted sound wave, blood flow is toward the transducer.

The magnitude of the change in frequency is proportional to blood flow velocity.


Changes in frequency of the reflected sound waves are converted into images showing blood flow direction and velocity.

Duplex Doppler ultrasonography combines the graphic display of spectral ultrasonography with the images of B-mode. For color Doppler ultrasonography, color is superimposed on a gray-scale anatomic image. The color indicates direction of blood flow. By convention, red indicates flow toward and blue indicates flow away from the transducer.

Doppler ultrasonography is also used to evaluate vascularity of tumors and organs, to evaluate heart function (eg, as for echocardiography), to detect occlusion and stenosis of blood vessels, and to detect blood clots in blood vessels (eg, in deep venous thrombosis).

Disadvantages Quality of images depends on the skills of the operator. Obtaining clear images of the target structures can be technically difficult in overweight patients.

Ultrasonography cannot be used to image through bone or gas, so certain images may be difficult to obtain.


Images

Large bladder stone

50 year-old male patient referred for ultrasound due to difficulty passing urine and macroscopic haematuria. Ultrasound showed a 3.5cm bladder calculus.


Multiple gallstones

45 year old female, a Hepatitis B carrier. Routine scan showed normal liver but multiple gallstones.


Large BPH and bladder stone


CT Scan

Introduction

CT scanning—sometimes called CAT scanning—is a noninvasive medical test that helps physicians diagnose and treat medical conditions.

CT scanning combines special x-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor or printed.

History

CT was discovered independently by a British engineer named Sir Godfrey Hounsfield and Dr. Alan Cormack. It has become a mainstay for diagnosing medical diseases. For their work, Hounsfield and Cormack were jointly awarded the Nobel Prize in 1979.

CT scanners first began to be installed in 1974. Because of advances in computer technology, CT scanners have vastly improved patient comfort because they are now much faster. These improvements have also led to higher-resolution images, which improve the diagnostic capabilities of the test. For example, the CT scan can show doctors small nodules or tumors, which they cannot see on an x-ray.

Technology

CT images are produced by x-ray beams that penetrate a patient and to varying degrees, strike a detector.

The placement of the x-ray tube relative to the detectors determines the generation scanner.

The CT process is broken down into three segments: data acquisition, image reconstruction, and image display.

To acquire data, a generator, gantry, and table are necessary.

The generator supplies the energy source to the gantry.


The x-ray tube, data acquisition system, collimators, and detectors are housed in the gantry.

Because the number of exposures typical of a CT scanner and the high x-ray energy output of those scans, tubes must be designed to withstand huge amounts of heat.

The amount of heat that the tube can withstand and the rate at which heat is dissipated are key factors in the cost specific scanners.

Bean hardening artifacts occur because x-ray beams are not uniform in energy.

These artifacts alter the image’s Hounsfield values.

Filters are included in most systems to reduce the amount of low energy x-ray beams to reach the patient.

Source collimators operate like tiny shutters to allow only thin slivers of x-ray beams to emerge.

The collimators can be adjusted by the operator.

The low scatter radiation in CT scanning is attributed to this fine collimation.

Detectors are of two general types: pressurized xenon gas and solid-state crystals.

When a solid-state crystal is struck by x-ray beams it emits light.

There are advantages and disadvantages to both types of detectors.

Raw data include all measurements obtained from the detector array.

Some of these raw data are used in the creation of image data.

After the raw data are averaged and each pixel is assigned a Hounsfield number, an image can be reconstructed.

The data that form this image are then referred to as image data.


These same principles of tomographic imaging can also be applied to radionuclide scanning, in which the sensors for emitted radiation encircle the patient and computer techniques convert the sensor data into tomographic images; examples include single-photon emission CT (SPECT) and positron-emission tomography (PET).

Uses Compared with plain x-rays, the tomographic slices of CT provide more spatial detail and can better differentiate between various soft-tissue densities. Because it provides so much more information, CT is preferred to plain x-rays for imaging most intracranial, head and neck, spinal, intrathoracic, and intra-abdominal structures. Three-dimensional images of lesions can help surgeons plan surgery. CT is the most accurate study for detecting and localizing urinary calculi.

CT may be done with or without IV contrast. Noncontrast CT is used to detect acute hemorrhage in the brain, urinary calculi, and lung nodules, as well as to characterize bone fractures and other skeletal abnormalities. IV contrast is used to improve imaging of tumors, infection, inflammation, and trauma in soft tissues and to assess the vascular system, as when pulmonary embolism, aortic aneurysm, or aortic dissection is suspected.

Oral or occasionally rectal contrast is used for abdominal imaging; sometimes gas is used to distend the lower GI tract and make it visible. Contrast in the GI tract helps distinguish the GI tract from surrounding structures. Standard oral contrast is barium-based, but low-osmolar iodinated contrast should be used when intestinal perforation is suspected or when risk of aspiration is high.

Variations

Virtual colonoscopy: After gas is introduced into the rectum via a flexible, thin-diameter rubber catheter, CT of the entire colon is done. Virtual colonoscopy produces high-resolution 3-dimensional images of the colon that somewhat simulate the appearance of optical colonoscopy, hence the name. This technique can show colon polyps and colon mucosal lesions as small as 5 mm. It is an alternative to conventional colonoscopy.

CT IV pyelography (CT IVP) or urography: IV contrast is injected. The procedure produces detailed images of the kidneys, ureters, and bladder. It is an alternative to conventional IV urography.


CT angiography: After a rapid bolus injection of IV contrast, thin-slice images are rapidly taken as the contrast opacifies arteries and veins. Advanced computer graphics techniques are used to remove images of surrounding soft tissues and to provide highly detailed images of blood vessels similar to those of conventional angiography. CT angiography is a less invasive alternative to conventional angiography.

Disadvantages CT accounts for most diagnostic radiation exposure to patients collectively. If multiple scans are done, the total radiation dose may be high, placing the patient at potential risk Patients who have recurrent urinary tract stones or who have had major trauma are most likely to have multiple CT scans. The risk of radiation exposure vs benefit of the examination must always be considered, as the effective radiation dose of one abdomen CT is equal to 500 chest x-rays.

Some CT scans use IV contrast, which has certain risks If barium extravasates outside the GI tract lumen, it can induce severe inflammation; if aspirated, barium can induce severe pneumonia. Barium can also become hard and inspissated, potentially precipitating intestinal obstruction. Gastrografin is safer, but the contrast and images of the GI tract it provides are not as good.


Images

Normal CT scan

It is worth spending a few minutes familiarising yourself with the appearances of a normal CT scan. It is much easier to detect abnormalities once you are accustomed to normal appearances. The scan below is a slice through the human brain and you should imagine that you are viewing it as if looking up from the patient's feet. Therefore, the patient's left is to the right of the screen. The shape of the ventricles is quite distinctive and they are shown outlined in green and orange. The presence of the third ventricle in the midline is one of the first things to look for. If the third ventricle is either not visible, or shows signs of shift away from the midline, this suggests that there is an abnormality. The basal cisterns is the fluid filled space around the back of the midbrain outlined here in purple. Blood clots, or swelling of the brain may cause this to become narrowed, or not visible altogether. Note in this scan, that the frontal horns of the lateral ventricles are symmetrical, with the septum between them in the midline


Acute Subdural Hematoma Demonstrating Midline Shift:Midline shift >5mm Intracranial haematoma - non evacuated Cortical contusion >1cm in diameter Obliteration of 3rd Ventricle (not seen - refer to normal CT scan)


Acute Subdural HaematomaIntracranial haematoma - non-evacuated

This scan demonstrates a left sided acute subdural haematoma. The scan is taken through a slightly higher part of the brain and shows the bodies of the lateral ventricles. The left lateral ventricle has been compressed and the midline is deviating to the right. The right lateral ventricle is actually slightly larger than normal and this is because the increased pressure is preventing escape of the cerebrospinal fluid from that ventricle. Dilatation of the contralateral ventricle like this indicates that there is very significant pressure on the brain. This scan would be classified as "Intracranial haematoma - non evacuated" on the Early Outcome Form


Acute Extradural Haematoma:Intracranial haematoma - non-evacuated

This scan shows another intracranial haematoma, namely an extradural. You will note that this haematoma has a concave shape, a bit like the human lens and this is because it is occurring between the bone and the dura and is not actually lying on the surface of the brain itself. The points of attachment of the dura limit the extension of this haematoma anteriorly and posteriorly. You can see that there is shift of the midline. Look at the frontal horns in their relation to the falx cerebri (falx cerebri is outlined on the normal scan). This scan would be classified "Intracranial haematoma - non evacuated."


Diffuse Axonal Injury:One or more petechial haemorrhages within the brain

The presence of petechial haemorrhages is usually an indication of a very severe primary brain injury. Petechial haemorrhages tend to occur at the interface of grey and white matter. It can also occur in the dorsolateral quadrant of the midbrain at the middle orange arrow, as well as elsewhere within the brain substance. Note on this scan, that the lateral ventricles and the third ventricle are visible and there is no midline shift. It is often a characteristic of diffuse axonal injury, in which there are numerous petechial haemorrhages that there is no evidence of brain swelling, or midline shift. This scan would be classified as showing one, or more, petechial haemorrhages within the brain.


Cerebral Contusion:Cortical contusion >1cm in diameter

This is a scan of a patient who has sustained a severe head injury. There is extensive bruising of the right side of the brain, showing up as a large, diffuse grey area. You can also see that there are patches of white within the grey area. This represents bleeding. The grey area represents swelling (oedema). The area of the cortical contusion is outlined in purple. You will normally find a centimetre scale at the right hand side of a CT scan. This scan would be classified on the Early Outcome Form as "Cortical contusion - greater than 1cm in diameter.


PET scanA positron emission tomography (PET) scan is an imaging test that uses a radioactive substance (called a tracer) to look for disease in the body.

Unlike magnetic resonance imaging (MRI) and computed tomography (CT) scans, which reveal the structure of and blood flow to and from organs, a PET scan shows how organs and tissues are working.

A PET scan uses radiation, or nuclear medicine imaging, to produce 3-dimensional, color images of the functional processes within the human body. PET stands for positron emission tomography. The machine detects pairs of gamma rays which are emitted indirectly by a tracer (positron-emitting radionuclide) which is placed in the body on a biologically active molecule. The images are reconstructed by computer analysis. Modern machines often use a CT X-ray scan which is performed on the patient at the same time in the same machine.

PET scans can be used to diagnose a health condition, as well as for finding out how an existing condition is developing. PET scans are often used to see how effective an ongoing treatment is.

Technology

Radiotracer - Before carrying out a PET scan, a radioactive medicine is produced in a cyclotron (a type of machine). The radioactive medicine is then tagged to a natural chemical. This natural chemical could be glucose, water, or ammonia. The tagged natural chemical is known as a radiotracer. The radiotracer is then inserted into the human body.

When it is inside the radiotracer will go to areas inside the body that use the natural chemical. For example, FDG (fluorodeoxyglucose - a radioactive drug) is tagged to glucose to make a radiotracer. The glucose goes into those parts of the body that use glucose for energy. Cancers, for example, use glucose differently from normal tissue - so, FDG can show up cancers.

Detecting positrons - A PET scan detects the energy emitted by positively-charge particles (positrons). As the radiotracer is broken down inside the patient's body positrons are made. This energy appears as a 3-dimensional image on a computer monitor.


Indication

PET scans are generally used alongside X-rays or MRI (magnetic resonance imaging) scans. Doctors use PET scans as a complementary test to these main ones. They are used to make a diagnosis or to get more data about a health condition. As mentioned above, they are also useful in finding out how effective current treatment is. The use of combined imaging technologies may hold the key to stopping - and even preventing - heart attacks, a study revealed.

The biggest advantage of a PET scan, compared to an MRI scan or X-ray, is that it can reveal how a part of the patient's body is functioning, rather than just how it looks. Medical researchers find this aspect of PET scans particularly useful.

PET scans are commonly used to investigate the following conditions:

Epilepsy - it can reveal which part of the patient's brain is being affected by epilepsy. This helps doctors decide on the most suitable treatments.MRI and/or CT scans are recommended for people after a first seizure, this study explains.

Alzheimer's disease - it is very useful in helping the doctor diagnose Alzheimer's disease. A PET scan that measures uptake of sugar in the brain significantly improves the accuracy of diagnosing a type of dementia often mistaken for Alzheimer's disease.

Cancer - PET scans can show up a cancer, reveal the stage of the cancer, show whether the cancer has spread, help doctors decide on the most appropriate cancer treatment, and give doctors an indication on the effectiveness of ongoing chemotherapy. A PET scan several weeks after starting radiation treatment for lung cancer can indicate whether the tumor will respond to the treatment. This article looks at whether PET scans are beneficial during cancer diagnosis, staging and monitoring.

Heart disease - a PET scan helps detect which specific parts of the heart have been damaged or scarred. Any faults in the working of the heart are more likely to be revealed with the help of a PET scan. A study revealed how comprehensive diagnosis of heart disease based on a single CT scan is possible.

Medical research - researchers, especially those involved in how the brain functions get a great deal of vital data from PET scans.


What is difference between a PET scan and CT or MRI scans?

A CT or MRI scan can assess the size and shape of body organs and tissue. However, they cannot assess function. A PET scan looks at function. In other words, MRI or CT scans tell you what is looks like, while a PET scan can tell you how it is working.

Who should not have a PET scan?

Pregnant women and women who are breastfeeding should not have a PET scan as there is a risk for the baby. Any woman who is pregnant should tell her doctor straight away (before the scan).

Anybody who has just had a PET scan should stay away from pregnant women, babies and young children for a few hours after the scan.


Images

PET scan and PET-CT Fusion

PET scan, or Positron Emission Tomography, is a powerful tool for detecting several types of cancer. It is useful for the accurate detection of cancer spread in patients with an established diagnosis of cancer, or for the noninvasive evaluation of nodules detected by chest x-ray or CT. PET works by having the ability to detect sites of high metabolic activity. Since many cancers have significantly higher metabolism than normal tissues or noncancerous masses,


PET allows sensitive detection of even small cancers.

PET-CT Fusion is a newer refinement of the technique that allows the most accurate correlation of anatomic information (from the CT) and metabolic information (from the PET scan) and helps to ensure the highest degree of accuracy for the exam.


Biopsy

Removal of tissue for examination under a microscope for the purpose of diagnosis or therapeutic measure.

Tissue samples for biopsy can be obtained by either surgery or needle. The doctor should decide the type of biopsy technique depending on the nature and location of the lump, as well as the patient’s general health.

Surgical biopsies can be either excisional or incisional

An excisional biopsy removes the entire lump or suspicious area. Excisional biopsy is currently the standard procedure for lumps that are smaller than an inch or so in diameter. In effect, it is similar to a lumpectomy, surgery to remove the lump and a margin of surrounding tissue. Lumpectomy is usually used in combination with radiation therapy as the basic treatment for early breast cancer.

An excisional biopsy is typically performed in the outpatient department of a hospital. A local anesthetic is injected into the woman's breast. Sometimes she is given a tranquilizer before the procedure. The surgeon makes an incision along the contour of the breast and removes the lump along with a small margin of normal tissue. Because no skin is removed, the biopsy scar is usually small. The procedure typically takes less than an hour. After spending an hour or two in the recovery room, the woman goes home the same day.

An incisional biopsy removes only a portion of the tumor (by slicing into it) for the pathologist to examine. Incisional biopsies are generally reserved for tumors that are larger. They too are usually performed under local anesthesia, with the woman going home the same day.

Whether or not a surgical biopsy will change the shape of your breast depends partly on the size of the lump and where it is located in the breast, as well as how much of a margin of healthy tissue the surgeon decides to remove. You should talk with your doctor beforehand, so you understand just how extensive the surgery will be and what the cosmetic result will be.


Needle biopsies

Performed with either a very fine needle or a cutting needle large enough to remove a small nugget of tissue.

Fine needle aspiration (FNAC)uses a very thin needle and syringe to remove either fluid from a cyst or clusters of cells from a solid mass. Accurate fine needle aspiration biopsy of a solid mass takes great skill, gained through experience with numerous cases.

Core needle biopsy uses a somewhat larger needle with a special cutting edge. The needle is inserted, under local anesthesia, through a small incision in the skin, and a small core of tissue is removed. This technique may not work well for lumps that are very hard or very small. Core needle biopsy may cause some bruising, but rarely leaves an external scar, and the procedure is over in a matter of minutes.

At some institutions with extensive experience, aspiration biopsy is considered as reliable as surgical biopsy; it is trusted to confirm the malignancy of a clinically suspicious mass or to confirm a diagnosis that a lump is not cancerous. Should the needle biopsy results be uncertain, the diagnosis is pursued with a surgical biopsy. Some doctors prefer to verify all aspiration biopsy results with a surgical biopsy before proceeding with treatment.

Localization biopsy

Also known as needle localization,this is a procedure that uses mammography to locate and a needle to biopsy breast abnormalities that can be seen on a mammogram but cannot be felt (nonpalpable abnormalities). Localization can be used with surgical biopsy, fine needle aspiration, or core needle biopsy.

For a surgical biopsy, the radiologist locates the abnormality on a mammogram (or a sonogram) just prior to surgery. Using the mammogram as a guide, the radiologist inserts a fine needle or wire so the tip rests in the suspicious area -- typically, an area of microcalcifications. The needle is anchored with a gauze bandage, and a second mammogram is taken to confirm that the needle is on target.


The woman, along with her mammograms, goes to the operating room, where the surgeon locates and cuts out the needle-targeted area. The more precisely the needle is placed, the less tissue needs to be removed.

Sometimes the surgeon will be able to feel the lump during surgery. In other cases, especially where the mammogram showed only microcalcifications, the abnormality can be neither seen nor felt. To make sure the surgical specimen in fact contains the abnormality, it is x-rayed on the spot. If this specimen x-ray fails to show the mass or the calcifications, the surgeon is able to remove additional tissue.

Stereotactic localization biopsy

This is a newer approach that relies on a three-dimensional x-ray to guide the needle biopsy of a nonpalpable mass. With one type of equipment, the patient lies face down on an examining table with a hole in it that allows the breast to hang through; the x-ray machine and the maneuverable needle "gun" are set up underneath. Alternatively, specialized stereotactic equipment can be attached to a standard mammography machine.

The breast is x-rayed from two different angles, and a computer plots the exact position of the suspicious area. (Because only a small area of the breast is exposed to the radiation, the doses are similar to those from standard mammography.) Once the target is clearly identified, the radiologist positions the gun and advances the biopsy needle into the lesion.

Tissue Studies

The cells or tissue removed through needle or surgical biopsy are promptly sent (along with the x-ray of the specimen, if one was made) to the pathology lab. If the excised lump is large enough, the pathologist can take a preliminary look by quick-freezing a small portion of the tissue sample. This makes the sample firm enough to slice into razor-thin sections that can be examined under the microscope. A "frozen section" provides an immediate, if


provisional, diagnosis, and the surgeon may be able to give you the results before you go home.

The results of a frozen section are not 100 percent certain, however. A more thorough assessment takes several days, while the pathologist processes "permanent sections" of tissue that can be examined in greater detail.

When the biopsy specimen is small--as is often the case when the abnormality consists of mammographic calcifications only--many doctors prefer to bypass a frozen section so the tiny specimen can be analyzed in its entirety.

The pathologist looks for abnormal cell shapes and unusual growth patterns. In many cases the diagnosis will be clear-cut. However, the distinctions between benign and cancerous can be subtle, and even experts don't always agree. When in doubt, pathologists readily consult their colleagues. If there is any question about the results of biopsy, make sure your biopsy slide has been reviewed by more than one pathologist.


Images

In this prostate biopsy, malignant glands are seen surrounded by adipose tissue. This is an example of extraprostatic extension (EPE). Other examples of EPE that may be encountered in needle biopsies include tumor adjacent to pigmented epithelium of seminal vesicle or within skeletal muscle.

The photomicrograph shows metastatic medullary carcinoma of breast in an axillary lymph node. Patients with medullary carcinoma have axillary lymph node metastases less frequently than those with infiltrating ductal carcinoma of breast.


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