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Research title: Computerized Assisted Tomography (CAT/CT)

Submitted to: Prof. Dr. Moshira M. Abdul LatifBy: Ahmed T. M. El-Shanawany

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fac1. Introduction.

Computed Tomography (CT) has been one of the major advancements in diagnosticradiology and oncology. Most modern hospitals have a CT scanner in their shock-trauma

centers for immediate scans to explore for major internal injuries such as internal bleedingand aortic aneurysm. This research describes CT history, principles, clinical applications,

advantages and limitations.

2. Definition.

According to the Merriam Webster Dictionary, computerized tomography is

defined as "radiography in which a three-dimensional image of a body structure is

constructed by computer from a series of plane cross-sectional images made along an axiscalled also computed axial tomography, computerized axial tomography, computerized

tomography".

It is more simplified according to the Encyclopedia Britannica as it is defined as "a

diagnostic imaging method using a low-dose beam of X-rays that crosses the body in a

single plane at many different angles".

3. Associated Terms.

1. Radigraphy.

Radiography is the use of ionizing electromagnetic radiation such as X-rays to view objects.

2. Medical Radiography.

Medical Radiography is the use of ionizing electromagnetic radiation as a

diagnostic aid in the identification of medical conditions.

3. X-ray.

According to the Encyclopedia Britannica X-ray is "anelectromagneticradiation of extremely short wavelength and high frequency, with wavelengths

ranging from about 108 to 1012 meter and corresponding frequencies from about

1016

to 1020

hertz (Hz)".

4. Terminology.

Computerized Assisted Tomography (CAT/CT) consists of two main words

"computerized" and "tomography".

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ComputerizedorComputerized Assisted; means that the analysis and production ofthe image is based on a computerized program and the operator can not do it himself.

Tomography; The word "tomography" is derived from the Greektomos (slice) and

graphein (to write).

Computed tomography was originally known as the "EMI scan" as it was

developed at a research branch of EMI, a company best known today for its music andrecording business. It was later known as computed assisted tomography (CAT or CT

scan) and body section rntgenography.

According to Eric Whaites in histextbook 'Essentials of Dental

Radiography and Radiology',

"Tomography is a specialized techniquefor producing radiographs showing only a

section orslice of a patient". Eric Whaites

described the concept of tomography in avery simple way when he descried it as

dividing up the patient like a loaf of sliced

bread. The section is thus referred to as thefocal plane or focal trough. Structuresoutside the section (i.e. the rest of theloaf)

are blurred and out of focus. By taking

multipleslices, three-dimensionalinformation aboutthe whole patient can be

obtained.

Types of tomography; the following Table lists the various types of tomography

according to the source of data

Source of data Name Abbreviation

Atom probe Atom probe tomography APT

Laser scanning confocal

microscopy

Confocal microscopy (Laser scanning

confocal microscopy)LSCM

Cryo-electron microscopy Cryo-electron tomography Cryo-ET

Electrical capacitance Electrical capacitance tomography ECT

Electrical resistivity Electrical resistivity tomography ERT

Electrical impedance Electrical impedance tomography EITMagnetic resonance Functional magnetic resonance imaging fMRI

Magnetic induction Magnetic induction tomography MIT

Nuclear magnetic momentMagnetic resonance imaging or nuclear

magnetic resonance tomographyMRI MRT

Neutron Neutron tomography

Sonar Ocean acoustic tomography

Interferometry Optical coherence tomography OCT

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Optical microscope Optical projection tomography OPT

Photoacoustic spectroscopy Photoacoustic imaging in biomedicine PAT

Positron emission Positron emission tomography PET

Positron emission & X-ray Positron emission tomography PET-CT

Quantum state Quantum tomography

Gamma raySingle photon emission computed

tomographySPECT

Seismic waves Seismic tomography

Photoacoustic spectroscopy Thermoacoustic imaging TAT

Ultrasound Ultrasound-modulated optical

tomographyUOT

Ultrasound transmission tomography

X-ray X-ray tomographyCT,

CATScan

Zeeman effect Zeeman-Doppler imaging

5. Historical Notes before CT.

The invention of computed tomography is considered to be the greatest innovationin the field of radiology since the discovery of X-rays. This cross-sectional imaging

technique provided diagnostic radiology with better insight into the pathogenesis of the

body, thereby increasing the chances of recovery.In 1979, G.N. Hounsfield and A.M. Cormack were awarded the Nobel Prize in medicine

for the invention of CT.

Today, CT is one of the most important methods of radiological diagnosis. It

delivers non-superimposed, cross-sectional images of the body, which can show smallercontrast differences than conventional X-ray images. This allows better visualization ofspecific differently structured soft-tissue regions, for example, which could otherwise not

be visualized satisfactorily.

Since the introduction of spiral CT in the nineties, computed tomography has seen aconstant succession of innovations.

And here you are a brief notes about the historic dates till the introduction on CT;

11/8/1895; Discovery of X-ray radiation.

Discoverer: The physicist and later Nobel Prize winner Wilhelm Conrad

Roentgen (18451923), dean at the Julius Maximilian University of Wurzburg and

holder of the chair of physics.

1896.

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F.H. Williams succeeds in taking the first chest X-ray in Boston, and CarlSchleussner develops the first silver bromide coated photographic X-ray plates in

Frankfurt a. Main, Germany.

Diagnostic results can now be archived; until then, fluorescent screensresulting in high radiation exposure had been used.

1903.

E.A.O. Pasche builds a collimator for suppressing scattered radiation

Radiation protection for all parties involved for the first time; until then, both

patients and physicians always had to face the "bare" X-ray tube.

6. History of CT.

The reconstruction of images from projections was attempted as early as 1940

without the use of the modern computer technology. In 1940, Gabriel Frank was able to

describe the basic idea of modern tomography including such concepts as Sinograms (i.e.

representation of measurement data as linear samples versus view samples) and opticalback projection.

In 1956, Allan M. Cormack conducted experiments on reconstructive tomographyin medical applications. He reconstructed attenuation coefficients of tissues to improve the

accuracy of radiation treatment which lead to the development of a mathematical theory for

image reconstruction. However, due to difficulty of calculations, his work was not

recognized at the time.

The first clinical CT scanner was developed in 1967 by Godfrey N. Hounsfield at

the Central Research Laboratories of EMI, Ltd., in England. When he was investigatingpattern recognition techniques, he concluded that X-ray measurements taken through a

body from different directions would allow the reconstruction of its internal structure. Due

to the low-intensity of the gamma source, it took 9 days to complete the data acquisitionand construct the image including the computation of 28,000 simultaneous equations in 21

hours.

After further refinement of the data acquisition, images were constructed in less

than 5 minutes. This led to the installation of the first clinical CT device at Atkinson-

Morley Hospital in September 1971. A month later, the first patient with a large cyst wasscanned and the pathology was confirmed from the image. In 1979, Cormack and

Hounsfield shared the Nobel Prize for their contributions in the development of computed

tomography in the field of physiology and medicine.

7. Timeline.

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1917

Johann Radon demonstrated that the image of a 3-dimensional object can be

recostructed from an infinite number of 2-dimsneisonal projections of theobject

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1956

Ronald Bracewell publishes paper mapping sunspots using a series of one-

dimensional images to reconstruct a two-dimensional image using Fouriertransform

1958 William Oldendorf builds a model CT scanner without a computer

1960 Oldendorf applies for a patent for his model

1963Alan Cormack publishes results from experimental scanner using a computerto reconstruct images from data

1966David Kuhl publishes paper with the transmission images of a subject's

thorax

1967 Bracewell reconstructs lunar images without using Fourier transforms

1968EMI patents Godfrey Hounsfieild's method apparatus and the apparatus for

scanning the body with X-rays

1971The first CT scanner, limited to the head, demonstrated by EMI at Atkinson

Morley's hospital in London

1972 The first CT scanner demonstrated in the United States

1973 Robert Ledley markets ACTA, a whole body CT scanner

1975Second generation Delta CT scanners are marketed

GEs third generation CT scanners are marketed

1979Cormack and Hounsfield are awarded the Nobel Prize in Medicine for theinvention of CT

1985 Superfast CT is developed by Douglas Boyd

1989 First spiral CT enters the market

8. CT Principles; (Conventional Radiography vs. ComputerizedTomography).

The principal of CT is the measuring of the spatial distribution of physical materialto be examined from different directions and to compute superposition free images from

this data. It is basically a technique of X-ray photography by which a single plane of a

patient is scanned from various angles in order to provide a cross-sectional image of the

internal structure of that plane.

For conventional radiography, the relative distribution of X-ray intensities is what

is being measured. The following Figure demonstrates how this is achieved.

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An X-ray source of intensity Io is used to send uniform intensity X-rays through apatient. The X-rays then exit the other side with an intensity of I(x,y) and interact with a

radiography film sheet. The exiting X-rays are attenuated by the varying material densities

that they pass through. The different paths through the material will attenuate the X-rays by

varying amounts, based only on the mass attenuation coefficient (), since the distance (d)is the same on all point of the radiography film. It is this variance that is recorded by the

two dimensional radiography film and is shown as lighter or darker contrasts.

This process has some limitations. Specifically, the image captured is a two

dimensional representation of three dimensional anatomy. As a result, structures are

overlapping on the image and make positional details hard to see. Another limitation is thatthe mass attenuation coefficients for tissues do not vary greatly. Thus, it is difficult to

resolve some internal structures. However, computed tomography (CT) provides solutions

to these limitations.

The principle of CT is to have many measurements of attenuation through the plane

of a finite thickness cross section of the patient. The following Figure shows this concept.

An X-ray source is used to scan a patient along this plane, while a detector on the

opposite side measures the attenuated X-rays along this plane and the computer records this

capture. Once the patient has been scanned from one side of the plane to the other side,both X-ray source and detector rotate around the patient by a predetermined amount and

the translational scan is repeated. The internal components of the patient are interpreted by

the computer as a group of small volumes, each with their own average mass attenuationcoefficient. These volumes are called voxels (like pixels on a TV screen). The smaller the

voxel volume, the higher the resolution of the image.

In order to generate an image of the cross section, the computer must attempt tocalculate the average mass attenuation coefficients () of each of the voxel volumes. This

could be determined algebraically with a very large number of simultaneous equations;

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however a simpler method called filtered back-projection was used in the early CTscanners and remains in use today. X-ray scans are collected in sets called projections,

which are made across the patient in a particular direction in the section plane. To

reconstruct the image from the X-ray measurements, each voxel must be viewed from

multiple different directions. A complete data set requires many projections at rotationalintervals of 1 or less around the cross section. Back-projection effectively reverses the

attenuation process by adding the attenuation value of each X-ray in each projection backthrough the reconstruction image. This requires a significant computer power to quickly

generate the patient image. Because this process initially generates a blurred image, the

data from each projection are mathematically altered (filtered) prior to back-projection to

eliminate the blurring.

9. CT Generations.

1. First Generation: Parallel-Beam Geometry.

Parallel-beam geometry is the simplest technically and the easiest with which

to understand the important CT principles. Multiple measurements of x-ray

transmission are obtained using a single highly collimated x-ray pencil beam anddetector. The beam is translated in a linear motion across the patient to obtain a

projection profile. The source and detector are then rotated about the patient isocenter

by approximately 1 degree, and another projection profile is obtained. This translate-rotate scanning motion is repeated until the source and detector have been rotated by

180 degrees. The highly collimated beam provides excellent rejection of radiation

scattered in the patient; however, the complex scanning motion results in long

(approximately 5-minute) scan times. This geometry was used by Hounsfield in hisoriginal experiments [Hounsfield, 1980] but is not used in modern scanners.

2. Second Generation: Fan Beam, Multiple Detectors.

Scan times were reduced to approximately 30 s with the use of a fan beam of

x-rays and a linear detector array. A translate-rotate scanning motion was stillemployed; however, a larger rotate increment could be used, which resulted in

shorter scan times. The reconstruction algorithms are slightly more complicated than

those for first-generation algorithms because they must handle fan-beam projectiondata.

3. Third Generation: Fan Beam, Rotating Detectors.

Third-generation scanners were introduced in 1976. A fan beam of x-rays is

rotated 360 degrees around the isocenter. No translation motion is used; however, the

fan beam must be wide enough to completely contain the patient. A curved detectorarray consisting of several hundred independent detectors is mechanically coupled to

the x-ray source, and both rotate together. As a result, these rotate-only motions

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acquire projection data for a single image in as little as 1 s. Third-generation designshave the advantage that thin tungsten septa can be placed between each detector in

the array and focused on the x-ray source to reject scattered radiation.

4.Fourth Generation: Fan Beam, Fixed Detectors.

In a fourth-generation scanner, the x-ray source and fan beam rotate about theisocenter, while the detector array remains stationary. The detector array consists of

600 to 4800 (depending on the manufacturer) independent detectors in a circle that

completely surrounds the patient. Scan times are similar to those of third-generation

scanners. The detectors are no longer coupled to the x-ray source and hence cannotmake use of focused septa to reject scattered radiation. However, detectors are

calibrated twice during each rotation of the x-ray source, providing a self-calibrating

system. Third-generation systems are calibrated only once every few hours.

Two detector geometries are currently used for fourth-generation systems: (1)

a rotating x-ray source inside a fixed detector array and (2) a rotating x-ray sourceoutside a notating detector array. The following Figure shows the major components

in the gantry of a typical fourth-generation system using a fixed-detector array.

Both third- and fourth-generation systems are commercially available, andboth have been highly successful clinically. Neither can be considered an overall

superior design.

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5. Fifth Generation: Scanning Electron Beam.

Fifth-generation scanners are unique in that the x-ray source becomes anintegral part of the system design. The detector array remains stationary, while a

high-energy electron beams is electronically swept along a semicircular tungsten strip

anode, as illustrated in the following Figure.

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X-rays are produced at the point where the electron beam hits the anode,

resulting in a source of x-rays that rotates about the patient with no moving parts[Boyd et al., 1979]. Projection data can be acquired in approximately 50 ms, which is

fast enough to image the beating heart without significant motion artifacts [Boyd andLipton, 1983].

An alternative fifth-generation design, called the dynamic spatial

reconstructor (DSR) scanner, is in use at the Mayo Clinic [Ritman, 1980, 1990]. This

machine is a research prototype and is not available commercially. It consists of 14x-ray tubes, scintillation screens, and video cameras. Volume CT images can be

produced in as little as 10 ms.

10. Process.

X-ray slice data is generated using an X-ray source that rotates around the object;X-ray sensors are positioned on the opposite side of the circle from the X-ray source. The

earliest sensors were scintillation detectors, withphotomultiplier tubes excited by

(typically) cesium iodide crystals. Cesium iodide was replaced during the 1980s by ionchambers containing high-pressureXenon gas. These systems were in turn replaced by

scintillation systems based onphotodiodes instead of photomultipliers and modern

scintillation materials with more desirable characteristics. Many data scans areprogressively taken as the object is gradually passed through the gantry.

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Newer machines with faster computer systems and newer software strategies canprocess not only individual cross sections but continuously changing cross sections as the

gantry, with the object to be imaged slowly and smoothly slid through the X-ray circle.

These are called helicalorspiral CTmachines. Their computer systems integrate the data

of the moving individual slices to generate three dimensional volumetric information (3D-CT scan), in turn viewable from multiple different perspectives on attached CT workstation

monitors. This type of data acquisition requires enormous processing power, as the data arearriving in a continuous stream and must be processed in real-time.

In conventional CT machines, an X - ray tube and detector are physically rotated

behind a circular shroud (see the image above right); in theelectron beam tomography(EBT), the tube is far larger and higher power to support the high temporal resolution. The

electron beam is deflected in a hollow funnel-shaped vacuum chamber. X-rays are

generated when the beam hits the stationary target. The detector is also stationary. This

arrangement can result in very fast scans, but is extremely expensive.

CT is used in medicine as a diagnostic tool and as a guide for interventional

procedures. Sometimes contrast materials such as intravenousiodinated contrast are used.This is useful to highlight structures such as blood vessels that otherwise would be difficult

to delineate from their surroundings. Using contrast material can also help to obtain

functional information about tissues.

Once the scan data has been acquired, the data must be processed using a form of

tomographic reconstruction, which produces a series of cross-sectional images. The most

common technique in general use is filtered back projection, which is straight-forward toimplement and can be computed rapidly. In terms of mathematics, this method is based on

the Radon transform. However, this is not the only technique available: the original EMI

scanner solved the tomographic reconstruction problem by linear algebra, but this approach

was limited by its high computational complexity, especially given the computertechnology available at the time. More recently, manufacturers have developed iterative

physical model-based expectation-maximization techniques. These techniques are

advantageous because they use an internal model of the scanner's physical properties and ofthe physical laws of X-ray interactions. By contrast, earlier methods have assumed a

perfect scanner and highly simplified physics, which leads to a number of artifacts and

reduced resolution - the result is images with improved resolution, reduced noise and fewerartifacts, as well as the ability to greatly reduce the radiation dose in certain circumstances.

The disadvantage is a very high computational requirement, which is at the limits of

practicality for current scan protocols.

Pixels in an image obtained by CT scanning are displayed in terms of relative radio -

density. The pixel itself is displayed according to the mean attenuation of the tissue(s) thatit corresponds to on a scale from +3071 (most attenuating) to -1024 (least attenuating) onthe Hounsfield scale. Pixel is a two dimensional unit based on the matrix size and the field

of view. When the CT slice thickness is also factored in, the unit is known as aVoxel,

which is a three-dimensional unit. The phenomenon that one part of the detector cannot

differentiate between different tissues is called the "Partial Volume Effect". That meansthat a big amount of cartilage and a thin layer of compact bone can cause the same

attenuation in a voxel as hyperdense cartilage alone. Water has an attenuation of 0

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Hounsfield units (HU), while air is -1000 HU, cancellous bone is typically +400 HU,cranial bone can reach 2000 HU or more (os temporale) and can cause artifacts. The

attenuation of metallic implants depends on atomic number of the element used: Titanium

usually has an amount of +1000 HU, iron steel can completely extinguish the X-ray and is,

therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts arecaused by abrupt transitions between low- and high-density materials, which results in data

values that exceed the dynamic range of the processing electronics.

Contrast mediums used for X-ray CT, as well as forplain film X - ray, are called

radiocontrasts. Radiocontrasts for X-ray CT are, in general, iodine-based. Often, images are

taken both with and without radiocontrast. CT images are called precontrast or native-phase images before any radiocontrast has been administrated and postcontrast after

radiocontrast administration.

11. Radiation Dose.

CT scanning is a relatively high dose procedure that is becoming much more

common worldwide. The Helical and Multislice CT scanners typically have larger dosesthan the conventional CT scans, due to the continuous nature of the scan. The electron

beam CT scanner will deliver approximately 20% less radiation than a patient would

receive from a conventional CT scan. The primary explanation for this is that the Electron

Beam CT scanner is essentially a fast shuttered camera only turning on for brief periods of50 to 100 msec as needed to acquire the images.

The following Table shows the various doses from CT scans, along with some other

activities. Estimates of radiation exposure are given in rem (radiation equivalent man)which is based on the total amount of X-ray expected to be absorbed by the patient (100

millirem = 1 milliSievert).

Source of Radiation Dose (mrem)Natural Background (Annual) 350

Average Dose to Nuclear Energy Worker 170

Chest X-ray 10

Conventional CT Chest 800

Conventional CT Abdomen 1000

Helical CT Chest 700

Helical CT Body Scan 1800

Electron Beam CT Body Scan 320

It can be seen that the doses for CT scans are higher than those for normal X-ray

radiography, or those typically received by a Nuclear Energy Worker. Because CTprocedures involve far higher radiation exposures than those received in conventional X-

ray exams, there is a growing concern that such exposure could contribute to the

development of a radiation-induced cancer later in life. This concern is currently beinginvestigated by the U.S. Food and Drug Administration. Due to the high radiation dose that

a patient could receive from a CT scan, screening without symptoms is usually not

justified. As for utilizing the CT scans for certain diagnostic purposes, the radiation does is

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minimal in comparison to the benefits achieved. Technological advancement in detectorsensitivity would allow a decrease in patient dose, while not compromising image quality.

12. Artifacts.

Although CT is a relatively accurate test, it is liable to produce artifacts, such as the

following:

1. Streak artifact.

Streaks are often seen around materials that block most X-rays, such as metal

or bone. These streaks can be caused by undersampling, photon starvation, motion,

beam hardening, or scatter. This type of artifact commonly occurs in the posteriorfossa of the brain, or if there are metal implants. The streaks can be reduced using

newer reconstruction techniques.

2. Partial volume effect

This appears as "blurring" over sharp edges. It is due to the scanner being

unable to differentiate between a small amount of high-density material (e.g., bone)and a larger amount of lower density (e.g., cartilage). The processor tries to average

out the two densities or structures, and information is lost. This can be partially

overcome by scanning using thinner slices.

3. Ring artifact.

Probably the most common mechanical artifact, the image of one or many"rings" appears within an image. This is usually due to a detector fault.

4. Noise artifact.

This appears as graining on the image and is caused by a low signal to noise

ratio. This occurs more commonly when a thin slice thickness is used. It can alsooccur when the power supplied to the X-ray tube is insufficient to penetrate the

anatomy.

5. Motion artifact.

This is seen as blurring and/or streaking, which is caused by movement of the

object being imaged. Motion blurring might be reduced using a new technique called

IFT (incompressible flow tomography).

6. Windmill.

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Streaking appearances can occur when the detectors intersect the

reconstruction plane. This can be reduced with filters or a reduction in pitch.

7.Beam hardening.

This can give a "cupped appearance". It occurs when there is moreattenuation in the center of the object than around the edge. This is easily corrected

by filtration and software.

13. Clinical Applications.

CT scan has many diagnostic clinical applications. It improves the diagnosis

accuracy by delineating details of the organs including soft tissues and bones. CT scan can

provide information about the spread of an infection or tumors to different body parts andcan assist surgical interventions, biopsies, and radiotherapies. Some of the clinical

applications of a CT scan are further described in the following subsections.

13.1 Contrast Agents and Drugs.

In a CT scan, the use of different non-radioactive contrast agents is often

required to enhance the visibility of blood vessels, soft tissues, and certain organs.Contrast agents can be administered through various methods. Agents containing

iodine are injected into the vein to enhance the imaging of blood vessels and organs

such as kidneys. It also accentuates the appearance between normal and abnormal

tissue in organs like liver and spleen. Barium sulfate and gastrografin can be orallyconsumed to enhance CT images of the abdomen and pelvis. Barium sulfate can

also be administered by enema for imaging the colon. For very special cases oflungand brain imaging, a xenon contrast agent can be inhaled by the patient. In

addition to the contrast agents, for imaging of certain organs such as colon, a drug

may also be injected to slow down the normal movement of the bowel. As this

movement could distort the scan and make it more difficult to interpret the image.

13.2 Body Imaging and Diagnosis.

CT scan is used as a diagnostic tool for cancer, trauma, musculoskeletal

disorders, infections and cardiovascular diseases. Not only CT scan can detect and

confirm the presence of cancers, but can also reveal the size, location, and extent ofa tumor. Usually in a CT scan, benign tumors such as neurofibromas and lipomas

can be differentiated from malignant tumors based on their density.

In addition, a CT scan can help distinguish between tumor and abscess since

the later appears as a soft tissue mass with more lucent center. A CT scan can also

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define tumor borders, cartilage invasion, and the anatomy of the surroundingtissues.

Due to the high spatial contrast resolution of CT scans, most body parts and

tissues can be accurately investigated. Imaging of head or brain by CT enablesdetection of blood clots, enlarged ventricles, internal bleeding, skull fracture, and

obstruction in the drainage pathway of the sinus.

CT exam of abdomen can reveal abnormalities in kidneys (e.g., kidney

stones), liver, adrenal glands, pancreas, and appendicitis. It can also identify lump,

enlarged lymph nodes or glands and occult fractures in the neck area. Herniateddisc, spinal stenosis and fractures in the spine can also be detected via CT scans.

A quantitative measurement of bone mineral content for the detection ofosteoporosis can be obtained using a specific CT technology known as Quantitative

CT (QCT). An advantage of QCT is that it can measure bone in three-dimensional

sections and separate between cortical and trabecular bone with great anatomicdetail. This information is useful for detection of fracture and determination of bone

mineral content.

Another application of CT technology known as CT angiography, utilizescontrasting agents to accentuate the blood vessels in different organs. This allows

for the detection of vascular disorders and diseases which could lead to kidney

failure, stroke or gangrene.

13.3 Surgical Intervention.

Another application of CT where continuous images can be acquired is

known as fluoroscopic CT (FCT). This technique allows for continuous monitoring

of the surgical instrument, its path, and the targeted body part. This will eliminatethe need for many exploratory surgical procedures such as thoracotomy and

laparotomy. FCT is used in surgical interventions such as guided diagnostic

biopsies to remove a sample tissue for pathologic testing. FCT can also be used for

drainage of fluids from cyst, abscess, lymphoceles, or hematomas. In addition, FCTis effective in pain therapy treatments such as in spinal disk space therapeutic

injections, and in minimally invasive operations like cyst removal and ablation of

tumors.

13.4 Surgical and Radiotherapy Planning.

The extent and location of the tumor are essential in the surgical and

radiotherapy planning. CT imaging offers a detailed depiction of the tumor andadjacent tissues as well as staging of the tumor. The CT scan is more beneficial for

small tumors which require higher precision during radiotherapy or surgical

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planning as compared to large tumors. 3D images constructed from CT scans arehelpful when planning radiotherapy treatments. These images enable optimization

of dose and radiation beams to destroy the cancerous cells while avoiding or

minimizing dose to the major surrounding organs.

13.5 Surgical and Therapeutical Success Determination.

CT scan plays an important role in determining the success of surgical and

therapeutical procedures. In cancer treatments, several CT scans may be needed at

different stages to confirm the degree of success in therapeutic treatment. For

example, after tumor treatments, the extent of tumor removal could be determinedusing a follow-up CT scan. In the case of chemotherapy treatment of metastases,

CT scan may not be as efficient in the success determination due to its small size

and large spread in the body.

13.6 Virtual Endoscopy.

Conventional endoscopy involves the use of instruments to visualize and

explore the internal organs of the body. Due to the invasive nature of the

endoscopic procedure, serious side effects such as perforation, infection and

hemorrhage can be encountered. Conventional CT scans produce cross section ofthe body which needs to be viewed sequentially to extrapolate and construct the

actual 3 dimensional anatomy.

With the advent of spiral CT and Multislice CT along with the advancement

of computing technology, direct 3D imaging of human anatomy is now available

and is known as virtual endoscopy. This is a non-invasive diagnostic tool whichprovides simulated 3D visualizations of organs similar to those produced by

conventional endoscopic procedures. Virtual endoscopy not only avoids the risks

associated with conventional endoscopy, but also can visualize body parts whichare not accessible or compatible with conventional endoscopy. Examples of virtual

endoscopy include virtual colonoscopy and bronchoscopy.

13.7 Screening.

Medical screening tests are usually beneficial since they can detect diseases

in an earlier stage while they can be treated. Although screening with CT couldidentify certain diseases, it may not always be accurate. Thus, confirmatory tests

and aggressive treatments such as chemotherapy or surgery may be required, which

could lead to serious side effects. As a result, screening by CT is not currentlyrecommended for people who do not present with symptoms.

14. Advantages.

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There are several advantages that CT has over traditional 2D medical radiography.First, CT completely eliminates the superimposition of images of structures outside the

area of interest. Second, because of the inherent high-contrast resolution of CT, differences

between tissues that differ in physical density by less than 1% can be distinguished.

Finally, data from a single CT imaging procedure consisting of either multiple contiguousor one helical scan can be viewed as images in the axial, coronal, or sagittal planes,

depending on the diagnostic task. This is referred to as multiplanar reformatted imaging.

CT is regarded as a moderate- to high-radiation diagnostic technique. The improved

resolution of CT has permitted the development of new investigations, which may have

advantages; compared to conventional radiography, for example, CT angiography avoidsthe invasive insertion of a catheter. CT Colonography (also known as Virtual Colonoscopy

or VC for short) may be as useful as a barium enema for detection of tumors, but may use a

lower radiation dose. CT VC is increasingly being used in the UK as a diagnostic test forbowel cancer and can negate the need for a colonoscopy.

The radiation dose for a particular study depends on multiple factors: volumescanned, patient build, number and type of scan sequences, and desired resolution and

image quality. In addition, two helical CT scanning parameters that can be adjusted easily

and that have a profound effect on radiation dose are tube current and pitch. Computed

tomography (CT) scan has been shown to be more accurate than radiographs in evaluatinganterior inter-body fusion but may still over-read the extent of fusion.

15. Hazards and Disadvantages.

Despite the many benefits mentioned, several hazards and disadvantages are

present with CT imaging. One of the main hazards of CT imaging is the risk of allergicreaction (nephrotoxicity) to the contrast agent which may cause itching, hives or swelling

of body parts. CT imaging involves exposure to small amount of ionized radiation which is

considered a hazard for pregnant women and children. CT scanning may also involveuncomfortable body posture in order to obtain imaging of the desired body part. In

addition, due to the physical shape of the CT equipment, claustrophobic patients may

experience anxiety. Furthermore, early detection of diseases with CT scan may lead tomore aggressive treatments such as chemotherapy or radiotherapy which may cause more

serious side effects than if diseases were diagnosed based on symptoms. Early detection of

diseases is also not 100% accurate. Hence, it may lead to confirmatory procedures, such asinvasive biopsies, that in fact may not be necessary.

16. Recent Trends.

16.1 Perfusion CT.

Any new CT scanner with a proper setup and advanced software can be

used for Perfusion CT scanning. Perfusion CT is performed by periodic scanning of

the patient prior to, during and subsequent to the injection of contrast agent

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containing iodine. It relies upon the extraction of functional information rather thananatomical data from the CT scan.

Perfusion CT is a relatively new technique which is currently well

established for brain imaging. It shows the volume and flow rate of blood present inthe brain in addition to revealing the structure of brain tissue. Perfusion CT is

useful for noninvasive diagnosis of cerebral ischemia (stroke), infarction, andassessment of cerebrovascular reserve for vascular stenoses. For instance, in case of

an ischaemic stroke, perfusion CT can indicate whether brain tissues have died due

to lack of blood, or whether some could be revived if corrective therapeutic

treatments are provided. Perfusion CT can also be used to map tumors and assesstheir growth rate and stage. Although Perfusion CT scanning of other body organs

such as liver or kidneys is currently feasible, it still requires further research to

validate its use in some conditions.

16.2 PET/CT.

The PET/CT scanner stands for positron emission tomography combined

with computed tomography scanner. PET provides information regarding growth of

tissues within the body by monitoring glucose metabolism whereas CT provides

detailed information about the location, size, and shape of various body parts andlesions. The PET and CT technologies are integrated in the PET/CT scanner to

provide both metabolic and anatomical information simultaneously. Metabolic

activities of organs appear as colored images in PET/CT scan due to the chemicalchanges in tissues. For example, cancerous tumors are more active than normal

tissues and hence appear in different colors.

This combined information allows for higher accuracy in detecting tumors

and locating different cancers such as breast, esophageal, cervical, melanoma,

lymphoma, colorectal, and ovarian cancer. PET/CT also reduces errors in biopsysampling, improves radiotherapy planning, and enhances the assessment of

response to treatments such as chemotherapy.

17. References.

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Cunningham, Ian A., and Philip F. Judy. The Biomedical Engineering Handbook: Second

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Eliseleblanc. "CT: History and Development." WikiRadiography. 20 June 2009. Web. 22

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Gedgaudas-McClees, R. K, and W. E. Torres.Essentials of Body Computed Tomography.

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CT Following Gastrectomy."Radiographics 22 (2002): 323-36. Print.

Klingebiel, R., M. Busch, G. Bohner, C. Zimmer, O. Hoffmann, and F. Masuhr. "Multislice

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Principles and Clinical Applications."Electromedia 68 2 (2000): 94-105. Print.

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