Introduction to Chest Radiology - ACR

Non-Interpretive SkillsIntroduction to Radiology

Before You Begin

This module is intended primarily for clinical medical students or interns intending to learn or review non-interpretive radiology skills.

Please note that while not integral, this module series assumes some familiarity with basic imaging techniques and interpretive skills. If you wish to learn or review these concepts, please see our “Interpretive Skills” module series.

If material is repeated from another module, it will be outlined as this text is so that you are aware

Learning Objectives

• Describe how images are produced using different radiographic techniques

• Recognize correct orientation of a chest x-ray

• Locate right and left on a properly oriented x-ray

• Locate right and left, anterior and posterior on a CT scan image

• Name two different x-ray views

• Categorize different tissue densities as most lucent to most opaque on an x-ray

Types of Radiology Exams

• X-rays

• Fluoroscopy

• Computed tomography (CT)

• Magnetic resonance imaging (MR)

• Ultrasound

• Nuclear medicine

Film

X-rays

• Directed toward patient

• Some x-rays are absorbed

and others pass through the

body

• The more x-rays that hit the

film, the darker it will appear

Chest X-ray

Areas that

are white

have

absorbed

a majority

of x-rays

Areas that

are dark

have

absorbed

few x-rays

Shoulder X-ray

Abdominal X-ray

1. Density

2. Thickness

3. Superimposition of different structures

X-rays

Degree of whiteness seen on an x-ray is an effect of three different things…

Film

X-ray at the extremes

Metal plate

X-ray at the extremes

Metal plate

Film

X-ray at the extremes

Air

X-ray at the extremes

Air

Air Fat Tissue Bone

Imaging properties: Density

• Density of structures effects their appearance

• Four basic densities• Air

• Fat

• Soft tissue

• Bone

Imaging properties: Density

Imaging properties: Thickness

• Two cups with different amounts of H2O

• Similar density when x-rayed from side

• Cup with more water whiter when x-rayed from top

Imaging Properties: Super-Imposition of Different Structures

Overlapping

structures cause

tissues to look

“whiter” or more

dense

Where the two

ribs overlap they

appear more

dense

Where the heart

and spine

overlap they

appear more

dense

Where the lung

and breast tissue

overlap the lungs

appear more

dense

Benefits of X-rays

• They’re fast and

easy!

• Only take a few

seconds to obtain,

similar to taking a

photo

• They can be

portable!

• We have portable x-

ray machines that

can be brought to

the patient’s bedside

Benefits of X-rays

• They can be

portable!

• We have portable x-

ray machines that

can be brought to

the patient’s bedside

Benefits of X-rays

• They can be

portable!

• We have portable x-

ray machines that

can be brought to

the patient’s bedside

If the patient is well enough, the quality of an x-ray is usually

better if the patient can be transported to the Radiology dept

Benefits of X-rays

• They can be

portable!

• We have portable x-

ray machines that

can be brought to

the patient’s bedside

But if the patient is very ill or in the intensive care unit, portable

films are very useful!

Benefits of X-rays

• They’re not very

sensitive or specific

• In other words…• We can miss

disease when it’s

present

• We can’t always tell

the difference

between different

diseases

Drawbacks of X-rays

• There is an area of

increased density in

the lung which is

abnormal

• But…we can’t tell

what it is for sure

• Other types of

radiology exams

are better at giving

a definitive answer

Drawbacks of X-rays

• There is an area of

increased density in

the lung which is

abnormal

• But…we can’t tell

what it is for sure

• Other types of

radiology exams

are better at giving

a definitive answer

Drawbacks of X-rays

X-ray Orientation

Right Left

HEART

X-ray Orientation

R L

Don’t confuse “right hand side” or “left hand side” with

radiologic right and left. It’s opposite!

Shoulder X-ray

Shoulder X-ray (same film…just flipped!)

Shoulder X-ray All films need a marker

Film

X-ray Views • View describes the position of

the patient relative to the x-ray

beam

• In this example the beam

enters from posterior to

anterior

• This is called a “PA” film

(posterior to anterior)

Film

X-ray Views • View describes the position of

the patient relative to the x-ray

beam

• In this example the beam

enters from anterior to

posterior

• This is called a “AP” film

(posterior to anterior)

Items closer to film appear smaller!

Object

Film

Items closer to film appear smaller!

Object

Film

AP PA

Heart appears larger on an AP film

AP View

X-ray Views

Most x-rays that show a “frontal” image are AP.

Chest x-rays are really the only exception.

Lateral view of the chest

Film

Lateral View of the Chest

PosteriorAnterior

Inferior

Superior

Lateral View of the Knee

AnteriorPosterior

What structures or organs can we evaluate with X-rays?

Bones

Heart and lungs

Bowel

What structures or organs can we evaluate with X-rays?

What soft tissues can we see?

• Bladder

• Psoas muscle

• Bowel loops

Must be of

different density

than the tissue

next to it!

Fluoroscopy

Fluoroscopy

• Uses “real time” x-rays

• Can watch the images on a video screen while the patient changes positions etc…

Fluoroscopy

• Often used to evaluate swallowing or bowel abnormalities

• An oral contrast agent which appears dense is often used to make the bowel lumen visible on x-ray

Fluoroscopy

• Often used to evaluate swallowing or bowel abnormalities

• Can give functional information, since were not just seeing a single point in time

Computed Tomography (CT) Scans

• Uses x-rays

• X-ray camera rotates around patient

• Film (detectors) senses x-rays that pass through patient

• Mathematical equation makes an image of the inside of the body

CT Scans

• An x-ray tube rotates around thepatient in a circle

• X-rays pass through the patient and then are “read” by multipleradiation sensitive detectors

• CT produces a volume of data that the computer can translate into cross sectional images

• Because CT uses x-raysmany of the imaging properties are the same as for plain film x-rays

Red arrow =

rotating x-ray

tube

White arrows =

x-ray detectors

Viewing CT

• CT scans are acquired as cross-sectional (axial, transverse) images

• Viewed as if looking up from the feet• Patient’s right is on

viewer’s left

• If patient supine (face up) -anterior is up

Right

Anterior

Posterior

Left

CT Scans: Orientation

Essentially, CT scans are oriented as if you are a doctor standing at the foot of a patients bedside looking up toward their head as in the illustration below

Right Left

Posterior

Anterior

CT Image provided by Dr. Richard Breiman

CT scans may be obtained at any

location within the body. The next slide

shows CT scans through multiple

locations within the body including the

following:

1.Head

2.Neck

3.Chest

4.Abdomen

5.Mid thigh

Computed Tomography (CT) Scans

Benefits: ➢ Fast

➢ More sensitive and specific

➢ Better soft tissue detail

➢ Better “3D” anatomic evaluation

Computed Tomography (CT) Scans

Benefits: ➢ Fast

➢ More sensitive and specific

➢ Better soft tissue detail

➢ Better “3D” anatomic evaluation

Benefits: ➢ Fast

➢ More sensitive and specific

➢ Better soft tissue detail

➢ Better “3D” anatomic evaluation

Computed Tomography (CT) Scans

Benefits: ➢ Fast

➢ More sensitive and specific

➢ Better soft tissue detail

➢ Better “3D” anatomic evaluation

Computed Tomography (CT) Scans

CT Reformations

Coronal Sagittal

Fracture of Acetabulum?

Transverse or Axial Coronal

CT of the Hip

Confirms fracture

of posterior

acetabulum!

Magnetic Resonance Imaging

• Uses a magnet and radiofrequency pulses

• Images hydrogen protons

• H+ protons are themselves small magnets

• Radiofrequency pulse lines up all H+ protons perpendicular to magnet

• Lined up protons rotate

• We sense this rotation

MRI Imaging

• Measures signal, NOT density

• Signal of tissues different with different MRI settings

• Very specific indications• Brain tumors

• Soft tissues and bones

• Characterization of masses (e.g. liver)

• Heart

MRI Imaging

Comparatively difficult to scan patients :

➢ Long scan times

➢ Have to hold still

➢ Claustrophobia

➢ Loud

➢ Can only scan one body part at a time

Comparatively difficult to scan patients :

➢ Long scan times

➢ Have to hold still

➢ Claustrophobia

➢ Loud

➢ Can only scan one body part at a time

MRI Imaging

Comparatively difficult to scan patients :

➢ Long scan times

➢ Have to hold still

➢ Claustrophobia

➢ Loud

➢ Can only scan one body part at a time

MRI Imaging

Comparatively difficult to scan patients :

➢ Long scan times

➢ Have to hold still

➢ Claustrophobia

➢ Loud

➢ Can only scan one body part at a time

MRI Imaging

Comparatively difficult to scan patients :

➢ Long scan times

➢ Have to hold still

➢ Claustrophobia

➢ Loud

➢ Can only scan one body part at a time

MRI Imaging

Safety issues:

• Very strong magnet!

• Projectiles

• Metal implants, foreign bodies & prosthetic devices

MRI Imaging

MRI Imaging

• Why do we do it then???

• Because it’s the best imaging test for certain

things- Musculoskeletal injuries

- Spine

- Brain tumors

MRI Imaging

Ultrasound

• Ultrasound or sonography uses sound waves to create image

• Like MRI there is no radiation (x-rays)

• Different tissues reflect the sounds waves to different degrees. The more reflective a tissue, the brighter it appears on the image

• Images are obtained “real time”by an ultrasound technician (sonographer) or radiologist

Ultrasound

• Ultrasound is used

frequently to image children

and fetuses because there

is no radiation exposure

Ultrasound

• A technologist or physician holds a transducer on the surface of a patient

• The transducer produces very rapid high frequency sound pulses that travel into the patient

• Tissues reflect a small percentage of these sound waves back to the transducer

Ultrasound

• Most tissues have similar acoustic impedances (attenuate the sound beam)

• Stronger attenuators include bone and air

• When sound passes from one tissue (with a particular acoustic impedance) to another tissue (with a different acoustic impedance), some energy is reflected at the interface

• The greater the difference in impedance between the tissues, the greater the reflection

Ultrasound

• The more sound waves are reflected, the whiter a tissue will appear

• The transducer can calculate the depth of the tissue that reflected the sound waves by measuring the time between their production and return

• Using these two pieces of information (tissue depth and reflectivity), the ultrasound machine creates an image

Fat Muscle

Sound wave or “pulse”

Reflectionor “echo”

When the sound beam passes from one tissue to another (with different acoustic impedences), some of the energy is reflected at the interface between the two tissues

Fat Muscle Liver Fluid

Since the impedence values are similar for most tissues, only a small fraction of the sound beam is reflected at interfaces. This allows most of the energy to penetrate deeper (to the next tissue interface) and be reflected to form an image there, and so on through the depth of the area being imaged.

Fluid (bile) in gallbladder

Ultrasound

• Ultrasound images

seem difficult to

interpret because they

are of lower resolution

• One general rule with

ultrasound is that fluid

appears black

Nuclear Medicine

• Something is tagged with radioactive material

• A tiny amount is injected into the body

• Images are taken with a gamma camera

• Physiologic imaging

• Very poor anatomic resolution

Learning Objectives• Describe how images are produced using different radiographic

techniques

• Recognize correct orientation of a chest x-ray

• Locate right and left on a properly oriented x-ray

• Locate right and left, anterior and posterior on a CT scan image

• Name two different x-ray views

• Categorize different tissue densities as most lucent to most opaque on an x-ray

END