Intro to Imaging

Question 1

X-rays (photons) from the tungsten target pass through the body to expose the…

Answer 1

Recording plate

Question 2

In X-rays, the greater the attenuation or absorption of the photons by tissues, the (WHITER/DARKER) the density will appear.

Answer 2

Whiter

***Organs with air appear dark, bone appears white, and soft tissues and water have intermediate density.

Question 3

How does the position of the patient influence the recorded image of an X-ray?

Answer 3

It depends on what you’re trying to get an image of. For example, the heart lies more anteriorly so we would want the recording plate to be anterior as well and take a Posteroanterior view. If it was posterior, and we recorded the image in Anteroposterior view then we can get a false magnification of certain things. In this case, the heart looks enlarged.

***For the kidneys, we would want an Anteroposterior view because they lie more posteriorly!

Question 4

This is the term for a continuous stream of X-rays to view the movement of structure in real time.

Answer 4

Fluoroscopy

Question 5

In Fluoroscopy, the X-ray source is (ABOVE/BELOW) the patient and an image intensifier and data capture equipment are (ABOVE/BELOW) the patient.

Answer 5

Below

Above

Question 6

In Fluoroscopy, how is the whole apparatus able to be rotated to give 3D information?

Answer 6

With the C-arm

Question 7

What can Fluoroscopy be used for?

Answer 7

• • Barium contrast studies of GI tract
• • Angiographic studies
• • Catheter and tube placement
• • Fracture repair and apparatus placement in ortho sx

Question 8

In Fluoroscopy, X-ray images are taken at _______ frames per second for peripheral vascular studies and _______ frames per second for coronary artery studies.

Answer 8

2-3

15-30

Question 9

This is a form of fluoroscopy that takes a rapid series of X-rays viewed in real-time. An image taken before contrast injection is used to digitally “subtract” bones and other tissues from the view after contrast is administered. This allows for better imaging of the vessels.

Answer 9

Digital Subtraction Angiography (DSA)

Question 10

What can DSA be used for?

Answer 10

• • Balloon angioplasty
• • Stent placement
• • Guide catheter placement

Question 11

What is a downside of DSA?

Answer 11

It’s an invasive procedure (percutaneously gain access vasculature via artery)

Question 12

In contrast to a DSA, these two procedures are relatively noninvasive and only require introduction of an intravenous catheter in an arm vein for contrast injection.

Answer 12

CTA (Computed Tomography Angiography)
MRA (Magnetic Resonance Angiography)

***MRA downside – takes a long time

Question 13

Explain how Computed Tomography works?

Answer 13

Images are generated with X-rays passing through the body in a helical fashion as the patient moves through a rotating X-ray tube. Detectors on the opposite side of the tube collect the X-rays that have passed through the body. Mathematical algorithms reconstruct axial (transverse) 3D images of body.

Question 14

T/F. For CT, images in the sagittal and coronal planes can be reconstructed on the computer from the axial (transverse) images.

Answer 14

True

Question 15

For CT, the gray-scale image can be manipulated on the monitor, allowing you to do what?

Answer 15

Enhance certain structures you want to see

Question 16

CT density numbers are attenuation units measured by what scale (named after British dude)?

Answer 16

Hounsfield Scale

Question 17

The number on the Hounsfield Scale set to middle gray is referred to as the _______ _______, and the range of the gray scale mapped onto the Hounsfield Scale is called the _______ _______.

Answer 17

Window level

Window width

Question 18

All CT numbers below the window width display as (WHITE/BLACK). CT numbers above the window width display as (WHITE/BLACK).

Answer 18

Black

White

Question 19

A wide window width is good for imaging _______, while a narrow window width is better for _______ _______ because it has a higher contrast.

Answer 19

Bone

Soft tissue

Question 20

What are the advantages of using CT?

Answer 20

• • Quick (a few seconds for whole body)
• • Motion not really a problem
• • Gray scale can be manipulated on screen
• • Resolution excellent for many areas
• • Widely available and cheaper than MRI

Question 21

What are disadvantages of using CT?

Answer 21

• • Uses ionizing radiation
• • Renal function must be evaluated if contrast used
• • Some patients allergic to iodine contrast

Question 22

What is the main benefit of MRI over CT?

Answer 22

Does NOT use ionizing radiation

Question 23

Briefly explain how an MRI works.

Answer 23

A big magnet aligns atoms (nuclear spin), then the atoms are knocked out of whack. As the atoms relax back into alignment, they leave a different gray scale that can be used to identify the different tissues.

Question 24

This type of weighted MR measures the time taken for spinning protons to realign with the external magnetic field. Fluid (i.e., CSF) is dark in these images.

Answer 24

T1 (Longitudinal relaxation time)

Question 25

This type of weighted MR measures the time taken for spinning protons to lose phase coherence among the nuclei spinning perpendicular to the main field. Fluid (i.e., CSF) is light in these images.

Answer 25

T2 (Transverse relaxation time)

Question 26

What are the advantages of using MRI?

Answer 26

• • No ionizing radiation
• • Better soft tissue contrast than CT
• • Extremely versatile (variety of pulse sequences can be used to visualize specific tissues and pathology)

Question 27

What are disadvantages of using MRI?

Answer 27

• • Longer time
• • More expensive
• • Images cannot be manipulated onscreen
• • Tube narrower for patients (bad for claustrophobia)
• • No metal in patient’s bodies
• • Contrast can’t be used in pregnant women
• • Patients with renal dysfunction have higher risk of NSF
• • Noisy

Question 28

This type of imaging measures physiological activity rather than anatomy.

Answer 28

Nuclear medicine imaging

Question 29

Explain how nuclear medicine imagining works.

Answer 29

Radioactive molecules are attached to other compounds to form radiopharmaceuticals that are administered orally or intravenously. These then bind to and/or are uptake by specific cells in specific organs and their radioactivity is recorded by an external gamma camera.

Question 30

In nuclear medicine imagine, pathology can be detected by identifying focal areas of increased activity, known as ______ ______, or decreased activity which are called _______ _______.

Answer 30

Hot spots

Cold spots

Question 31

This is a noninvasive imaging technique based on “pulse-echo” sound wave energy.

Answer 31

Ultrasound

Question 32

Explain how an ultrasound works.

Answer 32

A transducers moving over the skin emits pulses of sound waves into the body and then functions as a receiver that records the energy from the “echo” or reflection of sound waves from tissue interfaces within the body.

Question 33

With ultrasound, a computer interprets the sound waves as real-time images. What are high-frequency transducers (7-15 MHz) used to visualize?

Answer 33

Structures near the surface – i.e., neck vessels, thyroid glands, breasts, and testes

Question 34

With ultrasound, a computer interprets the sound waves as real-time images. Lower-frequency sound waves (1-3.5 MHz) have greater penetrating power but less resolution and are used for imagining what structures?

Answer 34

Deep structures – i.e., abdomen and pelvis

Question 35

Why are tissues deep to bone and air difficult to visualize with ultrasound?

Answer 35

Because bone absorbs mot of the sound energy and air reflects most of it.

Question 36

What type of ultrasound measures blood flow?

Answer 36

Doppler ultrasound

Question 37

What are the advantages of using ultrasound?

Answer 37

• • Portable
• • Inexpensive
• • No ionizing radiation
• • Good at capturing motion