Computed Tomography

Question 1

Computed Tomography (CT)

Answer 1

non-invasive x-ray technology with a computer

Question 2

What does it provide?

Answer 2

detailed, digital, cross-sectional images of the body in any plane = “slices”

Question 3

True or False: A CT is relatively free from superimposition of different tissues.

Answer 3

True

Question 4

What are the two components necessary to take a CT?

Answer 4

1. high intensity x-ray tube
2. x-ray imaging detectors

Question 5

What houses the components necessary to take a CT image?

Answer 5

the gantry

Question 6

What function does the motorized patient table play during a CT?

Answer 6

moves the patient through the circular opening in the CT machine continually during the examination

Question 7

True or False: The process to obtaining a CT is similar to obtaining a radiograph.

Answer 7

true

Question 8

Describe “the science” behind a CT.

Answer 8

• during the rotation, x-ray source produces a fan-shaped beam of x-rays
• attenuation occurs
• imaging detectors create a snapshot
• many snapshots at different angles are collected in one rotation
• snapshots sent to computer
• computer reconstructs snapshots into cross-sectional images of the tissues

Question 9

True or False: Radiographs carry a higher radiation dose than a CT scan.

Answer 9

false - CT scans have a higher radiation dose than radiographs.

Question 10

What is the issue with ordering a CT on a child?

Answer 10

larger window for opportunity for expression of radiation damage due to children being more sensitive to radiation than adults

Question 11

How can we accommodate pediatric patients that absolutely need a CT?

Answer 11

change the settings on the CT to adjust radiation dose to a smaller body size

Question 12

What is key when considering ordering a CT for a pediatric patient?

Answer 12

order ONLY IF NECESSARY!

Question 13

2 to 3 CT head scans equals how many mGy to the brain?

Answer 13

50-60

Question 14

Children with a greater exposure reported a ______________ increase in risk of brain tumor or leukemia than those with 5mGy exposure.

Answer 14

threefold

Question 15

Do the same principles of radiodensity and radiographic density that we utilize with x-rays apply to CT scans?

Answer 15

yes

Question 16

What are the two characteristics of object radiodensity?

Answer 16

atomic #
Thickness

Question 17

Relative radiodensity are displayed based on the average values of what scale?

Answer 17

hounsfield scale

Question 18

how does the computer apply average values to display overlapping tissues?

Answer 18

overlapping tissues are displayed in one shade of grey

Question 19

radiodensity represents sum of ____________ & ____________ tissues

Answer 19

osseous & tendinous

Question 20

Hyperdense represents __________ and appears ________.

Answer 20

bone, white

Question 21

Isodense represents __________ and appears _________.

Answer 21

brain matter/muscle tissue, grey

Question 22

Hypodense represents _________ and appears __________.

Answer 22

fluid/fat/air, grey-black or black

Question 23

How may metals impede image interpretation?

Answer 23

metals lead to streaking artifacts

Question 24

In a CT, how is an axial view read?

Answer 24

anatomic position from the feet up

Question 25

In a CT, how is a sagittal view read?

Answer 25

from left to right

Question 26

In a CT, how is a front view read?

Answer 26

anatomic position facing the viewer

Question 27

When would you choose to obtain a CT for a musculoskeletal concern?

Answer 27

- subtle fx - complex fx - when MRI is contraindicated - infectious processes

Question 28

What is the preferred imaging method for a suspected spinal fx?

Answer 28

CT

Question 29

What are the ABC'S when viewing a CT?

Answer 29

Alignment Bone density Cartilage joint or canal spaces Soft tissues

Question 30

Where should cortical bone be more dense?

Answer 30

along the margins

Question 31

What are upper extremity indications for a CT?

Answer 31

- shoulder complex fx - elbow complex fx - wrist/hand complex fx

Question 32

When would you choose to obtain a CT for a neurological concern?

Answer 32

- acute trauma to the brain (bleeding & hemorrhaging) - tumor, cysts, abscesses - spinal cord eval when MRI is contraindicated

Question 33

In the brain, how does grey and white matter appear?

Answer 33

grey matter appears lighter than white matter

Question 34

What occurs in the grey matter?

Answer 34

where the processing happens (cell bodies, dendrites, axon terminals)

Question 35

What occurs in the white matter?

Answer 35

communication (axons)

Question 36

In an acute hemorrhage, how does blood appear on a CT?

Answer 36

bright white (hyperdense)

Question 37

In a subacute hemorrhage, how does blood appear on a CT?

Answer 37

fades to grey (isodense)

Question 38

In a chronic hemorrhage, how does blood appear on a CT?

Answer 38

fades to darker grey/black (hypodense)

Question 39

Can a chronic hemorrhage or ischemic stroke be seen on an MRI?

Answer 39

no

Question 40

CT arthrography

Answer 40

intravenous injection that is specific to a joint

Question 41

CT myelogram

Answer 41

CT imaging + myelography injection of water-soluble contrast medium into posterior subarachnoid space, then performing a CT scan

Question 42

A CT myelogram enhances the ability to visualize abnormalities affecting the -

Answer 42

spinal cord, spinal canal, spinal nerve roots & blood vessels of the spinal cord

Question 43

Is a CT myelogram commonly used?

Answer 43

no - not since the invention of the MRI. it is an invasive examination w/increased risk

Question 44

When is CT myelogram indicated over MRI?

Answer 44

contraindication to MRI