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Diagnostic Imaging > CT Scan > Flashcards

CT Scan Flashcards

1
Q

What are the 3 major elements of a CT scanner?

A
  • The gantry
  • Operators console
  • The computer
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2
Q

How many detectors are arranged around a patient in a CT scan?

A
  • Up to 1000

- 4 to 16 rows of detectors

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3
Q

What is the data acquisition system of a CT scanner?

A
  • Amplifies signal from amplifies signal from detectors
  • Converts from analog to digital
  • Sends to computer
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4
Q

What is a scout image?

A
  • 2-d digital radiograph produced by CT

- Determines localized structures to be scanned.

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5
Q

What is a CT scanner’s pitch?

A

The amount the table advances during each subsequent scan. Modern CT scanners move continuously, and do not have a pitch.

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6
Q

What is the mondern spiral technology of CT scanners called?

A

multislice CT (MSCT) volumetric scanning.

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7
Q

What type of slice does a MSCT scanner make?

A

A helical.

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8
Q

What does a pixel represent?

A
  • The radiodensity in the cell of a matrix formed from converting digital signals of the computer that resulted from the scan.
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9
Q

How is a pixel represented in the image?

A

A shade of grey.

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10
Q

What is three-dimensional CT?

A

3-D images created by CT data that can be rotated in space.

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11
Q

What is CT myelography?

A

Injection of a contrast agent into the subarachnoid space to explore the space in the spinal column.

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12
Q

Why is CT myelography more accurate than MRI?

A
  • Better distinguishes osteophytes, ligamental infolding, and annular material.
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13
Q

What is a voxel?

A

A slice created by a CT scan ranging from 0.1mm to 10mm thick.

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14
Q

What is volume averaging?

A

The averaging of all the tissues in a voxel to one radiodensity.

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15
Q

How is an axial image viewed?

A

As if the patient were supine, and the viewer were looking up from below.

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16
Q

How are sagittal images viewed?

A

From left to right.

17
Q

What is windowing?

A
  • Selecting range of specific radiodensities to be displayed in the image.
18
Q

What 3 factors improve spatial resolution?

A
  • Large matrix size
  • Small field of view
  • Thin slices
19
Q

What 3 factors degrade image quality?

A
  • Hardening
  • Artifacts
  • Motion artifacts
20
Q

When must thinner slices be used? What is the effect on the image?

A
  • Areas with finer anatomical detail
  • More radiation
  • More noise in the image due to less radiodensity
21
Q

What does CT image best?

A
  • Subtle fractures/ complex fractures
  • Degenerative changes
  • Multiple injuries to osseous and soft tissue
  • Spinal stenosis
  • Intervertebral disks
  • Loose bodies in a joint
22
Q

What advantages does CT have over MRI?

A
  • Less expensive
  • Accurate measurement of bone in any plane
  • Less problematic for patients with claustrophobia
23
Q

What are 2 disadvantages of CT?

A
  • Not sensitive to histological properties

- Huge radiation exposure

24
Q

In what type of settings is CT the modality of choice for neuroimaging?

A
  • Acute settings

- Trauma

25
Q

How is ischemic stroke imaged on CT?

A

Thrombis in vessel causes vessel itself to be more radiodense than the surrounding brain tissue.

26
Q

How is ischemic stroke imaged on MRI?

A
  • T2 MRI picks up on edema associated with brain death.
27
Q

How is cerebral hemmorage/ hematoma imaged on CT in the acute phase?

A

Acute: Parenchyma is bright; blood in CSF is bright

28
Q

How is cerebral hemmorage/ hematoma imaged on CT in the subacute phase?

A
  • Hemorrhagic area less radiodense than surrounding tissue,.
29
Q

How is acute cerebral hemorrhage/ hematoma imaged on MRI?

A
  • T1: high signal intensity
  • T2: Low

Pronounced edema –> high in T2

30
Q

How is chronic hemorrhage/ hematoma imaged on MRI?

A

T1: Low intensity
T2: High intensity

Diagnostic Imaging (14 decks)

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