CT Registry Study Flashcards

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Questions and Answers

How do you reduce beam hardening? (Select all that apply)

Reduce collimation and slice thickness (correct)

Increase dose (correct)

Use a thicker slice

Increase window width (correct)

At what level does the abdominal aorta bifurcate?

What is the typical scan delay after injection of contrast media for studies of the liver?

30-45 seconds

What window settings provide the best tissue differentiation within the liver?

window width = 140, level = 60 Signup and view all the answers

What is the window setting that provides the best bone window for the pelvis?

window width = 2000, window level = 350 Signup and view all the answers

What mAs is typically used in routine CT exams of the abdomen?

200-300 mAs Signup and view all the answers

What is the result of the bifurcation of the abdominal aorta?

The right and left common iliac arteries Signup and view all the answers

What is the anode target angle?

12 degrees Signup and view all the answers

At what level do the common carotids bifurcate into the internal and external carotid arteries?

C3-C4 Signup and view all the answers

The floor of the orbit is formed by the __________ bones.

maxillary and zygomatic Signup and view all the answers

The lateral wall of the orbit is formed by the ___________ bones.

zygomatic and sphenoid Signup and view all the answers

The medial wall of the orbit is formed by the _________ bones.

ethmoid and lacrimal bones Signup and view all the answers

How do you calculate effective mAs?

mAs/pitch Signup and view all the answers

Define window level and window width.

Window level: a chosen midpoint in the grayscale; Window width: number of grayscale values above and below the level. Signup and view all the answers

Give window levels for brain, lung, abdomen, and bone.

Brain: W80, L+40; Lung: W1500, L-400; Abdomen: W400, L+50; Bone: W1600, L+500 Signup and view all the answers

What is beam hardening?

As the X-ray beam passes through an object, lower energy photons are removed, leaving a 'harder beam' of high energy photons. Signup and view all the answers

What are the two types of beam hardening artifacts?

Cupping and streak artifacts Signup and view all the answers

Is the focal spot large or small?

Large Signup and view all the answers

Which of the following will result in an increased voxel size? (Select all that apply)

Increased slice thickness Signup and view all the answers

If a tissue with a CT number of +300 appears white on the image, which of the following are the window width and window level selected? (Select the correct answer)

Window level = 0, window width = 500 Signup and view all the answers

What is the volume of a voxel if a slice thickness of 3 mm, a 512x512 matrix & a reconstruction field of view of 25.6 cm are used? (Select the correct answer)

0.75 mm³ Signup and view all the answers

Study Notes

Beam Hardening

Beam hardening occurs when lower energy photons are filtered out as X-rays pass through an object, resulting in a "harder" beam of higher energy photons.
Two types of beam hardening artifacts:
- Cupping: the center of a round object appears darker than the periphery; commonly seen in the head.
- Streak: dark bands create in lines between two dense objects where nearly all photons are absorbed.
Compensation methods for beam hardening include:
- Filtration: Removing low energy photons before the beam reaches the object.
- Calibration: Using phantoms to set compensated mA/kVp.
- Correct software applications: Iterative reconstruction can mitigate issues.
- Avoidance: Adjusting the gantry position or patient positioning to minimize effects.

Aorta Bifurcation

The abdominal aorta bifurcates at the L4 level into the right and left common iliac arteries.

Contrast Media and Liver Scans

Typical scan delay after injection of contrast media for liver studies is 30-45 seconds.
Optimal window settings for tissue differentiation in the liver:
- Window width: 140
- Window level: 60

Window Settings

Best bone window settings for pelvis:
- Window width: 2000
- Window level: 350
Various window levels for different body parts include:
- Brain: Window width = 80, Level = +40
- Lung: Window width = 1500, Level = -400
- Abdomen: Window width = 400, Level = +50
- Bone: Window width = 1600, Level = +500

mAs Usage

Typical mAs values for routine CT exams of the abdomen range from 200 to 300 mAs.

Anatomic Formations

The floor of the orbit is constructed by the maxillary and zygomatic bones.
The lateral wall of the orbit comprises the zygomatic and sphenoid bones.
The medial wall is formed by the ethmoid and lacrimal bones.
Common carotids bifurcate into internal and external carotid arteries at the C3-C4 level.

Effective mAs Calculation

Effective mAs is calculated as mAs divided by the pitch.

Window Level and Width Definitions

Window level is the midpoint in grayscale, while window width measures the range of grayscale values.
Wider window widths correspond to lower contrast, allowing more grayscale values.

Voxel and Image Construction

Voxel volume calculation involves slice thickness, matrix size, and field of view; example with 3 mm slice thickness, 512x512 matrix, and 25.6 cm FOV yields a voxel volume of 0.75 mm³.
Increased voxel size can result from increased slice thickness.

Artifacts and Calibration

Ring artifacts arise from calibration errors or defective detectors causing consistent erroneous readings across angular positions.
The focal spot size is typically large (0.6-1.2 mm) to prevent overheating of the anode due to high mA.

CT Number Interpretation

If a tissue with a CT number of +300 appears white, it likely corresponds to a window level of 0 and a window width of 500.

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Description

Prepare for the CT Registry with these essential flashcards that cover key concepts and procedures in CT imaging. This selection excludes anatomy but includes critical tips like beam hardening reduction and optimal scan delays. Ace your CT Registry exam with concise, focused study material!