Physics Test 5

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Physics Test 5

All things CT

If the scanner mA is reduced by 50% by what factor does image noise increase? *

1/2

√2

√(1/2)

What does CTDIvol represent? *

Radiation dose to a patient

Radiation dose to a population

Radiation output for a given acquisition technique

Radiation output corrected for patient size

What is a typical window width (W) and window level (L) of a CT of the abdomen (to visualize soft tissue)?

W = +80, L = -40

W = +400, L = +40

W = 1500, L = -40

W = 1600, L = +40

Clear selection

What is the role of the CT reconstruction kernel?

It adjusts the visible window width (amount of visible grayscale values)

it adjusts the visible window level (centers the grayscale to a tissue type)

It adjusts the the visible spatial frequencies in the image (e.g., emphasizing edges or reducing noise)

Clear selection

What is a typical Hounsfield unit (HU) for fat? *

-1000 HU

-100 HU

0 HU

100 HU

1000 HU

How is the size specific dose estimate (SSDE) for a toddler's abdomen CT exam different than an adult's abdomen scan? *

Lower

The same

Higher

The following is an example of what artifact? *

Out of field of view (FoV)

Helical interpolation

Beam Hardening

Patient motion

CTDIvol modifies CTDIw by accounting for what CT parameter? *

Helical pitch

Gantry rotation speed

At what time point does a retrospective cardiac CT acquire images of the heart?

Acquire images of the heart at a fixed time point after the R peak

Acquire images of the heart at a percent delay of the R to R peak interval

Acquire images of the heart at all points along the cardiac trace

Clear selection

What is the nomenclature for a dual energy CT reconstruction that emphasizes iodine in the image vs. water?

Iodine only

Iodine(Water)

Water(Iodine)

Water subtracted

Clear selection

what is the mathematical definition of CTDIw? *

1/3*CTDI_center + 2/3*CTDI_periphery

1/2*CTDI_center + 1/2*CTDI_periphery

1/4*CTDI_center + 1/2*CTDI_periphery

1/3*CTDI_center + 1/2*CTDI_periphery

How is the CT number equation defined? *

CT(𝐻𝑈)=1000*(𝜇_object−𝜇_fat)/𝜇_fat

CT(𝐻𝑈)=1000*(𝜇_object−𝜇_water)/𝜇_water

CT(𝐻𝑈)=1000*(𝜇_object−𝜇_air)/𝜇_air

CT(𝐻𝑈)=1000*(𝜇_object−𝜇_bone)/𝜇_bone

What does the CT geometric efficiency calculation refer to? *

The amount of helical over ranging

The amount of axial overbeaming

The helical pitch value

The sensitivity of the detectors

The following is an example of what artifact? *

Out of FoV

Helical overbeaming

Beam hardening

Photon starvation

What action is vitally important to maintain CT # accuracy? *

Daily QC

weekly QC

Monthly QC

Annual QC

Which photon interaction predominates in soft tissue for CT? *

Rayleigh Scattering

Photoelectric Effect

Compton Scattering

Auger electron Effect

What is a typical delay used between injecting iodine IV contrast and scanning a patient's abdomen to visualize the late portal venous phase (for a typical healthy adult) ?

20 sec

40 sec

70 sec

100 sec

Clear selection

What is the principle role of iterative reconstruction in CT?

Reduce image noise

Reduce reconstruction time

Increase image edge definition

Increase image contrast

Clear selection

The following is an example of what artifact? *

Out of FoV

Helical overbeaming

Beam hardening

Photon starvation

What is a typical effective dose of an adult brain examination? *

1 mSv

10 mSv

15 mSv

20 mSv

CT dose length product (DLP) is calculated by modifying CTDIvol by what factor? *

Scan length

Patient thickness

CT table speed

Bow tie filter selection

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