Imaging Modalities Flashcards by Greg Thomas

Another name for Spatial Accuracy

Spatial Resolution and Positional Accuracy

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What imaging technique provides the best spatial resolution, what is threshold?

Film; «< 1mm

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List in order, with the threshold, the quality of spatial resolution, from best to worst:

Film <<< 1mm, 
Flouro << 1mm, 
CT = 0.5mm, 
MRI = 1 - 2mm, 
PET = 4 - 5mm,
SPECT = 10 -12mm

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What is the CT# accuracy

2%, +-3HU, 5HU

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CT# of Compact Bone

500 - 1000

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CT# of Spongy Bone

150 - 500

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CT# of Thyroid

60 - 80

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CT# of Liver

60 - 75

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CT# of Blood

50 - 60

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CT# of Pancreas

30 - 50

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CT# of Kidney

20 - 40

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CT# of White Matter

20 - 40

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CT# of CSF

0 - 20

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CT# of Water

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CT# of Fat

-50 to -100

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CT# of Lung

-100 to -1000

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What is the CT# equation

CT# = [(u_t - u_w) / u_w] x 1000

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What is DRR quality based on?

# slices
CT# Accuracy
Slice Thickness
Technique used
Reconstruction Algorithm

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Which CT technique has better resolution?

Axial Scanning

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Depending on pitch, which CT technique gives less dose to the pt?

Spiral Scanning (or helical)

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What does CTDI mean, what does it measure?

CT Dose Index; dose of single slice

What is CT DLP mean, what does it measure?

CT Dose Length Product; dose of multiple slices;

CTDI x # of slices = CTDLP

CTDLP x fudge factor = _____

CT Effective Dose

What is the Effective Dose for Head CT (axial)

2.1 mSv

What is the Effective Dose for Chest CT (helical)

9.3 mSv

What is the Effective Dose for Abdomin/Pelvis CT (helical)

14.0 mSv

What is the Effective Dose for natural background radiation

3.0 mSv

Define CT Leveling:

CT# at the center of the window

Define CT Window:

Width (CT#s) of the ramp is used to map CT# to brightness

As Window width _____, the contrast in the image is _____

decreases; enhanced

What CT#s can be seen given L = 0 and W = 2000, L = 40 and W = 40, and L = -400 and W = 400?

-1000 to 1000; 20 to 60; -600 to -200

What is MRI better for compared to CT?

GYN, prostate, brain

What are disadvantages of MRI?

1. Image Distortion - non-uniform magnetic field | 2. No electron density info

What are advantages of MRI?

1. Multiplanar Imaging 2. Unaffected by bone 3. Good for CNS tumor localization 4. Various Clinical Uses

``` How do the following look for T1 MRI: CSF Gray Matter White Matter Fat Bone Air Blood ```

``` CSF = Dark Gray Matter = Grey White Matter = Bright Fat = Bright Bone = Dark Air = Dark Blood = Dark ```

``` How do the following look for T2 MRI: CSF Gray Matter White Matter Fat Bone Air Blood ```

``` CSF = Bright Gray Matter = Grey White Matter = Grey Fat = Grey Bone = Dark Air = Dark Blood = Dark ```

What type of contrast is used for T1?

Gadolinium

Most common isotope for PET, how much is given?

F-18; 10-15mCi FDG

What is the SUV threshold for cancer?

2.5 and greater

What organs have normal uptake of PET radionuclide?

Brain, heart, liver, kidneys, bladder

Nuclear Med radionuclides decay by

gamma decay

PET radionuclides decay by

Beta+

As uptake increases in PET aggressiveness of tumor _____?

Aggressiveness of tumor increases

Disadvantages of FDG?

1. infection 2. inflammation 3. Atclectasis 4. healing tissues 5. muscular activity

For staging purposes, PET is best in determining

nodal involvement and metastasis

Limitations of SUV include:

1. Definition of ROI 2. Tumor Heterogeneity: Necrosis - lack of uptake in necrotic tissue does not mean cancer is not there 3. Tumor volume changes with time 4. Small tumors (size and resolution)

Port films are contaminated by

Compton Scattered Electrons

MVCT vs kVCT is produced by what:

Compton Scattering; Photoelectric Effect

What is the typical FOV for kV CBCT

50cm D x 25cm L

``` kV CBCT Specs of following: Energy Resolution Dose Beam Hardening Artifacts Metal Artifacts Accurate CT# ```

``` Energy - 80-140 kVp (good) Resolution - 0.5mm (good) Dose - 1-3 cGy (good) BHA - Yes (disadvantage) Metal Artifacts - Yes (disadvantage) Accurate CT# - +-1% (good) ```

``` MV CBCT Specs of following: Resolution Dose Beam Hardening Artifacts Metal Artifacts Accurate CT# ```

``` Resolution - 0.5mm ( good) Dose - 4-8cGy (not Good) BHA - No (advantage) Metal Artifacts - No (advantage) Accurate CT# - +-2% (good) ```

``` MVCT (tomo) Specs of following: Resolution Dose Beam Hardening Artifacts Metal Artifacts Accurate CT# ```

``` Resolution - 1-2mm (not good) Dose - 1-3cGy (Good) BHA - No (advantage) Metal Artifacts - No (advantage) Accurate CT#s - +-5% (not as good) ```