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Dose Tolerances > Imaging Modalities > Flashcards

Imaging Modalities Flashcards

1
Q

Another name for Spatial Accuracy

A

Spatial Resolution and Positional Accuracy

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2
Q

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

A

Film; «< 1mm

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3
Q

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

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

What is the CT# accuracy

A

2%, +-3HU, 5HU

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5
Q

CT# of Compact Bone

A

500 - 1000

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6
Q

CT# of Spongy Bone

A

150 - 500

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7
Q

CT# of Thyroid

A

60 - 80

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8
Q

CT# of Liver

A

60 - 75

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9
Q

CT# of Blood

A

50 - 60

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10
Q

CT# of Pancreas

A

30 - 50

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11
Q

CT# of Kidney

A

20 - 40

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12
Q

CT# of White Matter

A

20 - 40

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13
Q

CT# of CSF

A

0 - 20

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14
Q

CT# of Water

A

0

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15
Q

CT# of Fat

A

-50 to -100

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16
Q

CT# of Lung

A

-100 to -1000

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17
Q

What is the CT# equation

A

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

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18
Q

What is DRR quality based on?

A
  1. # slices
  2. CT# Accuracy
  3. Slice Thickness
  4. Technique used
  5. Reconstruction Algorithm
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19
Q

Which CT technique has better resolution?

A

Axial Scanning

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20
Q

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

A

Spiral Scanning (or helical)

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21
Q

What does CTDI mean, what does it measure?

A

CT Dose Index; dose of single slice

22
Q

What is CT DLP mean, what does it measure?

A

CT Dose Length Product; dose of multiple slices;

CTDI x # of slices = CTDLP

23
Q

CTDLP x fudge factor = _____

A

CT Effective Dose

24
Q

What is the Effective Dose for Head CT (axial)

A

2.1 mSv

25
Q

What is the Effective Dose for Chest CT (helical)

A

9.3 mSv

26
Q

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

A

14.0 mSv

27
Q

What is the Effective Dose for natural background radiation

A

3.0 mSv

28
Q

Define CT Leveling:

A

CT# at the center of the window

29
Q

Define CT Window:

A

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

30
Q

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

A

decreases; enhanced

31
Q

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

A

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

32
Q

What is MRI better for compared to CT?

A

GYN, prostate, brain

33
Q

What are disadvantages of MRI?

A
  1. Image Distortion - non-uniform magnetic field

2. No electron density info

34
Q

What are advantages of MRI?

A
  1. Multiplanar Imaging
  2. Unaffected by bone
  3. Good for CNS tumor localization
  4. Various Clinical Uses
35
Q 
How do the following look for T1 MRI:
CSF
Gray Matter
White Matter
Fat
Bone
Air
Blood
A 
CSF = Dark
Gray Matter = Grey
White Matter = Bright
Fat = Bright
Bone = Dark
Air = Dark
Blood = Dark
36
Q 
How do the following look for T2 MRI:
CSF
Gray Matter
White Matter
Fat
Bone
Air
Blood
A 
CSF = Bright
Gray Matter = Grey
White Matter = Grey
Fat = Grey
Bone = Dark
Air = Dark
Blood = Dark
37
Q

What type of contrast is used for T1?

A

Gadolinium

38
Q

Most common isotope for PET, how much is given?

A

F-18; 10-15mCi FDG

39
Q

What is the SUV threshold for cancer?

A

2.5 and greater

40
Q

What organs have normal uptake of PET radionuclide?

A

Brain, heart, liver, kidneys, bladder

41
Q

Nuclear Med radionuclides decay by

A

gamma decay

42
Q

PET radionuclides decay by

A

Beta+

43
Q

As uptake increases in PET aggressiveness of tumor _____?

A

Aggressiveness of tumor increases

44
Q

Disadvantages of FDG?

A
  1. infection
  2. inflammation
  3. Atclectasis
  4. healing tissues
  5. muscular activity
45
Q

For staging purposes, PET is best in determining

A

nodal involvement and metastasis

46
Q

Limitations of SUV include:

A
  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)
47
Q

Port films are contaminated by

A

Compton Scattered Electrons

48
Q

MVCT vs kVCT is produced by what:

A

Compton Scattering; Photoelectric Effect

49
Q

What is the typical FOV for kV CBCT

A

50cm D x 25cm L

50
Q 
kV CBCT Specs of following:
Energy
Resolution
Dose
Beam Hardening Artifacts
Metal Artifacts
Accurate CT#
A 
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)
51
Q 
MV CBCT Specs of following:
Resolution
Dose
Beam Hardening Artifacts
Metal Artifacts
Accurate CT#
A 
Resolution - 0.5mm ( good)
Dose - 4-8cGy (not Good)
BHA - No (advantage)
Metal Artifacts - No (advantage)
Accurate CT# - +-2% (good)
52
Q 
MVCT (tomo) Specs of following:
Resolution
Dose
Beam Hardening Artifacts
Metal Artifacts
Accurate CT#
A 
Resolution - 1-2mm (not good)
Dose - 1-3cGy (Good)
BHA - No (advantage)
Metal Artifacts - No (advantage)
Accurate CT#s - +-5% (not as good)

Dose Tolerances (23 decks)

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