Imaging Modalities Flashcards
Another name for Spatial Accuracy
Spatial Resolution and Positional Accuracy
What imaging technique provides the best spatial resolution, what is threshold?
Film; «< 1mm
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
What is the CT# accuracy
2%, +-3HU, 5HU
CT# of Compact Bone
500 - 1000
CT# of Spongy Bone
150 - 500
CT# of Thyroid
60 - 80
CT# of Liver
60 - 75
CT# of Blood
50 - 60
CT# of Pancreas
30 - 50
CT# of Kidney
20 - 40
CT# of White Matter
20 - 40
CT# of CSF
0 - 20
CT# of Water
0
CT# of Fat
-50 to -100
CT# of Lung
-100 to -1000
What is the CT# equation
CT# = [(u_t - u_w) / u_w] x 1000
What is DRR quality based on?
- # slices
- CT# Accuracy
- Slice Thickness
- Technique used
- Reconstruction Algorithm
Which CT technique has better resolution?
Axial Scanning
Depending on pitch, which CT technique gives less dose to the pt?
Spiral Scanning (or helical)
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?
- Image Distortion - non-uniform magnetic field
2. No electron density info
What are advantages of MRI?
- Multiplanar Imaging
- Unaffected by bone
- Good for CNS tumor localization
- 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?
- infection
- inflammation
- Atclectasis
- healing tissues
- muscular activity
For staging purposes, PET is best in determining
nodal involvement and metastasis
Limitations of SUV include:
- Definition of ROI
- Tumor Heterogeneity: Necrosis - lack of uptake in necrotic tissue does not mean cancer is not there
- Tumor volume changes with time
- 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)
