Imaging Flashcards
How far does an F18 positron travel in water?
0.5 mm
What is the post-injection uptake period for FDG PET?
1 hr
What is a typical dose of FDG PET?
10-20 mCi
What are the 2 broad techniques for automated image registration?
geometry (detects/aligns edges of objects) and intensity (compares the intensity of the voxels themselves) -based metrics
What kind of image registration metric is best for aligning CT to MRI?
mutual information - a special type of intensity-based metric needed because the absolute intensity of MRI and CT differ greatly, and the greater soft-tissue contrast in MRI creates more/different edges making geometry-based registration hard
How does a mutual information registration algorithm work?
tries to minimize the number of voxel-intensity pairings rather than trying to minimize the difference between the voxel intensities themselves
What is the pulse sequence for T1 MRI imaging?
short-short (TR ~ 500 ms, TE < 15 ms)
what is T1 imaging used for in radiotherapy?
to assess nodal invasion
What is the pulse sequence for T2 MRI imaging?
long-long (TR ~ 2000 ms, TE ~ TR)
How to tumors appear on a T2 image?
they tend to be bright (not always, but usually)
What is the pulse sequence for proton density weighted MRI?
long-short
What is T1 relaxation in MRI?
longitudinal relaxation - spin-lattice - the amount of time it takes the protons to realign with the magnetic field (to regrow to 63% of the max value)
What is T2 relaxation in MRI?
transverse relaxation - the amount of time it takes the transverse signal to fade away (to decay to 37% of the max value) after relaxation
What is TR in MRI?
the amount of time between excitation RT pulses
What is TE in MRI?
the time between excitation and signal acquisition
What does TR control in MRI?
T1 weighting
What does TE control in MRI
T2 weighting
How does imaging dose vary with kVp, mAs, and pitch?
proportional to kVp^2, mAs, and 1/pitch
What is the Rose criteria?
SNR must be at least 5 to resolve an object in an image
What is the nyquist frequency?
principle that says you must sample at least 2x the frequency you want to resolve, so in imaging, you need at least 2 pixels per dimension you want to see - so 1 cycle/ 2 pixels
What is the MTF limit of detectability by humans?
0.1
Draw the Noise Power Spectrum triangle thing
What is QDE in imaging?
Quantum Detective Efficiency - how good the imager is at collecting information - n collected / n incident
What is DQE in imaging?
Detective Quantum Efficiency - how good it is at converting information carriers into an image - SNRout^2/SNRin^2
What are some advantages/disadvantages of radiochromic film as a dosimeter?
- better dosimetric accuracy
- tissue equivalent
- energy independent
- no chemical processing (gives you the better accuracy)
X - requires higher minimum dose
What are some advantages/disadvantages of radiographic film?
- highest spatial resolution
- more sensitive (higher minimum dose requirement)
X- only energy independent for MV beams
X- higher uncertainty (because of development error, fogging in visible light)
X- strong energy dependence in kV range
what is CTDI vol?
CTDI_w / pitch
What is the dose-length product (DLP)?
CTDI_vol * L_scan
What is regularization in image registration?
like a penalty function to prevent overfitting, restricts unrealistic motion (like bending of bones)
About how much dose do the staff get for an FDG-PET imaging procedure?
~25 microGy
