Instrument/computer Stuff GW Flashcards
1 word = ____ bytes
2
1 byte = ___ bits
8
1 word = ____ bits
16
Word mode max number of pixels
2^16
Byte mode max number of pixels
2^8
Increasing distance to detector with diverging collimator
Decreases magnification
Increasing distance to detector with converging collimator
Increases magnification
Increasing distance to thyroid with pinhole collimator
Decreases magnification
Decreasing distance to thyroid with collimator
Increases magnification
Frame mode or list mode more common
Frame mode
List mode
Counts are stored sequentially as x and y coordinates
Length of time each image is acquired
Framing rate
Frame mode
All counts are collected into one storage matrix in a given time period
Acquiring in zoom mode _______ resolution
Increases
applying zoom factor post acquisition _______ resolution
Decreases
What do you have to do if zoom mode is used during SPECT
You have to acquire a uniformity correction flood at the same zoom mode and apply it to match the pixel size
Information density = what?
Directly affects what?
= the number of counts per square cm
Directly affects resolution
What increases target to background ratio
Subtracting background
What decreases signal to noise ratio
Acquiring more counts
Normalization
Used when comparing two images with different max counts
Doubles the lower count image to better compare the two
Correction factor for normalization
number of pixels in larger ROI (organ) / number of pixels in smaller ROI (background)
If critical frequency is set too high
Grainy/pixelated picture
If critical frequency is too low
Study is over filtered, too smoothed
High the power factor
Steeper the slope
More high frequencies removed
The lower the power factor
The more high frequencies are preserved
Butterworth uses
Cutoff frequency and power factor
Hanning filter uses
Cutoff frequency - the frequency at which the filter reaches 0
Lower the cutoff
Smoother the image
Drawback of FBP
Assumes no attenuation
-No attenuation correction
