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20 Cards in this Set
- Front
- Back
- 3rd side (hint)
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A patient is having a cardiac MUGA scan. The scan is acquired in 32 frames per cycle. The patients pulse is 68/min and count rate is 1.2 mil cpm. How many minutes will pass before 200,000 counts per frame are reached?
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Total counts = 200,000 c/f x 32 frames = 6,400,000
so 6,400,000c/1,200,000 cpm = 5.3 minutes |
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What is the major difference between planar imaging and SPECT?
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Planar images are 2 planes while SPECT incorporates a third cross sectional plane, similar to CT and MRI
How is this done? |
The 3rd plane is reconstructed by the computer
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What is the major advantage of SPECT imaging?
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improved target to non-target ratio, effectively removing superimposed non-target anatomy.
What are 2 other advantages of SPECT? |
1. 3D localization
2. quantification of radionuclide distributions |
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Why do SPECT images tend to have poor resolution and increased processing time?
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In order to get better resolution it would require acquistion time to be beyond the tolorance of the patient. This shorter time results in poor statistics and resulting longer processing time.
What is more critical then in dealing with the camera in SPECT imaging? |
Camera performance is more critical than in planar imaging, which necessitates more quality control
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As in all imaging modalities there is an art to getting the best image in an efficient way by trading off parameters.
For example when sensitivity is increased what decreases? |
resolution
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What matrix size is normally used in SPECT imaging?
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64 x 64 or 128 x 128
why would you not increase this? |
because increasing the size increases the time of acquisition beyond what the computer and patient tolerance
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How do you determine the pixel size?
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D = FOV/n
where D = pixel size FOV = field of view n = matix or # of pixels example with a FOV of 380 x 380 mm and a matrix of 128 x 128 what is the pixel size? |
3mm x 3 mm
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How do you determine the pixel size when the a rectangular head camera?
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you just divide the matrix into both dimensions
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Why is Tc99m a much better imaging agent then Tl201?
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It allows for a larger dose and results in improved counting statistics with less imaging time
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When considering a SPECT image and viewing a 2 dimensional image, what does it actually represent?
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It also is showing thickness of the tissue, normally 1-3 mm. so it is length, width and thickness. This then is not really a pixel but is called a ?
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Voxel
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A 128 x 128 matrix will use __ times as much disk space and the reconstructed image will use __ times the disk space as a corresponding 64 x 64 matrix image.
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A 128 x 128 matrix will use 4 times as much disk space and the reconstructed image will use 8 times the disk space as a corresponding 64 x 64 matrix image.
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How do you mathematically arrive at the best matrix size for a camera's resolution?
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Divide the FWHM/3
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How is FWHM determined?
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by measuring the line spread function of an image of a line source and by plotting a histogram of the image
example: The FWHM of a camera is 9mm at a distance of 10cm, what should be the optimal matix pixel size and matrix if using a 380 mm FOV? |
9/3 = 3 mm pixel size
so applying pixel size = FOV/matrix 3=380/matrix; then matrix = 380/3=128 x 128matrix size |
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How can we increase resolution without increasing matrix size, especially when imaging a small organ?
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Use Zoom mode acquistion
How do you mathematically determine pixel size in zoom mode? |
D=FOV/(Zxn)
D=pixel size FOV=field of view n=number of pixels Z=magnification factor (zoom) |
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In general when doing a SPECT study what is the minimum # of projections required to have a useful image?
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60
What is the simple rule to remember the number of projections to use in a SPECT study? |
The number of projections must be equal to or greater than the matrix size. ie. 64 x 64 will require 64 projections, etc
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A cardiac SPECT study has 120 projections, a count rate of 150,000 cpm and acquires for 20 sec/projection.
What are the total counts acquired? |
120 x 150,000 x 20/60 = 6 million counts
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What is the primary reason for poor resolution in SPECT imaging?
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The inconsistent source to detector distance as the camera orbits around patient?
Where is the only place where the source to detector distance is constant? |
at the center of rotation
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normally a SPECT study is done in a 360 deg rotation, cardiac is the only time 180 deg is used, why is this and what is the advantage?
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360 deg is not necessary to get a good image of the heart and will result in reduction of time, a greater number of counts can be collected and can have reduced source to detector distance
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Why do you not want to use a high resolution collimator in a SPECT study?
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because the counts are not very high and the resolution is poor
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What can be the result of doing a study with a tilted detector instead of having it level?
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can have artifacts making it a false positive study
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