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This is study of almost perfect quality. There is evidence of moderate severe stress induced ischemia in the inferior wall, typical RCA territory. The quantification confirms the findings. |
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screen size image.....full size image.... |
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1. IIMotion
-- There is no evidence of patient motion.
2. IIAlignment
--The alignment is very good.
3. IICount Increase
--The myocardial max counts increases in the stress study as
expected.
4. IINormalization
--Both studies are normalized to the portion within the
myocardium with the highest uptake.
5. IIExtra-Cardiac
Activity --There is no significant extra cardiac activity.
IIII (There is low level of liver
uptake, which has been almost completely eliminated during
processing).
The LV contour is sharp. No blurring or jumps.
Patient motion leads typically to artifacts like: Opposite located
defects, the so-called hurricane sign, or smearing.
sample case - horizontal motion sample case - vertical motion
Most myocardial perfusion studies consist of two parts representing perfusion in two different situations. The studies are compared and analyzed for differences. It is therefore very important that the two studies are aligned properly, insuring that the same portions of the myocardium are compared between the two studies.
The first images (left) in both studies contain the most apical portion of the myocardium. The last images (right) in both studies contain the most basal portion of the myocardium. The studies are thus well aligned. In this layout, three 5 mm slices have been added starting from the apex. A good gamma camera has a spatial resolution of about 10 mm. If 5 mm slices are displayed, one must identify any given abnormality in 3 consecutive slices to ensure it is not a random variation. Slices can, with advantage, be added giving 10-15 mm thick myocardial portions. This reduces random variations, increases specificity, and deals with clinically relevant myocardial volumes.
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In a typical one-day protocol, the second tracer dose is 2.5 to 3 times higher than the first. The maximal myocardial count in the second study should consequently be about 2-3 times higher than in the first study. If the second tracer dose is partially or completely infiltrated, the counts in the second study will be less than expected, or even less than in the first study.
By displaying the myocardial max counts in both studies, and verifying the expected increase in myoardial counts in the second study, one can be certain that the second dose reached the heart.
sample case - low counts sample case - infiltration
In all digital images the pixel with the highest count will automatically be set to 100%, and all other pixels normalized (scaled) to this pixel.
In an almost perfect study like this, the pixel (or voxel) with the highest number of count is, in both studies within the myocardium. All other myocardial pixels in each studies are therefore normalized to that portion of thr heart. This should always be the case.
If there is any extracardiac object with higher count /pixel than the myocardium, the image will automatically be normalized (scaled) to this object. All slices will be normalized (scaled) to this object, not only the slice where the object is located. The "hot" object may be detectable on the slices containing the heart, or may even be on slices not containing the heart and thus not displayed.
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If there is a normalization problem, the study must be
re-prosessed. The maximal cardiac uptake must be identified and
the total reconstructed study must be renormalized (re-scaled)
to this value. Short axis, sagittal, and transaxial data sets
must be reprocessed individually.
This is usually done manually by systematically searching the
slices for the maximal myocardial counts/pixel, and then
normalizing (re-scale) the study to this value.
In the recently released "Emory Cardiac
Toolbox" package there is a computerized method for correct
normalization.
EXTRA-CARDIAC ACTIVITY:
Extra-cardiac activity that may interfere with assesment of
myocardial perfusion is usually sub-diaphragmatic:
High liver uptake below and to the right of the heart
(remember, the heart is resting on the left liver lobe), or
bowel/gastric uptake below and to the left of the heart.
However, now and then a bowel loop can sneak up laterally to
the heart (hernia or right hemi-diaphragm). Reflux to the
stomach and even esophagus has also been reported.
sample case - liver uptake sample case - bowel uptake sample case - liver and bowel uptake
Tc based tracers are excreted by the liver, accumulate in the gall blader, and then passed on to the intestine. Some patients are slow liver "excreters". There is no known way of predicting the individual patients speed of excretion. Food may help speed up liver excretion.
Much of the extra-cardiac activity can be excluded during reconstruction but some can not. Bowel uptake to the left to the heart can be especially problematic.
Extra-cardiac activity can lead to two problems:
In some cases the inferior or lateral walls are impossible to read due to such overlying or close proximity extra-cardiac activity -- only by repeating the study with different timing this problem can be solved.
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