Accuracy And Limitations - Carestream Vue PACS MR Diffusion User Manual

12. Accuracy and Limitations

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Image quality—The calculation of perfusion parameters is limited by the scan quality.
Excessive noise, patient movement or image artifacts in the original images will ultimately
have an impact on the perfusion analysis and the calculated maps. The user should inspect
original data and verify that the images are of diagnostic quality and that any patient
movement has been corrected using the motion correction algorithm. If image artifacts are
present in the original images, the same areas on the maps may not contain valid values.
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Relative units—Some of the values are quoted in relative values (rCBV, rCBF). As such, the
values extracted from these maps are valid up to arbitrary constants and therefore should not
be confused with absolute measurements. Moreover, the units of these relative values are not
normally associated with CBV or CBF measurements.
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Accuracy of values— In places where the standard deviation is given along with the average
value, the user is encouraged to examine these values. A large standard deviation compared
with acceptable values may indicate noise or artifact in the images.
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Temporal resolution—Preferably, the temporal resolution should not be lower than the
resolution of one image per 4 seconds. In general, the better the resolution, the more
accurate the deconvolution algorithm.
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Contrast material—The scan duration should allow the contrast material to wash into the
different tissues and then wash out of the tissues, with a possible recirculation. This can be
verified by visually inspecting the raw images.
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AIF—The MR perfusion application assumes that the AIF describes a well-defined signal
originating in the contrast agent injection. The signal should start from a baseline value, climb
to a maximum value and show a gradual drop to low values, possibly showing recirculation
effects. It is the user's responsibility to review the AIF graph and ascertain that a correct AIF
signal is used.
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Spatial resolution—The resolution does not affect the deconvolution algorithm itself. However,
a low spatial resolution might introduce partial volume effects. The user is advised to view the
TMIN image to assess partial volume effects.
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Scan duration—The scan duration should allow the contrast material to pass through the
arteries, into the tissue and out of the veins enabling correct assessment of the perfusion
parameters. Therefore, the user should examine both AIF and VOF and verify that both
exhibit a rise and fall of the contrast material.
Vue PACS MR Perfusion User Guide
AE9362 C
Vue PACS MR Perfusion User Guide - AE9362.docx
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