Perfusion Study with CMR and
CMR has the great advantage to allow for high resolution
assessment of myocardial perfusion, that is certainly better than a
perfusion study with radiotracers such as Thallium or SestaMIBI. Moreover,
there is no radiation burden. Moreover, viability can by assessed
with delayed post contrast imaging as shown on the figure to the left
(subendocardial infarction (Radiology 2001; 218:215–223). Such a pathology is not easily identified on
perfusion studies, even when you use PET.
|Gd-DTPA usually 20
ml is injected as a bolus through the antecubital vein. The bolus is
tracked within the heart using 4 slices from apex to base with a slice
thickness of 10 mm, a gap between 10-15 mm, a trigger delay of 200-300 ms,
a breath hold of maximally 26 sec, and a TFE shot duration of 80-100 ms. The
avi file shows a bolus tracking within four slices of the left ventricle
in a healthy volunteer. The bolus increases signal intensity within the
myocardium, which can be quantified in different ways. Because of a too
long breath hold, the volunteer had to breath at the end of the scan. This
motion artifact is however not a problem for the perfusion ananlysis,
since peak to maximum contrast has been reached before the diaphragmatic
perfusion software (MEDIS.NL) that
allows for detection of ischemia in subepi-, subendocardial and transmural
layers of the heart can be used.
Several parameters can be chosen to characterize
perfusion. To improve diagnostic performance, normal databases have to be
built and compared to established marker of perfusion abnormalities such
as nuclear tracers.
Further, delayed imaging may improve the diagnostic accuracy, especially
with respect to specificity of "ischemia" in comparison to the invasive
|Quantification of myocardial
In this example, a signal intensity analysis has been performed which
looks for the time to the maximal upslope of signal intensity. This may be
one of the best parameters for the accurate assessment of perfusion
abnormalities in comparison to perfusion tracers and coronary angiography.
However, it is crucial to develop normal databases for a given imaging
protocol, starting from Gd-DTPA injection dose, injection rate, imaging
procotol and patient variables. Think e.g. of a patient with a supply of
blood via the internal mammarian graft. Contrast media traveling time
might be longer than via naturales and create a false ischemia in the
myocardium supplied by the IMA graft.