Myocardial Perfusion Study with CMR and 

Gd-DTPA

 

Rationale

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.
Protocol

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 motion.

 
Drawing ROI's

A dedicated 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 procedure.

 

 

 

 

 
Quantification of myocardial perfusion:

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.