Effects of missing dynamic images on myocardial perfusion reserve index calculation: comparison between an every heartbeat and an alternate heartbeat acquisition.

A commonly used method for analysis of first pass myocardial perfusion imaging is the calculation of a myocardial perfusion reserve index (MPRI) obtained by dividing the upslopes of the time-intensity curves at stress and rest. Perfusion data can be acquired with several different sequences with images acquired at every single, 2nd, or 3rd heartbeat. During data acquisition, some images of the dynamic series can be missed due to extra beats. Twenty-six patients underwent first-pass magnetic resonance perfusion imaging, acquiring images every heartbeat at rest and stress. The maximal upslopes of the myocardium and the left ventricle were calculated for the original image series and for the image series from which dynamics of every 2nd heartbeat were removed. Additionally for each of these situations the upslope calculations were repeated but with the removal of one or two dynamics during the maximal upslope. Images acquired every 2nd heartbeat yielded a lower upslope for the myocardium and the left ventricle, but the resulting MPRI was unchanged. Removing dynamics during the upslope resulted in a change of the MPRI by up to 44% for every heartbeat acquisition and by up to 56% for an alternate sampling. In conclusion, missing data points may affect the calculation of MPRI values and should be taken into account when using such values to define a threshold, which discriminates between normally and abnormally perfused myocardium. Furthermore, it may lead to false positive or negative results in individual cases. This effect is increased if data are acquired only every 2nd heartbeat.