Multi-shot EPI for improvement of myocardial tag contrast: comparison with segmented SPGR

Abstract

To assess the potential value of multi-shot EPI relative to segmented k-space SPGR for myocardial tagging, we measured tag contrast for both sequences in a phantom and human study and compared it with theoretical predictions. In the human heart, EPI tag contrast was three times that of SPGR at the end of systole. Tag duration was lengthened with EPI to at least 600 ms. In addition, the entire heart was examined in a total of 32 heartbeats with EPI versus 152 heartbeats with SPGR.

FIG. 1

The SPGR and EPI pulse sequences are shown in (a) and (b), respectively. The tagging pulse is ECG-triggered and is followed by multiple imaging pulses. The tag lines are placed perpendicular to the readout direction. The SPGR sequence is made as short as possible. A spectral-spatial excitation RF pulse is used in EPI to reduce chemical shift artifacts.

FIG. 2

The tag contrast in SPGR and EPI images as a function of time after the ECG trigger. The solid and dotted lines represent the theoretical predictions of SPGR and EPI tag contrast, respectively. The crosses and circles represent the tag contrasts of SPGR and EPI images, respectively.

FIG. 3

The tag contrast in SPGR and EPI images when T₂* is 20 ms. The solid and dotted lines represent the theoretical predictions of SPGR and EPI tag contrast, respectively. The tag contrast of EPI images is 100% and 260% higher than that in SPGR images in 30 and 330 ms after the ECG trigger, respectively. The tag contrast of EPI image in 600 ms after ECG trigger is approximately equal to the contrast of SPGR image in 200 ms after ECG trigger.

FIG. 4

Comparison of tag contrast with SPGR (a) and EPI (b) images. The left column shows images acquired 30 ms after the ECG trigger. The right column shows the same slice acquired at 330 ms after the ECG trigger.

FIG. 5

The tag contrast of myocardium measured in the series of SPGR and EPI images shown in Fig. 4. The tag contrast of EPI images is about 70% and 200% higher than SPGR images at 30 and 330 ms after the ECG trigger, respectively.