Tobias Wech^{1,2}, Tina Urbanek^{1,3}, Andreas Max Weng^{1}, Daniel Stäb^{4}, Peter Speier^{5}, Thorsten Alexander Bley^{1}, and Herbert Köstler^{1,2}

MS-CAIPIRINHA is a valuable technique to extend the anatomical coverage in myocardial first-pass perfusion imaging. In our previous studies, dual-band excitation was applied in conjunction with three SR-prepared acquisition blocks per RR interval to obtain six 2D-slices with a temporal resolution of one heartbeat. Especially in obese patients, however, the SNR occasionally turned out to be marginal, ultimately complicating the assessment of perfusion defects. In this work, an according approach using tri-band RF excitation was tested with respect to potential SNR benefits.

In this work, the technique was compared to an alternative approach: Two SR preparations were performed per RR-interval and each was followed by an undersampled MS-CAIPIRINHA with tri-band excitation. Aim of the study was to evaluate whether the new approach results in a higher signal-to-noise-ratio (SNR).

In this work, tri-band RF pulses were implemented in order to excite three slices at the same time. The RF phases in the three slices were varied according to $$$\phi_1(j)=0$$$, $$$\phi_2(j)=\frac{2\pi}{3}j$$$ and $$$\phi_2(j)=\frac{4\pi}{3}j$$$ with the excitation index $$$j$$$, in order to shift the slices by ⅓ FOV with respect to each other and equally distribute the slice aliasing along the phase encoding direction. Two SR-preparations were applied per RR-interval to obtain six slices, in accordance with the dual-band approach.

First, both techniques were compared in a first-pass perfusion investigation of a patient with primary hyperaldosteronism. Data were acquired on a 3T whole-body MR-scanner (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany) equipped with a body and spine phase array coil using 34 elements in total. For each measurement, a 10 ml bolus of gadoterate meglumine (Dotarem, Guerbet, Aulnay-sous-Bois, France) was injected and observed over 60 RR-intervals. The overall PI acceleration factor corresponded to 5 (R

An SNR study was then performed for a quantitative comparison of the dual- and the tri-band techniques. Phantom data were acquired on the same scanner. For an objective comparison, the total number of PES was kept equal for both acquisitions. The dual-band MS-CAIPIRINHA measurement was performed using three SR preparations, each followed by 45 phase-encoding steps (135 PES in total, R

The dual-band acquisition with three SR preparations is therefore the method of choice. This is also justified by a shorter acquisition window for each multi-slice time frame, which comes with less cardiac motion and less signal variation due to the ongoing recovery of the magnetization.