Myocardial Perfusion using radial MS-CAIPIRINHA

Tobias Wech^{1}, Michael Braun^{1,2}, Daniel Stäb^{3}, Peter Speier^{4}, Henning Neubauer^{1}, Walter Kullmann^{2}, Thorsten A. Bley^{1}, and Herbert Köstler^{1}

A pulse sequence was developed by in-house modifying the TurboFLASH prototype sequence presented in [6]. A dual-band pulse was used to excite two slices simultaneously, while the RF-phase of the first slice was kept unmodulated and the phase of the second slice was toggled between 0° and 180°. Radial readouts were applied, such that the information of the second slice cancels out in the central k-space of a standard gridding reconstruction. The conjugate gradient SENSE (CG-SENSE) algorithm described in [3] was implemented in MATLAB (The MathWorks, Natick, MA) to reconstruct two fully sampled slices. The L-curve of the residual-norm [7] was consulted to define a termination criterion for this iterative reconstruction.

In a first experiment, a phantom was scanned using both Cartesian and radial MS-CAIPIRINHA (MAGNETOM Skyra, Siemens Healthcare, Erlangen, Germany; dual-slice mode, slice distance = 24mm, TE = 1.4ms, TR = 3.1ms, slice thickness = 8mm, in-plane resolution = 2mm x 2mm, 37 phase-encoding steps or radial projections, image matrix = 128 x 128) together with a measurement of noise amplitude and correlation in the phased-array receiver. To allow for a fair comparison, both the radial and the Cartesian scan were reconstructed using the CG-algorithm described above. A fully sampled measurement was performed to determine the coil sensitivities. The method described in [8] was used to obtain g-factor maps for the two techniques.

The radial sequence was applied to perform a saturation-recovery-prepared and ECG-triggered perfusion measurement in the heart of a healthy volunteer (same scanner, dual-slice mode, slice distance between adjacent slices =7.7mm, slice distance between simultaneously acquired slices = 23mm, saturation preparation & ECG triggering, TE = 1.5ms, TR = 2.6ms, slice thickness = 5mm, in-plane resolution = 2.5mm x 2.5mm, 52 radial projections per image pair, image matrix = 160 x 160). A bolus of 6 ml Gadovist (Bayer Schering Pharma, Berlin, Germany) was injected and observed over 60 RR-intervals with 3x2 short-axis slices, acquired within each interval. A pre-scan was performed to determine the coil sensitivities needed for the CG-reconstruction.

g-factors for accelerated Cartesian and radial
MS-CAIPIRINHA. In both cases the two slices were acquired by applying a
dual-band RF pulse and 37 readouts. Images (top row, matrix size 128x128) were
reconstructed using CG-SENSE, the g-factor maps (bottom row) were obtained by
using the pseudo multiple replica method described in [8].

3x2 short-axis slices of the perfusion
investigation in a healthy volunteer. Images in the same column were acquired
simultaneously.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)

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