Cardiac imaging at 7 tesla: Single‐ and two‐spoke radiofrequency pulse design with 16‐channel parallel excitation. Issue 5 (10th September 2013)

• Record Type: Journal Article
• Authors: Schmitter, Sebastian; DelaBarre, Lance; Wu, Xiaoping; Greiser, Andreas; Wang, Dingxin; Auerbach, Edward J.; Vaughan, J. Thomas; Uğurbil, Kâmil; Van de, Pierre‐François
• Is Part Of: Magnetic resonance in medicine. Volume 70:Issue 5(2013:Nov.)
• Page Start: 1210
• Page End: 1219
• Publication Date: 2013-09-10
• Subjects: Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.24935
• Languages: English
• ISSNs: 0740-3194

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="mrm24935-sec-0001" sec-type="section"> <title>Purpose</title> <p>Higher signal to noise ratio (SNR) and improved contrast have been demonstrated at ultra‐high magnetic fields (≥7 Tesla [T]) in multiple targets, often with multi‐channel transmit methods to address the deleterious impact on tissue contrast due to spatial variations in B<sub>1</sub><sup>+</sup> profiles. When imaging the heart at 7T, however, respiratory and cardiac motion, as well as B<sub>0</sub> inhomogeneity, greatly increase the methodological challenge. In this study we compare two‐spoke parallel transmit (pTX) RF pulses with static B<sub>1</sub><sup>+</sup> shimming in cardiac imaging at 7T.</p> </sec> <sec id="mrm24935-sec-0002" sec-type="section"> <title>Methods</title> <p>Using a 16‐channel pTX system, slice‐selective two‐spoke pTX pulses and static B<sub>1</sub><sup>+</sup> shimming were applied in cardiac CINE imaging. B<sub>1</sub><sup>+</sup> and B<sub>0</sub> mapping required modified cardiac triggered sequences. Excitation homogeneity and RF energy were compared in different imaging orientations.</p> </sec> <sec id="mrm24935-sec-0003" sec-type="section"> <title>Results</title> <p>Two‐spoke pulses provide higher excitation homogeneity than B<sub>1</sub><sup>+</sup> shimming, especially in the more challenging posterior region of the heart. The peak value of channel‐wise RF energy was reduced, allowing for a higher flip angle, hence increased tissue contrast. Image quality with two‐spoke excitation proved to be stable throughout the entire cardiac cycle.</p> </sec> <sec id="mrm24935-sec-0004" sec-type="section"> <title>Conclusion</title> <p>Two‐spoke pTX excitation has been successfully demonstrated in the human heart at 7T, with improved image quality and reduced RF pulse energy when compared with B<sub>1</sub><sup>+</sup> shimming. Magn Reson Med 70:1210–1219, 2013. © 2013 Wiley Periodicals, Inc.</p> </sec> </abstract>