Highly‐accelerated Bloch‐Siegert |B1+| mapping using joint autocalibrated parallel image reconstruction. Issue 4 (1st July 2013)

• Record Type: Journal Article
• Authors: Sharma, Anuj; Tadanki, Sasidhar; Jankiewicz, Marcin; Grissom, William A
• Is Part Of: Magnetic resonance in medicine. Volume 71:Issue 4(2014:Apr.)
• Page Start: 1470
• Page End: 1477
• Publication Date: 2013-07-01
• Subjects: Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.24804
• Languages: English
• ISSNs: 0740-3194

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <sec id="mrm24804-sec-0001" sec-type="section"> <title>Purpose</title> <p>To reconstruct accurate single‐ and multichannel Bloch–Siegert transmit radiofrequency (<alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftcvc" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0002" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives>) field maps from highly accelerated data.</p> </sec> <sec id="mrm24804-sec-0002" sec-type="section"> <title>Theory and Methods</title> <p>The approach is based on the fact that the <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftcwx" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0003" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives>‐to‐phase encoding pulse for each transmit coil and off‐resonance frequency applies a unique phase shift to the same underlying image. This enables joint reconstruction of all images in a Bloch–Siegert acquisition from an augmented set of virtual receive coils, using any autocalibrated parallel imaging reconstruction method.</p> </sec> <sec id="mrm24804-sec-0003" sec-type="section"> <title>Results</title> <p>Simulations with an eight channel transmit/receive array head coil at 7T show that accurate <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftcxg" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0004" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives> maps can be produced at acceleration factors of 16× and 6× for Cartesian and spiral sampling, respectively. A phantom experiment with a six channel transverse electromagnetic (TEM) transceive array coil allowed accurate reconstruction at 16× acceleration. 7T in vivo experiments performed using 32 channel receive and two‐channel transmit coils further demonstrate the proposed method's ability to produce high‐quality <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftcz1" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0005" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives> maps at accelerations of 32× and 8× for Cartesian and spiral trajectories, respectively. Reconstruction accuracy is improved using disjoint k‐space sampling patterns between acquisitions.</p> </sec> <sec id="mrm24804-sec-0004" sec-type="section"> <title>Conclusion</title> <p>The proposed approach allows high acceleration factors in Bloch–Siegert <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftd6d" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0006" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives> mapping and can significantly reduce the scan time requirements for mapping the <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4t0ftd7z" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley::media:mrm24804:mrm24804-math-0007" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>|</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo>|</mml:mo></mml:mrow></mml:math></alternatives> fields of transmit arrays. <bold>Magn Reson Med 71:1470–1477, 2014. © 2013 Wiley Periodicals, Inc</bold>.</p> </sec> </abstract>