A fast, analytically based method to optimize local transmit efficiency for a transmit array. Issue 1 (14th February 2013)

• Record Type: Journal Article
• Authors: Carluccio, Giuseppe; Collins, Christopher M.; Erricolo, Danilo
• Is Part Of: Magnetic resonance in medicine. Volume 71:Issue 1(2014:Jan.)
• Page Start: 432
• Page End: 439
• Publication Date: 2013-02-14
• Subjects: Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.24653
• Languages: English
• ISSNs: 0740-3194

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="mrm24653-sec-0001" sec-type="section"> <title>Purpose</title> <p>To develop an analytically based algorithm for rapid optimization of the local radiofrequency magnetic <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg3zsg8jmh" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley:07403194:media:mrm24653:mrm24653-math-0002" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo stretchy="true">(</mml:mo><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup><mml:mo stretchy="true">)</mml:mo></mml:mrow></mml:math></alternatives> field intensity for a given radiofrequency power through a transmit array. The analytical nature of the method will yield insight to optimization requirements and provides a valuable reference for numerically based searches.</p> </sec> <sec id="mrm24653-sec-0002" sec-type="section"> <title>Methods</title> <p>With the knowledge of the <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg3zsg8jn2" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley:07403194:media:mrm24653:mrm24653-math-0003" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></alternatives> field distribution generated by each single coil of the array, both the phases and the amplitudes of each coil current are optimized to maximize the magnitude of the <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg3zsg8jjd" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley:07403194:media:mrm24653:mrm24653-math-0004" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></alternatives> field in a specific location of the body per unit of power transmitted through the array and, consequently, minimizing the whole body specific absorption rate for a given pulse sequence.</p> </sec> <sec id="mrm24653-sec-0003" sec-type="section"> <title>Results</title> <p>Simulations considering the human body show that the proposed method can reduce the whole‐body specific absorption rate for a given <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg3zsg8jkz" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" altimg="urn:x-wiley:07403194:media:mrm24653:mrm24653-math-0005" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msubsup><mml:mi>B</mml:mi><mml:mn>1</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math></alternatives> magnitude at the location of interest by a factor of about 6.3 compared to the classic birdcage current configuration, and by a factor of 3.2 compared to phase‐only shimming in a case with significant coupling between the elements of the array.</p> </sec> <sec id="mrm24653-sec-0004" sec-type="section"> <title>Conclusion</title> <p>The proposed method can rapidly provide valuable information pertinent to the optimization of field distributions from transmit arrays. Magn Reson Med 71:432–439, 2014. © 2013 Wiley Periodicals, Inc.</p> </sec> </abstract>