Accurate field mapping in the presence of B0 inhomogeneities, applied to MR thermometry. Issue 6 (27th June 2014)

• Record Type: Journal Article
• Authors: Mei, Chang‐Sheng; Chu, Renxin; Hoge, W. Scott; Panych, Lawrence P.; Madore, Bruno
• Is Part Of: Magnetic resonance in medicine. Volume 73:Issue 6(2015:Jun.)
• Page Start: 2142
• Page End: 2151
• Publication Date: 2014-06-27
• Subjects: Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.25338
• Languages: English
• ISSNs: 0740-3194

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="mrm25338-sec-0001" sec-type="section"> <title>Purpose</title> <p>To describe how <italic>B</italic><sub>0</sub> inhomogeneities can cause errors in proton resonance frequency (PRF) shift thermometry, and to correct for these errors.</p> </sec> <sec id="mrm25338-sec-0002" sec-type="section"> <title>Methods</title> <p>With PRF thermometry, measured phase shifts are converted into temperature measurements through the use of a scaling factor proportional to the echo time, <italic>TE</italic>. However, <italic>B</italic><sub>0</sub> inhomogeneities can deform, spread, and translate MR echoes, potentially making the "true" echo time vary spatially within the imaged object and take on values that differ from the prescribed <italic>TE</italic> value. Acquisition and reconstruction methods able to avoid or correct for such errors are presented.</p> </sec> <sec id="mrm25338-sec-0003" sec-type="section"> <title>Results</title> <p>Tests were performed in a gel phantom during sonication, and temperature measurements were made with proper shimming as well as with intentionally introduced <italic>B</italic><sub>0</sub> inhomogeneities. Errors caused by <italic>B</italic><sub>0</sub> inhomogeneities were observed, described, and corrected by the proposed methods. No statistical difference was found between the corrected results and the reference results obtained with proper shimming, while errors by more than 10% in temperature elevation were corrected for. The approach was also applied to an abdominal in vivo dataset.</p> </sec> <sec id="mrm25338-sec-0004" sec-type="section"> <title>Conclusion</title> <p>Field variations induce errors in measured field values, which can be detected and corrected. The approach was validated for a PRF thermometry application. Magn Reson Med 73:2142–2151, 2015. © 2014 Wiley Periodicals, Inc.</p> </sec> </abstract>