T1 bias in chemical shift‐encoded liver fat‐fraction: Role of the flip angle. Issue 4 (15th November 2013)

• Record Type: Journal Article
• Authors: Kühn, Jens‐Peter; Jahn, Christina; Hernando, Diego; Siegmund, Werner; Hadlich, Stefan; Mayerle, Julia; Pfannmöller, Jörg; Langner, Sonke; Reeder, Scott
• Is Part Of: Journal of magnetic resonance imaging. Volume 40:Issue 4(2014)
• Page Start: 875
• Page End: 883
• Publication Date: 2013-11-15
• Subjects: Magnetic resonance imaging -- Periodicals; 616
• DOI: 10.1002/jmri.24457
• Languages: English
• ISSNs: 1053-1807

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="jmri24457-sec-0001" sec-type="section"> <title>Purpose</title> <p>To investigate flip angle (FA)‐dependent T1 bias in chemical shift‐encoded fat‐fraction (FF) and to evaluate a strategy for correcting this bias to achieve accurate MRI‐based estimates of liver fat with optimized signal‐to‐noise ratio (SNR).</p> </sec> <sec id="jmri24457-sec-0002" sec-type="section"> <title>Materials and Methods</title> <p>Thirty‐three obese patients, 14 men/19 women, aged 57.3 ± 13.9 years underwent 3 Tesla (T) liver MRI including MR‐spectroscopy and four three‐echo‐complex chemical shift‐encoded MRI sequences using different FAs (1°/3°/10°/20°). FF was estimated with R2* correction and multi‐peak fat spectral modeling. The FF for each FA with and without T1 correction was compared with spectroscopy as a reference standard, using linear regression. Relative SNR of the magnitude data were assessed for each flip angle.</p> </sec> <sec id="jmri24457-sec-0003" sec-type="section"> <title>Results</title> <p>The correlation between chemical shift‐encoded MRI and spectroscopy was high (R<sup>2</sup> ≈ 0.9). Without T1 correction, the agreement of both techniques showed no significant differences in slope (<italic>P<sub>FlipAngle1</sub><sub>°</sub></italic> = 0.385/<italic>P<sub>FlipAngle3</sub><sub>°</sub></italic> = 0.289) using low FA. High FA resulted in significant different slopes (<italic>P<sub>FlipAngle10</sub><sub>°</sub></italic> = 0.016/<italic>P<sub>FlipAngle20</sub><sub>°</sub></italic> = 0.014. T1 bias was successfully corrected using the T1 correction strategy (slope:<italic>P<sub>FlipAngle10</sub><sub>°</sub></italic> = 0.387/<italic>P<sub>FlipAngle20</sub><sub>°</sub></italic> = 0.440). Additionally, the use of high FA (near the Ernst angle) improved the SNR of the magnitude data (<italic>FA1 vs. FA3; respectively FA1 vs. FA10 P</italic> ≤ 0.001).</p> </sec> <sec id="jmri24457-sec-0004" sec-type="section"> <title>Conclusion</title> <p>T1 bias is a strong confounder in the assessment of liver fat using chemical shift imaging with high FA. However, using a larger flip angle with T1 correction leads to higher SNR, and residual error after T1 correction is very small. <bold>J. Magn. Reson. Imaging 2014;40:875–883</bold>. © <bold>2013 Wiley Periodicals, Inc</bold>.</p> </sec> </abstract>