Technical Note: DTI measurements of fractional anisotropy and mean diffusivity at 1.5 T: Comparison of two radiofrequency head coils with different functional designs and sensitivities

• Published in: Medical physics (Lancaster) Vol. 38; no. 6; pp. 3205 - 3211
• Main Authors: Giannelli, Marco, Belmonte, Gina, Toschi, Nicola, Pesaresi, Ilaria, Ghedin, Piero, Claudio Traino, Antonio, Bartolozzi, Carlo, Cosottini, Mirco
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.06.2011
• Subjects: Adult; Anisotropy; Applied neuroscience; biodiffusion; Biomedical imaging; biomedical measurement; biomedical MRI; Brain; Computer software; data acquisition; Diffusion; diffusion tensor imaging; Diffusion Tensor Imaging - instrumentation; DTI; Equipment Design; Female; fractional anisotropy; Humans; Image Processing, Computer-Assisted; Instrumentation; least mean squares methods; Magnetic anisotropy; Magnetic fields; magnetic resonance imaging; Male; mean diffusivity; Medical image noise; medical image processing; Medical imaging; Radio Waves; Tensor methods; Young Adult; DTI; diffusion tensor imaging; fractional anisotropy; magnetic resonance imaging; mean diffusivity
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3592013

Purpose: Diffusion tensor imaging (DTI) is highly sensitive to noise and improvement of radiofrequency coil technology represents a straightforward way for augmenting signal-to-noise ratio (SNR) performance in magnetic resonance imaging (MRI) scanners. The aim of this study was to characterize the dependence of DTI measurements of fractional anisotropy (FA) and mean diffusivity (MD) on the choice of head coil, comparing two head coils with different functional designs and sensitivities. Methods: Fourteen healthy subjects underwent DTI acquisitions at 1.5 T. Every subject was scanned twice, using a standard quadrature birdcage head coil (coil-A) and an eight-channel array head coil (coil-B). FA and MD maps, estimated using both the linear least squares (LLS) and nonlinear least squares (NLLS) methods, were nonlinearly normalized into a standard space. Then, volumetric regions of interest encompassing typical white and gray matter structures [splenium of the corpus callosum (SCC), internal capsule (IC), cerebral peduncles (CP), middle cerebellar peduncles (MCP), globus pallidus (GP), thalamus (TH), caudate (CA), and putamen (PU)] were analyzed. Significant differences and trends of variation in DTI measurements were assessed by the Wilcoxon test for paired samples with and without Bonferroni correction for multiple comparisons, respectively. Results: The overall SNR of coil-B was ∼30% higher than that of coil-A. When comparing DTI measurements (coil-B versus coil-A), mean FA values (SCC, IC, and TH), mean MD values (IC, CP, GP, and TH), FA standard deviation (CP, MCP, GP, and CA), and MD standard deviation (IC, CP, TH, and PU) resulted decreased (significant difference,p cor < 0.05, or trend of variation, p uncor < 0.05) in several gray and white matter regions of the human brain. With the exception of CP, the results in terms of revealed significant difference or trend of variation were independent of the method (LLS and NLLS) used for estimating the diffusion tensor. Conclusions: In various gray and white matter structures, the eight-channel array head coil yielded more precise and accurate measurements of DTI derived indices compared to the standard quadrature birdcage head coil.