title: 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.
abstract: OBJECTIVE
  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.
authors.affiliation: Unit of Medical Physics, Azienda Ospedaliero-Universitaria Pisana, 56126 Pisa, Italy. m.giannelli@ao-pisa.toscana.it
authors.forename: Marco
authors.initials: M
authors.lastname: Giannelli
authors.forename: Gina
authors.initials: G
authors.lastname: Belmonte
authors.forename: Nicola
authors.initials: N
authors.lastname: Toschi
authors.forename: Ilaria
authors.initials: I
authors.lastname: Pesaresi
authors.forename: Piero
authors.initials: P
authors.lastname: Ghedin
authors.forename: Antonio Claudio
authors.initials: AC
authors.lastname: Traino
authors.forename: Carlo
authors.initials: C
authors.lastname: Bartolozzi
authors.forename: Mirco
authors.initials: M
authors.lastname: Cosottini
mesh_terms: D000328:Adult; D016880:Anisotropy; D001921:Brain; D056324:Diffusion Tensor Imaging / Q000295:instrumentation*; D004867:Equipment Design; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D011846:Radio Waves; D055815:Young Adult