Quality assurance for diffusion tensor imaging using an ACR phantom: Comparative analysis with 6, 15, and 32 directions at 1.5T and 3.0T MRI systems

Although diffusion tensor imaging (DTI) has been widely used for the quantitative analyses of the integrity of white matter in the brain in clinical and research fields, quality assurance (QA) for DTI has not been fully established. Thus, we suggest a QA guideline for DTI using the American College of Radiology (ACR) Magnetic resonance imaging (MRI) head phantom. In this study, the geometric accuracy, slice-position accuracy, image intensity uniformity, percent signalghosting, low-contrast object detectability, image distortion, fractional anisotropy (FA), and apparent diffusion coefficient (ADC) were measured and evaluated in 1.5T and 3.0T MRI scanners equipped with an 8-channel SENSE head coil. The standard axial spin echo (SE) T1-weighted MR images and DTI with 6, 15 and 32 directions were obtained. Concerning geometric accuracy, image twisting in the three directions was observed due to the inhomogeneity of echo planar imaging (EPI). Image intensity uniformity was significantly lower for DTI than for the standard SE T1-weighted MR images. Percent signal ghosting was higher for images from 3.0T MRI than for images from 1.5T MRI. Low-contrast object detectability was visually identified and measured at a low contrasttonoise ratio (CNR) and a low signaltonoise ratio (SNR). Image distortion changed remarkably to the phaseencoding direction. The present study using the ACR MRI phantom suggests a QA method for DTI with high reproducibility and easy accessibility.