Efficient gradient calibration based on diffusion MRI

Abstract

PurposeTo propose a method for calibrating gradient systems and correcting gradient nonlinearities based on diffusion MRI measurements.MethodsThe gradient scaling in x, y, and z were first offset by up to 5% from precalibrated values to simulate a poorly calibrated system. Diffusion MRI data were acquired in a phantom filled with cyclooctane, and corrections for gradient scaling errors and nonlinearity were determined. The calibration was assessed with diffusion tensor imaging and independently validated with high resolution anatomical MRI of a second structured phantom.ResultsThe errors in apparent diffusion coefficients along orthogonal axes ranged from −9.2% ± 0.4% to + 8.8% ± 0.7% before calibration and −0.5% ± 0.4% to + 0.8% ± 0.3% after calibration. Concurrently, fractional anisotropy decreased from 0.14 ± 0.03 to 0.03 ± 0.01. Errors in geometric measurements in x, y and z ranged from −5.5% to + 4.5% precalibration and were likewise reduced to −0.97% to + 0.23% postcalibration. Image distortions from gradient nonlinearity were markedly reduced.ConclusionPeriodic gradient calibration is an integral part of quality assurance in MRI. The proposed approach is both accurate and efficient, can be setup with readily available materials, and improves accuracy in both anatomical and diffusion MRI to within ±1%. Magn Reson Med 77:170–179, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Resolving Fine Cardiac Structures in Rats with High-Resolution Diffusion Tensor Imaging

“…As the applied b-value depends on the square of the gradient amplitude, calibration of diffusion measurements in a reference phantom with known diffusivity offers a quick, sensitive and accurate method for gradient calibration 19 . This calibration method was performed prior to the high resolution DTI experiments.…”

“…However, obtaining robust DTI measurements at high spatial resolution remains a challenge, even ex vivo . Current limitations of DTI include poor signal-to-noise ratio (SNR), long acquisition times 18 , sensitivity to gradient calibration 19 and temperature variations 20 , and difficulty distinguishing v 2 from v 3 in the presence of noise 21 . To overcome these obstacles, we implemented a set of refinements to increase SNR and spatial resolution, minimise orientation bias in diffusion-weighting, and reduce temperature variation in DTI.…”

Regional variations in ex-vivo diffusion tensor anisotropy are associated with cardiomyocyte remodeling in rats after left ventricular pressure overload

“…The TR was specified at 250 ms to maximize signal-to-noise (SNR) efficiency, and TE was set to a minimum (9.3 ms). Other imaging parameters were as follows: echo spacing = 4.9 ms, echo train length = 8, FOV = 21.6 × 14.4 × 14.4 mm 3 , resolution = 100 × 100 × 100 μm 3 , number of diffusion weighted (DW) directions = 30 forward + 30 reverse, number of non-DW (b = 0) images = 4, b effective = 1000 s/mm 2 [32], diffusion gradient duration (δ) = 2 ms, diffusion time (Δ) = 5.5 ms. Total acquisition time per heart was 11.5 h.…”

Multicenter Evaluation of Geometric Accuracy of MRI Protocols Used in Experimental Stroke

“…Recently, other larger and more complex phantom designs have been proposed for monitoring geometric accuracy or performing 3D geometric distortion correction in preclinical MRI [18, 29–31], but their size inhibits their use with various imaging coils, they generally have lower construction precision and are currently not as cost-effective; as such, they were not used in this multicenter study. LEGO bricks were also used successfully for the development of clinical phantoms before [25].…”