A quality assurance protocol for diffusion tensor imaging using the head phantom from American College of Radiology

Abstract

Purpose: To propose a quality assurance procedure for routine clinical diffusion tensor imaging (DTI) using the widely available American College of Radiology (ACR) head phantom.

Methods: Analysis was performed on the data acquired at 1.5 and 3.0 T on whole body clinical MRI scanners using the ACR phantom and included the following: (1) the signal-to-noise ratio (SNR) at the center and periphery of the phantom, (2) image distortion by EPI readout relative to spin echo imaging, (3) distortion of high-b images relative to the b= 0 image caused by diffusion encoding, and (4) determination of fractional anisotropy (FA) and mean diffusivity (MD) measured with region-of-interest (ROI) and pixel-based approaches. Reproducibility of the measurements was assessed by five repetitions of data acquisition on each scanner.

Results: The SNR at the phantom center was approximately half of that near the periphery at both 1.5 and 3 T. The image distortion by the EPI readout was up to 7 mm at 1.5 T and 10 mm at 3 T. The typical distortion caused by eddy currents from diffusion encoding was on the order of 0.5 mm. The difference between ROI-based and pixel-based MD quantification was 1.4% at 1.5 T and 0.3% at 3 T. The ROI-based MD values were in close agreement (within 2%) with the reference values. The ROI-based FA values were approximately a factor of 10 smaller than pixel-based values and less than 0.01. The measurement reproducibility was sufficient for quality assurance (QA) purposes.

Conclusions: This QA approach is simple to perform and evaluates key aspects of the scanner performance for DTI data acquisition using a widely available phantom.

Figure 1

SNR was quantified from circular ROIs at slice 7. (A) The b = 0 image was used for signal measurement. (B) The noise image was generated from 30 high-b-value DW images as described in the text.

Figure 2

Locations of 21 grid points where the relative shift in EPI and SE images was measured at slice 5. (A) T1 weighted SE image. (B) DTI b = 0 image.

Figure 3

Evaluation of distortion by diffusion-encoding gradient at 3 T. (A) The segments indicate the locations where the gridline profile was compared between the B₀ and average of high-b-value images. (B) The grid profile for a segment in (A). The solid line was the gridline profile on b = 0 image, the dashed line was the profile of the averaged high-b images, and dotted line was fit by Eq. (1). The intensity of the high-b-value profile was multiplied by 7.5.