Quality Assurance Phantom Testing of an Echo-Planar Diffusion-Weighted Sequence on a 3T Scanner

Abstract

Purpose: This work investigated the behaviour of a high-field MR system relative to a range of pulse sequence parameter changes and image artefacts resulting from image acquisition employing an Echo-Planar Diffusion-Weighted (EPI-DW) sequence modified for musculoskeletal imaging of the Achilles Tendon (AT). Methods and Materials: MR scanning was undertaken on a 3T Philips Achieva MR scanner with an 8-channel foot/ ankle coil. Image quality evaluation was based on images acquired using two phantoms: 1) an L-shaped foot/ ankle phantom containing Nickel Chloride (NiCl2) in water and 2) a small cylindrical plastic phantom containing copper sulphate (CuSO4) in water. Quality control (QC) measurements were based on the American College of Radiology (ACR) specifications. Signal-to-noise ratio (SNR), image intensity uniformity, percentage ghosting, and geometric distortion were measured for phantom images acquired using four sequences (T1W SE, T2W TSE, STIR, EPI-DW). Results: The performance of the EPI-DW sequence was tested according to ACR specifications and compared to three standard pulse sequences routinely used for scanning of the AT. The EPI-DW sequence met the ACR criteria for SNR and image intensity uniformity, but failed to meet geometric distortion criteria. In terms of percentage ghosting, artefacts were evident in the EPI-DW and ADC map images. However, when quantified, these images remained within ACR specifications for image ghosting. Conclusion: When modifying a pulse sequence for a new application, it is essential to understand in advance the technical performance characteristics of the MR system and their potential impact on resultant MR image quality. This study demonstrated that the results of image quality testing revealed important findings that facilitated further optimisation of the EPI-DW sequence prior to its application for Achilles tendon scanning in human subjects.