Implementing diffusion-weighted MRI for body imaging in prospective multicentre trials: current considerations and future perspectives

Abstract

For body imaging, diffusion-weighted MRI may be used for tumour detection, staging, prognostic information, assessing response and follow-up. Disease detection and staging involve qualitative, subjective assessment of images, whereas for prognosis, progression or response, quantitative evaluation of the apparent diffusion coefficient (ADC) is required. Validation and qualification of ADC in multicentre trials involves examination of i) technical performance to determine biomarker bias and reproducibility and ii) biological performance to interrogate a specific aspect of biology or to forecast outcome. Unfortunately, the variety of acquisition and analysis methodologies employed at different centres make ADC values non-comparable between them. This invalidates implementation in multicentre trials and limits utility of ADC as a biomarker. This article reviews the factors contributing to ADC variability in terms of data acquisition and analysis. Hardware and software considerations are discussed when implementing standardised protocols across multi-vendor platforms together with methods for quality assurance and quality control. Processes of data collection, archiving, curation, analysis, central reading and handling incidental findings are considered in the conduct of multicentre trials. Data protection and good clinical practice are essential prerequisites. Developing international consensus of procedures is critical to successful validation if ADC is to become a useful biomarker in oncology.Key Points• Standardised acquisition/analysis allows quantification of imaging biomarkers in multicentre trials.• Establishing “precision” of the measurement in the multicentre context is essential.• A repository with traceable data of known provenance promotes further research.

Diffusion MRI of cancer: From low to high b‐values

“…Towards that end, the literature has already shown an encouraging progress on the validation of ADC as a cancer imaging marker in multicenter trials, through implementing standardized protocols across multivendor platforms together with methods for quality assurance during the processes of data collection, archiving, curation, and analysis. 118…”

Prostate diffusion MRI with minimal echo time using eddy current nulled convex optimized diffusion encoding

“…Prostate DWI is known to be sensitive to distortion artifacts that lead to inaccurate localization and representation of prostate tissues, including cancer . Eddy current fields originating from the use of large gradient amplitudes for diffusion encoding, if not carefully compensated or corrected, can have an enduring impact during the EPI readout and contribute one source of distortion artifacts in prostate DWI . Our phantom and ex vivo imaging experiments used identical imaging parameters as clinical in vivo prostate DWI, with the benefit of no patient motion and minimal susceptibility effects; thus, distortion could be attributed to eddy current effects with high confidence.…”

“…Eddy‐current‐induced distortion artifacts were evaluated for each diffusion encoding scheme by measuring the pixelwise coefficients of variation (CoV) across diffusivity maps of each diffusion direction . The mean CoV within edge voxels (CoV edge ) at the tube‐water interfaces were measured, and the global mean CoV edge across all tubes was computed and compared between the diffusion encoding schemes.…”

“…BIPOLAR uses a modified gradient design and a second refocusing pulse to mitigate eddy current fields that are produced by each gradient lobe at the end of diffusion encoding, but at a cost of substantially increased TE (and lower signal‐to‐noise ratio [SNR]) compared to MONO . In general, both a short TE and reduced eddy current‐induced distortion artifacts are desired to maintain sufficient SNR (or improve acquisition speed) and minimize overall image distortion in prostate DWI . However, these two desired features are not achievable at the same time using current encoding schemes (MONO or BIPOLAR).…”

Imaging biomarkers in oncology: Basics and application to MRI

“…[31][32][33][34][35][36][37][38][39] The variability of ADC in clinical studies has been reported to be relatively low at 15% 40 and in ice-water phantom studies as low as 3%. 41 Nevertheless, there are considerations to be made in the trial setting 42 and technical challenges to acquiring robust diffusion-weighted biomarkers and qualification as a biomarker. 26 TR should be sufficiently long to avoid underestimation of ADC due to T 1 saturation effect; TE should be minimized to achieve better signal-to-noise ratio (SNR), to minimize motion and susceptibility artifacts.…”