Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients,in-vitroandin-vivoreproducibility

Abstract

There is considerable disparity in the published apparent diffusion coefficient (ADC) values across different anatomies. Institutions are increasingly assessing repeatability and reproducibility of the derived ADC to determine its variation, which could potentially be used as an indicator in determining tumour aggressiveness or assessing tumour response. In this manuscript, a review of selected articles published to date in healthy extracranial body diffusion-weighted magnetic resonance imaging is presented, detailing reported ADC values and discussing their variation across different studies. In total 115 studies were selected including 28 for liver parenchyma, 15 for kidney (renal parenchyma), 14 for spleen, 13 for pancreatic body, 6 for gallbladder, 13 for prostate, 13 for uterus (endometrium, myometrium, cervix) In addition, six phantom studies and thirteen in vivo studies were summarized to compare repeatability and reproducibility of the measured ADC. All selected phantom studies demonstrated lower intra-scanner and inter-scanner variation compared to in vivo studies. Based on the findings of this manuscript, it is recommended that protocols need to be optimised for the body part studied and that system-induced variability must be established using a standardized phantom in any clinical study. Reproducibility of the measured ADC must also be assessed in a volunteer population, as variations are far more significant in vivo compared with phantom studies. Core tip: Diffusion-weighted magnetic resonance imaging was highlighted as a potential cancer imaging biomarker by a team of experts in a report published in 2009. We review the variability of published diffusion values in the major extra-cranial organs and focus on the validation literature, both in vivo and in vitro . A total of 115 studies were selected including for liver parenchyma, kidney, pancreatic body, spleen, gallbladder, prostate, uterus (endometrium, myometrium, cervix) and breast. We also look in detail at the published repeatability and reproducibility studies, both in vivo and in phantoms. A series of recommendations based on our findings are given at the end of this review.Jafar MM, Parsai A, Miquel ME. Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients, in vitro and in vivo reproducibility.

Quantitative imaging biomarkers alliance (QIBA) recommendations for improved precision of DWI and DCE‐MRI derived biomarkers in multicenter oncology trials

“…The biggest differences found between different MRI protocols are in: FOV, number of slices, TR, and TE. Therefore, in practice, variability between DWI protocols influences the measured ADC value, and the differences found across measurements are about 10% from the literature value . The most significant differences were observed between MRI system manufacturers due to distinct gradient designs leading to spatially‐dependent bias in diffusion weighting b ‐values …”

Imaging biomarkers in oncology: Basics and application to MRI

“…The variability of ADC in clinical studies has been reported to be relatively low at ≤15% and in ice‐water phantom studies as low as 3% . Nevertheless, there are considerations to be made in the trial setting and technical challenges to acquiring robust diffusion‐weighted biomarkers and qualification as a biomarker .…”

Liver MRI: From basic protocol to advanced techniques

“…In clinical practice, b-values higher than 1000 s/mm 2 are seldom used due to the relatively short T2-relaxation time of the normal liver parenchyma [15]. EPI sequences are very sensitive to magnetic field inhomogeneity and susceptibility artefacts, which lead to image degradation and distortion.…”

“…There may be also potential roles in tumour grading and liver fibrosis assessment [3,15]. The ADC measurements are affected by the sequence acquisition protocol and suffer from a lack of reproducibility, particularly in respiratory triggering techniques, left liver lobe seated lesions, smaller size and lesion heterogeneity [11,12,15]. Accurate estimation of ADC can be improved by acquiring a large number of b-values, taking into consideration the diffusion profile of the specific tissue, which might be multiexponential [11].…”

“…The ADC map is the graphical representation of the ratio of DW signal intensities and its measurements may discriminate between benign and malignant lesions [12,14]. There may be also potential roles in tumour grading and liver fibrosis assessment [3,15]. The ADC measurements are affected by the sequence acquisition protocol and suffer from a lack of reproducibility, particularly in respiratory triggering techniques, left liver lobe seated lesions, smaller size and lesion heterogeneity [11,12,15].…”