Table 1.

Summary of literature review on test–retest reproducibility of ADC measurements

Author/year of publication	Design, number of participants/ lesions	Assessment criteria	Results summary
Michoux 9 Eur Radiol2021	3T MRI 24 healthy volunteers	ROIs in a single slice of the parapspinal muscle, prostate, liver, kidney, spleen, L5 vertebra, posterior iliac crest, femur and white matter (cerebrum) with different sizes.	CV of ADC was not influenced by the centre or the reader. Change in ADC must be superior to 66% in lumbar vertebra and 50% in posterior iliac crest and 94% in acetabulum to be significant (other values mentioned for different organs).
Wennmann 10 Invest Radiol 2021	1.5 and 3T MRI 37 patients with monoclonal plasma cell disorder	Manual ROIs were placed in BM at posterior iliac crests and muscle tissue using ADC and B800 images. Additional ROI was placed in body of S1 body.	Maximal CV was 16.2% of the interrater variability and repeatability. Comparing 1.5 to 3T, larger relative biases of up to −0.526. Normalisation to muscle reduced the bias of T 1W and T 2W but not ADC.
Barrett 11 EJR 2019	3T MRI 10 prostate cancer patients Retest same day	ROIs drawn by consensus of two expert readers on ADC map ADC histogram analysis MATLAB including media ADC, 10th/90th percentiles, IQR, skewness.	10th, 90th centile, and median ADC good repeatability. Bland–Altman plots showed good repeatability for test and retest analysis for median, percentile and mean range values. More advanced measures of heterogeneity such as histogram skew, IQR, or mean local range may be limited by their repeatability.
Newitt J 12 Magn Reson Imaging2018	1.5 or 3T MRI 71 Breast cancer patients Same day, same imaging session	Mean and median ADC values were calculated for each composite whole-tumour ROI (using manual segmentation) 20 cases for intra/inter observer variability.	ADC repeatability was excellent: wCV = 4.8% (95% CI 4.0, 5.7%), ICC = 0.97 (95% CI 0.95, 0.98), AI = 0.83 (95% CI 0.76, 0.87), and RC = 0.16 * 10–3 mm2/sec (95% CI 0.13, 0.19). Reproducibility was excellent: interreader ICC = 0.92 (95% CI 0.80, 0.97) and intrareader ICC = 0.91 (95% CI 0.78, 0.96).
Sun 13 Medicine 2017	3T MRI 26 patients with rectal cancer 20–30 min between two DWI scans (same session, patient still on the table).	ADC and IVIM parameters (D, pure diffusion; f, perfusion fraction; D∗, pseudodiffusion coefficient) were, respectively, calculated. ROIs were manually drawn to contour the border of the rectal cancers on the slice (DWI images) with the maximum lesion size Another circular ROI (100 mm2) was drawn and placed free hand within the left gluteal muscle on the same slice selected above for the first DWI sequence. The DW-MRI-derived parameters’ values were calculated using the pixel-by-pixel fitting method and expressed as the mean values of all the pixels within the ROI	There was no significant difference in the test and retest values of the DWI-derived parameters (p = .170 [ADC], p = .065 [D], p = .079 [f], and p = .301[D∗]). The test-retest repeatability coefficient for ADC, D, f, and D∗ was 19.1%, 24.5%, 126.3%, and 197.4%, respectively, greater than the intraobserver values. ADC and D have better short-term test–retest reproducibility than f and D∗. Considering the poor testintravoxel incoherent motion retest reproducibility for f and D,∗ variance in these two parameters should be interpreted with caution in longitudinal studies on rectal cancer in which treatment response and recurrence are monitored.
Latifoltojar 14 Eur Radiol 2017	3T MRI Nine healthy volunteers, 1–11 weeks (median 4 weeks)	Seven single slice skeletal ROIs (T10 and L4 vertebral bodies, sacroiliac joint and sacral ala, iliac crest, femoral head and neck, mid-shaft femur and distal femur), 2 cm3 circular ROI of the spleen on ADC maps and 3 cm3 circular ROI of subcutaneous adipose tissue at the level of right femoral greater trochanter on mDixon using Osirix	Bone sFF repeatability was excellent (ICC 0.98) and better than bone ADC (ICC 0.47).
WellerA 15 Eur Radiol 2017	1.5T MRI 23 patients (30 Malignant lung lesions > 2 cm) Scanned > 1 h to <1 week	Whole tumour segmentation using region growing technique (ADEPT) and freehand technique (Osirix) Assessed lesions that are > 2 cm, and present at least three slices (25 lesions) whole tumour median ADC (ADCmed) was assessed with Bland–Altman plots	ADC repeatability coefficient-of-variation is 7.1% for lung tumours > 2 cm. ADC repeatability coefficient-of-variation is 3.9% for lung tumours > 3 cm. ADC measurement precision is unaffected by the postprocessing software used. In multicentre trials, 22% increase in ADC indicates positive treatment response.
Messiou C 16 Eur Radiol 2011	1.5 T MR Nine healthy volunteers FU within 7 days	1.3 cm2 ROIs were placed in the L5 vertebral body and right and left iliac bones on the ADC map and mean ADC was documented.	The Bland–Altman limit of reproducibility of mean ADC of bone marrow in normal subjects was 2:0 +/- −86 × 10–6 mm2s-1 Coefficient of repeatability (r%) expressed as a percentage of the baseline average was 14.8%.
BraithwaiteA 17 Radiology 2009	3T MRI 16 healthy volunteers Mean of 147 days (SD = 2) for follow up scan	The mean ADCs for three ROIs in five anatomic locations (right hepatic lobe, spleen, and head, body, and tail of pancreas). The ADC and CV data were then analysed by using repeated-measures analysis of variance	There were no significant differences in ADCs between imaging sessions 1 and 2. The mean CV for ADC measurement reproducibility was 14% (95% CI, 13–15%) Treatment effects of less than approximately 27% (change in ADC divided by pretreatment ADC) will not be clinically detectable with confidence with one acquisition in a single individual

ADC: apparent diffusion coefficient, CV: coefficient of variation, ICC: intraclass correlation coefficient, ROI : region of interest, sFF: signal fat fraction, wCV: within-subject coefficient of variation.