3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1205-1216.

Purpose: To evaluate different non-Gaussian representations for the diffusionweighted imaging (DWI) signal in the b-value range 200 to 3000 s/mm 2 in benign and malignant breast lesions. Methods: Forty-three patients diagnosed with benign (n = 18) or malignant (n = 25) tumors of the breast underwent DWI (b-values 200, 600, 1200, 1800, 2400, and 3000 s/mm 2 ). Six different representations were fit to the average signal from regions of interest (ROIs) at different b-value ranges. Quality of fit was assessed by the corrected Akaike information criterion (AICc), and the Friedman test was used for assessing representation ranks. The area under the curve (AUC) of receiver operating characteristic curves were used to evaluate the power of derived parameters to differentiate between malignant and benign lesions. The lesion ROI was divided in central and peripheral parts to assess potential effect of heterogeneity. Sensitivity to noise-floor correction was also evaluated. Results: The Padé exponent was ranked as the best based on AICc, whereas 3 models (kurtosis, fractional, and biexponential) achieved the highest AUC = 0.99 for lesion differentiation. The monoexponential model at b max = 600 s/mm 2 already provides AUC = 0.96, with considerably shorter acquisition time and simpler analysis. Significant differences between central and peripheral parts of lesions were found in malignant lesions. The mono-and biexponential models were most stable against varying degrees of noise-floor correction. 1012 | VIDIĆ et al.

BackgroundIncreased deposition and reorientation of stromal collagen fibers are associated with breast cancer progression and invasiveness. Diffusion‐weighted imaging (DWI) may be sensitive to the collagen fiber organization in the stroma and could provide important biomarkers for breast cancer characterization.PurposeTo understand how collagen fibers influence water diffusion in vivo and evaluate the relationship between collagen content and the apparent diffusion coefficient (ADC) and the signal fractions of the biexponential model using a high b‐value scheme.Study TypeProspective.Subjects/SpecimensForty‐five patients with benign (n = 8), malignant (n = 36), and ductal carcinoma in situ (n = 1) breast tumors. Lesions and normal fibroglandular tissue (n = 9) were analyzed using sections of formalin‐fixed, paraffin‐embedded tissue stained with hematoxylin, erythrosine, and saffron.Field Strength/SequenceMRI (3T) protocols: Protocol I: Twice‐refocused spin‐echo echo‐planar imaging with: echo time (TE) 85 msec; repetition time (TR) 9300/11600 msec; matrix 90 × 90 × 60; voxel size 2 × 2 × 2.5 mm3; b‐values: 0 and 700 s/mm2. Protocol II: Stejskal–Tanner spin‐echo echo‐planar imaging with: TE: 88 msec; TR: 10600/11800 msec, matrix 90 × 90 × 60; voxel size 2 × 2 × 2.5 mm3; b‐values [0, 200, 600, 1200, 1800, 2400, 3000] s/mm2.AssessmentArea fractions of cellular and collagen content in histologic sections were quantified using whole‐slide image analysis and compared with the corresponding DWI parameters.Statistical TestsCorrelations were assessed using Pearson's r. Univariate analysis of group median values was done using the Mann–Whitney U‐test.ResultsCollagen content correlated with the fast signal fraction (r = 0.67, P < 0.001) and ADC (r = 0.58, P < 0.001) and was lower (P < 0.05) in malignant lesions than benign and normal tissues. Cellular content correlated inversely with the fast signal fraction (r = –0.67, P < 0.001) and ADC (r = –0.61, P < 0.001) and was different (P < 0.05) between malignant, benign, and normal tissues.Data ConclusionOur findings suggest stromal collagen content increases diffusivity observed by MRI and is associated with higher ADC and fast signal fraction of the biexponential model.Level of Evidence: 3Technical Efficacy Stage: 3J. Magn. Reson. Imaging 2020;51:1868–1878.

Purpose: The purpose of this study was to investigate the effects of echo time dependence in IVIM quantification of the pseudo‐diffusion fraction in breast cancer and whether correcting for the echo time dependence offers added clinical value. Materials and methods: Fifteen patients with biopsy‐proven breast cancer underwent a 3 T MRI examination with an extended DWI protocol at two different echo times (TE = 53 ms, b = 0, 50 s/mm2; TE = 77 ms, b = 0, 50, 120, 200, 400, 700 s/mm2). Volumes of interest were delineated around the tumors. In addition, simulated MRI data were generated for different levels of signal‐to‐noise ratio and two values for the blood T2 relaxation time (T2p = 100 ms and 150 ms). The pseudo‐diffusion signal fraction was estimated from the simulated and in vivo tumor data using both the standard IVIM model and an extended IVIM model that accounts for the echo time dependence arising from distinct transverse relaxation times. Results: Simulations showed that the standard IVIM model overestimated the pseudo‐diffusion fraction by 25% (T2p = 100 ms) and 60 % (T2p = 150 ms) (p < 0.0001 at SNR = 50). In vivo, the estimated apparent T2 value at b = 50 s/mm2 was around 8% lower than at b = 0 s/mm2 (p = 0.01) demonstrating a removal of the signal contribution from blood with long T2 associated with pseudo‐diffusion. Using two different fixed values for T2p = 100, 150 ms, the pseudo‐diffusion fraction was 15% and 46% higher in the standard model compared with the echo‐time‐corrected model (p < 0.01). Conclusion: The standard IVIM model was found to overestimate the pseudo‐diffusion fraction by 15% to 46% compared with the echo‐time‐corrected model in breast tumor DWI data acquired at 3 T. Our results suggest that a corrected model may give more accurate results in terms of signal fractions, but may not justify the added time needed to acquire the additional data in terms of clinical value.