The relationship between parameters measured using intravoxel incoherent motion and dynamic contrast-enhanced MRI in patients with breast cancer undergoing neoadjuvant chemotherapy: a longitudinal cohort study

Purpose The primary aim of this study was to explore whether intravoxel incoherent motion (IVIM) can offer a contrast-agent-free alternative to dynamic contrast-enhanced (DCE)-MRI for measuring breast tumor perfusion. The secondary aim was to investigate the relationship between tissue diffusion measures from DWI and DCE-MRI measures of the tissue interstitial and extracellular volume fractions. Materials and methods A total of 108 paired DWI and DCE-MRI scans were acquired at 1.5 T from 40 patients with primary breast cancer (median age: 44.5 years) before and during neoadjuvant chemotherapy (NACT). DWI parameters included apparent diffusion coefficient (ADC), tissue diffusion (D t ), pseudo-diffusion coefficient (D p ), perfused fraction (f), and the product f×D p (microvascular blood flow). DCE-MRI parameters included blood flow (F b ), blood volume fraction (v b ), interstitial volume fraction (v e ) and extracellular volume fraction (v d ). All were extracted from three tumor regions of interest (whole-tumor, ADC cold-spot, and DCE-MRI hot-spot) at three MRI visits: pre-treatment, after one, and three cycles of NACT. Spearman’s rank correlation was used for assessing between-subject correlations (r), while repeated measures correlation was employed to assess within-subject correlations (r rm ) across visits between DWI and DCE-MRI parameters in each region. Results No statistically significant between-subject or within-subject correlation was found between the perfusion parameters estimated by IVIM and DCE-MRI (f versus v b and f×D p versus F b ; P=0.07–0.81). Significant moderate positive between-subject and within-subject correlations were observed between ADC and v e (r=0.461, r rm =0.597) and between D t and v e (r=0.405, r rm =0.514) as well as moderate positive within-subject correlations between ADC and v d and between D t and v d (r rm =0.619 and 0.564, respectively) in the whole-tumor region. Conclusion No correlations were observed between the perfusion parameters estimated by IVIM and DCE-MRI. This may be attributed to imprecise estimates of fxD p and v b , or an underlying difference in what IVIM and DCE-MRI measure. Care should be taken when interpreting the IVIM parameters (f and f×D p ) as surrogates for those measured using DCE-MRI. However, the moderate positive correlations found between ADC and D t and the DCE-MRI parameters v e and v d confirms the expectation that as the interstitial and extracellular volume fractions increase, water diffusion increases.