Background:
It is possible to obtain the true diffusion coefficient through Intravoxel incoherent motion (IVIM) which reflects cell density and the perfusion fraction indicating the microcirculation of tumors. Therefore, IVIM may reflect tumor behavior resulting from the therapeutic effect of locoregional treatment (LRT) in Hepatocellular Carcinoma (HCC).
 Objectives:
To evaluate the diagnostic accuracy of conventional and IVIM-based DWI parameters for assessment of tumor response in patients who had received LRT due to HCC.
 Methods:
We included 15 patients with HCC with history of LRT (11 Trans arterial Radioembolization (TARE), 4 Trans arterial chemoembolization (TACE)). In addition to routine MRI sequences, IVIM with 16 different b values varying from 0 to 1300 s/mm2 and conventional DWI with 3 different b factors of 50, 400, 800 s/mm2 were obtained using a single-shot echo planar spin echo sequence before and 6 weeks after LRTs. MR imaging response was evaluated according to Response Evaluation Criteria in Solid Tumors (RECIST), modified RECIST (mRECIST), and European Association for the Study of the Liver (EASL) criteria on postcontrast arterial phase MR images. Quantitatively, conventional apparent diffusion coefficient (ADC) and IVIM parameters including mean D (true diffusion coefficient), D* (pseudo-diffusion coefficient associated with blood flow), and f (perfusion fraction) values were calculated before and after LRTs. The differences in these values were analyzed.
 Results:
A significant decrease in arterial enhancement was observed according to mRECIST and EASL criteria (-38,43±16,49 and -39,314±31,98, respectively). The ADC and D values after LRTs were significantly higher than those of pre-treatment (p=0.012 and p=0.002) (mean ADC was 1,00±0,21x10-3 mm2/s for before LRTs; 1,46 ±0,37x10-3 mm2/s for after LRTs; mean D was 0,74±0,30x10-3 mm2/s for before LRTs; 1,39±0,31x10-3 mm2/sn for after LRTs). The f values (%) after LRTs was significantly lower than those of before ones (p=0.016) (mean f was 37,61±7,99 for before LRTs; 8,58±2,66 for after LRTs).
Conclusion:
ADC values and IVIM parameters appear to reflect the response of LRTs of HCCs, promising new horizons especially in patients with renal or hepatic insufficiency clinical settings, owing to elimination of contrast media administration. The main limitation of this study is small patient number, necessitating further studies with larger series to provide a consensus on these parameters.