Intravoxel incoherent motion (IVIM) can distinguish the molecular diffusion from the pseudo-diffusion of microcircular perfusion to obtain true diffusion coefficient (D),pseudo-diffusion coefficient (D*) and perfusion fraction (f),which are sensitive to detect alterations in cellularity and microcirculation perfusion.IVIM can also evaluate early therapeutic effects,optimize treatment plan,predict prognoses,and provide information for choosing appropriate treatment methods.In this paper,the principle of IVIM and its application in tumor response evaluation were reviewed.

Objective To prospectively evaluate the short-term test-retest reproducibility of intravoxel incoherent motion (IVIM) parameters for lung cancer,and to investigate its impact factors.Methods Thirty-eight lung cancer patients underwent twice free breathing IVIM scanning (0.5-1.0 h interval).Two radiologists independently analyzed IVIM images to obtain true diffusion coefficient (D),pseudo-diffusion coefficient (D*) and perfusion fraction (f).All the parameters were compared between repeated measurements and scans.Intra-and inter-observer,test-retest reproducibility was assessed with interclass correlation coefficients (ICCs).The impact of lung cancer type (peripheral and central),size (the largest diameter ≥2 cm and ＜2 cm) and location (upper,mid,and lower lung field) on short-term reproducibility were compared by using coefficient of variations (WCVs).Results There was no significant difference between repeated measurements for all parameters (all P＞ 0.05).All the parameters showed good intra-and inter-observer agreement.WCVsof D* and f (19.88％-36.83％) were higher than those of D (2.97％-4.62％).WCVs of D were higher for central lung cancer and the largest diameter ＜2 cm,and increasing from apical to lower zone.WCV of f was larger in the central lung cancer and the largest diameter ≥2 cm,while D* was greatly influenced by type,size and location of lung cancer.Conclusion The test retest reproducibility of D is good,while of D* and f are poor in lung cancer.The type,size and location of lung cancers are the impact factors of IVIM parameters.

Objective To investigate the ADC value and intravoxel incoherent motion (IVIM) parameters to predict the early response to chemotherapy in patients with locally advanced non-small cell lung cancer (NSCLC). Methods Twenty-six patients with pathologically confirmed NSCLC in our hospital from June 2015 to January 2017 were prospectively studied. MR routine scan, DWI and IVIM scans were performed before and at the end of the first cycle of chemotherapy. The ADC value, pure diffusion parameter (D), perfusion parameter (D*) and perfusion fraction (f) before and after chemotherapy were recorded respectively, and the maximum diameter of tumor (MDMRI) was measured on T2WI. The effective group and the ineffective group were divided according to RECIST 1.1. Intra- and interobserver reproducibility were assessed with intraclass correlation coefficient (ICC). The differences of the parameters and their change rate were compared pre-and posttreatment, in the effective and the ineffective groups by using t test. Receiver operating characteristic (ROC) curves were generated to explore the optimal parameters and thresholds for early prediction of the efficacy of chemotherapy. Z test was used to compare the differences in the areas under the ROC curves. Results The repeatability of D*was relatively poor (ICC 0.507-0.716). The ADC and D values of the effective group before chemotherapy were (1.28±0.21)×10-3 and (1.05±0.14)×10-3mm2/s, respectively, and those of the ineffective group were (1.55 ± 0.25) × 10-3 and (1.29 ± 0.18) × 10-3mm2/s, respectively. The differences between two groups were statistically significant (t=-2.989, -3.755, respectively, P all<0.05). While there was no significant difference in f between the effective and ineffective groups before chemotherapy (t=-1.034, P=0.312). The ADC, D and f values of the effective group before chemotherapy were lower than those after chemotherapy, and the differences were statistically significant (t=-3.969,-5.617 and-2.876, respectively, P all<0.05). While there was no significant difference in ADC and D values in ineffective group (t=-0.737, -0.866, P>0.05, respectively). The difference of f was statistically significant (t=-2.731, P<0.05).ΔADC％,ΔD％andΔMDMRI％in effective group were (23.90 ± 22.28)％, (32.58 ± 20.63)％ and (18.77 ± 10.36)％, respectively, and those in ineffective group were (1.19 ± 11.35)％, (6.22 ± 21.63)％ and (9.35 ± 8.26)％, respectively. The differences between two groups were statistically significant (t=3.393, 3.154 and 2.487, respectively, P all<0.05). There was no significant difference inΔf％between two groups (t=1.346, P=0.191). ROC curve analysis showed that the area under curve (AUC) of preADC, preD, ΔADC％, ΔD％ and ΔMDMRI％ was 0.788, 0.848, 0.800, 0.830 and 0.727, respectively. When setting the preD=1.20×10-3 mm2/s as the boundary under the largest AUC, however, there was no significant differences in AUC compared with preADC, ΔADC％, ΔD％ and ΔMDMRI％ (Z=1.336, 0.363, 0.136, 1.395, P>0.05). Conclusion The ADC value, D value before chemotherapy and the early change rate after chemotherapy can better predict the early response of chemotherapy in NSCLC patients.