Intra-voxel incoherent motion parameters of rectal cancer at 3.0 T MRI:effect of region of interest on measurement consistency of parameters / 中华放射学杂志

ABSTRACT

Objective To determine the measurement consistency of diffusion coefficient D, perfusion fraction f and pseudodiffusion coefficient D*in rectal cancers based on different ROIs. Methods Forty-three patients with histologically proven rectal cancers were examined using echo-planar DW-MRI with eight b values (0 to 1 000 s/mm2). Intravoxel incoherent motion parameters were measured on intravoxel incoherent motion map that contained the largest tumor cross-section, according to two distinct ROI protocolsfreehand outline ROI and semi-automatic tumor center ROI. The two protocols were compared for differences in IVIM parameters and the interclass correlation coefficient (ICC) were also calculated. intra-and inter-observer variability using paired t test and Bland-Altman plot. Results The IVIM parameters(D, f and D*) obtained by ROIs for outlined and center analysis were (1.08 ± 0.24) × 10-3mm2/s, (0.16 ± 0.06), (26.59 ± 19.54) × 10-3mm2/s and (1.06 ± 0.27) × 10-3mm2/s, (0.17 ± 0.07), (30.79 ± 20.85) × 10-3mm2/s, respectively. No significant differences were observed between the means of the IVIM parameters (D, f, D*) calculated by the two methods (t=1.113,-0.259,-1.660;P=0.272, 0.797,0.104, respectively),and the relative ICC were 0.863, 0.469, 0.663, respectively. The intra-observer 95% limits of consistency of IVIM parameters were (-0.012—0.038) × 10-3mm2/s, (-0.003—0.007), (-0.923—1.166) × 10-3mm2/s with ROI outline tumor, respectively;(-0.024—0.044)×10-3mm2/s, (-0.005—0.015), (-1.670—4.195)×10-3mm2/s with center ROI, respectively. The inter-observer 95% limits of consistency of perfusion parameters were (-0.047—0.009) × 10-3mm2/s, (-0.015—0.009), (-7.206—3.190) × 10-3mm2/s with ROI outlined tumor, respectively;(-0.068—0.048) × 10-3mm2/s, (-0.005—0.041), (-17.657—0.779) × 10-3mm2/s with center ROI, respectively. Conclusions There was no statistically significant difference between the outlined ROI and tumor center ROI analysis of rectal cancers' IVIM parameters. The tumor analysis by outlined ROI protocol appropriately improves intra-and inter-observer consistency and can provide more reproducible and stable results.