[Effects of different computed high b-values on diffusion weighted imaging scores in Prostate Imaging Reporting and...

Objective: To determine the effects of different computed high b-value on diffusion weighted imaging (DWI) scores in Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) of prostate cancer in peripheral zone. Methods: A retrospective study of 104 cases of prostate cancer in peripheral zone was conducted, all of the patients were histopathologically confirmed by transrectal ultrasound guided saturation biopsy or radical prostatectomy in Tongji Hospital of Tongji University from January 2012 to December 2015.All MRI imaging examinations were performed by using a 3.0T Siemens Verio MRI scanner.The imaging protocol consisted of high-resolution axial and sagittal T(2) weighted imaging (T(2)WI), axial acquired diffusion weighted imaging (aDWI) with b=0, 50, 1 000 s/mm(2) and dynamic contrast-enhanced (DCE) scans.Computed diffusion weighted imaging (cDWI) images with b=1 000, 1 400, 2 000 s/mm(2) were processed by Matlab.These three groups of cDWI images were analyzed according to the PI-RADS v2 criteria, and signal intensity of ratio (SIR) of lesions were analyzed by independent t test and one-way ANOVA in each group. Results: The numbers of cases with a DWI score of 2 and 5 were similar among three groups.Nine cases (33.3%) in all 27 cases with a DWI score of 3 on b=1 000 s/mm(2) upgraded to score 4 when b-value rose to 1 400 and 2 000 s/mm(2).The ratios of SIR of lesions in cases upgraded from DWI score 3 to 4 to those unchanged cases on b=1 400 and 2 000 s/mm(2) were 1.86±0.21 to 1.61±0.27 and 2.18±0.26 to 1.75±0.30, respectively (t=2.486, t=3.671, both P<0.05). In these 9 cases who upgraded to DWI score 4, SIRs of the lesion were significantly different between groups when b=1 000, 1 400 and 2 000 s/mm(2) (F=10.907, 33.768, 8.043, all P<0.05), and their SIRs increased with the rising of b-value. Conclusions: The computed high b-value (b≥1 400 s/mm(2)) mainly affects cases with a DWI score of 3, but DWI scores would not change neither in b=1 400 s/mm(2) nor in 2 000 s/mm(2) cases. For DWI score in PI-RADS v2 of prostate cancer in peripheral zone, b=1 400 s/mm(2) is probably of more scoring value than b=1 000 or 2 000 s/mm(2).