Relationship between T2 relaxation and apparent diffusion coefficient in malignant and non-malignant prostate regions and the effect of peripheral zone fractional volume

Objective: To establish whether T2 relaxation and apparent diffusion coefficient (ADC) in normal prostate and tumour are related and to investigate the effects of glandular compression from an enlarged transition zone (T-2) on peripheral zone (PZ) T2 and ADC by correlating them with the peripheral zone fractional volume (PZFV). Methods: 48 consecutive patients prospectively underwent multiecho T-2 weighted (T2W) (echo times 20, 40, 60, 80, 100 ms) and diffusion-weighted (b=0, 100, 300, 500, 800 s mm(-2)) endorectal MRI. In 43 evaluable patients, single slice whole PZ, TZ and tumour focal hypointense signal on T2W images in a biopsy-positive octant) regions of interest were transferred to T-2 and ADC maps by slice matching. T-2 and ADC values were correlated, and PZ values were correlated with PZFV. Results: T-2 and ADC values were significantly different among groups [T-2 mean +/- standard deviation (SD) PZ, 149 +/- 49ms; TZ, 125 +/- 26ms; tumour, 97 +/- 23ms; PZ vs TZ, p=0.002; PZ vs tumour, p<0.0001; TZ vs tumour, p<0.0001; ADCx10(-6) mm(2) s(-1) mean +/- SD PZ, 1680 +/- 215; TZ, 1478 +/- 139; tumour, 1030 +/- 205; p<0.0001]. Significant positive correlations existed between T-2 and ADC for PZ, TZ, PZ and TZ together, but not for tumour (r=0.515, p<0.0001; r=0.300, p=0.03; r=0.526, p<0.0001; and r=0.239, p=0.32, respectively). No significant correlation existed between PZFV and PZ T-2 (r=0.10, p=0.5) or ADC (r=0.03, p=0.8). Conclusion: The correlation between T-2 and ADC that exists in normal prostate is absent in tumour. PZ compression by an enlarged TZ does not alter PZ T-2 or ADC to affect tumourPZ contrast. Advances in Knowledge: Microstructural features of tumours alter diffusivity independently of their effects on T-2 relaxation.