In all patients, the DCE-MRI examination was performed 1 or 2 days before the systematic octant biopsy. All images were obtained using a 1.5 T superconducting MR system (Gyroscan Intera, Philips Medical Systems, Best, The Netherlands) with a 5-channel phased array coil. After obtaining three plain localizer images, T2 weighted turbo spin-echo images were acquired in the axial plains using the following parameters: (4700/120/17 [repetition time (TR), ms/echo time (TE), ms/echo train length]) four signal excitations; axiaalT1 weighted images (500/9/5), two signal excitations; and sagittal T2weighted images (4700/120/17). All examinations were performed using a 4 mm section thickness, a 0.4 mm intersection gap, a 200 mm field of view and a 256 × 256 matrix. A right-to-left phase-encoding direction was used to decrease motion artefacts from the abdominal wall. The DCE-MRI was obtained using a 3D-fast field echo sequence in the axial plain (4.5/1.5/30 [TR/TE/flip angle]) with a 50 mm slab thickness and 10 partitions, a 200 mm field of view and a 64 × 128 matrix. In most patients, the scan slab allowed a full coverage from the apex to the base of the prostate gland. After a bolus injection (3 ml s−1) of 0.1 mmol of gadopentetate dimeglumine (Magnevist, Nihon Schering, Osaka, Japan) per kilogram body weight using an auto injector (SPECTRIS, Nihon Medrad, Osaka, Japan) with a 15 ml saline flush, dynamic MRIs were obtained every 3 s for 3 min. In total 600 DCE-MRI images were obtained. Finally, post-contrast fat suppressed T1 weighted turbo spin-echo images (500/9/5) were obtained using two signal excitations.
Dynamic MRIs were transferred to a diagnostic workstation (EasyVision, Philips Medical Systems, Best, The Netherlands) and dynamic MR analysis software was used for the evaluation. First, multislice dynamic MRIs were displayed in cine mode with subtraction from the first scan image for every slice position. For both the right and left peripheral zones, one slice was selected if a strongly enhanced lesion, as compared with the surrounding tissue, was observed. A region of interest (ROI) was placed and traced on the enhanced lesion on a consensus basis by two radiologists who were aware only of the PSA and DRE findings and were not involved in obtaining the TRUS or PDUS findings. Despite knowledge of PSA and DRE findings, we selected ROIs with only subtracted images. If a strongly enhanced lesion was not visible, a slice through the middle of the gland was selected and a ROI was placed over the area encompassing both peripheral zones. For the right and left inner glands, a slice through the middle of the gland was selected and ROIs were placed over the area encompassing both sides of the inner gland because there was inhomogeneous enhancement from coexisting benign prostatic hyperplasia (BPH) in many cases.
A time–intensity curve (TIC) for each site was obtained from the dynamic images. TICs were classified into three types, based on their shapes (Figure 1⇓). The time-to-peak was defined as the delay time between the point on the curve of enhancement at which the signal was above the noise level and signal peak of TIC. The Type A TIC was characterized by an early peak enhancement and a time-to-peak value of no more than 60 s. The Type B TIC was characterized by an intermediate early enhancement and a time-to-peak value of no less than 60 s, and not greater than 100 s. The Type C TIC was characterized by delayed enhancement and no signal peak after a continuous increase in signal intensity for 3 min.
For the peripheral zone sites, we defined Type A and B TICs as positive and Type C TIC as negative on DCE-MRI. Most normal peripheral zones did not show hypervascularity. As to the inner gland sites, normal inner glands and coexisting BPH often showed moderate vascularity. Thus, we defined only Type A TIC as positive and Type B and C TICs as negative on DCE-MRI.
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