Patients
The Institutional Review Board of our institution approved this retrospective study,
and waived the requirement for informed consent.
From August 2015 to July 2016,
188 patients with biopsy-proven prostate cancer underwent multiprarametric prostate MRI followed by radical prostatectomy.
The exclusion criteria were as follows: outside MRI (n = 27) or MRI without DWI1500 (n = 3),
preoperative androgen deprivation therapy (n = 1),
and prostate sarcoma (n = 2).
Finally,
154 consecutive patients (mean age,
64 years; range,
43-78 years) were included in our study.
MR techniques
All MR imaging was performed with a 3T MR system (Intera Achieva 3T,
Philips Medical System,
Best,
The Netherlands) equipped with a 6-channel SENSE coil (Philips Healthcare,
Best,
The Netherlands).
Before scanning,
each patient received an intramuscular injection of 20 mg butyl scopolamine (Buscopan,
Boehringer,
Ingelheim,
Ingelheim am Rhein,
Germany) to suppress bowel peristalsis.
All patients underwent T1-weighted imaging (T1WI),
T2WI,
DWI and dynamic contrast-enhanced MRI (DCE-MRI).
T2-weighted turbo spin-echo images [repetition time (TR)/echo time (TE),
3407/100 ms; slice thickness,
3 mm; interslice gap,
1 mm; matrix,
568×341; field of view (FOV),
200 mm; number of signals acquired (NSA),
3] were acquired in three orthogonal planes (transverse,
sagittal,
and coronal).
Transverse DCE-MRI was obtained using a 3D fast field echo sequence.
DWI was acquired in the transverse plane using the single-shot echo planar imaging (EPI) technique with parallel imaging and fat suppression (TR/TE,
5250/68; slice thickness,
3 mm; interslice gap,
1 mm; matrix,
124 × 121; FOV,
20 cm; SENSE factor 2).
Diffusion-encoding gradients were applied as four b values (0,
100,
1000,
and 1500 s/mm2).
The ADC maps were automatically constructed on a pixel-by-pixel basis for DWI1000 (using b = 100 and 1000 s/mm2) and DWI1500 (using b = 100 and 1500 s/mm2).
Image analysis
All MR images were archived using a picture archiving and communication system (PACS; PathSpeed Workstation; GE Medical Systems,
Milwaukee,
WI,
USA).
Two independent radiologists with 10 years (reader 1) and one year (reader 2) of experience in prostate MRI who were unaware of the clinical,
surgical,
and histological findings analyzed the MR images retrospectively.
The two readers evaluated the location of the index lesion as follows: base (right and left),
mid-gland (right and left),
and apex (right and left) in the PZ or the transition zone (TZ) of the prostate.
Based on the anatomical details of T2WI,
the lesions on DWI1000 and DWI1500 were analyzed using PI-RADS v2 scoring system,
respectively.
Statistical analysis
The sensitivity,
specificity and diagnostic accuracy were evaluated for the presence of CSC in the PZ regarding each imaging data set and readers.
The CSC was defined as Gleason score ≥7,
and/or volume ≥ 0.5cc and/or extracapsular extension.
The PI-RADS v2 scores of 3 to 5 were considered “present” for CSC.
The variability of DWI scoring and inter-reader variability between the two readers were evaluated using κ statistics.
A κ value of up to 0.20 was considered to indicate slight agreement,
0.21–0.40 fair agreement,
0.41–0.60 moderate agreement,
0.61–0.80 substantial agreement,
and 0.81 or greater almost perfect agreement [11].
The receiver operating characteristic (ROC) curves were generated for the presence of CSC in PZ using different b values in the two readers.
The diagnostic performance was then assessed by calculating the area under the curve (AUC).
A P value < 0.05 was considered indicative of a statistically significant difference.