Approval was obtained from the institutional ethical review board,
and the study was compliant with the Health Insurance Portability and Accountability Act.
Written informed consent was obtained from all participating patients.
Patients
20 men presenting to our prostate cancer MRI clinic as part of a diagnostic workup were prospectively consented to be scanned using an external phased array wearable pelvic coil (WPC) in addition to the standard diagnostic sequences obtained using a endorectal coil (ERC) and standard pelvic phased array coil (PPA) at 3T. All patients were presenting for the assessment of known or suspected prostate cancer.
Two patients were excluded,
one of whom did not tolerate ERC insertion and the other having undergone prior prostatectomy.
18 patients were included in the study.
The age range was 49-72 (mean 63) and the prostate specific antigen (PSA) range was 2.0-10.1 (mean 10.0).
A PSA level was unvailable for one patient,
having been measured at an outside instution.
MRI Technique
All imaging was performed on the same 3T MR system (Discovery MR750w,
GE Healthcare,
Waukesha WI,
USA).
The wearable pelvic coil (PROCURE Prostate/Pelvic Coil,
ScanMed,
Omaha NE,
USA) was applied to the patient,
and axial T2w fast spin echo images and diffusion weighted images were acquired using scan parameters given in Table 1.
The WPC was then removed,
and the endorectal coil (Medrad eCoil,
Bayer Medical Care,
Indianola PA,
USA) was inserted in usual fashion and the balloon inflated with 50-60 mL of air.
The 32 channel pelvic phased array coil (GEM flex torso coil,
GE Healthcare,
Waukesha WI,USA) was positioned over the anterior lower abdomen and pelvis.
Glucagon 1mg IM was administered immediately following ERC insertion.
Axial,
coronal and sagittal localizers were performed to assess ERC position and adjustments were made if necessary.
A standard diagnostic PI-RADS v2 prostate MRI protocol was then performed [10,13].
As part of this protocol,
axial T2w fast spin echo images were acquired using the ERC and PPA in unison.
Two separate diffusion weighted sequences were performed,
one using the PPA coil only,
and the other using the ERC only.
The remainder of the sequences acquired as part of the standard diagnostic MRI were not used for the purposes of the study.
Qualitative Image Analysis
All images were reviewed on a diagnostic Picture Archiving and Communication System (PACS) workstation (Centricity PACS RA1000; GE Healthcare,
Barrington IL,
USA).
Qualitative image analysis was performed in consensus by two readers (ROD and RMD) with experience in prostate MRI.
Wearable pelvic coil and endorectal coil T2w images were rated using six criteria (Table 2),
some of which have been employed in previous studies assessing prostate MR image quality [14,15]. The T2w image criteria used were: definition of the posterior prostate gland border (1 to 5),
the definition of zonal anatomy i.e.
the ability to distinguish the peripheral zone and transitional zone (ZA; 1 to 5),
visualization of the neurovascular bundle (NVB; 1 to 4),
visualization of the seminal vesicles (SV; 1 to 5),
the severity of artifacts (SA; 1 to 4) and overall image quality (IQ; 1 to 5).
The three sets of DWI images were scored using five criteria (Table 2),
and some of these criteria were employed in a previous study assessing prostate DWI image quality [11]. The criteria used were margin demarcation defined by the ability to trace the prostate margin clearly (GD; 1 to 5),
zonal anatomy defined by the ability to distinguish the peripheral zone and transitional zone clearly (ZA; 1 to 5),
geometric distortion defined by distortion of the image due to field inhomogeneity using the T2w images as a reference (GD; 1 to 5),
the severity of artifacts (SA; 1 to 4) and overall image quality (IQ; 1 to 5).
In the case of both T2w and DWI,
the nature of any artifacts was recorded.
Quantitative Image Analysis
For the estimation of signal to noise ratio (SNR) in the T2w and b1400 diffusion weighted images,
elliptical regions of interest (ROI) were placed over the peripheral zone of the prostate,
transitional zone of the prostate and obturator internus muscle,
avoiding any artifacts or focal lesions.
The mean signal intensity was measured in the peripheral zone ROI and in the transitional zone ROI,
and these two values were averaged to give a value for mean prostate gland signal.
The standard deviation of the signal in the obturator internus muscle ROI was recorded to provide an estimation of image noise,
and the SNR was calculated by dividing the mean prostate gland signal by the image noise [11,16,17].
Statistical Analysis
All ordinal and continuous data are summarized as a mean ± standard deviation.
The Wilcoxon matched-pairs signed rank test was used to test each variable for statistical significance.
A p value of <0.05 was considered to indicate a statistically significant difference.
Statistical analysis was performed using the GraphPad Prism software package (Version 7.0c,
La Jolla,
CA,
USA).