Pharmacokinetic analysis of prostate cancer using independent component analysis.

Dynamic contrast enhanced (DCE)-MRI combined with pharmacokinetic (PK) modeling of a tumor provides information about its perfusion and vascular permeability. Most PK models require the time course of contrast agent concentration in blood plasma as an input, which cannot be measured directly at the tissue of interest, and is approximated with an arterial input function (AIF). Variability in methods used in estimating the AIF and inter-observer variability in region of interest selection are major sources of discrepancy between different studies. This study had two aims. The first was to determine whether a local vascular input function (VIF) estimated using an adaptive complex independent component analysis (AC-ICA) algorithm could be used to estimate PK parameters from clinical dynamic contrast enhanced (DCE)-MRI studies. The second aim was to determine whether normalizing the input function using its area under the curve would improve the results of PK analysis. AC-ICA was applied to DCE-MRI of 27 prostate cancer patients and the intravascular signal was estimated. This signal was converted into contrast agent concentration to give a local vascular input function (VIF) which was used as the input function for PK analysis. We compared K(trans) values for normal peripheral zone (PZ) and tumor tissues using the local VIF with those calculated using a conventional AIF obtained from the femoral artery. We also compared the K(trans) values obtained from the un-normalized input functions with the KN(trans) values obtained after normalizing the AIF and local VIF. Normalization of the input function resulted in smaller variation in PK parameters (KN(trans) vs. K(trans) for normal PZ tissue was 0.20±0.04mM.min(-1) vs. 0.87±0.54min(-1) for local VIF and 0.21±0.07mM.min(-1) vs. 0.25±0.29min(-1) for AIF) and better separation of the normal and tumor tissues (effect-size of this separation using KN(trans) vs. K(trans) was 0.89 vs. 0.75 for local VIF and 0.94 vs. 0.41 for AIF). The AC-ICA and AIF-based analyses provided similar (KN(trans)) values in normal PZ tissue of prostate across patients. Normalizing the input function before PK analysis significantly improved the reproducibility of the PK parameters and increased the separation between normal and tumor tissues. Using AC-ICA allows a local VIF to be estimated and the resulting PK parameters are similar to those obtained using a more conventional AIF; this may be valuable in studies where an artery is not available in the field of view.

A prospective comparison of MRI-US fused targeted biopsy versus systematic ultrasound-guided biopsy for detecting clinically significant prostate cancer in patients on active surveillance.

BACKGROUND: In active surveillance (AS) patients: (i) To compare the ability of a multiparametric MRI (mpMRI)-ultrasound biopsy system to detect clinically significant (CS) prostate cancer with systematic 12-core biopsy (R-TRUSBx), and (ii) To assess the predictive value of mpMRI with biopsy as the reference standard. METHODS: Seventy-two men on AS prospectively underwent 3T mpMRI . MRI-ultrasound fusion biopsy (UroNavBx) and R-TRUSBx was performed. CS cancer was defined using two thresholds: 1) GS ≥ 7 (CS7) and 2) GS = 6 with >50% involvement (GS6). CS cancer detection rates and predictive values were determined. RESULTS: CS7 cancers were found in 19/72 (26%), 7 (37%) identified by UroNavBx alone, 2 (11%) by R-TRUSBx alone (P = 0.182). UroNav targeted biopsy was 6.3× more likely to yield a core positive for CS7 cancer compared with R-TRUSBx (25% of 141 versus 4% of 874, P < 0.001). Upgrading of GS occurred in 15/72 patients (21%), 13 (87%) detected by UroNavBx and 10 (67%) by R-TRUSBx. The NPV of mpMRI for CS7 cancer was 100%. MRI suspicion level significantly predicted CS cancer on multivariate analysis (OR 3.6, P < 0.001). CONCLUSION: UroNavBx detected CS cancer with far fewer cores compared with R-TRUSBx, and mpMRI had a perfect negative predictive value in this population.

Prostate imaging: evaluation of a reusable two-channel endorectal receiver coil for MR imaging at 1.5 T.

PURPOSE: To prospectively compare image quality with use of a two-channel solid reusable phased-array endorectal receiver coil (SPAC) with that of the single-channel inflatable endorectal balloon coil currently in widespread use for 1.5-T magnetic resonance (MR) imaging of the prostate. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Multiparametric prostate MR imaging at 1.5 T was performed in patients who were suspected of having cancer. Thirty consecutive patients were included (mean age, 66.1 years; range, 49-76 years). The first 15 patients were imaged by using a balloon coil and an eight-channel external array, and the remaining 15 were imaged with a SPAC alone. One patient was imaged with both techniques. Axial T2-weighted images acquired at both standard and high spatial resolution were used to compare image quality between coils. Qualitative assessments of image quality were made separately by three radiologists. Signal-to-noise ratio (SNR) profiles were determined on a pixel-by-pixel basis in a 1-cm central band in the prostate by using T1-weighted axial images at the apex, midgland, and base. Interrater reliability was determined by using a two-way intraclass correlation coefficient, qualitative scores were compared by using the Student t test for independent samples, and SNR profiles were plotted by using a Biot-Savart curve approximation. RESULTS: SNR of the SPAC was significantly better compared with that of the balloon coil at distances up to 3.0 cm at the apex and 3.5 cm at the base and midgland (P < .001). There was a 7% improvement in SNR at the mean maximal anteroposterior prostate dimension in this cohort and a 96% improvement at half this distance. At both standard and high spatial resolution, significant improvements in overall image quality (P = .015 and P < .001, respectively), visibility of the anterior gland (P = .009 and P < .001, respectively), and noise (P < .001 and P < .001, respectively) were seen when the SPAC was used. Interrater reliability was 0.536 (95% confidence interval: 0.461, 0.603). CONCLUSION: Both SNR and image quality were significantly improved with use of the SPAC at 1.5 T compared with use of the single-channel inflatable endorectal balloon coil.

Incorporating endorectal MR elastography into multi-parametric MRI for prostate cancer imaging: Initial feasibility in volunteers.

PURPOSE: To investigate the tolerability and technical feasibility of performing endorectal MR elastography (eMRE) in human volunteers within the representative age group commonly affected by prostate cancer. MATERIALS AND METHODS: Endorectal MRE was conducted on seven volunteers in a 1.5 Tesla (T) MR imager using a rigid endorectal coil. Another five volunteers were imaged on a 3T MR imager using an inflatable balloon type endorectal coil. Tolerability was accessed for vibration amplitudes of ±1-50 µm and for frequencies of 100-300 Hz. RESULTS: All 12 volunteers tolerated the displacements necessary to successfully perform eMRE. Shear waves with frequencies up to 300 Hz could propagate across the entire prostate using both coil designs. CONCLUSION: The results of this study motivate further investigation of eMRE in prostate cancer patients to help determine if there is an added value of integrating eMRE into existing multi-parametric prostate MRI exams.

Implantable cardioverter-defibrillator implantation as a bridge to cardiac transplantation.

Implantable cardioverter-defibrillators (ICDs) have been shown to reduce sudden cardiac death in select patients with impaired left ventricular function. However, consensus guidelines on ICD use have not historically addressed patients waiting for heart transplantation, and further evidence is needed to broaden and strengthen current recommendations. The objective of the present study was to review all patients listed for heart transplantation at a single institution and evaluate the impact of ICD implantation while waiting. All consecutive patients listed for heart transplantation at the Queen Elizabeth II Health Sciences Center, Halifax, Nova Scotia, from 1995 to July 2006, were included in the study (n = 124). We observed 12 deaths while waiting among patients listed for transplantation (10%), with all deaths occurring in the non-ICD patients. In patients who did have an ICD prior to transplantation, 17% received appropriate defibrillation therapy while awaiting transplantation, and 3 of 12 patients in the non-ICD population who died while waiting died suddenly, suggesting that ICDs could be used as a "bridge to transplantation" in patients with refractory heart failure who are to be listed for heart transplantation.