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Background: Interpretation of diffusion in conjunction with T2 -weighted MRI is essential for assessing prostate cancer; however, the combination of apparent diffusion coefficient (ADC) with quantitative T2 mapping remains unexplored.Purpose: To document the T2 components and ADC of untreated and irradiated nonmalignant prostate tissue as a measure of their glandular luminal and cellular compartments and to compare values with those of tumor.Study Type: Prospective.Population: Twenty-four men with prostate cancer (14 untreated; 10 with biochemical recurrence following radiation therapy).Field Strength/sequences: Endorectal 3 T MRI including a 32-echo gradient echo and spin echo (GRASE) and an 8 b-value diffusion-weighted sequence.Assessment: Regions of interest were drawn on ADC maps and T2 -weighted images around focal lesions in areas of biopsy-positive prostate cancer and in nonmalignant areas of untreated and irradiated peripheral zone (PZ), and untreated transitional zone (TZ). Multiecho T2 data were fitted with mono-/biexponential decay and nonnegative least squares functions. The luminal water fraction (LWF) was derived.Statistical Tests: The preference between mono- and biexponential decay was assessed using the Bayesian information criterion. Differences in fitted parameters between tissue types were compared (paired t-test within groups, Kruskal-Wallis and Wilcoxon rank-sum test between groups) and correlations between ADC and T2 components assessed (Spearman rank correlation test).Results: LWF in tumor (0.09) was significantly lower than in PZ or TZ (0.27 and 0.18, P < 0.01, respectively), but tumor values were comparable to nonmalignant irradiated prostate (0.08). The short T2 relaxation rate was lower in tumor than in nonmalignant untreated or irradiated tissue (significant compared with TZ, P = 0.01). There was a strong correlation between LWF and ADC in normal untreated tissue (r = 0.88, P < 0.001). This relationship was absent in nonmalignant irradiated prostrate (r = -0.35, P = 0.42) and in tumor (r = -0.04, P = 0.88).Data Conclusion: T2 components in conjunction with ADC can be used to characterize untreated and irradiated nonmalignant prostate and tumor. LWF is most useful at discriminating tumor in the untreated prostate.Level Of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:619-627. [ABSTRACT FROM AUTHOR]

Purpose: Diffusion-weighted (DW) and dynamic contrast-enhanced magnetic resonance imaging (MRI) are increasingly applied for the assessment of functional tissue biomarkers for diagnosis, lesion characterization, or for monitoring of treatment response. However, these techniques are vulnerable to the influence of various factors, so there is a necessity for a standardized MR quality assurance procedure utilizing a phantom to facilitate the reliable estimation of repeatability of these quantitative biomarkers arising from technical factors (e.g., B1 variation) affecting acquisition on scanners of different vendors and field strengths. The purpose of this study is to present a novel phantom designed for use in quality assurance for multicenter trials, and the associated repeatability measurements of functional and quantitative imaging protocols across different MR vendors and field strengths. Methods: A cylindrical acrylic phantom was manufactured containing 7 vials of polyvinylpyrrolidone (PVP) solutions of different concentrations, ranging from 0% (distilled water) to 25% w/w, to create a range of differentMR contrast parameters. Temperature control was achieved by equilibration with ice-water. Repeated MR imaging measurements of the phantom were performed on four clinical scanners (two at 1.5 T, two at 3.0 T; two vendors) using the same scanning protocol to assess the long-term and short-term repeatability. The scanning protocol consisted of DW measurements, inversion recovery (IR) T1 measurements, multiecho T2 measurement, and dynamic T1-weighted sequence allowing multiple variable flip angle (VFA) estimation of T1 values over time. For each measurement, the corresponding calculated parameter maps were produced. On each calculated map, regions of interest (ROIs) were drawn within each vial and the median value of these voxels was assessed. For the dynamic data, the autocorrelation function and their variance were calculated; for the assessment of the repeatability, the coefficients of variation (CoV) were calculated. Results: For both field strengths across the available vendors, the apparent diffusion coefficient (ADC) at 0 ◦C ranged from (1.12±0.01)×10−3 mm2/s for pure water to (0.48±0.02)×10−3 mm2/s for the 25% w/w PVP concentration, presenting a minor variability between the vendors and the field strengths. T2 and IR-T1 relaxation time results demonstrated variability between the field strengths and the vendors across the different acquisitions. Moreover, the T1 values derived from the VFA method exhibited a large variation compared with the IR-T1 values across all the scanners for all repeated measurements, although the calculation of the standard deviation of the VFA-T1 estimate across each ROI and the autocorrelation showed a stability of the signal for three scanners, with autocorrelation of the signal over the dynamic series revealing a periodic variation in one scanner. Finally, the ADC, the T2, and the IR-T1 values exhibited an excellent repeatability across the scanners, whereas for the dynamic data, the CoVs were higher. Conclusions: The combination of a novel PVP phantom, with multiple compartments to give a physiologically relevant range of ADC and T1 values, together with ice-water as a temperaturecontrolled medium, allows reliable quality assurance measurements that can be used to measure agreement between MRI scanners, critical in multicenter functional and quantitative imaging studies. [ABSTRACT FROM AUTHOR]

Purpose To evaluate the effect on diffusion-weighted image-derived parameters in the apparent diffusion coefficient (ADC) and intra-voxel incoherent motion (IVIM) models from choice of either free-breathing or navigator-controlled acquisition. Materials and Methods Imaging was performed with consent from healthy volunteers ( n = 10) on a 1.5T Siemens Avanto scanner. Parameter-matched free-breathing and navigator-controlled diffusion-weighted images were acquired, without averaging in the console, for a total scan time of ∼10 minutes. Regions of interest were drawn for renal cortex, renal pyramid, whole kidney, liver, spleen, and paraspinal muscle. An ADC diffusion model for these regions was fitted for b-values ≥ 250 s/mm2, using a Levenberg-Marquardt algorithm, and an IVIM model was fitted for all images using a Bayesian method. Results ADC and IVIM parameters from the two acquisition regimes show no significant differences for the cohort; individual cases show occasional discrepancies, with outliers in parameter estimates arising more commonly from navigator-controlled scans. The navigator-controlled acquisitions showed, on average, a smaller range of movement for the kidneys (6.0 ± 1.4 vs. 10.0 ± 1.7 mm, P = 0.03), but also a smaller number of averages collected (3.9 ± 0.1 vs. 5.5 ± 0.2, P < 0.01) in the allocated time. Conclusion Navigator triggering offers no advantage in fitted diffusion parameters, whereas free-breathing appears to offer greater confidence in fitted diffusion parameters, with fewer outliers, for matched acquisition periods. J. Magn. Reson. Imaging 2014;39:235-240. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In addition to the diffusion coefficient, fitting the intravoxel incoherent motion model to multiple b-value diffusion-weighted MR data gives pseudo-diffusion measures associated with rapid signal attenuation at low b-values that are of use in the assessment of a number of pathologies. When summary measures are required, such as the average parameter for a region of interest, least-squares based methods give adequate estimation accuracy. However, using least-squares methods for pixel-wise fitting typically gives noisy estimates, especially for the pseudo-diffusion parameters, which limits the applicability of the approach for assessing spatial features and heterogeneity. In this article, a Bayesian approach using a shrinkage prior model is proposed and is shown to substantially reduce estimation uncertainty so that spatial features in the parameters maps are more clearly apparent. The Bayesian approach has no user-defined parameters, so measures of parameter variation (heterogeneity) over regions of interest are determined by the data alone, whereas it is shown that for the least-squares estimates, measures of variation are essentially determined by user-defined constraints on the parameters. Use of a Bayesian shrinkage prior approach is, therefore, recommended for intravoxel incoherent motion modeling. Magn Reson Med 71:411-420, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Pyruvate-lactate exchange is mediated by the enzyme lactate dehydrogenase (LDH) and is central to the altered energy metabolism in cancer cells. The measurement of exchange kinetics using hyperpolarized 13C NMR has provided a biomarker of response to novel therapeutics. However, the observable signal is restricted to the exchanging hyperpolarized 13C pools and the endogenous pools of 12C-labelled metabolites are invisible in these measurements. In this study, we investigated an alternative in vitro 1H NMR assay, using [3-13C]pyruvate, and compared the measured kinetics with a hyperpolarized 13C NMR assay, using [1-13C]pyruvate, under the same conditions in human colorectal carcinoma SW1222 cells. The apparent forward reaction rate constants ( kPL) derived from the two assays showed no significant difference, and both assays had similar reproducibility ( kPL = 0.506 ± 0.054 and kPL = 0.441 ± 0.090 nmol/s/106 cells; mean ± standard deviation; n = 3); 1H, 13C assays, respectively). The apparent backward reaction rate constant ( kLP) could only be measured with good reproducibility using the 1H NMR assay ( kLP = 0.376 ± 0.091 nmol/s/106 cells; mean ± standard deviation; n = 3). The 1H NMR assay has adequate sensitivity to measure real-time pyruvate-lactate exchange kinetics in vitro, offering a complementary and accessible assay of apparent LDH activity. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]