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To investigate diffusion anisotropy in whole human prostate specimensSeven whole radical prostatectomy specimens were obtained with informed patient consent and institutional ethics approval. Diffusion tensor imaging was performed at 9.4 Tesla. Diffusion tensors were calculated from the native acquired data and after progressive downsamplingFractional anisotropy (FA) decreased as voxel volume increased, and differed widely between prostates. Fixation decreased mean FA by ∼0.05-0.08 at all voxel volumes but did not alter principle eigenvector orientation. In unfixed tissue high FA (0.6) was found only in voxels of volume0.5 mm(3) , and then only in a small fraction of all voxels. At typical clinical voxel volumes (4-16 mm(3) ) less than 50% of voxels had FA 0.25. FA decreased at longer diffusion times (Δ = 60 or 80 ms compared with 20 ms), but only by ∼0.02 at typical clinical voxel volume. Peripheral zone FA was significantly lower than transition zone FA in five of the seven prostatesFA varies widely between prostates. The very small proportion of clinical size voxels with high FA suggests that in clinical DWI studies ADC based on three-direction measurements will be minimally affected by anisotropy. Magn Reson Med 76:626-634, 2016. © 2015 Wiley Periodicals, Inc.

Non-Gaussian diffusion dynamics was investigated in the two distinct water populations identified by a biexponential model of diffusion in prostate tissue. Diffusion-weighted MRI (DWI) signal attenuation was measured ex vivo in two formalin-fixed prostates at 9.4 T with diffusion times Δ = 10, 20 and 40 ms, and b values in the range 0.017-8.2 ms/µm(2) . A conventional biexponential model was compared with models in which either the lower diffusivity component or both of the components of the biexponential were stretched. Models were compared using Akaike's Information Criterion (AIC) and a leave-one-out (LOO) test of model prediction accuracy. The doubly stretched (SS) model had the highest LOO prediction accuracy and lowest AIC (highest information content) in the majority of voxels at Δ = 10 and 20 ms. The lower diffusivity stretching factor (α2 ) of the SS model was consistently lower (range ~0.3-0.9) than the higher diffusivity stretching factor (α1 , range ~0.7-1.1), indicating a high degree of diffusion heterogeneity in the lower diffusivity environment, and nearly Gaussian diffusion in the higher diffusivity environment. Stretched biexponential models demonstrate that, in prostate tissue, the two distinct water populations identified by the simple biexponential model individually exhibit non-Gaussian diffusion dynamics.

To investigate the microscopic diffusion properties of formalin-fixed breast tissue.Diffusion microimaging was performed at 16.4T with 40-μm isotropic voxels on two normal and two cancer tissue samples from four patients. Results were correlated with histology of the samples.Diffusion-weighted images and mean diffusivity maps demonstrated distinct diffusivity differences between breast tissue components. Mean diffusivity (MD) in normal tissue was 0.59 ± 0.24 μm(2) /ms for gland lobule (voxels containing epithelium and intralobular stroma) and 1.23 ± 0.34 μm(2) /ms for interlobular fibrous stroma. In the cancer samples, MD = 0.45 ± 0.23 μm(2) /ms for invasive ductal carcinoma (voxels contain epithelium and intralobular stroma) and 0.61 ± 0.35 μm(2) /ms for ductal carcinoma in situ. There were significant MD differences between all tissue components (P 0.005), except between gland lobule and ductal carcinoma in situ (P = 0.71). The low diffusivity of epithelium-rich cancer tissue and of normal epithelium relative to its supporting fibrous stroma was similar to that reported for prostate tissue and the esophageal wall.Diffusion microimaging demonstrates distinct diffusivity differences between breast tissue glandular structures. Low diffusivity may be a distinctive feature of mammalian epithelia.

To compare the theoretical information content of four popular models of diffusion-weighted signal attenuation.Four whole prostates were imaged fresh unfixed and fixed at 9.4T. Biexponential, kurtosis, stretched exponential, and monoexponential models were ranked using Akaike's Information Criterion (AIC) with validation by a leave-one-out test of model prediction error.For unfixed tissue measurements (b-value range: 17-2104 s/mm(2)) the biexponential and kurtosis models had similar information content to each other and this was distinctly higher than for the stretched and monoexponential models. In fixed-tissue measurements (b-value range: 17-8252 s/mm(2)), the biexponential model had much higher information content than the three other models.AIC-based model ranking is consistent with an independent prediction accuracy test. Biexponential and kurtosis models consistently perform better than stretched and monoexponential models. The biexponential model has increasing superiority over all three other models as maximum b-value increases above ∼2000 s/mm(2).

To directly compare the responsiveness of quantitative imaging measures of disease progression in knee osteoarthritis (OA). In the medial compartment of the knee comparison was made between: 1) radiographic joint space narrowing (JSN); 2) global quantitative magnetic resonance imaging (qMRI) of cartilage volume; 3) regional qMRI of cartilage thickness; and 4) regional analysis using an ordered value (OV) methodology.3T MRI and weight-bearing radiography of the knees were performed at baseline and 1-year timepoints in 23 subjects (mean age 63 years) with symptomatic knee OA. Standardized response means (SRM) were calculated for each measure. Statistical analysis to determine significance of change between timepoints was performed with a two-tailed Student's t-test (JSN, global, regional analysis) and nonparametric Mann-Whitney test (ordered values).At 1 year, global cartilage volume losses of 2.3% (SRM -0.44) in the medial tibia and 6.9% in the medial femur (SRM -0.74) were recorded. SRM for JSN was -0.46. Regional analysis revealed largest reductions in cartilage thickness in the external (SRM -0.84) weight-bearing subregion of the medial femur and in the posterior subregion of the medial tibia (SRM -0.79). OV analysis in the medial compartment revealed areas of cartilage thinning (four ranked OV) and cartilage thickening (two ranked OV).The MRI OV approach proved to be a superior analysis tool for detecting changes in cartilage morphology over a 1-year period. Radiographically defined JSN was found to be the least responsive measurement method of knee OA disease progression.

To assess the utility of knee cartilage volumetry using an unspoiled fat-suppressed 3D fast gradient echo (FGRE) sequence at 3T.Sagittal magnetic resonance (MR) images were obtained with an unspoiled fat-suppressed 3D FGRE sequence in eight porcine knees. Manual segmentation was used to derive the cartilage volume. This volume was compared to a volume measurement of cartilage scraping specimens obtained by water displacement. Imaging was repeated five times in four of the knees to assess interscan volume measurement reproducibility and calculate precision error. A single 3D dataset was manually segmented five times at weekly intervals to assess intraobserver volume measurement reproducibility.Total cartilage volume obtained from MRI and water displacement correlated well (r = 0.75). The interscan reproducibility of total volume measurements, expressed as the coefficient of variation (CV), was 4.2%, and the precision error (root mean square [RMS] CV) was 4.1%. The CV of intraobserver estimates of total cartilage volume by MRI was 3.6%.Interscan reproducibility of quantification of total cartilage volume and reproducibility of the manual segmentation technique were both high (95%). Accurate and reproducible cartilage volumetry can be obtained by using a clinical unspoiled fat-suppressed 3D FGRE acquired at 3T MRI.

Diffusion tensor microimaging at 16.4 T with 40 μm isotropic voxels was used to investigate anisotropic water diffusion in prostate tissue at spatial resolution approaching the cellular scale. Nine normal glandular tissue samples were collected from the peripheral zone of six formalin fixed radical prostatectomy specimens. Fibromuscular stromal tissue exhibited microscopic diffusion anisotropy (mean fractional anisotropy range 0.47-0.66) significantly higher (P0.01, Student's t-test) than in epithelium-containing voxels (mean fractional anisotropy range 0.31-0.54) in six of the seven normal tissue samples in which both compartments could be measured. Fiber tracking demonstrated principle stromal fiber directions consistent with myocyte orientation seen on light microscopy of the same sample. Diffusion tensor microimaging may be valuable for investigation of variable results from attempts to measure diffusion anisotropy in the prostate in vivo.

MR microimaging at 16.4 T with 40-μm isotropic voxels was used to investigate compartmentation of water diffusion in formalin-fixed prostate tissue. Ten tissue samples (~ 28 mm(3) each) from five organs were imaged. The mean diffusivity of epithelial, stromal, and ductal/acinar compartments was estimated by two methods: (1) manual region of interest selection and (2) Gaussian fitting of voxel diffusivity histograms. For the region of interest-method, the means of the tissue sample compartment diffusivities were significantly different (P0.001): 0.54 ± 0.05 μm(2)/ms for epithelium-containing voxels, 0.91 ± 0.17 μm(2)/ms for stroma, and 2.20 ± 0.04 μm(2)/ms for saline-filled ducts. The means from the histogram method were also significantly different (P0.001): 0.45 ± 0.08 μm(2)/ms for epithelium-containing voxels, 0.83 ± 0.16 μm(2)/ms for stroma, 2.21 ± 0.02 μm(2)/ms for duct. Estimated partial volumes of epithelial, stromal, and ductal/acinar compartments in a "tissue only" subvolume of each sample were significantly different (P0.02) between cancer and normal tissue for all three compartments. It is concluded that the negative correlation between apparent diffusion coefficient and cancer Gleason grade observed in vivo results from an increase of partial volume of epithelial tissue and concomitant decrease of stromal tissue and ductal space.

Phosphate transport was studied in phosphate-starved Candida utilis using 31P-NMR and in situ pH and K(+)-specific electrodes. A transient efflux of K+ was associated with the initial net influx of orthophosphate across the plasma membrane and decrease of both the plasma membrane pH gradient and the cytosol pH. Recovery of cytosol pH, and the plasma membrane pH gradient after phosphate uptake, was slow when extracellular K+ was depleted, but rapid when K+ was added to the suspension either with orthophosphate or after phosphate uptake. Net phosphate transport into the vacuole occurs against its concentration gradient and is associated with an increase of the tonoplast pH gradient. It is proposed that transport of orthophosphate into the vacuole is mediated by an electrical uniport and driven by the tonoplast membrane potential.

The recovery of Candida utilis from phosphate starvation was studied using 31P-NMR. The phosphate analogue methylphosphonate was found to be a useful indicator of cytosol pH. Added orthophosphate was rapidly accumulated by the cells and stored mainly In a stable pool of polyphosphate of mean chain-length at least 200 units. Observed pH changes in the medium and cytosol during uptake of orthophosphate and methylphosphonate are consistent with the transport of these compounds across the plasma membrane by a proton/phosphate symport. However, transport of phosphate across the vacuole membrane occurs by a mechanism for which methylphosphonate is not a substrate. In the cytosol pH changes are strongly correlated with changes in orthophosphate concentration, however, this is not the case in the vacuole.

A device is described which maintains homogeneous aerobic or anaerobic cell and organelle suspensions within an NMR sample tube. Line broadening due to magnetic field inhomogeneity is reduced by elimination of gas bubbles from the area of the probe receiver coils. The linewidth of the extracellular orthophosphate resonance of a yeast suspension in 31P NMR was 0.21 ppm compared with 0.4-0.7 ppm in conventionally aerated suspensions. Recirculation of the sample results in complete mixing within 90 s of addition of aliquots of acid or alkali. The maximum rate of oxygen transfer from the gaseous to the liquid phase was approximately 600 microM min-1 when aerated with 95% oxygen/5% carbon dioxide. A 60% wet weight suspension of yeast cells was recirculated for 20 h without settling of cells occurring. A method for estimating oxygen transfer rate is described.