Diffuse reflectance near infrared spectroscopy can distinguish normal from enzymatically digested cartilage.

A non-destructive, diffuse reflectance near infrared spectroscopy (DR-NIRS) approach is considered as a potential tool for determining the component-level structural properties of articular cartilage. To this end, DR-NIRS was applied in vitro to detect structural changes, using principal component analysis as the statistical basis for characterization. The results show that this technique, particularly with first-derivative pretreatment, can distinguish normal, intact cartilage from enzymatically digested cartilage. Further, this paper establishes that the use of DR-NIRS enables the probing of the full depth of the uncalcified cartilage matrix, potentially allowing the assessment of degenerative changes in joint tissue, independent of the site of initiation of the osteoarthritic process.

High-resolution measurements of small field beams using polymer gels.

Small field sizes are increasingly becoming important in radiotherapy particularly since the introduction of intensity-modulated radiation therapy (IMRT) techniques. It is normally a challenging task to reliably measure the delivered dose and to determine its distribution in a medium for such small fields using conventional-type dosimeters such as gas ionisation chambers. Recently, attempts have been made to use films, but they are not tissue equivalent, they measure the dose only in two dimensions and they are not as responsive to radiations. In the present work, polyacrylamide gel (PAG) dosimeters are employed to measure the dose and its distribution in three dimensions for very small field sizes, such as those typically used in stereotactic radiosurgery. Field sizes of 6 x 6 and 18 x 18 mm in width are investigated. The results show an agreement with radiochromic film and ionisation diode measurements, with some variation in measured doses near the edge of the field, where the gel data decreases more rapidly than the other methods.

Diffusion tensor imaging of articular cartilage as a measure of tissue microstructure.

OBJECTIVE: To use diffusion tensor MR micro-imaging to observe differences in magnitude and anisotropy of water diffusion between 'healthy' cartilage and cartilage enzymatically degraded to simulate arthritic damage. METHODS: Diffusion tensor images (156 x 156 microm in-plane resolution, 2mm slice thickness) of bovine cartilage were obtained at either 4.7 or 7.0 T using pulsed field gradient spin echo sequences. The parameters determined were: maximum and mean diffusivity, direction of the maximum diffusion eigenvector with respect to the normal to the articular surface and fractional anisotropy (FA) of diffusion. RESULTS: Both maximum and mean diffusion eigenvalues were found to decrease, respectively, from approximately 1.95 x 10(-9) and 1.80 x 10(-9) m2 s(-1) at the articular surface to approximately 1.08 x 10(-9) and 0.79 x 10(-9) m2 s(-1) in the deep zone. A systematic change was observed in the direction of the eigenvector corresponding to maximum diffusivity, reflecting the expected change in orientation of the collagen macrofibrillar bundles. Degradation with trypsin to remove proteoglycans resulted in a 10-15% increase in apparent diffusion coefficient of water in the cartilage, with no apparent change in FA. CONCLUSIONS: These methods have the potential to be used to probe local changes in tissue microstructure and the hydrodynamic status of cartilage during development of osteoarthritis.

Refractive index distribution and optical properties of the isolated human lens measured using magnetic resonance imaging (MRI).

Using a non-invasive MRI technique for measuring the refractive index distribution through the crystalline lens, refractive index maps were obtained through 20 intact isolated human lenses (7-82years). Focal length measurements, obtained by simulated light ray propagation through each index map were found to be in agreement with direct measurements performed on a scanning laser apparatus. With increasing age, the refractive index profiles became flatter in the central region, accompanied by steepening of the profile in the periphery. This appears to be an important mechanism underlying the observed changes in power and longitudinal aberration of the human lens.

Comparison of high-resolution MRI, optical microscopy and SEM for quantitation of trabecular architecture in the rat femur.

Magnetic resonance imaging (MRI) has been used to analyze trabecular bone architecture in femur heads taken from adult Wistar rats. The aim of this study was to validate the use of MRI in assessing trabecular structure and morphology by comparing standard measures of bone morphology in the rat femur obtained from high resolution MRI with those obtained by conventional optical microscopy and by scanning electron microscopy (SEM). MR images were obtained on a Bruker 4.7 T micro-imaging system using a three-dimensional spin echo sequence with spatial resolution of 23 microm in-plane and a slice thickness of 39 microm. Optical images were obtained by de-calcifying the bone in EDTA and then sectioning 5-microm-thick slices. SEM images were obtained from bone embedded in epoxy resin with surface preparation by diamond polishing. Values of standard bone morphological parameters were compared and correlation coefficients between the MRI and the optical- and SEM-derived measures of morphology were calculated. Partial volume effects in MRI were minimized in this study by the use of very thin slices, yielding better agreement with optical- and SEM-derived measures of trabecular bone morphology than have been obtained in previous studies. Correlations between the MRI and optical data were significantly lower than those between the MRI and SEM data. Effects of de-calcification were also investigated. The results indicate that comparison of MRI with thin (de-calcified) optical images may be inherently flawed due to the destructive de-calcification and sectioning process used to prepare samples for the optical imaging.

The effect of water molecular self-diffusion on quantitative high-resolution MRI polymer gel dosimetry.

In polymer gel dosimetry, magnetic resonance imaging (MRI) is used to determine the spin-spin relaxation rate (R2) which in turn can be correlated with absorbed dose to provide a map of the spatial distribution of the absorbed dose in the irradiated dosimeter. High accuracy, precision and reproducibility of these dose maps are essential. Moreover, for dose verification around brachytherapy sources used for intravascular brachytherapy, a high spatial resolution is required (typically 0.01-0.1 mm). To achieve these microscopic resolutions, strong imaging gradients are applied. The Brownian motion of water molecules in the presence of these strong magnetic field gradients causes an attenuation of the MR signal. When using a multiple spin-echo sequence, this may result in a significant deviation in the measured R2. The diffusion-related change in R2 at high resolutions was investigated experimentally and correlated with predictions that were obtained numerically and algebraically. Diffusion weighting is determined by the self-diffusion coefficient D, and imaging parameters, quantified by the b-factor. The b-factor was calculated for a multiple spin-echo sequence for different gradient strengths and gradient pulse durations. The variations in R2 that were observed when changing the matrix size and slice thickness are explained. It is shown that a linear correlation between the matrix size and the variation in R2 is based on the diffusion weighting caused by the read-out gradients and slice selective gradients. In conclusion, the essence of taking into account molecular self-diffusion to quantify variations in the measured dose-R2 response when using high-resolution MRI in polymer gel dosimetry is emphasized.

11B magnetic resonance imaging and MAS spectroscopy of trimethylborate-treated radiata pine wood.

Boron-11 nuclear magnetic resonance imaging and spectroscopy have been used to characterise the nature and distribution of boron compounds after preservative treatment of radiata pine wood with trimethylborate (TMB). One day after treatment, 11B magnetic resonance imaging microscopy showed significant differences in the morphological distribution of boron species, with there apparently being no treatment penetration of the latewood. 11B MAS NMR spectroscopy of freshly preservative-treated radiata pine wood, which had been separated into latewood and earlywood, showed the only boron species present in the latewood to be boric acid while in the earlywood both TMB and boric acid were initially present. Due to quadrupolar broadening and a short T2 value, the boric acid signal relaxed too quickly to be observable and this caused the apparent lack of 11B in the image when only boric acid was present. TMB undergoes hydrolysis to form boric acid and in radiata pine latewood, this hydrolysis reaction is rapid.