Biomedical subjects
Publications and source records attributed to G A Morris.
A relationship between the 1H NMR chemical shifts of the ring F resonances and orientation of the H3-27 group has been derived for the establishment of 25R- and 25S-stereochemistry in spirostane type of steroidal sapogenins.
The signals in NMR spin echoes which are refocused by 90 degrees pulses are spatially modulated. The spatial modulation is not normally observed in images or profiles obtained using Hahn or stimulated echoes, but may cause errors if the sample structure varies on the distance scale of the modulation. Localized spectra measured using stimulated echoes will also show errors under these conditions. Simple Fourier-transform arguments show that conditions which allow the modulation to become visible in an image or profile have the effect of introducing a second echo into the time-domain acquisition window. Phase cycling may be used to remove the spatial dependence of the signals.
The use of on-resonance 121 binomial composite pulses in two- or three-dimensional magnetization-prepared gradient-recalled echo magnetic resonance imaging experiments generates rotary echoes, leading to an increase in contrast range that is, in part, determined by the ratio of T2 to T1. In comparison with other fast gradient-recalled echo imaging techniques designed for enhanced T2 contrast, this method is more robust with respect to radiofrequency field inhomogeneity and less sensitive with respect to motion artifacts. Three-dimensional parametric images may be calculated using least-squares fitting based on a simple model for steady-state longitudinal magnetization during the imaging sequences.
A new method of acquiring two-dimensional (2D) and three-dimensional (3D) fat/water decomposed images on a 0.5 T magnetic resonance (MR) imaging system is described. The method uses a gradient-recalled echo (GRE) sequence incorporating a composite 121 pulse, originally used for magnetization transfer contrast (MTC) experiments, for frequency-selective pre-saturation. By applying the 121 pulse off resonance, a sharp discrimination between the chemically shifted water and fat signals may be obtained using a composite pulse as short as 4 ms. Phantom studies demonstrate that suppression ratios as high as 50:1 are achievable. The new method has been applied to volunteers and patients, and good fat/water images of limb, abdomen, head and neck obtained. The new method can be incorporated into other pulse sequences related to GRE, such as phase contrast (PC) and time-of-flight (TOF), and represents the first practical (i.e. rapid) method for 3D fat/water imaging at an operating field as low as 0.5 T.
Saturating irradiation far off-resonance can lead to diminution in the water signal seen in MRI, giving rise to magnetization transfer contrast. This results from transfer of magnetization between "solid" protons with restricted motion, which give rise to a band some tens of kilohertz wide, and the narrow signal from mobile protons. In the work reported here a high-power pulse spectrometer, which can detect signals from both mobile and immobile protons, was used to investigate the dynamics of magnetization transfer in cartilage in vitro. Magnetization transfer in modified Hoffman-Forsén inversion transfer experiments was well-described by a single rate constant model; full analytical solutions are offered for the resultant biexponential magnetization recovery curves. The use of pulsed methods to generate magnetization contrast may in some circumstances offer advantages over the steady-state saturation methods used hitherto.
Palladium and platinum homologues of the copper-containing tetrapyridinotetraazaporphin cationic dye Cuprolinic blue were prepared. The affinities of all three dyes for a series of polyanions, with and without nucleotide bases, were assessed using the CEC (critical electrolyte concentration) approach, and expressed as molarities of MgCl2. Whereas Cuprolinic blue bound to RNA with much greater avidity than to DNA, the Pt and Pd analogues showed very high affinity for both. Patterns of affinities for non-nucleotide polyanions showed no differences. 1H and 13C NMR spectra showed that, although the Cu compound was planar, the Pt and Pd homologues must be non-planar. Taken together with previous findings, on e.g. methyl green and pyronin, these results suggest that DNA finds it easier to accommodate pairs of out-of-plane aromatic rings than RNA in stable complexes. CEC analyses can, as demonstrated here, uncover quite subtle differences between molecular recognition patterns of very closely related reagents.
Explore the source record for details and available documents.
A trial application of a recent two-dimensional nuclear magnetic resonance experiment to the polypeptide antibiotic siomycin A is described. Proton--carbon-13 chemical shift correlation measures the proton and carbon-13 chemical shift for each directly bonded CH group in a molecule, in a single experiment. The resultant map of correlated chemical shifts enables the carbon-13 spectrum to be assigned directly from the known proton shifts, and allows individual proton signals to be identified without problems of overlap. The signal-to-noise ratio available from such techniques should enable their application to aqueous protein solutions using currently available high-field spectrometers.
The potential of 31P-NMR saturation transfer experiments for determining motional characteristics (in the millisecond to second time scale) of phospholipids in model and biological membranes is demonstrated. A technique to separate membrane phospholipid 31P-NMR signals from those of small water-soluble phosphates in intact cells in liver tissue is also illustrated.
Explore the source record for details and available documents.
Arthrography revealed an abnormal tract of contrast agent dissecting from the suprapatellar bursa into the soft tissue anterior to the patella and downward to a level 9 cm beneath the tibial plateau in a patient with complete rupture of the quadriceps tendon. The bursal anatomy of the anterior portion of the knee is reviewed in relation to the capsule-forming structures of the quadriceps expansion. The use of knee arthrography for the assessment of quadriceps tendon injury is advocated.
Explore the source record for details and available documents.
The distribution of CD1a antigen in gingival epithelium of clinically healthy gingiva was examined and compared with the distribution in gingival epithelium of adult periodontitis lesions. Cryostat sections were examined with monoclonal antibodies to CD1a antigen using the ABC immunoperoxidase technique. In healthy gingiva, CD1a was limited to Langerhans cells (LC) which were observed throughout the length of the external epithelium and orosulcular epithelium. The numbers of LC expressed either per unit length of orosulcular epithelium or per mm2 were similar to the numbers in external gingiva. Junctional epithelium contained few if any dendritic LC. The numbers of LC in pocket epithelium of adult periodontitis lesions were significantly lower compared with orosulcular epithelium of healthy tissue and compared with external gingiva of diseased tissue (p less than 0.005). In many sections, no LC were identified in pocket epithelium. In 5 of 8 adult periodontitis sites, CD1a was also observed in association with the membranes of suprabasal keratinocytes in external and pocket epithelium in areas where no LC were identified. These findings provide further evidence that changes in gingival epithelial cells occur in periodontal disease which are analogous to those documented in dermatological diseases and suggest that epithelium may play a role in gingival homeostasis and in the pathogenesis of periodontal diseases.