PubMed Health⌕ Search

Biomedical subjects

D J Bryant

Publications and source records attributed to D J Bryant.

At least 19 recordsLinked to original sources
PubMed1995

Effect of orientation in haptic reproduction of line length.

We investigated the accuracy of haptic reproduction of line length and whether accuracy is influenced by line orientation. 13 blindfolded subjects felt along different line lengths at various orientations in the horizontal plane, then reproduced the line lengths in the same orientation as that felt. Efforts were made to equate learning and reproductive scanning movements. Reproductions of line lengths were a nonveridical power function of their true lengths, but the power function exponents did not differ across spatial orientations. It was concluded that people can encode line lengths across spatial orientations by a common power function if care is taken to equate proprioceptive information across learning and reproduction.

Adult↗
PubMed1992

Phosphorus-31 magnetic resonance spectroscopy of the human liver using chemical shift imaging techniques.

Phosphorus-31 magnetic resonance spectroscopy of the human liver was undertaken in 28 healthy adult individuals and in 49 patients with liver disease of varying aetiology. Data localised to the liver were obtained using chemical shift imaging techniques. The mean (+/- 1 S.D.) of the peak area ratio phosphomonoesters (PME)/phosphodiesters (PDE) in healthy adult individuals, from spectra obtained with pulse angle 45 degrees and repetition time 1 s, was 0.24 +/- 0.07. The intra-examination variability of this ratio was 20%, the intra-subject variability 27% and the inter-subject variability 32%. An increase in the PME/PDE was observed in the 31P hepatic MR spectrum from primary or secondary tumours in all 17 patients studied, which invariably represented an increase in PME/ATP and, in some cases, a reduction in PDE/ATP. The spectra did not show aetiological characteristics. A non-specific elevation in PME/PDE was also observed in the 31P hepatic MR spectra of 10 (40%) of 25 patients studied who had diffuse liver diseases, such as cirrhosis and infiltrating malignancies. The spectral pattern did not distinguish between diseases of varying aetiologies, but there was a linear correlation between increasing PME/PDE and a reduction in plasma albumin concentrations (p = 0.03). In three patients with hepatic malignancy and abnormal hepatic 31P-MRS, marked spectral changes were observed after successful treatment to debulk the tumour. Only minor changes were observed in the abnormal spectrum of a fourth patient in whom treatment was unsuccessful. Hepatic 31P-MR spectroscopy may prove useful for monitoring disease processes and treatment effects in well characterised patient populations.

Adenocarcinoma↗
PubMed1992

Fat suppression in magnetic resonance imaging at low field strength using binomial pulse sequences.

The use of binomial pulse sequences for fat suppression in MRI at low field strength (0.15 T) was investigated. Both spin-echo and inversion-recovery sequences were used and images obtained of the limbs, head and neck, and pelvis of volunteers and patients. Good fat suppression was seen particularly in small fields of view. Despite technical problems, chemical shift selective techniques can be applied at low field strength.

Adipose Tissue↗
PubMed1991

Exceptions to recognition failure as a function of the encoded association between cue and target.

The relation of the recognition failure of recallable words to overall recognition rates is largely invariant across conditions that influence both recall and recognition separately. In two experiments, the influence of the integration of the members of A-B word pairs on this relation was investigated. In Experiment 1, it was found that deviations of observed recognition failure from predictions of the Tulving-Wiseman function (Tulving & Wiseman, 1975) were produced by shallow, nonsemantic encoding. In Experiment 2, the association of category-to-instance pairs was varied. It was found that weak associates caused larger deviations of observed recognition failure from predicted recognition failure than did strong associates. Such results suggest that a strongly encoded association between cue and target elements of A-B pairs is a necessary condition for the adherence of data to the Tulving-Wiseman function. The implications of these findings for general models of memory are discussed.

Cognition↗
PubMed1990

31P magnetic resonance spectroscopy of the human paediatric liver.

Localized 31P NMR spectroscopy was used to study the developing human liver in three neonates and one infant, all with neonatal intracranial problems, but normal liver function. A prominent resonance was present in the phosphomonoester (PME) region of the spectrum of the neonates; the PME/ATP ratio was 1.0 +/- 0.4 (repetition time 1 s), compared to the mean adult liver value of 0.2 +/- 0.1. The saturation factor of PME in the neonates was large, indicating that the increase in PME/ATP reflected an increase in relative PME concentration. The chemical shift of the PME peak in the neonatal liver (6.8 +/- 0.1) was similar to that found in neonatal brain, suggesting that phosphorylethanolamine may be a major constituent. The phosphodiester (PDE)/ATP ratio in these patients (0.4 +/- 0.1) was decreased compared with the mean adult value (1.3 +/- 0.2), and the saturation factor of PDE was small. The results from the infant were different from both the neonates and adults; PME/ATP was decreased compared to the neonates, but increased compared to adults. The saturation factor of PDE was increased compared to neonates. The biochemical implications of the observed changes in PME and PDE in paediatric liver are discussed in relation to membrane turnover.

Brain Diseases↗
PubMed1990

Implicit associative responses influence encoding in memory.

In list-learning experiments, the orienting question asked of one item may influence the processing of, and memory for, later items in the list. Four experiments demonstrated that words that are not related to their own orienting question, but that are semantically related to the question asked of a previous item, are better recalled than are words that are not related to any question in the list. Factors that influence this memory enhancement include the number of times relevant orienting questions appear during study, as well as the retention interval. Experiment 4 revealed that this effect is contingent upon conscious awareness: Item-category relations do not enhance recall if the subject is not aware of them. The results of the four experiments imply that semantic categories can be primed as implicit associative responses to words, which influence memory.

Adult↗
PubMed1989

Use of ultralong echo time imaging to assist in measuring the velocity of perfused flow in vivo.

The measurement of the velocity of perfused flow in tissue in vivo is complicated by the presence of stationary as well as moving spins and by a variety of dephasing phenomena which affect signal amplitudes. This paper describes a technique by which, using flow-sensitized spin-echo sequences with a set of very long TE times, the velocity of the moving component can be assessed.

Blood Circulation↗
PubMed1989

Problems with achieving saturation using methods based on bursts of rf pulses with spoilers in magnetic resonance imaging.

Attempts at saturation by nonselective rf pulses, followed by gradient spoiler pulses, are sometimes used as the basis of a method of measuring T1 in magnetic resonance imaging, because a method of this type is perceived as being less affected by slice shape artifact than partial saturation methods. This note suggests that, unless care is taken, this assumption can be quite erroneous.

Evaluation Studies as Topic↗
PubMed1989

31P magnetic resonance spectroscopy of the normal human brain: approaches using four dimensional chemical shift imaging and phase mapping techniques.

The use of four-dimensional chemical shift imaging to monitor phosphorus metabolites within the human brain is illustrated. Saturation effects are described, and acquisition conditions are discussed in relation to quantification and sensitivity. The effects of magnetic field variations on spectral parameters are assessed and the use of a field mapping technique is illustrated.

Adult↗
PubMed1988

Four-dimensional phosphorus-31 chemical shift imaging of carcinoid metastases in the liver.

Four-dimensional chemical shift imaging was used to map spatial variations in phosphorus metabolites in a patient with carcinoid metastases in the liver. The results were compared to those from an age and sex matched volunteer, with no known previous history of liver disease. In the patient local abnormalities were observed. These included elevated phosphomonoester and decreased phosphodiester concentrations relative to adenosine triphosphate. The regions of abnormality corresponded to regions containing metastases identified with x-ray computed tomography and magnetic resonance imaging.

Adult↗
PubMed1987

Spectral resolution in clinical magnetic resonance spectroscopy.

We observe linewidths of 0.1-0.4 ppm in 31P spectra of human muscle, liver, and brain. T2 measurements of muscle phosphocreatine, together with previous brain studies, indicate that further improvements in linewidth to 0.02-0.05 ppm might often be achieved, but in some lesions magnetic susceptibility variations may limit spectral resolution.

Brain↗
PubMed1985

Variations in slice shape and absorption as artifacts in the determination of tissue parameters in NMR imaging.

Existing models for the contrast between one tissue and another in NMR imaging have shown that there are regions of ambiguity particularly in spin-echo sequences. This paper indicates that there are further problems due to variations in slice formation with tissue parameters, and that it is necessary to be very conservative in assessing the magnitude of T1 in any imaging system. The change in shape affects the appearance of images due, in essence, to adjustments in partial volume effects, with some of the contributions to the signal from lesions with long T1 coming from different regions to those for normal tissue. A simple model for a slice is used because the actual form in a real imaging situation is the result of a number of factors which are usually not accurately enough known.

Brain Diseases↗
PubMed1984

Measurement of flow with NMR imaging using a gradient pulse and phase difference technique.

A method for determining flow by nuclear magnetic resonance (NMR) imaging is described. A conventional spin-echo imaging sequence is employed with the addition of balanced gradient pulses on either side of the pi radiofrequency pulse. Flow velocities in the direction orthogonal to the image plane are determined by the phase shifts in the NMR image. Experimental validation of the technique in vitro was achieved with a phantom designed to give a continuous flow of water. The flow rate measured by NMR agreed well with the volume flow rate through the phantom. In vivo, NMR flow measurements on the carotid and femoral arteries of two volunteers were compared with Doppler ultrasound results. Velocity measurements were in general agreement. Rapid changes in flow are difficult to follow with the NMR method unless particular care is taken in gradient profile design. The technique can readily be used in existing NMR imaging machines and may have a useful clinical role.

Blood Flow Velocity↗
PubMed1984

Magnetic resonance imaging of the kidneys.

A study of the magnetic resonance imaging (MRI) appearances of the kidneys in six normal volunteers and 52 patients is reported. Corticomedullary differentiation was seen with the inversion-recovery (IR 1400/400) sequence in the normal volunteers and in patients with functioning transplanted kidneys and acute tubular necrosis. Partial or total loss of corticomedullary differentiation was seen in glomerulonephritis, acute and chronic renal failure, renal artery stenosis, and transplant rejection. The T1 of the kidneys was increased in glomerulonephritis with nephrotic syndrome, but the T1 was within the normal range for renal medulla in glomerulonephritis without nephrotic syndrome, renal artery stenosis, and chronic renal failure. A large staghorn calculus was demonstrated with MRI, but small calculi were not seen. Fluid within the hydronephrosis, simple renal cysts, and polycystic kidneys displayed very low signal intensity and long T1 values. Evidence of recent hemorrhage into cysts was seen in polycystic kidneys. Tumors displayed varied appearances. Hypernephromas were shown to be hypo- or hyperintense with the renal medulla on the IR 1400/400 sequence. After intravenous injection of gadolinium-DTPA, there was marked decrease in the tumor T1.

Adolescent↗
PubMedDate not supplied

The benefits of increasing spatial resolution as a means of reducing artifacts due to field inhomogeneities.

All users of NMR equipment are familiar with the desirability of achieving as high a quality of field as possible. On the other hand, it is easy to forget that the field quality of relevance in both imaging and spectroscopy is that over individual voxels, and not the whole volume. This note demonstrates in practice how performance in poor fields is improved substantially by reducing voxel size (or increasing spatial resolution), offering a potential alternative to additional shimming under appropriate circumstances. It argues that the best criterion for assessing magnet quality in spatially localized systems is the maximum field error gradient in the volume of usable field, rather than the maximum deviation in the field.

Humans↗