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Biomedical subjects

D G Thomas

Publications and source records attributed to D G Thomas.

299 records · Page 17Linked to original sources
PubMedDate not supplied

Clinical magnetic susceptibility mapping of the brain.

A field mapping technique was used to detect changes in the local magnetic field in 14 tumors, five hematomas, one lacunar infarct, and two cases of multiple sclerosis. These changes were attributed to variations in the tissue susceptibility. A partial or complete rim of changed susceptibility was detected at the margin of five of the tumors and localized changes were seen within two of the tumors. All five hematomas displayed susceptibility effects. These were seen at the rim of the hematoma in all cases but central effects were also seen in four cases. One area of probable lacunar infarction also displayed susceptibility effects. The effects described may be due to the paramagnetic contribution of species such as deoxyhemoglobin, methemoglobin, free ferric iron, hemosiderin, and other breakdown products of blood. Local field inhomogeneities due to changes in tissue susceptibility have implications for magnetic resonance (MR) image interpretation and the performance of MR spectroscopy.

Brain Diseases↗
PubMedDate not supplied

Clinical use of rapid T2 weighted partial saturation sequences in MR imaging.

Rapid T2 dependent field echo [partial saturation (PS)] sequences were used in 38 patients with brain tumors, intracerebral hematomas, and cerebral infarction as well as other neurological and abdominal disease. Reduction in the radiofrequency excitation angle (alpha) from 90 to 30 degrees produced an increase in lesion contrast as did change of echo time (TE) from 33 to 59 or 120 ms using repetition time (TR) values in the range of 120-500 ms. The PS sequence showing most lesion contrast was compared with conventional spin echo (SE 1,500/80 and SE 1,500/120) and inversion recovery (IR 1,500/500/44 and IR 1,500/100/44) sequences. Although PS sequences with TE = 39 ms were usually inferior to conventional SE sequences, those with TE = 59 or 120 ms were comparable and in some cases (particularly hematomas) superior. The PS sequences with alpha of approximately 30 degrees, TR of 80-250 ms, and TE of 60-120 ms offer considerable savings in time compared with conventional sequences although more work will be required to explore the limits of this approach and to optimize sequences at different field strengths.

Brain Diseases↗
PubMedDate not supplied

Assessment of brain perfusion with MR imaging.

A technique for assessing brain perfusion with magnetic resonance (MR) imaging is described. This technique uses two spin echo sequences that are identical except that the second is sensitised to blood flow by use of a pair of unipolar gradients on either side of the 180 degree pulse. Differences in phase between the two sequences are displayed with a sensitivity to flow rates of +/- 0.5, +/- 1, and +/- 2 mm/s per full scale (+/- pi radians) deflection. The technique was validated for measurement of flow at these rates with a water phantom. Ten patients with cerebrovascular disease, multiple sclerosis, cerebral tumor, periventricular leukomalacia, and meningitis were studied. Differences between grey and white matter were normally seen in adults. Infants displayed differences between central and peripheral regions of the brain. Abnormalities were seen in all clinical cases. The technique will require further validation but it appears to provide a totally noninvasive method for assessing brain perfusion.

Adult↗
PubMedDate not supplied

Analysis of the magnitude of susceptibility effects in disease of the brain: implications for MR spectroscopy.

The results of 165 clinical examinations of the brain in which phase mapping was used to display susceptibility effects have been analysed. Significant changes were frequently observed when hemorrhage was a primary or secondary event. A substantial fraction of the examinations, including those of tumor, trauma, hemorrhage, and other patients, showed changes of up to 1 ppm. Spectral interpretation may be made more difficult in many clinical circumstances by susceptibility effects.

Adult↗
PubMedDate not supplied

Proton MR spectroscopy of intracranial tumours: in vivo and in vitro studies.

Proton magnetic resonance spectroscopy (1H MRS) was used to investigate intracranial tumours in vitro and in vivo. Biopsy specimens were studied from 47 patients, 11 of whom were also examined in vivo. Analysis was based on the signals from N-acetylaspartate (NAA), phosphocreatine plus creatine (Cr), choline-containing compounds (Cho), alanine (Ala), and lactate. Biopsy data from 26 astrocytomas showed that the NAA/Cr ratio differs significantly in all grades from its value in normal white matter and that the Cho/Cr ratio differs significantly in grade IV tumours from its value in the other grades. Meningiomas have an unusually high Ala/Cr ratio. Spectra obtained in vivo are consistent with in vitro results from the same patients, and their lactate signal provides additional information about abnormal metabolism. We conclude that 1H MRS has a clear role in the diagnosis and biochemical assessment of intracranial tumours and in the evaluation and monitoring of therapy.

Adult↗
PubMedDate not supplied

Aspergillosis of the nervous system. Report of two cases.

Two cases of Aspergillus infection of the nervous system are reported. In the first case it occurred in a healthy individual and presented as a space occupying lesion mimicking a tuberculous granuloma. In the second case it was an opportunistic infection in a patient with predisposing conditions and manifested as chronic meningitis with fatal arteritis.

Adult↗
PubMedDate not supplied

Antigenic expression by cells derived from human gliomas does not correlate with morphological classification.

We have found that cell populations derived from human gliomas can be divided into antigenic classes which are not predictable on the basis of standard morphological analysis and which, most frequently, do not support the lineage assignations of various tumours as determined by traditional neuropathological methods. For example, only 6/60 cultures derived from astrocytomas expressed glial fibrillary acidic protein (GFAP), an astrocyte specific marker, and all six of these cultures were derived from morphological categories which more frequently gave rise to populations which did not express GFAP. None of the seven oligodendrogliomas or four oligo-astrocytomas examined expressed antigens specifically expressed by oligodendrocytes. Most tumour-derived populations, from all classes of tumour and all grades of malignancy, expressed cell-surface fibronectin, an extracellular matrix protein only rarely found on the surfaces of CNS macroglia; such cells did not express glial-specific antigens (e.g., GFAP) in vitro. Investigation of antigen expression in tumour biopsies indicated that some tumours also consisted largely or wholly of cells which expressed fibronectin in situ. Fibronectin-expressing cells were aneuploid and were not contact inhibited in their growth, indicating that they were transformed cells. We have also identified two previously unknown antigenic phenotypes among the gliomas.

Antigens, Neoplasm↗
PubMedDate not supplied

Prenatal diagnosis of smith-magenis syndrome (del 17p11.2).

Smith-Magenis syndrome is associated with a microdeletion of the short arm of chromosome 17 with phenotypic abnormalities including dysmorphic facies, self-injurious behavior, mental and neurologic disturbances, and congenital cardiac defects. The majority of patients present in mid-childhood or adulthood. We describe a fetus in which the diagnosis of Smith-Magenis syndrome was made at 16 weeks of gestation following amniocentesis for increased risk for Down syndrome detected by second-trimester maternal serum screening. Ultrasound evaluation revealed multiple fetal anomalies. The pregnancy was terminated at 20 weeks of gestation. Post-mortem findings included dysmorphic facial features, tetralogy of Fallot, a thymic duct remnant, pancreatic islet cell hyperplasia, and abnormal lung fissuring. This represents the second case of prenatally diagnosed Smith-Magenis syndrome. Molecular genetic techniques in the diagnosis of the Smith-Magenis syndrome and other small deletions are becoming an important tool in the genetic evaluation of ultrasound abnormalities.

Abnormalities, Multiple↗
PubMedDate not supplied

Information processing and interhemispheric transfer in left- and right-handed adults.

Two experiments are reported using simple reaction time (SRT) and visual evoked potentials (VEP) to measure information processing and interhemispheric transfer time (IHTT) in left- and right-handed subjects. Study 1 used an SRT procedure to estimate IHTT in 30 left-handed and 30 right-handed subjects. No differences in IHTT were indicated, but left- and right-handers were found to have opposite visual field advantages on the SRT task, indicating possible hemispheric differences in visual information processing. Study 2 was designed to test hypotheses generated in Study 1, using a VEP procedure to provide additional measures of visual information processing and IHTT. VEPs were collected during an SRT procedure in 20 left-handers and 20 right-handers, and SRT response hand and visual field advantages were replicated among right-handers only. Left-handers in Study 2 demonstrated no significant response hand or visual field effects on SRT. Analysis of the VEP N160 latency data indicated no significant laterality, hemisphere, or visual field effects, except for a robust hemisphere by visual field interaction, which reflects IHTT. The significant SRT left visual field advantage in right-handers was not reflected by hemispheric asymmetries in VEP N160 latency. It is concluded that left-handers and right-handers do not differ in IHTT in two functional regions of the corpus callosum, nor do they vary in simple visual receptive processing. Results are more consistent with variability in SRT resulting from differences in complex heteromodal processes beyond the striate and extrastriate visual cortex.

Adult↗
PubMedDate not supplied

Contrast-enhanced MR imaging of malignant brain tumors.

Magnetic resonance (MR) imaging was performed before and serially after intravenous injection of 1 mmol/kg gadolinium-DTPA (Schering) in 17 patients with clinical and histologic diagnosis of malignant cerebral tumors. There was a decrease of 1% in T1 and 10% in T2 in normal white matter and a decrease of 8% in T1 and 14% in T2 in normal gray matter. Contrast enhancement was observed in 16 of the 17 tumors. In the region of maximal enhancement a mean decrease of 16% in T1 was observed in low-grade gliomas, a mean decrease in T1 of 29% was seen in high-malignancy gliomas, and a mean decrease in T1 of 33% was observed in metastases. The decreases in T1 persisted for at least 50 min. In one case the central cystic region of the tumor displayed a decrease in T1 and T2. Measurements of signal intensity displayed maximal contrast enhancement with an IR 1500/500/44 sequence, much less with SE 1500/44, and least with SE 1500/80. Edema was observed on precontrast images in 14 cases, but satisfactory definition of the tumor-edema margin was only possible in four cases. After contrast enhancement this margin was defined in 10 cases. In four of the 17 cases areas of apparent "edema" seen before administration of Gd-DTPA displayed significant contrast enhancement and probably represented tumor infiltration. Comparison with CT showed a greater degree of contrast enhancement on MR images in eight cases, an equal degree in eight cases, and greater enhancement on CT in one case.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Edema↗