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Biomedical subjects

L Gray

Publications and source records attributed to L Gray.

At least 199 records · Page 11Linked to original sources
PubMed1975

Mantle field dosimetry comparing 4 MV with cobalt 60.

Three off-axis dosimetric parameters were evaluted for identical mantle fields using the Varian 4 MV linear accelerator and a Picker C8M cobalt-60 unit. These parameters were dose distribution, skin dose and integral dose. Comparisons showed higher doses in all three categories with the 4 MV accelerator when the tumor dose is specified at the central axis midline. These results emphasize the importance of off-axis dosimetry with both machines.

Cobalt Radioisotopes↗
PubMedDate not supplied

Acute spinal ligament disruption: MR imaging with anatomic correlation.

Disruption of spinal ligaments can lead to instability that jeopardizes the spinal cord and nerve roots. Magnetic resonance (MR) imaging can directly image spinal ligaments; however, the sensitivity with which this modality demonstrates ligament injury has, to the authors' knowledge, not been reported. On a biomechanical testing machine, 28 cadaveric spines were subjected to controlled injury that resulted in ligament tears. The spines were then imaged with plain radiography, computed tomography, and MR imaging (1.5 T). The images were analyzed for evidence of ligament injury before dissection of the specimen. Forty-one of 52 (79%) ligament tears of various types were correctly identified at MR imaging. Disruptions of the anterior and posterior longitudinal ligaments were most conspicuous and were detected in all seven cases in which they were present (no false-positive or false-negative results); disruptions of the ligamentum flavum, capsular ligaments, and interspinous ligaments could also be identified but less reliably (three false-positive and 11 false-negative results). That MR imaging can reliably and directly allow assessment of spinal ligament disruption in this in vitro model suggests its potential utility for this assessment in patients.

Acute Disease↗
PubMedDate not supplied

Value of assessment of pretest probability of deep-vein thrombosis in clinical management.

BACKGROUND: When ultrasonography is used to investigate deep-vein thrombosis, serial testing is recommended for those who test negative initially. Serial testing is inconvenient for patients and costly. We aimed to assess whether the calculation of pretest probability of deep-vein thrombosis, with a simple clinical model, could be used to improve the management of patients who present with suspected deep-vein thrombosis. METHODS: Consecutive outpatients with suspected deep-vein thrombosis had their pretest probability calculated with a clinical model. They then underwent compression ultrasound imaging of proximal veins of the legs. Patients at low pretest probability underwent a single ultrasound test. A negative ultrasound excluded the diagnosis of deep-vein thrombosis whereas a positive ultrasound was confirmed by venography. Patients at moderate pretest probability with a positive ultrasound were treated for deep-vein thrombosis whereas patients with an initial negative ultrasound underwent a single follow-up ultrasound 1 week later. Patients at high pretest probability with a positive ultrasound were treated whereas those with negative ultrasound underwent venography. All patients were followed up for 3 months for thromboembolic complications. FINDINGS: 95 (16.0%) of all 593 patients had deep-vein thrombosis; 3%, 17%, and 75% of the patients with low, moderate, and high pretest probability, respectively, had deep-vein thrombosis. Ten of 329 patients with low pretest probability had the diagnosis confirmed, nine at initial testing and one at follow-up. 32 of 193 patients with moderate pretest probability had deep-vein thrombosis, three diagnosed by the serial (1 week) test, and two during follow-up. 53 of 71 patients with high pretest probability had deep-vein thrombosis (49 by the initial ultrasound and four by venography). Only three (0.6%) of all 501 (95% CI 0.1-1.8) patients diagnosed as not having deep-vein thrombosis had events during the 3-month follow-up. Overall only 33 (5.6%) of 593 patients required venography and serial testing was limited to 166 (28%) of 593 patients. INTERPRETATION: Management of patients with suspected deep-vein thrombosis based on clinical probability and ultrasound of the proximal deep veins is safe and feasible. Our strategy reduced the need for serial ultrasound testing and reduced the rate of false-negative or false-positive ultrasound studies.

Algorithms↗
PubMedDate not supplied

Preoperative transarterial embolization of spinal column neoplasms.

PURPOSE: To determine the safety and value of vertebral column embolization before surgical resection of vascular neoplastic disease. PATIENTS AND METHODS: Thirty preoperative embolization procedures were performed in 20 patients with vascular neoplasms of the vertebral column (C-2 to sacrum). Fourteen patients had metastatic renal cell carcinoma. Distal embolic agents were used in 27 cases and were coupled with more proximal agents in six. Gelatin pledgets alone were used in three cases. Twenty-six of the 27 surgical procedures involved partial to complete tumor resection. RESULTS: Seventy-two arteries were embolized (one to six per procedure). All surgical procedures were successful, and none were terminated because of blood loss. Massive blood loss occurred in one patient with paraganglioma, but embolization allowed complete vertebral resection at two levels. When this patient was excluded, blood loss ranged from 300 to 5,000 mL (mean, 1,871 mL). Transfusions required in 22 surgical procedures ranged from 1 to 10 units of packed red blood cells. Symptoms became worse after embolization in one case but improved with surgical decompression. CONCLUSION: Embolization before surgery for spinal column neoplasms appears to safely and effectively limit blood loss.

Adolescent↗
PubMedDate not supplied

A family of related ATP-binding subunits coupled to many distinct biological processes in bacteria.

Many biological processes are coupled to ATP hydrolysis. We describe here a class of closely related ATP-binding proteins, from several bacterial species, which are associated with a variety of cellular functions including membrane transport, cell division, nodulation in Rhizobium and haemolysin export. These proteins comprise a family of structurally and functionally related subunits which share a common evolutionary origin, bind ATP and probably serve to couple ATP hydrolysis to each of these biological processes. This finding suggests a specific role for ATP in cell division, nodulation during nitrogen fixation and protein export, and allows us to assign a probable function to one of the protein components from each of these systems.

Adenosine Triphosphate↗
PubMedDate not supplied

MR imaging of thoracic extradural arachnoid cysts.

Two extradural arachnoid cysts of the thoracic spine were studied with magnetic resonance imaging, myelography, and CT. Magnetic resonance imaging correctly characterized the extradural location of the cysts as well as the cyst contents as CSF, thus establishing the diagnosis. Magnetic resonance is helpful in the assessment of the extent of cord atrophy and myelomalacia and may be of predictive value in the postoperative prognosis.

Arachnoid↗
PubMedDate not supplied

Dose distributions around cylindrical 241Am sources for a clinical intracavitary applicator.

Encapsulated, cylindrical sources containing 2, 5, and 8 Ci of 241Am have been designed and fabricated for intracavitary irradiation of uterine cancers. Exposure rates in air and dose rates in water around these sources have been measured using an ionization chamber and a lithium fluoride thermoluminescent dosimetry system. Dose rates in water at a distance of 2.5 cm from the source center along a direction transverse to the source axis were found to be 10.4, 24.3, and 23.3 cGy/h for the 2-, 5-, and 8-Ci sources, respectively, using an ionization chamber. Under the same conditions, the thermoluminescent dosimetry system yielded the values of 10.3, 23.1, and 22.3 cGy/h. It was observed that the ratio of dose-to-water and exposure in air is sensitive to the scattering geometry and source geometry in the case of 241Am photons. This ratio was found to increase substantially as conditions of full scattering were approached. A three-dimensional integration model was employed for the determination of dose distributions around these sources. Results of this dose computation model have been compared against the measured data and were found to be in good agreement with each other. Average deviations of calculated data from measured data were in the range of 0.2 to 0.5 cGy/h and larger deviations were observed in the paraxial region, where the effects of oblique filtration are more severe.(ABSTRACT TRUNCATED AT 250 WORDS)

Americium↗
PubMedDate not supplied

Statistical correlations among supraglottic cancers.

The purpose of this study was to quantify the extent to which the presence or absence of cancer in endoscopically evaluable regions of the supraglottic larynx predicted occurrence in a region less easy to visualize but of critical importance to the nature of treatment. Histologic findings from 32 specimens were subjected to two separate statistical analyses. In the first analysis, the presence of cancer on the floor of the ventricle was the best predictor of tumor below this level. The combination of variables with the best correlation was cancer on the floor of the ventricle and in the vestibular folds. In the second analysis, involvements of the deep structures in the aryepiglottic folds and in the infrahyoid epiglottis were the only significant predictors of tumor extending to the preepiglottic space. The results suggest that such statistical analyses may provide guidelines for selection of treatment.

Glottis↗
PubMedDate not supplied

Meningioma of the fourth ventricle.

Meningiomas are primary meningeal based tumors of the central nervous system that rarely are located strictly within the fourth ventricle. We report a 72-year-old man operated upon for such a tumor. The pre-operative magnetic resonance images revealed a well circumscribed mass in the fourth ventricle that exhibited a low signal on T1-weighted magnetic resonance images and homogenously enhanced with gadolinium. By light microscopy the tumor was composed of tightly packed spindle cells separated by collagen. Immunohistochemistry showed the tumor cells to be positive for vimentin and epithelial membrane antigen, and negative for glial fibrillary acidic protein. Electron microscopy revealed typical findings of meningioma, including interdigitating cell processes, desmosomes, and intermediate filaments. Although rare, fibroblastic meningioma must be included in the differential diagnosis of a fourth ventricular spindle cell tumor in elderly patients.

Aged↗