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R H Britt

Publications and source records attributed to R H Britt.

At least 19 recordsLinked to original sources
PubMed1987

Correlation of neuropathologic findings, computerized tomographic and high-resolution ultrasound scans of canine avian sarcoma virus-induced brain tumors.

The location, size, geometry and neuropathological findings of anaplastic astrocytomas (AA), gliosarcomas and sarcomas induced by the avian sarcoma virus (ASV) in dogs were compared with images generated using computerized tomography (CT) and real time high-resolution ultrasound (HRUS). Seven AA showed a wide range of findings on CT. Pre-contrast CT scans showed that the tumors could be hyper, hypo, or isodense. Three of seven AA had no contrast enhancement; two of these tumors were also isodense which resulted in a false-negative CT exam. Partial enhancement was seen in one tumor. This resulted in a sensitivity of detection of 72%. Real time HRUS was able to define tumor location, size and geometry of the AA missed or incompletely imaged by CT. All tumors were hyperechoic. Inhomogeneity of the echo pattern was due to hemorrhage, cyst formation, and necrosis within the tumors. Such secondary tumor characteristics were more accurately defined by HRUS compared to CT. Vasogenic edema in the brain surrounding tumors was of low density on CT and hypoechoic or indistinguishable from normal brain on US. Similar findings were seen in six gliosarcomas, two of which were not visualized by either pre- or post-contrast enhanced CT scans (sensitivity of 66%). Sarcomas differed in that they were either hyper or isodense; none were hypodense. The area of increased density matched the tumor geometry and correlated with dense cellularity and reticulin deposition. All 13 sarcomas showed contrast enhancement (100% sensitivity), but in two tumors, contrast enhanced CT underestimated the size of the tumor. Because of the large size and multiplicity of the sarcomas, HRUS imaging was not able to resolve the entire tumor volume because of limited imaging access. Intravenously injected horseradish peroxidase (HRP) crossed the tumor blood-brain barrier (BBB) only in those tumors in which contrast enhancement was seen. These studies suggest that intraoperative HRUS imaging may be useful in detecting and delineating human AA incompletely visualized by CT.

Animals↗
PubMed1986

Use of a flexible epidural stimulating electrode for intraoperative monitoring of spinal somatosensory evoked potentials.

The use of an epidural stimulating spinal electrode has been adapted for recording spinal somatosensory evoked potentials (SSEP) during spinal surgery. This technique utilizes a flexible, 1 mm diameter electrode with four platinum contacts that is easily slipped into the epidural space both rostral and caudal to the exposed surgical field. The flexibility of the electrode assembly ensures against dural penetration. Incoming somatosensory spinal evoked potentials recorded using the lumbosacral electrode are compared with the SSEP recorded above the surgical site (rostral electrode). The spinal SEPs were generally triphasic (thoracic) or polyphasic (lumbosacral) with an amplitude of 5 microV. This system has been used for intraoperative monitoring during 33 major spinal operations. Waveform morphology, as well as the latencies and amplitudes of the component peaks of the spinal SEPs remained relatively constant compared with the cortical SEPs.

Electric Stimulation↗
PubMed1986

Spinal and cortical somatosensory evoked potential monitoring during corrective spinal surgery with 108 patients.

To reduce the incidence of neurologic complications following spinal surgery, somatosensory evoked potentials (SEPs) were monitored in 108 patients. An electrode with four in-line contacts was used to record spinal SEPs in the epidural space in 33 patients at locations both rostral and caudal to the surgical site. Cortical SEPs were successfully monitored in 107/108 patients and spinal SEPs in all 33 attempted epidurally. Spinal conduction velocities were found to range from 43.9 to 110.5 m/s depending on vertebral level and the time location of the measured peak in the response waveform. Frequency power spectra of the SEP waveforms were found to be a reliable adjunct to peak latency amplitude analysis in the time domain. Use of caudal and rostral epidural, subcortical, and cortical electrode sites were found to be the most reliable technique for the maximum patient safety.

Adolescent↗
PubMed1986

Experimental brain abscess development in the chronically immunosuppressed host. Computerized tomographic and neuropathological correlations.

The neuropathological progression of brain abscess formation was studied experimentally in paired immunosuppressed and control dogs. The immunosuppressed animals received azathioprine and prednisone beginning 7 days prior to intracerebral inoculation with alpha streptococcus. Histological findings were correlated with computerized tomography (CT) brain scans. The evolution of brain abscess in the immunosuppressed animals could be divided into three stages based on histological evaluation: cerebritis stage (1 to 11 days), early-capsule stage (12 to 17 days), and late-capsule stage (18 days and later). There was a significant delay in the evolution of alpha streptococcus brain abscess compared to the authors' previous studies. Histologically, abscesses in immunosuppressed dogs were characterized by a decrease and delay in collagen formation, a reduction in polymorphonuclear leukocytes and macrophages, longer persistence of bacterial organisms, and an increase in gliosis. During the cerebritis stage, abscesses in control animals were consistently larger and more edematous than those in immunosuppressed animals and reached their maximum size by Day 8, whereas abscesses in immunocompromised animals reached their maximum size around Day 12. In the late-capsule stage, abscesses in immunosuppressed animals remained larger than those of control animals and continued to show signs of delayed development. This was evidenced by diffusion of contrast medium into the lucent center of ring-enhancing lesions on delayed CT scans. The results suggest that the decreased inflammatory response and edema formation in the immunosuppressed host resulted in less initial mass effect from brain abscess, but that the eventual size and area of the abscess may have become larger due to the less effective host response.

Animals↗
PubMed1986

Chronic histological effects of ultrasonic hyperthermia on normal feline brain tissue.

The histopathological changes associated with ultrasonic heating of normal cat brain have been correlated with thermal distributions. Ultrasound energy was applied for 50 min at different intensities to generate tissue temperatures from 42 to 48 degrees C. Animals were sacrificed at various intervals from 1 to 56 days. The organization and resolution of thermal damage was characterized by three stages of histopathological changes within the nervous tissue. The acute stage (Days 1-3) was defined by (1) extensive coagulation necrosis, (2) pyknosis of neuronal elements in the gray matter, (3) edema and vacuolation in the white matter, and (4) polymorphonuclear leukocytes. The subacute stage (Days 3-21) was characterized by (1) the appearance of lipid-laden macrophages, (2) liquefaction of the necrotic regions, (3) fibroblastic proliferation, and (4) vascular proliferation with some perivascular inflammatory infiltration (lymphocytes). Lastly, the chronic stage (Days 21-56) was defined by (1) fibrosis (reticulin and collagen formation) and (2) gliosis (reactive astrocytic proliferation) occurring around the fluid-filled necrotic center. Analysis of these data has also included a study of the lesion size versus the dose (temperature for 50 min) of heating. The results demonstrate a significant linear dose-response correlation. The results of this study indicate that the histological appearance and time course of repair of thermal injury in the normal brain tissue are analogous to acute brain necrosis resulting from cerebral infarction, except the thermal damage does not result in significant hemorrhage.

Animals↗
PubMed1985

Immunohistochemical study of glial fibrillary acidic protein in avian sarcoma virus-induced gliomas in dogs.

Anaplastic astrocytomas, gliosarcomas and sarcomas were induced in 33 neonatal dogs by intracerebral injection of purified Schmidt-Ruppin strain of avian sarcoma virus (ASV). A total of 11 anaplastic gliomas, 7 gliosarcomas and 18 sarcomas were induced. Ten of the 11 anaplastic astrocytomas and all 7 gliosarcomas were positive for GFAP using the peroxidase-antiperoxidase method on formalin-fixed, paraffin embedded tissue. None of the sarcomas were positive for GFAP. One anaplastic astrocytoma was analyzed by gel electrophoresis and immunoblot and the amount of GFAP in the tumor was compared with comparable samples from normal white and gray matter. Densitometric analysis of the GFAP stained gels showed that 12-13% of tumor protein was GFAP compared with 2-3% for the non-neoplastic white and gray matter. The results of this study add further evidence to the astrocytic origin of many of the induced anaplastic primary brain tumors by ASV.

Animals↗
PubMed1985

Digital heart rate monitor derived from the arterial pressure pulse.

This monitor displays heart rate without the need for electrical contact with the experimental animal. The device uses a quartz pressure transducer connected to an arterial catheter and has a full scale accuracy of +/- 3 beats min-1; its range is 0-400 beats min-1. There is an output voltage proportional to heart rate and internal calibration facilities are provided at 60 and 360 beats min-1.

Animals↗
PubMed1985

Temperature measurements in high thermal gradients: I. The effects of conduction.

Two temperature probes (a fluoroptic sensor and a metallic thermistor), which are both suitable for stereotaxic implantation, were used in comparative thermometry studies during interstitial microwave heating of the brain in vivo. Thermal distributions having large temperature gradients (5-10 degrees C/cm) were routinely observed. The temperature differentials (delta T) between the 2 probes were position dependent within the thermal field. The maximum difference in temperatures measured, using the 2 probes along identical tracks without a catheter, ranged between 0.5 degree C and 1.8 degree C. Near the brain/air surface, the thermistor measured lower temperatures than the optical probe; however, medial to the antenna, the thermistor temperatures were higher than the optic sensor. The measured temperature discrepancies are the result of smearing due to thermal conduction along the axial length of the metallic thermistor probe. These effects are significantly accentuated when the temperature probes are tracked in catheters. Experiments performed in a nonperfused phantom, heated with the interstitial microwave antenna, demonstrated similar conductive effects. Studies in a nonelectromagnetic environment (flow cell-thermal step gradient) additionally confirmed that thermal conductive artifacts were the major source of temperature error.

Animals↗
PubMed1985

Temperature measurements in high thermal gradients: II. Analysis of conduction effects.

Measurement errors associated with thermal conduction along a temperature probe in regions of high thermal gradients are examined. An analysis of a conducting probe inserted into an insulating catheter for the purpose of temperature mapping gives a means for estimating the effects of thermal smearing on the measured distribution. A comparison is made between the theory and an experimental test case (flow cell-thermal step gradient). Also, an iterative algorithm is developed to correct thermally smeared temperature distributions in order to reconstruct the desired unsmeared distributions. The algorithm is checked for self consistency in the flow cell experiment and is applied to in vivo data obtained during interstitial microwave heating in normal dog brain. Data from flow cell measurements are used to make relative comparisons of the probe conduction artifact for several different temperature probes (2 thermocouple needle probes, a thermistor needle probe and an optical probe) and assorted teflon catheters (16, 18 and 20 ga).

Animals↗
PubMed1985

Brain abscess.

Explore the source record for details and available documents.

Adrenal Cortex Hormones↗
PubMed1985

Tumors of the central nervous system studied by computed tomography and ultrasound.

Intraoperative ultrasound (US) was compared to computed tomography (CT) in 41 intracranial and 6 spinal cord tumors. The studies correlated closely except for primary gliomas. Eight of the 22 primary intracranial gliomas (37%), including 1 low-grade and 7 anaplastic tumors, were larger and more extensive on US than on CT. Margins of non-enhanced primary astrocytomas were shown by US but not CT. Four anaplastic tumors (19%) exhibited echogenicity extending beyond the enhanced area. In 4 patients an enhanced lesion contained a lucent center which proved to be echogenic. Low-grade astrocytomas were relatively homogeneous on US, while anaplastic astrocytomas were more inhomogeneous. Cysts could be found in both types of astrocytomas and were often small and multiple. The echo pattern was not helpful in differentiating metastases from primary tumors, although all of them had sharp margins. Sonography of the central nervous system can provide valuable information about tumor morphology and margins.

Astrocytoma↗
PubMed1984

Dynamic computed tomographic scans in experimental brain abscess.

Dynamic computed tomographic scans were performed in an experimental brain abscess model to establish criteria that could be utilized in abscess staging. The vascular phase of the time-density curves did not differentiate cerebritis and capsule stages. The amount of residual enhancement after the first pass of an intra-arterial contrast bolus differed between major abscess stages, the greater residual enhancement being noted in the capsule stage.

Animals↗
PubMed1984

Effects of hypothermia on the cat brain-stem auditory evoked response.

Effects of systemic hypothermia on the brain-stem auditory evoked responses (BAERs) in 4 pentobarbital anesthetized adult cats placed on total cardiopulmonary bypass were investigated. Hypothermia was achieved by slowly cooling the bypass blood through a heat exchanger. Serial BAERs were recorded at 2 min intervals as brain temperature was lowered from 37 to 22 degrees C and then rewarmed over a 1-2 h period. Temperatures were recorded from the brain, esophagus and rectum. Three effects were produced by controlled systemic hypothermia. First, latencies of each component wave (I-V) of the BAER increased exponentially as brain temperature was lowered to 19 degrees C. Latencies of earlier waves (I-III) increased less than those of the later waves (IV-V). Arrhenius plots of inverse latency (rate) versus reciprocal of the absolute temperature generated a family of straight lines of similar slope for each of the 5 component waves of the BAER. The activation energy for each of the 5 BAER waves was derived from the slope of the Arrhenius plot. The mean and standard deviation of the activation energy of all 5 waves was 9.7 +/- 0.5 kcal/mole degree C. The fact that the activation energy was similar for each BAER component wave (I-V) indicated that the increase in latencies for all 5 waves was governed by the same rate-limiting, temperature-dependent process(es). Second, the rise time and duration of each of the component waves of the BAER increased with decreasing temperature. Third, wave amplitudes increased from 37 to 32 degrees C in a quasiparabolic relation and then, decreased at approximately a linear rate. The BAER wave form completely disappeared below 20.3 degrees C. Slow rewarming of the brain to its initial temperature restored the BAER component waves to their original latencies and amplitudes.

Animals↗
PubMed1984

Computer-controlled temperature multiplexer for thermal dosimetry studies.

Thermistor probes are widely used for mapping thermal distributions in hyperthermia research. To facilitate multi-probe mapping, a computer-controlled multiplexer for automated thermistor impedance measurement and temperature conversion is described. A complete hardware interface schematic is shown. An algorithm which calculates individual temperature values as a function of thermistor impedance is tested. Total error is quantified by calculating the absolute error between the theoretical temperatures obtained from the algorithm and the experimental calibration temperatures obtained from a National Bureau of Standards referenced mercury thermometer. If calibration intervals of 1.00 degree C or less are used, the total error of the system is less than 0.10 degree C.

Biomedical Engineering↗
PubMed1984

Analysis of the frequency following response in the cat.

The generators of the frequency following response (FFR) were characterized for three frequency ranges by studying changes in FFR response after lesioning the nuclei within the central brainstem auditory pathway. Responses to low frequency (200-500 Hz) stimulation demonstrated changes in the complexity of the FFR waveform in both time and frequency domains following lesions in the brainstem auditory pathway. The results indicate that the complexity of the low frequency FFR is due to activity from multiple sites within the auditory pathway. The intermediate frequency (700-1500 Hz) responses showed unpredictable amplitude changes following similar lesions and no conclusion could be drawn about the generators of the FFR in this frequency range. The responses to high frequency (3-8 Hz) stimulation showed no reduction in amplitude following serial lesioning. These results, combined with other experimental evidence presented, indicate that the high frequency FFR response originates from the cochlear microphonic. Different electrode configurations were used to evaluate the low frequency FFR. In contrast to multiple generator sources recorded with the standard vertex-mastoid electrode configuration, we were able to record a response contributed primarily by the inferior colliculi with a less peripherally sensitive electrode configuration (vertex-linked-pinnae) at low intensity stimulation. The fact that auditory brainstem nuclei contribute to the FFR in varying amounts depending on the electrode configuration may explain some of the conflicting characterizations of this response in the literature. Despite this difficulty, the FFR neural generators were identified and characterized in the low frequency range using our most sensitive electrode configuration (vertex-mastoid) and in the high frequency range where the single generator is the cochlear microphonic.

Animals↗
PubMed1984

Primary lymphoma of the central nervous system. Clinicopathological study of experience at Stanford.

The authors present 22 cases of primary lymphoma of the central nervous system (CNS) from Stanford University Medical Center. Fifteen other published series comprising 400 patients with this disease are also reviewed. Males were affected more often than females. The majority of patients were in the sixth decade of life. The most common presenting symptoms were headache, nausea, vomiting, and mental status changes. The most common presenting signs were hemiparesis and papilledema. An elevated protein concentration was the most common cerebrospinal fluid (CSF) abnormality. The CSF cytology was rarely positive prior to surgery. If a mass was seen on computerized tomography, it always enhanced with infusion of contrast material. On angiography, the tumor was generally seen as an avascular mass. The most and least common sites of involvement supratentorially were the frontal and occipital lobes, respectively. Infratentorially, the cerebellum was most often involved. Histologically, the most common tissue type according to the Rappaport and Working Formulation systems were diffuse histiocytic lymphoma and immunoblastic lymphoma, respectively. Therapy primarily involved surgery for biopsy or subtotal resection and radiation therapy. The majority of patients died, and the median survival time of those dying was distinctly shorter than the follow-up period of those patients still alive. This difference in survival time suggests that primary CNS lymphoma consists of more than one disease group. Statistical analysis of our series showed those patients with either a diffuse mixed lymphoma histology or an infratentorial location of disease had a poorer prognosis. These two factors cannot totally account for the division of cases into separate survival-related groups.

Adolescent↗