Biomedical subjects

R G Gonzalez

Publications and source records attributed to R G Gonzalez.

At least 19 recordsLinked to original sources

PubMed1999

Normal diffusion-weighted MRI during stroke-like deficits.

BACKGROUND: Diffusion-weighted MRI (DWI) represents a major advance in the early diagnosis of acute ischemic stroke. When abnormal in patients with stroke-like deficit, DWI usually establishes the presence and location of ischemic brain injury. However, this is not always the case. OBJECTIVE: To investigate patients with stroke-like deficits occurring without DWI abnormalities in brain regions clinically suspected to be responsible. METHODS: We identified 27 of 782 consecutive patients scanned when stroke-like neurologic deficits were still present and who had normal DWI in the brain region(s) clinically implicated. Based on all the clinical and radiologic data, we attempted to arrive at a pathophysiologic diagnosis in each. RESULTS: Best final diagnosis was a stroke mimic in 37% and a cerebral ischemic event in 63%. Stroke mimics (10 patients) included migraine, seizures, functional disorder, transient global amnesia, and brain tumor. The remaining patients were considered to have had cerebral ischemic events: lacunar syndrome (7 patients; 3 with infarcts demonstrated subsequently) and hemispheric cortical syndrome (10 patients; 5 with TIA, 2 with prolonged reversible deficits, 3 with infarction on follow-up imaging). In each of the latter three patients, the regions destined to infarct showed decreased perfusion on the initial hemodynamically weighted MRI (HWI). CONCLUSIONS: Normal DWI in patients with stroke-like deficits should stimulate a search for nonischemic cause of symptoms. However, more than one-half of such patients have an ischemic cause as the best clinical diagnosis. Small brainstem lacunar infarctions may escape detection. Concomitant HWI can identify some patients with brain ischemia that is symptomatic but not yet to the stage of causing DWI abnormality.

Aged↗

PubMed1999

Human brain activation under controlled thermal stimulation and habituation to noxious heat: an fMRI study.

Brain activity was studied with functional magnetic resonance imaging (fMRI) following thermal stimulation. Two groups (n = 6/group) of human male volunteers were given up to four noxious (46 degrees C) and four non-noxious (41 degrees C) stimuli. In the 46 degrees C experiment, positive signal changes were found in the frontal gyri, anterior and posterior cingulate gyrus, thalamus, motor cortex, somatosensory cortex (SI and SII), supplementary motor area, insula, and cerebellum. Low-level negative signal changes appeared in the amygdala and hypothalamus. All regions activated by 46 degrees C were also activated by 41 degrees C. However, except for SI and thalamus, significantly more activation was observed for the 46 degrees C stimulus. A significant attenuation of the signal change was observed by the third stimulus for the 46 degrees C, but not for 41 degrees C experiment. Similar findings were replicated in the second group. These fMRI findings specify differences between somatosensory and pain sensation and suggest a number of rich avenues for future research.

Adult↗

PubMed1999

Hyperacute stroke: simultaneous measurement of relative cerebral blood volume, relative cerebral blood flow, and mean tissue transit time.

PURPOSE: To investigate additional information provided by maps of relative cerebral blood flow in functional magnetic resonance (MR) imaging of human hyperacute cerebral ischemic stroke. MATERIALS AND METHODS: Diffusion-weighted and hemodynamic MR imaging were performed in 23 patients less than 12 hours after the onset of symptoms. Maps of relative cerebral blood flow and tracer mean tissue transit time were computed, as were maps of apparent diffusion and relative cerebral blood volume. Acute lesion volumes on the maps were compared with follow-up imaging findings. RESULTS: In 15 of 23 subjects (65%), blood flow maps revealed hemodynamic abnormalities not visible on blood volume maps. A mismatch between initial blood flow and diffusion findings predicted growth of infarct more often (12 of 15 subjects with infarcts that grew) than did a mismatch between initial blood volume and diffusion findings (eight of 15). However, lesion volumes on blood volume and diffusion maps correlated better with eventual infarct volumes (r > 0.90) than did those on blood flow and tracer mean transit time maps (r approximately 0.6), likely as a result of threshold effects. In eight patients, blood volume was elevated around the diffusion abnormality, suggesting a compensatory hemodynamic response. CONCLUSION: MR imaging can delineate areas of altered blood flow, blood volume, and water mobility in hyperacute human stroke. Predictive models of tissue outcome may benefit by including computation of both relative cerebral blood flow and blood volume.

Acute Disease↗

PubMed1999

Human acute cerebral ischemia: detection of changes in water diffusion anisotropy by using MR imaging.

PURPOSE: To (a) determine the optimal choice of a scalar metric of anisotropy and (b) determine by means of magnetic resonance imaging if changes in diffusion anisotropy occurred in acute human ischemic stroke. MATERIALS AND METHODS: The full diffusion tensor over the entire brain was measured. To optimize the choice of a scalar anisotropy metric, the performances of scalar indices in simulated models and in a healthy volunteer were analyzed. The anisotropy, trace apparent diffusion coefficient (ADC), and eigenvalues of the diffusion tensor in lesions and contralateral normal brain were compared in 50 patients with stroke. RESULTS: Changes in anisotropy in patients were quantified by using fractional anisotropy because it provided the best performance in terms of contrast-to-noise ratio as a function of signal-to-noise ratio in simulations. The anisotropy of ischemic white matter decreased (P = .01). Changes in anisotropy in ischemic gray matter were not significant (P = .63). The trace ADC decreased for ischemic gray matter and white matter (P < .001). The first and second eigenvalues decreased in both ischemic gray and ischemic white matter (P < .001). The third eigenvalue decreased in ischemic gray (P = .001) and white matter (P = .03). CONCLUSION: Gray matter is mildly anisotropic in normal and early ischemic states. However, early white matter ischemia is associated with not only changes in trace ADC values but also significant changes in the anisotropy, or shape, of the water self-diffusion tensor.

Adult↗

PubMed1999

Acute stroke: improved nonenhanced CT detection--benefits of soft-copy interpretation by using variable window width and center level settings.

PURPOSE: To assess the use of nonstandard, variable window width and level review settings in computed tomography (CT) without contrast material administration in the detection of acute stroke. MATERIALS AND METHODS: Nonenhanced CT was performed in 21 patients with acute (< 6 hours) middle cerebral arterial stroke and nine control patients. Two blinded neuroradiologists rated all scans for presence of parenchymal hypoattenuation. Images were reviewed at a picture archiving and communication system (PACS) workstation, with standard, locally determined center level and window width settings of 20 and 80 HU and with variable soft-copy settings initially centered at a level of 32 HU with a width of 8 HU. Reviewers altered settings to accentuate gray and white matter contrast. RESULTS: With standard viewing parameters, sensitivity and specificity for stroke detection were 57% and 100%. Sensitivity increased to 71% with variable window width and center level settings, without loss of specificity. Receiver operating characteristic analysis revealed a significant improvement in accuracy with nonstandard, soft-copy review settings (P = .03, one-tailed z test). CONCLUSION: In nonehanced CT of the head, detection of ischemic brain parenchyma is facilitated by soft-copy review with variable window width and center level settings to accentuate the contrast between normal and edematous tissue.

Acute Disease↗

PubMed1999

Diffusion-weighted imaging identifies a subset of lacunar infarction associated with embolic source.

BACKGROUND AND PURPOSE: Small infarcts in the territory of penetrator arteries were described as causing a number of distinct clinical syndromes. The vascular pathophysiology underlying such infarcts is difficult to ascertain without careful pathological study. However, the occurrence of multiple, small infarcts, linked closely in time but dispersed widely in the brain, raises the possibility of an embolic mechanism. The current study determines the frequency and clinical characteristics of patients with well-defined lacunar syndromes and the diffusion-weighted imaging (DWI) evidence of multiple acute lesions. METHODS: Sixty-two consecutive patients who presented to the emergency room with a clinically well-defined lacunar syndrome were studied by DWI within the first 3 days of admission. RESULTS: DWI showed multiple regions of increased signal intensity in 10 patients (16%). A hemispheric or brain stem lesion in a penetrator territory that accounted for the clinical syndrome ("index lesion") was found in all. DWI-hyperintense lesions other than the index lesion ("subsidiary infarctions") were punctate and lay within leptomeningeal artery territories in the majority. As opposed to patients with a single lacunar infarction, patients with a subsidiary infarction more frequently (P<0.05) harbored an identifiable cause of stroke. CONCLUSIONS: Almost 1 of every 6 patients presenting with a classic lacunar syndrome has multiple infarctions demonstrated on DWI. This DWI finding usually indicates an identifiable cause of stroke and therefore may influence clinical decisions regarding the extent of etiologic investigations and treatment for secondary prevention.

Adult↗

PubMed1999

Early changes measured by magnetic resonance imaging in cerebral blood flow, blood volume, and blood-brain barrier permeability following dexamethasone treatment in patients with brain tumors.

OBJECT: In this study the authors assessed the early changes in brain tumor physiology associated with glucocorticoid administration. Glucocorticoids have a dramatic effect on symptoms in patients with brain tumors over a time scale ranging from minutes to a few hours. Previous studies have indicated that glucocorticoids may act either by decreasing cerebral blood volume (CBV) or blood-tumor barrier (BTB) permeability and thereby the degree of vasogenic edema. METHODS: Using magnetic resonance (MR) imaging, the authors examined the acute changes in CBV, cerebral blood flow (CBF), and BTB permeability to gadolinium-diethylenetriamine pentaacetic acid after administration of dexamethasone in six patients with brain tumors. In patients with acute decreases in BTB permeability after dexamethasone administration, changes in the degree of edema were assessed using the apparent diffusion coefficient of water. CONCLUSIONS: Dexamethasone was found to cause a dramatic decrease in BTB permeability and regional CBV but no significant changes in CBF or the degree of edema. The authors found that MR imaging provides a powerful tool for investigating the pathophysiological changes associated with the clinical effects of glucocorticoids.

Antineoplastic Agents, Hormonal↗

PubMed1998

Correlation of high-resolution magic angle spinning proton magnetic resonance spectroscopy with histopathology of intact human brain tumor specimens.

High-resolution magic angle spinning proton (HRMAS 1H) magnetic resonance spectroscopy produces well-resolved spectra of metabolites from intact tissue specimens. Here we report the results of a preliminary study of 19 human brain tumors obtained by applying this method. Among these 19 cases were 2 low-grade astrocytomas, 1 anaplastic astrocytoma, 8 glioblastomas, 6 meningiomas, and 2 schwannomas. In addition, autopsy human brain tissues from two subjects without any known neurological diseases were used as normal controls. The HRMAS 1H magnetic resonance spectroscopy measurements were performed at 2 degrees C on a 400-MHz NMR spectrometer with a HRMAS speed of 2.5 kHz. From these HRMAS 1H MR spectra, we measured the concentrations of 11 metabolites, the ratios of 15 metabolites (resonances) to creatine (at 3.03 ppm), and the spin-spin relaxation time for these metabolites (resonances). Our results indicate that these parameters have the potential to characterize tumor types and grades with statistical significance as well as identify tumor biochemical characteristics. In particular, we found that compared with metabolite concentrations and metabolite spin-spin relaxation time, the metabolic ratios presented the highest sensitivity in differentiating normal tissue from tumors, as well as in distinguishing between tumor groups. Of 15 analyzed metabolic ratios, 12 showed statistical significance in differentiating normal tissue from low-grade and anaplastic astrocytomas, 13 showed statistical significance in differentiating normal tissue from glioblastomas, 14 showed statistical significance in differentiating normal tissue from schwannomas, and 9 showed statistical significance in differentiating normal tissue from meningiomas. Moreover, our results strongly indicate that the resonance ratio of inositol (at 4.05 ppm) to creatine may help distinguish tumor type. Our results suggest that the HRMAS method for intact tissue measurement may function as an adjunct to histopathology and contribute to improved accuracy for brain tumor diagnoses.

Amino Acids↗

PubMed1998

Acute plasticity in the human somatosensory cortex following amputation.

We studied a patient after amputation of an arm and found that in less than 24 h stimuli applied on the ipsilateral face were referred in a precise, topographically organized, modality-specific manner to distinct points on the phantom. Functional magnetic resonance imaging (fMRI) performed one month later showed that brush-evoked activity in the brain demonstrates objective signal changes which correlate with perceptual changes in the phantom hand. This finding in humans corresponds to the observations of immediate plasticity in cortical pathways described in animals, including primates. The results suggest that reorganization of sensory pathways occurs very soon after amputation in humans, potentially due to the unmasking of ordinarily silent inputs rather than sprouting of new axon terminals.

Adult↗

PubMed1998

Evaluating human breast ductal carcinomas with high-resolution magic-angle spinning proton magnetic resonance spectroscopy.

We report the results of a study of human breast ductal carcinomas, conducted by using high resolution magic angle spinning proton magnetic resonance spectroscopy (HRMAS 1HMRS). This recently developed spectroscopic technique can measure tissue metabolism from intact pathological specimens and identify tissue biochemical changes, which closely correspond to tumor in vivo state. This procedure objectively indicates diagnostic parameters, independent of the skill and experience of the investigator, and has the potential to reduce the sampling errors inherently associated with procedures of conventional histopathology. In this study, we measured 19 cases of female ductal carcinomas. Our results demonstrate that: (1) highly resolved spectra of intact specimens of human breast ductal carcinomas can be obtained; (2) carcinoma-free tissues and carcinomas are distinguishable by alterations in the intensities and the spin-spin relaxation time T2 of cellular metabolites; and (3) tumor metabolic markers, such as phosphocholine, lactate, and lipids, may correlate with the histopathological grade determined from evaluation of the adjacent specimen. Our results suggest that biochemical markers thus measured may function as a valuable adjunct to histopathology to improve the accuracy of and reduce the time frame required for the diagnosis of human breast cancer.

Adult↗

PubMed1998

A mobile computed tomographic scanner with intraoperative and intensive care unit applications.

INTRODUCTION: A mobile computed tomographic scanner has been developed in which the scan plane is selected by means of gantry translation, rather than by translation of the patient table. This permits computed tomographic scanning in situ of any patient who is positioned on a radiolucent surface that fits within the inner diameter of the gantry. We report the design of and initial experience with this scanner as used with adapters for intraoperative and bedside computed tomography (CT). METHODS: The scanner is equipped with wheels, draws power from wall outlets (120 V, 20 A) in combination with batteries, and has a translating gantry. Preclinical studies of image quality were performed with phantoms. An operating table adapter was built for use with a radiolucent cranial fixation device. A bedside adapter was built that holds the head and shoulders of a patient in the intensive care unit. RESULTS: The preclinical phantom studies showed satisfactory image spatial resolution (0.8 mm) and low-contrast resolution signal-to-noise relative standard deviation (0.37%). Experience to date with 12 patients has confirmed the feasibility of intraoperative CT on demand. Experience to date with 26 patients has confirmed the feasibility of routine bedside CT in the intensive care unit. CONCLUSION: With these adaptations, mobile CT may increase the efficiency of intraoperative scanning by making it available to multiple operating rooms without committing it to any room for an entire operation and may increase the efficiency and safety of CT of critically ill patients who currently need to leave the intensive care unit to travel to a fixed CT installation and back.

Child↗

PubMed1998

Time course of lesion development in patients with acute stroke: serial diffusion- and hemodynamic-weighted magnetic resonance imaging.

BACKGROUND AND PURPOSE: We sought to characterize the evolution of acute ischemic stroke by MRI and its relationship to patients' neurological outcome. METHODS: Fourteen patients with acute ischemic stroke underwent MRI within 13 hours of symptom onset (mean, 7.4+/-3 hours) and underwent repeated imaging and concurrent neurological examination at 8, 24, 36, and 48 hours and 7 days and >42 days after first imaging. RESULTS: Diffusion-weighted imaging (DWI) lesion volumes increased between the first and second scans in 10 of 14 patients; scans with maximum DWI lesion volume occurred at a mean of 70.4 hours. Initial DWI lesion volume correlated with the largest T2 lesion volume (r=0.97; P<0.001). Final lesion volume was smaller than maximum lesion volume in 12 of 14 patients. There was positive correlation between the follow-up National Institutes of Health Stroke Scale score and the initial DWI lesion volume (r=0.67; P=0. 01) and maximum T2 lesion volume (r=0.77; P<0.01) and negative correlation with initial mean apparent diffusion coefficient ratio (ADCr) (r=-0.64; P<0.05). The ADCr was 0.73 at initial imaging and fell between the initial and second scans in 10 of 14 patients. Mean ADCr did not rise above normal until 42 days after stroke onset (P<0. 001). CONCLUSIONS: Serial MRI demonstrates the dynamic nature of progressive ischemic injury in acute stroke patients developing over hours to days, and it suggests that both primary and secondary pathophysiological processes can be valuable targets for neuroprotective interventions.

Acute Disease↗

PubMed1998

Posterior leukoencephalopathy without severe hypertension: utility of diffusion-weighted MRI.

OBJECTIVE: Standard MRI confirms the diagnosis of posterior leukoencephalopathy syndrome (PLES), recently associated with an increasing number of medical conditions. In PLES, T2-weighted MRI demonstrates hyperintensity spreading out from posterior brain regions; the pathophysiology remains mysterious. In the acute setting, diffusion-weighted imaging (DWI), but not standard MR imaging, can distinguish ischemic injury from those conditions known to cause vasogenic brain edema. DWI is potentially valuable in understanding the pathophysiology of PLES and in diagnosing patients who do not have previously known risk factors. METHODS: Serial CT and MRI studies (including DWI, apparent diffusion coefficient [ADC] maps, and, in one instance, perfusion-weighted imaging) were performed in three female patients with a neurologic syndrome consistent with PLES while hospitalized for treatment of other conditions. RESULTS: None of the patients had previously described risk factors for PLES; all had only mild elevations in blood pressure. MRI showed large, abnormal, T2 hyperintense regions in the posterior cerebrum with corresponding hyperintensity on ADC maps-signal characteristics predominantly consistent with vasogenic edema. There were also smaller patchy posterior cortical regions with decreased ADC and bright DWI consistent with infarction in one, and dramatic conversion of a large region to an ischemic pattern in another. CONCLUSIONS: ADC maps and DWI can successfully differentiate PLES from early cerebral ischemia, thus playing a pivotal role in treatment decisions. PLES is associated with a wider variety of conditions than has been previously reported and is not always reversible. Hyperintense DWI signal in patients with the syndrome likely marks a tissue stage of permanent brain injury.

Adult↗

PubMed1998

Magnetic resonance imaging of cerebral infarction.

The clinical application of diffusion-weighted and perfusion-weighted magnetic resonance (MR) imaging techniques has revolutionized the diagnosis and management of acute cerebral infarction. This article discusses the physical basis of these advanced techniques and briefly demonstrates their application along with standard MR imaging and MR angiography in the setting of acute stroke.

Acute Disease↗

PubMed1997

MRI measurements of water diffusion and cerebral perfusion: their relationship in a rat model of focal cerebral ischemia.

The aim of this study was to examine the quantitative relationship between changes in apparent diffusion coefficient (ADC) and transverse relaxivity (delta R2*) measurements of relative perfusion deficits within the gradients of a focal ischemic insult. Sixty minutes after permanent occlusion of the middle cerebral artery, rats (n = 7) were subjected to spin echo diffusion-weighted scans followed by fast low-angle shot (FLASH) perfusion-sensitive scans. Diffusion-weighted images showed clear ischemic lesions in the affected basal ganglia and cortex. Ischemic deficits were demonstrated as a decrease in first-pass transit of injected boluses of gadodiamide. ADC maps were generated and regions of interest (ROIs) were obtained to span the range of ADC reductions from the lesion center or core to the periphery or penumbra. Corresponding ROIs from the bolus injection images were used to calculate perfusion indexes relative to contralateral levels as ratios of delta R2* integrals and ratios of delta R2* peak values. In all animals, the degree of ADC reductions was related to the degree of delta R2* perfusion deficits, ranging from severe ischemia in the core of the lesion to intermediate and moderate changes toward the lesion periphery. In the ischemic periphery, ADC reductions were linearly correlated with delta R2* peak ratios. However, no significant correlation was found between ADC reductions and delta R2* integral ratios. These data suggest that magnetic resonance measurements of ADC and delta R2* peak ratios can be used to quantitatively assess the variable gradients in focal ischemia, including potentiallyn critical areas at risk in the ischemic periphery.

Animals↗

PubMed1997

Diffusion-weighted imaging discriminates between cytotoxic and vasogenic edema in a patient with eclampsia.

BACKGROUND: The pathophysiology of eclampsia remains unclear. While the majority of patients develop reversible T2 hyperintense signal abnormalities on MR scans and reversible neurological deficits, some patients do develop infarctions (permanent T2 hyperintense abnormalities) and permanent neurological impairment. Routine MRI cannot prospectively differentiate between these two patient groups. Echo-planar diffusion-weighted imaging, however, is a new technique that clearly differentiates between cytotoxic and vasogenic edema. CASE DESCRIPTION: A 30-year-old woman developed symptoms consistent with eclampsia 24 hours after delivering premature twins. An MRI demonstrated extensive, diffuse T2 hyperintense signal abnormalities involving subcortical white matter and adjacent gray matter with a posterior predominance, consistent with either infarction or hypertensive ischemic encephalopathy. Diffusion-weighted images demonstrated increased diffusion, consistent with vasogenic edema and hypertensive ischemic encephalopathy. CONCLUSIONS: Unlike routine MRI, diffusion-weighted imaging reliably differentiates between vasogenic edema and cytotoxic edema. Consequently, in eclamptic patients diffusion-weighted imaging can afford clear differentiation between hypertensive ischemic encephalopathy and infarction, two very different entities with very different treatment protocols. Diffusion-weighted imaging should be performed in all eclamptic patients and should greatly affect their management.

Adult↗

PubMed1997

FDG hypermetabolism associated with inflammatory necrotic changes following radiation of meningioma.

PET with 18F-fluoro-2-deoxy-D-glucose (FDG) is currently the noninvasive gold standard for distinguishing brain tumor recurrence from radiation necrosis. We present a case report that appears to contradict this doctrine. The patient had a history of atypical meningioma and was treated with surgical resection and postoperative proton-beam radiation therapy. Approximately 16 mo after completion of therapy, MRI demonstrated two new regions of enhancement, and an FDG-PET study was performed to further characterize these lesions. FDG-PET demonstrated an area of intense hypermetabolism, and wide surgical resection was performed. Histological examination of the surgical specimen revealed reactive changes and areas of necrosis. There was no evidence of either recurrent or radiation-induced tumor.

Aged↗

PubMed1997

Functional imaging of the AIDS dementia complex and the metabolic pathology of the HIV-1-infected brain.

The AIDS-dementia complex remains one of the more common neurologic disorders associated with human immunodeficiency virus (HIV) infection. Despite several advances that have been made in elucidating some of its clinical and biological features, pathogenesis is not well understood, and effective treatments are scarce. This article reveals the results of these studies and discusses how these different approaches have already enabled clinicians to study further the effects of HIV infection on brain function and to explore the functional anatomy of this important clinical syndrome.

AIDS Dementia Complex↗