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Biomedical subjects

A Alavi

Publications and source records attributed to A Alavi.

At least 289 records · Page 16Linked to original sources
PubMed1988

Cerebral metabolism and patterned visual stimulation: a positron emission tomographic study of the human visual cortex.

We studied the impact of visual stimulation upon cerebral metabolism in normal young men using FDG-PET. Results obtained from subjects receiving patterned visual stimulation while performing an ocular fixation task were compared with results from ocular fixation alone. Visual stimulation in the macular region of either hemifield produced significant increases in metabolism of the contralateral posterior striate cortex. Visual stimulation induced highly significant asymmetries in metabolism of the prefrontal and inferior parietal cortices. Metabolic activation in extrastriate areas tended to be right-sided. These findings support the classic notion of retinotopic organization within the primary visual sensory cortex. They also indicate that the patterns of cerebral metabolism are not equivalent between the two cerebral hemispheres. This latter finding suggests that in humans the right cerebral hemisphere may be specialized for visual processing.

Adolescent↗
PubMed1988

Positron emission tomography in a patient with progressive multifocal leukoencephalopathy.

A 56-year-old man with chronic lymphocytic leukemia, progressive multifocal leukoencephalopathy, and a dense left homonymous hemianopia had 18F-fluorodeoxyglucose positron emission tomography. Cortical glucose metabolism was decreased in the right cerebral hemisphere and the left cerebellar hemisphere. To our knowledge, this is the first demonstration of cerebral and cerebellar hypometabolism due solely to white matter disease.

Aged↗
PubMed1988

Resolving metabolic abnormalities in a case of pure alexia.

We report resolving metabolic abnormalities corresponding to clinical improvement in a patient with pure alexia secondary to acute cerebral infarction. Local cerebral glucose metabolism (lCMRgl) was measured with positron emission tomography (PET) using 18F-fluorodeoxyglucose (18F-FDG) close to ictus and 4 1/2 months later. Serial CTs and a subsequent MRI demonstrated small, unchanging left-hemispheric lesions involving the area of the lateral geniculate body and the splenium of the corpus callosum. PET demonstrated the evolution of the metabolic abnormality resulting from intrahemispheric (lateral geniculate) and interhemispheric (splenium) disconnection in the absence of occipital lobe infarction. This case illustrates that cerebral disconnection can result in the syndrome of pure alexia. The factors accounting for focal hypometabolism in the absence of cerebral infarction are discussed.

Brain↗
PubMed1988

Positron emission tomography in the investigation of central nervous system disorders.

Positron emission tomography is a noninvasive tomographic technique for measuring regional tissue concentrations of labeled radionuclides in man. Detection of two photons emitted from the annihilation of a positron and an electron is used to reconstruct the distribution of a positron-emitting isotope within an organ. PET provides the capacity to measure quantitatively the local tissue distribution of a variety of radionuclides that are attached to compounds that distribute according to function. Commonly measured functions include local cerebral metabolism using 18F-fluorodeoxyglucose or 11C-deoxyglucose, cerebral blood flow, cerebral oxygen utilization, and cerebral blood volume. Clinical applications of PET are multiple, involving normal and disease states. By demonstrating the metabolic alterations, PET adds another dimension to our understanding of the brain, which up until recently has been based on the structural changes seen on CT and MRI.

Aging↗
PubMed1988

Indium-111-labeled white blood cells in the detection of osteomyelitis complicated by a pre-existing condition.

Forty-six patients (23M, 23F) ranging in age from 19 to 79 yr with a clinical history of a nonunion fracture, surgery, diabetes or a soft-tissue infection were studied with [111In]oxine WBCs to detect osteomyelitis. There were 27 true-positive, nine true-negative, two false-positive and one false-negative. The false-positives and the false-negative occurred in patients with soft-tissue infections overlying the area of interest. All diagnoses were confirmed by intraoperative bone biopsies and cultures. Bone biopsy and scan were performed within 2 days of each other in 39 patients. The overall sensitivity was 97% (27/28), specificity, 82% (9/11) and the diagnostic accuracy, 92% (36/39). The remaining seven patients had negative [111In]WBC scans several months after positive bone biopsies and definite antibiotic treatment. This suggests that [In]WBC scans become negative after appropriate therapy is undertaken. Interobserver data was obtained from four nuclear physicians of varying experience blinded to clinical information. A high degree of agreement was found in over 90% of the cases. This study demonstrates the utility of [111In]WBC scans in the diagnosis and follow-up of complicated osteomyelitis and a high level of interobserver agreement in scan interpretation.

Adult↗
PubMed1987

Radioimmunodetection of human glioma xenografts by monoclonal antibody to epidermal growth factor receptor.

Murine IgG2a monoclonal antibody (MAb) 425 specifically detects epidermal growth factor receptor, which is expressed on human gliomas and tumors of other tissue origin but rarely on normal brain tissues, and not at all on bone marrow and peripheral blood cells. 131I-labeled F(ab')2 fragments of this MAb injected into nude mice grafted with U-87 MG glioma cells preferentially localized in tumor tissue compared to normal mouse tissues, as determined by differential tissue counting of radioactivity. The mean tumor-to-tissue ratios of radioactivity ranged between 8.2 (blood) and 55.8 (muscle) at 2 days after the injection of 15 muCi of 131I-425 F(ab')2/mouse. Radiolabeled fragments of an anti-hepatitis virus IgG2a MAb did not localize in tumors. The localization index derived from the ratios of specific antibody to indifferent antibody in tumor tissue relative to blood was 9.94 at 2 days following the MAb injection. The labeled MAb did not localize in a xenograft of colorectal cancer tumor, which does not express the epidermal growth factor receptor. Tumors could be located by whole-body gamma-scintigraphy without background subtraction following the injection of 100 muCi of radiolabeled MAb 425 F(ab')2 fragments. The data suggest that MAb 425 is a likely candidate for clinical diagnostic and radioimmunotherapy trials.

Animals↗
PubMed1987

Cerebral glucose consumption following verbal auditory stimulation.

We studied the effect of auditory stimulation upon cerebral glucose metabolism in young normals. The stimulus consisted of a non-English discourse which was presented monaurally to 10 normal blindfolded subjects (5 left ear, 5 right); the opposite ear was plugged. Six subjects studied blindfolded and with ears plugged served as controls. Sixteen discrete homologous cortical and subcortical regions of interest were examined. Regional glucose consumption and side-to-side differences in glucose metabolism were analyzed. Monaural stimulation produced significant increases in temporal metabolism contralateral to the side of stimulation. Significant asymmetries in metabolism were found at the temporoparietal junction, inferior parietal region, insula and corpus collosum. The left frontal speech areas remained unaffected. These findings demonstrate that in man the primary auditory pathways retain a contralateral organization. Further, cerebral activation induced by non-meaningful verbal stimulation is widespread within the left temporal and parietal regions but does not impact upon the frontal speech cortices.

Adult↗
PubMed1987

Regional brain function in schizophrenia. I. A positron emission tomography study.

Local cerebral glucose metabolism was determined with 18-F-fluorodeoxyglucose using positron emission tomography in a sample of 12 unmedicated schizophrenics and 12 matched normal controls. The data were analyzed for absolute metabolic rates and region/whole-brain ratios using the cortical-subcortical, antero-posterior, and laterality dimensions. Lobar areas within cortical regions were also compared. Across groups, subcortical metabolism was higher than cortical metabolism. Patients had lower metabolism, cortically and subcortically, and a steeper subcortical to cortical gradient. Patients with higher scores on the Brief Psychiatric Rating Scale had higher absolute metabolism and higher left relative to right hemispheric metabolism than did patients with lesser severity. The results did not show "hypofrontality" in schizophrenia. These findings provide some support for cerebral dysfunction in schizophrenia and indicate the need for further examination of the cortical-subcortical dimension.

Brain↗
PubMed1987

Regional brain function in schizophrenia. II. Repeated evaluation with positron emission tomography.

Cerebral glucose metabolism was measured twice in a sample of 15 schizophrenics and eight controls, using positron emission tomography (PET) with 18-F-fluorodeoxyglucose. Studies were separated by three to 33 weeks. Patients were unmedicated during the first study, and the majority were receiving neuroleptics during the second study. There were no changes from study 1 to study 2 in average whole-brain metabolic rates, regional cortical activity, or the gradient of subcortical to cortical activity. The steeper subcortical to cortical gradient in schizophrenics, present in the first study, persisted in the second. Changes in this gradient were uncorrelated with changes in clinical status. Laterality (right-left) was stable across studies, and changes toward higher right relative to left hemispheric metabolism were correlated with clinical improvement. The results support the hypothesis of abnormal hemispheric activity in schizophrenia and implicate the subcortical-cortical gradient as another dimension that merits further exploration.

Adult↗
PubMed1987

Recovery of vision after ischemic lesions: positron emission tomography.

We used [18F]fluoro-2-deoxyglucose positron emission tomography (PET) to study serial changes in the local cerebral metabolic rate of glucose in 5 patients with ischemic lesions of the posterior afferent visual system causing homonymous visual field defects. All 5 patients had striking impairment of glucose metabolism in the striate cortex shortly after ictus. In 2 patients, visual field defects abated, and repeat PET scans showed reduced size of the metabolic lesion and improvement of striate metabolism. Three patients did not recover vision, and repeat PET scans did not show improvement. Patients who recovered vision had ischemic lesions outside the occipital lobe, while those who did not experience improvement had primary damage to the occipital lobe itself.

Aged↗
PubMed1987

Indium-111 leukocyte scintigraphic detection of subclinical osteomyelitis complicating delayed and nonunion long bone fractures: a prospective study.

Twenty patients were studied prospectively with indium-labeled leukocyte imaging to evaluate its effectiveness in differentiating noninfected delayed or nonunion from osteomyelitis complicating these entities. All patients underwent an open surgical procedure within 24 h of the scan. Bone specimens from the nonunion site were obtained for microbiological and histological analysis to confirm the presence or absence of osteomyelitis. In these twenty patients, the sensitivity of the indium scintigraphy was 100%, the specificity 100%, and the overall accuracy 100%. Indium-labeled leukocyte scintigraphy is significantly more accurate than 99mtechnetium and 67gallium imaging had been, when studied earlier, in detecting subclinical osteomyelitis complicating nonunion. Indium-labeled leukocyte scintigraphy should supplant sequential technetium and gallium studies in this patient population when the surgeon must determine whether subclinical osteomyelitis is complicating fracture management of delayed and nonunions.

Adult↗
PubMed1987

Regional cerebral glucose metabolism in aphemia: a case report.

Local cerebral metabolism was determined in a patient suffering aphemia following cerebral infarction using the 18FDG-PET technique. The syndrome was characterized by profound ictal nonfluency with sparing of other language functions. Speech subsequently improved so that content and grammar were appropriate but mild dysprosody persisted. Conventional CT showed no lesion of the left hemisphere while PET revealed a discrete focus of hypometabolism on the left which partially resolved on serial studies. The metabolic lesion could be localized to the region of the inferior precentral gyrus and the adjacent subcortical space.

Aged↗
PubMed1987

The effect of anxiety on cortical cerebral blood flow and metabolism.

The relation between anxiety and cortical activity was compared in two samples of normal volunteers. One group was studied with the noninvasive xenon-133 inhalation technique for measuring cerebral blood flow (CBF) and the other with positron emission tomography (PET) using 18Flurodeoxyglucose (18FDG) for measuring cerebral metabolic rates (CMR) for glucose. The inhalation technique produced less anxiety than the PET procedure, and for low anxiety subjects, there was a linear increase in CBF with anxiety. For higher anxiety subjects, however, there was a linear decrease in CBF with increased anxiety. The PET group manifested a linear decrease in CMR with increased anxiety. The results indicate that anxiety can have systematic effects on cortical activity, and this should be taken into consideration when comparing data from different procedures. They also suggest a physiologic explanation of a fundamental behavioral law that stipulates a curvilinear, inverted-U relationship between anxiety and performance.

Adolescent↗
PubMed1987

The cholescintigraphic pattern of small bowel obstruction.

An elderly patient presenting with acute abdominal pain, nausea, and vomiting underwent a hepatobiliary scan. This demonstrated normal filling of the gallbladder but dilatation of the small bowel, which was found to correspond radiographically to partial small bowel obstruction.

Aged↗
PubMed1987

Sequential computerized tomography and positron emission tomography studies in a patient with malignant glioma.

Computerized tomography (CT) and positron emission tomography (PET) using fluorine-18-deoxyglucose were performed in a patient with malignant glioma over a one-year period. Postoperatively and during radiation therapy, there was slight improvement in metabolic activity in the hemisphere ipsilateral to the tumor. After radiation therapy and during chemotherapy, there was a rapid and then gradual decline in whole brain metabolic rate by 39%. This might have been explained by radiation effect on brain. The tumor area was metabolically similar to the adjacent brain until one year after diagnosis, when an area of abnormal increased activity was noted. Even though CT scans showed minimal evidence of tumour growth, a large glioblastoma multiforme was found at autopsy at the site of the increased activity. Radiation leukoencephalopathy was also observed at autopsy. It is concluded that PET studies may offer new information regarding the metabolic effects of anti-tumor therapy, and may demonstrate regrowth of tumor prior to CT.

Brain↗
PubMed1987

Femoral head avascular necrosis: correlation of MR imaging, radiographic staging, radionuclide imaging, and clinical findings.

To better correlate the appearance of avascular necrosis (AVN) of the femoral head on magnetic resonance (MR) images with the stage of disease, MR images of 56 proved AVN lesions were compared with staging from corresponding radiographs (n = 56), Tc-99m scans (n = 41), and grade of symptoms (n = 28). Fractures complicating AVN were seen in 28 (50%) of 56 radiographs (radiographic stages III-V). With long repetition (TR) and echo delay (TE) times, a characteristic "double line sign" consisting of high signal intensity inside a low-intensity peripheral rim was seen in 45 lesions (80%). The central region within the rim was isointense with marrow fat on both short and long TR and TE images in 20 (71%) of 28 lesions uncomplicated by fracture (stages I-II) but in only four (14%) of 28 stage III-V lesions (P less than .001). Symptoms were least severe in lesions isointense with fat and most severe in lesions with low-signal central regions at short and long TRs and TEs. The peripheral double line sign on long TR/TE images may add specificity to the diagnosis of AVN by MR imaging. A chronologic pattern of central MR signal features is presented which may allow staging of AVN by MR imaging.

Female↗
PubMed1987

Thyroid imaging with high-field-strength surface-coil MR.

Magnetic resonance (MR) imaging of the thyroid was performed with a 1.5-T system and local receiver coil in 19 "healthy" subjects and 34 patients with various focal and diffuse thyroid disorders. The normal gland was typically homogeneous with increased intensity relative to that of muscle on images obtained with long repetition times (TRs) and long echo times (TEs). Adjacent structures in the neck and upper mediastinum were well displayed. Thyroid nodules as small as 4-5 mm were identified. Follicular adenomas appeared as well-circumscribed nodules of heterogeneous intensity, increasing significantly in signal with long TRs/TEs. Colloid cysts and hemorrhagic cysts had homogeneous high signal with both short and long TRs/TEs. Two of three carcinomas were seen as poorly marginated lesions with associated cervical lymphadenopathy clearly depicted as increased intensity with long TRs/TEs. A follicular adenoma containing microscopic papillary carcinoma appeared similar to other benign adenomatoid nodules. A functioning nodule was isointense with normal gland at all pulse sequences. Characteristic patterns of diffuse abnormality were observed in cases of multinodular goiter, Hashimoto thyroiditis, and Graves disease, although additional cases are required to determine specificity. High-field-strength surface-coil MR imaging appears to be a sensitive method for identifying gross morphology of focal, multinodular, and diffuse disorders of the thyroid and involvement of surrounding structures in the neck.

Adult↗