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Biomedical subjects

W T Yuh

Publications and source records attributed to W T Yuh.

At least 55 records · Page 3Linked to original sources
PubMed1996

Echo-planar FLAIR imaging in evaluation of intracranial lesions.

Fluid-attenuated inversion-recovery (FLAIR) imaging is a magnetic resonance imaging technique that improves lesion detection in the brain. This technique suppresses signal from free water in cerebrospinal fluid and maintains the hyperintense lesion contrast of T2-weighted spin-echo imaging. Unfortunately, conventional FLAIR imaging requires a long acquisition time and provides a limited number of sections. A combination of echo-planar imaging and FLAIR imaging offers the image contrast effects of FLAIR imaging and the speed of echo-planar imaging. Clinically, the echo-planar FLAIR technique is most helpful in detecting subtle, early lesions that do not enhance, such as early infarct, demyelinating disease, early infection, and trauma. The increased magnetic susceptibility effect associated with the echo-planar technique can be clinically useful in detecting subtle hemorrhage and cavernous angioma. Echo-planar FLAIR imaging is a practical and efficient means of screening the entire brain in a short time.

Brain Diseases↗
PubMed1996

Neuroradiology.

Explore the source record for details and available documents.

Humans↗
PubMed1996

MR of optic papilla protrusion in patients with high intracranial pressure.

PURPOSE: To evaluate the signal characteristics of the optic papilla (optic nerve head) on routine cranial MR images in patients with clinical evidence of optic papilla elevation caused by high intracranial pressure, and to compare these findings with findings in healthy adult volunteers. METHODS: We reviewed retropectively the MR imaging examinations of 15 patients who were referred with objectively decreased visual acuity and funduscopic findings of optic papilla elevation. T1-weighted and T2-weighted axial MR images were obtained by using conventional spinecho acquisitions on 1.5-T MR imagers. In addition, the MR imaging studies in 10 healthy adult volunteers without visual impairment were reviewed as controls. RESULTS: In 10 (67%) of the 15 patients, visual elevation of the optic papilla was shown by MR imaging. In all 15 patients, the MR signal intensity of the optic papilla was hypointense relative to the vitreous of the globe on T2-weighted images. In the healthy volunteer group, the optic papillae were all similarly hypointense relative to the vitreous of the globe on T2-weighted images; however, these optic papillae were flat. CONCLUSION: Clinical examination and MR imaging may show elevation of the optic papilla in patients with high intracranial pressure. When chronic, optic papilla elevation has been shown to correlate well with severe loss of vision. Actual edema of the optic papilla seems to play little role in the physical elevation observed clinically in the chronic stages of this pathologic process.

Adolescent↗
PubMed1995

Magnetic resonance versus computed tomographic imaging in acute stroke.

BACKGROUND AND PURPOSE: This study was an attempt to determine whether CT and MRI are comparable or if one is superior to the other in the early detection of ischemic stroke or hematoma. METHODS: Patients with acute stroke were sought within 3 hours of onset for clinical examination and prospective evaluation by concurrently performed CT and MRI. Repeated clinical and imaging studies were undertaken when possible immediately after imaging and at 24 hours, 3 to 5 days, and 3 months. The study neurologists were blinded to the results of imaging, as were the study radiologists to the clinical findings. The study radiologists read the scans in sequence, mapping each imaging on standard templates before viewing a later scan. No retrospective revisions of imaging mapping of earlier images were undertaken. RESULTS: Sixty-eight patients were recruited within 4 hours and an additional 12 patients within 24 hours. Seventy-five strokes were due to infarction and five to hemorrhage. The median time to first scan was 132 minutes. Although some of the infarctions in 75 patients were detected within 1 hour, the fraction of positive first scans approached an asymptote at 2 to 3 hours. Overall, with the use of conventional non-contrast-enhanced CT and T1- and T2-weighted MRI, neither was superior in the very early detection of either hematoma or infarction. There was a marginally significant correlation between early positive brain imaging and the severity of the stroke. Some patients had initially positive CT and/or MRI scans, but their neurological examination had returned to normal by 24 hours. Overall, CT was better than baseline MRI at predicting 24-hour outcome. After 24 hours, both CT and MR more conspicuously defined the lesion limits than they did at baseline. CONCLUSIONS: With the technology available through 1991, neither CT nor MRI proved superior in the detection of the earliest signs of stroke.

Adolescent↗
PubMed1995

Brain morphology in first-episode schizophrenia.

OBJECTIVE: Neuroimaging studies have provided robust evidence that schizophrenia is associated with structural brain abnormalities. However, the underlying pathophysiology of these changes is still unknown. By evaluating brain morphology early in the course of illness, confounding effects of treatment and duration of illness are minimized. The goal of this study was to evaluate brain structure in patients early in the course of schizophrenia who had received no or minimal neuroleptics. METHOD: Magnetic resonance imaging was used to evaluate 12 male and 12 female patients experiencing their first episode of schizophrenia (mean duration of psychotic episode = 14 weeks) and 12 male and 12 female normal volunteers equivalent in age, height, and parents' socioeconomic status. A totally automated method was used to analyze scans, yielding volumes of brain tissue and CSF, divided into lobes. RESULTS: The patient group had significantly more total CSF than the comparison subjects. This was accounted for by higher levels of intersulcal CSF as well as ventricular CSF. There were no differences in total volume of brain tissue between the two groups, but patients had a significant regionally specific decrement in frontal lobe tissue compared with the normal subjects. CONCLUSIONS: These findings indicate that structural brain abnormalities are present very early in schizophrenia and may not be due to factors such as treatment or chronicity of illness. Rather, since the abnormalities are present near the onset of the illness, a neurodevelopmental mechanism may be suggested.

Adult↗
PubMed1995

Effects of diagnosis, laterality, and gender on brain morphology in schizophrenia.

OBJECTIVE: Structural neuroimaging and neuropathological studies have demonstrated a variety of aspects of brain morphology that appear to distinguish schizophrenic patients from comparison subjects (diagnostic effects), a predominance of left-sided pathology (laterality effects), and a greater likelihood of brain abnormality among males (gender effects). However, findings have been inconsistent across studies, perhaps reflecting limited power due to small study group sizes. The goal of this study was to examine diagnostic, laterality, and gender effects of brain morphology as assessed by magnetic resonance imaging in a large, carefully evaluated group of schizophrenic and comparison subjects. METHOD: One hundred two patients with schizophrenia (DSM-III-R) (70 men and 32 women) and 87 normal comparison subjects, chosen to be equivalent to the patients in terms of familial socioeconomic background, underwent magnetic resonance imaging with a 1.5-tesla scanner. All regions of interest were outlined manually by an experienced technician on all slices in which they were visualized. Region of interest volumes were compared across groups, and age, sex, and stature were controlled. RESULTS: Schizophrenic patients were found to have larger lateral and third ventricles and smaller thalamic, hippocampal, and superior temporal volumes than comparison subjects. No significant differences were demonstrated for intracranial, cerebral, cerebellar, temporal lobe, caudate nuclei, or temporal horn volumes. There were no significant Laterality by Diagnosis effects and no significant Gender by Diagnosis effects for any of the regions of interest. CONCLUSIONS: Many, but not all, of the hypotheses informed by earlier studies regarding diagnostic effects were confirmed, while hypotheses regarding gender and laterality interactions with diagnosis were not supported.

Adult↗
PubMed1995

Temporal changes of MR findings in central pontine myelinolysis.

We report central pontine myelinolysis in orthotopic liver transplant patients. Sequential MR imaging of these patients with central pontine myelinolysis shows progressive decrease of T2-weighted MR signal in the pons, which may not resolve despite complete neurologic recovery.

Adult↗
PubMed1995

MR staging of acute dural sinus thrombosis: correlation with venous pressure measurements and implications for treatment and prognosis.

PURPOSE: To correlate parenchymal brain changes, venous sinus pressure measurements, and outcome in 29 patients with acute dural sinus thrombosis. METHODS: A retrospective review of 29 patients with angiographically proved acute dural sinus thrombosis was made from January 1989 to December 1993. MR examinations were performed on either a 0.5- or 1.5-T superconductive scanner in multiple planes. Direct dural sinus venography, cerebral angiography, and MR venography were performed. Venous sinus pressure measurements were obtained in 11 of 29 patients. RESULTS: We identified five distinct stages of brain parenchymal changes; each stage correlated with increasing intradural sinus pressure. The pressures measured in this study ranged from 20 to 50 mm Hg. Brain parenchymal changes were reversible up to stage III if thrombolytic treatment was performed. Beyond stage III, there were some residual changes, even after thrombolysis. All stage V patients died. CONCLUSION: Acute dural sinus thrombosis leads to distinct stages of parenchymal changes, the severity of which depends on the degree of venous congestion, which, in turn, is closely related to intradural sinus pressure. As intradural sinus pressure increases, progression from mild parenchymal change to severe cerebral edema and/or hematoma may occur if thrombolysis is delayed.

Acute Disease↗
PubMed1995

The effect of contrast dose, imaging time, and lesion size in the MR detection of intracerebral metastasis.

PURPOSE: To evaluate the effect of MR contrast dose versus delayed imaging time on the detection of metastatic brain lesions based on lesion size. METHODS: Contrast MR examinations with gadoteridol were obtained in 45 patients with brain metastases. The patients were divided into two groups: 16 received cumulative standard dose (0.1 mmol/kg) and 29 received cumulative triple dose (0.3 mmol/kg). Both groups were evaluated at two dose levels (lower dose and higher dose) with two separate injections. Each patient received an initial bolus injection of either 0.05 (cumulative standard dose) or 0.1 (cumulative triple dose) mmol/kg of gadoteridol to reach the lower-dose level and underwent imaging immediately and 10 and 20 minutes later. Thirty minutes after injection, an additional bolus injection of 0.05 (cumulative standard dose) or 0.2 (cumulative triple dose) mmol/kg was administered to reach the cumulative higher-dose level (cumulative standard dose, 0.1 mmol/kg; cumulative triple dose, 0.3 mmol). Images were acquired immediately. RESULTS: There was no difference in the detection rate for lesions larger than 10 mm among T2-weighted, lower-dose immediate and delayed, or immediate higher-dose images in both study groups. Lesions smaller than 10 mm had improved detection with delayed imaging in both study groups; however, the immediate higher-dose studies still had the highest detection rate. CONCLUSION: In the evaluation of small central nervous system metastases, either delayed imaging after the injection of standard contrast dose or higher contrast dose may improve their detection, and therefore affect clinical management. Higher contrast dose (cumulative triple dose) studies appear to be more effective than delayed imaging with standard dose.

Brain↗
PubMed1994

Regional brain abnormalities in schizophrenia measured with magnetic resonance imaging.

OBJECTIVE: To determine general and regional indices of structural brain abnormality in schizophrenia. DESIGN: Case-control comparison study. SUBJECTS: Fifty-two patients diagnosed as having schizophrenia according to the criteria of the Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition, were compared with 90 healthy volunteers recruited from the community. MEASUREMENTS: Structural brain images were acquired using magnetic resonance; measurements were obtained using three-dimensional visualization of volume-rendered brains and an automated atlas-based dissection of specific regions. General measures included the volume of total brain tissue, total cerebrospinal fluid (CSF), and CSF within the ventricular system. Regional measures included the volume of tissue and CSF in the frontal, temporal, parietal, and occipital lobes and the cerebellum. RESULTS: Compared with the controls, the patients had a smaller average volume of total brain tissue and a greater average volume of total and ventricular CSF. A specific relative decrease in brain tissue was found only in the frontal lobes, although the volume of CSF was greater in patients than in controls in all brain regions. CONCLUSION: In addition to the generalized brain abnormalities observed in schizophrenia, a regional abnormality may be present in frontal regions. Since the frontal lobes integrate multimodality information and perform a variety of "higher" cognitive and emotional functions that are impaired in schizophrenia, the frontal abnormality noted is consistent with the clinical presentation of the illness. Impaired frontal function and a disruption in its complex circuitry (including thalamocortical projections) may explain why patients with schizophrenia often have significant deficits in formulating concepts and organizing their thinking and behavior.

Adult↗
PubMed1994

Thalamic abnormalities in schizophrenia visualized through magnetic resonance image averaging.

Schizophrenia is a complex illness characterized by multiple types of symptoms involving many aspects of cognition and emotion. Most efforts to identify its underlying neural substrates have focused on a strategy that relates a single symptom to a single brain region. An alternative hypothesis, that the variety of symptoms could be explained by a lesion in midline neural circuits mediating attention and information processing, is explored. Magnetic resonance images from patients and controls were transformed with a "bounding box" to produce an "average schizophrenic brain" and an "average normal brain." After image subtraction of the two averages, the areas of difference were displayed as an effect size map. Specific regional abnormalities were observed in the thalamus and adjacent white matter. An abnormality in the thalamus and related circuitry explains the diverse symptoms of schizophrenia parsimoniously because they could all result from a defect in filtering or gating sensory input, which is one of the primary functions of the thalamus in the human brain.

Brain↗
PubMed1994

Evaluating and validating two methods for estimating brain structure volumes: tessellation and simple pixel counting.

Developments in imaging technology have made three-dimensional visualization of internal brain structures possible with excellent resolution. Since improved visualization implies improved measurement, these advances hold promise to more accurately measure the volumes of internal structures. As new technologies and techniques emerge, evaluating the relative benefits of measurement methods becomes necessary. We compared and evaluated two methods of estimating volumes from images of brain structures. One method counted pixels within a region of interest, while the other method tessellated the surface between tracings on adjacent slices. Our study assessed both measurement error for true phantom volumes and method disparity for in vivo structures in a randomly selected sample of subjects (n = 100). For our comparisons, we focused on the temporal lobe, ventricular system, and hippocampus. Bias, independence of measurement errors and maximal discrimination of individual differences are properties that are relevant to validating and evaluating measurements of cerebral structure. Pixel counting proved to be the more robust of the two methods, being less sensitive to nuisance-interactions between size of object, shape, and slice thickness. Clinical and research applications of imaging techniques may have distinctive but overlapping needs when evaluating and validating new developments in imaging.

Adult↗
PubMed1994

Initial clinical experience with dextran-coated superparamagnetic iron oxide for detection of lymph node metastases in patients with head and neck cancer.

PURPOSE: To investigate the efficacy of magnetic resonance (MR) imaging with dextran-coated superparamagnetic iron oxide in the differentiation of metastatic and benign nodes in patients with head and neck cancer. MATERIALS AND METHODS: MR imaging was performed before and after intravenous administration of iron oxide in 12 patients. Ninety-one pathologically proved nodes were visually analyzed, and 66 lymph nodes were quantitatively analyzed by measuring signal intensity in visually selected regions of interest. RESULTS: Forty of 42 histologically proved metastatic nodes and 41 of 49 benign nodes were detected, yielding 95% sensitivity and 84% specificity. The signal intensity ratio of benign nodes was substantially lower than that of metastatic nodes, indicating better differentiation of metastatic and benign nodes. Furthermore, 13 of 14 normal-sized nodes were detected. CONCLUSION: MR imaging with iron oxide can enable specific differentiation of metastatic and benign nodes in patients with head and neck cancer. This agent may potentially enhance the detection of metastatic lymph nodes and deserves further investigation.

Adult↗
PubMed1994

Brain parenchymal infection in bone marrow transplantation patients: CT and MR findings.

OBJECTIVE: The purpose of this study was to assess the MR and CT appearance of brain infection after bone marrow transplantation and to correlate the appearances with laboratory and pathologic findings. MATERIALS AND METHODS: We retrospectively reviewed the records of seven bone marrow transplant recipients with radiologic evidence of brain infection. RESULTS: Forty-one lesions were detected in seven patients with proved infectious foci outside the brain before brain infection was suspected clinically. Six patients had low total WBC or lymphocyte counts and one patient had normal total WBC and lymphocyte counts. Most lesions in patients with low total WBC or lymphocyte counts showed no appreciable edema or contrast enhancement. However, all lesions detected in the patient with normal total WBC and lymphocyte counts showed marked vasogenic edema and ring enhancement. CONCLUSION: Brain infection in bone marrow transplant recipients during immunosuppression exhibited MR characteristics different from those typically seen in immunocompetent patients. This appearance may be related to a diminished immunologic/inflammatory response.

Adult↗