Radiology of biological weapons--old and the new?
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Anthrax↗
Biomedical subjects
C C Tchoyoson Lim
Publications and source records attributed to C C Tchoyoson Lim.
Acute symptomatic seizures and hippocampus damage: DWI and MRS findings.
The authors describe diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) changes in the hippocampus within 48 hours of acute symptomatic seizures or status epilepticus in 12 patients. DWI showed increased signal and a decreased apparent diffusion coefficient (ADC) in all patients, with corresponding lactate detected on MRS in six patients and EEG seizure activity in nine patients. On follow-up, the atrophic hippocampus had an increased ADC in six patients. DWI and MRS may predict development of hippocampal sclerosis.
Adolescent↗
Cerebral perfusion mapping using a robust and efficient method for deconvolution analysis of dynamic contrast-enhanced images.
Dynamic contrast-enhanced (DCE) imaging using MRI or CT is emerging as a promising tool for diagnostic imaging of cerebral disorders and the monitoring of tumor response to treatment. In this study, we present a robust and efficient deconvolution method based on a linearized model of the impulse residue function, which allows for the mapping of functional cerebral parameters such as cerebral blood flow, volume, mean transit time, and permeability. Monte Carlo simulation studies were performed to study the accuracy and stability of the proposed method, before applying it to clinical study cases of patients with cerebral tumors imaged using DCE CT. Functional parameter maps generated using the proposed method revealed the locations of the cerebral tumors and were found to be of sufficiently good clarity for marked regional differences in tissue vascularity and permeability to be assessed. In particular, tumor visualization and delineation were found to be better on the parameter maps that were indicative of the breakdown of the blood-brain barrier.
Adenoma↗
Singapore National Medical Image Resource Centre (SN.MIRC): a world wide web resource for radiology education.
Radiology education is heavily dependent on visual images, and case-based teaching files comprising medical images can be an important tool for teaching diagnostic radiology. Currently, hardcopy film is being rapidly replaced by digital radiological images in teaching hospitals, and an electronic teaching file (ETF) library would be desirable. Furthermore, a repository of ETFs deployed on the World Wide Web has the potential for e-learning applications to benefit a larger community of learners. In this paper, we describe a Singapore National Medical Image Resource Centre (SN.MIRC) that can serve as a World Wide Web resource for teaching diagnostic radiology. On SN.MIRC, ETFs can be created using a variety of mechanisms including file upload and online form-filling, and users can search for cases using the Medical Image Resource Center (MIRC) query schema developed by the Radiological Society of North America (RSNA). The system can be improved with future enhancements, including multimedia interactive teaching files and distance learning for continuing professional development. However, significant challenges exist when exploring the potential of using the World Wide Web for radiology education.
Computer-Assisted Instruction↗
A distributed parameter model of cerebral blood-tissue exchange with account of capillary transit time distribution.
Quantitative estimates of physiological parameters associated with cerebral blood flow can be derived from the analysis of dynamic contrast-enhanced (DCE) images, using an appropriate model of the underlying tissue impulse residue function. The theoretical formulation of a distributed parameter model of tissue microcirculation, which accounts for the effects of capillary permeability and transit time distribution, is presented here. This model considers a statistical distribution of capillary-tissue units, each described by a distributed parameter model that accounts for convective transport within the capillary and transcapillary axial diffusion. Monte Carlo simulations were performed to study the confidence of the parameter estimates, and the model was used to analyze DCE CT images of patient study cases with metastatic cerebral tumors. The tumors were found to yield significantly higher estimates than normal tissues for the parameters associated with the extravasation of tracer and for the standard deviation of capillary transit times. The proposed model can be used with DCE imaging to study the microcirculatory characteristics of cerebral tumors.
Aged↗
Imaging collateral circulation: magnetic resonance angiography and perfusion magnetic resonance imaging at 3 T.
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Adult↗
Giant spinal ganglioneuroma.
Ganglioneuromas are rare benign tumours, which may affect any part of the spine and spinal cord. They occasionally grow to a large size but total excision using microsurgical techniques is often possible, and may be curative. This case report illustrates the clinical and histopathological features of two rare giant ganglioneuromas of the spinal cord.
Adult↗
Malformations of cortical development: high-resolution MR and diffusion tensor imaging of fiber tracts at 3T.
Patients with malformations of cortical development and epilepsy may have a variety of abnormal brain findings, including abnormal gyral patterns, cortical thickening, decreased volume of white matter, and increased diffusion of white matter. The status of individual white matter fiber tracts, however, is unknown. We present a case of bilateral frontal schizencephaly and subcortical heterotopia and illustrate alterations of white matter fascicles by combined structural and functional diffusion tensor imaging at 3 T.
Adult↗
Comparison of magnetic resonance spectroscopy and perfusion-weighted imaging in presurgical grading of oligodendroglial tumors.
OBJECTIVE: Oligodendroglial tumors form an uncommon, but distinct, subgroup of gliomas with longer survival, better treatment response, and characteristic genetic alterations. Noninvasive grading of oligodendroglial tumors using functional and metabolic magnetic resonance imaging may be helpful in guiding the treatment approach and predicting malignant transformation of these tumors. We used perfusion-weighted magnetic resonance imaging and proton magnetic resonance spectroscopic imaging (MRSI) to predict the oligodendroglioma grade. METHODS: Twenty-four patients with pathologically confirmed oligodendrogliomas underwent dynamic contrast-enhanced perfusion-weighted magnetic resonance imaging and/or proton MRSI before surgery. We assessed the ability of tumor contrast enhancement, normalized cerebral blood volume, normalized choline, and the presence of either lactate or lipid metabolites to correctly predict the World Health Organization tumor grade. The accuracy of tumor grading using each method was also compared. RESULTS: Tumor contrast enhancement (P = 0.069) and normalized cerebral blood volume (P = 0.181) were not significantly different between low and high-grade oligodendrogliomas. The MRSI measurement of normalized choline was significantly higher in high-grade (2.82 +/- 0.64) than in low-grade (1.62 +/- 0.46) oligodendrogliomas (P < 0.001), and the presence of lactate or lipid metabolites also correctly predicted high-grade tumors (P = 0.014). The maximum accuracy of contrast enhancement, normalized cerebral blood volume, normalized choline, and lactate or lipid metabolites in grading oligodendroglioma was 71, 83, 90, and 85%, respectively. CONCLUSION: MRSI measurements are more accurate than perfusion-weighted magnetic resonance imaging or conventional contrast enhancement in differentiating oligodendroglial tumor grade. In these inherently vascular tumors, metabolic measurements of mitosis and necrosis may be better than measures of neovascularity in presurgical grading.
Adolescent↗
MRI findings in Susac's syndrome.
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Adult↗
Dynamic contrast-enhanced CT of intracranial meningioma: comparison of distributed and compartmental tracer kinetic models--initial results.
Dynamic contrast material-enhanced computed tomographic images of intracranial meningioma were analyzed by using both distributed-parameter and conventional compartmental tracer kinetic models. The distributed-parameter models were found to yield consistently better fitting of data sets than were conventional compartmental models. Although linear correlations were found between the kinetic parameters of the two models, some of these parameters (such as perfusion and mean transit time) did not correspond quantitatively. For all models, the kinetic parameters associated with the extravasation of tracer were found to be distinctly higher in meningiomas than in normal white- and gray-matter tissues.
Contrast Media↗
Medical Image Resource Center--making electronic teaching files from PACS.
A picture archive and communications system (PACS) is a rich source of images and data suitable for creating electronic teaching files (ETF). However, the potential for PACS to support nonclinical applications has not been fully realized: at present there is no mechanism for PACS to identify and store teaching files; neither is there a standardized method for sharing such teaching images. The Medical Image Resource Center (MIRC) is a new central image repository that defines standards for data exchange among different centers. We developed an ETF server that retrieves digital imaging and communication in medicine (DICOM) images from PACS, and enables users to create teaching files that conform to the new MIRC schema. We test-populated our ETF server with illustrative images from the clinical case load of the National Neuroscience Institute, Singapore. Together, PACS and MIRC have the potential to benefit radiology teaching and research.
Computer Communication Networks↗
Large artery ischaemic stroke in severe acute respiratory syndrome (SARS).
Of the 206 patients who contracted Severe Acute Respiratory Syndrome (SARS) in Singapore five developed large artery cerebral infarctions. Four patients were critically-ill and three died. Intravenous immunoglobulin was given to three patients. An increased incidence of deep venous thrombosis and pulmonary embolism was also observed among the critically-ill patients. We believe our experience warrants an increased vigilance against stroke and other thrombotic complications among critically-ill SARS patients in future outbreaks, especially if treatment such as intravenous immunoglobulin, that increases pro-thrombotic tendency, is contemplated.
Adult↗
Combined MR spectroscopic imaging and diffusion tensor MRI visualizes corticospinal tract degeneration in amyotrophic lateral sclerosis.
Motor neuron damage and cortical spinal tract (CST) degeneration are pathological features of amyotrophic lateral sclerosis (ALS). We combined whole-brain diffusion tensor imaging (DTI) and three-dimensional magnetic resonance spectroscopic imaging (MRSI) to study the CST at different locations. Eight ALS patients were compared with normal controls. Fractional anisotropy (FA) and mean diffusivity (MD), and the ratio of N-acetyl-aspartate (NAA) to creatine (Cr) were measured at various locations in the CST, including the subcortical white matter (SWM), centrum semiovale (CS), periventricular white matter (PV), posterior limb of the internal capsule (PIC) and cerebral peduncle (CP). Patients showed significantly lower FA than controls in the CST, including the SWM, CS, PV and PIC. Although there was a trend towards elevated MD in ALS patients, this did not reach statistical significance. NAA/Cr ratios were also decreased in ALS patients compared with normal controls, with significant differences in the SWM and PV but not in PIC. Combined whole-brain DTI and MRSI can detect axonal degeneration in ALS. Measurements of FA obtained in the SWM, CS, PV and PIC, and NAA/Cr ratios in the SWM and PV yield the most robust results.
Adult↗
Combined diffusion-weighted and spectroscopic MR imaging in Creutzfeldt-Jakob disease.
A 49-year-old woman presented with progressive dementia. Diffusion-weighted MR images showed abnormalities in the cerebral cortex as well as the putamen and caudate head bilaterally. MR spectroscopic imaging revealed marked asymmetric decrease of normal metabolites in the right basal ganglia, with concordant hypoperfusion on single photon emission computed tomography. Diffusion-weighted MR imaging is more sensitive to cortical involvement in sporadic Creutzfeldt-Jakob Disease, and MR spectroscopy may yield evidence of asymmetric involvement. Combined functional and metabolic MR imaging may be useful in studying CJD.
Brain↗
Susac syndrome: serial diffusion-weighted MR imaging.
Susac syndrome (SS) is a clinical triad of hearing loss, retinal artery occlusion and encephalopathy. The typical MR imaging findings of multiple focal lesions in the corpus callosum and subcortical white matter can be easily misdiagnosed as multiple sclerosis. On diffusion-weighted (DW) MR imaging, new lesions were hyperintense, with reduced apparent diffusion coefficient (ADC). These lesions later became less prominent or hypointense on subsequent DW MR imaging. Serial DW imaging and ADC maps may be useful in differentiating SS from demyelinating diseases.
Adrenal Cortex Hormones↗
Neuropsychiatric sequelae of Nipah virus encephalitis.
The authors followed nine patients with Nipah virus encephalitis over the course of 24 months. Eight of the nine developed psychiatric features assigned to the encephalitis. Three patients developed major depressive disorder immediately after recovering from the encephalitis, and two developed depression approximately 1 year after the outbreak. Two patients developed personality changes, and two suffered chronic fatigue syndrome. Neuropsychological testing was accomplished in eight of the nine patients. Deficits in attention, verbal, and/or visual memory were substantial in seven of the eight patients tested. Verbal memory was more impaired than visual memory in these patients. Comparison between psychiatric and cognitive impairment and total number of brain lesions showed no discernible trends.
Adult↗
Spinal schwannoma with acute subarachnoid hemorrhage: a diagnostic challenge.
We report a case of spinal intradural schwannoma presenting with intracranial subarachnoid hemorrhage. Cerebral angiography studies were negative, but MR imaging of the spine revealed a large hemorrhagic tumor in the thoraco-lumbar junction. The tumor was misdiagnosed as ependymoma of the conus medullaris. This case illustrates the importance of a high index of suspicion for spinal disease in angiographically-negative subarachnoid hemorrhage and pitfalls in MR diagnosis of thoraco-lumbar tumors.
Acute Disease↗