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Biomedical subjects

V P Mathews

Publications and source records attributed to V P Mathews.

At least 55 records · Page 3Linked to original sources
PubMed1993

Regional brain atrophy in HIV-1 infection: association with specific neuropsychological test performance.

Quantified magnetic resonance imaging (MRI) was related to neuropsychological (NP) test scores in an asymptomatic HIV-1 seropositive group, a non-demented AIDS/ARC group, a group of subjects with HIV-1 dementia, and a seronegative control group. The MRIs were quantified using three planimetric measures of brain structure: the bicaudate ratio (a measure of caudate region atrophy), the bifrontal ratio (a measure of frontal region atrophy), and the ventricle to brain ratio (a measure of overall cerebral atrophy). Cognitive performance was assessed with standard NP tests. Significant correlations between the MRI ratios and many of the NP tests were observed. Of the tests grooved pegboard, part B of the trail making test, the verbal fluency test, and the digit span forward were associated with MRI abnormalities. The bicaudate ratio was most closely associated with the NP tests. These findings indicate that ventricular enlargement, especially in the region of the caudate, is closely related to poor NP test performance in HIV-1 infection.

Acquired Immunodeficiency Syndrome↗
PubMed1992

MR imaging of cerebral perfusion by phase-angle reconstruction of bolus paramagnetic-induced frequency shifts.

Phase-angle images are acquired dynamically during bolus paramagnetic contrast injection and demonstrate a phase-enhancement effect in perfused cerebral tissues. Signal-to-noise is comparable to that of susceptibility-based signal loss (delta R*) images. Assuming that phase shift is proportional to the tissue paramagnetic agent concentration, as supported by experimental data, the integrated area of the phase time response curves estimated the relative gray to white matter blood volume as 1.8:1 and was sensitive to acute ischemia. The relation between tissue phase shift and concentration is considered.

Animals↗
PubMed1992

Magnetic resonance evaluation of stroke.

Stroke is not a specific disease but is, instead, a symptom complex reflecting destruction of brain tissue by cerebrovascular disease. Several different specific diseases are included in the "stroke" category, including intra- and extracerebral hemorrhage as well as ischemic infarction. These different types of stroke have major differences regarding etiology, management, and prognosis. The goal of stroke imaging is to diagnose the type of stroke at clinical presentation, allowing prompt and appropriate management. Magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and magnetic resonance spectroscopy (MRS) provide powerful noninvasive means to evaluate the pathologic and metabolic changes that occur in acute stroke. These techniques allow the early detection of stroke and greatly increase the ability to determine the etiology of the stroke. One or more of these methods will surely become a standard means of evaluating acute stroke. The information provided, combined with new stroke therapies, should result in improved patient outcome.

Acute Disease↗
PubMed1992

Imaging of neurodegenerative diseases.

Neuroimaging of degenerative brain disorders has continued to advance, primarily with MR imaging, single-photon emission CT, and positron emission tomography. Information gained from these morphologic and functional imaging studies provides insight into the pathologic and pathophysiologic changes associated with these diseases. Recent papers relating to various neurodegenerative disorders such as Alzheimer's disease, vascular dementias, acquired immunodeficiency syndrome-related dementia, Pick's disease, Huntington's disease, progressive supranuclear palsy, and others are reviewed and discussed.

AIDS Dementia Complex↗
PubMed1990

Neuroimaging of disseminated germ cell neoplasms.

The purpose of this study was to determine the role of neuroimaging in the management of patients with metastatic germ cell tumors. Retrospective evaluation of 299 patients treated in 1986 and 1987 for initial presentation or recurrence of testicular, retroperitoneal, and mediastinal germ cell tumors was performed to determine indications for neuroimaging, frequency and site of CNS metastases, and occurrence of other CNS abnormalities. Sixty-six patients required CNS imaging with myelography, CT, or MR. Studies were normal in 24 patients. Twenty patients had CNS metastases including 11 with intracranial metastases, eight with spine lesions, and one with both brain and spine involvement. Sixteen had cerebral or cerebellar atrophy of unclear origin and functional significance. Two patients had ventriculomegaly without symptoms of hydrocephalus. Four patients had questionable lesions that were never confirmed. None of the 25 asymptomatic patients with elevated serum tumor markers had brain metastases. Fifteen of 17 patients with focal neurologic deficits and three of six patients with seizures had CNS metastases. CNS imaging to detect germ cell tumor metastases is most useful in the presence of neurologic deficits or seizures but is not useful in patients with unexplained elevation of serum tumor markers in the absence of neurologic deficits.

Adolescent↗
PubMed1989

Dyke award. Gd-DTPA-enhanced MR imaging of experimental bacterial meningitis: evaluation and comparison with CT.

Gd-DTPA-enhanced MR images of experimental bacterial meningitis were obtained after Staphylococcus aureus was inoculated directly into the cisterna magna of four dogs. Each animal was studied with both unenhanced and enhanced MR and CT with Gd-DTPA and meglumine iothalamate, respectively. The enhancement patterns resulting from these techniques were compared and images were correlated with histopathology. All animals demonstrated abnormal leptomeningeal enhancement on MR with Gd-DTPA, but only one of four dogs exhibited abnormal contrast enhancement on CT. In these animals Gd-DTPA-enhanced MR also identified complications of meningitis, such as ventriculitis and cerebritis, more effectively than CT did. Unenhanced MR was not helpful in identifying meningitis. Histologic evaluation demonstrated that the abnormal areas of contrast enhancement on MR and CT correlated with inflammatory cell infiltration. However, some regions of mild leptomeningitis, ependymitis, and cerebritis identified histologically did not demonstrate abnormal enhancement. Since the animal model used was clinically and pathologically similar to human meningitis, we propose that Gd-DTPA-enhanced MR will subsequently be found more effective than unenhanced MR and IV contrast-enhanced CT for demonstrating meningitis and its complications in humans.

Animals↗
PubMedDate not supplied

Effects of contrast dose, delayed imaging, and magnetization transfer saturation on gadolinium-enhanced MR imaging of brain lesions.

This paper discusses the types of paramagnetic agents available for clinical brain imaging and reviews investigations that have sought to optimize the use of these agents by varying the administered dose, delaying the imaging time after contrast administration, and altering image contrast by using magnetization transfer saturation pulses.

Blood-Brain Barrier↗
PubMedDate not supplied

Quantitation of proton NMR spectra of the human brain using tissue water as an internal concentration reference.

The use of cerebral water as an internal intensity standard for the quantitation of spatially localized proton spectra of the human brain is investigated. The method is validated on standard samples of N-acetyl aspartate (NAA) and lactate, and possible sources of error are discussed. Using the STEAM pulse sequence, concentrations of choline, creatine and NAA in frontal lobe white matter are found to be 1.9 +/- 0.5, 10.6 +/- 1.3 and 16.6 +/- 2.3 mumol/g wet wt, respectively, in 10 normal volunteers. In the thalamus, the concentrations are 2.0 +/- 0.4, 11.6 +/- 2.0 and 17.2 +/- 1.3 mumol/g wet wt, respectively. Choline and creatine concentrations are in good agreement with conventional biochemical values: NAA concentrations are found to be three-fold higher, suggesting overlap of the NAA signal with other compounds. Quantitation relative to tissue water is a convenient and rapid means of quantitating proton spectra of the human brain.

Adult↗
PubMedDate not supplied

Cortical activation response to acoustic echo planar scanner noise.

PURPOSE: Our goal was to determine the distribution of auditory and language cortex activation in response to acoustic echo planar scanner noise with functional MRI (fMRI). METHOD: Acoustic scanner noise and spoken text, reproduced on high output cassette tape, were separately delivered at equivalent intensities to six normal hearing adult volunteers through earphones during fMRI data acquisition. In nine other subjects, taped scanner noise was delivered in five successive iterations of the task to assess the consistency of cortical activation to the noise stimulus. Gyri of the auditory and language system were divided into 10 different subregions for analysis of cortical activation. The number of activated pixels and proportion of volunteers activating each cortical subregion were determined using a cross-correlation analysis. RESULTS: Cortical activation to taped acoustic scanner noise was present within the transverse temporal gyrus (primary auditory cortex) in all subjects, but activation was highly variable between subjects in auditory association and language relevant cortex. Auditory association cortex activation was seen in the planum polari, planum temporali, and middle temporal gyrus/superior temporal sulcus regions in one-half to two-thirds of the volunteers. There was no significant difference in the distribution of cortical activation within individual subjects across five successive iterations of the scanner noise task. Listening to spoken text consistently activated primary and association auditory cortex bilaterally as well as language relevant cortex in some cases. The mean number of activated pixels was significantly greater for text listening than acoustic scanner noise in auditory association and language relevant cortical subregions (p < 0.01), although the distribution of activity was similar between the two tasks. CONCLUSION: This preliminary investigation suggests that the complex sounds produced by the echo planar pulse sequence can activate relatively large regions of auditory and language cortex bilaterally, with the extent of activation outside the primary auditory cortex being variable between subjects. However, the distribution of activation within individual subjects was relatively constant across several iterations of the scanner noise stimulus.

Adult↗
PubMedDate not supplied

Acoustic echoplanar scanner noise and pure tone hearing thresholds: the effects of sequence repetition times and acoustic noise rates.

PURPOSE: Our goal was to determine the effects of acoustic echoplanar scanner noise on pure tone hearing thresholds in normal volunteers and to determine the influence of echoplanar sequence repetition time on threshold effects. METHOD: With use of a calibrated audiometer, pure tones ranging from 125 to 8,000 Hz were delivered monaurally to 10 normal-hearing volunteers in a quiet MR scanner suite and in the presence of acoustic scanner noise produced by three separate single shot blipped echoplanar pulse sequences varying only in repetition time (TR = 1,000, 2,000, or 3,000 ms), with all other parameters including the number of slices held constant. The magnitude of noise-induced threshold changes and the slopes of the threshold curves produced by each of the three echoplanar pulse sequences were then analyzed using multiple comparisons and a least significant difference method. The shapes of the threshold curves produced in each background state were best fit using a quadratic effect for frequency in a mixed effects linear model and compared using F test statistics. RESULTS: All of the volunteers demonstrated entirely normal hearing thresholds throughout the full range of tonal frequencies tested (< 25 dB) when no acoustic scanner noise was present in the scanner suite. Pure tone hearing thresholds significantly increased (p < 0.01) in the presence of acoustic scanner noise, with the magnitude of change inversely proportional to the repetition time and therefore the rate of periodic noise production by the echoplanar sequence used. The shape of the threshold curve in the presence of noise produced by the 1,000 ms TR sequence was not equivalent across the frequency spectrum tested but had a quadratic distribution with peak effects at 750-2,000 Hz. As the repetition time was increased and the periodic noise rate decreased, the magnitude of the noise-induced threshold changes significantly lessened (p < 0.01) and the quadratic distributions of the threshold curves changed significantly (p < 0.01), tending toward a more planar configuration. CONCLUSION: Background acoustic echoplanar scanner noise can significantly increase pure tone thresholds in the optimal frequency hearing range (125-8,000 Hz). However, the threshold effects are not equivalent across the frequency spectrum, and the magnitude of threshold changes is dependent on the rate at which periodic acoustic scanner noises are produced for a given sequence repetition time.

Acoustic Stimulation↗
PubMedDate not supplied

Depiction of intracranial vessels with MRA: utility of magnetization transfer saturation and gadolinium.

PURPOSE: The purpose of this work was to quantitate the individual and combined effects of magnetization transfer (MT) saturation and gadolinium (Gd) on the visualization of intracranial vessels with MR angiography (MRA). METHOD: Thirty-five subjects underwent two three-dimensional time-of-flight MRA sequences without and with MT and/or Gd. There were 14 MR angiograms without Gd or MT, 18 with MT only, 17 with Gd only, and 21 with both Gd and MT. On a projection image, a region of interest was drawn to delineate the arteries in the middle cerebral artery territory. The total area of blood vessels in the region of interest was calculated for each MR angiogram. Mean vessel areas for the four types of MRA were compared with analysis of variance. RESULTS: MRA with either MT or Gd alone showed significantly more vessel area than MRA without either (p < 0.05). MRA with MT alone and MRA with Gd alone were not different from each other (p = 0.29). The improvement in vessel area measured by using MT and Gd together was significantly more than expected from the cumulative improvement of adding each alone (p < 0.05). CONCLUSION: Combining MT and Gd synergistically improved the visualization of intracranial vessels on MRA.

Adult↗
PubMedDate not supplied

Comparison of fMRI and intraoperative direct cortical stimulation in localization of receptive language areas.

PURPOSE: The purpose of this work was to compare the cortical localization of receptive speech using functional MRI (fMRI) and direct intraoperative electrical stimulation. METHOD: Three strongly right-handed patients with primary neoplasms of the left parasylvian region underwent fMRI while subjected to a passive listening task designed to activate receptive language areas. All three subjects then underwent awake intraoperative language mapping using direct electrical stimulation of the cortex. RESULTS: In all three subjects, similar, but nonidentical, cortical regions were identified as involved in receptive language function by fMRI and direct cortical stimulation mapping. CONCLUSION: fMRI provides excellent receptive language mapping, but its results must be interpreted with caution due to conceptual and technical differences from direct cortical stimulation mapping.

Auditory Cortex↗
PubMedDate not supplied

The jugular foramen: a review of anatomy, masses, and imaging characteristics.

A variety of lesions may occur in the jugular foramen, arising from the structures normally found within the jugular foramen or from contiguous structures. The most common jugular foramen lesions are nontumoral pseudolesions (eg, asymmetrically enlarged jugular foramen, high or protruding jugular bulb) and tumors (eg, paraganglioma, metastasis). In nontumoral pseudolesions, computed tomography (CT) demonstrates smooth, intact margins of the jugular foramen. Turbulent or slow flow in a high or protruding jugular bulb can result in loss of the flow void and contrast enhancement at magnetic resonance (MR) imaging, thereby mimicking real disease. Use of flow-sensitive techniques or MR angiography will help clarify confusing cases. In cerebral venous thrombosis, CT findings are often normal. At conventional MR imaging, flow-related enhancement and in-plane, turbulent, or slow flow can cause loss of the flow void and thus mimic thrombosis. Consequently, phase-contrast MR venography is the imaging modality of choice in the assessment of cerebral venous thrombosis. Most tumoral lesions of the jugular foramen manifest at CT as areas of infiltrative bone destruction, although schwannoma and meningioma cause smooth enlargement of the jugular foramen. In addition, most of these tumors have low to intermediate signal intensity on T1-weighted MR images and intermediate to high signal intensity on T2-weighted MR images and enhance strongly after the administration of contrast material. Careful analysis of these imaging features and correlation with clinical manifestations can allow a more specific diagnosis.

Brain Diseases↗
PubMedDate not supplied

Imaging features and clinical significance of perineural spread or extension of head and neck tumors.

Perineural spread of head and neck tumors is a form of metastatic disease in which tumor disseminates to noncontiguous regions along the endoneurium or perineurium. Both computed tomography (CT) and magnetic resonance (MR) imaging can help detect perineural spread, although MR imaging is the modality of choice because of its multiplanar capability, its superior soft-tissue contrast, and the decreased amount of artifact from dental hardware. Perineural spread most commonly occurs in adenoid cystic carcinoma and squamous cell carcinoma. Nerve enlargement may lead to foraminal enlargement and, ultimately, to foraminal destruction, findings that are best seen at CT. Extension through the foramen ovale and involvement of the Meckel cave is best seen on coronal T1-weighted MR images, and nerve enhancement is best seen on fat-suppressed T1-weighted MR images. Other radiologic findings include obliteration of fat planes at foraminal openings, neuropathic atrophy, cavernous sinus enlargement, and replacement of the trigeminal subarachnoid cistern with soft tissue. The pathway of perineural tumor spread is predictable with knowledge of the pertinent cranial nerve anatomy; however, patients with radiologically or pathologically proved perineural spread may have normal nerve function at clinical examination. Therefore, it is imperative that the radiologist be familiar with both normal cranial nerve anatomy and the radiologic appearance and assessment of perineural tumor extension.

Cranial Nerve Neoplasms↗
PubMedDate not supplied

AIDS-related CNS cryptococcosis: radiologic-pathologic correlation.

PURPOSE: This study evaluates the effectiveness of cranial CT and MR in detecting autopsy findings of AIDS-related CNS cryptococcosis. METHODS: Final imaging studies compared with pathology were CT in eight patients (five with contrast) and MR in five patients (all with Gd-DTPA). RESULTS: Neither modality effectively identified cryptococcal meningitis. Punctate hyperintensities were seen in all patients with MR and corresponded pathologically to both perivascular spaces dilated by cryptococcal infection and cryptococcomas. Pathologically, cryptococcomas were more common than dilated perivascular spaces. MR detected more cryptococcomas than did CT, but both modalities underestimated the number of lesions seen at autopsy. Contrast enhancement of cryptococcomas and cryptococcal meningitis was uncommon. CONCLUSIONS: CNS cryptococcosis was more effectively demonstrated by MR than by CT, but both modalities underestimated the pathologic extent of the disease. Cryptococcal lesion contrast enhancement was unusual possibly because of the immunocompromised state of our patients and the unique characteristics of the organism itself.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Neuroimaging of disseminated germ cell neoplasms.

The purpose of this study was to determine the role of neuroimaging in the management of patients with metastatic germ cell tumors. Retrospective evaluation of 299 patients treated in 1986 and 1987 for initial presentation or recurrence of testicular, retroperitoneal, and mediastinal germ cell tumors was performed to determine indications for neuroimaging, frequency and site of CNS metastases, and occurrence of other CNS abnormalities. Sixty-six patients required CNS imaging with myelography, CT, or MR. Studies were normal in 24 patients. Twenty patients had CNS metastases including 11 with intracranial metastases, eight with spine lesions, and one with both brain and spine involvement. Sixteen had cerebral or cerebellar atrophy of unclear origin and functional significance. Two patients had ventriculomegaly without symptoms of hydrocephalus. Four patients had questionable lesions that were never confirmed. None of the 25 asymptomatic patients with elevated serum tumor markers had brain metastases. Fifteen of 17 patients with focal neurologic deficits and three of six patients with seizures had CNS metastases. CNS imaging to detect germ cell tumor metastases is most useful in the presence of neurologic deficits or seizures but is not useful in patients with unexplained elevation of serum tumor markers in the absence of neurologic deficits.

Adult↗