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Biomedical subjects

J G Hirsch

Publications and source records attributed to J G Hirsch.

At least 19 recordsLinked to original sources
PubMed2004

Detection of delayed focal MR changes in the lateral hippocampus in transient global amnesia.

BACKGROUND: There is still limited knowledge on the location and etiology of transient global amnesia (TGA). MR studies including diffusion-weighted imaging (DWI) have been unable to demonstrate consistently the location and underlying pathology of TGA. OBJECTIVE: To investigate patients with TGA using serial DWI performed from the day of symptom onset through days 1 and 2. METHODS: After reporting negative DWI results in a previous study, the authors used a modified study design to investigate patients with TGA using serial DWI performed from the day of symptom onset through days 1 and 2. RESULTS: Of 31 consecutive patients studied, 26 developed a small, punctate DWI lesion in the lateral aspect of the hippocampal formation (pes and fimbria hippocampi) on either side (left, n = 15; right, n = 6) or bilaterally (n = 5). Lesions were rarely noted in the hyperacute phase (n = 2), but all became visible regularly at 48 hours. CONCLUSIONS: The study confirms the involvement of hippocampal parenchyma in the pathophysiology of TGA. The delayed detectability of the lesions may explain the incongruence of previous MR DWI studies in TGA patients.

Adult↗
PubMed2003

Clinicotopographical correlation of corticospinal tract stroke: a color-coded diffusion tensor imaging study.

UNLABELLED: Background- Small capsular strokes are difficult to assess with regard to the precise location and the extent of pyramidal tract damage with conventional brain imaging. Color-coded diffusion tensor imaging (CDTI) provides a means to visualize the course of the corticospinal tract within the white matter. In addition to T2-weighted MRI, diffusion-weighted MRI and CDTI were used to analyze the topographical patterns of small lacunar corticospinal tract strokes. METHODS: We examined 15 patients with pyramidal tract strokes in the subacute phase (days 3 to 7). Lesions were identified on diffusion-weighted MRI and superimposed on CDTI images. The anatomic location and pattern of the lesion were visualized on CDTI with regard to the corticospinal tract and subsequently compared with the clinical presentation. In addition, infarct areas were evaluated with quantitative parameters: mean diffusivity and lattice anisotropy index of lesions were determined. RESULTS: We identified 5 different patterns of corticospinal tract stroke falling into 2 clinical subgroups: (1) those with marked deficits and minor improvement (6/15) and (2) those with good recovery (9/15). Group 1 had long lesions centered in the pyramidal tract, involving the basal ganglia (anterior choroidal artery); group 2 lesions were very small and/or located anteriorly and medially (periventricular anterior choroidal artery territory; thalamogeniculate, tuberothalamic, and lateral striate branches). Lesions showed a significant increase of mean diffusivity and decrease of lattice anisotropy. CONCLUSIONS: CDTI allows in vivo differentiation of distinct subcortical stroke subtypes. Improved anatomic definition of lesion localization using CDTI may help in better establishing the prognosis for patients after subcortical stroke.

Aged↗
PubMed2001

Acute and chronic changes of the apparent diffusion coefficient in neurological disorders--biophysical mechanisms and possible underlying histopathology.

Diffusion-weighted imaging (DWI) of the brain has become a valuable tool for the reliable detection and diagnosis of several neurological disorders. Although DWI is in wide use in daily practice, the underlying biophysical mechanisms that contribute to changes in the apparent diffusion coefficient (ADC) are still under discussion. Alterations in the apparent water diffusion rate reflect pathological changes in the brain tissue state, via changes in the diffusion characteristics of the intra- and extra-cellular water compartments including restricted diffusion, water exchange across permeable boundaries, the concept of the extra-cellular tortuosity and the intra- and extra-cellular volume fraction. A reduction of the ADC has been detected in acute neurological diseases, while disease states associated with dominant acute vasogenic edema formation or chronic tissue destruction usually show elevations of the ADC. Compromise of energy metabolism is likely to contribute to a reduction of the ADC while already minor structural disintegration may contribute to elevations of the ADC.

Acute Disease↗
PubMed2001

[Diffusion tensor imaging (DTI) and functional magnetic resonance tomography (fMRI) expand methodological spectrum in psychiatric research].

In psychiatric research, there is a growing interest in the microstructural and functional characteristics of brain networks, which often form the basis of current etiological concepts. As a result of novel magnetic resonance imaging techniques, the pathogenic characteristics of neuronal activity and connectivity can be examined in a noninvasive, safe, and repeatable manner. Functional magnetic resonance imaging (fMRI) uses blood oxygenation level-dependent (BOLD) measures for identifying the gray matter contribution to cognition. Diffusion tensor imaging (DTI) reveals the course and structural integrity of white matter projections. Because DTI does not require special motivation and performance, group differences in psychiatry are more easily interpreted in terms of underlying pathology. To date few studies have tried to investigate both, i.e. dynamic and microstructural data in the sense of a modern multi-dimensional investigation approach. The combination of both techniques, however, seems to offer a promising vehicle to further extent our current understanding of mental disorders and to identify populations at risk. In addition to addressing findings in psychiatric research, the present article presents a technical overview of DTI and examines the limitations and potential applications of both techniques.

Anisotropy↗
PubMed2000

Failure to demonstrate peri-infarct depolarizations by repetitive MR diffusion imaging in acute human stroke.

BACKGROUND AND PURPOSE: Peri-infarct depolarizations (PIDs) have been demonstrated with diffusion-weighted MRI (DWI) in experimental stroke and are regarded as an important mechanism of ischemic injury. We tested the hypothesis that PIDs are of relevance for the early enlargement of human brain infarcts. METHODS: Ten stroke patients were investigated by repetitive imaging of the apparent diffusion coefficient (ADC) in the acute phase (7 patients) or subacute phase (3 patients) of developing cortical infarction. In each patient, 20 ADC maps were obtained from serially measured echo-planar DWI (interval of 45 seconds). Data analysis focused on the potential spatial and temporal ADC changes, including structured qualitative analysis, calculation of subtraction images, serial analysis of regions of interest positioned in the infarct core and border, and calculation of hemispheric lesion areas, depending on various ADC thresholds ranging between 0 and 800 microm(2)/s. RESULTS: Data analysis was unable to disclose any time-dependent changes in ADC that would resemble PID. In ischemic regions, the ADC reduction significantly progressed from the infarct border (555+/-96 microm(2)/s) to the infarct core (431+/-104 microm(2)/s, P:<0.01). CONCLUSIONS: By using an MRI protocol with high temporal resolution and elaborated postprocessing, we were unable to demonstrate a pattern of diffusion changes that would be indicative of PID in human stroke. Experimental infarction and human stroke may differ in the detectability of PID.

Acute Disease↗
PubMed1999

Comparison of diffusion anisotropy measurements in combination with the flair-technique.

Fluid-attenuated inversion recovery (FLAIR) technique offers an effective tool to diminish partial-volume averaging effects from cerebrospinal (CSF) signal with in vivo magnetic resonance imaging. CSF-suppressed and unsuppressed direction-dependent diffusion-weighted (DW) images are obtained with a DW spin-echo EPI sequence in a single acquisition scheme. Comparison of unsuppressed and CSF-suppressed apparent diffusion coefficient (ADC) maps yields consistent values for brain tissue in volunteers when no partial-volume effects are expected, but differs considerably at borders of parenchyma to ventricles and sulci. From theory and phantom studies, a corrected anisotropy index is introduced considering differences of statistical fit errors. Anisotropy of white matter is observed in normal brain of volunteers. Anisotropy index maps reveal destruction of fiber tracts in pathologic areas. Results of a preliminary study on 12 patients with intra-axial tumors indicate an improved delineation of tumor boundaries of FLAIR ADC maps against unsuppressed acquisition.

Adult↗
PubMed1999

Suicide and violence prevention: parent education in the emergency department.

OBJECTIVE: To determine prospectively whether parental receipt of injury prevention education is associated with new action limiting access to lethal means and if so, what action was taken for which means. METHOD: Prospective follow-up of 103 adults whose children made an emergency department visit for mental health assessment or treatment. Record review assessed whether hospital staff provided injury prevention education. Logistic regression was used to determine the likelihood of new caretaker action limiting access to the following potentially lethal means: firearms, alcohol, prescription medications, and over-the-counter medications. RESULTS: Significant associations were found between exposure to injury prevention education and action to limit access (adjusted odds ratio = 3.6, 95% confidence interval = 1.1-12.1, p = .04). Five of 8 adults whose households contained firearms took new action to limit access after injury prevention education, whereas none of the 7 firearm-owning families who did not receive injury prevention education took new action to limit firearm access. Similar patterns were seen for other means. Adults more often chose to lock up rather than dispose of lethal means. CONCLUSIONS: Injury prevention education should be provided to parents during child/adolescent emergency department mental health-related visits. Potential for violence prevention is real because parents do take new action to limit access to lethal means when means restriction education is provided.

Adolescent↗
PubMed1978

Understanding the adolescent patient.

The chapter has presented a frame of reference with which to approach adolescent patients with skin disease. To be most effective, the physician must understand the complexities of adolescent development and the various biological, social, and psychological circumstances and reactions with which young people must cope. Suggestions are made regarding approaches to the management of the adolescent skin patient, in the wish to maximize the usefulness of the physician--patient relationship as a resource for helping young people to health and happiness.

Adaptation, Psychological↗
PubMed1976

Physiopathologic responses of the rhesus monkey to live Escherichia coli.

The present study was designed to develop an animal model applicable to the clinical patient in the investigation of the pathogenesis of septic shock. The model currently described is a lightly anesthetized, unrestrained monkey, carefully monitored during a 24 hour observation period. Varying doses of live Excherichia coli organisms were infused intravenously during a 30 minute period, and a variety of hemodynamic, respiratory and metabolic parameters were monitored. Doses of organisms varied between 7.6X10(9) and 3.0X10(11) organisms per kilogram of body weight, and there was no obvious correlation between size of dose and survival time. Two of nine experimental monkeys survived the Excherichia coli, while times of death of the remaining monkeys varied between three and 27 hours. Two control monkeys, not administered organisms, survived the 24 hour period with minimal changes in all measured parameters. Results reveal two patterns in response to organism administration. These were early acute death, after three to four hours, and prolonged life, death after 20 to 27 hours. The acute response was characterized by marked systemic hypotension, hypoglycemia, hypoinsulinemia, increased lactate level, decreased pH or respiratory depression. The other type of response involved profound sustained hypotension with hypoglycemia and hypoinsulinemia in most monkeys and elevations in lactate, blood urea nitrogen potassium creatinine, serum glutamicoxalacetic, lactic dehydrogenase and fractionatedlactic dehydrogenase levels. Depressions in respiration were not evident in the group which survived a longer period of time. Renal fibrin thrombi, prominent in baboons administered Escherichia coli, were absent in the rhesus monkey regardless of the size of the dose of organisms. The results of this study suggest the operation of a multifactiorial mechanism in septic shock with interactions between hemodynamic and metabolic factors varying within the species.

Animals↗
PubMed1975

Assessment in vitro of immunity against Toxoplasma gondii.

Studies have been made on humoral and cellular immune respones in mice immunized with an attenuated strain of Toxoplasma gondii. Heat-inactivated antitoxoplasma serum did not cause morphologic changes in the organisms, but did markedly influence their interactions with host cells. Toxoplasma exposed to antibody were no longer capable of entering fibroblasts or HeLa cells. They were readily engulfed by macrophages, but the antibody treatment strikingly altered the intracellular fate of the parasites leading to killing and digestion of the toxoplasmas in phagolysosomes. Addition of antitoxoplasma antibody immediately after infection of macrophages in vitro had no effect on intracellular multiplication of the organism. The division time of virulent toxoplasmas in mouse peritoneal macrophages in vitro was markedly prolonged in cells from immunized mice. During the first 2-3 mo after immunization, the macrophages harvested from the peritoneal cavity demonstrated this cellular immunity directly; thereafter exposure of the macrophages to immune lymphocytes and toxoplasma antigen, or to supernates from such an interaction was required for induction of the maximal capacity to inhibit growth of toxoplasmas. Induction of the alternation in macrophages by the lymphocyte product was detectable in 6 h and maximal at 18-24 h. Cultivation in vitro of macrophages from immunized animals for periods longer than 48 h rendered the cells nonresponsive to the immune lymphocyte-toxoplasma product. Macrophages from the peritoneal cavities of normal, nonimmunized mice were also incapable of developing the capacity to inhibit growth of toxoplasmas in response to this product. The nonresponsiveness of normal macrophages, or of macrophages cultured for several days in vitro was not changed by exposure of the cells to antitoxoplasma serum.

Animals↗