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M Ashtari

Publications and source records attributed to M Ashtari.

43 records · Page 3Linked to original sources
PubMed1990

Boron neutron capture enhancement of 252Cf brachytherapy.

Dosimetric and radiobiological studies were undertaken to investigate the potential enhancement in dose, dose distribution and cell killing effectiveness of 252Cf brachytherapy achievable when boron-10 enriched compounds are incorporated into simulated 252Cf brain implants. Thermal neutron distributions in a human head phantom containing a 252Cf source were measured by gold foil activation and calculated using a 1-dimensional transport code. This information was then used to modify measured event size distributions for 252Cf neutrons to determine the corresponding increase in dose and dose equivalent throughout the phantom. The addition of subtoxic levels of boron-10 to a typical 252Cf implant was found to significantly enhance both the absorbed dose and the high LET event frequency at distances of 3 to 5 cm from individual sources. Some unexpected geometric considerations are discussed. Reduced survival of cultured Chinese hamster cells correlated with the predicted increase in absorbed dose from the capture events with a concentration of about 60 micrograms 10B per ml in the culture medium. It was found that boron increased alpha (the "single-hit" parameter of the linear quadratic survival model) by 32% and decreased beta (the "double-hit" parameter) by 8%. The alpha/beta ratio increased to 4.34 Gy in the presence of boron, from 3.03 Gy in its absence. This translated to an 8% reduction in californium dose needed to effect 10% cell survival. It is concluded that there is a sufficiently high thermal neutron fluence present during californium brachytherapy for boron neutron capture dose augmentation to be feasible.

Animals↗
PubMed1990

Reduced temporal limbic structure volumes on magnetic resonance images in first episode schizophrenia.

Pathomorphology of the limbic system has been described in post-mortem studies of schizophrenia. To determine whether this could be detected in living patients and was not secondary to the treatment or the chronicity of the disease itself, we measured the volumes of the hippocampus-amygdala complex and adjoining temporal horns of 34 patients in their first episode of schizophrenia and 25 normal volunteers using T1 weighted contiguous coronal magnetic resonance images of 3.1 mm width. The results demonstrate abnormal medial temporal lobe morphology in a subgroup of patients at the onset of their illness. There were clear laterality effects and sex differences: hippocampal tissue was significantly smaller only in the left hemisphere of male patients, whereas enlargement of the whole temporal horn or its anterior portion was present on the left side in both sexes. Dysfunction of the limbic mesiotemporal structures might explain some of the clinical features of the disease.

Adolescent↗
PubMed1990

Computerized volume measurement of brain structure.

Morphometric analysis of brain structures recently has become a main focus of interest in studies of some neuropsychiatric diseases. Limitations in imaging and mensuration methodology that is available currently for quantitative measurement of anatomic structures have prompted the development of a computerized system to study brain morphometry. A menudriven semi-automated computer system has been developed to assess in vivo brain morphometry using three-dimensional (3-D) magnetic resonance (MR), gradient echo, contiguous images of the whole brain. Accuracy of the system was tested with phantoms creating white on black contrast to simulate the brain tissue surrounded by subarachnoid cerebrospinal fluid (CSF), and a second set of phantoms creating black on white contrast to simulate the ventricular system in the brain tissue. The first set of phantoms was composed of three water-filled balloons (spherical, elliptical, and multiform) and a fresh postmortem brain. The second set of phantoms consisted of three rods of different diameters from a simple geometric plexiglass rod phantom and a life size cast of a human ventricular phantom. System accuracy was generally within 2.0% of the true volumes. System reliability was evaluated in three patient populations; 12 patients with Alzheimer's disease, nine with schizophrenia and nine healthy controls age-matched to the patients with Alzheimer's disease. Two independent observers measured the ventricular systems of these patients. Reliability of the system was addressed by the correlation between the two sets of measurements. For the sample as a whole, and each of the subgroups, the correlation between the two observers was 0.99. This system compares favorably with other morphometric methods reported.

Cerebral Ventricles↗
PubMed1985

Therapeutic dosimetry for Cf-252 neutron brachytherapy of pelvic cancer.

252Cf (Cf) was used to treat tumors of the cervix and uterus with neutron brachytherapy (NT) in an ongoing clinical trial. Tandem and ovoids insertions were used and combinations of single and multiple applications along with high dose whole pelvic irradiation. Dosimetric analysis of treated cases for patterns of tissue dose were carried out. Tissue dose for Cf-NT was, in general, high for neutron components in the central pelvis only, and fell off rapidly with distance from the applicators. The majority and balance of therapeutic dose was contributed by low linear energy transfer (LET) high energy photon beam radiation to the whole pelvis. Comparison with fast neutron beam therapy (NBT) isodose curves showed that much more homogeneous neutron dose was delivered to the pelvic tumor and organs by NBT. Complication frequency has been reported to be higher for neutron beam therapy than for Cf-NT. It appears that the higher integral neutron biological dose to normal tissues for NBT compared to intracavitary Cf-NT probably contributed to the frequency of side effects.

Brachytherapy↗
PubMedDate not supplied

Abnormalities of the septum pellucidum on MR scans in first-episode schizophrenic patients.

PURPOSE AND METHODS: Cavities in the septum pellucidum have been widely regarded in clinical neurology or in autopsy series as incidental findings of little clinical importance; however, an association between this developmental anomaly and a diagnosis of psychosis has been reported. We compared MR brain scans of schizophrenic patients with normal control subjects to determine the prevalence of this finding in the two groups: RESULTS: A cavum septum pellucidum was found in 14 of 62 (23%) schizophrenic patients and only one of 46 control subjects (2%). Pronounced enlargement of the cavum septum and a cavum vergae were seen only in two schizophrenic subjects. A partial agenesis of the corpus callosum was also seen in one of the schizophrenic cases with the largest cavum septum pellucidum. CONCLUSIONS: The increased prevalence of a cavum septum pellucidum, the cavum vergae, and partial callosal agenesis in schizophrenics support the hypothesis that anomalous development of the brain is an important aspect of this disorder. The disturbed structures are closely linked developmentally to the limbic system which has been implicated etiologically in studies of schizophrenia.

Adult↗
PubMedDate not supplied

Three-dimensional fast low-angle shot imaging and computerized volume measurement of the hippocampus in patients with chronic epilepsy of the temporal lobe.

This study investigated the use of three-dimensional fast low-angle shot (FLASH) imaging and computer-assisted morphometry for identifying hippocampal changes associated with unilateral temporal lobe seizures. Contiguous 3.1-mm coronal FLASH images were obtained in 28 patients with electroencephalographically verified left (n = 17) or right (n = 11) temporal lobe seizures and 28 age- and sex-matched control subjects. Hippocampal volumes were calculated with the use of a computerized mensuration system developed for detailed morphometric assessment. The results of a multivariate analysis of variance revealed a significant group difference by hemisphere interaction (F = 26.3, p less than .001). Significant reductions in left hippocampal volume (32%, p less than .001) were exhibited in patients with left temporal lobe seizures, and significant reductions in right hippocampal volume (35%, p less than .001) were seen in patients with right temporal lobe seizures. A discriminant analysis with the use of left and right hippocampal volumes classified patients with left temporal lobe seizures with 94% sensitivity and 73% specificity and patients with right temporal lobe seizures with 89% sensitivity and 94% specificity. The results of this study demonstrate that unilateral temporal lobe seizures are accompanied by significant reductions in hippocampal volume ipsilateral to the seizure focus. The use of FLASH imaging and computer-assisted morphometry of the hippocampus appears to provide valuable structural information for confirming the laterality of the electroencephalographic seizure focus.

Adolescent↗