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S T Hecht

Publications and source records attributed to S T Hecht.

34 records · Page 2Linked to original sources
PubMed1991

Hemodynamics of the central nervous system arteriovenous malformation nidus during particulate embolization. A computer model.

We have modelled the hemodynamics of the nidus of the central nervous system (CNS) arteriovenous malformation (AVM) during the process of particulate embolization. The model accurately reproduces the visually apparent incremental slowing observed during such embolization of CNS AVMs. The model is simple and proposes that the nidus is composed of many identical microchannels. As the microchannels are occluded by particles at a constant rate, the rate of change of flow reduction with each bolus of emboli constantly increases exponentially. A rapid reduction in apparent flow rate occurs immediately prior to complete occlusion. With a more accurate understanding of the working of the nidus of CNS AVMs we can increase the safety of therapeutic particulate embolization.

Cerebrovascular Circulation↗
PubMed1991

Primary CT diagnosis of abdominal masses in a PACS environment.

Whether the display medium--film versus cathode ray tube (CRT)--affects observer performance during interpretation of computed tomographic (CT) images is an important research issue in these times of implementation and growth of picture archiving and communications systems in radiology. The authors performed a multiobserver receiver operating characteristic (ROC) study to determine the performance of radiologists who read abdominal CT studies displayed on film, as well as on a high-resolution workstation (video monitor) that made use of three different display modes. A total of 166 examinations were evaluated by eight radiologists, who recorded their ordinal confidence ratings of the demonstration of presence or absence of abdominal masses. ROC analysis showed small differences in the confidence ratings assigned by individual readers for the detection and interpretation tasks. Results for the group as a whole showed no significant reduction or improvement in observer performance when ratings for any one of the workstation display modes were analyzed. The results of this study demonstrate that current CRT display technology is adequate for enabling the primary detection of abdominal masses with CT examinations.

Abdominal Neoplasms↗
PubMed1990

Use of acetazolamide-challenge xenon CT in the assessment of cerebral blood flow dynamics in patients with arteriovenous malformations.

Arteriovenous malformations (AVMs) may cause symptoms related to a reduction of cerebral blood flow (CBF) to surrounding brain parenchyma. To evaluate this compromise of hemodynamic reserve (commonly referred to as steal phenomenon), we used acetazolamide challenge and stable-xenon CT (Xe/CT). Baseline Xe/CT studies in 13 patients with AVMs were followed by an acetazolamide challenge to the vascular reserve. Blood flow maps were quantitated by using region-of-interest (ROI) software. ROI findings were categorized into four groups on the basis of the presence or absence of normal baseline CBF and presence or absence of normal augmentation of CBF. ROIs were designated as near site (within the vascular territory supplying the AVM) or far site (outside the vascular territory supplying the AVM). One patient had a normal baseline and normal augmentation of CBF (group 1). The other patients had a combination of one or more of the other three categories. Ten patients had parenchymal areas that exhibited either a normal or low baseline CBF with decreased augmentation; both conditions were interpreted as decreased vascular reserve (groups 2 and 3). Eleven patients had parenchymal areas that showed a low baseline CBF and normal augmentation with acetazolamide (group 4), interpreted as having a decreased demand for CBF but having a normal vascular reserve. Decreased vascular reserve was found in 27% of the nearsite areas and 17% of the far-site areas. No patients had only far-site abnormal vascular reserve. We believe that compromised vascular reserve can best be evaluated with a challenge study, such as this acetazolamide-challenge Xe/CT study.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetazolamide↗
PubMed1983

Intracranial hemorrhage: late onset in the preterm neonate.

Neonatal intracranial hemorrhages usually occur during the first week of life. Late intracranial hemorrhages have rarely been reported. Seventeen infants were identified whose hemorrhages occurred after the first postpartum week. The latest hemorrhage occurred eight weeks postpartum. Most of the hemorrhages were small and restricted to the region of the germinal matrix. Sixteen of the infants were premature, with an estimated postconceptual age at the time of hemorrhage of 33 weeks or less.

Cerebral Hemorrhage↗
PubMed1982

CT localization of occult secretory tumors in children.

Three seemingly occult secretory tumors in children (pheochromocytoma, ganglioneuroblastoma and islet cell carcinoma) were localized within the abdomen by computed tomography after other diagnostic imaging procedures had failed. The superb density resolution and tomographic formating of CT images make CT uniquely suited for the demonstration of small abdominal lesions. CT is recommended as a primary imaging modality for secretory tumors in children.

Adenoma, Islet Cell↗
PubMed1982

Pneumocystis carinii pneumonia in homosexual men.

The clinical records and radiographs of 12 homosexual men with symptomatic biopsy-proved Pneumocystic carinii pneumonia were reviewed. At presentation, the most common radiographic finding in the chest was a diffuse, coarse, ground-glass pattern. Normal findings on chest radiographs or only minimal abnormalities did not preclude P. carinii pneumonia. Progression of the radiographic findings varied. Rapid development of diffuse consolidation in 2--5 days occurred most commonly. Thoracic lymphadenopathy and pleural effusions were each seen in two patients. Clearing of the lungs often took many weeks. Six of the 12 patients died in 2 weeks to 8 months. In the appropriate clinical setting, early transbronchial biopsy should be strongly advocated to ensure initiation of suitable antimicrobial therapy.

Adult↗
PubMed1981

Endotracheal tube orifice abutting the tracheal wall: a cause of infant airway obstruction.

Effects of endotracheal tube and infant head positions upon the orientation of the beveled tube orifice to the tracheal wall were studied in living infants receiving ventilatory assistance and in infant cadavers. Radiographs of infant cadavers showed that when the endotracheal tube orifice faces one direction and the infant's head faces the opposite direction, the tube orifice can abut the tracheal wall and thus obstruct the airway. This obstructive relationship was more readily produced with relatively high tube positions (above the level of T1) and/or with full neck flexion. Measurement of mean pulmonary resistance in living infants showed a position-dependent increase above the baseline of up to 487% (from 31 to 182 cm H2O/l/sec) when the tube orifice abutted the tracheal wall. The radiologist who observes the tube orifice against the tracheal wall should alert the clinician immediately so that endotracheal tube alignment can be adjusted to relieve obstruction.

Airway Obstruction↗
PubMed1976

Rapid method for the detection and identification of mycolic acids in aerobic actinomycetes and related bacteria.

A rapid method for the identification of lipids characteristic of the genera Corynebacterium, Mycobacterium, Nocardia, and the "rhodochrous group" has been developed. Modifications of previously described methods make this procedure suitable for use in the clinical laboratory. Thin-layer chromatography is used to demonstrate the presence of the lipid characteristic of Nocardia spp. (type A) in some corynebacteria, nocardias, and members of the "rhodochrous group." Precipitation in ether and ethanol is used to demonstrate the presence of mycobacterial mycolic acids. Since this procedure can be carried out in less than 2 days and the lipids are extracted from the same batch of cells grown for diaminopimelic acid and whole-cell sugar analyses, it can readily be added to the battery of tests performed in reference laboratories that deal with aerobic actinomycetes and related bacteria.

Actinomycetales↗
PubMedDate not supplied

Palliative embolization of fibrosarcoma for control of tumor-induced hypoglycemia.

A 77-year-old woman with prior long-standing insulin-dependent diabetes presented with malignant hypoglycemia secondary to insulin-like substances excreted from a large unresectable fibrosarcoma of the left thigh. Partial embolization of the tumor supply from the deep femoral artery was performed using 150-250 microns polyvinyl alcohol foam particles. After embolization, the patient's serum glucose levels reverted to normal and she could be discharged from the hospital.

Aged↗
PubMedDate not supplied

Impaired cerebral vasoreactivity after embolization of arteriovenous malformations: assessment with serial acetazolamide challenge xenon CT.

Embolization of a portion of the nidus of an arteriovenous malformation not only may alter hemodynamics within the nidus, but also may change blood flow dynamics in adjacent normal vessels. Sequential acetazolamide-challenge xenon CT cerebral blood flow studies were performed in eight patients before and after embolization of arteriovenous malformations to assess the hemodynamic effects on the major vascular territories supplying the malformation. Acetazolamide is a potent cerebral vasodilator, and its administration combined with cerebral blood flow studies allows assessment of cerebral vasoreactivity. In seven of the eight patients, one or more parenchymal areas exhibited a normal cerebral blood flow augmentation response to acetazolamide before embolization, but diminished acetazolamide flow augmentation was seen after embolization, indicating abnormal vasoreactivity. We found that the decrease in vasoreactivity peaked 6-10 days after embolization. In one of the eight patients, a temporary delayed neurologic deficit developed during a period of impaired cerebral vasoreactivity following embolization. Our results suggest that embolization of an arteriovenous malformation can induce vasoreactivity changes in adjacent normal vessels. Because these changes appear to be somewhat time-dependent, an appropriate interval should be observed between embolization stages or before surgical resection of an arteriovenous malformation following embolization to allow hemodynamic equilibration to occur. Acetazolamide challenge combined with serial cerebral blood flow studies following embolization enables determination of this hemodynamic equilibration.

Acetazolamide↗
PubMedDate not supplied

Treatment of arteriovenous malformations of the brain with combined embolization and stereotactic radiosurgery: results after 1 and 2 years.

Seven patients with large arteriovenous malformations (AVMs) of the brain were selected for combined therapy with particulate embolization, followed by radiosurgery of the residual nidus. The goal of embolization was to reduce the patient nidus to a size that facilitated successful stereotactic radiosurgery. Angiograms obtained 1 and 2 years after radiosurgery were evaluated for changes in nidus size, flow rate, and feeding and draining vessels. One year after stereotactic radiosurgery, one AVM was angiographically undetectable. Three other AVMs demonstrated a volume reduction of greater than 50%, in addition to decreased shunt speed and altered angioarchitecture at 1-year follow-up. At 2-year follow-ups, two of seven AVMs were cured, and an additional two of seven had a greater than 98% reduction in nidus volume. Although one patient experienced a transient deficit from embolotherapy, none of our patients suffered a new neurologic deficit or a hemorrhage during the follow-up period. Our data support the efficacy of combined embolotherapy and radiosurgery for definitive therapy of selected large AVMs of the brain.

Adult↗
PubMedDate not supplied

Blood pressure changes in feeders to cerebral arteriovenous malformations during therapeutic embolization.

We recorded blood pressures in feeding arteries of cerebral arteriovenous malformations with microcatheters before, during, and after embolization in awake patients. Our embolization results corroborate reports of intraoperative measurements that show an immediate increase in blood pressure after ligation. Demonstration of abrupt hemodynamic changes gives additional credence to the theory of normal perfusion pressure breakthrough and to theories of neurologic change based on vascular steal phenomena. Furthermore, pressure changes occurred earlier than visible slowing of flow during the embolization, suggesting that this is a more sensitive guide with which to monitor the progress of the embolization than is serial angiography.

Adult↗
PubMedDate not supplied

Failure as teacher.

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Aged↗