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Biomedical subjects

N M Alpert

Publications and source records attributed to N M Alpert.

At least 127 records · Page 7Linked to original sources
PubMed1983

An ambulatory ventricular function monitor: validation and preliminary clinical results.

A device for the continuous measurement of left ventricular (LV) function was tested in a series of 34 subjects. The instrument consisted of 2 arrays of radiation sensitive cadmium telluride detectors held in place over the region of the left ventricle and lung by a vest-like garment (hence the name VEST). The VEST electronic instrumentation included analog-to-digital converters, a battery pack, microprocessor and gating device, which were worn in a back pack. Data generated by the VEST, including the digitized average electrocardiogram, RR interval, counts/13 ms in each radiation detector, and time since commencement of data recording, were recorded on a cassette tape recorder every 2 minutes for subsequent analysis. At the conclusion of conventional multigated blood pool imaging, the VEST was positioned and worn by the subjects while supine, standing in place and walking. The correlation of ejection fraction calculated independently from the VEST and scintillation camera data was greater than 0.95. The inter-record reproducibility of the ejection fraction measured by the VEST in sedentary subjects was less than 3%.

Ambulatory Care↗
PubMed1983

Effects of reduced coronary flow on thallium-201 accumulation and release in an in vitro rat heart preparation.

To study the relation between myocardial thallium-201 (TI-201) uptake, TI-201 release, and reduced coronary flow, isolated Langendorff rat hearts (n = 8) were perfused for 3 hours at constant flows ranging from physiologic (12 ml/min) to severely ischemic (1.5 ml/min); thallium activity was monitored with a scintillation probe. Each heart was perfused for 1 hour with thallium buffer, followed by 2 hours with thallium-free buffer at the same flow rate. Accumulation curves for all 4 flows were monoexponential. However, release curves during the 2 hours of washout with thallium-free buffer demonstrated a biexponential configuration. The early fast release component decreased with reductions in coronary flow, and the later slow release component did not vary significantly with flow. These data show that thallium clearance has at least 2 components: a rapid (possibly extracellular) component related to coronary flow and a slow (possibly intracellular) component independent of coronary flow. These findings should be useful in providing a better understanding of thallium redistribution observed clinically.

Animals↗
PubMed1983

Quantitation of regional cerebral glucose metabolism.

Kinetic analysis of 18F-labeled 2-fluoro-2-deoxy-D-glucose (2FDG) has been carried out in 28 studies on 25 subjects. The object of the analysis was to determine the practical problems of quantitation of glucose metabolic rate (GMR) using the Sokoloff model with 2FDG. We found that arterial and venous plasma concentration of 2FDG yielded equivalent values of the integrated plasma concentration (IPC*) and that one arterial or venous plasma sample at 30 min serves to predict IPC* to within +/- 7%. These observations suggest that quantitation is indeed possible in such subjects without using complex arterial or venous sampling procedures. The average values of K1, K2, and K3 are observed to be 0.14 +/- 0.08, 0.20 +/- 0.10, and 0.030 +/- 0.012 min-1. The data are consistent with a value of lumped constant of 0.4 and a considerable spread in global values of GMR (30%) in an unselected group of subjects.

Blood Glucose↗
PubMed1983

Effects of ischemic-like insult on myocardial thallium-201 accumulation.

Despite extensive clinical use of thallium-201 (201TI) for myocardial imaging, the effect of ischemia on myocardial accumulation and release of 201TI independent of flow has not been fully defined. Therefore, myocardial accumulation of 201TI in response to ischemic-like myocardial injury was assessed in vitro using the cultured fetal mouse heart preparation. Cultured fetal mouse hearts (n = 311) were subjected to injury simulating ischemia by deprivation of oxygen and oxidizable substrates for periods ranging from 15 minutes to 10 hours. The extent of irreversible injury was determined by the percentage of lactic dehydrogenase (LDH) lost from the hearts to the culture medium during recovery from injury. Injury was essentially reversible at 1 hour of insult. The fraction of 201TI content in injured compared with control hearts was not significantly lower after 1 hour of insult. By 3 hours of insult, irreversible injury as assessed by loss of LDH was detectable and the extent of injury increased progressively through 10 hours. During the 3-10-hour period of irreversible injury, 201TI accumulation within injured hearts compared with controls was related in a monotonically decreasing fashion to the loss of LDH as described by a mathematical kinetic model that fit the observations closely (R2 greater than 0.99). These results indicate that in this organ culture preparation, in which there is effectively an unlimited reservoir of 201TI and no confounding effects of perfusion, the time-dependent 201TI accumulation is determined by the extent of irreversible injury.

Animals↗
PubMed1983

Cerebral blood flow and cerebrovascular CO2 reactivity in stroke-age normal controls.

We used the noninvasive 133-xenon inhalation technique to determine cerebral hemodynamics in 55 normal volunteers aged 18 to 88. Values for cerebral blood flow and cerebrovascular CO2 reactivity in fast-clearing tissue (flow gray) and slow-clearing tissue (flow white) were examined as functions of age and in relation to hematocrit, blood pressure, and evidence of extracranial vascular disease. Flow gray declined linearly with age, but no corresponding change was found in flow white or in CO2 reactivity. The data suggest that the progressive fall in flow gray is due to a physiologic aging process.

Adolescent↗
PubMed1983

A variable angle slant-hole collimator.

A variable-angle slant-hole (VASH) collimator was constructed to show the feasibility of using multiple sliding plates to achieve a range of collimator channel inclinations. One hundred and sixty tungsten plates, 0.125 mm thick and 14 cm square, were photoetched to produce 3025 1.5-mm2 holes in each plate, separated by 0.8-mm septa. Along with the collimator holes, registration holes and positioning grooves were also etched. The plates were placed in a holder and stacked to form a collimator 2.0 cm high. The holder permitted the plates to be "sheared" to achieve viewing angles from 0 to 40 degrees from the vertical. Resolution and sensitivity were determined both across and along the shear directions. Resolution of a thin Tc-99m source, 1.24 mm diam and 7 cm long, located 5 cm from the collimator face in air, was 1.1 cm FWHM at 0 degree shear and remained unchanged with increasing slant. The resolution was similar both across and along the shear plane. Sensitivity was determined with a point source placed 7 cm from the collimator face. At 0 degree slant the sensitivity was 169 cps/MBq (6.24 csp/mu Ci). A general all purpose (GAP) collimator had a FWHM of 1 cm for the line source in air at 5 cm, and a sensitivity of 205 cps/MBq (7.58 cps/mu Ci) for the point source at 7 cm. The data suggest that a variable-angle slant-hole collimator can be constructed of laminated plates.

Evaluation Studies as Topic↗
PubMed1982

Positron brain imaging--normal patterns and asymmetries.

Regional brain physiology was investigated in 11 normal resting right-handed subjects using positron emission tomography. Cerebral blood flow was studied in all subjects. Cerebral oxygen metabolism was studied in six subjects, and cerebral glucose metabolism was also studied in one subject. In five subjects, physiological activity was higher in left frontotemporal regions than right. These findings may be related to structural cerebral asymmetries or to activation of brain language centers.

Adult↗
PubMed1981

Positron imaging in ischemic stroke disease using compounds labeled with oxygen 15. Initial results of clinicophysiologic correlations.

Initial results in over 50 patients with stroke suggest that positron images made during continuous inhalation of carbon dioxide labeled with oxygen 15 and molecular oxygen labeled with oxygen 15 provide data on tissue function that may be relevant to acute stroke management. Five cases illustrate the following findings: 15O-activity patterns observed in areas of ischemic injury or infarction are what one would expect if the 15O distributions represented physiologic functions, such as cerebral blood flow and metabolism. Areas of abnormal 15O activity correlate with the clinical or computed tomographic (CT) localization of the deficit. In studies performed acutely, changes in 15O distributions anticipate alterations in CT scans and may be predictive of outcome. Data related to oxygen metabolism correlate better with tissue viability than do those reflecting cerebral blood flow.

Aged↗
PubMed1981

F-18-labeled 3-deoxy-3-fluoro-D-glucose for the study of regional metabolism in the brain and heart.

Glucose is the major physiological substrate of the brain and an important physiological substrate for the myocardium. [19F]fluoro-3-deoxy-glucose [3-FDG(F-18)] was studied to determine whether it is a suitable tracer for evaluating the metabolic function of the brain and myocardium. 3-FDG(F-18) was rapidly accumulated in the mouse myocardium (10-12% injected dose/g) and remained constant up to 120 min. Blood, liver, and lung activities exhibited a rapid accumulation of activity (4% injected dose/g) at 1 min, followed by elimination of activity up to 30 min (2% injected dose/g), and then remaining unchanged for a period of 120 min. The arterial blood curve in the dog was fit best by three exponential components (T 1/2 = 0.52 min, 2.75 min, and 142.8 min). Transverse-section images were obtained of the dog's brain and myocardium. From sequential two-dimensional images, a clearance half-time of 26.88 min was determined for the canine brain. Radiation doses for man were calculated from tissue distribution data for mice.

Animals↗
PubMed1979

Noninvasive estimation of pulmonary arterial pressure by analysis of pulmonary blood-flow distribution.

To determine whether a correlation exists between pulmonary arterial (PA) pressure (Pa) and the distribution of pulmonary blood flow, this distribution was measured in four upright dogs in the control state and during intravenous infusions of epinephrine or prostaglandin F2 alpha. During suspension of respiration, 15 mCi of Xe-133 were injected intravenously, and perfusion and equilibration lung images were recorded with a scintillation camera. The procedure was performed several times on each dog, with and without pharmacological elevation of PA pressure by 5 to 50 cm H2O. For each scintigram, the relative blood flow per unit ventilated lung volume (F) was plotted against centimeters above the hilum (h). Pulmonary arterial pressure was derived from each curve, assuming the relation F = B(Pa - hD)2, where B = constant and D = specific gravity of blood. Calculated PA pressure correlated strongly (r = 0.83) with measured PA pressure, suggesting a possible means of noninvasive estimation of PA pressure.

Animals↗
PubMed1978

A model for regional cerebral oxygen distribution during continuous inhalation of 15O2, C15O, and C15O2.

Equilibrium positron brain scans were obtained during continuous inhalation of C15O, C15O2, and 15O2. Inhalation of C15O labels hemoglobin, whereas C15O2 instantaneously labels stable water to H215O. During the continuous inhalation of 15O2, body tissues extract it from the blood in proportion to local metabolism and ultimately convert it to water of metabolism. After 6-8 min of inhalation, a steady-state equilibrium is established in which the inflow of tracer is balanced by its disappearance due to radioactive decay (T1/2 = 2 min) and biologic removal. Mathematical models of the steady-state distributions of C15O, C15O2/H215O, and 15O/H215O are derived. The major results are: a) The steady-state distribution of C15O is insensitive to variations in blood flow and essentially measures blood volume. b) The distribution of H215O during inhalation of C15O2 is dependent, though nonlinearly, on blood flow. c) The distribution of H215O during inhalation of 15O2 depends linearly on the oxygen extraction fraction and nonlinearly on blood flow. d) The dependence on blood flow in the 15O2 steady-state image can be removed by the division, point by point, of the 15O2 image by the C15O2 image.

Brain↗
PubMed1976

Initial assessment of a simple functional image of ventilation.

Several methods for quantitatively measuring regional ventilation using an inert gas such as Xe133 have been described. One such method provides a functional image of washout. A particularly simple functional image may be derived from the mean transit time for clearance. Regional ventilation may thus be represented as a single image in which the spatial distribution of washout from multiple small regions of the lung is displayed. In 100 patients for whom such a functional image of ventilation was obtained, the functional image was found to be generally more useful and easier to interpret than sequential images taken during the period of washout. Distributions of half-time (t1/2) for washout and the mean transit time (t) in the same population were similar in shape, but the t distribution peaked about 15 sec later than the t1/2 distribution. The mathematical simplicity of the functional image described here should permit its implementation on virtually any nuclear medicine computer system.

Adult↗
PubMed1975

NUMEDICS: a system for on-line data processing in nuclear medicine.

A multiterminal system --NUMEDICS--has been developed to study the problems of on-line acquisition, processing, and display of scintigraphic data. The hardware-software configuration of NUMEDICS permits simultaneous and independent operation of terminals in the Division of Nuclear Medicine, the Physics Research Laboratory, and the Cyclotron Laboratory of the Massachusetts General Hospital. This paper describes the hardware and software developments in NUMEDICS which have been proven to be of value in clinical and research applications. These features are illustrated by applications to the evaluation of left ventricular performance, three-dimensional imaging, and functional imaging of rCBF.

Nuclear Medicine↗
PubMedDate not supplied

Using locations to store shape: an indirect effect of a lesion.

This study had three general points. First, it examined possible visual consequences of frontal lesions. A patient with focal damage to the subcortical regions of the left frontal lobe, and a small amount of damage near Broca's area, was predicted to have impaired brain function in posterior regions that are anatomically connected to the damaged site. Second, it showed the utility of using positron emission tomography (PET) in conjunction with magnetic resonance imaging to characterize "functional lesions." PET revealed reduced metabolism in posterior cortical loci that are innervated by fibers from the damaged regions. Some of the affected areas are hypothesized to be involved in visual functions, specifically the encoding of lines and edges. Third, a series of tests was designed to document that the patient had difficulty encoding visual stimuli, and then to distinguish among alternative possible causes of this deficit. The results suggested that the patient encoded shapes as sets of filled locations if possible, which allowed him to use intact processes subserved by brain areas that were not affected by the damage. The data were best explained if the lesion slowed processing in the ventral system (which encodes object properties), allowing the dorsal system (which encodes spatial properties) to produce a response more quickly than the ventral system.

Adult↗