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Biomedical subjects

A Kuruc

Publications and source records attributed to A Kuruc.

14 recordsLinked to original sources
PubMed1997

Kinetic analysis of rubidium and thallium as deposited myocardial blood flow tracers in isolated rabbit heart.

Evaluation of myocardial perfusion with tracers such as thallium and rubidium is based on the assumption that tissue tracer content is proportional to flow. The purpose of this study was to evaluate the relationship between flow and tissue tracer content of 201Tl and 83Rb in the isolated perfused rabbit heart. 83Rb (86-day half-life), an isotope that is not used clinically, was used as a subsitute for 82Rb (76-s half-life) to improve the accuracy and precision of data acquisition. The multiple indicator-dilution technique was employed with two independent computational approaches. The first approach explicitly deconvolved 201Tl and 83Rb venous concentration curves by the intravascular reference tracer curve. The second approach used a conventional analysis. Both approaches showed that there was more early washout of 83Rb than 201Tl and that the heart retained 201Tl better than 83Rb within 2 min after isotope introduction. These data indicate that 201Tl is a better perfusion tracer than 83Rb in the isolated rabbit heart.

Animals↗
PubMed1987

Estimating the plasma time-activity curve during radionuclide renography.

Quantitative analysis of the radionuclide renogram requires an estimate of the plasma time-activity curve. This estimate is usually obtained from an externally detected blood-pool curve that is calibrated with a single plasma sample. However, external probes detect activity in the extravascular as well as the intravascular space. This may lead to significant errors in estimating the plasma time-activity curve. A method for overcoming this problem by using a continuously varying calibration factor based upon multiple plasma samples was therefore evaluated. Externally detected blood-pool curves were used to estimate the plasma time-activity curves obtained from rabbits during radionuclide renography. Estimates obtained using the externally detected curves calibrated with a constant calibration factor were found to be significantly biased, while estimates obtained using the externally detected curves calibrated with the continuously varying calibration factor were not.

Animals↗
PubMed1984

Right ventricular and left ventricular ejection fraction in pediatric patients with normal hearts: first-pass radionuclide angiocardiography.

First-pass radionuclide angiocardiography was used to estimate right ventricular (RV) ejection fraction (EF) and left ventricular (LV) EF in infants, children, and teenagers with normal hearts. The right ventricle was analyzed in 74 patients and the left ventricle in 72 patients. Mean RVEF for the group was 0.53 +/- 0.06 (range 0.43 to 0.73); mean LVEF for the group was 0.68 +/- 0.09 (range 0.49 to 0.86). Lower values tended to be present in younger patients. However, there was no statistical difference in EFs between age groups and no linear correlation between magnitude of EF and age or EF and heart rate for either ventricle. Data obtained demonstrated that RVEF and LVEF in children with normal hearts are similar to those in adults with normal cardiovascular systems. A RVEF of 0.41 to 0.47 or a LVEF of 0.50 to 0.59 would suggest borderline systolic function; a RVEF less than 0.41 (mean -2 SD) or LVEF less than 0.50 (mean -2 SD) would be considered abnormal when this technique of first-pass radionuclide angiocardiography is used.

Adolescent↗
PubMed1984

An automated algorithm for radionuclide angiocardiographic quantitation of circulatory shunting.

Circulatory shunting may be quantitated by analysis of time-activity curves obtained from radionuclide angiocardiography. A new automated algorithm for performing this analysis is proposed. The algorithm uses mathematical deconvolution techniques to increase the temporal separation of the components of this curve and thereby improves the accuracy of the analysis. The stability of the algorithm to random data errors was assessed by experiments on simulated time-activity curves degraded with pseudorandom noise. Excellent performance was obtained on a set of test problems previously used in the literature. The algorithm was used to quantitate left-to-right shunting in patients undergoing radionuclide angiocardiography during cardiac catheterization. A strong correlation (r = 0.96) was found between pulmonary to systemic flow ratios (Qp:Qs) obtained using the algorithm on radionuclide angiocardiographic data and Qp:Qs values obtained by oximetry at cardiac catheterization.

Adolescent↗
PubMed1984

Radionuclide estimation of cerebrospinal fluid shunt flow. Evidence supporting an alternative theoretical model.

Flow of cerebrospinal fluid through a surgically implanted valve may be estimated by analyzing the disappearance curve resulting from the injection of a radiotracer into the valve. The standard method for estimating flow assumes an exponential disappearance of the tracer from the valve. This method models the valve as a single well-mixed compartment. Experimental evidence, showing that estimates of flow were dependent upon the site of injection, is at variance with this assumption. An alternative method of analyzing the disappearance curves, based on the area to height ratio (A/H) of the curves, was found to be more consistent with the experimental evidence and resulted in greater precision than the exponential method. It was concluded that optimal results are obtained using the A/H method with a fixed injection technique.

Cerebral Ventriculography↗
PubMed1983

Radionuclide angiocardiography: an improved deconvolution technique for improvement after suboptimal bolus injection.

Deconvolution is a mathematical technique used to improve radionuclide angiocardiography after suboptimal injection of radiopharmaceutical. A new deconvolution algorithm designed to be relatively insensitive to the random errors that occur in experimental data was tested. First-pass radionuclide angiocardiography using iridium-191m was performed to quantitate left-to-right shunting in normal dogs and dogs with atrial septal defects. Deconvolution was used to correct for injection shape. Four quantitation techniques were studied (good injection/no deconvolution, good injection/deconvolution, fragmented injection/no deconvolution, fragmented injection/deconvolution). The mean (p less than .001) and standard deviation (p less than .0001) of the fragmented injection/no deconvolution technique were significantly different from the other three techniques, which were not significantly different from each other (mean or standard deviation) at the p = 0.05 level. This deconvolution method made it possible to accurately quantitate left-to-right shunts even with fragmented injections.

Animals↗
PubMed1983

The effect of contrast media on immature renal function. Comparison of agents with high and low osmolality.

Contrast media having high osmolality (methylglucamine diatrizoate; 1,510 mOsm/kg) and low osmolality (triiodoisophthaldiamide, 616 mOsm/kg) were compared in 15 functionally immature rabbits 2-3 weeks of age. Renal function was assessed with a gamma camera and whole-body counter, using excretion of technetium-99m-tin-DTPA as an index of glomerular filtration rate. Both DTPA and the contrast agent (2 ml/kg) were injected as a single intravenous bolus in 15 seconds. After 40 minutes, per cent DTPA excreted was 33.0 +/- 2.3 for triiodoisophthaldiamide and 28.2 +/- 1.5 (p less than 0.01) for methylglucamine diatrizoate. Excretion of DTPA was reduced with the latter (p less than 0.005) but not the former agent (p greater than 0.6). Thus contrast materials with high osmolality depress renal function in immature rabbits, suggesting that agents with low osmolality are preferable for use in newborns.

Animals↗
PubMed1983

Radionuclide evaluation of circulatory shunts.

With first-pass radionuclide angiography, it is possible to visualize sequentially the cardiovascular structures and to obtain computer-generated time-activity curves for regions of interest over these structures. Analysis of these curves permits the detection, localization, and quantitation of intracardiac shunts and shunts between the great arteries. The authors present the formulae used for the quantitative analysis and discuss clinical applications.

Ductus Arteriosus, Patent↗
PubMed1983

Accuracy of deconvolution algorithms assessed by simulation studies: concise communication.

Deconvolution has been used to correct first-pass radionuclide angiocardiography for the time course of the delivery of radiopharmaceutical into the cardiopulmonary system. The extreme sensitivity of deconvolution to random errors in the data may account for some of the problems encountered in practice. We implemented several deconvolution algorithms that were suitable for use with the unimodal and multimodal superior vena caval and pulmonary curves found in left-to-right shunt quantification. The sensitivity of the algorithms to random errors was assessed using mathematical test problems degraded with pseudorandom noise. An algorithm that constrained the deconvolved pulmonary curve to be expressable as the non-negative sum of a set of lagged normal curves was found to have the smallest maximum error on the curves tested. Comparison with results from a previously published test problem indicated an error reduction of greater than 50% over previously used algorithms. Use of this algorithm may permit more accurate deconvolution of pulmonary time-activity curves and thereby improve shunt quantification.

Heart↗
PubMed1982

Low radiation iridium 191m radionuclide angiography: detection and quantitation of left-to-right shunts in infants.

Radionuclide angiography using iridium 191m was carried out in 34 premature infants and young children for detection and quantitation of left-to-right shunts. Ir-191m has a physical half-life of 4.96 seconds and can be imaged with conventional gamma scintillation cameras. The whole body radiation absorbed dose from Ir-191m is 3.5 mrad/mCi, which is about 40 times less radiation than with technetium 99m. Other advantages of Ir-191m include high photon flux for improved imaging and the possibility of multiple studies within a short period of time without background. Nine patients had simultaneous measurement of pulmonary-to-systemic flow ratio by Ir-191m angiography and oxymetry during cardiac catheterization; the correlation coefficient was 0.90. Radionuclide angiography with Ir-191m is a method with virtually no risk, rapid, accurate, and reproducible, and is ideally suited for the evaluation of left-to-right shunts in small children.

Angiography↗
PubMed1981

Alterations in brain norepinephrine metabolism and behavior induced by environmental stimuli previously paired with inescapable shock.

After exposure to a single session of inescapable footshock, rats show deficits in escape performance 24 h later when required to lever press on a fixed ratio (FR-3) schedule. Footshock stress produces an immediate increase in brain levels of 3-methoxy-4-hydroxyphenylglycol sulfate (MHPG-SO4), a major metabolite of norepinephrine in rat brain. Twenty-four hours after a single or repeated session(s) of footshock stress, when levels of MHPG-SO4 returned to baseline, increases in brain levels of MHPG-SO4, crouching and defecation behavior were elicited in rats by neutral environmental stimuli that had been previously paired with inescapable footshock stress. These results suggest that sensitization or conditioning of noradrenergic neuronal systems may be induced by environmental stimuli previously paired with stress, and may help to explain, at least in part, the deficits in escape performance observed 24 h after exposure to inescapable shock.

Animals↗
PubMed1980

Alterations in brain norepinephrine metabolism induced by environmental stimuli previously paired with inescapable shock.

Footshock stress produced an immediate increase in brain concentrations of 3-methoxy-4-hydroxyphenylglycol sulfate (MHPG-SO4), a major metabolite of the neurotransmitter norepinephrine, in the rat brain. Twenty-four hours after footshock stress, when concentrations had returned to baseline, increases in MHPG-SO4 and emotional behavior could be elicited by previously neutral environmental stimuli that had been paired with the stress.

Animals↗