Effects of dietary magnesium deficiency on thallium-20 1 kinetics and distribution in rat myocardium: concise communication.

Kinetics and distribution of TI-201 were studied in myocardium of rats with chronic dietary induced Mg deficiency. Rats were fed the Mg-deficient diet for 30 days and were then injected intravenously with 0.2 mCi of TI-201. Comparable control animals were fed a standard laboratory diet. One-half hour after injection, rats were killed and a segment of myocardium was washed with nonradioactive Krebs solution in a special chamber. Radioactivity in the tissue was recorded continuously for 1 hr. A three-compartment model (extracellular, main intracellular, and subcellular) was found to describe adequately the kinetics of TI-201. In myocardium of Mg-deficient animals, significant changes in values of transport rate constants and compartment sizes for TI-201 indicated a moderate decrease in extracellular compartment and a threefold enlargement in subcellular compartment (presumably mitochondrial) at the expense of the main intracellular compartment, which underwent a marked reduction. Bulk TI-201 uptake in myocardium of Mg-deficient rats was unchanged. The findings are interpreted as being consistent with mitochondrial alterations reported in Mg-deficient animals. Clinical implications are discussed.

Effects of exercise on kinetics and distribution of K-43 and Tl-201 in isolated myocardium: concise communication.

Kinetics and distribution of K-43 and Tl-201 were studied in isolated myocardial tissue from rats to assess the effects of exercise. The experimental design was as follows. Rats in some groups were forced to swim for 2 hr; immediately after swimming, they were injected with 0.2 mCi of 43KCl or 201TlCl; at 0.5 or 3 hr after injection they were killed and a myocardial segment was obtained and subjected to washouts with nonradioactive Krebs fluid in a special chamber. The radioactivity remaining in the tissue was recorded continuously for 1 hr. In control groups ("rested") the exercise was omitted. Altogether there were four groups of ten animals each for both K-43 and Tl-201. A three-compartment model (extracellular, main intracellular, and subcellular) was used; transport rate constants and relative compartment sizes were determined. The most striking finding was the unchangeability of K-43 parameters with regard to experimental condition (rest compared with exercise) and sampling time (0.5 compared with 3 hr after radionuclide injection). On the other hand, Tl-201 parameters were modified by exercise and sampling time. Notable differences between K-43 and Tl-201 kinetics were found. The hypothesis that alterations at the cellular level may affect regional myocardial distribution of a radionuclide is discussed.

Partition of thallium-201 in isolated myocardial tissue of rats previously injected at rest or after exercise.

The kinetics and distribution of TI-201 in isolated myocardial tissue of rats injected i.v. with this radionuclide are compared at rest and after exercise (2 hr of forced swimming). At 1/2 and 3 hr after injection, a myocardial segment was obtained and subjected to continuous washout with the radioactivity remaining in the tissue recorded each 10 sec for 1 hr. Altogether there were four groups of ten animals each. A three-compartment model (extracellular, main intracellular, and subcellular) was found to describe adequately the kinetics of TI-201. In the groups studied 1/2 hr after TI-201 injection the most dramatic effect of exercise was a translocation of TI-201 into the subcellular compartment. The change was also present but less marked in samples from exercised rats obtained 3 hr after TI-201 injection, which suggests a transition to the resting stage. The findings suggest the possibility of structural subcellular differences in myocardial uptake for TI-201 in clinical images visualized after exercise and at rest.

Radioisotopic pulmonary lobectomy: feasibility study in dogs.

In search for an alternate treatment for inoperable cancer of the lung in humans, we investigated the possibility that introduction of radioactive material into a selected lobe of the canine lung would effectively destroy that lobe without systemic effects or radiation injury to adjacent organs. Ten million ion exchange microspheres labeled with 740 MBq of phosphorus-32 (32P) were injected through a catheter placed in a selected lobar branch of a pulmonary artery in 12 anesthetized dogs. Six additional dogs served as controls and received 10 million microspheres not labeled with 32P. Organs were harvested from 1 wk to 12 mo after injection and examined grossly and histologically. There was progressive organization and contraction of each necrosed 32P treated lobe which was reduced to a scarred remnant by 12 mo, whereas only minimal inflammatory changes occurred in controls. Of the 32P injected dose, 94% remained in injected lobe, 4%-5% in nontargeted lobes and less than 0.08% in blood. Radioactivity in liver, kidneys, spleen, heart, and bone marrow was less than 0.1% for each organ. Thus, large doses of radiation in the order of 1,500 Gy can be effectively delivered to a selected lobe to produce a "radioisotopic pulmonary lobectomy."

Differences between 201Tl and 43K tissue distribution in rested and exercises rats.

A comparison is made of relative organ-to-plasma uptake of 43K and 201Tl in rats at rest and after exercise (two hour swimming). Organs were obtained 0.5 or 3 hrs after radionuclide injection. Thus, there were four groups each for 43K and 201 Tl. For 201Tl the triad kidneys-heart-adrenals was very consistent throughout the four experimental situations in showing the highest uptake, whereas for 43K adrenals-heart-liver predominated at 0.5 hrs and thymus-liver at 3 hrs. The ratio 201Tl/43K in myocardium was always greater than unity in all four experimental situations. The heart-to-lung and heart-to-liver uptake ratios were lower in all cases for 43K vs. 201Tl. One of the most important findings was that exercise always determined an increase of these ratios for 201Tl, but it had an unfavorable effect on the 43K heart/lung ratio and no definite effect on the 43K heart/liver ratio. Our findings are analyzed in the light of previous publications. It is concluded that these two ions have biologically important different characteristics and that excessive and seemingly unjustified emphasis has been made on their physiological similarity.

Visualization by dynamic and static osseous scintigraphy of pelvic chondrosarcoma in multiple hereditary exostosis.

Malignant degeneration to chondrosarcoma occurred in the left hemipelvis of a patient with multiple hereditary exostosis. Tc-99m HDP bone scintigraphy revealed markedly increased focal uptake in the areas of left superior pubic ramus, obturator foramen, and ischium with displacement of the urinary bladder. Of particular interest was the presence of vascularities seen in the flow and blood pool scintigrams. Following surgical exeresis, the gross appearance and histologic features of the tumor were identified as those of a low grade chondrosarcoma.

Innocent intramural gastric uptake of gallium-67 in a case of AIDS.

In a patient with AIDS, marked uptake of Ga-67 in the stomach walls initially was regarded with a high degree of suspicion for gastric involvement. Results of subsequent intragastric tests, including biopsy and culture, proved negative. Caution should be exercised when considering further costly and/or invasive procedures after gastric visualization on Ga-67 scintigraphy.

Improved computerized quantitation of TI-201 myocardial scintigrams by combining two views.

An improved computerized procedure involving minimal operator intervention has been developed for the automated quantitative evaluation of circumferential profiles of TI-201 myocardial perfusion scintigrams to diagnose coronary artery disease. The optimal criteria for evaluating the profiles of the left anterior oblique and anterior views have been empirically determined for both immediate and delayed scintigrams. Information from both views is combined to determine values for sensitivity and specificity. In this study, 29 patients underwent both TI-201 scintigraphy and contrast coronary angiography. The computerized quantitative procedure to interpret TI-201 scintigrams was tested against the results of coronary angiography. The values of 95% for sensitivity and 100% for specificity compare well with the results of other methods and are free of most of the variables associated with visual interpretation or operator intervention on the computer.

Cellular sodium transport in arterial wall--summary of studies by digital computer simulation.

The distribution of electrolytes between extracellular and intracellular compartments is of greater functional significance in biological tissues than the total amount. A method commonly employed for the study of a substance distribution among different spaces is the continuous outflow and radioisotope counting of a fragment of tissue previously incubated with a radioactive tracer (here 22Na+). The experimental data can be analyzed within the frame of a compartmental analysis system which is defined by transport rate constants (kij) and solved when all kij are numerically determined. In practical applications the direct solution requires measurements in different compartments or knowledge of the initial condition for each compartment, but this is not possible in most biological tissues where the experimentally observable data represent the summation of tracer in all compartments at each point in time. The availability of the SAAM (Simulation, Analysis And Modelling) computer program allows for a powerful simulation procedure to arrive at values for kij. Experimental data and specifications for a chosen model are entered in the SAAM format. A simulated 'inflow' experiment is made by the computer by assigning to kij some estimate values. All initial conditions are now zero, since at the beginning there is no radioactive tracer in any compartment. After a time equivalent in the experimental realm to achieving constant specific activity, a 'time change' programmed into the computer takes place so that the outflow part of the experiment is developed with the same kij as for the inflow part, the final conditions for the inflow before the time change being the initial conditions for the outflow. An iterative procedure modifies the initial estimates of kij to seek the best fit. By coupling a powerful simulation procedure to an advanced radionuclide tracer biological methodology, we have been able to find effects of the hormone aldosterone and of experimental hypertension on Na+ distribution in arterial wall years before such effects were demonstrated by purely conventional experimental techniques. This computer simulation procedure may be suited to other experimental situations in which outflow data are the only available.

The saga of BHT and BHA in life extension myths.

The phenolic antioxidants BHT and BHA have been widely used for many years in small concentrations for foods, pharmaceutical preparations and cosmetic products to prevent oxidation of labile lipoid components. Recently, in an aggressive campaign, daily 2 g doses of these compounds have been recommended, without scientific grounds, to combat senescence, genital herpes and cancer. However, information in the bio-medical literature reveals that the recommended human dose of 2 g/day is simply one order of magnitude below the lethal dose in animals. Obviously, these high dose levels, if not immediately lethal for humans, must produce pathological effects. Physicians and health authorities should be familiar with the consequences of prolonged administration of large doses of BHT and BHA and forbid their use except as fat stabilizers for food and pharmaceutical products.

Review: a comparison of computerized quantitative methods for interpreting Tl-201 myocardial scintigraphs.

Thallium-201 is a cation extracted very rapidly by myocardial cells from the coronary artery blood supply. Areas with insufficient blood flow (ischemic) or non-viable tissue (infarcted) do not pick up Tl-201. Images (scintigraphs) can be obtained from the radiation emanating from the myocardial walls. By visual methods scintigraphic interpretation is difficult. The object of this review is to present essential characteristics of some methods using computerized quantitative Tl-201 scintigraphy as well as their degree of sensitivity and specificity. Computerized evaluation offers the advantage of consistency of interpretation. Furthermore, many computerized methods achieve improved sensitivity and specificity over visual methods. The above technique may also be extended to other radionuclides.

Role of the biomedical engineer in nuclear medicine.

Throughout the short history of the development of radioactivity applied in the biomedical field, there have been many contributions made by engineers. With the advent of Nuclear Medicine as a well systematized specialty and its mushrooming in hospitals, the opportunities for biomedical engineers have increased. This article is written from the viewpoint of historic perspective in order to display the different aspects and situations where engineers, and particularly biomedical and clinical engineers, can participate in Nuclear Medicine. Finally, a more detailed survey is made of the activities of biomedical engineers in the nuclear medicine department.

Sodium kinetics in aorta of spontaneously hypertensive rats.

Transport rate constants (kij) for Na exchanges in isolated aorta of normotensive and spontaneously hypertensive rats (SHR) were determined with the use of 33Na as a tracer and the aid of digital computer simulation. A three-compartment model consisting of 1) extracellular, 2) intracellular, and 3) "endointracellular" spaces (compartments) was found to describe adequately the kinetics of 22Na. Results show that in SHR: I) K01, which is related to the overall Na outflow from tissue, was increased by 41%; ii) k12, describing Na movements from intra- to extracellular compartment, was increased by 67%; iii) k21, representative of Na movements from extra-to intracellular compartment, was decreased by 39%. These results indicate a faster turn-over of Na and a relative accumulation or translocation of Na into the extracellular space in aorta of SHR. The findings are interpreted in the light of recent reports on the role of Na in contractile response or reactivity of arteries. A humoral mechanism operative at the arterial wall level for the development of hypertension is at the arterial wall level for the development of hypertension is suggested. The main significance of the methodology employed in this work is that the values found for the kij are not subject to fluctuations intrinsic to auxiliary indicators of extracellular space.