Hexakis (2-methoxy isobutylisonitrile) technetium-99m and thallium-201 chloride: uptake and release in cultured myocardial cells.

Hexakis (2-methoxy isobutylisonitrile) technetium-99m [(99mTc]MIBI), a new tracer of myocardial blood flow, was compared with 201TI CI in cultures of myocardial cells of newborn rats. The kinetics of uptake and release of both tracers were assessed in basal conditions and in the presence of 5 mM cyanide, an inhibitor of the respiratory chain, 0.1 mM iodoacetate, an inhibitor of glycolysis, 10 microM ouabain, an inhibitor of the Na-K ATPase, or with various pH values. The amplitude and frequency of contractions of the cells were also monitored in the same conditions. Results show that the washin and washout kinetics of [99mTc]MIBI are slower than 201TI(T1/2) of the washout curves were, respectively, of 28 min and 6 min). The kinetics of release of both tracers were not influenced by any of the inhibitors. There was a strong effect of the pH on the 201TI uptake only. Moreover 201TI uptake was decreased by 34% in the presence of cyanide plus iodoacetate. Otherwise the uptakes of 201TI and [99mTc]MIBI were not decreased by any of the drugs. The cellular contractility was significantly diminished by cyanide and it was abolished by cyanide plus iodoacetate. It is concluded that (a) impaired contractility can be associated with normal 201TI and [99mTc]MIBI kinetics in myocardial cells in culture, (b) that 201TI uptake may depend on the level of ATP devoted to the maintenance of membrane integrity, (c) that [99mTc]MIBI shows slower kinetics but is less sensitive to metabolic inhibitors than 201TI.

Reorientation of the left ventricular long-axis on myocardial transaxial tomograms by a linear fitting method.

A method is described for reorientating the left ventricular (LV) long-axis from myocardial transaxial tomographic data. On a midventricular transverse slice and on a midventricular sagittal slice, the apical and basal limits are selected successively by the operator. The linear activity profiles between these two limits are plotted line by line. In each profile, the two points with the maximum counts in the septal and lateral walls on the transverse slice, or in the anterior and inferior walls on the sagittal slice, are detected. The intermediate point with the minimum counts is then determined. The set of points with minimum counts are fitted by a straight line using the least squares method. This line is taken as the LV long-axis. In a series of 15 cases with stress-delayed 201Tl SPECT, the reproducibility of the reorientation with this semi-automatic method was compared with manual selection of the LV long-axis. In all patients, a successful reorientation was obtained with the present method. The reproducibility was significantly better with the semi-automatic method than with the manual selection of the LV long-axis.

Dissolution rate and transit times of technetium-99m DTPA-labeled tablets.

In this study we demonstrate that the dissolution rate and gastroduodeno-cecal transit time of radiolabeled tablets of theophylline can be determined in vivo using technetium-99m (99mTc). Six healthy male volunteers ingested a tablet containing 300 mg of theophylline mixed with 3.7 MBq of [99mTc]DTPA. Anterior and posterior scintigraphic views of the abdomen were collected serially over 8 hr, after which a 200-ml solution containing 37 MBq of [99mTc] pertechnetate was ingested in order to visualize the contours of the stomach. The in vivo activity contained in the tablet was calculated from the scintigraphic views after correction of background activity, radioactive decay, and depth attenuation. The dissolution rate of [99mTc] DTPA was also measured in vitro and compared with the dissolution rate of theophylline. The results showed close dissolution rates between [99mTc]DTPA and theophylline in vivo (T1/2 184 min and 176 min, respectively), and a faster early dissolution rate of [99mTc]DTPA in vitro (T1/2 92 min versus 156 min for theophylline). The mean gastroduodenal and duodenocecal times were 72 +/- 25 min (m +/- s.d.) and 245 +/- 15 min, respectively. Scintigraphic imaging of labeled formulations with 99mTc present useful applications in pharmaceutics and pharmacology.

In vitro uptake of technetium-99m-teboroxime in carcinoma cell lines and normal cells: comparison with technetium-99m-sestamibi and thallium-201.

Since 201Tl, 99mTc-sestamibi and 99mTc-teboroxime concentrate in cardiac cells through different mechanisms, we compared their uptake in cultured normal cells and carcinoma cell lines in order to define their possible use for tumor evaluation in vivo. Four lines of normal cells from animals, including myocytes from newborn rats, and four lines of human carcinoma cell lines were incubated for 1 hr with 37 kBq of either tracer. Results, expressed in percent of the total activity taken up by 1 million cells, showed a 9% difference between the uptake of teboroxime by normal and carcinoma lines (24.6% +/- 2.8% versus 22.5% +/- 2.1%, respectively, p < 0.05). Mean uptake was 80% higher in tumor than in normal cells for 201Tl (5.39% +/- 1.33% versus 3.00% +/- 1.08%, respectively, p < 0.001) and nearly 4 times higher for sestamibi (5.37% +/- 2.34% versus 1.44% +/- 1.88%, p < 0.001). For both agents, uptake by the myocytes and carcinoma cells was comparable (5.14% +/- 0.11% for 201Tl and 5.28% +/- 1.03% for sestamibi). When the myocytes are excluded from the group of normal cells, the uptake is 112% higher in tumor than in normal cells for 201Tl (5.39% +/- 1.33% versus 2.54% +/- 0.44%, p < 0.001) but it becomes nearly nine times higher for sestamibi (5.37% +/- 2.34% versus 0.60% +/- 0.23%, p < 0.001). It is concluded that these experiments show that the uptake of sestamibi was the most discriminant to separate between normal and malignant cells, while teboroxime was the less discriminant. Potential clinical applications for tumor visualization based on differences in sestamibi and teboroxime uptake could be envisioned.

Uptake of technetium-99m-teboroxime in cultured myocardial cells: comparison with thallium-201 and technetium-99m-sestamibi.

The effects of metabolic inhibition on the uptake of 99mTc-teboroxime were assessed in cultured myocardial cells and compared with 201Tl and 99mTc-sestamibi. Metabolic impairment was induced by cyanide (CN), a blocker of the mitochondrial respiratory chain, iodoacetate (IAA), an inhibitor of the glycolytic pathway, and ouabain, an inhibitor of Na(+)-K+ sarcolemmal ATPase. Cellular viability was appreciated by the trypan blue exclusion method. The effects of low temperature and of cellular death resulting from osmotic lysis were also assessed. Net cellular uptake of the radiotracers and the amount of proteins in the culture dishes were measured. All experiments were performed in parallel with control conditions and the results were expressed relatively to the control values. Teboroxime uptake was clearly decreased at low temperature (29.6% +/- 2.2% at 0 degree C, p < 0.001), while metabolic inhibition or osmotic lysis had no definite effect. The uptake of 201Tl and sestamibi was severely diminished in the presence of a mixture of 5 mM CN and 0.1 mM IAA, but 201Tl was less resistant than sestamibi (13.7% +/- 0.3% and 73.5% +/- 3.3%, respectively, after 1 hr of preincubation, p < 0.001 for both). Uptake of both tracers was very low in the presence of dead cells (12.1% +/- 1.3% for 201Tl and 4.1% +/- 0.2% for sestamibi, p < 0.001 for both). Ouabain had a detrimental effect only on 201Tl uptake at doses higher than 100 microM. Of these three currently available coronary blood flow imaging agents, teboroxime shows the lowest sensitivity to metabolic impairment.

Value of myocardial defect size measured by thallium-201 SPECT: results of a multicenter trial comparing heparin and a new fibrinolytic agent.

In a multicenter randomized double-blind trial comparing heparin and a new fibrinolytic agent, anisoylated plasminogen streptokinase activator complex (APSAC), 231 patients presenting with a less than 5 hr acute myocardial infarction underwent a contrast angiography (CA) before the end of the first week of admission, and radionuclide cardiac blood-pool imaging and a 201Tl single photon emission computed tomography (SPECT) study before the end of the third week. Left ventricular ejection fraction (LVEF) and a wall motion score (WM) were calculated from CA. LVEF was also obtained from cardiac blood-pool imaging, and defect size (DS) from 201Tl SPECT. Results demonstrated that all parameters were significantly improved in patients treated with APSAC versus heparin (contrast LVEF 53 +/- 13 vs. 47 +/- 14 p less than 0.01, WM 9.8 +/- 6.5 vs. 13.3 +/- 7.9 p less than 0.001, radionuclide LVEF 43 +/- 12 vs. 40 +/- 13 p less than 0.05, DS 14 +/- 12 vs. 18 +/- 14 p less than 0.05). When the patients were divided according to infarct site and infarct-related coronary artery patency, it was demonstrated with all four parameters that the beneficial effect of APSAC can be largely explained by the lower incidence of vessel obstruction in this group (37% vs. 77% in the heparin group, p less than 0.001). It is concluded that (a) when compared with heparin and in the conditions of the trial, APSAC significantly improves the cardiac function and decreases the DS and (b) DS measured by 201Tl SPECT is as valuable a quantitative parameter of therapeutic evaluation as are LVEF and WM.

Estimation of left ventricular mass in normal and infarcted canine hearts using thallium-201 SPECT.

A new automated edge detection program has been developed to estimate left ventricular mass from single photon emission computed tomographic (SPECT) 201Tl images and 14 dogs were studied. Six of the 14 dogs underwent imaging before and 5 hr after coronary artery occlusion with a closed-chest technique. True left ventricular mass was determined at time of killing within 1 hr of the last 201Tl study. Left ventricular mass determined by tomography correlated well with autopsy left ventricular mass (r = 0.94; p less than 0.001, s.e.e. = 5.9 g) over a range of 62-156 g. The intraobserver variation between repeated measurements of the same SPECT study yielded an r = 0.99; p less than 0.0001; s.e.e. = 2.3 g. The reproducibility of the mass determination was assessed in four animals with two studies performed 10-14 days apart. The estimate of left ventricular mass from the two studies were highly correlated (r = 0.98; p less than 0.001) with a mean absolute difference of 4 g (3.3%). In the six dogs with a control and postinfarct study the mean total left ventricular mass by 201Tl tomography varied by less than 3.8% (r = 0.89; p less than 0.001). In conclusion, tomographic imaging with 201Tl can define left ventricular mass accurately and reproducibly in the dog model. The ability of this 201Tl tomographic left ventricular mass program to measure both normal and infarcted tissue accurately suggests the possibility of documenting interventions designed to alter left ventricular mass and of sizing acute infarcts and assessing interventions that may alter acute infarct size.

Comparison between 180 degrees and 360 degrees data collection in technetium-99m MIBI SPECT of the myocardium.

In a series of 12 patients presenting with a single-vessel coronary artery disease and who were injected with 370 MBq of 99mTc-2-methoxyisobutylisonitrile at peak exercise, two consecutive single photon emission computed tomography (SPECT) data collections, i.e., 32 views of 30 sec during a 180 degrees rotation and 64 views of 15 sec during a 360 degrees rotation, were performed 1 hr later. In both cases, transverse sections were reconstructed using (a) a backprojection method with a ramp filter, (b) a correction for downscatter, (c) a correction for depth attenuation by the Chang method, or (d) both corrections. Each reconstructed myocardium was then divided into four short-axis sections which were radially divided into nine sectors. Sectors with an activity below 80% of the maximum were considered as abnormal. Sensitivity and specificity were calculated relative to a sector-by-sector theoretical anatomic distribution of the perfusion abnormalities. Results demonstrate that, of all situations, the best balance between sensitivity and specificity was achieved with the 180 degrees data collection and no correction at reconstruction. Using the 360 degrees data sampling technique mainly lowered the sensitivity in the patients with a circumflex or right coronary artery disease. It is concluded that there does not seem to be any definite advantage in performing a 360 degrees rather than a 180 degrees data collection in 99mTc myocardial SPECT.

Effects of grisorixin on the distribution of thallium-201 and on the oxidative metabolism in cultured myocardial cells.

Previous experiments in the dog and guinea-pig have shown that grisorixin, a monocarboxylic ionophore, can significantly increase the coronary blood flow and the myocardial uptake of 201Tl, as well as have a stimulant effect on the heart. In this study, cultures of myocardial cells were used in order to isolate the cells from the vascular and extracardiac influences so that any ionophorous effect on 201Tl could be evidenced. The effects of grisorixin on the oxidative metabolism were simultaneously studied. The technique described by Harary was used to prepare the cultures. The activity of the 14CCO2 produced by oxidation of [14C]glucose and [14C]octanoate added to the medium of culture and the intra/extracellular ratio of 201Tl concentrations (Tl i/e) were measured. In the controls (n = 8), the Tl i/e was 40 +/- 10 while it was 17 +/- 6 (p less than 0.05) in the cells that received 201Tl and grisorixin at the same time (n = 4), and 19 +/- 5 (p less than 0.05) in the flasks where 201Tl was injected after grisorixin (n = 7). A significant decrease of the [14C]octanoate oxidation was found in the flasks treated with grisorixin (n = 4, -50 +/- 16%, p less than 0.01) while the [14C]glucose oxidation was not significantly lowered (n = 3; -11 +/- 12%). The conclusion is that grisorixin decreases both the intracellular concentration of 201Tl and the fatty-acids oxidation in cultured myocardial cells. The beneficial effects previously observed in vivo were probably the consequence of the strong coronary dilatation and of an indirect stimulation.

Simultaneous maximal exercise radionuclide angiography and thallium stress perfusion imaging.

Gold-195m is a new ultra-short-lived radionuclide that can be used for cardiac studies. Accurate, reproducible ejection fraction and ventricular wall motion studies can be obtained from first-transit angiography using commercially available imaging and image-processing equipment. The short half-life of gold-195m (30.5 seconds) makes simultaneous dual isotope imaging possible and substantially reduces the radiation exposure from the isotope angiography. The feasibility and possible benefits of performing dual radionuclide studies were evaluated during a single exercise stress test in 24 subjects with known coronary artery disease (CAD) and in 20 normal volunteers. High-quality first-transit angiograms were obtained in all subjects. An 83% sensitivity and 95% specificity for detecting CAD with thallium-201 imaging was noted in this investigation, suggesting that its diagnostic accuracy was not altered by simultaneous dual isotone imaging. When segmental left ventricular (LV) wall motion was compared with thallium-201 perfusion imaging, divergent results were noted in 15 of 44 subjects. An analysis of the ejection fraction (EF) results at rest and stress provided additional information that could be useful in assessing the clinical significance of such differences in segmental wall motion and perfusion. Simultaneous dual isotope imaging appears to be appropriate for situations in which both LV perfusion and function require evaluation. The use of gold-195m allows such information to be obtained from a single exercise test and can thereby reduce the cost and time required for noninvasive evaluations of patients for CAD.

Comparison between thallium-201 and technetium-99m methoxyisobutyl isonitrile defect size in single-photon emission computed tomography at rest, exercise and redistribution in coronary artery disease.

Defect size on myocardial tomograms was measured in 30 patients who underwent 2 separate studies, 1 with thallium-201 (TI-201), the other with technetium-99m-methoxyisobutyl isonitrile (MIBI). A group of 15 patients with myocardial infarction was studied at rest and received both tracers on the same day. The other 15 patients had documented coronary artery disease. They were were given injections of TI-201 at peak exercise and underwent imaging immediately after exercise and again 4 hours later. They then received a dose of MIBI for imaging at rest. A week later they underwent a second exercise test with the same work load and received a second dose of MIBI. Defect size on single-photon emission computed tomographic images was measured and repeated twice. Results were expressed in percentage of the volume of the whole myocardium. Reproducibility of the defect size measurement was high for TI-201 (r = 0.978; SEE = 1.59) as well as for MIBI (r = 0.981; SEE = 0.80). In patients with coronary artery disease the mean size of the defects was significantly larger with TI-201 than with MIBI at exercise (6.7 +/- 5.2 vs 4.6 +/- 5.2%, respectively, p less than 0.05) and at redistribution (5.1 +/- 4.4 vs 2.8 +/- 3.2%, respectively, p less than 0.05), where no difference was seen in patients with myocardial infarction studied only at rest (11.2 +/- 10.4 vs 12.0 +/- 11.5%, respectively, p = not significant). Smaller MIBI defect sizes, when compared with TI-201, in the exercise and redistribution studies were not due to technical artefacts since there was no difference when they were compared at rest.

Comparable uptake of thallium-201 and technetium-99m MIBI in hibernating and "maimed" myocardium.

Thallium-201 and technetium-99m-MIBI uptake are comparable in "maimed" (i.e., partially viable) and hibernating myocardium. The appreciation of myocardial viability should be based not only on the presence of a regional contractility improvement, but also on the evaluation of the initial level of contractility and of tracer uptake in the concerned area.

Relationship between 201Tl uptake and oxidative metabolism in cultured myocardial cells.

The uptake of thallium-201 (201Tl) by myocardial cells in cultures was assessed in the presence of 10(-3) M potassium cyanide (KCN), an inhibitor of mitochondrial respiration, and 10(-4) M dinitrophenol (DNP), an uncoupler of oxidative phosphorylation. The cultures were incubated with 14C-glucose or 14C-octanoate, allowing the measurement of the oxidative metabolism and beta-oxidation from the production of 14CO2. The results demonstrated a moderate decrease in the ratio between the intra/extracellular concentration of 201Tl (Tl i/e) in the presence of KCN (28.9 +/- 8.1 versus 35.6 +/- 9.7 in the controls, n.s.) and no change with DNP (37.6 +/- 9.7). Glycolysis and fatty acid oxidation were lowered with KCN (-28 +/- 15 and -45 +/- 22% respectively, p less than 0.05 in both cases) and were non significantly increased with DNP (+37 +/- 23 and +10 +/- 52% respectively). These results show that 201Tl intracellular uptake is not related directly, but is not totally independent of glycolysis and fatty acid oxidation.

[An in-vitro study of 99mTc sestamibi uptake by normal and neoplastic cell lines]. / Studiul in vitro pe linii celulare normale si neoplazice al captarii 99mTc sestaMIBI.

The hexakis (2-methoxy isobutyl isonitrile) technetium (I) (99mTc MIBI) is a representative molecule for a class of monocationic lipophile 99mTc compounds, knowing to be initially used like myocardial scintigraphic agents, and now also in oncological scintigraphy. This present study aims to compare the in vitro 99mTc MIBI cellular uptake on some normal and neoplastic cells. Three tumoral cell lines were used: M4Beu (pigmented melanoma), M3Dau (pigmented melanoma), MCF7 (breast cancer), in comparison with newborn rat cardiac myocytes and fibroblasts. Monolayers cultures cell were incubated for 1 hour with 37 kBq of 99mTc MIBI. Our results: (a) confirm a preferentially 99mTc MIBI uptake on the myocytes in comparison of the fibroblasts; (b) show that this uptake is very different on the neoplastic studied cultures cells, depending on the cell type (higher on M3Dau in comparison of the other two malignant cell lines, and also higher than the myocytes. The neoplastic cellular mechanisms to accumulate 99mTc MIBI, are only hypothetically understand; there are thought to be also in relation with the Nernst equations, applied at the plasmatic and mitochondrial membranes level, like in normal cells. A correlation with some phenotypic neoplastic cells characteristics, in relation with the malignancy tumoral potential seems possible. If there is the case, this can be a possible explanation of some in vivo imaging results, obtained with 99mTc MIBI, in oncologic scintigraphy.

Uptake and release of two new Tc-99m labeled myocardial blood flow imaging agents in cultured cardiac cells.

Two new neutral lipophilic 99mTc labeled molecules, chloro (methylboron (1-)-tris[1,2-cyclohexane-dionedioxime (1-)]-N,N',N'',N''',N'''',N''''') (SQ 30217) and Bis [1,2-cyclohexanedione dioximato (1-)-0]-[1,2-cyclohexane-dione dioximato (2-)-0] borato (2-N,N',N'',N''',N'''',N''''')-chloro Tc (SQ 32014), were studied in cultures of beating myocardial cells of newborn rats. The uptake and release kinetics, the effects of various pH levels of the medium, and the effects of three metabolic inhibitors, i.e., ouabain, cyanide and iodoacetate were assessed. Results show that T1/2 of uptake were less than 2 min with both tracers, and T1/2 of release were 12 and 13 min with SQ 32014 and SQ 30217, respectively. The intra/extracellular tracer concentrations was about 15 times higher with SQ 30217 than with SQ 32014. Intracellular concentration was decreased for both tracers at high pH levels, and was only moderately modified otherwise, including in the presence of the metabolic inhibitors. It is concluded that both tracers present very interesting properties for myocardial blood flow imaging, although a higher contrast should be expected with SQ 30217 than with SQ 32014.

Factor analysis in left ventricular first-pass radionuclide angiography: value of the ventricular factor to measure ejection fraction.

Factor analysis theoretically generates the time-activity curves of the various physiological compartments, or factors, which are superimposed in a dynamic series of scintigraphic frames. An image of the spatial distribution of each of these factors is also displayed. We tested the ability of one of these, the ventricular factor, to measure the left ventricular ejection fraction (LVEF) in first-pass radionuclide angiography (FPRA). Forty-nine patients divided into three groups were studied. In a group of 32 patients, factor analysis was compared to a conventional scintigraphic method and to contrast angiography. The coefficient of correlation was similar for both techniques (r = 0.83). To test reproducibility, another group of 10 patients received two successive injections of Au-195m, three minutes apart. The reproducibility of LVEF was r = 0.78 with factor analysis and r = 0.81 with the conventional method. In a third group of seven patients, three successive injections of Au-195m were performed in the right and in the left anterior oblique projections. The reproducibility of LVEF was r = 0.71 with factor analysis. However LVEF was significantly lower in LAO than in RAO, 50 +/- 11% vs 58 +/- 17% respectively. It is concluded that factor analysis does not offer a more reliable means of calculating LVEF than a conventional method.

Thallium-201 single-photon emission computed tomographic estimates of left ventricular mass in patients with and without ischemic heart disease.

A new automated edge detection program has been developed to estimate left ventricular mass from single-photon emission computed tomographic (SPECT) thallium-201 images of patients. Left ventricular (LV) mass was measured from contrast angiograms in 21 patients and was compared with LV mass estimated from thallium-201 tomographic studies. A comparison of angiographic mass to mass estimated from stress studies yielded an r = 0.97 (SEE = 21.6 gm) and a comparison of angiographic mass to mass determined from the redistribution images yielded r = 0.96 (SEE = 23.0 gm). Values of mass from stress and redistribution studies varied 7.3% +/- 6.7 and 8.8% +/- 9.2, respectively, when compared with values obtained by cineangiography. LV mass derived from the stress and redistribution studies were highly correlated (r = 0.97; SEE = 21.9 gm). Linear regression analysis revealed a slope of 1.06 (stress ventricular mass = 1.06 X redistribution mass - 14.9 gm). Thirteen patients had two thallium-201 SPECT studies performed approximately 1 month apart. Estimated LV mass was highly correlated when the two studies were compared (r = 0.94; SEE = 21.7 gm comparing the two stress studies; and r = 0.93, SEE = 19.4 gm for the two redistribution studies). We conclude that SPECT thallium-201 imaging can define LV mass accurately and reproducibly in normal, ischemic, or infarcted tissue.

Gastrointestinal scintigraphy with 99mTc-DTPA labeled tablets in fed and fasting subjects.

The in vitro and in vivo dissolution of a sustained release theophylline formulation labeled with 99mTc-diethyltriaminepentaacetic acid (DTPA) has been monitored in six subjects with a scintillation camera. The study was performed in fasting conditions and was repeated after ingestion of a standardized meal. Results showed that the presence of food in the stomach dramatically increased the oesoduodenal transit time of the tablet (74 +/- 27 min vs 352 +/- 77 min, P less than 0.001) but did not modify the biodisponibility of theophylline. This study is another example when scintigraphy can be of definite value in pharmacokinetics.