UNLABELLED:In recent years, several of 99mTc-labeled myocardial perfusion imaging agents have been developed, such as 99mTc-sestamibi, 99mTc-tetrofosmin and 99mTc-furifosmin. Although images obtained with these new tracers have a general similar appearance, there are differences in the myocardial kinetics, body distribution, general quality of images and imaging protocols. The aim of this study was to quantitatively compare normal exercise planar and SPECT data files obtained with 201TI and 99mTc-labeled agents.METHODS:Lower-limit-of-normal curves were generated for each specific radiopharmaceutical from normal subjects with low (< 3%) pretest likelihood of coronary artery disease using circumferential count distribution profiles from planar and SPECT exercise images. Lower-limit-of-normal curves were statistically compared using the nonparametric Kruskall-Wallis and Wilcoxon tests.RESULTS:Planar and SPECT lower-limit-of-normal curves generated for each radiopharmaceutical showed general similarities. Statistically significant differences among the lower-limit-of-normal curves were found in the planar left anterior oblique view and in the planar left lateral view (p < 0.05 for each). No statistically significant differences existed between lower-limit-of-normal curves of various radiopharmaceuticals on the planar anterior view and on SPECT imaging.CONCLUSION:For quantitative analysis of planar images, radiopharmaceutical-specific normal data files are mandatory. Although SPECT normal data files of various radiopharmaceuticals are not statistically different, they are not identical. It appears, nevertheless, prudent to use radiopharmaceutical-specific normal data files for quantitative analysis of SPECT images.

Tetrofosmin is a 99mTc-labeled myocardial perfusion imaging agent that has shown encouraging results in Phase I and II clinical trials. The purpose of this study was to determine the biokinetics of this agent following administration during exercise and at rest in order to determine an optimal imaging protocol. Twenty patients with suspected coronary artery disease underwent symptom-limited treadmill exercise. Six to 8 mCi of 99mTc-tetrofosmin was injected at peak exercise and 22-24 mCi was injected 4 hr later at rest. Serial 5-min planar images were obtained in the left anterior oblique view at 5, 10, 15, 30, 60, 120 and 180 min after the radiotracer injection. Regions of interest were drawn on the serial images around the entire heart and portions of liver, lung, spleen, gallbladder and gastrointestinal tract. Average decay-corrected counts per pixel in each organ were plotted against time. In addition, heart-to-adjacent organ ratios were also determined. On stress images, the heart had the highest activity at all times, with the exception of gallbladder in the first 15 min. On rest images, the gallbladder, liver and gastrointestinal tract initially had higher activity than the heart; but the activity in these organs cleared rapidly over the subsequent 30-60 min. Heart-to-adjacent organ ratios were > 1.0 at all times in the stress images. Heart-to-organ ratios were < 1.0 in the first 15 min on the rest images for the liver and gastrointestinal tract. However, 30 min later, all ratios on the rest images were > or = 1.0. Technetium-99m-tetrofosmin images were considered to be of good to excellent quality with good myocardial delineation and adequate contrast between the heart and background. These These observations indicate that a convenient one-day tetrofosmin imaging protocol similar in duration to conventional 201Tl imaging is feasible.

Redistribution thallium-201 imaging 2 to 4 h after exercise may be incomplete and therefore may be inadequate to fully assess myocardial variability. Late redistribution imaging 24 h after exercise has been proposed to overcome this limitation of thallium stress imaging. However, because of poor count density the image quality on these studies is often suboptimal. In the present study the diagnostic information on 24-h planar thallium redistribution images was compared with that on images obtained after a reinjection of thallium at rest. Eighty-four patients with a stress thallium-201 defect had delayed redistribution imaging after 2 to 4 h and 24 h later, and again after an injection of thallium at rest. Defect reversibility on 24-h redistribution images was compared quantitatively with that on images after injection of thallium at rest. The quality of thallium images at rest was consistently better than that of 24-h redistribution images. Poor quality studies occurred in 13% of 24-h redistribution images compared with 0.4% of the studies at rest. Significantly more defect reversibility was detected on images after the reinjection at rest. Of 41 patients who appeared to have a fixed defect at 2- to 4-h redistribution imaging, 11 (27%) had a reversible defect by 24-h redistribution imaging compared with 29 (71%) after thallium-201 reinjection. No clinical variables at the time of stress testing were predictive of late defect reversibility. It is concluded that in patients with fixed a thallium defect at 2 to 4 h after exercise, reimaging after a reinjection at rest provides better diagnostic information than does 24-h late redistribution imaging.

In previous research, we have demonstrated that parenterally administered terbutaline can augment resting cardiac function in patients with chronic obstructive pulmonary disease (COPD). Because the oral form of terbutaline is more widely utilized, a double-blind, randomized, crossover, placebo-controlled trial of the cardiopulmonary effects of oral terbutaline was conducted in ten patients with COPD. Right and left ventricular ejection fractions (RVEF and LVEF) were determined by first pass radionuclide angiography. There were no differences in spirometry and hemodynamic measurements between treatment and placebo days. Following 5 mg of oral terbutaline, there was a small but statistically significant increase in forced expiratory volume in 1 second and in heart rate, but no significant change in forced vital capacity or blood pressure. LVEF improved significantly with terbutaline both at rest (62% ± 6% vs. 67% ± 9%, mean ± SD) and during submaximal steady state exercise (61% ± 5% vs. 67% ± 10%). RVEF improved significantly at rest (64% ± 6% vs. 69% ± 5%), but not during sub-maximal steady state exercise (65% ± 6% vs. 68% ± 7%). Thus, oral terbutaline produces significant improvement in biventricular systolic pump performance at rest, and increases left ventricular ejection fraction during sub-maximal exercise in patients with moderate to severe COPD.

The noninvasive measurement of left ventricular filling has relied predominantly on radionuclide-derived peak filling rate normalized to end-diastolic volume. Doppler echocardiography also has the ability to measure peak filling rate, but wide application of this technique has been limited by technical errors involved in quantitative echocardiographic determination of mitral anulus cross-sectional area and ventricular volumes.