Dynamic acquisition with a three-headed SPECT system: application to technetium 99m-SQ30217 myocardial imaging.

A method for SPECT data acquisition, "continuous repetitive rotation acquisition," was developed with a high-sensitivity three-headed SPECT system. The method was applied to the dynamic imaging of 99mTc-SQ30217, a new myocardial imaging agent. After acquisition and reconstruction of SPECT data every minute, projection images at arbitrary intervals were used for tomographic reconstruction to determine the best timing of SPECT imaging in 99mTc-SQ30217. Based on a comparison of several possible acquisition intervals, SPECT data acquisition within 9 min after injection is recommended because of high myocardial uptake (myocardium-to-lung ratio, 2.83 +/- 0.42 (mean +/- s.e.m.) at 3-6 min) and relatively low hepatic uptake (myocardium-to-liver ratio, 0.85 +/- 0.13 at 3-6 min). The rate constant of the clearance of 99mTc-SQ30217 from the myocardium obtained by SPECT was: k1 = 0.249 +/- 0.050 per min (average half-life = 2.8 min) and k2 = 0.012 +/- 0.004/min (average half-life = 58 min). The continuous repetitive rotation acquisition SPECT study appears useful for imaging SQ30217 with its rapidly changing myocardial distribution.

Application of a continuous ventricular function monitor with miniature cadmium telluride detector to patients with coronary artery bypass grafting.

A continuous ventricular function monitor with a miniature cadmium telluride detector was evaluated and applied to patients with coronary bypass surgery (CABG). Ejection fraction (EF) at rest and change in EF from rest to exercise and postexercise (Y) measured with the device correlated with that of the gamma camera (X) (Y = 0.86x + 6.8(%), r = 0.87, n = 110, p less than 0.001, and Y = 0.96x + 0.4(%), r = 0.90, n = 37, p less than 0.001 respectively). Left ventricular function during and after supine ergometer exercise was monitored in 54 patients before and after CABG. The EF change from baseline to peak exercise improved from -5.9% +/- 8.9% before CABG to 7.2% +/- 7.9% after CABG (p less than 0.001). In all patients but two, a rapid EF increase just after exercise over baseline EF was observed. This EF "overshoot" during recovery increased from 11.5% +/- 6.5% to 16.4% +/- 6.0% (p less than 0.001) after CABG. The time from the cessation of exercise to EF overshoot decreased from 153 +/- 80 sec to 76 +/- 49 sec (p less than 0.001) after CABG. The continuous ventricular function monitor with a miniature cadmium telluride detector is able to measure EF reliably. Following successful aortocoronary bypass, EF response during exercise improved and the EF overshoot in the recovery phase became faster and higher.

Forward cardiac output measurement with first-pass technique using 99mTc-labeled myocardial perfusion imaging agents.

UNLABELLED: The aim of this study was to develop and validate a new first-pass method for the measurement of forward cardiac output (CO) using 99mTc-labeled myocardial perfusion imaging agents. METHODS: In protocol 1, to test the new method for measuring CO, the conventional method and the new method for CO measurement were performed in 1 d in 57 patients (32 men, 25 women; age 68 +/- 11 y). In the conventional method, radionuclide angiography (1 frame/s) with in vivo 99mTc labeling (110 MBq) of red blood cells was performed for 2 min in the left anterior oblique projection. Five minutes later, a 1-min equilibrium image was obtained, and a blood sample was taken for calculation of the distribution volume. To obtain data for the new method, further radionuclide angiography (1 frame/sec) with 99mTc labeling (600-740 MBq) of red blood cells was then performed in the anterior projection. CO was calculated using the following equation: CO = Cmax x V(LV)/integral of f(t)dt, where Cmax is the background-corrected peak count of the whole thorax during angiography, integral of f(t)dt is the area under the gamma variate-fitted left ventricular (LV) time-activity curve after background correction and V(LV) is the LV volume obtained by the area length method applied to the radionuclide angiography and myocardial tomography. In protocol 2, to evaluate the new method, 24 patients (16 men, 8 women; age 71 +/- 9.2 y) underwent radionuclide angiography with 99mTc-tetrofosmin (600-740 MBq), and the measured CO was compared with the CO obtained by the conventional method with 99mTc-labeled red blood cells. RESULTS: In protocol 1, good correlation was observed between the CO by the new method (Y) and the CO by the conventional method (X): Y = 1.0X + 57 mL/min and r = 0.95. There was good agreement between the two methods (mean difference -56 +/- 381 mL/min). Inter- and intraobserver correlation coefficients were 0.96 and 0.98, respectively. In protocol 2, the CO by the new method using 99mTc-tetrofosmin (Y) showed a good correlation with the CO by the conventional method (X): Y = 0.90X + 453 mL/min and r = 0.93. Good agreement between the two methods was observed (mean difference 73 +/- 390 mL/min). Inter- and intraobserver correlation coefficients were 0.95 and 0.98, respectively. CONCLUSION: This new method permits accurate forward CO measurement using the first-pass data with 99mTc-terofosmin, which is applicable to other 99mTc-labeled myocardial perfusion imaging agents.

[Residual activity or defect reversibility on stress-redistribution-reinjection 201T1 SPECT: which is the better marker of myocardial viability?].

Although both residual T1 activity and defect reversibility are used as a marker of myocardial viability on stress-redistribution-reinjection T1 (T1-RI) imaging, it is not yet fully understood which marker better predicts reversible dysfunction after revascularization. The aim of this study was to assess the comparative efficacies of these criteria for prediction of functional recovery after revascularization. Twenty-five patients (LVEF 41%) who underwent successful revascularization were studied with T1-RI SPECT and gated blood pool scintigraphy before revascularization. The gated blood pool study was repeated at mean 2 months after revascularization. The left ventricular myocardium was divided into 9 segments and the mean regional activities were calculated for each segment. In this study, two independent criteria were used as a viability index; (A) the presence of residual T1 activity (> 50% of peak) on the final image (reinjection image), (B) reversible defect (> 10% increase on the subsequent images) or normal T1 uptake (> 80% of peak) on the initial image. Functional recovery occurred in 51 of 88 dysfunctional segments. The presence of residual T1 activity was a highly sensitive (96%) but poorly specific (35%) marker of reversible dysfunction, while a reversible defect or normal T1 uptake was a less sensitive (67%) but more specific (59%) predictor of functional recovery. In conclusion, defect reversibility provides unique information on myocardial viability which cannot be obtained by assessing residual T1 activity alone.

[Value of 123I-BMIPP scintigraphy in patients with ischemic heart disease: comparison with exercise 201Tl SPECT].

To evaluate 123I labeled beta-methyl-branched fatty acid (BMIPP) myocardial uptake at rest in the segment with and without stress induced ischemia in patients with coronary artery disease, 123I-beta-methyl-branched fatty acid myocardial scintigraphy was performed at rest and was compared with the findings of stress-reinjection 201Tl myocardial scintigraphy in 31 patients with coronary artery disease. In 159 ischemic myocardial segments, equally decreased uptake on both reinjection 201Tl and fatty acid images was observed in 64 segments, more severely decreased uptake of fatty acid in 76 segments, and more severely decreased uptake of reinjection thallium in 19 segments. On the other hand, in 53 non-reversible defects, each patterns was observed in 41, 3, and 9 segments respectively. When comparing the ischemic segments with more reduced uptake of fatty acid than reinjection thallium (Group 1) and the ischemic segments with equally or less reduced fatty acid uptake than reinjection thallium (Group 2), wall motion was more severely impaired in Group 1 than in Group 2 (severe hypo- to dyskinesis was present in 32 of 54 segments in group 1 and in 21 of 75 segments in group 2, p < 0.005). In conclusion, in patients with coronary artery disease, resting fatty acid uptake was frequently more reduced than reinjection 201Tl in the segments with stress induced ischemia and wall motion was more impaired in these segments. BMIPP myocardial imaging may provide information on metabolic alterations at rest independent of perfusion abnormalities in patients with coronary artery disease.

[Basic evaluation of an ambulatory ventricular function monitor with a a cadmium telluride detector].

The reliability of a new ambulatory ventricular function monitor (VEST) with cadmium telluride (Cd-Te) detector was validated. No counting loss was observed under 20 kcps. In phantom study, more than 200 ml with 6 cm distance from the detector and more than 300 ml with 6-12 cm distance, underestimation of volume was observed. Ejection fraction (EF) calculated in phantom study showed close value to the true EF in 50-400 ml of end-diastolic volume. In 10 patients, 1-2 cm detector shift toward right upper, upper and left showed underestimation of EF. Good correlation of gamma camera EF (X) and VEST EF (Y) was obtained (Y = 0.96X + 3.6(%), n = 37, r = 0.93, p less than 0.001). EF change from rest values, obtained from each comparable exercise and post exercise stage by gamma camera (X) and VEST (Y), showed good correlation (Y = 0.95X + 0.8, n = 20, r = 0.85, p less than 0.001). In conclusion Cd-Te VEST was considered as a reliable EF measurement technique similar to gamma camera.

[Myocardial perfusion imaging with 99mTc-SQ30217: application of three-headed SPECT system].

The early dynamic change of a new myocardial imaging agent, 99mTc-SQ30217, was investigated in SPECT study. A three-headed high sensitivity SPECT system was employed to evaluate the serial changes of accumulation pattern in the heart, lung and liver using a "continuous repetitive acquisition" mode. The myocardial activity reached a peak rapidly and decreased with rapid clearance rate. The analysis of myocardial clearance curve showed a T1/2 of 2.8 minutes (k1 = 0.25 +/- 0.12/min) in the rapid phase, and a T1/2 of 57 minutes (k2 = 0.012 +/- 0.011/min) in the slow phase. The tracer clearance in the lung was more rapid, while the hepatic uptake reached a peak approximately 10 to 15 minutes after injection. When the serial SPECT images were reviewed, the early 3-minute acquisition within 10 minutes after injection showed better image quality than the images obtained after 10 minutes. The hepatic activity did not obscure the infero-septal wall in the earlier images, but did in the images 10 minutes after injection. Thus, quick SPECT data acquisition seemed to be desirable for this agent. We concluded that 99mTc-SQ30217 was a promising radiopharmaceutical for myocardial perfusion imaging.

[Evaluation of ischemic heart disease by thallium-201 washout-rate map using SPECT].

In thallium-201 myocardial perfusion scintigraphy, washout rate (WR) has been used for the evaluation of the severity of ischemic heart disease (IHD). The WR was calculated from the polar map (Bull's-eye display) of myocardial perfusion using SPECT. To analyze the abnormality of WR map, we computed the extent and severity scores of WR. Applications of two types of standards, absolute and relative standards from control group (n = 16), were compared. The multiple regression analysis showed that the global WR was a function of the severity of coronary artery stenosis and exercise level, i.e. WR (%) = -2.38 X (number of stenotic artery) + 0.093 X (rate-pressure product/100) + 19.7 (n = 62, r = 0.63). Thus in evaluating the severity of IHD by absolute WR, the correction of WR was necessary according to the exercise level. Whereas, to evaluate the score of WR abnormality in polar map, the relative standard separated each group with different number of stenotic artery better than absolute standard did. In conclusion, calculation of WR score from relative standard is recommended for the analysis of polar WR map, although absolute global WR is useful for the evaluation of severity of coronary artery disease.

[Measurement of myocardial blood flow increase rate at exercise with 99mTc-tetrofosmin radionuclide angiography].

UNLABELLED: We developed new method to calculate myocardial blood flow increase rate at exercise (MBF-IR) with 99mTc-tetrofosmin (TF) radionuclide (RN) angiography and myocardial perfusion SPECT and assessed its feasibility using clinical data. METHOD: Fifteen patients who were suspected to have coronary artery disease underwent TF RN angiography and SPECT at exercise and at rest. Seven patients had coronary stenosis and eight patients had no significant coronary stenosis in coronary angiography. MBF-IRs were calculated by the following equation: [formula: see text] where Cr = regional myocardial count at rest, Ce = regional myocardial count at exercise [formula: see text] = the area under ventricular time activity curve at rest and [formula: see text] = the area under ventricular time activity curve at exercise. RESULT: Rate pressure product (RPP) was similar in patients with and without coronary stenosis (24,509 +/- 6701.9 vs. 27,196 +/- 4862.4, p = 0.39). MBF-IR was 1.88 +/- 0.73 in the area covered by stenosed coronary artery, 2.53 +/- 0.75 in unstenosed coronary artery in patients who have significant coronary stenosis and 2.97 +/- 0.77 in normal coronary patients. MBF-IRs in the area covered by stenosed coronary arteries were significantly smaller than that of normal coronary artery patient (p = 0.037). Interobserver and intraobserber reproducibility were good (r = 0.96, 0.95 respectively). There was strong positive correlation between MBF-IR and RPP in normal patients (r = 0.69, p = 0.0018), suggesting MBF increase depends on the cardiac workload. CONCLUSION: MBF-IR can be estimated by the combination of TF RN angiography and SPECT at exercise and at rest.

[Estimation of cardiac output by first-pass data with technetium-99m-labeled myocardial perfusion imaging agent].

Technetium-99m-tetrofosmin, a myocardial perfusion imaging agent was used for estimation of cardiac output by means of first-pass radionuclide angiography performed in the anterior projection. Region of interests (ROIs) were assigned over right ventricle, left ventricle and whole chest, and time activity curves (TACs) were obtained. Cardiac output indices (COIs) were calculated by the following equation; COI = p3/2. Qc/[symbol: see text] A(s)ds, where p = number of pixels of the ventricular ROI, Qc = the peak count rate of the TAC obtained from the whole chest's ROI and [symbol: see text] A(s)ds = the area under ventricular TAC. The COI (y) determined by ROI over the left ventricle yield the best correlation with the cardiac output by conventional radionuclide method (x) (y = 0.0381x + 6.22, r = 0.828, n = 48, p < 0.001). In conclusion, cardiac output can be easily measured with first pass data using myocardial perfusion imaging agent.

[Evaluation of hypertrophic cardiomyopathy with 123I-metaiodobenzylguanidine].

Single-photon emission computed tomography was performed in 29 patients with hypertrophic cardiomyopathy (HCM) using 123I-metaiodobenzylguanidine (MIBG). Segmental myocardial uptake of MIBG and 201T1 was calculated in 21 patients with primary HCM without history of hypertension. Septal thickness was measured by echocardiography and the relationship to septal MIBG uptake was studied. Initial MIBG uptake and 201T1 uptake showed positive correlation with the septal thickness (R = 0.581, p = 0.0058 and R = 0.677, p = 0.0007). When the septal MIBG uptake was divided by the corresponding 201T1 uptake (MIBG/T1), both the early and delayed MIBG/T1 showed negative correlation with the septal thickness (R = -0.485, p = 0.0255 and R = -0.535, p = 0.0125). Significant positive correlation was observed between septal MIBG clearance and the thickness (R = 0.510, p = 0.0182). In patients with severe septal hypertrophy (greater than 20 mm), the MIBG clearance was significantly higher compared with less hypertrophic (less than or equal to 20 mm) group (13.4 +/- 8.0%/hr vs. 3.2 +/- 4.7%/hr, p = 0.0028). Thus, MIBG was useful for the evaluation of sympathetic innervation and activity in HCM. The MIBG clearance and uptake in conjunction with 201T1 study seemed to reflect the severity of hypertrophy in HCM.

[Cardiac response to exercise before and after coronary artery bypass grafting: evaluation by continuous ventricular function monitor].

Cardiac response to exercise was evaluated with continuous ventricular function monitor (VEST) with cadmium telluride detector. Thirty-nine patients (30 male and 9 female, aged 57 +/- 8, 23 had old myocardial infarction) were monitored with VEST during and after supine ergometer exercise before and 4 weeks after coronary artery bypass grafting (CABG). Left ventricular ejection fraction (EF) responses were classified into 4 types; type A showed EF increase greater than 5% till end of exercise, type B demonstrated initial increase followed by decrease in EF, type C revealed no significant EF change, type D showed continuous EF decrease. Before CABG, each EF response type A, B, C, and D consisted of 4, 2, 12, 21 patients respectively and after CABG each type included 18, 10, 9, 2. The EF change from rest to peak exercise (delta EF-Ex) improved from -6.4 +/- 8.8% to 5.0 +/- 7.4% (p less than 0.001) after CABG. All patients showed rapid EF increase after exercise or "EF overshoot" (EF-OS). After CABG, the EF change from rest to EF-OS (delta EF-OS) and time to EF-OS (T-OS) were improved from 9.9 +/- 5.2% to 14.9 +/- 5.3% (p less than 0.001) and 162 +/- 86 sec to 80 +/- 48 sec (p less than 0.001) respectively. Type A, B patients showed higher delta EF-OS and shorter T-OS than type C, D patients, suggesting EF overshoot was contingent upon cardiac function during exercise. After CABG, in patients with myocardial infarction, T-OS shortened but delta EF-OS showed less improvement than patients without infarction, suggesting loss of myocardium hampered EF-OS.

[The utility of quantitative 99mTc-GSA liver scintigraphy in the evaluation of hepatic functional reserve: comparison with 99mTc-PMT and 99mTc-Sn colloid].

Using data from 17 patients with liver cirrhosis and 3 patients with fatty liver, we have compared the utility of 3 hepatic imaging agents in the evaluation of hepatic functional reserve. Evaluated here were 99mTc-galactosyl human serum albumin (GSA) which is a new ligand for hepatic binding protein, 99mTc-N-pyridoxyl-5-methyl tryptophan (PMT) of a hepatobiliary agent, and 99mTc-Sn colloid. In each patient, we performed these 3 imaging studies within a week and also examined hepatic function tests (indocyanine green test, hepaplastin test, choline-esterase, etc). In each imaging study, serial images and dynamic data were obtained after the injection of 99mTc-GSA (185 MBq/3 mg), 99mTc-PMT (185 MBq), or 99mTc-Sn colloid (185 MBq). Using the obtained dynamic data, we analyzed the liver kinetics of the 3 agents based on 1 compartment model with 3 parameters (hepatic clearance, hepatic excretion rate, non-specific volume of distribution). From fitting the liver and heart data to this model, three unknown parameters were determined. Patlak plot was also applied in order to estimate liver uptake rate. Both curve fitting and Patlak plot could determine appropriate parameters in every study. In 99mTc-GSA, a nonlinear 3 compartment model was also applied in order to estimate hepatic blood flow, liver receptor density, and affinity of receptor-GSA binding separately. Using the obtained parameters, we analyzed the correlations between the parameters and the results of hepatic function tests. In all of the parameters, those obtained from 99mTc-GSA imaging showed the most significant statistical correlation with the results of hepatic function tests. From the present results, 99mTc-GSA imaging was concluded to be the best for evaluation of hepatic functional reserve.

[Evaluation of ischemia by exercise stress Tl-201 myocardial SPECT in silent and symptomatic ischemia].

Forty patients with ischemic heart disease confirmed by coronary arteriography were performed Tl-201 stress myocardial scintigraphy using SPECT. Fifteen patients had anginal attack during exercise Tl-201 myocardial perfusion study (symptomatic group), and 25 patients had horizontal or downsloping ST segment depression more than 0.1 mV without angina (asymptomatic group). The washout maps were derived from circumferential profile analyses of tomographic short-axis slices, and the data were plotted as a bull's eye map. The patient's washout map was compared with the lower limit of normal (mean--2 SD), and the extent and severity scores were calculated. On visual analysis 87% (13/15) of symptomatic patients showed redistribution, while only 56% (14/25) of asymptomatic patients showed redistribution (p less than 0.05). The extent score was significantly higher in the symptomatic group than in asymptomatic group (37.2 + 23.6 vs. 19.6 + 20.8, p less than 0.05), but severity score was slightly higher in symptomatic group (56.1 + 59.4 vs. 30.0 + 54.8, NS). In conclusion, symptomatic ischemia may be more severe than asymptomatic one and the degree of ischemia may be one of the factors that determine the presence of angina during ischemia.

[Separate evaluation of beta-methyl fatty acid uptake and perfusion in rat myocardium].

The kinetics and distribution of I-125 beta-methyl iodophenyl pentadecanoic acid (BMIPP) in rat's heart were studied for separate evaluation of perfusion and metabolism. Tl-201 and BMIPP were simultaneously injected. The experimental groups consisted of control (C), glucose (G) and sodium lactate loaded group (L). In C, myocardial uptake at 5 minutes after BMIPP injection was 3.60% ID/g and remained constant up to 60 minutes. The myocardium/lung ratio (2.44) and the myocardium/muscle ratio (4.55) of BMIPP were almost equal to those of Tl-201. But myocardium/liver ratio was low (1.31). In G, myocardial uptake of BMIPP (1.94 +/- 0.36% ID/g) and g-BMIPP/Tl (0.31 +/- 0.03) at 15 minutes after injection were significantly decreased (p less than 0.001) than those of C (3.16 +/- 0.18% ID/g and 0.48 +/- 0.05). In L. myocardial perfusion was decreased and g-BMIPP/Tl (0.73 +/- 0.14) was significantly higher (p less than 0.01) than those of C. Coefficient of variance of the density within a myocardium, and the ratio of inner to outer layer of myocardium (I/O ratio) were calculated from autoradiogram by videodensitometry. The myocardial distribution of BMIPP was more inhomogeneous, and the I/O ratio was lower than that of Tl-201, although these were not specific for metabolic interventions. In conclusion BMIPP is suitable for SPECT imaging and dual nuclide imaging by BMIPP and Tl-201 will provide informations about myocardial fatty acid metabolism and perfusion.

Quantitative analysis of 123I-meta-iodobenzylguanidine (MIBG) uptake in hypertrophic cardiomyopathy.

Myocardial scintigraphy with 123I-meta-iodobenzylguanidine (MIBG) and thallium-201 (201Tl) was performed in 29 patients with hypertrophic cardiomyopathy (HCM) using whole-body scintigraphy and single-photon emission computed tomography (SPECT). Nonhypertensive patients were classified into three groups according to the septal thickness determined by ultrasonography; group 1 (wall thickness less than 16 mm, n = 5), group 2 (from 16 to 20 mm, n = 12) and group 3 (greater than 20 mm, n = 4). The regional myocardial uptakes of both 201Tl and 123I-MIBG (percent of injected dose/cm3 myocardium) were higher in the more hypertrophic septa. However, when regional MIBG uptake at 3 hours was divided by the 201Tl uptake to calculate the MIBG uptake per unit of blood flow, the hypertrophic septa showed lower mean values--0.39 +/- 0.23 and 0.50 +/- 0.10 in groups 3 and 2, respectively (p less than 0.1 compared with 0.69 +/- 0.20 in group 1). The regional MIBG clearance rate in the septum was significantly higher in group 3 compared with group 1 (13.4 +/- 8.0%/hr versus 1.5 +/- 6.2%/hr, p less than 0.05). The uptake and 123I-MIBG clearance rate in the lateral wall showed a similar tendency. Myocardial uptake determined by whole-body scintigraphy was slightly increased in group 2 (3.5 +/- 0.6%, p less than 0.05) compared with group 1 (2.7 +/- 0.8%); however, it was lower in group 3 (2.7 +/- 0.4%). Myocardial 123I-MIBG distribution demonstrated various patterns in comparison with 201Tl distribution, suggesting that flow-independent changes in sympathetic innervation or activity may exist in patients with HCM.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole-body distribution of iodine 123 metaiodobenzylguanidine in hypertrophic cardiomyopathy: significance of its washout from the heart.

Whole-body distribution of iodine 123 metaiodobenzylguanidine (123I-mIBG) was evaluated in 27 patients with hypertrophic cardiomyopathy (HCM). At 1 and 4 h after injection, anterior and posterior whole-body images were obtained with a dual-headed, camera-computer system. Patients were classified into three groups based on the septal wall thickness as determined by echocardiography: group 1 consisted of 7 patients with less than or equal to 15 mm septal thickness, group 2 included 12 patients with 16-19 mm septal thickness, and group 3 included 6 patients with greater than or equal to 20 mm septal thickness. Although the myocardial mIBG uptakes at 1 h were similar among these groups (1.84% +/- 0.19%, 1.95% +/- 0.38%, 1.98% +/- 0.57%, respectively; NS), mIBG washout from the heart in group 3 was faster than in groups 1 and 2 (31.5% +/- 13.0% vs. 15.8% +/- 11.0% (group 1, P less than 0.05), 17.6% +/- 7.3% (group 2, P less than 0.01)). There was a significant positive correlation between mIBG washout from the heart and septal thickness, with correlation coefficient r = 0.52 (P less than 0.01). The liver, lung, parotid gland, spleen and skeletal muscle showed similar mIBG uptake and washout among the three groups. We conclude from these data that mIBG washout from the heart in HCM was faster in patients with severe hypertrophy than in patients with mild to moderate hypertrophy, and hence it may be a useful parameter for evaluating the severity of altered adrenergic innervation and activities.

Error of uptake in dual energy acquisition with 201Tl and 123I labeled radiopharmaceuticals.

In myocardial scintigraphy, simultaneous injection of two radionuclides and dual energy acquisition are potentially useful in the assessment of regional perfusion and metabolism. The feasibility of dual radionuclide study with 201Tl and 123I labeled radiopharmaceuticals (meta-iodobenzylguanidine I 123, in this study) was investigated in phantoms and patients. The crosstalk of one radionuclide to the other pulse height window was defined as the ratio of the 201Tl count in the 123I and 201Tl windows, R[I/Tl], and the ratio of the 123I count in the 201Tl and 123I windows, R[Tl/I]. The ratios were determined in planar images and SPECT studies. In clinical studies with whole body scintigraphy (n = 8), the value of R differed significantly in various organs. In the SPECT study (n = 13), R was not uniform and varied with time and location, resulting in significant errors in uptake and regional count ratio. Thus, dual energy acquisition with 201Tl and 123I labeled radiopharmaceuticals is generally not recommended because of varying amounts of crosstalk interference. Possible solutions to this problem are discussed. The feasibility of dual radionuclide study must be confirmed in human as well as in phantom studies.

Left ventricular dysfunction during exercise in patients with angina pectoris and angiographically normal coronary arteries (syndrome X)

Left ventricular function during exercise and recovery was investigated in patients with angina pectoris, ST segment depression during exercise and angiographically normal coronary arteries (syndrome X) using a continuous left ventricular function monitor with cadmium telluride detector (CdTe-VEST). Fourteen patients with syndrome X and 14 patients with atypical chest pain without ST segment depression during exercise and normal coronary arteries (control group) performed supine ergometric exercise after administration of 740-925 MBq of technetium-99m labelled red blood cells, and left ventricular function was monitored every 20 s using CdTe-VEST. Left ventricular ejection fraction (EF) response was impaired (< or = 5% increase from rest to peak exercise) in 11 or 14 patients with syndrome X but in none of the control patients. Resting EF was similar in the two groups (62.1% +/- 6.7% in patients with syndrome X, 61.9% +/- 6.2% in controls); however, EF increase from rest to peak exercise was lower in syndrome X (-3.1 +/- 9.5% vs 14.7% +/- 7.4%, P < 0.001). After cessation of exercise, all patients showed rapid EF increase over baseline and this EF overshoot was lower (19.3% +/- 8.3% vs 26.4% +/- 7.3%, P < 0.001) with the time to EF overshoot longer (114 +/- 43 s vs 74 +/- 43 s, P < 0.05) in patients with syndrome X. Thus, in patients with syndrome X, left ventricular dysfunction was frequently observed during exercise in spite of normal epicardial coronary arteries.