Myocardial single-photon emission computed tomographic imaging with technetium 99m tetrofosmin: Stress-rest imaging with same-day and separate-day rest imaging

Background

Technetium 99m tetrofosmin is a new ethylene diphosphine ligand for myocardial perfusion imaging and has unique properties. We have compared stress-rest single-photon emission computed tomographic (SPECT) imaging with^99mTc tetrofosmin with same-day and separate-day rest imaging to detect myocardial perfusion defects.

Methods and Results

Myocardial SPECT imaging was performed in 22 patients with coronary artery disease who had undergone planar thallium 201 imaging and coronary angiography. Single-day (stress-rest) and separate-day rest^99mTc tetrofosmin SPECT protocols were compared in the same patient. Images were assessed by a blinded panel to identify myocardial infarction, ischemia, or normal scans. Overall sensitivity for identification of patients with coronary artery disease was 86% (19/22) by both same-day stress-rest and separate-day rest protocols with^99mTc tetrofosmin (p=NS). Of a total of 396 segments studied, 107 abnormal segments were identified at exercise and 76 and 81 at the same-day and separate-day rest tests, respectively (p=NS). Same-day stress-rest and separate-day rest^99mTc tetrofosmin SPECT protocols were also useful for detecting individual coronary stenosis with a greater than 50% lesion: 80% of the left anterior descending, 93% of the right coronary, and 75% of the left circumflex coronary arteries were detected.

Conclusion

Excellent images were obtained with^99mTc tetrofosmin during both stress and rest.^99mTc tetrofosmin imaging with the same-day stress-rest and separate-day rest imaging protocols have similar diagnostic sensitivities for detection of coronary heart disease.     

Lung uptake of technetium 99m sestamibi: Relation to clinical,exercise, hemodynamic,and left ventricular function variables

Background

Technetium 99m sestamibi (2-methoxyisobutyl isonitrile [MIBI]) is a relatively new radiopharmaceutical with improved imaging characteristics for exercise myocardial perfusion studies compared with thallium 201. Although increased lung uptake of²⁰¹Tl has been shown to have important clinical significance, reflecting severity of coronary artery disease and left ventricular function, the factors affecting MIBI lung uptake are unknown. Therefore we examined the potential clinical, exercise, hemodynamic, myocardial perfusion, and ventricular function determinants of lung uptake of MIBI on exercise myocardial perfusion studies.

Methods and Results

The study cohort consisted of 103 patients referred for evaluation of coronary artery disease with exercise MIBI myocardial perfusion imaging. All patients underwent both a standard 1-day rest-stress MIBI planar imaging protocol and rest echocardiography. With the anterior-view stress images obtained 1 hour after MIBI injection, regions of interest were drawn over peak lung and myocardial activities and a lung/heart ratio was calculated. Multivariate regression analysis was used to relate the lung/heart ratio to clinical, exercise and hemodynamic, myocardial perfusion, and echocardiographic left ventricular function scores. We found no significant relation between lung/heart ratio and any patient variable.

Conclusions

Unlike²⁰¹Tl, lung uptake of MIBI is not related to indexes of exercise, left ventricular dysfunction, or perfusion abnormalities. Thus MIBI lung uptake does not appear to have the same clinical significance as²⁰¹Tl lung uptake.     

Identification of asynergic but viable myocardium in patients with chronic coronary artery disease by gated blood pool scintigraphy during isosorbide dinitrate and low-dose dobutamine infusion: Comparison with thallium-201 scintigraphy with reinjection

To evaluate the ability of low-dose dobutamine and isosorbite dinitrate (ISDN) gated blood pool scintigraphy (GBPS) and thallium SPECT with reinjection to identify viability in asynergic myocardium, both procedures were performed in 38 consecutive patients with chronic coronary artery disease and left ventricular dysfunction. Twenty-two of the 38 patients with successful revascularization were analyzed. GBPS was performed at the baseline and during continuous infusion of low dose dobutamine (5 μg/kg/min) and ISDN (2 μg/kg/min). Cine mode GBPS wall motion was scored from normal (0) to dyskinesis (4) semiquantitatively. Forty-seven of 110 segments with severe asynergy at the baseline were analyzed. Viability determined by GBPS was defined as wall motion score improvement by more than 1 grade. Thallium viability was defined as the segment with redistribution or fill in with severe initial perfusion defect. GBPS was 76.7% sensitive and 70.6% specific for predicting post vascularization wall motion improvement (p < 0.005). Of 47 segments with severe asynergy, concordance of judgement was obtained in 40 segments (85.1 %), and reversibility was correctly diagnosed in 34 of 40 patients (85.0%), but thallium with reinjection correctly identified tissue viability in 6 of 7 segments with discordance between 2 studies. These data suggest that most cases of reversible asynergy (hibernating myocardium) respond to ISDN and dobutamine, suggesting the possibility of predicting improvement by revascularization, although some underestimation of tissue viability remained to be resolved. Thallium with reinjection is superior to low-dose dobutamine + ISDN GBPS for the assessment of myocardial viability.     

One-year prognosis of patients with normal planar or single-photon emission computed tomographic technetium 99m-labeled sestamibi exercise imaging

Background.

The favorable prognostic significance of normal²⁰¹Tl stress perfusion images, even in the presence of known coronary artery disease, has been well documented. Relatively few data are available with regard to the prognostic significance of normal planar and single-photon emission computed tomographic (SPECT) stress^99mTc-labeled sestamibi (^99mTc-sestamibi) images.

Methods and Results.

The prognostic significance of normal exercise^99mTc-sestamibi myocardial perfusion imaging was evaluated in 208 consecutive patients. All patients were referred for evaluation of chest pain syndrome. One hundred eight patients (52%) underwent SPECT imaging, 79 patients (38%) underwent planar imaging, and 21 patients (10%) underwent both planar and SPECT imaging. One hundred seventy-five patients (84%) had a normal or nondiagnostic exercise electrocardiogram, and 33 patients (16%) had a positive exercise electrocardiogram. Follow-up was 13.5 ±2 months and was complete in 99.5% of patients. No patient died of cardiac causes during follow-up. One patient (0.5%) had a nonfatal myocardial infarction and four patients (2%) had unstable angina necessitating revascularization. There was no difference in rate of cardiac events between men and women or whether SPECT or planar imaging was used. However, 33 patients with normal^99mTc-sestamibi imaging and a positive exercise electrocardiogram had a significantly higher cardiac event rate than had patients with negative exercise electrocardiograms (9% vs 1%,p < 0.025).

Conclusion

Patients with normal^99mTc-sestamibi exercise SPECT or planar imaging results and a normal or nondiagnostic exercise electrocardiogram have a favorable 1-year prognosis. Patients with normal^99mTc-sestamibi images and a positive stress electrocardiogram have a less favorable outcome.     

Comparison of exercise,dipyridamole, and adenosine by use of technetium 99m sestamibi tomographic imaging

Background

Pharmacologic stress has been shown in animal studies to induce high degrees of myocardial hyperemia. At these levels of myocardial blood flow, the myocardial uptake of technetium 99m sestamibi may plateau and may affect the diagnostic accuracy. This study compared the effects of myocardial hyperemia induced by exercise, dipyridamole, and adenosine on^99mTc sestamibi tomographic imaging in normal subjects and patients with ischemic coronary artery disease.

Methods and Results

Twenty subjects (group I, 10 normal subjects; group II, 10 patients with known coronary artery disease) underwent^99mTc sestamibi tomographic imaging after rest, exercise, dipyridamole infusion, and adenosine infusions on separate occasions. Total and background-corrected myocardial counts of the resulting images were calculated. Visual and computer-generated quantitative myocardial perfusion defect analysis was performed in subjects in group II. For subjects in both groups I and II, there were no significant differences in the background-corrected myocardial counts obtained with exercise, dipyridamole, and adenosine stress. There were no significant differences in the myocardial perfusion defects obtained after the three different modes of stress, including percentage defect size, stress deficit percentage, percentage of ischemia, count deficit index, and defect nadir.

Conclusions

The myocardial uptake of^99mTc sestamibi in normal subjects and patients with coronary artery disease is comparable after exercise, dipyridamole, and adenosine stress. In addition, the defect sizes and intensities with^99mTc sestamibi after all forms of stress were equivalent. Thus^99mTc sestamibi, in combination with either adenosine or dipyridamole infusions, provides imaging data equivalent to those with exercise and may be considered an alternative in patients unable to undergo adequate exercise.     

Circulating forms of immunoreactive parathyroid hormone-related protein for identifying patients with humoral hypercalcemia of malignancy: A comparative study with C-terminal(109–141)- and N-terminal(1–86)-region-specific PTHrP radioassay

We evaluated the circulating forms of immunoreactive PTHrP in 115 healthy subjects and 122 patients with malignant diseases by using radioassay systems (RAS) specific for the C-terminal (109–141) fragment of PTHrP (C-RAS) and for the N-terminal(l–86) (N-RAS). PTHrP levels in healthy controls ranged from 1.5 to 38.2 (mean: 24.5) pmol/L with the C-RAS and from 0.9 to 2.5 (mean: 1.7) pmol/L with the N-RAS. The ratio of circulating N-terminal fragment (N) to C-terminal fragment (C)of PTHrP was calculated to be about 1:14.4 in the healthy subjects. Of the 122 patients with malignant diseases, 40 (32.8%) had circulating PTHrP levels undetectable with the N-RAS, but only 11 (9.0%) patients had levels undetectable with the C-RAS. Of the former 122 patients, 41 (33.6%) had high PTHrP as determined with the C-RAS, and 10 (8.2%) had high PTHrP as determined with the N-RAS. The former of these included only 8 (19.5%) HHM patients, while the latter included 8 (80.0%) HHM patients. The circulating N to C ratio was about 1:70.7 in the HHM patients. The N and C obtained with the different RASs showed a close correlation (r = 0.86). The values also showed a close correlation with serum Ca; r = 0.75 for C-RAS and r = 0.81 for N-RAS. In addition, the correlations between the PTHrP reading obtained with the different RAS s and serum Cr were: r = 0.42 with C-RAS and r = 0.26 with N-RAS. The circulating form of immunoreactive PTHrP fragments is therefore comprised mainly of PTHrP(109–141). In contrast, circulating concentrations of the PTHrP(l-86) fragment are very low, but detection of the PTHrP(l-86) fragment with the N-RAS is a more useful indicator of HHM with fewer false positive results and is less likely to be influenced by renal function than the detection of the PTHrP(109–141) fragment with C-RAS.     

Total body and regional bone mineral content in hemodialysis patients

Bone mineral content (BMC) in the total body and lumbar spine was evaluated in 126 hemodialysis patients (60 males, 66 females) by dual photon absorptiometry with the Norland DBD 2600. Measurements of: 1) total body BMC divided by lean body mass (BMC_TB/LBM), 2) bone mineral density (BMD) of total body, 3) BMD of four regional sections (head, trunk, pelvis, and legs), and 4) BMD of lumbar spine, generally showed a significant decrease in the hemodialysis patients compared to the reference population. However, arm BMD did not show a significant difference between patients and control populations. The z-score of BMC_TB/LBM declined significantly throughout the duration of hemodialysis, although that of the lumbar spine BMD did not. It should be noted that the degree of decrease in BMC was more prominent in the total body measurement than in the lumbar spine measurement. There was preferential osteopenia of the total body in the hemodialysis patients. Although the lumbar spine BMD showed a lower value than the control population, the lumbar spine is not the recommended region to monitor the BMD change in hemodialysis patients.     

Quantitative myocardial perfusion single-photon emission computed tomographic imaging: Quo vadis? (where do we go from here?)

Quantitative myocardial perfusion single-photon emission computed tomography can be improved further by technical advancements that are imminent in the clinical setting. These improvements are directed toward two main goals: (1) increasing the accuracy that the myocardial count distribution from tomographic slices represents the true tracer concentration and (2) increasing the accuracy of extracting this myocardial count distribution for quantitative analysis. Once these advancements are fully validated and implemented clinically, the clinical value of these cardiac diagnostic tests will be enhanced by increased accuracy of detecting and characterizing myocardial hypoperfusion and coronary artery disease.     

A comparative study of evaluating renal scars by99mTc-DMSA planar and SPECT renal scans,intravenous urography,and ultrasonography

The purpose of this prospective study is to compare 3 types of^99mTc-DMS A renal scan [(a) planar, (b) x-ray type film static SPECT presentation (SPECT-1) and (c) dynamic three-view display of SPECT slices (SPECT-2)], intravenous urography, and ultrasonography in the diagnosis of renal scars. All these studies were performed in 130 pediatric patients, with urinary tract infection (42 patients), vesicoureteral reflux (37), and unilateral or bilateral small kidney(s) (51). The number of renal scars detected was highest with the^99mTc-DMS A renal SPECT-1 scan and next came the^99mTc-DMSA renal SPECT-2 studies. There is a significant difference (p < 0.05) between the ability of planar and SPECT-1 to recognize renal defects. However, SPECT-2 may provide the best stereotactic localization and image quality of all the methods.     

Noninvasive identification of left main and three-vessel coronary artery disease by thallium-201 single photon emission computed tomography during adenosine infusion

Advanced coronary artery disease, defined as left main or three-vessel coronary disease, was identifiable noninvasively by means of adenosine Tl-201 single photon emission tomography. Among 75 consecutive patients with angiographically documented coronary artery disease, there were 11 patients with the presence (group 1) and 64 patients with the absence (group 2) of advanced coronary artery disease. The lung-to-heart ratio (L/H ratio) of Tl-201 uptake was calculated as the fraction of average Tl-201 counts per pixel in the lung divided by those in the myocardium. The left ventricular dilation ratio (LVDR) was determined as a ratio of left ventricular cavity size in the early image to that in the delayed image. The patients in group 1 had more defects (2.3 ± 0.6 seg. vs. 0.9 ± 0.7 seg., p < 0.001), ahigher L/H ratio (35 ± 4% vs. 28 ± 5%, p < 0.001) and a higher LVDR (1.13 ± 0.04 vs. 1.06 ± 0.04, p < 0.001) than those in group 2. The diagnostic accuracy of the identification of advanced coronary artery disease was 89% by perfusion defects, 68% by L/H ratio and 81% by LVDR. Stepwise discriminant analysis revealed that LVDR (F = 36.2, p < 0.0001) and perfusion defects (F = 8.9, p < 0.004) were the significant and independent discriminators of advanced coronary disease. Identification of patients with left main or three-vessel coronary disease was enhanced by additional analysis of cavity dilation of the left ventricle and increased Tl-201 activity in the lung.     

Combined assessment of regional perfusion and wall motion in patients with coronary artery disease with technetium 99m tetrofosmin

Background

Technetium 99m tetrofosmin is a new^99mTc-labeled myocardial perfusion agent that can be labeled easily and provides excellent myocardial perfusion images. In addition, bolus administration of the tracer allows first-pass radionuclide ventriculography.

Methods and Results

This study examined the diagnostic value of combined assessment of regional perfusion by tetrofosmin tomography and wall motion by first-pass radionuclide ventriculography both at rest and during stress in 24 patients suspected of having coronary artery disease. All patients underwent stress-rest tetrofosmin tomography, stress-delayed thallium 201 tomography, and coronary angiography. Stress tetrofosmin tomography showed abnormal perfusion in all 23 patients with angiographic evidence of coronary artery disease, whereas stress²⁰¹Tl tomography showed abnormal perfusion in 22 of the 23 patients. For detection of significant (≥50% diameter stenosis) stenotic coronary arteries, the two perfusion studies showed similar sensitivities (62% with²⁰¹Tl and 69% with tetrofosmin) and specificities (88% and 100%, respectively). When analysis of regional wall motion was combined with perfusion study, a slightly higher sensitivity was obtained (77%), with similar specificity. The regional wall motion score was concordant with the regional perfusion score in only 42% of the segments at rest and 50% during exercise.

Conclusions

These results suggest that stress tetrofosmin perfusion tomography and stress²⁰¹Tl tomography provided similar diagnostic accuracy for detection of coronary artery disease. The combined assessment of perfusion and function that is feasible with tetrofosmin may enhance diagnostic accuracy in patients with coronary artery disease.     

FDG-PET for the evaluation of tumor viability after anticancer therapy

To evaluate positron emission tomography with¹⁸F-fluorodeoxy glucose (FDG-PET) as an diagnostic tool to determine tumor viability after anticancer therapy, fourteen patients were examined by FDG-PET after the end of the treatment. The lesions with residual viable tumor cells showed higher uptake of FDG than surrounding normal soft tissue. The lesions, in which tumor viability was lost or very low, showed higher uptake of FDG in four cases and similar uptake to normal soft tissue in three cases. The residual increased uptake of FDG was considered to be caused by remaining tumor cells and/or inflammatory reaction to anticancer treatment. FDG-PET after anticancer treatment should be interpreted by considering the reaction due to the treatment and the partial volume artifact of PET caused by the limited spatial resolution.     

In vivo kinetics of99mTc labeled recombinant tissue plasminogen activator in rabbits

Our previous studies demonstrated that^99mTc labeled recombinant tissue plasminogen activator (rt-PA) retained high affinity with fibrinin vitro but showed unexpectedly low uptake in fresh thrombiin vivo. The present study was performed to determine thein vivo kinetics of radiolabeled t-PA in the rabbit. Sequential images and blood samples after the intravenous administration of^99mTc labeled rt-PA in thrombus-bearing rabbits were taken. The radioactivity and immunological level of t-PA and PAI-1 in the solution eluted to each fraction by gel permeation chromatography were measured by means of a well scintillation counter and enzyme-linked immunosorbent assay (ELISA). Most of the radioactivity was eluted in the fraction (Fr. 7) of larger molecular weight than that (Fr. 9) of intact t-PA. The level of intact rt-PA was increased with a regimen involving the preadministration of cold rt-PA which was followed by the administration of hot rt-PA. The level of PAI-1 in plasma showed an increased rebound 15 minutes after the intravenous injection. These results suggest two possible reasons why rt-PA retains high affinity with fibrinin vitro, once radiolabeled, but was ineffective in delineating fresh thrombi with a gamma camera: 1) some plasma components such as PAI-1 combine with circulating radiolabeled rt-PA and form a larger molecule immediately and/or 2) radiolabeled rt-PA is modulated as a consequence of the radiolabeling and forms a larger molecule than intact rt-PA.     

A clinical feature of myocardial stunning associated with acute myocardial infarction

We report a case of myocardial stunning after acute myocardial infarction. In the hyperacute phase of myocardial infarction, the patient’s coronary arteries showed normal features on coronary angiography during extensive ST-segment elevation observed on a standard 12-lead electrocardiogram and extensive akinesis observed on a left ventriculogram. Thallium-201 emission computed tomography revealed extensive perfusion abnormality. In the chronic phase, the perfusion abnormality was markedly improved. However, the electrocardiogram demonstrated poor R wave progression, and the left ventriculography revealed slight hypokinesis in the anterolateral wall. The acetylcholine provocation test disclosed coronary vasospasm of the left anterior descending coronary artery. About six months thereafter, left ventricular wall motion became completely normal and no poor R wave progression was observed on the electrocardiogram. The findings in this case indicate that myocardial stunning resulted from brief but severe ischemia due to vasospasm which led to cardiogenic shock, and that the recovery of findings for thallium-201 perfusion might be followed by those of electrocardiography and left ventriculography in the stunned myocardium.     

Response of right ventricular systolic function to exercise stress: Effects of pulmonary vascular resistance on right ventricular systolic function

To elucidate factors influencing responses of right ventricular systolic function to exercise stress, we evaluated the right ventricular ejection fraction and peak ejection rate with two different loading conditions, atrial septal defect and mitral stenosis, at rest and during exercise by means of gated equilibrium blood pool radionuclide ventriculography. In both atrial septal defect and mitral stenosis, strong correlations between changes in the right ventricular ejection fraction with exercise and pulmonary vascular resistance at rest (r = ?0.97, p < 0.001; r = ?0.86, p < 0.0005: respectively) were found. Significant correlations between changes in the right ventricular peak ejection rate with exercise and pulmonary vascular resistance at rest (r = ?0.85, p < 0.05; r = ?0.75, p < 0.01: respectively) were found in atrial septal defect and mitral stenosis. Both the right ventricular ejection fraction and peak ejection rate were lower during exercise than at rest when pulmonary vascular resistance at rest was more than 200 dynes·sec·cm^?5·m² in both atrial septal defect and mitral stenosis. In conclusion, right ventricular systolic function responding to exercise stress was influenced by the pulmonary vascular resistance in both atrial septal defect and mitral stenosis.     

FDG-PET for predicting the prognosis of malignant lymphoma

To evaluate the usefulness of FDG-PET as a predictor of prognosis, 34 patients with untreated malignant lymphoma in the head and neck region were studied. After FDG-PET and treatment, they were observed from 15 to 50 months. Tumors which were aggressive and resistant to treatment tended to show high uptake of FDG. The survival rate of patients with high uptake of FDG, DAR > 8, was lower than the rate of the other patients. It is considered to be useful to add FDG uptake of the tumor to other prognostic factors for predicting the prognosis.     

Analysis of factors affecting uptake of Tc-99m Sn-N-pyridoxyl-5-methyltryptophan by hepatocellular carcinoma

We performed Tc-99m PMT imaging in 176 patients with HCC and evaluated factors affecting^99mTc-PMT uptake by HCC with a logistic model. The probability of HCC showing increase in uptake of the radioisotope was 104.6 times higher in patients with the Ed I type than in those with the Ed III type and 12.1 times higher in patients with a tumor diameter of 5.0–7.9 cm than in those with a tumor diameter of 2.0–5.0 cm. Among the other variables, the serum AFP level and sex were suggested to have effects similar to those of the tumor size on Tc-99m PMT uptake by HCC. The grade of morphological differentiation of the tumor was therefore most markedly related to Tc-99m PMT uptake.     

Thallium-201 reinjection images can identify the viable and necrotic myocardium similarly to metabolic imaging with glucose loading18F-fluorodeoxyglucose (18FDG)-PET

We compared the usefulness of¹⁸F-fluorodeoxyglucose (¹⁸FDG)-PET with glucose loading and thallium-201 (²⁰¹Tl) reinjection imaging for determining the viability of the myocardium in 21 patients with an old anterior myocardial infarction. We obtained transaxial views during²⁰¹T1 reinjection imaging performed 10 minutes after post-exercise injection of 37 MBq²⁰¹Tl. PET imaging with 75 g oral glucose loading was performed 60 min after injection of 148 MBq of I8FDG. Wall motion was evaluated by echocardiography. Excellent¹⁸FDG-PET images were obtained in 19 of 21 subjects in whom plasma glucose levels were below 251 mg/d/. The results of²⁰¹Tl reinjection imaging and¹⁸FDG-PET imaging were in agreement in 20 of the 21 subjects. Echocardiography demonstrated hypokinesis or akinesis in segments identified as abnormal in imaging studies. Our results showed that²⁰¹Tl reinjection imaging identified the viable and necrotic myocardium similarly to metabolic imaging obtained by¹⁸FDG-PET with glucose loading.     

Autoradiographic analysis of [14C]deoxy-D-glucose in thyroid cancer xenografts: A comparative study with pathologic correlation

An experimental model of thyroid cancer was prepared for evaluating the accumulation of [¹⁴C]deoxy-D-glucose ([¹⁴C]DG) in thyroid cancer xenografts (AC2). A continuous cell line established from a biopsy specimen of a metastatic thyroid carcinoma possessed the ability to synthesize the cellular protein without increase in cell division after adding bovine TSHin vitro. The histological sections of the xenografts resected from the¹³¹I treated nude mice mainly consisted of structures showing follicular and trabecular growth. Immunohistochemically the cytoplasm of the tumor cells was positive for human thyroglobulin(hTg). These observations provide strong evidence that the AC2 cell originates in the thyroid follicular epithelium. By comparing autoradiographic accumulation patterns of [¹⁴C]DG and histopathological examinations, it was found that the uptake of [¹⁴C]DG was higher in the granulation tissues surrounding necrosis than in viable tumor cells of trabeculary growing and follicle forming tissues. It is suggested that the degree of [¹⁴C]DG content reflects not only tumor cell viability and proliferation but also the inflammatory and degenerative reaction accompanying tumor cell growth.     

Myocardial technetium 99m-labeled sestamibi single-photon emission computed tomographic imaging in the detection of coronary artery disease: Comparison between early (15 minutes) and delayed (60 minutes) imaging

Background

Previous studies have demonstrated that there is a “partial” myocardial redistribution of^99mTc-labeled sestamibi (MIBI) between 1 and 3 hours after intravenous injection at stress. The purpose of this prospective study was to compare MIBI single-photon emission computed tomographic (SPECT) imaging performed 15 and 60 minutes after the injection at stress in the detection of coronary artery disease.

Methods and results

Thirty-five patients with coronary artery disease (26 underwent coronary angiography and 23 had a positive²⁰¹Tl study result) were included in this study. SPECT imaging started 15 minutes after the injection of 25 to 30 mCi MIBI at peak stress (180-degree arc, 32 angles, 25 sec/view, and high-resolution collimator). Patients underwent reimaging at 60 minutes according to the same protocol and with the same gamma camera. A rest study was obtained 75 minutes after the injection of MIBI (25 to 30 mCi) at rest, 48 hours later. Images (divided for a total of 19 segments per patient) were interpreted by two blinded observers for patient diagnosis and segmental comparison. The patient diagnosis was the same for the two protocols: normal = 3, ischemia = 27, and scar = 5. The segmental agreement (k = 0.90) was 632/665 (95.0%). The imaging performed at 15 minutes detected normal, ischemia, and scar in 413, 189, and 63 segments, respectively, whereas the imaging performed at 60 minutes detected 422, 180, and 63 segments, respectively (difference not significant). The early and delayed images were placed side by side for subjective comparison of the extent of the defect. Early imaging showed slightly larger defects in six patients, equal defects in 24 patients, and slightly smaller defects in five patients. Ischemic/normal wall ratios were 0.67 ±0.16 at 15 minutes and 0.68 ±0.15 at 60 minutes.

Conclusions

There is no clinically significant difference between SPECT imaging performed at 15 minutes or 60 minutes after the injection of MIBI at stress. Furthermore, this study showed that it is feasible to obtain good-quality MIBI images even 15 minutes after the injection at stress.