Reverse redistribution in the stress thallium scan--correlation of coronary blood flow and myocardial damage

In order to make clear 'reverse redistribution (RR)' phenomenon in stress thallium scan we investigated 477 consecutive patients who were consisted of 74 cases with PTCA (PTCA group), 86 cases with coronary artery bypass graft (CABG group) and 317 cases without any revascularization (N group). RR was detected in 12 cases out of PTCA group (16%), in 11 cases out of CABG group (13%) and in 10 cases out of N group (3.2%), and the incidence of RR in PTCA or CABG group was higher than that of N group (p less than 0.01). In 33 patients with RR the cases without significant coronary artery stenosis were more than those with stenosis (p less than 0.01) and the cases with myocardial damage were more than those without damage (p less than 0.01). In quantitative analysis washout rate at the RR areas showed relatively high value, but it was not significant compared with normal value (53 +/- 9.0% vs. 49 +/- 1.9%). In conclusion, RR had a tendency to appear in the condition of normal myocardium mingled with scar and of sufficient coronary blood flow. The mechanism of the phenomenon was thought to be that initial uptake of thallium in the partially scarred area was as high as in the normal myocardium, but washout of thallium from its remaining normal myocardium is normal or faster so that the defect appears at the myocardium mingled with scar. Therefore existence of reverse redistribution suspects the myocardium mingled with scar and sufficient coronary blood flow to the remaining normal myocardium.     

Reverse redistribution on planar thallium scintigraphy: relationship to resting thallium uptake and long-term outcome

Reverse redistribution (RR) of thallium-201 has been associated with both acute and healed myocardial infarction, and with recent thrombolysis. The physiologic basis for RR in coronary artery disease (CAD) is unclear but may be related to an admixture of viable and scarred myocardium within the RR segment. We performed thallium reinjection imaging at rest to better characterize RR defects in patients with chronic CAD. We found enhanced uptake of²⁰¹Tl in 52% of RR segments after reinjection, consistent with significant regional viability that was not evident on redistribution images. We then used a logistic multiple regression analysis to determine whether RR alone or in combination with other scintigraphic findings could predict patient outcome. The results showed that severe RR was an independent predictor of patient outcome. We conclude that RR may have prognostic significance in chronic CAD.     

A bull's eye subtraction polar map for assessing thallium redistribution (1). Comparison with quantitative redistribution

A new bull's eye subtraction polar (BS) map has been developed for quantitative assessment of redistribution on stress-delayed thallium-201 SPECT studies. BS map was created after subtraction of a normalized stress bull's eye polar map from a normalized delayed polar map in 10 normal subjects and 33 patients with coronary artery disease to compare BS map with qualitative redistribution scores. The BS map showed less than 15% in all of the 50 segments in the normal subjects. Of 27 segments exhibiting persistent defect without redistribution, the BS map showed less than 10% in 20 segments (74%) and 10-15% in 6 segments (22%). On the other hand, of 34 segments exhibiting redistribution, the BS map showed greater than or equal to 15% in 25 segments (74%) and 10-15% in the remaining 9 segments (26%). Thus, significant redistribution was evident in the areas showing greater than or equal to 10-15% on the BS map. We conclude that the BS map is valuable for quantitative assessment of redistribution on stress-delayed thallium-201 SPECT imaging.     

Sodium bicarbonate-augmented stress thallium myocardial scintigraphy

It is well known that sodium bicarbonate in pharmacological doses induces transient alkalosis, causing intracellular transport of serum potassium. The aims of this study were (a) to investigate whether, in humans, myocardial thallium-201 uptake can be augmented by pretreatment with a single bolus of sodium bicarbonate at a pharmacological dose, (b) to verify general safety aspects of the intervention and (c) to evaluate the clinical implications of augmentation of ²⁰¹Tl uptake, if any. Routine exercise myocardial scintigraphy was performed twice in eight adult volunteers (five normal and three abnormal), once without intervention and the second time (within a week) following intravenous administration of sodium bicarbonate (88 mEq in 50 ml) as a slow bolus 1 h prior to the injection of ²⁰¹Tl. Conventional myocardial thallium study was compared with sodium bicarbonate interventional myocardial scintigraphy with respect to myocardial uptake (counts per minute per mCi injected dose), washout patterns in normal and abnormal myocardial segments, and overall clinical interpretation based on planar and single-photon emission tomographic (SPET) images. All patients remained asymptomatic after the intervention. A mean increase of 53% in myocardial uptake of thallium was noted in post-exercise acquisitions after the intervention, confirming uptake of the tracer via the potassium-hydrogen pump and its augmentation by transient alkalosis. The washout pattern remained unchanged. The visual quality of planar and SPET images improved significantly after the intervention. Out of the five abnormal myocardial segments identified in three cases, four showed significant filling-in after the intervention, causing the diagnosis to be upgraded from partial scar to ischaemia, or from ischaemia to normal. The overall scan impression changed in two out of three such cases. Sodium bicarbonate augmentation may have significant implications for stress-thallium scintigraphy and may be a new parameter for defining myocardial viability.     

Starting up stress thallium cardiac imaging services

This paper presents an evaluation of alternative methods for a hospital to establish stress thallium cardiac imaging services at a group of physicians' office. Volume-cost-profit analysis, break-even analysis and capital budgeting techniques were used to determine the most feasible method from a financial perspective without sacrificing quality of services. The main focus of this evaluation centers upon three alternative methods of procuring an imaging camera: (1) purchasing a new camera, (2) purchasing used equipment, or (3) leasing a new camera. Budgeted income statements were constructed using relevant revenue and cost information for each alternative. The payback period, net present value and the internal rate of return for each method of procuring a camera was computed. In addition, the break-even point was also determined for each alternative. After the analysis was completed, it was concluded that the method of choice, without sacrificing quality of service delivery, was that of purchasing a used camera.     

Variations in the referral patterns to stress nuclear imaging and stress echocardiography scans

Background  Stress myocardial perfusion imaging (MPI) and stress echocardiography (Echo) are commonly used for the noninvasive evaluation of patients with suspected coronary artery disease (CAD). Very few studies have compared the referral patterns to these imaging modalities in terms of the clinical profile of patients, reasons for referral, and type of referring physicians. Methods and Results  This was a prospective study of 1,020 consecutive patients who were referred for stress MPI (429 patients) or stress Echo (591 patients) at the American University of Beirut Medical Center in the year of 2008. Patients referred to MPI were older and had a higher prevalence of diabetes, hypertension, hypercholesterolemia, smoking, and previous myocardial infarction, coronary angioplasty, or bypass surgery. There were more abnormal scans in the stress MPI group (24% vs 15%, P < 0.001), as well as a higher prevalence of ischemia (15% vs 7.6%, P < 0.001) and impaired left ventricular function with an ejection fraction <50% (11% vs 1.7%, P < 0.001). A higher percentage of stress Echo studies were self-referred by physicians who themselves interpret the scans (31% vs 19%, P < 0.001). Conclusion  Patients referred for stress MPI are at a higher risk than those referred for stress Echo having more CAD risk factors, more prior history of coronary events, and an older age. These findings have important implications in the interpretation of studies that compare the diagnostic and prognostic power of these two imaging modalities.     

The value of thallium and three-phase bone scans in the evaluation of bone and soft tissue sarcomas

Thirty-seven patients with newly diagnosed or treated sarcomas had 47 sets of sequential thallium scans (TS) followed by three-phase bone scan (TPBS) on the same day. The diagnosis in all patients was verified by biopsy (n=40) or long-term follow-up studies (n=7). The sensitivity, specificity, and accuracy of TS and TPBS in detecting sarcomatous lesions was calculated: TS sensitivity was 88%, specificity 69%, and accuracy 83%; blood flow (BF) and blood pool (BP) sensitivity was 91%, specificity 54%, and accuracy 81 %; delayed bone scan (DB) sensitivity was 88%, specificity 38%, and accuracy 74%. In 17 studies the flow and blood pool parts of the TPBS and TS demonstrated the soft tissue component of sarcomas, which would have been missed if only the delayed bone scan had been performed. The TS lesion to normal tissue ratio alone was not very helpful in differentiating sarcomas from benign conditions because some benign lesions are highly cellular and vascular while some malignant lesions, such as chondrosarcoma, have poor vascularity and a less cellular chondroid matrix. However, when the thallium ratio was correlated with similar ratios calculated from yhe BP image, it was found that if the TS lesion to normal tissue ratio exceeded the BP lesion to normal tissue ratio (12 patients), the specificity for detecting sarcomatous lesions was 100%. Nevertheless, the reverse was not true. The positive predictive value of this observation was 100% and the negative predictive value was 37%.     

Immediate thallium re-injection after stress imaging for the detection of myocardial viability

Myocardial perfusion imaging with thallium is an established method to assess the presence of ischaemic and viable myocardium. Using planar imaging, images acquired 1 h after immediate thallium re-injection have been shown to be comparable to those of 3 h redistribution. The aim of this study was to clarify this using SPET. Twenty patients with chronic coronary artery disease with at least two perfusion defects on post-exercise images participated in this study. All patients received thallium re-injection after post-stress SPET and all had 1 h, 3 h and 24 h redistribution imaging. The thallium myocardial tomograms were divided into 14 segments for each patient. A total of 78 segments were studied. When the frequency of reversibility on 1 h, 3 h and 24 h redistribution images is compared, of the 78 SPET defects 18 (23.1%) showed reversibility by 1 h, 34 (43.6%) by combined 1 h and 3 h imaging (P < 0.05) and 50 (64.1%) by combined 1 h, 3 h and 24 h imaging (P < 0.05). Our results show that, compared to 3 h images, images acquired 1 h after immediate thallium re-injection underestimate the extent of viable myocardial segments and the incidence of late reversibility was not reduced by the immediate re-injection of thallium.     

A comparison of dobutamine and maximal exercise as stress for thallium scintigraphy

In the assessment and evaluation of patients with suspected coronary artery disease there is a need for pharmacological stress combined with thallium scintigraphy. Thallium images were obtained following stress both with dobutamine infusion (5–20 g kg^–1 min^–1) and with symptom-limited bicycle ergometry in 20 patients (age 39–70 years) with chest pain who had been admitted for coronary angiography. Percentage thallium uptake was calculated using a region of interest technique. Detailed comparison was performed of the presence, size and distribution of left ventricular thallium perfusion defects; the percentage thallium uptake in ventricles, lung and liver; and the haemodynamic response to stress. Each stress produced a similar number of abnormal segments in each of three views (total EX 166/300; DOB 167/295), but exercise produced larger defects in the anterior view (P<0.025). Thallium uptake in left and right ventricles and relative uptake to lungs were similar, but dobutamine produced higher relative liver uptake [EX 1.55 (0.67); DOB 2.97 (1.23) P<0.0001]. Fourteen patients were able to tolerate dobutamine 20 g kg^–1 min^–1. The ratio of peak stress to rest double product was smaller with dobutamine in both patients with (DOB 1.3; EX 2.0; P<0.0047) and patients without -blockade (DOB 1.5; EX 2.4; P<0.008). Dobutamine produced fewer conventional stress endpoints of chest pain and ST depression. In conclusion, dobutamine produces a well-tolerated incremental pharmacological stress with thallium images similar to maximal exercise, and provides a useful alternative stress in patients unable to perform adequate dynamic exercise.Correspondence to: D.R. Wallbridge     

Detection of coronary artery disease by stress thallium scintigraphy in diabetic patients

We investigated the efficacy of exercise stress thallium in the diagnosis of coronary artery disease in patients with diabetes mellitus. Forty-three patients with known diabetes and suspected of having coronary artery disease were included in the study. All the patients underwent coronary angiography, 24 had significant coronary artery stenosis and 19 had normal coronaries. Out of the 24 patients with a positive angiographic finding, thallium scintigraphy was positive in 21 patients (sensitivity, 87.5%); and false negative in only three of the 24 patients. Out of the 19 patients with normal angiography findings, 16 patients had a normal thallium scan (specificity, 84.2%) and the remaining three had a positive thallium scan. This gives thallium scintigraphy a positive predictive value of 87.5% and negative predictive value of 84.2% when compared with coronary angiography. The findings of this study suggest that stress thallium scintigraphy is a useful modality in screening of coronary artery disease in diabetic patients.     

Anomalous origin of the left coronary artery. Use of thallium perfusion scans in the evaluation of successful revascularization.

Thallium imaging was performed on a 2-month-old infant with a left coronary artery originating from the pulmonary artery. Imaging was performed before and after corrective surgery, which involved creating a new left coronary osteum from the ascending aorta. The radionuclide study documented successful revascularization postoperatively.     

Aneurysm-like wall motion abnormality in hibernating myocardium detected by stress thallium scintigraphy]

A 70-year-old female patient presented and ECG with QS patterns and ST elevation in V1-3. Left ventriculography showed severely abnormal wall motion of the anteroseptal similar to a left ventricular aneurysm. Based on previous experience that 201Tl myocardial scintigraphy revealed possible myocardial viability in a patient with left ventricular aneurysm suspected of having apparently no myocardial viability, percutaneous transluminal coronary angioplasty (PTCA) was performed for severe stenosis of the left anterior descending artery. Follow-up images 3 months later showed a remarkable improvement in parietal motility of the left ventricle and recovery of almost normal cardiac function. This case demonstrates that exercise myocardial scintigraphy is useful for diagnosing hibernating myocardium associated with severely abnormal parietal motility, such as left ventricular aneurysm.