Thallium-201 washout in coronary artery disease using SPECT--a comparison with coronary angiography

Modified Algorithm Using Total Count for Calculating Myocardial Washout Rate in Single-Photon Emission Computerized Tomography

Background: The arithmetic mean of washout rate (WR) (namely, AMWR) of each segment is a commonly used algorithm for calculating WR from a polar map in single-photon emission computerized tomography (SPECT). However, in this algorithm, uneven radiotracer uptake among segments affects WR calculation. To solve this possible issue, we formulated a modified algorithm for calculating WR based on the total count (namely, TCWR). Methods: The WR of iodine-123-β-methyl-p-iodophenylpentadecanoic acid (BMIPP) was calculated using TCWR and AMWR, and WR values using TCWR and AMWR were compared by disease. Participants included those without cardiovascular diseases (normal), those with CD36 deficiency, triglyceride deposit cardiomyovasculopathy (TGCV), TGCV with old myocardial infarction (OMI), and non-TGCV with OMI. Results: WR values using TCWR and AMWR did not differ significantly in the following groups: normal, 27.4±8.5 and 27.3±8.5% (p=0.97); CD36 deficiency, -3.2±6.5 and -4.1±7.4% (p=0.81); TGCV, 2.4±6.3 and 2.2±6.3% (p=0.93); and TGCV with OMI, -0.9±7.6 and -3.7±8.4% (p=0.32). However, AMWR showed a lower WR than TCWR in non-TGCV with OMI (4.8±8.7 and 18.9±6.7%, p=0.0008). Conclusions: TCWR is suitable for calculating WR using SPECT polar maps even in cases with heterogeneous radiotracer uptake, such as OMIs. TCWR may be applied to measuring the WR of radiopharmaceuticals other than BMIPP in investigating the pathophysiology of heart diseases.

Typical angina during exercise stress testing improves the prediction of future acute coronary syndrome

INTRODUCTION

The prognostic value of angina during exercise stress testing is controversial, possibly due to previous studies not differentiating typical from non-typical angina. We aimed to assess the prognostic value of typical angina alone, or in combination with ST depression, during exercise stress testing for predicting cardiovascular events.

METHODS

We conducted a prospective observational cohort study including all patients who performed a clinical exercise stress test at the department of Clinical Physiology, Kalmar County Hospital between 2005 and 2012. The association between typical angina/ST depression and incident acute coronary syndrome (ACS) and cardiovascular mortality were analysed using Cox regression for long-term and 1-year follow-up.

RESULTS

Out of 11605 patients (median follow-up 6.7 years), 623 (5.4%) developed ACS and 319 (2.7%) died from cardiovascular causes. Compared to patients with no angina and no ST depression, typical angina and ST depression were associated with increased risk of future ACS; hazard ratio (HR) 3.5 ([95%CI] 2.6-4.7). This association was even stronger for ACS within one year (typical angina with and without concomitant ST depression; HR 20.8 (13.9-31.3) and 9.7 (6.1-15.4), respectively). Concordance statistics for ST depression in predicting ACS during long-term follow-up was 0.58 (0.56-0.60) and 0.69 (0.65-0.73) for ACS within one year, and 0.64 (0.62-0.66) and 0.77 (0.73-0.81), respectively, when typical angina was added to the model.

CONCLUSIONS

Typical angina during exercise stress testing is predictive of future ACS, especially in combination with ST depression, and during the first year after the test.

[A Nationwide Survey on Additional Scan in Nuclear Medicine Imaging]

The aim of the present study was to clarify the routine protocols and the frequency of added or omitted imaging on nuclear medicine imaging in Japan. A nationwide survey on routine protocols and current state of added or omitted imaging in major nuclear medicine imaging were performed for Japanese nuclear medicine technologist. The survey showed that the routine protocols were almost 100% fixed, some of the routine protocols were found to be useful and percentage of imaging techniques such as single photon emission computed tomography/computed tomography that increased patient burden and reduced through put were low. Furthermore, the survey showed that additional or omission imaging were frequently performed on bone scintigraphy and positron emission tomography and added or omitted judgements were often depend upon the rule of thumb by nuclear medicine technologist. In this study, we have concluded that the quality of examination and the diagnosis might depend on the knowledge of nuclear medicine technologist, performed added or omitted imaging.

Accuracy of washout rate analysis for thallium-201 single-photon emission computed tomography myocardial perfusion imaging using cadmium zinc telluride detectors: A phantom study

Objective

The aim of this study was to assess the accuracy of washout rate (WOR) analysis for thallium-201 chloride (²⁰¹Tl) single-photon emission computed tomography myocardial perfusion imaging data acquired using cadmium zinc telluride detectors and a myocardial phantom.

Methods

A myocardial phantom was injected with 10.5 MBq ²⁰¹Tl, and 10-min acquisitions were performed at 0, 24, 46, and 62 h to accommodate natural radioactive decay over time. Global myocardial WOR (global-WOR) and regional WOR (regional-WOR, left anterior descending artery [LAD], right coronary artery [RCA], and left circumflex artery [LCX]) were analyzed between 0 and 24 h (infarction model), 0 and 46 h (ischemia model), and 0 and 62 h (normal model), respectively. We compared the calculated radioactive decay-rate as a reference standard and phantom imaging WOR (phantom-WOR).

Results

Decay-rate versus phantom-WOR were 20.4% vs. 20.8% (global-WOR), 21.3% (LAD), 21.2% (RCA), and 19.7% (LCX) for the infarction model; 35.4% vs. 35.6% (global-WOR), 35.5% (LAD), 36.2% (RCA), and 35.2% (LCX) for the ischemia model; and 44.5% vs. 45.1% (global-WOR), 45.4% (LAD), 44.7% (RCA), and 43.5% (LCX) for the normal model.

Conclusion

WOR analysis for ²⁰¹Tl single-photon emission computed tomography myocardial perfusion imaging using cadmium zinc telluride detectors is a reliable analysis method.

Imaging technology for myocardial perfusion single-photon emission computed tomography 2018 in Japan

AIM

Recently, nuclear cardiology has dramatically advanced by a new technology development such as the device, short-term acquisition system, image reconstruction algorithm and image analysis. Although these innovations have been gradually employed in routine examinations, we did not investigate the current use of image acquisition, image reconstruction, and image analysis with myocardial perfusion single-photon emission computed tomography (MPS). We investigated the current status of MPS imaging technology in Japan.

METHODS

We carried out a survey using a Web-based questionnaire system, the opening of which was announced via e-mail, and it was available on a website for 3 months. We collected data on the current use of MPS with ²⁰¹Tl and/or ^99mTc agents with respect to routine protocols, image acquisition, image reconstruction, and image analysis.

RESULTS

We received responses to the Web-based questionnaire from 178 and 174 people for ^99mTc and ²⁰¹Tl MPS, respectively. The routine protocols of MPS of stress-rest and rest-stress MPS on 1-day protocols with ^99mTc were 41.2% and 14.5%, respectively, and the rest-only scan response rate was 23.7%, whereas that of ²⁰¹Tl MPS was 65.9% with stress-rest MPS, 19.0% with rest-only MPS, and 10.9% with stress-rest MPS adding a rest scan 24 h after injection. The filtered back projection (FBP) method is most commonly used image reconstruction method, yielding 70.5% for ^99mTc MPS and 76.8% for ²⁰¹Tl MPS, including combined FBP and ordered subset expectation maximization method. The results for no-correction (NC) images were 49.2% with ^99mTc MPS and 55.2% with ²⁰¹Tl MPS including the response of NC and combined attenuation correction (AC) and scatter correction (SC) (i.e., ACSC) images. The AC or ACSC images of ^99mTc and ²⁰¹Tl were provided by 30-40% of the institutions surveyed.

CONCLUSIONS

We investigated the current status of MPS imaging technology in Japan, and found that although the use of various technical developments has been reported, some of these technologies have not been utilized effectively. Hence, we expect that nuclear medicine technology will be used more effectively to improve diagnosis.

An Exploratory Study of Washout Rate Analysis for Thallium-201 Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging Using Cadmium Zinc Telluride Detectors

The aim of this study was to assess the washout rate (WOR) for thallium-201-chloride single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using cadmium zinc telluride detectors for SPECT (CZT SPECT) versus conventional Anger-type SPECT (conventional SPECT). A total of 52 Japanese patients were examined using CZT SPECT and conventional SPECT, and the global WORs were compared. Additionally, the MPI WORs were compared for patients with a normal MPI versus those in whom MPI reflected the patients’ multivessel disease (MVD) MPI. Washout rates were similar when approximated by CZT SPECT versus conventional SPECT 12.59 ± 2.26%/h vs 12.57 ± 2.27%/h (P = .997), respectively. The WOR values for CZT SPECT versus conventional SPECT were 13.42%/h (1.53%/h) vs 13.93%/h (1.24%/h) (P = .337), respectively, for 7 normal MPI patients, and 10.64 ± 2.20%/h vs 10.84 ± 2.26%/h (P = .848), respectively, for 7 MVD-MPI patients. The WOR values for normal MPI versus MVD-MPI patients for CZT SPECT were 13.42 ± 1.53%/h vs 10.64 ± 2.20%/h (P = .025), respectively. Thallium-201-chloride WOR values obtained with high-efficiency CZT SPECT, which enabled significantly reduced imaging times and use of a low-dose protocol, were similar to those obtained with conventional SPECT.

Polar Presentation of Coronary Angiography and Thallium-201 Single Photon Emission Computed Tomography

Individual results of coronary angiography were compared with tomographic myocardial scintigraphy (SPECT) in 99 patients. Coronary angiography findings were transferred to polar maps. Borders between arteries were assigned angles in a coordinate system constructed as a compass-rose. Areas perfused by different arteries were described by sectors. Findings were visually compared with the perfusion defects in a polar presentation of thallium-201 SPECT also described by angles. The mean values and SD for the angles representing arterial borders and perfusion defects were presented. The left ventricular myocardium was perfused by 3 coronary arteries in 92/99 patients. Dominant left artery was present in 7/99 patients; 79 perfusion defects were related to 118 arterial sectors 84 per cent had totally or partially matched stenotic arteries. Inter-individual differences in distribution of coronary arteries influence the localization of perfusion defects in myocardial SPECT and can be estimated with this polar presentation method.

Coronary Angiography and Thallium-201 Single Photon Emission Computed Tomography in Multiple Vessel Coronary Artery Disease

Polar presentations of selective coronary angiography and myocardial 201T1 SPECT were compared in 141 patients with multiple vessel disease, 80 with 3-vessel disease, 34 with 2-vessel disease and 27 post-bypass patients. Perfusion defects were present in 125/141 patients (89%) and were located within the area supplied by 194/359 stenotic arteries (54%) and 9 non-stenotic arteries. The type and extent of disease was correctly indicated by 201T1 SPECT in 16/80 patients (20%) with 3-vessel disease, 5/34 patients (15%) with 2-vessel disease and 8/27 post-bypass patients (30%). Perfusion defects indicated the artery with the most severe lesion in 107/125 patients (86%). False negative isotope studies were present in 15 patients (11%).

Compartmental multivariate analysis of exercise ECGs for accurate detection of myocardial ischaemia

An accurate computer-assisted diagnostic method for detection of myocardial ischaemia, called MUSTA, is developed. MUSTA is based on compartmental multivariate analysis of variables available in the exercise ECGs, and is definitively implemented in Prolog. It is heuristically developed by determining diagnostic criteria, which interrelate a modified ST/HR-slope, ST-segment value and shape, and maximum heart rate, so that concordance with the TI-201 SPECT is maximised. In the learning group consisting of 47 patients, MUSTA provides a diagnostic accuracy of 98%, the detection of ischaemia being in absolute concordance with TI-201 SPECT. MUSTA is evaluated in a similar but independent group of 60 patients. Then, accuracy is 90%, and sensitivity is 94%. The performance characteristics are significantly better than those of the standard exercise ECG, whose diagnostic accuracy in these groups is 77% and 70%, respectively. This study suggests that MUSTA is a significant improvement for computerised assessment of myocardial ischaemia.

Technetium-99m teboroxime regional myocardial washout in subjects with and without coronary artery disease

The aim of this study was to test the hypothesis that regional myocardial washout of technetium-99m teboroxime is slowed in the presence of coronary stenosis. Washout was assessed in 33 catheterized patients and in 13 with a low likelihood of coronary artery disease, using a triple detector camera and dynamic single-photon emission computed tomography, with serial 1-minute acquisitions after injection of 20 to 25 mCi of teboroxime at the third minute of adenosine-induced hyperemia. Washout was measured as the percent change in counts between the first, second and third minutes after injection, as measured in 6 short-axis myocardial regions of interest. Myocardial regions were classified as ischemic (> or = 50% diameter stenosis and no prior myocardial infarct), infarcted, normal (no significant coronary stenosis) or "low likelihood" (from the 13 patients with a low likelihood of coronary artery disease). Teboroxime washout was significantly (p < 0.001) slowed in the ischemic myocardium (12.7 +/- 8.3%) compared with the normal (18.5 +/- 5.7%), low-likelihood (17.8 +/- 6.1%) and infarcted (17.8 +/- 4.4%) zones. There was regional variability in washout rates (% washout/min), with the anterior wall having the lowest (13.8 +/- 3.4%/min) and the inferior wall the highest (20.7 +/- 7.9%/min) values. In regard to individual coronary territories, 21 of 41 ischemic, noninfarcted territories (51%) had abnormal washout compared with 3 of 43 normal territories (7%) (p = 0.001). In conclusion, regional washout of teboroxime is detectably slowed in ischemic, noninfarcted myocardium. The clinical value of washout analysis in teboroxime single-photon emission computed tomography warrants further investigation.

Improved diagnostic performance of the exercise ECG test by computerized multivariate ST-segment/heart rate analysis

The exercise ECG test is the most widely used noninvasive method of evaluating myocardial ischemia. To determine whether it is possible to enhance its diagnostic power, the authors carried out computerized ECG measurements on 118 nonischemic patients and 38 ischemic patients with or without myocardial infarctions (MIs). Forty-seven (all ischemic and nine normal cases) underwent T1-201 SPECT. The diagnostic variables include ST-segment deviation, modified ST/HR-slope, ST-segment shape, and maximum heart rate. These variables are interrelated by means of compartmental and specific decision rules by computer. The diagnostic method discussed in this article is called the multivariate ST/HR analysis (MUSTA). When compared with MUSTA, the T1-201 SPECT images detected myocardial ischemia with a sensitivity of 100% and a specificity of 89%. Its diagnostic performance was influenced by neither previous MIs nor cardiac medication of the 47 patients tested. MUSTA was also compared to the nonmodified ST/HR analyses (ST60/HR and ST80/HR) and the standard exercise ECG test. It performed significantly better than these methods. The authors conclude that the multivariate ST/HR analysis is comparable to T1-201 SPECT in diagnosing myocardial ischemia among the study subjects. Furthermore, MUSTA is executed during the noninvasive exercise ECG test and is easily applied using an IBM/AT-compatible microcomputer. However, further evaluation of MUSTA with a separate and unselected patient population is needed.

Limitations of regional myocardial thallium clearance for identification of disease in individual coronary arteries

The purpose of this study was to critically evaluate the usefulness of postexercise regional myocardial thallium-201 clearance for identifying disease in individual coronary arteries. Exercise and redistribution planar imaging studies were performed in 114 subjects, including 19 normal volunteers and 95 patients undergoing cardiac catheterization (70 with and 25 without greater than or equal to 50% narrowing in one or more coronary arteries). Thallium clearance was measured from predefined myocardial regions corresponding to the left anterior descending, left circumflex and right coronary arteries and was expressed as the percent decrease in activity at 4 h, assuming monoexponential clearance. In regions perfused by a normal or insignificantly diseased coronary artery, mean 4 h clearance was 58.9 +/- 9.4% for normal volunteers, 43.1 +/- 15.5% for catheterized patients without coronary artery disease and 36.3 +/- 24.9% for catheterized patients with coronary artery disease (p less than 0.001 patients with coronary artery disease versus normal volunteers). Clearance from normal regions was significantly associated with two measures of exercise performance: percent of predicted maximal heart rate achieved (r = 0.49) and exercise duration (r = 0.35). In regions perfused by a stenotic coronary artery, mean clearance was lower (31.1 +/- 19.8%) but was not significantly different from that in normal regions in the same patients. Clearance from diseased regions was also associated with maximal exercise heart rate (r = 0.28) and exercise duration (r = 0.41), but not with percent coronary artery stenosis (r = 0.02). After taking exercise performance into account, the number of diseased vessels or the presence or absence of disease in a given vessel had little influence on regional thallium clearance. Although measurement of regional post-exercise thallium clearance may help to identify stenotic coronary arteries in selected patients, variability related to exercise performance and other physiologic and technical factors greatly limits the clinical usefulness of absolute thallium clearance measurements.