Decrease in the ability to detect elevated lung thallium due to delay in commencing imaging after exercise

Identification of advanced coronary artery disease with exercise myocardial perfusion imaging: the clinical value of a novel approach for assessing lung thallium-201 uptake

INTRODUCTION

The precise clinical utility of lung 201Tl uptake in exercise SPECT myocardial perfusion imaging remains open to research. This study validates an optimal index for lung 201Tl uptake measurement and assesses its value in the prediction of higher-risk coronary artery disease (CAD).

METHOD

Three hundred and ninety-eight patients underwent exercise SPECT myocardial perfusion imaging. They were separated into derivation (n = 217) and validation (n = 186) groups, both including sub-populations of lower- and higher-risk CAD, according to coronary angiography. Another 56 individuals with a low probability of CAD comprised the control group. From a planar, anterior, post-exercise acquisition, the lung (L) to heart (H) maximal (L/H(max)), total (L/H(mean)) and background-subtracted total (L/H(net)) ratios were calculated. These were also adjusted for confounding variables, as assessed from the control group. ROC analysis was used to compare the L/H ratios and define thresholds of abnormality. The performance of the optimal index was assessed in the derivation group and was then tested in the validation population. Subsequently, it was compared with other scintigraphic, exercise electrocardiography and clinical variables.

RESULTS

In the derivation group L/H(net) was a better discriminator for higher-risk CAD than both L/H(max) and L/H(mean). Similarly, the adjusted L/H(net) was a better discriminator than both the adjusted L/H(max) and the adjusted L/H(mean). No significant difference was attained between L/H(net) and the adjusted L/H(net). At the upper defined threshold of abnormality, sensitivity and specificity of L/H(net) in the detection of higher-risk CAD in the derivation and the validation cohorts were 52% and 92% versus 47% and 94%, respectively (p = ns). The results were similar at other defined thresholds. Moreover, L/H(net) was found to be a significant predictor of higher-risk CAD, superior to myocardial perfusion images, transient ventricular dilation measurements, and clinical and exercise testing variables (ROC analysis and logistic regression). By raising the threshold of abnormality of L/H(net), specificity and positive predictive value increased, whereas sensitivity and negative predictive value decreased.

CONCLUSION

Lung 201Tl assessment assists substantially in the identification of higher-risk CAD in exercise SPECT myocardial perfusion imaging and this is best achieved by L/H(net). This index is a significant predictor of higher-risk CAD, superior to myocardial perfusion images, and its value is associated with the probability of a disease state.

Exercise and rest technetium-99m-tetrofosmin lung uptake: correlation with left ventricular ejection fraction in patients with coronary artery disease

Increased lung uptake of thallium-201 (Tl-201) and technetium-99m (Tc-99m) MIBI in myocardial perfusion imaging is a reliable marker of left ventricular dysfunction. The goal of our study was to establish whether the lung-to-heart (L/H) uptake ratio with a newer cardiac imaging agent, Tc-99m tetrofosmin, can also provide valuable information about left ventricular function. We studied 60 patients with recent coronary artery diseases (CAD) undergoing first-pass radionuclide ventriculography to calculate left ventricular ejection fraction (LVEF) and myocardial perfusion imaging to calculate the L/H ratio. Group A consisting of 30 CAD patients with higher LVEF (> or =40%) had a significantly lower L/H ratio than group B consisting of 30 CAD patients with abnormal LVEF (<40%) during exercise and rest. In groups A and B, the exercise and rest L/H ratios did not differ significantly. However, a statistically significant inverse correlation was found between the L/H ratio and LVEF during exercise and rest among the 60 patients. L/H ratios, measured by 99mTc-tetrofosmin imaging, provide clinically useful information with which to predict left ventricular dysfunction in CAD patients.

Diagnostic value of Tl-201 lung uptake is dependent on measurement method

BACKGROUND

Increased lung uptake during exercise thallium 201 single photon emission computed tomography is related to left ventricular dysfunction and extent of coronary artery disease (CAD). We studied the influence of the lung region of interest (ROI), used to quantify Tl-201 lung uptake, on the diagnostic value of the lung-to-heart uptake ratio (LHR) in detecting CAD with Tl-201 myocardial single photon emission computed tomography.

METHODS AND RESULTS

We retrospectively studied 152 consecutive patients referred to our center for stress Tl-201 scanning. Of these, 116 had proven multivessel CAD and 36 had either normal findings on coronary angiogram or a low likelihood (<5%) of CAD. Poststress quantitative analysis was performed from a 4 x 4-pixel ROI over the hottest myocardial region, an 8 x 8-pixel left lung ROI, an 8 x 8-pixel right lung ROI, and a manual ROI encompassing the whole right lung. The LHR was calculated for each lung ROI. Right LHR (R-LHR) provided the best interobserver and intraobserver reproducibility. R-LHR and total R-LHR values were significantly higher in patients with CAD. Only history of myocardial infarction significantly influenced the R-LHR measurement.

CONCLUSIONS

The methodology of LHR measurement significantly influences the clinical contribution of Tl-201 lung uptake evaluation. Optimal reproducibility and diagnostic accuracy are provided by a right lung ROI.

Increased extra-cardiac background uptake on immediate and delayed post-stress images with 99Tcm sestamibi: determinants, independence, and significance of counts in lung, abdomen and myocardium

Extra-cardiac activity on stress scans with 99Tcm sestamibi (MIBI) may influence scan interpretation. Lung uptake represents a potential sign of severe disease, whereas abdominal uptake may interfere with visualization of myocardial defects. We assessed myocardial, lung and infradiaphragmatic abdominal activity on images at 4 min (IMM) and 1 h (DEL) post-stress in 1800 consecutive studies. Potential variation among patients in organ activity was reduced with a weight-based dosing protocol. Multifactorial analysis was used to compare organ activity, and background ratios, i.e lung/heart or abdomen/heart, on stress images to (1) result of tomography, (2) peak workload, and (3) protocol (same-day versus separate-day rest/stress). Lung/heart ratios were primarily related to tomographic abnormalities, and abdomen/heart ratios to low stress workload; neither was related to protocol, and the two measurements appeared independent. Elevated lung/heart ratios (compared to angiographic normals), present on 16% and 10% of IMM and DEL images respectively, were determined primarily by increases in regional lung activity. Lung activity (normalized for dose) was higher in cases with disease than in normals (P<0.0001 as assessed by tomography, P<0.05 in the subset with correlating angiography). Increased abdominal/heart ratios derived primarily from increased abdominal activity, but were partially dependent on reciprocal decreases in myocardial activity. Elevated MIBI lung uptake ratios on abnormal scans can be attributed primarily to increased lung persistence of the radiotracer, and would thus be consistent with their use as a sign of left ventricular failure. Elevated abdominal background is associated with both higher splanchnic activity and lower myocardial activity, and is a non-specific finding related to suboptimal exercise intensity.

The use of thallium-201 lung/heart ratios

This survey gives an overview of the methodology of thallium-201 lung/heart uptake ratios often used as an independent factor in the assessment of patients with coronary artery disease undergoing myocardial perfusion scintigraphy. Different techniques have been used in the past. The most sensitive method is one which calculates a lung/heart ratio from scintigraphy obtained immediately after cessation of exercise. If single photon emission tomography (SPET) is routinely performed the anterior projection of the data set obtained during tomographic acquisition should be used in preference to a separate planar anterior static images recorded before or after the SPET procedure. The lung/heart ratio is useful as a prognostic indicator of outcome as it accurately mimics the degree of left ventricular dysfunction. With the increasing popularity of pharmacological stress testing there is evidence that this ratio still offer valid information. Additional work in this field is nevertheless required to further confirm this observation. In routine clinical practice, the lung/heart ratio should help and enable physicians to prioritise patients for urgent intervention.