Christopher L. Hansen

Lower diagnostic accuracy of thallium-201 SPECT myocardial perfusion imaging in women: an effect of smaller chamber size.

OBJECTIVESnWe attempted to formally compare the diagnostic accuracy of thallium-201 single-photon emission computed tomographic (SPECT) myocardial perfusion imaging in men and women and the effect of chamber size on accuracy.nnnBACKGROUNDnThe diagnostic accuracy of conventional exercise testing has been shown to be lower in women. Less is known about the relative accuracy of perfusion imaging. Because of smaller body size, women have a smaller heart size than men, a factor that may reduce accuracy.nnnMETHODSnWe identified 323 patients undergoing thallium-201 SPECT myocardial perfusion imaging who either had < 5% probability of coronary artery disease (CAD) by Bayesian analysis or who underwent cardiac catheterization within 60 days of stress testing. Patients with documented history of infarction, coronary artery bypass grafting, pathologic Q waves on the electrocardiogram, left bundle branch block or nonischemic cardiomyopathy were not included. We performed strict quantitative analysis, and receiver operating characteristic (ROC) curves were generated and the area under the curve was calculated for men and women. A size index was generated from the number of short-axis slices and average radius of each slice, and the group was classified as having a large or a small chamber size. The ROC areas of men and women with a large and a small chamber size were then compared.nnnRESULTSnDiagnostic accuracy was lower in women than in men (ROC are 0.82 vs. 0.93, p < 0.05) despite similar values for peak heart rate and rate-pressure product and similar severity of CAD. There was a greater difference in accuracy between patients with a large versus a small chamber size (ROC area 0.94 vs. 0.73, p < 0.01) despite similar levels of exercise and severity of CAD. When we compared men and women in groups stratified by chamber size, we could not detect a significant difference between ROC area values of men and women (large: 0.94 men, 0.93 women, p = 0.77, power to detect difference in area of 0.15 = 91%; small: 0.79 men, 0.72 women, p = 0.58, power to detect difference in area of 0.15 = 35%).nnnCONCLUSIONSnThe diagnostic accuracy of thallium SPECT myocardial perfusion imaging is lower in women than in men. Most of the difference appears to be due to smaller left ventricular chamber size in women, although a small residual gender effect in smaller heart sizes cannot be entirely excluded. It is proposed that the most likely cause for this difference is the relatively greater effect of imaging blurring on smaller hearts.

Comparison of pulmonary uptake with transient cavity dilation after exercise thallium-201 perfusion imaging.

OBJECTIVESnThe purpose of the study was to evaluate the relationship between elevated lung/heart ratio (LHR) and transient ischemic dilation (TID) after stress thallium-201 myocardial perfusion imaging and to provide further insight into the mechanism of cavity dilation.nnnBACKGROUNDnBecause both LHR and TID have been identified as adjunctive markers of severe coronary disease they should be found in the same patients. Although the mechanism of LHR has been defined, that of transient dilation has not.nnnMETHODSnWe identified 4,618 consecutive patients undergoing maximal exercise perfusion imaging with thallium-201. Lung/heart ratio and a dilation index were derived and compared to each other and to relevant clinical parameters.nnnRESULTSnThere was a very weak relationship between the LHR and dilation index (r = 0.15, p < 0.001). Defining a dilation index > or =1.10 and LHR > or =50% as abnormal revealed that 322 of the patients (7%) had TID only, 351 (7.8%) had LHR only and 40 (0.9%) had both. When compared to patients without these findings both TID and LHR had higher thallium stress defect and redistribution scores. When comparing subjects who had elevated LHR uptake to those who had TID, it was found that those with LHR were more likely to have had prior myocardial infarction (MI) (29% vs. 9%), coronary artery bypass grafting (22% vs. 8%), lower ejection fraction (34+/-17% vs. 55+/-11%) and had more evidence of ischemia based on thallium stress defect and redistribution scores. However, patients with cavity dilation had a higher frequency of positive electrocardiographic response (31% vs. 19%) despite lower scintigraphic markers.nnnCONCLUSIONSnAlthough pulmonary uptake and transient cavity dilation have both been associated with severe coronary disease, they have a very weak correlation, which, in combination with the different clinical parameters associated with each, suggests that they represent different pathophysiologic responses to exercise-induced ischemia. Our data support the hypothesis that TID represents transient subendocardial ischemia rather than physical dilation from increased end-diastolic pressure.

Effect of patient obesity on the accuracy of thallium-201 myocardial perfusion imaging

The effects of patient habitus (e.g., breast attenuation in women and diaphragmatic attenuation in men) have long been recognized as factors that reduce the accuracy of myocardial perfusion imaging. Although it has long been assumed that patient obesity effects accuracy, this has never been formally evaluated. We studied the effects of patient obesity, defined as a body mass index (BMI) > or = 30, on 607 patients who underwent exercise thallium-201 single-photon emission computed tomography (SPECT). Because the effects of obesity are most likely mediated through increased photon attenuation and scatter, we also evaluated the effects of other markers of patient size: body surface area (BSA) and patient weight. Accuracy was determined by performing quantitative analysis and measuring the area under the receiver operating characteristic curve (AUC). Obesity was associated with significantly lower accuracy (AUC 0.86 +/- 0.03 vs 0.92 +/- 0.02, p <0.05) despite similar estimates of maximal coronary blood flow (as estimated by heart rate and rate-pressure product at peak exercise) and severity of coronary disease. There were no significant differences attributable to either patient weight or BSA. Weight and BSA correlated significantly with left ventricular chamber size whereas BMI did not. We conclude that the accuracy of quantitative SPECT thallium-201 is significantly reduced by patient obesity and that although BSA and weight are also associated with increased attenuation, they have no effect on accuracy, which is most likely due to the compensating effects of increased chamber size.

The "hurricane sign": evidence of patient motion artifact on cardiac single-photon emission computed tomographic imaging.

Single-photon emission computed tomography (SPECT) is frequently used with myocardial perfusion imaging in the assessment of patients with known or suspected coronary artery disease. The susceptibility of SPECT imaging to artifact, especially that caused by patient motion, has long been recognized. We report a characteristic artifact of patient motion, which we have termed the “hurricane sign” because of its similarity to the National Weather Service Symbol for a hurricane. This artifact is caused by varying contributions of different portions of the heart during image acquisition and their misalignment produced by patient motion.

Lower accuracy of Tl-201 SPECT in women is not improved by size-based normal databases or Wiener filtering

BackgroundWe have shown that the diagnostic accuracy of quantitative single photon emission computed tomography (SPECT) thallium 201 myocardial perfusion imaging is lower in women than in men and that much of the difference can be explained by the smaller size of the left ventricle in women. Therefore attempts at improving the accuracy of myocardial perfusion imaging in women should focus on the problem of lower accuracy in patients with small chamber size. We evaluated two strategies for this: size- and gender-based normal databases and inverse filtering with the Wiener filter.Methods and ResultsWe identified 618 patients undergoing exercise SPECT Tl-201 who either had a low pre-test probability of coronary artery disease or had catheterization-documented disease. Their images were analyzed on the basis of gender and chamber size: both gender and size- and gender-based normal databases were created. The studies were analyzed quantitatively, and the accuracy was evaluated by use of the area under the receiver operating characteristic (ROC) curve. Chamber size was significantly lower in women (size index 69±22 women vs 96±28 men; P<.0001). The accuracy of myocardial perfusion imaging was lower in women compared with men (ROC area: 0.92±0.01 men vs 0.85±0.03 women; P=.03), and there was an even greater difference in accuracy between patients with large versus small chamber size (ROC area: 0.94±0.01 large vs 0.81±0.03 small; P<.001). There was no improvement in the diagnostic accuracy either in women or in patients with small chamber size when a size-and gender-based normal database, Wiener filter, or the Wiener filter with a size- and gender-based normal database was used.ConclusionThe left ventricular chamber size in women is smaller than that in men. There is a significant difference in the accuracy of quantitative SPECT Tl-201 between men and women and an even greater difference between patients with large versus small chamber size. Neither size- and gender-based databases nor Wiener filtering significantly improves accuracy in women or in patients with small chamber size.

On myocardial perfusion, metabolism, and viability

The majority of the examinations performed in nuclear cardiology laboratories are perfusion studies obtained for the evaluation of coronary disease. The number of studies performed for the assessment of myocardial viability is growing and will continue to grow as more sophisticated techniques for revascularization are introduced and the number of patients with complex coronary disease increases. Many laboratories are now being consulted to assist in the difficult decision of whether a patient should be referred for high-risk revascularization versus cardiac transplantation. The report by Fujiwara et al.1 in this issue of the Journal evaluates the relatively newly described phenomenon of reverse redistribution on sestamibi imaging compared with BMIPP imaging to identify myocardial stunning in postinfarct patients who received emergent PTCA. This article raises many interesting questions about the relative roles of perfusion agents and metabolic tracers in identifying myocardial viability and how the results of these tests should be interpreted. Myocardial viability is an intuitively simple concept that becomes distressingly amorphous when it has to be defined precisely for a clinical study. The term represents a broad spectrum of clinical states which frequently overlap. The term stunned myocardium refers to regions that have a transient decrease in contractility after an episode of prolonged ischemia. 2 The term hibernating myocardium refers to an area where there has been down-regulation of myocardial contractility in response to chronic ischemia. 3 Stunned myocardium generally improves over time without further intervention; hibernating myocardium requires the restoration of adequate blood flow to improve function. Many investigators have limited their definition of viable myocardium to stunned and hibernating myocardium by defining it as regions expected to show improved contractility after the passage of time or revascularization. For the purposes of this editorial, we will define viable myocardium to encompass all noninfarcted myocardium: stunned, hibernating, and transiently ischemic and normal myocardium. This broader defini-

Attenuation smear: A ‘paradoxical’ increase in counts due to attenuation artifact

Background: Attenuation is a well recognized cause of reconstruction artifacts in SPECT imaging. Occasionally, we have noted an increase in activity extending from the apical septal portion of the ventricle in women with significant breast attenuation. Although the idea that attenuation can produce an increase in activity on the reconstructed images seems paradoxical at first, it is consistent with the process of filtered back projection. Methods: We filled a cardiac phantom with 1 mCi of Technetium-99m, placed it in a water filled anthropomorphic torso phantom and imaged it over a 180° orbit. Next, a breast phantom designed to simulate a significant degree of breast attenuation was placed on the torso phantom and imaging was repeated. The images were reconstructed first using conventional filtered back projection then with maximum likelihood. Results: When the phantoms with and without breast attenuation were reconstructed using filtered back projection and compared, the phantom with breast attenuation had a large ‘smear’ of activity extending anteriorly from the apical septal wall which was very similar to the abnormalities previously noted in clinical images; the phantom without breast attenuation had no such defect. This artifact was significantly less prominent when the images were reconstructed using the maximum likelihood technique. Conclusions: Attenuation artifact can also produce a seemingly paradoxical increase in counts on the reconstructed image but this phenomenon is consistent with the workings of filtered back projection.

1010-64 Left Ventricular Size Effects the Diagnostic Accuracy of SPECT Thallium-201 Perfusion Imaging in Both Men and Women

The diagnostic accuracy of SPECT TI-201 for coronary artery disease (CAD) is lower in women (F) than in men (M). Previous investigators have suggested a Bayesian explanation. More recently, it has been suggested that smaller left ventricular mass in women was the cause. The current study was undertaken to assess the effect of left ventricular size (LVsize) on the accuracy of SPECT TI-201. For this study patients who had either less than 5% pretest probability of CAD (nls) or had cardiac catheterization performed within 45 days of stress thallium testing without an intervening cardiac event (pts) were Identified. We excluded patients with pathologic Q waves, documented prior infarction, LBBB on EKG, prior CABG or non-ischemic cardiomyopathy. We Identified a total of 259 subjects (153 M, 106 F). Patients withxa0l50% stenosis on cath were analyzed as nl. Twenty M and 20 F were taken from the nls and processed separately to create normal limits. Images were reconstructed with a Hanning filter. The fraction of the left ventricle less than 1, 2, 2.5, 3 and 4 standard deviations was calculated and used to calculate the area under the receiver operating characteristic (ROC) curves using the Dorfman maximum likelihood technique. A measure of left ventricular size was generated from short axis slice diameter and the number of slices. The number of stenosed vessels (2.0xa0±xa00.8 vs. 1.9xa0±xa00.9, Pxa0=xa0NS) and worst stenosis (91xa0±xa012% vs. 89xa0±xa015%, pxa0=xa0NS) were similar for M and F. M exercised to higher workloads (estimated METS 6.7xa0±xa03.1 vs. 4.3xa0±xa02.3, pxa0lxa00.0001) but similar peak heart rates (HR) and percent of maximal predicted HR (133xa0±xa019 vs. 130xa0±xa022 and 78xa0±xa011% vs. 79xa0±xa013%, both pxa0=xa0NS). The LVsize was greater in men (105 vs. 79 pxa0lxa00.001). The area under the ROC curves for M was marginally greater than F (0.92 vs. 0.82 Pxa0=xa00.10). LV size significantly affected accuracy; the ROC area for M and F with LVsizexa0g75 was much greater than for thosexa0l75 (0.89 vs. 0.64 Pxa0=xa00.007). There was no significant difference in accuracy between M and F with LVsizexa0gxa075 (0.91vs. 0.85, Pxa0=xa00.47). We conclude that a small LVsize significantly reduces the accuracy of SPECT TI-201 in M and F, but since F have, on average, smaller LVsize, they are more likely to be affected.