The ratio of the apex/anterior wall: a marker of breast attenuation artifact in women.

BACKGROUND

Breast attenuation artifact is well known for reducing the accuracy of myocardial perfusion imaging in women. We have noticed the particular pattern of relative preservation of apical activity in women with breast attenuation and decreased anterior wall counts. This study was undertaken to see if this finding could be used to improve the accuracy of perfusion imaging in women.

METHODS

We identified 295 women referred for exercise stress testing using (201)Tl single photon emission computed tomography (SPECT) of whom 193 had less than 5% probability of coronary disease and 102 had coronary artery disease documented by catheterization within 60 days of stress testing (mean of 1.8+/-0.8 vessels with=50% stenosis). Patients with documented myocardial infarction, pathologic Q waves, left bundle branch block, non-ischaemic cardiomyopathy or prior bypass grafting were excluded. Volume-weighted bullseye plots were generated and normalized to 100; next, regions of interest were drawn over the anterior wall and apex in all patients and the ratio of the mean counts of each region was calculated. The normals were further divided into those with breast attenuation (defined as mean anterior counts <70% maximum) and those without. Defect scores of all patients were calculated; a formula to adjust the score for patients with breast attenuation was developed. Accuracy was assessed by calculating the area under the receiver operating curve.

RESULTS

The normals, overall, had a mean ratio of 1.0+/-0.08 vs. 0.9+/-0.16 for those with coronary disease (P<0.0001). In normals with breast attenuation the ratio was 1.1+/-0.08 compared to 0.99+/-0.07 (P<0.0001) without. By adjusting the anterior wall defect score in patients with apex/anterior ratio >1 we were able to improve the accuracy from 0.808+/-0.028 to 0.826+/-0.027 (P<0.01).

CONCLUSIONS

A ratio of the apex to the anterior wall >1 is not physiological and suggests the presence of significant breast attenuation artifact. This finding can be used to produce a small but statistically significant improvement in the accuracy of quantitative thallium SPECT in women who have not undergone coronary bypass grafting.