This study validated a new automatic algorithm for assessment of lung-to-heart ratio (L/H) of radiotracers in myocardial perfusion SPECT and assessed the diagnostic value of (99m)Tc-sestamibi L/H after exercise.
Methods: The new technique extracts a left ventricular region of interest (ROI) from a summed anterior projection image and generates a lung ROI by reshaping and translating the left ventricular ROI. This algorithm was applied to 230 patients who underwent exercise (99m)Tc-sestamibi SPECT (gated SPECT, n = 88) with first-pass ventriculography. Normal values were established in 26 patients in whom the likelihood of coronary artery disease (CAD) was 5% or less. An abnormality threshold for detecting severe and extensive CAD was defined in a subgroup of 109 patients who underwent coronary angiography and was validated in a prospective group (n = 72).
Results: The success rate of the automatic algorithm was 97%. Excellent correlation was found between automatic and manual L/H values (r = 0.95; P < 0.001). The mean L/H was higher in patients with a peak exercise ejection fraction (EF) less than 40% versus 40% or more (0.51 +/- 0.07 versus 0.43 +/- 0.05, P < 0.001) and in patients with a poststress EF less than 40% versus 40% or more (0.50 +/- 0.07 versus 0.44 +/- 0.06, P < 0.01). A threshold of L/H greater than 0.44 yielded a sensitivity and specificity of 63% and 81%, respectively, for identifying severe and extensive CAD in the prospective group and a sensitivity of 86% in identifying stenosis of 90% or more in the proximal left anterior descending artery.
Conclusion: The new automatic algorithm for assessing L/H correlated well with manually derived L/H for (99m)Tc-sestamibi as well as (201)TI SPECT. An increased postexercise (99m)Tc-sestamibi L/H adds significant diagnostic value to study myocardial perfusion SPECT as a marker of severe and extensive CAD and reduced ventricular function.