Effect of power Doppler and digital subtraction techniques on the comparison of myocardial contrast echocardiography with SPECT

Objective-To compare the accuracy and feasibility of harmonic power Doppler and digitally subtracted colour coded grey scale imaging for the assessmen t of perfusion defect severity by single photon emission computed tomograph y (SPECT) in an unselected group of patients. Design-Cohort study. Setting-Regional cardiothoracic unit. Patients-49 patients (mean (SD) age 61 (11) years; 27 women, 22 men) with k nown or suspected coronary artery disease were studied with simultaneous my ocardial contrast echo (MCE) and SPECT after standard dipyridamole stress. Main outcome measures-Regional myocardial perfusion by SPECT, performed wit h Tc-99m tetrafosmin, scored qualitatively and also quantitated as per cent maximum activity. Results-Normal perfusion was identified by SPECT in 225 of 270 segments (83 %). Contrast echo images were interpretable in 92% of patients. The proport ion of normal MCE by grey scale, subtracted, and power Doppler techniques w ere respectively 76%, 74%, and 88% (p < 0.05) at > 80% of maximum counts, c ompared with 65%, 69%, and 61% at < 60% of maximum counts. For each techniq ue, specificity was lowest in the lateral wail, although power Doppler was the least affected. Grey scale and subtraction techniques were least accura te in the septal wall, but power Doppler showed particular problems in the apex. On a per patient analysis, the sensitivity was 67%, 75%, and 83% for detection of coronary artery disease using grey scale, colour coded, and po wer Doppler, respectively, with a significant difference between power Dopp ler and grey scale only (p < 0.05). Specificity was also the highest for po wer Doppler, at 55%, but not significantly different from subtracted colour coded images. Conclusions-Myocardial contrast echo using harmonic power Doppler has great er accuracy than with grey scale imaging and digital subtraction. However, power Doppler appears to be less sensitive for mild perfusion defects.