Two-dimensional echocardiographic imaging: In vitro comparison of conventional and dynamically focused annular array transducers

Quantitative two-dimensional echocardiography has been adversely affected by a tendency for underestimation of cross-sectional areas of cardiac chambers, a difficulty that might be ameliorated by recent advances in imaging technology. To determine if this were so, we measured echocardiographic cross-sectional areas of 25 formalin-fixed animal left ventricular (LV) sections in vitro using conventional 13 mm and 15 mm diameter fixed-focused single element transducers, and a 15 mm diameter dynamically focused annular array transducer at 3 different distances between myocardial slice and transducer (2 cm, 6 cm and 10 cm) and compared the 2-dimensional echocardiographic areas to the corresponding anatomic cross-sectional areas of the same hearts. LV total and cavity area were measured by computer assisted planimetry of videotaped echo images, performed blinded to the transducer used, and photographed anatomic slices; LV myocardial area was derived by subtraction. Comparison of two-dimensional echocardiographic total, myocardial, and cavity areas with corresponding anatomic measurements showed excellent correlation for each transducer at all depths ( r = 0.97 to 0.98 for total area; r = 0.98 to 0.99 for cavity area; r = 0.93 to 0.97 for myocardial area). For total and myocardial cross-sectional areas, the slope of the relation between echographic and anatomic areas did not differ significantly from unity, but for LV cavity area this was achieved only by the dynamically focused transducer. In contrast, the conventional 13 mm transducer significantly underestimated larger LV cavity areas in both the near and middle fields (slopes = 0.90 and 0.91, respectively) and the 15 mm transducer yielded slopes from 0.86 to 0.91 in all fields. The results of this study support the theoretical prediction that dynamic focusing and narrowing of beam width by annular array technology would ameliorate underestimation of cardiac chamber cross-sectional areas by two-dimensional echocardiography.