Wavefront distortion measurements in the human breast
Published wavefront distortion (phase aberration) measurements for the human breast ranged from mild phase aberrations (8 ns r.m.s) to severe phase aberrations (67 ns r.m.s.). These measurements are required to specify arrays and assess the potentials of adaptive imaging. They require high inter-element uniformity so that receive signal variations between elements can be attributed to wave propagation effects. Array elements must be small to minimize the integration of the arriving wavefront across the face of the element. We have developed an apparatus to make concurrent pulse-echo and pitch-catch measurements in a clinical setting. The breast is stabilized between opposing transducers with light compression. After fixing the position of the transducers, pulse-echo and pitch-catch snapshots are captured sequentially with tissue and reference phantom targets. Data was collected from the left breast in twelve volunteers. Phase errors were significantly smaller for pulse-echo measurements (mean 25 ns r.m.s.) than for pitch-catch measurements (mean 55 ns r.m.s.).