Measurement and correction of ultrasonic pulse distortion produced by the human breast

Abstract

Ultrasonic wavefront distortion produced by transmission through breast tissue specimens was measured in a two-dimensional aperture. Differences in arrival time and energy level between the measured waveforms and references that account for geometric delay and spreading were calculated. Also calculated was a waveform similarity factor that is decreased from 1.0 by changes in waveform shape. For nine different breast specimens, the arrival time fluctuations had an average (+/- s.d.) rms value of 66.8 (+/- 12.6) ns and an associated correlation length of 4.3 (+/- 1.1) mm, while the energy level fluctuations had an average rms value of 5.0 (+/- 0.5) dB and a correlation length of 3.4 (+/- 0.8) mm. The corresponding waveform similarity factor was 0.910 (+/- 0.023). The effect of the wavefront distortion on focusing and the ability of time-shift compensation to remove the distortion were evaluated by comparing parameters such as the -30-dB effective radius, the -10-dB peripheral energy ratio, and the level at which the effective radius departs from an ideal by 10% for the focus obtained without compensation, with time-shift estimation and compensation in the aperture, and with time-shift estimation and compensation performed after backpropagation. For the nine specimens, the average -10-dB peripheral energy ratio of the focused beams fell from 3.82 (+/- 1.83) for the uncompensated data to 0.96 (+/- 0.18) with time-shift compensation in the aperture and to 0.63 (+/- 0.07) with time-shift compensation after backpropagation. The average -30-dB effective radius and average 10% deviation level were 4.5 (+/- 0.8) mm and -19.2 (+/- 3.5) dB, respectively, for compensation in the aperture and 3.2 (+/- 0.7) mm and -22.8 (+/- 2.8) dB, respectively, for compensation after backpropagation. The corresponding radius for the uncompensated data was not meaningful because the dynamic range of the focus was generally less than 30 dB in the elevation direction, while the average 10% deviation level for the uncompensated data was -4.9 (+/- 4.1) dB. The results indicate that wavefront distortion produced by breast significantly degrades ultrasonic focus in the low MHz frequency range and that much of this degradation can be eliminated using wavefront backpropagation and time-shift compensation.

Optimized Hyperthermia Treatment of Prostate Cancer Using a Novel Intracavitary Ultrasound Array

“…Three snapshots of the resulting pressure field are shown in Figure 6 superimposed on an image of the tissue model's sound speed variation. The computed fields show scattering and diffraction effects consistent with experimentally measured propagation effects in human breast tissue (Hinkelman et al, 1995).…”

Microcalcifications as elastic scatterers under ultrasound

“…The mean magnitude of our in vivo results is significantly smaller than other breast aberration measurements in the literature. Our measurements involve a shorter propagation path length than the through-transmission techniques used in these other published studies [25], [26]. As we expect phase error due to tissue inhomogeneities to accumulate over the propagation path, this path length difference may account for the difference between our measurements and other published findings.…”

A 2-D anatomic breast ductal computer phantom for ultrasonic imaging

“…It is hoped that this breast model will lead to a better understanding of the composition and the structure of the breast and their interaction with ultrasound [23] [24]. Improving our knowledge of these interactions will make it possible to design more efficient future equipment and to develop more powerful tissue characterization techniques.…”

“…Several groups have attempted to understand the physical causes of ultrasonic wavefront distortion either by performing direct measurements on the human breast [22] [23] or by devising models of breast tissues. In one case, [24] simulations were conducted through a simple two-dimensional model of the breast in order to study the limitations of the Born approximation used in ultrasound imaging techniques.…”