Description
(2) Material and Methods
Three patients scheduled for a mastectomy, were included in the study. Tissues of skin, nipple, intra-glandular fat, glandular tissue and breast carcinoma were analysed. Two experimental methods were developed. The first uses pulse-echo measurements to measure the speed of sound and frequency dependent attenuation; the second uses a pycnometer to measure the mass density. Two important adjustments were made to mimic in vivo conditions. First, a novel sample holder using a vacuum pump was developed. This has the advantage that the sample thickness could be obtained at each grid point separately without compressing the tissue. Second, physiological phosphate-buffered saline (PBS) solution of $37^o~C$ was used to prevent absorbing.
(3) Results
For fresh samples of fat, skin, glandular tissue and nipple, the following values are found for the sound speed: 1456 m/s, 1559 m/s, 1564 m/s and 1574 m/s; frequency dependent attenuation: 5.7 Np/m MHz$^{-1.3}$, 4.8 Np/m MHz$^{-1.7}$, 10.5 Np/m MHz$^{-1.5}$ and 4.6 Np/m MHz$^{-2.0}$; and mass density: 869 kg/m$^3$, 970 kg/m$^3$, 874 kg/m$^3$, 987 kg/m$^3$, respectively. Significant differences are observed when comparing the results with literature, see Fig. 1.
For density, higher values are found when using larger samples, see Fig. 1. An increase is seen for samples that are measured before and after being submerged in PBS. On the contrary, similar values are found for samples that are fresh, cooled, or submerged in formalin.
(4) Discussion and Conclusion
It is shown that protocols affect the results. To measure the parameters, it is recommended 1) to use only fresh samples and perform the measurements at 37$^°$C, 2) to avoid sample holders that deform samples, 3) to minimize submersion time to reduce absorption effects, 4) to measure properties at each location separately and 5) to use thin and smooth samples. Results suggest that PBS is not suitable as a reference medium for measuring the density and that formalin may be an alternative.
