PCM-CMM-2015 – 3rd Polish Congress of Mechanics & 21st Computer Methods in Mechanics September 8th–11th 2015, Gda ´ nsk, Poland PCM-CMM-2015 – 3rd Polish Congress of Mechanics & 21st Computer Methods in Mechanics September 8th–11th 2015, Gda ´ nsk, Poland PCM-CMM-2015 – 3rd Polish Congress of Mechanics & 21st Computer Methods in Mechanics September 8th–11th 2015, Gda ´ nsk, Poland Changes in ultrasound echoes of a breast tissue in vivo after exposure to heat - a case study. Barbara Gambin 1* , Eleonora Kruglenko 2 , Michal Byra 3 , Andrzej Nowicki 4 , Hanna Piotrzkowska-Wróblewska 5 , Katarzyna Dobruch-Sobczak 6 1,2,3,4,5,6 Department of Ultrasound, Institute of Fundamental Technological Research of the Polish Academy of Sciences Pawi´ nskiego 5B, 02-106 Warszawa, Poland, e-mail: bgambin@ippt.pan.pl 1 6 Cancer Center and Institute of Oncology. Maria Sklodowska-Curie Memorial Wawelska 15, 02-034 Warsaw, Poland Abstract A B-mode ultrasonography provides structural information on the tissue under investigation encoding the echo strength in gray scale in a two-dimensional image. Interpretation of the B-mode image of breast tissue is done by a physician. The analysis of statistical properties of backscattered RF signal has been recently applied successfully to distinct healthy tissue from tissue lesions regions as a new method of quantitative ultrasound (QUS). Up till now, the most reliable results were obtained for liver and renal tissue lesions, because their normal, healthy structures are nearly homogeneous while a heterogeneous breast tissue classification is still an open issue. The recent study revealed that the medium contraction and expansion induced by a temperature change may cause variations in the relative position of scatterers in a tissue. We have developed a new procedure of heating the patient breast and allowing to observe and record in vivo the influence of temperature changes on a B-mode image and properties of unprocessed radio frequency (RF) backscattered echoes. The initial, feasibility studies of influence of the temperature increase in breast tissue on the intensity, spectrum and statistics of ultrasonic echoes will be discussed. Keywords: breast tissue, RF signal, backscattered signal amplitude statistics, spectral properties 1. Introduction A B-mode ultrasonography provides structural information on the tissue under investigation encoding the echoes strength in gray scale in a two-dimensional image. Interpretation of the B- mode image of breast tissue is done by a physician. Recently new methods of quantitative ultrasound (QUS) dedicated to esti- mation of structural changes in tissue are being developed, cf. [4], [6]. Particularly, analysis of statistical properties of backscattered RF signal has been successfully applied to distinct healthy tissue from tissue lesions regions, see [5]. Up till now, the most reliable results were obtained for liver and renal tissues lesions, because their normal, healthy structures are nearly homogeneous while a heterogeneous breast tissue classification is still an open issue. A recent study revealed that the medium contraction and expan- sion induced by a temperature change can cause variations in the relative position of scatterers in a tissue. We have developed a novel algorithm of heating the patient breast and recording the changes in ultrasonic B-scans and in RF echoes. In the statistics of the signal information is encoded about the type of dissipative structures. The structural information on the type of dissipative tissue is encoded in the statistics of the returning signals. When a signal is backscattered from a large number of uniformly dis- tributed scatterers then random amplitude fluctuations are close to the Rayleigh distribution. Variations of the structure to a more heterogeneous in terms of the appearance of cell clusters in the distribution of scatterers or the scatterers reflectivity variations result in the amplitude distribution close to K-distribution or Nak- agami distribution. The experiments were carried out in order to evaluate the temperature influence on variation in statistical dis- tributions of signals recorded in tissue phantoms and samples of soft tissue in vitro, cf. [1],[2] and [3]. In what follows the ini- tial, feasibility studies of influence of the temperature increase in breast tissue on the signal intensity, spectrum and statistics of ultrasonic echoes will be discussed. The paper is organized as fol- lows: Sections II introduce the experiment description and meth- ods, Section III presents the results. In Section IV conclusions are drawn about the contributions of this study to the general ul- trasonography. 2. Material and Methods 2.1. Experiment description Backscattered ultrasound RF signals and B-mode images have been collected using ULTRASONIX, (SonixTOUCH, Canada) scanner, and standard linear array L14-5/38, 10 MHz transducer. focused at the depth 3,5 cm. The patient breast was scanned before and after heating by physician who has localized the lesion region to be analyzed. The heating process was done directly through the skin to which a rubber seal bag with hot wa- ter at c /a 50 o C during 10 minutes was applied. 2.2. Methods The signal frequency spectrum from the regions at two tem- perature levels has been also obtained. Next, for each sub regions of tissue the statistical parameters have been correlated to scat- terer strength, density and distribution. All scan lines were com- pensated for attenuation and then the amplitudes of all FR lines have been calculated using of Hilbert transform. Next, the fitting of amplitude histograms to different probability density functions together with the evaluation of the accuracy of matching by MSE (mean square error) was performed. * This work was partially supported by the National Science Centre (grant no. 2011/03/B/ST7/03347). 217