MICROSCOPIC ULTRASOUND CHARACTERIZATION OF BIOLOGICAL TISSUES

Emilie Franceschini, Eric Debieu
Collaboration LMA OR Méthodes d’Interface : Bruno Lombard, Joel Piraux
International collaboration : Guy Cloutier (Laboratory of Biorheology and Medical Ultrasonics, Quebec, Canada)

Microscopic ultrasound characterization of breast tissues

The development of microscopic ultrasound methods was motivated by already existing clinical methods based on optical microscopy analysis of excised tissues of the tumor (histological slice - figure 1). The tumor malignancy can be determined by the simple observation of the size and spatial arrangement of cells. The ultrasound scatterer size estimation methods allow to yield the same information, however further developments need to be accomplished. Our first aim is to identify the tissue microstructure responsible for scattering in order to develop an appropriate scattering model. Our second aim is to combine tomographic techniques with the ultrasound scatterer size estimation technique. The combined imaging system will yield an image set of microscopic and macroscopic parameters. Moreover the attenuation images reconstructed using tomographic techniques will be used to account for attenuation losses in the microscopic scatterer size estimation technique.

Fig 1 - Optical photomicrographs of a mammary carcinoma (malignant tumor). These images are used to obtain information about the size and spatial arrangement of cellular and sub-cellular structures.

Microscopic ultrasound characterization of erythrocyte aggregation

(collaboration with the Laboratory of Biorheology and Medical Ultrasonics, Montreal, Canada)

Ultrasonic (US) backscattered echoes from blood contain frequency-dependent information that can be used to obtain quantitative parameters reflecting the aggregation state of red blood cells (RBCs). Such quantitative parameters would be of great interest to elucidate the impact of RBC aggregation on several circulatory diseases (such as deep venous thrombosis and diabetes mellitus) in vivo and in situ.
The objective of our work is to develop a microscopic ultrasound characterization technique applicable in vivo in order to determine the size and spatial arrangement of RBC aggregates. For this purpose, an optimization method was proposed to simultaneously estimate total attenuation (i.e. attenuation caused by intervening tissue layers between the probe and the blood flow) and blood structure properties. In vitro and in vivo experiments allowed to assess the method ability to evaluate blood structural properties and total attenuation. We also studied numerical simulation of the ultrasound wave propagation to better understand the relation between the parameters describing the aggregation level and the backscatterer coefficient.

Fig 2 - Quantitative images of porcine blood sheared in a Couette device superimposed on the gray-scale B-mode images. Porcine blood were sheared in a Couette flow system, and ultrasonic rf echoes were obtained using a 25 MHz center-frequency transducer. Since skin is one of the most attenuating tissue layers during in vivo scanning, two skin-mimicking phantoms with different attenuation coefficients were successively introduced between the transducer and the blood flow. Parameters were estimated by the classical Structure Factor Size Estimator (Yu and Cloutier 2007) for the experiment without skin-mimicking phatom (top panel) and by the Structure Factor Size and Attenuation Estimator for the skin-mimicking phantoms.

Publications

• Franceschini E., Metzger B. & Cloutier G., Forward problem study of an effective medium model for ultrasound blood characterization, IEEE Trans. on Ultrason., Ferroelect., Freq. Contr., in press (2011)

• Saha R. K., Franceschini E. & Cloutier G., Assessment of accuracy of the structure-factor-size-estimator method in determining red blood cell aggregate size from ultrasound spectral backscatter coefficient, J. Acoust. Soc. Amer., 129(4) 2269-2277 (2011)

• Franceschini E., Yu F. T. H., Destrempes F. & Cloutier G., Ultrasound characterization of red blood cell aggregation with intervening attenuating tissue-mimicking phantoms, J. Acoust. Soc. Amer. 127(2) 1104-1115 (2010)

• Yu F. T. H., Franceschini E., Chayer B., Armstrong J. K., Meiselman H. J., & Cloutier G., Ultrasonic parametric imaging of erythrocyte agregation using the structure factor size estimator, Biorheology 123 343-363 (2009)

• Franceschini E., Yu F. T. H., & Cloutier G., Simultaneous estimation of attenuation and structure parameters of aggregated red blood cells from backscatter measurements, J. Acoust. Soc. Amer. 123 EL85-91 (2008)