A new methodology for the assessment of very low concentrations of cells in serous body fluids, based on the count of ultrasound echoes backscattered from cells.

A methodology for the assessment of cell concentration, in the range 5 to 100 cells/μl, suitable for in vivo analysis of serous body fluids is presented in this work. This methodology is based on the quantitative analysis of ultrasound images obtained from cell suspensions, and takes into account applicability criteria such as short analysis times, moderate frequency and absolute concentration estimation, all necessary to deal with the variability of tissues among different patients. Numerical simulations provided the framework to analyse the impact of echo overlapping and the polydispersion of scatterer sizes on the cell concentration estimation. The cell concentration range which can be analysed as a function of the transducer and emitted waveform used was also discussed. Experiments were conducted to evaluate the performance of the method using 7 μm and 12 μm polystyrene particles in water suspensions in the 5 to 100 particle/μl range. A single scanning focused transducer working at a central frequency of 20MHz was used to obtain ultrasound images. The method proposed to estimate the concentration proved to be robust for different particle sizes and variations of gain acquisition settings. The effect of tissues placed in the ultrasound path between the probe and the sample was also investigated using 3mm-thick tissue mimics. Under this situation, the algorithm was robust for the concentration analysis of 12 μm particle suspensions, yet significant deviations were obtained for the smallest particles.