Noninvasive measurement of the degree of red blood cell (RBC) aggregation is useful for evaluating blood properties. In the present paper, we proposed a method to estimate the size of RBC aggregates without using the power spectrum of the posterior wall by introducing a reference scattering spectrum. The reference power spectra were calculated using the power spectrum measured for an ultrafine wire with a hemispherical tip. They were applied to the size estimation of microparticles simulating RBC aggregates. The estimated sizes were close to the true values, which shows that the calculated reference power spectra were suitable for accurate size estimation. The proposed method was also applied to in vivo measurements, and the estimated sizes between at rest and in RBCs aggregated by avascularization were successfully differentiated. This demonstrates that the proposed method will be useful for estimating the size of RBC aggregates.

Red blood cell (RBC) aggregation is the reversible adhesion of RBCs among themselves. We previously reported a positive correlation between blood glucose level and the degree of RBC aggregation (the brightness of the B-mode image). In the present study, we investigated the contribution to the brightness according to the deviation from the central axis in measurements along with the long-axis view of the vein. The results show that the brightness changed significantly for a slight change in the lateral position in the short-axis image. We found that the stability of the measurements was not guaranteed in the long-axis view and estimated the correct analysis window range for the short-axis view.

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In this study, the attenuation coefficient of blood was measured in vivo in the frequency range of 10–45 MHz. A procedure to correct the distribution of sound pressure in the measurements was discussed. Further, in vivo measurements were applied on the dorsal hand vein of four healthy subjects at rest and during avascularization. As a preliminary result, less variation of the measured attenuation coefficients was achieved by the proposed method. The comparable results of the inclination of the attenuation coefficients were obtained at rest and during avascularization. Furthermore, the attenuation coefficients during avascularization were markedly higher than those at rest, reflecting the degree of red blood cell aggregation promoted by avascularization. This method may aid in the non-invasive evaluation of blood properties reflecting the degree of red blood cell aggregation.

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