Background: A simple method for the measurement of LDL particle sizes is needed in clinical laboratories because a predominance of small, dense LDL (sd LDL) has been associated with coronary heart disease. We applied dynamic light scattering (DLS) to measure lipoprotein particle sizes, with special reference to sd LDL. Methods: Human serum lipoproteins isolated by a combination of ultracentrifugation and gel chromatography, or by sequential ultracentrifugation, were measured for particle size using DLS. Results: The sizes of polystyrene beads, with diameters of 21 and 28 nm according to the manufacturer, were determined by DLS as 19.3 + 1.0 nm (mean + SD, n ¼ 11) and 25.5 + 1.0 nm, respectively. The coefficients of variation for the 21 and 28 nm beads were 5.1% and 3.8% (within-run, n ¼ 11), and 2.9% and 6.2% (between-run, n ¼ 3), respectively. The lipoprotein sizes determined by DLS for lipoprotein fractions isolated by chromatography were consistent with the elution profile. Whole serum, four isolated lipoprotein fractions (CM þ VLDL þ IDL, large LDL, sd LDL and HDL) and a nonlipoprotein fraction isolated by sequential ultracentrifugation were determined by DLS to be 13.1 + 7.5, 37.0 + 5.2, 21.5 + 0.8, 20.3 + 1.1, 8.6 + 1.5 and 8.8 + 2.0 nm, respectively. Conclusions: The proposed DLS method can differentiate the sizes of isolated lipoprotein particles, including large LDL and sd LDL, and might be used in clinical laboratories in combination with convenient lipoprotein separation.

For early diagnosis of rheumatoid arthritis (RA), it is important to visualize its potential marker, vascularization in the synovial membrane of the finger joints. Photoacoustic (PA) imaging, which can image blood vessels at high contrast and resolution, is expected to be a potential modality for earlier diagnosis of RA. In previous studies of PA finger imaging, different acoustic schemes, such as linear-shaped arrays, have been utilized, but these have limited detection views, rendering inaccurate reconstruction, and most of them require rotational detection. We are developing a PA system for finger vascular imaging using a ring-shaped array ultrasound (US) transducer. By designing the ring-array sensor based on simulations, using phantom experiments, it was demonstrated that we have created a system that can image small objects around 0.1 to 0.5 mm in diameter. The full width at half maximum of the slice direction of the system was within 2 mm and corresponded to that of the simulation. Moreover, we could clearly visualize healthy index finger vasculature and the location of the distal interphalangeal and proximal interphalangeal joints by PA and US echo images. In the future, this system could be used as a method for visualizing the three-dimensional vascularization of RA patients' fingers.

To realize three-dimensional (3D) optical imaging of the internal structure of an animal body, we have developed a new technique to reconstruct optical computed tomography (optical CT) images from two-dimensional (2D) transillumination images. In transillumination imaging of an animal body using near-infrared light, the image is blurred because of the strong scattering in the tissue. To overcome this problem, we propose a novel technique to apply the point spread function (PSF) for a light source located inside the medium to the transilluminated image of light-absorbing structure. The problem of the depth-dependence of PSF was solved in the calculation of the projection image in the filtered back-projection method. The effectiveness of the proposed technique was assessed in the experiments with a model phantom and a mouse. These analyses verified the feasibility of the practical 3D imaging of the internal light-absorbing structure of a small animal.

In diagnosis of chronic hepatitis, shear wave elastography is utilized for the evaluation of fibrosis progression by estimating the viscoelasticity from shear wave speeds. The dispersion slope method is studied to evaluate the viscosity and fibrosis stage. However, when the shear wave length is a little larger than the size of fibrous structure in liver fibrosis tissues, shear wave propagates repeating reflection or refraction and influences the dispersion slope. We simulate shear wave propagation in a model with a fibrous structure and compare the dispersion slope with a homogeneous model in order to investigate the effect of the fibrous structure. As a result, the dispersion slope is dependent on the viscosity in a high frequency range but affected by the fibrous structure in a low frequency range. Results show that the fibrous structure influences contents of low frequencies. Using different frequency ranges to estimate the dispersion slope can help more precise viscoelasticity analysis.

A constant sound speed (i.e., 1540 m/s) is generally used in various ultrasound (US) and photoacoustic (PA) image reconstruction algorithms based on the assumption of a homogeneous sound speed in human tissue. However, the variation of the sound speed in human tissue can be as great as 10%, which can lead to low contrast, distortion, and blurring in reconstruction images. We proposed an automatic method of selecting the mean sound speed based on optimum focusing of received PA signals to enhance the quality of reconstructed PA images. Optimum focusing is quantified by calculating the minimum sum of the deviation of beamformed PA signals from their mean value for various sound speeds. The proposed method was demonstrated by homogeneous and heterogeneous sound speed simulation models, and also evaluated by experiments with agar and porcine tissue-mimicking phantoms. The central vertical and lateral profiles of reconstructed absorbers verified the improvement of contrast, signal-to-noise ratio (SNR), and spatial resolution by using the estimated mean sound speed.