Patterned thin metal film for the lateral resolution measurement of photoacoustic tomography.

BACKGROUND: Image quality assessment method of photoacoustic tomography has not been completely standardized yet. Due to the combined nature of photonic signal generation and ultrasonic signal transmission in biological tissue, neither optical nor ultrasonic traditional methods can be used without modification. An optical resolution measurement technique was investigated for its feasibility for resolution measurement of photoacoustic tomography. METHODS: A patterned thin metal film deposited on silica glass provides high contrast in optical imaging due to high reflectivity from the metal film and high transmission from the glass. It provides high contrast when it is used for photoacoustic tomography because thin metal film can absorb pulsed laser energy. An US Air Force 1951 resolution target was used to generate patterned photoacoustic signal to measure the lateral resolution. Transducer with 2.25 MHz bandwidth and a sample submerged in water and gelatinous block were tested for lateral resolution measurement. RESULTS: Photoacoustic signal generated from a thin metal film deposited on a glass can propagate along the surface or through the surrounding medium. First, a series of experiments with tilted sample confirmed that the measured photoacoustic signal is what is propagating through the medium. Lateral resolution of the photoacoustic tomography system was successfully measured for water and gelatinous block as media: 0.33 mm and 0.35 mm in water and gelatinous material, respectively, when 2.25 MHz transducer was used. Chicken embryo was tested for biomedical applications. CONCLUSIONS: A patterned thin metal film sample was tested for its feasibility of measuring lateral resolution of a photoacoustic tomography system. Lateral resolutions in water and gelatinous material were successfully measured using the proposed method. Measured resolutions agreed well with theoretical values.

Estimation algorithm of the bowel motility based on regression analysis of the jitter and shimmer of bowel sounds.

Bowel sound (BS) signals can be used clinically as useful indicators of bowel motility. In this study, we devised a modified iterative kurtosis-based detector algorithm, in order to enhance the de-noising performance of BS signals, and an estimation algorithm of bowel motility based on the regression modeling of the jitter and shimmer of BS signals obtained by auscultation. The correlation coefficient, coefficient of determination and errors between the colon transit times measured by a conventional radiograph and the corresponding values estimated by our method were 0.987, 0.974 and 3.5 ± 3.3h, respectively. These results demonstrated that our method could be used as a complementary tool for the non-invasive diagnosis and monitoring of bowel motility, instead of conventional radiography.