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

Abstract

BackgroundImage 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.MethodsA 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.ResultsPhotoacoustic 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.ConclusionsA 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.

Comparison between optical-resolution photoacoustic microscopy and confocal laser scanning microscopy for turbid sample imaging

“…3(a)], was used for measuring the diffraction-limited lateral resolution of the ORPAM system. Thin chromium film generates strong photoacoustic signals 11 and is robust enough for focused illumination. However, applied laser radiant exposure (J∕cm 2 ) must be carefully adjusted when imaging through turbid media because the damage threshold of thin chromium film is lower than that of biological samples.…”

“…10 Targets comprised of a patterned thin metal film (PTMF) and photon-absorbing lines printed on transparent film were used to measure lateral resolution for PAT. 11,12 Thin metal film is highly effective in generating photoacoustic signal due to the high absorption coefficient of metal. Moreover, thin films are optimal for generating sound waves perpendicular to the target surface.…”