Abstract
Ultrasound sensor arrays for photoacoustic tomography (PAT) are investigated that create line projections of the pressure generated in an object by pulsed light illumination. Projections over a range of viewing angles enable the reconstruction of a three-dimensional image. Two line-integrating arrays are compared in this study for the in vivo imaging of vasculature, a piezoelectric array, and a camera-based setup that captures snapshots of the acoustic field emanating from the sample. An array consisting of 64 line-shaped sensors made of piezoelectric polymer film, which was arranged on a half-cylindrical area, was used to acquire spatiotemporal data from a human finger. The optical setup used phase contrast to visualize the acoustic field generated in the leg of a mouse after a selected delay time. Time-domain back projection and frequency-domain back propagation were used for image reconstruction from the piezoelectric and optical data, respectively. The comparison yielded an about threefold higher resolution for the optical setup and an about 13-fold higher sensitivity of the piezoelectric array. Due to the high density of data in the camera images, the optical technique gave images without streak artifacts, which were visible in the piezo array images due to the discrete detector positions. Overall, both detection concepts are suited for almost real-time projection imaging and three-dimensional imaging with a data acquisition time of less than a minute without averaging, which was limited by the repetition rate of the laser.
Highlights
Photoacoustic tomography (PAT), which is known as optoacoustic tomography, reveals the optical absorption properties of an object from acoustic signals generated by the absorption of modulated electromagnetic radiation
We have demonstrated a line detector array based on polyvinylidene fluoride (PVDF) sensors for the 3D imaging of phantoms and for 2D
We show in the following the raw data, projection images, and maximum amplitude projections (MAPs) for selected angles
Summary
Photoacoustic tomography (PAT), which is known as optoacoustic tomography, reveals the optical absorption properties of an object from acoustic signals generated by the absorption of modulated electromagnetic radiation. The used radiation is generated by short pulsed laser sources in the visible and near infrared spectral range, and the acoustic waves, which are caused by the thermoelastic effect, are detected by broadband ultrasound sensors. In three-dimensional (3D) PAT, the excitation laser pulses are absorbed in a large volume of the imaged object, and the broadband sensors are arranged in a way so as to gather the resulting acoustic waves over a large range of propagation directions on the surface of the object. This guarantees accurate image reconstruction from the acoustic signals. Data acquisition can be achieved by scanning a single detector across the surface of a sample, measuring at each position the ultrasound wave that is created by a single excitation
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