TY - JOUR A1 - Kirchner, Thomas A1 - Villringer, Claus A1 - Laufer, Jan T1 - Evaluation of ultrasound sensors for transcranial photoacoustic sensing and imaging JF - Photoacoustics N2 - Photoacoustic imaging through skull bone causes strong attenuation and distortion of the acoustic wavefront, which diminishes image contrast and resolution. As a result, transcranial photoacoustic measurements in humans have been challenging to demonstrate. In this study, we investigated the acoustic transmission through the human skull to design an ultrasound sensor suitable for transcranial PA imaging and sensing. We measured the frequency dependent losses of human cranial bones ex vivo, compared the performance of a range of piezoelectric and optical ultrasound sensors, and imaged skull phantoms using a PA tomograph based on a planar Fabry–Perot sensor. All transcranial photoacoustic measurements show the typical effects of frequency and thickness dependent attenuation and aberration associated with acoustic propagation through bone. The performance of plano-concave optical resonator ultrasound sensors was found to be highly suitable for transcranial photoacoustic measurements. KW - transcranial KW - ultrasound sensor KW - photoacoustic KW - optoacoustic KW - Fabry-Perot Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17993 SN - 2213-5979 VL - 33 PB - Elsevier ER - TY - CHAP A1 - Buchmann, Jens A1 - Zhang, Edward A1 - Scharfenorth, Chris A1 - Spannekrebs, Bastian A1 - Villringer, Claus A1 - Laufer, Jan T1 - Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition N2 - Fabry-Perot (FP) polymer film sensors offer high acoustic sensitivity, small element sizes, broadband frequency response and optical transmission to enable high resolution, backward mode photoacoustic (PA) imaging. Typical approaches to sensor fabrication involve the deposition of stacks of alternating dielectric materials to form interferometer mirrors, which are separated by a polymer spacer. If hygroscopic soft dielectric materials are used, a protective polymer layer is typically required. In this study, methods for the deposition of water-resistant, hard dielectric materials onto polymers were explored to improve the robustness and performance of the sensors. This involved the optimisation of the fabrication process, the optical and acoustic characterisation of the sensors, and a comparison of the frequency response with the output of an acoustic forward model. The mirrors, which were separated by a 20 μm Parylene spacer, consisted of eight double layers of Ta2O5 and SiO2 deposited onto polymer substrates using temperature-optimised electron vapour deposition. The free spectral range of the interferometer was 32 nm, its finesse FR = 91, and its visibility V = 0.72. The noise-equivalent pressure was 0.3 kPa (20 MHz bandwidth). The measured frequency response was found to be more resonant at 25 MHz compared to sensors with soft dielectric mirrors, which was also in good agreement with the output of a forward model of the sensor. The sensors were used in a PA scanner to acquire 3-D images in tissue phantoms. KW - Fabry-Perot KW - ultrasound KW - photoacoustic KW - imaging KW - sensor Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-15289 SP - 920 EP - 928 PB - Society of Photo-Optical Instrumentation Engineers (SPIE) ER - TY - CHAP A1 - Kirchner, Thomas A1 - Villringer, Claus A1 - Gutke, Marko A1 - Laufer, Jan T1 - Plano-concave optical sensor for transcranial photoacoustic measurements T2 - Opto-Acoustic Methods and Applications in Biophotonics VI N2 - Biomedical photoacoustics is usually used to image absorption-based contrast in soft tissues up to depths of several centimeters and with sub-millimeter resolution. By contrast, measuring Photoacoustic (PA) signals through hard bone tissue shows severe signal degradation due to aberration and high attenuation of high frequency acoustic signal components. This is particularly noticeable when measuring through thicker, human, skull bone. Which is the main reason why transcranial PA imaging in humans has so far proved challenging to implement. To tackle this challenge, we developed an optical resonator sensor based on a previous planar-concave design. This sensor was found to be highly suitable for measuring the low-pressure amplitude and low acoustic frequency signals that are transmitted through human cranial bone. A plano-concave optical resonator sensor was fabricated to provide high sensitivity in the acoustic frequency range of DC to around 2 MHz, a low noise equivalent pressure and a small active element size enabling it to significantly outperform conventional piezoelectric transducers when measuring PA waves transmitted through ex vivo human cranial bones. KW - transcranial KW - ex vivo KW - human KW - brain KW - optical resonator KW - photoacoustic KW - optoacoustic Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-17840 PB - Society of Photo-Optical Instrumentation Engineers (SPIE) ER -