Photoacoustic Imaging with a double-ring sensor

Laser-induced acoustic waves in tissue can be detected by measurement of the pressure transient or displacement at the tissue surface. Measurement of these pressure transients using piezoelectric sensors is the most commonly used method in photoacoustics. Although optical methods for detection of acoustic waves have been developed as well [1-6], piezoelectric sensors have the advantage that broadband sensors are easier to construct and have a slightly better sensitivity than optical detection systems [7]. The shape and size of the piezoelectric element determine the characteristics, such as the directivity pattern and the frequency response of the sensor. Sensors with a small element size (“point sensors”) have a very large angular aperture, and thus are able to detect acoustic signals originating from a large volume in the tissue. As a result, reconstruction algorithms are needed to obtain an image. In contrast, for sensors with a narrow angular aperture, e.g., ring-shaped or annular sensors, the time traces can be regarded as 1D depth images (amplitude (A)-scans) of photoacoustic sources inside the measurement volume. Comparable to an echographic B-scan, imaging with such a ring-shaped sensor is carried out by scanning the sensor over the tissue surface, permitting real-time reconstruction of the corresponding part of the image without the need for information on adjacent sensor positions.