Fig. 4.

(a) Photograph of an ink-stained leaf skeleton before embedding in agarose. The strong branches at the lower boarder of the skeleton measure approximately 160–190 µm in diameter. (b) Photoacoustic projection image of leaf skeleton based on signals with a bandwidth of 300 kHz to 10 MHz. Imaging artifacts around the leaf are clearly visible. Within the leaf, the occurrence of artifacts seems to be lower. The resulting image with a signal-bandwidth of 4 MHz is shown in (c). The leaf stands out more clearly from the artifact background. However, finer details are lost. In (d)-(f) different reconstructions based on forward simulated data using the k-Wave toolbox [21] are shown. For reconstruction (d) 253 sensor positions were used. In (e) only sensor positions available in the measurement were considered and the forward simulated data was frequency filtered to achieve a bandwidth of 300 kHz-10MHz. Also, noise comparable to the actual measurement noise was added. The same forward data, however at 127 positions, were used to calculate image (f). From (d)-(f) it can be concluded that the artifact background in the measurement (b) around the leaf originates from the limited number of sensor positions.