The versatility and real-time imaging capability of commercial linear array transducers make them widely used in clinical ultrasound and photoacoustic imaging. However, they often suffer from limited detection view. For instance, acoustic waves traveling at a grazing angle to the transducer surface are difficult to detect. In this letter, we propose a simple and easy approach to ameliorate this problem by using a 45-deg acoustic reflector. The reflector forms a virtual array that is perpendicular to the physical array, thereby doubling the detection coverage. The improvement in image quality in photoacoustic tomography was demonstrated through a hair phantom, a leaf skeleton phantom, and an ex vivo mouse ear experiment.
Photoacoustic and thermoacoustic phantom images obtained with a multi-channel breast scanner designed for breast
cancer screening are presented here. A tunable laser system (OPOTEK Vibrant 355 I, Calsbad,CA) with a pulse duration
of 5 ns was used for photoacoustic irradiation, and a 3.0 GHz microwave source with a pulse width of 0.3-1 μs was used
for thermoacoustic tomography. Multiple (>=16) 2.25 MHz
single-element unfocused ultrasonic transducers at different
depths were scanned simultaneously for a full 360° to obtain a full data set for three-dimensional (3D) tomography.
Negative acoustic lenses were attached to these unfocused transducers to increase their acceptance angles. An ultrasound
receiving system with 64 parallel receiving channels (Verasonics Inc. Redmond, WA) was used for data acquisition. A
filtered backprojection algorithm was used to reconstruct
two-dimensional (2D) and 3D images. Different phantoms
were imaged to evaluate the performance of the scanner. A lateral resolution of less than 1 mm and an elevational
resolution of less than 5 mm were achieved. The phantom studies demonstrate that this scanner can potentially provide
high-resolution, dual-modality, three-dimensional images and can potentially be used for human breast cancer screening.