Three-dimensional photoacoustic tomography of small animal brain with a curved array transducer

We present the application of an optimized curved array photoacoustic tomographic imaging system, which can provide rapid, high-resolution photoacoustic imaging of small animal brains. The system can produce a B-mode, 90-degree field-of-view image at sub-200 μm resolution at a frame rate of ~1 frame/second when a 10-Hz pulse repetition rate laser is employed. By rotating samples, a complete 360-degree scan can be achieved within 15 seconds. In previous work, two-dimensional ex vivo mouse brain cortex imaging has been reported. In the current work, we report three-dimensional small animal brain imaging obtained with the curved array system. The results are presented as a series of two-dimensional cross-sectional images. Besides structural imaging, the blood oxygen saturation of the animal brain cortex is also measured in vivo. In addition, the system can measure the time-resolved relative changes in blood oxygen saturation level in the small animal brain cortex. Finally, ultrasonic gel coupling, instead of the previously adopted water coupling, is conveniently used in near-real-time 2D imaging

Real-time monitoring of small animal cortical hemodynamics by photoacoustic tomography

For the first time, the hemodynamics within the entire cerebral cortex of a mouse were studied by using photoacoustic tomography (PAT) non-invasively and in real time. The PAT system, based on a 512-element full-ring array with cylindrical focusing, received the PA signal primarily from a slice of about 2 mm thickness. This system can provide not only high resolution brain vasculature images but also hemodynamic functional images. We recorded the wash-in process of a photoacoustic contrast agent in a mouse brain in real time. Our results demonstrated that PAT is a powerful imaging modality to study real-time small animal neurofunctional activities that cause changes in hemodynamics

Photoacoustic tomography of small animal brain with a curved array transducer

This is the published version. Copyright © 2009 Society of Photo-Optical Instrumentation EngineersWe present the application of a curved array photoacoustic tomographic imaging system that can provide rapid, high-resolution photoacoustic imaging of small animal brains. The system is optimized to produce a B-mode, 90-deg field-of-view image at sub-200-μm resolution at a frame rate of ∼1frame∕second when a 10-Hz pulse repetition rate laser is employed. By rotating samples, a complete 360-deg scan can be achieved within 15s. In previous work, two-dimensional (2-D) ex vivo mouse brain cortex imaging has been reported. We report three-dimensional (3-D) small animal brain imaging obtained with the curved array system. The results are presented as a series of 2-D cross-sectional images. Besides structural imaging, the blood oxygen saturation of the animal brain cortex is also measured in vivo. In addition, the system can measure the time-resolved relative changes in blood oxygen saturation level in the small animal brain cortex. Last, ultrasonic gel coupling, instead of the previously adopted water coupling, is conveniently used in near-real-time 2-D imaging

Photoacoustic tomography of small animal brain with a curved array transducer

This is the published version. Copyright © 2009 Society of Photo-Optical Instrumentation EngineersWe present the application of a curved array photoacoustic tomographic imaging system that can provide rapid, high-resolution photoacoustic imaging of small animal brains. The system is optimized to produce a B-mode, 90-deg field-of-view image at sub-200-μm resolution at a frame rate of ∼1frame∕second when a 10-Hz pulse repetition rate laser is employed. By rotating samples, a complete 360-deg scan can be achieved within 15s. In previous work, two-dimensional (2-D) ex vivo mouse brain cortex imaging has been reported. We report three-dimensional (3-D) small animal brain imaging obtained with the curved array system. The results are presented as a series of 2-D cross-sectional images. Besides structural imaging, the blood oxygen saturation of the animal brain cortex is also measured in vivo. In addition, the system can measure the time-resolved relative changes in blood oxygen saturation level in the small animal brain cortex. Last, ultrasonic gel coupling, instead of the previously adopted water coupling, is conveniently used in near-real-time 2-D imaging

A fast 512-element ring array photoacoustic imaging system for small animals

A 512-element photoacoustic tomography system for small animal imaging using a ring ultrasound array has been developed. The system features a 5 MHz piezocomposite transducer array formed into a complete circular aperture. Custom receiver electronics consisting of dedicated preamplifiers, 8:1 multiplexed post-amplifiers, and a 64-channel data acquisition module provide full tomographic imaging at up to 8 frames/second. We present details of the system design along with characterization results of the resolution, imaging volume, and sensitivity. Small animal imaging performance is demonstrated through images of mice brain vasculature at different depths and real-time spectroscopic scans. This system enables real-time tomographic imaging for functional photoacoustic studies for the first time

A real-time photoacoustic tomography system for small animals

A real-time 512-element photoacoustic tomography system for small animal imaging using a ring ultrasound array has been developed. The system, based upon a 5 MHz transducer array formed along a 50 mm circular aperture, achieves sub-200 micron lateral resolution over a 2 cm disk-shaped region. Corresponding elevation resolutions of 0.6 to 2.5 mm over the central volume enable depth-resolved 3D tomographic imaging with linear translation. Using 8:1 electronic multiplexing, imaging at up to 8 frame/sec is demonstrated for both dynamic phantoms and in vivo mouse and brain samples. The real-time, full 2D tomographic capability of the system paves the way for functional photoacoustic tomographic imaging studies in small animals with sub-second time frame

Experimental investigation of target and transducer effects on quantitative image reconstruction in photoacoustic tomography

In principle, absorbed energy profiles can be exactly reconstructed from photoacoustic measurements on a closed surface. Clinical applications, however, involve compromises due to transducer focus, frequency characteristics, and incomplete measurement apertures. These tradeoffs introduce artifacts and errors in reconstructed absorption distributions that affect quantitative interpretations as well as qualitative contrast between features. The quantitative effects of target geometry, limited measurement surfaces, and bandpass transducer frequency response have been investigated using a ring transducer system designed for small animal imaging. The directionality of photoacoustic radiation is shown to increase with target aspect ratio, producing proportionate overestimates of absorption values for two-dimension apertures less than approximately 150 degrees. For all target geometries and orientations, mean absorption values approach the full view values for hemicircular measurement surfaces although the true spatial uniformity is recovered only with the complete surface. The bandpass transducer frequency spectrum produces a peaked amplitude response biased toward spatial features ranging from 1 to 8 times the system resolution. We discuss the implications of these results for design of clinical systems

Small animal imaging using a curved array photoacoustic tomography system

We report experimental imaging results with mice using an array-based photoacoustic tomography system designed for small animal imaging. The system features a 128-element curved transducer array with stage rotation to enable complete two-dimensional tomographic imaging in less than 15 seconds. High fidelity imaging of ex vivo mouse brain vasculature was achieved with resolution of vessels less than 200 microns in diameter in the cortex as well as the cerebellum. Images obtained using varying measurement surface angular spans clearly illustrate the impact on feature definition with orientation. The high sensitivity of the system was demonstrated by images of the brain vasculature with an overlying turbid medium (μ_a = 0.03 cm^(-1) and μ_s' ~ 7 cm^(-1) at 780 nm) of over 2 cm depth. In phantom experiments, high-quality images of blood tubing in a turbid medium were achieved at depths greater than 3 cm for incident fluences of less than 15 mJ/cm^2. These results illustrate the suitability for near real-time small animal imaging of deep tissue with high definition

Curved array photoacoustic tomographic system for small animal imaging

We present systematic characterization of a photoacoustic imaging system optimized for rapid, high-resolution tomographic imaging of small animals. The system is based on a 128-element ultrasonic transducer array with a 5-MHz center frequency and 80% bandwidth shaped to a quarter circle of 25mm radius. A 16-channel data-acquisition module and dedicated channel detection electronics enable capture of a 90-deg field-of-view image in less than 1s and a complete 360-deg scan using sample rotation within 15s. Measurements on cylindrical phantom targets demonstrate a resolution of better than 200μm and high-sensitivity detection of 580-μm blood tubing to depths greater than 3cm in a turbid medium with reduced scattering coefficient μ′s =7.8cm^(−1). The system is used to systematically investigate the effects of target size, orientation, and geometry on tomographic imaging. As a demonstration of these effects and the system imaging capabilities, we present tomographic photoacoustic images of the brain vasculature of an ex vivo mouse with varying measurement aperture. For the first time, according to our knowledge, resolution of sub-200-μm vessels with an overlying turbid medium of greater than 2cm depth is demonstrated using only intrinsic biological contrast