Characterization of a Fiber Bundle-Based Real-Time Ultrasound/Photoacoustic Imaging System and Its In Vivo Functional Imaging Applications

Abstract

Photoacoustic (PA) imaging is an attractive technology for imaging biological tissues because it can capture both functional and structural information with satisfactory spatial resolution. Current commercially available PA imaging systems are limited by their bulky size or inflexible user interface. We present a new handheld real-time ultrasound/photoacoustic imaging system (HARP) consisting of a detachable, high-numerical-aperture (NA) fiber bundle-based illumination system integrated with an array-based ultrasound (US) transducer and a data acquisition platform. In this system, different PA probes can be used for different imaging applications by switching the transducers and the corresponding jackets to combine the fiber pads and transducer into a single probe. The intuitive user interface is a completely programmable MATLAB-based platform. In vitro phantom experiments were conducted to test the imaging performance of the developed PA system. Furthermore, we demonstrated (1) in vivo brain vasculature imaging, (2) in vivo imaging of real-time stimulus-evoked cortical hemodynamic changes during forepaw electrical stimulation, and (3) in vivo imaging of real-time cerebral pharmacokinetics in rats using the developed PA system. The overall purpose of this design concept for a customizable US/PA imaging system is to help overcome the diverse challenges faced by medical researchers performing both preclinical and clinical PA studies.

In Vivo Assessment of Hypoxia Levels in Pancreatic Tumors Using a Dual-Modality Ultrasound/Photoacoustic Imaging System

“…Each fiber had a core diameter of 47 µm (50 µm with cladding) and an NA of 0.66. The fiber efficiency was estimated to be approximately 60-70% based on the measurements of the input and output energy at the ends of the fiber bundle-based illumination system [9]. The axial resolution was calculated as the full width at half maximum of each Gaussian function and was previously measured to be 124 ± 31 µm for our PA imaging system [4].…”

“…A customized, precision 3D translation stage with motorized x-, y-, and z-axes was used to control the transducer to obtain A-scan, B-scan (i.e., two-dimensional; one axis is the lateral scanning distance, and the other axis is the imaging depth), and C-scan (i.e., three-dimensional) images [9]. Both the phantoms and probe were immersed in a water tank for in vitro imaging.…”

“…Tube phantoms containing blue or red ink to mimic oxygenated and deoxygenated blood were then placed in the Intralipid mixture for imaging. B-scan images of the tubes were obtained at the focal zone of the transducer (10 mm in depth from the transducer surface) using laser excitation at 750 nm (strong absorption for red ink) and 850 nm (strong absorption for blue ink) [9]. C-scan images composed of serial cross-sectional images of the tubes were also obtained at a scanning range of 6 mm with 0.05 mm step size.…”

“…Arterial blood SO 2 and heart rate were monitored throughout the experiment using the MouseOX Plus small animal vital signs monitoring system (Starr Life Sciences Corp., Oakmont, PA, USA). B-scan images were obtained at 750 nm due to the strong absorption by deoxyhemoglobin at that wavelength [9].…”

“…Previously, we developed a functional PA microscopy (fPAM) technique that can preclinically evaluate the changes in functional cerebral blood volume (CBV) and SO 2 in the rat cortex in studies of ischemic stroke [6][7][8]. The dual-wavelength PA technique uses hemoglobin as an intrinsic contrast agent and thus does not require an exogenous contrast agent for blood volume and SO 2 imaging [9]. Numerous fPAM applications, especially in preclinical studies, have been gradually developed in recent years [10][11][12][13].…”