We present the development of a photoacoustic tomography (PAT) imaging system with the demonstrated capability of obtaining high-throughput scans at a sustained rate of under 1 minute per animal using integrated robotics to assist in 3D PAT collection. This is a considerable achievement as there is currently no existing commercial or research PAT whole-body imaging system capable of high-throughput applications (15-20 animals per hour). High-throughput experimentation is imperative in the development, characterization, and use of rodent models of human diseases as it increases the number of animals that can be evaluated within a single experiment and may reduce the time under anesthesia for each animal, thereby improving the stability, duration, and confidence of longitudinal studies The developed system features coordinated automation for robotic animal manipulation, anesthesia distribution, temperature regulation, water management, laser excitation, and photoacoustic detection. Furthermore, as shown in validation studies using phantoms and live murine models, the prototype imaging platform demonstrates high-throughput performance while retaining high sensitivity and high resolution.
We developed an indocyanine green J-aggregated (ICG-JA) nanoparticle platform for near infrared photoacoustic imaging (NIR-PAI). This platform achieves a facile synthesis, size tunability and direct functionalization. In an in vitro setting, we compared the PA signal of ICG-JA (at its optical absorption peak of 895 nm) to be two times that of whole blood. We then imaged HeLa cells with ICG-JA functionalized with RGD-peptide using NIR-PAI. Using a multi-wavelength NIR-PAI system, TriTom™, volumetric whole-body images were acquired of mice administed with RGD-peptide functionalized ICG-JA. Results indicated enhanced visualization of the liver, spleen and thoracic arteries with a contrast-to-noise-ratio of 2.42.
SignificanceTo effectively study preclinical animal models, medical imaging technology must be developed with a high enough resolution and sensitivity to perform anatomical, functional, and molecular assessments. Photoacoustic (PA) tomography provides high resolution and specificity, and fluorescence (FL) molecular tomography provides high sensitivity; the combination of these imaging modes will enable a wide range of research applications to be studied in small animals.AimWe introduce and characterize a dual-modality PA and FL imaging platform using in vivo and phantom experiments.ApproachThe imaging platform’s detection limits were characterized through phantom studies that determined the PA spatial resolution, PA sensitivity, optical spatial resolution, and FL sensitivity.ResultsThe system characterization yielded a PA spatial resolution of 173 ± 17 μm in the transverse plane and 640 ± 120 μm in the longitudinal axis, a PA sensitivity detection limit not less than that of a sample with absorption coefficient μa = 0.258 cm − 1, an optical spatial resolution of 70 μm in the vertical axis and 112 μm in the horizontal axis, and a FL sensitivity detection limit not <0.9 μM concentration of IR-800. The scanned animals displayed in three-dimensional renders showed high-resolution anatomical detail of organs.ConclusionsThe combined PA and FL imaging system has been characterized and has demonstrated its ability to image mice in vivo, proving its suitability for biomedical imaging research applications.
Vasoactivity is an important physiological indicator of cardiovascular health which is frequently measured using ex vivo vessels to determine functional mechanisms and evaluate pharmacological responses. Currently, there are no imaging methods available to assess vasoactivity in multiple vascular beds of living animals noninvasively. In this work, we have developed methods to use photoacoustic tomography to assess vasoactivity in vivo in systemic vasculature of living animals. A spherical-view photoacoustic tomography system was used to monitor acute vasodilation in the whole abdomen of a pregnant mouse in response to injection of G-1. After 3D image reconstruction, the diameter of the iliac artery and photoacoustic signal intensity of a placenta over time was measured. The artery and placenta had differential response to the vasodilator G-1. We validated the observed vasodilation of artery by monitoring the change in cross-sectional diameter of an individual artery using standard B-mode ultrasound imaging.
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