Compact and low-cost handheld quasibright-field linear-array probe design in photoacoustic computed tomography

Illumination-adjustable photoacoustic and harmonic ultrasound for tracking magnetically driven microrobots

The development of microrobots for biomedical applications has enabled tasks such as targeted drug delivery, minimally invasive surgeries, and precise diagnostics. However, effective in vivo navigation and control remain challenging due to their small size and complex body environment. Photoacoustic (PA) and ultrasound (US) imaging techniques, which offer high contrast, high resolution, and deep tissue penetration, are integrated to enhance microrobot visualization and tracking. Traditional imaging systems have a narrow effective illumination area, suffer from severe reflection artifacts, and are affected by strong electromagnetic fields. To address this, we present an illumination-adjustable PA and harmonic US imaging system with a customized pushrod mechanism for real-time focus adjustment. Experiments demonstrate high-resolution imaging and accurate microrobot positioning, showcasing the potential for biomedical applications, especially in minimally invasive procedures.

Cylindrical lens configuration for optimizing light delivery in a curvilinear endocavity photoacoustic imaging system

Curvilinear endocavity ultrasound images capture a wide field of view with a miniature probe. In adapting photoacoustic imaging (PAI) to work with such ultrasound systems, light delivery is challenged by the trade-off between image quality and laser safety concerns. Here, we present two novel, to the best of our knowledge, designs based on cylindrical lenses that are optimized for transvaginal PAI B-scan imaging. Our simulation and experimental results demonstrate that, compared to conventional light delivery methods for PAI imaging, the proposed designs are safer for higher pulse energies and provide deeper imaging and a wider lateral field of view. The proposed designs could also improve the performance of endoscopic co-registered ultrasound/photoacoustic imaging in other clinical applications.

Video-Rate Dual-Modal Wide-Beam Harmonic Ultrasound and Photoacoustic Computed Tomography

Dual-modal ultrasound (US) and photoacoustic (PA) imaging has tremendous advantages in biomedical applications, such as pharmacokinetics, cancer screening, and imaging-guided therapy. Compared with ring-shaped arrays, a linear piezoelectric transducer array applies to more anatomical sites and has been widely used in US/PA imaging. However, the linear array may limit the imaging quality due to narrow bandwidth, partial detection view, or sparse spatial sampling. To meet clinic demand of high-quality US/PA imaging with the linear transducer, we develop dual-modal wide-beam harmonic ultrasound (WBHUS) and photoacoustic computed tomography at video rate. The harmonic US imaging employs pulse phase inversion to reduce clutters and improve spatial resolution. Wide-beam US transmission can shorten the scanning times by 267% and enables a 20-Hz imaging rate, which can minimize motion artifacts in in vivo imaging. The harmonic US imaging does not only provide accurate anatomical references for locating PA features but also reduces artifacts in PA images. The improved image quality allows us to acquire high-resolution anatomical structures in deep tissue without labeling. The fast-imaging speed enables visualizing interventional procedures and monitoring the pulsations of the thoracic aorta and radial artery in real-time. The video-rate dual-modal harmonic US and single-shot PA computed tomography use a clinical-grade linear-array transducer and thus can be readily implemented in clinical US imaging.

LightSpeed: A Compact, High-Speed Optical-Link-Based 3D Optoacoustic Imager

Wide-scale adoption of optoacoustic imaging in biology and medicine critically depends on availability of affordable scanners combining ease of operation with optimal imaging performance. Here we introduce LightSpeed: a low-cost real-time volumetric handheld optoacoustic imager based on a new compact software-defined ultrasound digital acquisition platform and a pulsed laser diode. It supports the simultaneous signal acquisition from up to 192 ultrasound channels and provides a hig-bandwidth direct optical link (2x 100G Ethernet) to the host-PC for ultra-high frame rate image acquisitions. We demonstrate use of the system for ultrafast (500Hz) 3D human angiography with a rapidly moving handheld probe. LightSpeed attained image quality comparable with a conventional optoacoustic imaging systems employing bulky acquisition electronics and a Q-switched pulsed laser. Our results thus pave the way towards a new generation of compact, affordable and high-performance optoacoustic scanners.

Multiangle Long-Axis Lateral Illumination Photoacoustic Imaging Using Linear Array Transducer

Photoacoustic imaging (PAI) combines optical contrast with ultrasound spatial resolution and can be obtained up to a depth of a few centimeters. Hand-held PAI systems using linear array usually operate in reflection mode using a dark-field illumination scheme, where the optical fiber output is attached to both sides of the elevation plane (short-axis) of the transducer. More recently, bright-field strategies where the optical illumination is coaxial with acoustic detection have been proposed to overcome some limitations of the standard dark-field approach. In this paper, a novel multiangle long-axis lateral illumination is proposed. Monte Carlo simulations were conducted to evaluate light delivery for three different illumination schemes: bright-field, standard dark-field, and long-axis lateral illumination. Long-axis lateral illumination showed remarkable improvement in light delivery for targets with a width smaller than the transducer lateral dimension. A prototype was developed to experimentally demonstrate the feasibility of the proposed approach. In this device, the fiber bundle terminal ends are attached to both sides of the transducer’s long-axis and the illumination angle of each fiber bundle can be independently controlled. The final PA image is obtained by the coherent sum of subframes acquired using different angles. The prototype was experimentally evaluated by taking images from a phantom, a mouse abdomen, forearm, and index finger of a volunteer. The system provided light delivery enhancement taking advantage of the geometry of the target, achieving sufficient signal-to-noise ratio at clinically relevant depths.

Targeted imaging of orthotopic prostate cancer by using clinical transformable photoacoustic molecular probe

BACKGROUND

To obtain high-yield histological samples by targeted prostate cancer (PCa) biopsy is the current trend compared with transrectal ultrasound (TRUS)-guided systematic histological biopsy, which is regarded as the gold standard for prostate cancer (PCa) diagnosis. In this paper, we present a targeted PCa imaging strategy using a real-time molecular photoacoustic imaging system integrated with a handheld US probe (PAI/US) and synthesized an integrin α_vβ₃ targeted probe based on ICG (cRGD-ICG).

METHODS

To prepare cRGD-ICG, ICG-NHS was linked to cRGD through carboxyl-co-reaction. In vitro PA imaging ability of cRGD-ICG was tested. Orthotopic PCa-bearing rats were used as animal models. After injected with either cRGD-ICG or non-targeted probe, rats were implemented with PA imaging to confirm the specific accumulation of cRGD-ICG at tumor region. Moreover, pathological frozen slices were made to observe distribution of the probe in prostate tissue ex vivo.

RESULTS

A small molecular PAI probe was synthesized and exhibited excellent targeted imaging ability in vitro. In vivo photoacoustic imaging was carried out after intravenous injection of cRGD-ICG in orthotopic PCa-bearing rats under the facilitation of the PAI/US system. Maximum molecular photoacoustic signals were observed in the tumor area in vivo after the probe injection, which showed 3.8-fold higher signal enhancement than that in the control group (P < 0.05). Significantly higher cRGD-ICG accumulation was observed under confocal microscopy in the tumor region than in normal prostate tissue.

CONCLUSIONS

All our results showed that the comprehensive strategy provided a high-yield and reliable method for PCa diagnosis and targeted prostate biopsy, with great clinical translation potential.