Photoacoustic Tomography with a Ring Ultrasound Transducer: A Comparison of Different Illumination Strategies

Abstract

Photoacoustic (PA) imaging is a methodology that uses the absorption of short laser pulses by endogenous or exogenous chromophores within human tissue, and the subsequent generation of acoustic waves acquired by an ultrasound (US) transducer, to form an image that can provide functional and molecular information. Amongst the various types of PA imaging, PA tomography (PAT) has been proposed for imaging pathologies such as breast cancer. However, the main challenge for PAT imaging is the deliverance of sufficient light energy horizontally through an imaging cross-section as well as vertically. In this study, three different illumination methods are compared for a full-ring ultrasound (US) PAT system. The three distinct illumination setups are full-ring, diffused-beam, and point source illumination. The full-ring system utilizes a cone mirror and parabolic reflector to create the ringed-shaped beam for PAT, while the diffuse scheme uses a light diffuser to expand the beam, which illuminates tissue-mimicking phantoms. The results indicate that the full-ring illumination is capable of providing a more uniform fluence irrespective of the vertical depth of the imaged cross-section, while the point source and diffused illumination methods provide a higher fluence at regions closer to the point of entry, which diminishes with depth. In addition, a set of experiments was conducted to determine the optimum position of ring-illumination with respect to the position of the acoustic detectors to achieve the highest signal-to-noise ratio.

Optimizing Irradiation Geometry in LED-Based Photoacoustic Imaging with 3D Printed Flexible and Modular Light Delivery System

“…So, utilizing an LED-based system (or a source with similar divergence) for either deep tissue lesions or superficial lesions would be less cumbersome in terms of source alignment by offering the freedom to choose a wide range of irradiation angles without losing CNR in the images. In contrast, spatially coherent sources would require stringent alignment strategies for illuminating lesions at various depths [57,58]. The modular light delivery system and results presented in this study can serve as a priori knowledge for future LED-based PA system designs and aid in further catapulting its utility in both preclinical and clinical applications.…”

Dual-Wavelength Photoacoustic Computed Tomography with Piezoelectric Ring-Array Transducer for Imaging of Indocyanine Green Liposomes Aggregation in Tumors

“…To date, a variety of piezoelectric transducers with different geometries have been used in PACT systems, especially ring-array transducers [7,14,15,18,19]. Ring-array transducers can achieve high spatial resolution and rich optical contrast in deep tissues, due to their wide field of view (FOV) [14,20]. Thus, it is essential to develop a ring-array-based PACT system for biomedical imaging (e.g., molecular imaging) [6,21].…”

Efficacy of High Temporal Frequency Photoacoustic Guidance of Laser Ablation Procedures

“…16,18,19 Superior features, including the ability to detect tissue’s molecular composition, 20 small molecules and nano-sized contrast agents, 21 as well as providing high-contrast images of external objects such as stents, 22 needles, 23 and catheters, 8,11,13,24 has enabled PA imaging to be used in preclinical and clinical applications. 8,11,14,15,25–29 These unique features of PA imaging were used for accurate ablation catheter tracking and real-time temperature monitoring. Our previous studies 8,11 have validated the capability of PA imaging for ablation catheter positioning and temperature monitoring during ablation procedures.…”