We describe the ongoing development and performance of a high-pulse-energy wavelength-cycling laser system for three-dimensional optoacoustic tomography of the breast. Joule-level energies are desired for achieving the required penetration depths while maintaining safe fluence levels. Wavelength cycling provides a pulse sequence which repeatedly alternates between two wavelengths (approximately 756 and 797 nm) that provide differential imaging. This improves co-registration of captured differential images and quantification of blood oxygen saturation. New design features have been developed for and incorporated into a clinical prototype laser system, to improve efficacy and ease of use in the clinic. We describe the benefits of these features for operation with a clinical pilot optoacoustic / ultrasound dual-modality three-dimensional imaging system.
Globally, cancer is a major health issue as advances in modern medicine continue to extend the human life span. Breast cancer ranks second as a cause of cancer death in women in the United States. Photoacoustic (PA) imaging (PAI) provides high molecular contrast at greater depths in tissue without the use of ionizing radiation. In this work, we describe the development of a PA tomography (PAT) system and a rapid wavelength-cycling Alexandrite laser designed for clinical PAI applications. The laser produces 450 mJ/pulse at 25 Hz to illuminate the entire breast, which eliminates the need to scan the laser source. Wavelength cycling provides a pulse sequence in which the output wavelength repeatedly alternates between 755 nm and 797 nm rapidly within milliseconds. We present imaging results of breast phantoms with inclusions of different sizes at varying depths, obtained with this laser source, a 5-MHz 128-element transducer and a 128-channel Verasonics system. Results include PA images and 3D reconstruction of the breast phantom at 755 and 797 nm, delineating the inclusions that mimic tumors in the breast.
We describe the ongoing development of laser systems for advanced photoacoustic imaging (PAI). We discuss the characteristics of these laser systems and their particular benefits for soft tissue imaging and next-generation breast cancer diagnostics. We provide an overview of laser performance and compare this with other laser systems that have been used for early-stage development of PAI. These advanced systems feature higher pulse energy output at clinically relevant repetition rates, as well as a novel wavelength-cycling output pulse format. Wavelength cycling provides pulse sequences for which the output repeatedly alternates between two wavelengths that provide differential imaging. This capability improves co-registration of captured differential images. We present imaging results of phantoms obtained with a commercial ultrasound detector system and a wavelength-cycling laser source providing ~500 mJ/pulse at 755 and 797 nm, operating at 25 Hz. The results include photoacoustic images and corresponding pulse-echo data from a tissue mimicking phantom containing inclusions, simulating tumors in the breast. We discuss the application of these systems to the contrast-enhanced detection of various tissue types and tumors.
We present work on a laser system operating in the near- and mid-IR spectral regions, having output characteristics
designed to be optimal for cutting various tissue types. We provide a brief overview of laser-tissue interactions and the
importance of controlling certain properties of the light beam. We describe the principle of operation of the laser system,
which is generally based on a wavelength-tunable alexandrite laser oscillator/amplifier, and multiple Raman conversion
stages. This configuration provides robust access to the mid-IR spectral region at wavelengths, pulse energies, pulse
durations, and repetition rates that are attractive for neurosurgical applications. We summarize results for ultra-precise
selective cutting of nerve sheaths and retinas with little collateral damage; this has applications in procedures such as
optic-nerve-sheath fenestration and possible spinal repair. We also report results for cutting cornea, and dermal tissues.
An intense pulsed capillary discharge source operating at 13.5 nm and 11.4 nm, suitable for use in conjunction with Mo:Si or Mo:Be coated optics, has produced an average power of approximately 1.4W within a 0.3 nm emission bandwidth from the end of the capillary when operated at a repetition rate of 100 Hz. The source is comprised of a small capillary discharge tube filled with xenon gas at low pressure to which electrodes are attached at each end. When a voltage is applied across the tube, an electrical current is generated for short periods within the capillary that produces highly ionized xenon ions radiating in the EUV. Issues associated with plasma bore erosion are currently being addressed from the standpoint of developing such a source for operation at repetition rates of greater than 1 kHz.