Raman Laser Tuner for Deep Tissue Photoacoustic Imaging
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Solution Overview
Problem
Vibrational photoacoustic tomography (VPAT) has not been effectively demonstrated due to the unavailability of a laser source with sufficient energy for diffused photon excitation of harmonic vibrations, limiting the imaging depth and contrast in tissue imaging.
Innovation Solution
A Raman-based laser tuner is used to generate laser pulses with energy greater than 100 mJ, which selectively excites overtone transitions in tissue molecules, and the resulting acoustic signals are converted into images using an ultrasonic transducer and processor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If conventional laser sources are used for vibrational photoacoustic tomography, then the system can operate, but the imaging depth is limited due to insufficient pulse energy for diffused photon excitation
Solution Approach 1:
The patent employs a Raman-based laser tuner that dynamically adjusts the laser wavelength to match specific vibrational transitions of target molecules. This dynamic tuning capability allows the system to optimize excitation efficiency at different depths by selecting wavelengths that resonate with molecular vibrations, thereby extending imaging depth beyond conventional fixed-wavelength systems.
Solution Approach 2:
The invention changes the fundamental parameter of laser pulse energy from conventional levels to greater than 100 mJ per pulse. This parameter change enables diffused photon excitation throughout deeper tissue layers, overcoming the limitation of ballistic photon-only excitation and achieving effective vibrational photoacoustic tomography at clinically relevant depths.
2Length of stationary object
If high energy laser pulses are used to excite deep tissue, then imaging depth improves, but tissue damage risk increases
Solution Approach 1:
The system uses periodic pulsed laser excitation with carefully controlled duty cycles. The pulsed nature allows tissue to cool between pulses, preventing cumulative thermal damage while maintaining sufficient average power for deep imaging. Each pulse delivers high peak energy for deep penetration, followed by a pause that allows thermal dissipation.
Solution Approach 2:
The invention uses Raman scattering as an intermediary mechanism. Instead of directly absorbing high energy photons that could cause damage, molecules scatter photons inelastically, converting a small portion of photon energy into vibrational energy. This intermediary process allows high pulse energy delivery while limiting direct thermal damage to tissue, as the energy conversion is efficient and localized to specific molecular bonds.
3Length of stationary object
If Raman-based laser tuner is used to achieve sufficient pulse energy, then imaging depth and contrast improve, but device complexity increases
Solution Approach 1:
The Raman-based laser tuner serves multiple functions: it generates high pulse energy (>100 mJ), provides wavelength tunability across different vibrational transitions, and enables selective excitation of various molecular bonds. This multi-functionality consolidates what would otherwise require separate laser systems into a single versatile platform, managing complexity through functional integration.
Solution Approach 2:
The Raman crystal within the laser tuner utilizes the pump laser's own output to generate the desired wavelength through stimulated Raman scattering. The system essentially uses itself to convert the pump wavelength to the target wavelength, eliminating the need for external frequency conversion equipment and reducing overall system complexity.
Data Source
AI summary
A method of noninvasively imaging tissue within a body includes irradiating the tissue using an imaging laser including a Raman-based laser tuner, the radiation including a plurality of laser pulses, each having energy greater than 100 mJ; receiving an acoustic signal generated by vibrational energy in the tissue, wherein the vibrational energy is a result of selective overtone excitation of molecules in the tissue by the radiation; and automatically converting the acoustic signal to an image representative of the tissue using a processor. An imaging system includes an imaging laser configured to irradiate tissue with a plurality of laser pulses using a Raman-based laser tuner. An ultrasonic transducer receives an acoustic signal generated by vibrational energy in the tissue due to overtone excitation by the radiation. A processor is configured to automatically produce an image representative of the tissue using the received acoustic signal.