Photoacoustic Microscopy Using Sinusoidal Modulation for Deep Tissue Imaging
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Solution Overview
Problem
Conventional photoacoustic microscopy systems face limitations in achieving high spatial resolution and deep tissue imaging due to the dominance of single-photon absorption, which buries nonlinear multi-photon photoacoustic signals in noise and lacks spectral sensitivity and selectivity, and the use of high pulse energy causes photo-toxicity and limited penetration depth.
Innovation Solution
The system employs a pulsed light source with pure sinusoidal modulation and a focusing device to generate nonlinear photoacoustic waves, using endogenous or exogenous contrast agents, and an ultrasonic transducer module for frequency domain analysis to extract multi-harmonics of the fundamental frequency, enabling high spectrum sensitivity and frequency selectivity for imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high pulse energy is used to induce multi-photon photoacoustic effect, then nonlinear photoacoustic signals can be generated, but photo-toxicity occurs and penetration depth is limited
Solution Approach 1:
The patent employs periodic sinusoidal modulation of the laser beam envelope at a fundamental frequency, creating time-varying excitation that enables multi-harmonics generation through nonlinearity. This periodic action allows the system to induce multi-photon photoacoustic effects using lower peak powers compared to conventional pulsed methods, thereby reducing photo-toxicity while maintaining signal generation capability.
Solution Approach 2:
The system changes the temporal parameter of light delivery from conventional pulsed excitation to continuous sinusoidal modulation. By transforming the excitation waveform and operating in the frequency domain to detect multi-harmonics, the system achieves multi-photon photoacoustic imaging at reduced peak power levels, extending penetration depth and reducing photodamage.
2Device complexity
If conventional single-photon photoacoustic detection is used, then detection is simplified, but nonlinear multi-photon signals are buried in noise and spectral sensitivity is lost
Solution Approach 1:
The patent applies the concept of vibration to acoustic wave detection by using sinusoidal modulation to generate photoacoustic waves at a fundamental frequency and its multi-harmonics. The ultrasonic transducer detects these frequency-specific acoustic vibrations, allowing frequency-domain filtering that separates nonlinear signals from noise, thereby improving signal-to-noise ratio while maintaining practical detection implementation.
Solution Approach 2:
The system introduces frequency domain analysis as an intermediary processing step between signal generation and detection. By transforming the detection approach to analyze multi-harmonics of the fundamental frequency, the system extracts nonlinear photoacoustic signals that would otherwise be buried in noise, achieving spectral sensitivity without excessive system complexity.
3Manufacturing precision
If ultrasonic frequency is increased to improve lateral resolution, then spatial resolution is enhanced, but penetration depth decreases due to acoustic attenuation
Solution Approach 1:
The patent transitions from spatial domain imaging to frequency domain imaging by detecting multi-harmonics of the modulated laser beam. This dimensional change in the detection space allows the system to achieve high lateral resolution through optical focusing while maintaining deep penetration depth by using lower frequency ultrasonic detection, effectively decoupling the resolution-depth tradeoff.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves a spatial resolution of approximately 1 μm and a maximum penetration depth of 1 mm with improved signal-to-noise ratio, overcoming the limitations of conventional systems by isolating nonlinear signals and enhancing imaging depth and resolution.
Implementation Method 1
a pulsed light source configured to emit at least one laser beam, at least one light modulation module configured to amplitude modulate the beam envelop of the laser beam for pure sinusoidal modulation... so as to be excited to generate nonlinear photoacoustic waves in the sample
Implementation Method 2
multi-photon photoacoustic microscopy (MPPAM), a hybrid technique combining multi-photon absorption and PAM... the high light intensity in the center of the focal area induces nonlinearity
Implementation Method 3
An ultrasonic transducer module is used to receive, transform nonlinear photoacoustic waves into electrical signals and to detect frequency signals within the electrical signals
Data Source
AI summary
The present application discloses optical microscopy systems and related method that use modulation techniques and contrast agents to enable the systems to detect nonlinear photoacoustic signals with high spectrum sensitivity and frequency selectivity for imaging. A laser beam is amplitude modulated for pure sinusoidal modulation using either the loss modulation technique or the single light amplitude modulation technique. The sample used in the invention is an endogenous contrast agent by itself or is treated by at least one exogenous contrast agent to produce or enhance photoacoustic effect induced by multi-photon absorption. The modulated laser beam is focused via a focusing device onto a sample which absorbs multiple photons simultaneously and generates ultrasonic (acoustic) waves via nonlinear photoacoustic effect. The ultrasonic waves are received and transformed into electrical signals and the frequency signals within the electrical signals are detected and recorded to create images.