Frequency domain diffuse optical spectroscopy device and optical detector calibration method
Inventors
Stillwell, Roy A. • Kitsmiller, Vincent James • O'Sullivan, Thomas D.
Assignees
Publication Number
US-12004843-B2
Publication Date
2024-06-11
Expiration Date
2039-04-05
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Abstract
A frequency domain diffuse optical spectroscopy (FD-DOS) device and calibration method. The FD-DOS device includes a radio frequency signal generator, a driver, a light source, a silicon photomultiplier, an analog to digital conversion circuit, and an electronic processing circuit. The light source is configured to generate modulated light at a plurality of different wavelengths and modulation frequencies. The silicon photomultiplier is configured to generate analog detection signals indicative of detected optical signals. The analog to digital conversion circuit is configured to generate digital sample values from the analog detection signals. The electronic processing circuit is configured to determine absorption values and scattering values based on the digital sample values. The electronic processing circuit is also configured to determine concentration values based on the absorption values and the scattering values. The electronic processing circuit is further configured to determine an image stream based on the concentration values.
Core Innovation
The invention provides a frequency domain diffuse optical spectroscopy (FD-DOS) device that incorporates a silicon photomultiplier (SiPM) as the optical detector. The FD-DOS device comprises a handheld housing with a light source that generates modulated light at multiple wavelengths and modulation frequencies, directed at a biological sample. The SiPM, which operates at lower voltage bias with a significantly smaller high voltage module footprint, detects the amplitude and phase of radio frequency modulation components resulting from the interaction of modulated light with the sample.
An analog to digital conversion circuit then converts the analog signals from the SiPM into digital sample values, which are processed by an electronic processing circuit. The processing circuit determines absorption and scattering values using algorithms such as a Fourier transform or Goertzel algorithm, and calculates concentration values (e.g., chromophore concentrations) based on the absorption and scattering data. The circuit also generates an image stream, capable of real-time output, based on the calculated concentrations. This system aims to maintain compactness and portability while providing reliable optical property measurements.
Additionally, the disclosure introduces a method for calibrating optical detectors, especially addressing the non-linear amplitude response of SiPMs, which traditional FD-DOS calibration approaches cannot handle. The calibration method involves measuring known samples to generate a measured power response, calculating an inverse response, and adjusting measured frequency responses to account for nonlinearities. Correction factors are subsequently determined for accurate frequency response, enabling more flexible and dynamic FD-DOS measurements with SiPM and other non-linear detectors.
Claims Coverage
There is one independent claim in this patent, which covers the main inventive features of the device and its integrated system.
Handheld frequency domain diffuse optical spectroscopy device with silicon photomultiplier
The device comprises: - A housing sized to be handheld, with the light source at a first end; - A radio frequency signal generator and a driver coupled to it; - A light source coupled to the driver and configured to generate modulated light at multiple wavelengths and modulation frequencies, emitting modulated light onto a sample; - A silicon photomultiplier to generate analog detection signals indicating amplitude and phase of the detected optical signals from the sample; - An analog to digital conversion circuit (ADC) coupled to both the radio frequency signal generator and the silicon photomultiplier, to generate digital sample values from the analog detection signals; - An electronic processing circuit (EPC), receiving digital sample values from the ADC, configured to: - Determine absorption values and scattering values from digital sample values, - Determine concentration values based on the absorption and scattering values, - Determine an image stream based on the concentration values.
The claims cover a portable FD-DOS device incorporating a silicon photomultiplier, detailed signal pathway from modulated light emission to digital imaging, and onboard computation of absorption, scattering, concentration, and real-time imaging using the digital signals.
Stated Advantages
SiPMs provide equal or better performance than APDs or PMTs in FD-DOS applications while operating at a much lower voltage bias and allowing for high-voltage modules with extremely small footprints, enabling compact and portable system designs.
SiPMs have about 10 to 30 decibels greater signal to noise ratios than comparably sized APDs and can detect significantly lower light levels, enabling increased depth penetration and extended source-detector separations.
The calibration method disclosed allows use of non-linear optical detectors, such as SiPMs, in FD-DOS systems by enabling accurate frequency response calibration, which increases dynamic range and measurement flexibility.
The overall system enables quantitative measurement of tissue chromophore concentrations and real-time imaging in a device small enough to be handheld.
Documented Applications
Non-invasive optical imaging of biological tissue using FD-DOS, for characterization of tissue optical properties.
Monitoring chemotherapy treatments of breast cancer, distinguishing benign and malignant lesions, and quantifying breast density for breast cancer risk assessment.
Optical mammography for breast imaging applications.
Brain imaging using frequency domain diffuse optical spectroscopy.
Monitoring response to neoadjuvant chemotherapy in breast oncology.
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