Photon Migration Instrument Research Articles

MAESTROS: A Multiwavelength Time-Domain NIRS System to Monitor Changes in Oxygenation and Oxidation State of Cytochrome-C-Oxidase.

We present a multiwavelength, multichannel, time-domain near-infrared spectroscopy system named MAESTROS. This instrument can measure absorption and scattering coefficients and can quantify the concentrations of oxy- and deoxy-haemoglobin ([HbO2], [HHb]), and oxidation state of cytochrome-c-oxidase ([oxCCO]). This system is composed of a supercontinuum laser source coupled with two acousto-optic tuneable filters. The light is collected by four photomultipliers tubes, connected to a router to redirect the signal to a single time-correlated single-photon counting card. The interface between the system and the tissue is based on optical fibres. This arrangement allows us to resolve up to 16 wavelengths, within the range of 650–900 nm, at a sampling rate compatible with the physiology (from 0.5 to 2 Hz). In this paper, we describe the system and assess its performance based on two specifically designed protocols for photon migration instruments, the basic instrument protocol and nEUROPt protocols, and on a well characterized liquid phantom based on Intralipid and water. Then, the ability to resolve [HbO2 ], [HHb], and [oxCCO] is demonstrated on a homogeneous liquid phantom, based on blood for [HbO2], [HHb], and yeast for [oxCCO]. In the future, the system could be used to monitor brain tissue physiology.

Multi-channel medical device for time domain functional near infrared spectroscopy based on wavelength space multiplexing

We have designed a compact dual wavelength (687 nm, 826 nm) multi-channel (16 sources, 8 detectors) medical device for muscle and brain imaging based on time domain functional near infrared spectroscopy. The system employs the wavelength space multiplexing approach to reduce wavelength cross-talk and increase signal-to-noise ratio. System performances have been tested on homogeneous and heterogeneous tissue phantoms following specifically designed protocols for photon migration instruments. Preliminary in vivo measurements have been performed to validate the instrument capability to monitor hemodynamic parameters changes in the arm muscle during arterial occlusion and in the adult head during a motor task experiment.

A new path integral approximation to photon propagation in turbid media

The path integral approach is applied to describe the propagation of photons in bounded homogeneous turbid media. Introducing a new controlled perturbative expansion centred on the diffusion limit, new analytic solutions for continuous wave reflectance and transmittance are determined, as relevant for non-invasive measurements of tissue optical properties based on continuous wave photon migration instruments. A comparative analysis with the diffusion approximation of radiative transfer theory is made to show that non-diffusive effects are enhanced in turbid regions with increasing absorption coefficients and decreasing reduced scattering coefficients as well as when the distance between interface boundaries increases. The relation between the transport equation (which is the starting point for the path integral approach) and multiple scattering theory is also discussed.

Design and testing of a miniature broadband frequency domain photon migration instrument

A board-level broadband frequency domain photon migration (mini-FDPM) instrument has been constructed to replace a conventional network-analyzer-based FDPM instrument. The mini-FDPM instrument with four wavelengths (681, 783, 823, and 850 nm), matches conventional FDPM instrument in performance (-88 dBm noise level, 100 dB dynamic range) and bandwidth (1 GHz), and recovers the same optical properties within about 6% in absorption and 4% in reduced scattering for liquid phantoms covering a wide range of relevant optical properties. Compared to the conventional FDPM instrument, the mini-FDPM instrument is more than 5x faster (approximately 200 ms per 401 modulation frequencies) and several orders of magnitude less in size and cost. Standard fiber-optic-based probes can be used with the mini-FDPM instrument, which increases applications in a number of clinically relevant measurement scenarios. By drastically reducing size and cost, FDPM miniaturization lowers barriers to access and will help promote FDPM in clinical research problems. The mini-FDPM instrument forms the core of a modular broadband diffuse optical spectroscopy instrument that can be used for a variety of clinical problems in imaging and functional monitoring (i.e., breast/skin cancer, brain activation, and exercise physiology).

Fully automated time domain spectrometer for the absorption and scattering characterization of diffusive media

We describe a system for absorption and scattering spectroscopy of diffusive media based on time-resolved reflectance and transmittance measurements. The system is operated with mode-locked lasers tunable in the 550-1050 nm spectral range and on a detection chain based on time-correlated single-photon counting. All measurement procedures such as laser tuning and optimization, signal conditioning, data acquisition, and analysis are completely automated, permitting spectral measurements over the whole range in a few minutes. The criticalities of the system are discussed together with the strategies to compensate them. The Medphot protocol devised for the characterization of photon migration instruments was applied to assess the system performances in terms of accuracy, linearity, noise, stability, and reproducibility. Finally, an example of application of the instrument to the spectroscopy of powders is presented.

Performance assessment of photon migration instruments: the MEDPHOT protocol

We propose a comprehensive protocol for the performance assessment of photon migration instruments. The protocol has been developed within the European Thematic Network MEDPHOT (optical methods for medical diagnosis and monitoring of diseases) and is based on five criteria: accuracy, linearity, noise, stability, and reproducibility. This protocol was applied to a total of 8 instruments with a set of 32 phantoms, covering a wide range of optical properties.

Low-cost frequency-domain photon migration instrument for tissue spectroscopy, oximetry, and imaging

We described a low-cost, frequency-domain photon migration spectroscopy instrument by using in-phase and quadrature demodula- tion technique in a 140-MHz homodyne system. A time constant of 1 ms was obtained. A frequency-division multiplexing technique was used for multiposition or multiwavelength applications, such as for tissue oxim- etry. By conducting several experiments on tissue/blood models, we show that the optical properties of tissue can be determined with this system by either using multiple source-detector separations at accuracy better than 8% or using single source-detector separation. The accuracy with the latter method can be improved to be 10% or better by choosing a proper calibration sample. A frequency-sweep system (30 to 700 MHz) was also implemented; the phase and amplitude measured on a tissue- like solution at 780 nm agreed to their theoretical values within 5% and 10% accuracy, respectively. © 1997 Society of Photo-Optical Instrumentation En- gineers. (S0091-3286(97)03005-5) Subject terms: photon migration; frequency-domain spectroscopy; in-phase and quadrature demodulation; frequency-division multiplex; absorption and scattering coefficients; noninvasive tissue oximetry.

Frequency-domain photon migration measurements of normal and malignant tissue optical properties in a human subject

A 1-GHz multifrequency, multiwavelength frequency-domain photon migration instrument is used to measure quantitatively the optical absorption (mu(a)) and effective optical scattering (mu(s) ?) of normal and malignant tissues in a human subject. Large ellipsoidal (~10-cm major axis, ~6-cm minor axes) subcutaneous malignant lesions were compared with adjacent normal sites in the abdomen and back. Absorption coefficients recorded at 674, 811, 849, and 956 nm were used to calculate tissue hemoglobin concentration (oxyhemoglobin, deoxyhemoglobin, and total), water concentration, hemoglobin oxygen saturation, and blood volume fraction in vivo. Our results show that the normal and the malignant tissues measured in the patient have clearly resolvable optical and physiological property differences that may be broadly useful in identifying and characterizing tumors.

Portable, high-bandwidth frequency-domain photon migration instrument for tissue spectroscopy

We describe a novel frequency-domain photon migration instrument employing direct diode laser modulation and avalanche photodiode detection, which is capable of noninvasively determinating the optical properties of biological tissues in near real time. An infinite medium diffusion model was used to extract absorption and transport scattering coefficients from 300-kHz to 800-MHz photon-density wave phase data. Optical properties measured in tissue-simulating solutions at 670 nm agreed to within 10% of those expected.