E. Sultan

Modeling and tissue parameter extraction challenges for free space broadband fNIR brain imaging systems

Fiber based functional near infra-red (fNIR) spectroscopy has been considered as a cost effective imaging modality. To achieve a better spatial resolution and greater accuracy in extraction of the optical parameters (i.e., μa and μs), broadband frequency modulated systems covering multi-octave frequencies of 10-1000MHz is considered. A helmet mounted broadband free space fNIR system is considered as significant improvement over bulky commercial fiber fNIR realizations that are inherently uncomfortable and dispersive for broadband operation. Accurate measurements of amplitude and phase of the frequency modulated NIR signals (670nm, 795nm, and 850nm) is reported here using free space optical transmitters and receivers realized in a small size and low cost modules. The tri-wavelength optical transmitter is based on vertical cavity semiconductor lasers (VCSEL), whereas the sensitive optical receiver is based on either PIN or APD photodiodes combined with transimpedance amplifiers. This paper also has considered brain phantoms to perform optical parameter extraction experiments using broadband modulated light for separations of up to 5cm. Analytical models for predicting forward (transmittance) and backward (reflectance) scattering of modulated photons in diffused media has been modeled using Diffusion Equation (DE). The robustness of the DE modeling and parameter extraction algorithm was studied by experimental verification of multi-layer diffused media phantoms. In particular, comparison between analytical and experimental models for narrow band and broadband has been performed to analyze the advantages of our broadband fNIR system.

Development challenges of brain functional monitoring using untethered broadband frequency modulated fNIR system

Spectroscopic measurements of brain matter is considered at near infra-red region, where optical properties are characterized by the refractive index n, absorption coefficient μa, modified scattering coefficient μs, and anisotropy factor g. Development of a free space optical system over broadband is optimized in terms of improved signal to noise ratio. The data collected by sensor is communicated to a remote processor using an ultra wideband communication system to provide wireless access and full mobility.

Accurate optical parameter extraction procedure for broadband near-infrared spectroscopy of brain matter

Abstract. Modeling behavior of broadband (30 to 1000 MHz) frequency modulated near-infrared (NIR) photons through a phantom is the basis for accurate extraction of optical absorption and scattering parameters of biological turbid media. Photon dynamics in a phantom are predicted using both analytical and numerical simulation and are related to the measured insertion loss (IL) and insertion phase (IP) for a given geometry based on phantom optical parameters. Accuracy of the extracted optical parameters using finite element method (FEM) simulation is compared to baseline analytical calculations from the diffusion equation (DE) for homogenous brain phantoms. NIR spectroscopy is performed using custom-designed, broadband, free-space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 780, and 820 nm. Differential detection between two optical Rx locations separated by 0.3 cm is employed to eliminate systemic artifacts associated with interfaces of the optical Tx and Rx with the phantoms. Optical parameter extraction is achieved for four solid phantom samples using the least-square-error method in MATLAB (for DE) and COMSOL (for FEM) simulation by fitting data to measured results over broadband and narrowband frequency modulation. Confidence in numerical modeling of the photonic behavior using FEM has been established here by comparing the transmission mode’s experimental results with the predictions made by DE and FEM for known commercial solid brain phantoms.

UWB wireless link design and implementation challenges in broadband frequency modulated fNIR biomedical imaging

Functional spectroscopic measurements of brain matter using near IR wavelengths are characterized by absorption coefficient μa and scattering coefficient μs. To increase the accuracy of parameter extraction, a broadband frequency modulated system is proposed and design and implementation challenges of a completely untethered and field deployable unit and a high speed wireless communication system is considered to complement a free space optical communication system.

Comparison of tethered and untethered helmet mounted fNIR systems for TBI application

Blast or accident related damages to brain leads to traumatic brain injury (TBI) and early detection of TBI and its severity avoids disability. Broadband near-infrared spectroscopy system of 30-1000 MHz provides accurate functional imaging that could be instrumental in diagnosis of any TBI. This paper addresses design challenges and performance comparison of helmet mounted broadband functional near infra-red (fNIR) designs of both tethered and un-tethered communications with a remote analysis unit. Performance comparison of both systems in terms of size, power consumption, and data throughput are discussed and merits of the tethered and untethered helmet mounted broadband fNIR is discussed. The photon migration of NIR light is accomplished using broadband optical transmitters and reception of diffused photons at various positions on head that are 1.5 cm away from each individual optical transmitter. Optical transmitter and receiver are custom designed to perform photon migration spectroscopy through head and brain at wavelengths of 680nm, 780nm, 820nm, and 980nm. The untethered helmet structure consists of RF electronic for reception of UWB signals of 4.5–5.5GHz and transmission of 50Mb/s data after local signal processing of the received diffused photons. Low frequency electrical connections using microcoax are employed for interfacing the broadband 30–1000MHz reference source to the multi-wavelength optical transmitters and process the received RF signal component of diffused photon density waves.

3D Numerical modeling and its experimental verifications for an inhomogeneous head phantom using broadband fNIR system

Modeling behavior of broadband (30-1000 MHz) frequency modulated near infrared photons through a multilayer phantom is of interest to optical bio-imaging research. Photon dynamics in phantom are predicted using three-dimension (3D) finite element numerical simulation and are related to the measured insertion loss and phase for a given human head geometry in this paper based on three layers of phantom each with distinct optical parameter properties. Simulation and experimental results are achieved for single, two, and three layers solid phantoms using COMSOL (COMSOL AB, Tegnérgatan 23, SE-111 40, Stockholm, Sweden) (for FEM) simulation and custom-designed broadband free space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 795, and 850 nm. Standard error is used to compute error between two-dimension and 3D FE modeling along with experimental results by fitting experimental data to the functional form of afrequency+b. Error results are shown at narrowband and broadband frequency modulation. Confidence in numerical modeling of the photonic behavior using 3D FEM for human head has been established here by comparing the reflection modes experimental results with the predictions made by COMSOL for known commercial solid brain phantoms.