Realization and Performance Comparison of Untethered and Minimally Tethered Helmet Mounted Broadband fNIR A. M. Khwaja, K. Manseta, E. Sultan, P. Daruwalla, Y. Malallah, L. Najafizadeh # , A. Madjar, K. Pourrezaei + , A. Gandjbakhche $ , A.S. Daryoush Department of ECE, Drexel University, Philadelphia, PA USA 19104 + School of Biomedical Engineering and Health Systems, Drexel University, Philadelphia, PA USA 19104 # Henry Jackson Foundation, 1401 Rockville Pike, Rockville, MD USA 20852 $ National Institutes of Health, 9000 Rockville Pike, Bethesda, MD USA 20892 daryoush@ece.drexel.edu Abstract —Broadband (30-1000MHz) frequency modulated spectroscopic measurements of brain tissue using near infra red wavelengths is used to get an accurate extraction of absorption and scattering coefficients of various regions of brain. The design and realization challenges of developing this system are discussed in this paper. The challenges lie in developing small size, low power consuming, efficient custom designed modules on a helmet for broadband NIR spectroscopy and high speed wireless or minimally wired communications to a remote processing unit. The design requirements and expected performance of the custom designed modules is conducted using IBM 90nm CMOS technology. Finally, a comparison between the system level performance of untethered and a minimally tethered systems is shown in terms power consumption and implementation. Index Terms — Near IR Imaging, Brain Tissue Parameters, Optical Transmitters and Receivers, Wireless Communication design, CMOS technology. I. INTRODUCTION Diffused photon near near-infrared (DPNIR) is a non- invasive optical spectroscopy technique that employs NIR light to quantify the level of oxygenated and de-oxygenated hemoglobin using optical properties of tissues (i.e., absorption and scattering). Quantitative DPNIR methods employing time or frequency domain photon migration have recently been applied for breast tumor detection, functional brain monitoring, wound healing prognosis, and pain assessment [1]. A broadband frequency domain DPNIR method monitors level of oxygenated and deoxygenated blood in the brain with high accuracy and spatial resolution, which could lead to understanding the functionality of different parts of brain as functional NIR (fNIR). Spectroscopic studies at 680nm, 780nm, 830nm, and 980nm reveals level of oxygenated/de-oxygenated hemoglobin, blood and water flow in tissue. Therefore, any disorder in brain functionality could then be registered [2] as excess changes in the absorption of oxygenated and de-oxygenated hemoglobin. Commercial fiber based fNIR systems [3] are significantly tethered and are not field deployable. Moreover, these systems are designed based on unmodulated or narrow band frequency domain operation and higher extraction accuracy and spatial resolution is reported in broadband than narrow band frequency modulated systems [4]. The system block diagram is shown in Fig. 1. It consists of 18 optical transmitters and 22 optical receivers along with wireless transceiver chip placed on a helmet structure. The design challenges for free-space optical transmitter and receiver are addressed earlier[5-6], while this paper addresses custom hardware realization of a broadband fNIR system on chip (SOC) using 90nm CMOS technology from IBM for low power design constraints . Fig. 1. a) Block diagram of untethered free-space fNIR brain imaging system in wireless communication with remote monitoring; b) Block diagram of fNIR brain imaging system using custom designed optical transmitters in low profile TO-49 cans and the optical receiver ferrules. (a) (b)