Project Abstract Magnetic resonance imaging (MRI) provides high dynamic range soft tissue contrast and full volumetric data sets without the use of ionizing radiation. The combination of MR imaging with other imaging and treatment modalities, specifically with Positron Emission Tomography (PET/MR) and radiation therapy (MR guided Radiation Therapy, MRgRT), has gained attention as technological advances in these systems have allowed for their release into the clinical workflow. MR image quality is directly dependent on RF coil arrays, localized antennae that serve as the main component of the receive chain; and coil performance is dependent on proximity to the anatomy of interest, so most MR systems use a suite of anatomy specific arrays for various applications. However, in hybrid systems 𝛾-ray interactions with these coil arrays is a significant obstacle to patient care, limiting image quality in PET/MR and contributing to decreased target dose and increased skin dose from scattering in MRgRT. Additionally, their traditionally bulky and rigid form can render them incompatible with RT immobilization hardware, especially for head and neck imaging. Incompatibility with immobilization hardware also limits the use of MR imaging for radiation therapy simulation before treatment (MR-Sim). Our goal is to develop a suite of flexible, conformal, radiation transparent head/neck arrays that are compatible with PET/MR, MRgRT, MR-Sim and traditional MRI. Phase I SBIR Specific Aims focused on optimizing coil and hardware technology for radiation-transparency and MR performance, developing and testing a 24-channel flexible array for 3T PET/MR, and analyzing the feasibility of scaling this technology to other field strengths and coil designs. The objectives of this Phase II proposal center around the application of this novel technology to an open market need: conformal head/neck arrays for multi-modality systems compatible with varying patient anatomies. Because commercially available PET/MR and MRgRT systems cover a large range of MR system frequencies, coil development will be pursued at the most clinically impactful field strengths for multi-modality MR systems: 3T, 1.5T, and 0.35T. Our project will produce a head/neck array suite, covering patients from pediatric to adult, and will be designed to ensure consistent performance in the upper c-spine and neck despite highly variable patient anatomies. This suite of coils will include small, medium, and large arrays (24- 28- and 32-channels respectively) which attach to the system through a universal cable and connector and are compatible with standard head/neck immobilization hardware. By completing these goals, we aim to improve patient experience and outcomes by producing an optimized suite of head/neck coils for 3T MR/PET, 1.5T MRgRT, and all MR-Sim systems, and developing the technology for expansion to 0.35T MRgRT.