PROJECT SUMMARY Gradient-recalled echo (GRE)–based echo planar imaging (EPI) has been the gold standard functional magnetic resonance imaging (fMRI) technique for nearly three decades due to its ability to rapidly acquire whole brain volumes with MR T2* sensitivity to blood oxygenation — a well-known surrogate marker for brain activity. This immensely utilized technique, however, suffers from high acoustic noise, ghosting and motion artifacts, magnetic field inhomogeneity–related artifacts, low sensitivity compared to other neuroimaging modalities, and poor spatial specificity. An fMRI sampling technique that addresses these problems has the potential to change day-to-day fMRI practices. In particular, such a development would be of great benefit to the emerging rodent fMRI community as anesthesia and stress confounds can be avoided. Additionally, most rodent fMRI studies are performed under high magnetic field strengths (> 7T), wherein susceptibility artifacts in GRE-EPI are exacerbated. Imaging sequences with “zero” acquisition delay and minimal increment of gradients are insensitive to problems stated above and have the potential to provide superior specificity and sensitivity compared to GRE- EPI-fMRI. The overarching goal of this project is to advance, validate, and disseminate a novel 3D brain- wide imaging sequence: Steady-state On-the-Ramp Detection of INduction-decay signal with Oversampling (SORDINO) for the preclinical animal fMRI community. In addition, we will investigate SORDINO contrast mechanisms and explore a contrast-enhanced method that may further augment SORDINO sensitivity. Our developments will be benchmarked in mice, wherein a head-fixation approach can be utilized to image mice in an awake condition. In Aim 1, we will develop and disseminate the SORDINO sequence and reconstruction package in a preclinical animal MRI platform. In Aim 2, we will inform the most robust imaging parameters and benchmark them against modeled SORDINO performance and GRE-EPI-fMRI and zero echo time (ZTE)-fMRI data. This will facilitate future SORDINO-fMRI applications and enable new capabilities to study large-scale, functionally and behaviorally relevant brain networks in awake mice. In Aim 3, we will examine the SORDINO contrast mechanisms using MR-compatible invasive recordings, which are crucial for data interpretation. The contrast mechanisms, if proven to be local tissue oxygenation, cerebral blood flow, and cerebral blood volume, will clarify SORDINO as a spatially specific approach for functional brain mapping. In Aim 4, we will leverage the expected sensitivity gain of SORDINO at shorter baseline T1 values and use a simple manganese-enhanced MRI (MEMRI) strategy, a method widely utilized by many preclinical MRI labs, to further augment awake mouse SORDINO-fMRI sensitivity. Overall, we expect the knowledge and deliverables in this work to have widespread implications and will significantly advance fMRI technologies. We also expect this work to have extended impacts on studies requiring rapid mapping of T1 changes such as dynamic-contrast-enhanced MRI and molecular MRI.