ABSTRACT Lung transplantation (LT) is the only definitive therapy for many patients with end-stage lung diseases, but many LT recipients experience allograft failure with high morbidity and mortality. Evidence suggests that early detection of allograft rejection can change their prognosis by optimizing therapies before irreversible damage occurs. Unfortunately, we do not have good diagnostic methods to address this need. In this proposal, we plan to develop new diagnostic and guidance tools to address this deficiency using Hyperpolarized Gas MRI (HGMRI). Our group has reported that HGMRI can detect and endotype regional abnormalities occurring in several lung diseases with high definition and resolution, including lung transplants. We anticipate that incorporating HGMRI signatures into the standard clinical workflow will significantly increase the detection rate of acute cellular rejection (ACR) in asymptomatic LT recipients. Herein, our aims will test the performance of our HGMRI signatures to enhance the detection and endotyping of ACR. Three sub-aims of Aim 1 are; (1) Aim 1a - correlating the results of the tissue pathology (current clinical gold standard) with HGMRI signatures; (2) Aim 1b - determining the HGMRI signature responses before and after ACR treatment; and (3) Aim 1c - determining the correlation between HGMRI signatures and single-cell RNA-sequence (scRNA-seq) transcriptomic signatures, showing dysregulated host immune responses. Two sub-aims of Aim 2 are; (1) Aim 2a – determining if the regional ACR diagnosis by HGMRI signatures and tissue pathology persists from Visit 1 at baseline (Aim 1) to Visit 2 at 12-month follow-up (Aim 2); and (2) Aim 2b - determining additional correlations at 12 months between the HGMRI and scRNA-seq signatures and test if HGMRI signatures reflect underpinning immunopathology in LT recipients with rejection. Successful completion of this proposal will ready HGMRI signatures with which ACR can be detected early, followed noninvasively, and corroborated by the state-of-the- art scRNA-seq transcriptomic signatures. Our proposal will test the performance of HGMRI signatures by independent but corroborating approaches to maintain scientific rigor with the potential to advance the field of pulmonary transplant medicine.