Quantitative MRI Reveals Bone Marrow Regeneration Following Targeted Marrow Irradiation and Transplantation in a Sickle Cell Disease Model

Abstract

Sickle cell disease (SCD) is associated with chronic bone marrow stress, altered hematopoiesis, and reduced adiposity. Whether marrow-selective conditioning followed by transplantation normalizes these abnormalities remains unclear. We investigated bone marrow remodeling in Townes mice by comparing SCD control (SCD-Con) with mice that received total marrow irradiation (TMI) followed by bone marrow transplantation (SCD-TMI-BMT). Multiparametric micro-MRI at 7 T quantified proton density water fraction (PDWF), proton density fat fraction (PDFF), and R2*(1/T2*), and micro-CT assessed trabecular structure in the femur. SCD-Con marrow showed higher water content (elevated PDWF), reduced adiposity (lower PDFF), and imaging features consistent with erythroid hyperplasia and elevated iron burden (shorter T2* with reciprocal increase in R2*). In contrast, SCD-TMI-BMT mice demonstrated smaller R2*, reduced PDWF, and partial restoration of adiposity, accompanied by reciprocal shifts in R2*, consistent with decreased cellular iron and marrow remodeling. Micro-CT revealed an improved trabecular architecture after BMT compared to SCD control. MRI imaging biomarkers aligned with histologic evidence of reduced cellularity and larger adipocyte voids. In conclusion, a TMI-BMT SCD model promotes partial normalization of the marrow microenvironment. Multiparametric MRI with micro-CT provides a practical, non-invasive framework for monitoring marrow remodeling and skeletal health after curative therapy.