Mapping skeletal muscle mitochondrial oxidative phosphorylation (OXPHOS) in childhood acute lymphoblastic leukemia survivors using a novel technique oxcest MRI Free

Introduction. Mitochondrial oxidative phosphorylation (OXPHOS) is the primary energy pathway powering skeletal muscle activity and physical function. Non-invasive Magnetic Resonance-based imaging methods can dynamically assess OXPHOS activity by measuring the rate of recovery of phosphocreatine (PCr) or creatine (Cr) following exercise. We developed OXPHOS Chemical Exchange Saturation Transfer (OXCEST), a novel CEST MRI technique that uses a standard 1H volume coil to achieve improved temporal resolution, enabling accurate, high spatial resolution Cr maps and Cr recovery rates. Our preliminary results demonstrate that OXCEST-derived Cr recovery times closely match those obtained with gold standard 31-phosphorous magnetic resonance spectroscopy (³¹P-MRS), while also providing muscle-specific OXPHOS maps that ³¹P-MRS cannot provide.

Disrupted mitochondrial function is a common feature of neuromuscular and metabolic diseases. Among neuromuscular diseases, childhood cancer survivors, including those with childhood acute lymphoblastic leukemia (ALL), are at increased risk for premature loss of physiological reserve, characterized by low lean mass (sarcopenia), weakness (frailty), and heightened morbidity and mortality. These deficits likely originate during cancer therapy and often persist or worsen throughout survivorship. Reduced muscle mass and quality predispose survivors to early aging and premature onset of chronic diseases. However, the extent to which ALL and its treatment impact muscle mitochondrial metabolism is not well understood.

Aim. To develop and establish OXCEST MRI for skeletal muscle OXPHOS imaging in healthy participants, validate it against ³¹P-MRS, and apply OXCEST to assess muscle mitochondrial energetics in adult survivors of childhood ALL.

Methods. We acquired OXCEST and ³¹P-MRS from seven healthy adult subjects (male=5, age=34.6±6.1Y) across two sessions to compare OXCEST-derived post-exercise Cr recovery time constant (T_Cr) with PCr recovery time constant (T_PCr) from ³¹P-MRS. The OXCEST protocol consisted of pre- and post-exercise reference images, B₀/B₁ mapping and OXCEST scans separated by a 2-minute plantar flexion exercise. OXCEST measurements targeted the lateral (LG) and medial gastrocnemius (MG), and soleus (Sol) muscle groups. During each acquisition, participants performed mild plantar flexion exercise inside the scanner. The post-exercise recovery curves were modeled using mono-exponential recovery fits to derive recovery time constants.

Additionally, we acquired OXCEST in three adult survivors of childhood ALL (male=3, 31.3±2.9Y) with no history of cranial radiation, implanted medical devices, or current peripheral motor neuropathy.

Results. In healthy participants, OXCEST-derived post-exercise Cr recovery in the LG and MG muscle groups followed a mono-exponential decay (R2>0.97). The T_Cr values were 56±19s in the LG, 58±29s in the MG, and 52±33s in the Sol. The unlocalized T_PCr measured using ³¹P-MRS in the same cohort was found to be 51±15s. OXCEST derived mean T_Cr of LG and MG showed strong correlation with gold standard ³¹P-MRS-derived T_PCr (R²=0.83, p=0.005).

In the three ALL survivors, T_Cr values were found to be 1.4 to 2.2 times longer compared to sex- and age-matched healthy subjects (ALL survivor cohort: 126±59s in the LG, 108±77s in the MG, 55±47s in the Sol; healthy cohort; 70±13s in the LG, 75±28s in the MG, and 25±17s in the Sol), indicative of impaired skeletal muscle mitochondrial function.

Conclusions. OXCEST enables high-temporal resolution, muscle-specific assessment of post-exercise Cr recovery, and shows strong agreement with the gold-standard ³¹P-MRS. This non-invasive technique is a promising tool for evaluating skeletal muscle OXPHOS and is translatable to clinical settings. Importantly, its application in ALL survivors reveals prolonged Cr recovery kinetics, consistent with mitochondrial dysfunction, and highlights highlighting the potential of OXCEST MRI to monitor metabolic impairments in populations at risk for treatment-related sarcopenia and early physiological decline.