MRI assessment of regional differences in phosphorus‐31 metabolism and morphological abnormalities of the foot muscles in diabetes

Purpose To assess differences in the phosphorus-31 (31P) metabolism and morphology in multiple muscle regions in the forefoot of diabetic patients and normal subjects. Materials and Methods Fifteen diabetic patients and 15 normal subjects were assessed for muscle atrophy by 1H magnetic resonance imaging (MRI) at 3T to grade the flexor hallucis, adductor hallucis, interosseous regions, and entire foot cross-section. Each region and the entire foot were also quantitatively evaluated for metabolic function using 31P imaging for spatial mapping of the inorganic phosphate (Pi) to phosphocreatine (PCr) ratio (Pi/PCr). The ratio of viable muscle area to the predefined region areas (31P/1H) was calculated. The variability of each method was assessed by its coefficient of variation (CV). Results Muscle atrophy was significantly more severe in diabetic compared to normal subjects in all regions (P < 0.01). The 31P/1H area ratio was significantly larger in the adductor hallucis than in the other two regions (P < 0.05). The Pi/PCr ratio was significantly different between the two groups in the flexor hallucis and interosseous regions (P < 0.05) but not adductor hallucis region. The CV for Pi/PCr ranged from 10.13 to 55.84, while it ranged from 73.40 to 263.90 for qualitative grading. Conclusion Changes in atrophy and metabolism appear to occur unequally between different regions of the forefoot in diabetes. The adductor hallucis region appears more capable of maintaining structural and metabolic integrity than the flexor hallucis or interosseous regions. The CV analysis suggests that the quantitative 31P methods have less variability than the qualitative grading. J. Magn. Reson. Imaging 2016;44:1132–1142.