Correlation between fat signal ratio on T1-weighted MRI in the lower vertebral bodies and age, comparing 1.5-T and 3-T scanners

BACKGROUND: The hypothesis was that the fat-dependent T1 signal intensity in vertebral bodies increases with age due to red-yellow marrow conversion. PURPOSE: To analyze the increasing fatty conversion of red bone marrow with age. MATERIAL AND METHODS: A continuous sample of 524 patients (age range 2–96 years) with normal lumbar spine MRIs (T11–L5) was retrospectively selected in order to get a representative sample from our 1.5-T and 3-T MRI units (Siemens, Erlangen, Germany). Four radiologists read the images independently. Absolute T1 signal intensities were measured in the lower vertebral bodies and standardized by dividing their value by the signal of the subcutaneous fat on lumbar and sacral level. RESULTS: The standardized T1 signal correlated significantly with patients’ age at the 1.5-T unit, with the best correlation demonstrated by thoracic vertebra T11, followed by lumbar vertebra L1, with correlation coefficients (R) of 0.64 (95% CI 0.53–0.72, P < 0.0001) and 0.49 (95% CI 0.38–0.59, P < 0.0001), respectively. For women and men, the R values were similar in thoracic vertebra T11 at 0.62 (95% CI 0.49–0.72) and 0.64 (95% CI 0.44–0.77), respectively. The vertebral signal correlated significantly better with age in the 1.5-T compared to the 3-T unit on all vertebral levels: the best R value of the 3-T unit was only 0.20 (95% CI 0.09–0.30, P < 0.0001). Our study showed an average increase of the relative T1 signal in T11 of 10% per decade. CONCLUSION: T1 fat signal ratio increases with age in the vertebral bodies, which could help estimating the age of a person. Best age correlation was found when measuring T1 signal in T11, standardized by the sacral subcutaneous fat signal and using a 1.5-T MRI.