WATER FRACTION OF LUMBAR VERTEBRAL BONE-MARROW ESTIMATED FROM CHEMICAL-SHIFT MISREGISTRATION ON MR-IMAGING - NORMAL VARIATIONS WITH AGE ANDSEX

OBJECTIVE. Our objective was to use the chemical-shift misregistration effect of MR imaging to measure the variation in the water fraction i n vertebral bone marrow with respect to patient age and sex. SUBJECTS AND METHODS. We examined prospectively 211 subjects (5-84 years old; 1 08 male and 103 female subjects) who had no history of hematologic dis orders. We obtained midsagittal proton density-weighted spin-echo imag es (2500/22 [TR/TE]) with a narrow sampling bandwidth (6250 Hz). Misre gistered signals from lipid protons of 6-10 mm (upward shift in the re adout direction) were obtained with the chemical-shift effect, By meas uring the mean signal intensities of the water voxels and the water-pl us-lipid voxels, we calculated a region of interest in each vertebral body from L1 to L3. The water fraction of bone marrow was then calcula ted as 100 x (signal intensity of water voxels/signal intensity of wat er-plus-lipid voxels). Individual water fractions were calculated from the average values for the water fractions of the L1-L3 bodies. RESUL TS. In male subjects, the water fraction showed a rapid decrease in th e older patients in the 5- to 34-year-old group, (Mean water fractions for male patients who were 5-14, 15-24, and 25-34 years old were 75.2 %, 69.0%; and 53.7%, respectively.) For male patients more than 25 yea rs old, the water fraction remained almost constant (similar to 50%). In female subjects who were 5-44 years old, the water fraction exceede d 69% and remained almost constant. However, the water fraction rapidl y decreased in women more than 45 years old. (Mean water fractions for female patients who were 35-44, 45-54, and 55-64 years old were 70.9% , 61.1%, and 49.7%, respectively.) A comparison between male subjects and female subjects showed that the water fraction for women who were 25-54 years old exceeded the water fraction for men in the same age gr oup (25-34 years old, p < .0001; 35-44 years old, p < .001; 45-54 year s old, p < .05). CONCLUSION. MR imaging showed that male and female su bjects convert hematopoietic marrow to fatty marrow in the lumbar vert ebral bodies in significantly different ways, The data obtained for th e normal water fraction of bone marrow may prove useful for evaluating diseases that affect marrow.