Ultrashort TE MR imaging of bovine cortical bone: the effect of water loss on the T1 and T2* relaxation times.

The effects of water loss on the T1 and T2* of bovine cortical bone were investigated using ultrashort echo time sequences with signals excited either by a short hard pulse or by two longer half pulses. Nine bovine femur samples were prepared and sequentially air- and oven-dried. On average 3.42% of bone by weight was lost after air-drying for 3 days, with another 5.98% of bone weight loss after oven-drying at 100°C for 24 h. T1 and T2* were measured after every 1% decrease in weight, with 9-10% bone weight loss at the termination of the drying process. After both forms of drying, the overall T1 decreased 33% from 153±18 ms to 102±17 ms when measured using the hard pulse and from 186±25 ms to 122±23 ms when using the half pulses. T2* decreased by 45-50% from 368±29 μs to 201±19 μs using the hard pulse and from 379±35 μs to 191±17 μs using the half pulses. A steady decrease of 26-31% was observed in both T1 and T2* with the first 3-4% bone water loss after air-drying. Oven-drying at 100°C for 24 h resulted on an additional 4% T1 reduction but 25% T2* reduction.