Ultrashort TE MR imaging of bovine cortical bone: The effect of water loss on the T 1 and T 2 * relaxation times

The effects of water loss on the T 1 and T 2 * 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. T 1 and T 2 * 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 T 1 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. T 2 * 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 T 1 and T 2 * with the first 3–4% bone water loss after air‐drying. Oven‐drying at 100°C for 24 h resulted on an additional 4% T 1 reduction but 25% T 2 * reduction. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.