Nima Kokabi, Presenter: Nothing to Disclose

Won Bae, Abstract Co-Author: Nothing to Disclose

Christine B. Chung MD, Abstract Co-Author: Research grant, General Electric Company

Graeme M. Bydder MBChB, Abstract Co-Author: Research grant, General Electric Company

Jiang Du, Abstract Co-Author: Grant, General Electric Company Research collaboration, General Electric Company

To investigate the effect of sequential water loss on T1 and T2* relaxation times of human cortical bone using ultrashort time-to-echo (UTE) MR imaging on a clinical 3T MR scanner.

Six fresh bovine cortical bone fragments were imaged using the UTE technique (TE = 8 us) during sequential drying. Air-drying at room temperature for 4 hours resulted in a decrease of up to 3% in the initial weight of the bone fragment. Subsequent drying was achieved by using a laboratory oven with a gradual increase in temperature from 35 to 100°C until the rate of weight decrease became negligible and bone signal became undetectable with UTE imaging. T1 and T2* were measured for each bone sample after every 1% decrease in weight. The loss in bone weight was converted to loss in water volume. Using the UTE acquisition technique, T1 was measured using a saturation recovery sequence with the following times: 10, 25, 50, 100, 200, 400 and 800 ms. T2* was measured with a series of TE delays of 8, 200, 500, 1000 and 2000 us. Single component exponential curve fitting was used to extract T1 and T2* values.

On average, 29.5% (by volume) of each bone sample was lost at the termination of the drying process. ANOVA analysis indicated a significant reduction in both T1 and T2* values with sequential bone water loss. The overall T1 decreased by 30% (95% confidence interval, CI) from 187 ms to 130 ms while T2* decreased by 53% (95% CI) from 396 us down to 185 us. A steady decrease of 28% was observed in both T1 and T2* with sequential bone water loss up to 10% of bone volume. This correlated well with previously published figure of around 12% for bone bulk water volume. The loss of an additional 20% water, which is likely to be bulk water in small pores as well as water bound to the collagen matrix, resulted in only 4% T1 reduction but 25% T2* reduction, indicating that T2* is more sensitive to the presence of bound water.

The loss of bulk water affected both the T1 and T2* of cortical bone, while the loss of bound water mainly affected T2*. UTE detects signal from both bulk water and bound water, and has the potential for clinical non-invasive evaluation of bone quality.

UTE T1 and T2* measurements provide information on bone bulk and bound water, allowing quantitative evaluation of bone quality from a new perspective of proton compartmentalization in bone.

Kokabi, N, Bae, W, Chung, C, Bydder, G, Du, J, The Effect of Sequential Bone Water Loss on T1 and T2* Relaxation Times of Cortical Bone.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9011127.html