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Published online before print July 15, 2008, 10.1148/radiol.2482071995
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(Radiology 2008;248:824-833.)
© RSNA, 2008

Experimental Studies

Cortical Bone Water: In Vivo Quantification with Ultrashort Echo-Time MR Imaging1

Aranee Techawiboonwong, PhD, Hee Kwon Song, PhD, Mary B. Leonard, MD, and Felix W. Wehrli, PhD

1 From the Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, 3400 Spruce St, 1 Founders, MRI Education Center, Philadelphia, PA 19104 (A.T., H.K.S., F.W.W.); and Children's Hospital of Philadelphia, Pa (M.B.L.). Received November 15, 2007; revision requested January 14, 2008; revision received January 29; accepted March 5; final version accepted March 11. Supported by National Institutes of Health grants RO1 AR49553, RO1 AR50068, Clinical and Translational Science Award UL1-RR-24134. Address correspondence to F.W.W. (e-mail: wehrlif{at}uphs.upenn.edu).

Purpose: To develop and evaluate a method based on ultrashort echo-time radial magnetic resonance (MR) imaging to quantify bone water (BW) concentration as a new metric of bone quality in human cortical bone in vivo.

Materials and Methods: Human subject studies were institutional review board approved and HIPAA compliant; informed consent was obtained. Cortical BW concentration was determined with custom-designed MR imaging sequences at 3.0 T and was validated in sheep and human cortical bone by using exchange of native water with deuterium oxide (D2O). The submillisecond T2* of BW requires correction for relaxation losses during the radiofrequency pulse. BW was measured at the tibial midshaft in healthy pre- and postmenopausal women (mean age, 34.6 and 69.4 years, respectively; n = 5 in each group) and in patients receiving maintenance hemodialysis (mean age, 51.8 years; n = 6) and was compared with bone mineral density (BMD) at the same site at peripheral quantitative computed tomography, as well as with BMD of the lumbar spine and hip at dual x-ray absorptiometry. Data were analyzed by using the Pearson correlation coefficient and two-sided t tests as appropriate.

Results: Excellent agreement was obtained ex vivo between the water displaced by using D2O exchange and water measured with respect to a reference sample (r2 = 0.99, P < .001). In vivo, BW in the postmenopausal group was greater by 65% (28.7% ± 1.3 [standard deviation] vs 17.4% ± 2.2, P < .001) than in the premenopausal group, and patients with renal osteodystrophy had higher BW (41.4% ± 9.6) than the premenopausal group by 135% (P < .001) and the postmenopausal group by 43% (P = .02). BMD showed an opposite behavior, with much smaller group differences. Because the majority of BW is in the pore system of cortical bone, this parameter provides a surrogate measure for cortical porosity.

Conclusion: A new MR imaging–based method for quantifying BW noninvasively has been demonstrated.

© RSNA, 2008


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In Vivo Quantification of Cortical Bone Water with Ultrashort Echo-Time MR Imaging: A New Parameter to Measure Bone Quality?
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