INSTITUTE OF PHYSICS PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 15 (2004) 1–9 PII: S0957-0233(04)57547-1 The characterization of human compact bone structure changes by low-field nuclear magnetic resonance Qingwen Ni 1,3 , J Derwin King 1 and Xiaodu Wang 2 1 Southwest Research Institute, San Antonio, TX, USA 2 Department of Mechanical Engineering and Biomechanics, University of Texas, San Antonio, TX, USA E-mail: qni@tamiu.edu Received 6 December 2002, in final form 17 September 2003 Published Online at stacks.iop.org/MST/15/1 (DOI: 10.1088/0957-0233/15/0/000) Abstract A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spin relaxation is described for characterizing the porosity and (effective) pore size distribution in vitro in human compact bone. The technique involves spin–spin relaxation measurement and inversion spin–spin relaxation spectral analysis methods. The spin–spin relaxation decay curve is converted into a T 2 distribution spectrum by a sum of single exponential decays. The advantages of using low-field NMR for the spin–spin relaxation technique are illustrated. The results obtained from NMR methodology are compared with the results obtained from currently available but destructive histomorphometry and mercury porosimetry methods. The NMR porosities correlate well with the results obtained from the histomorphometry measurements of eight samples from donors of ages 21–89 years. The pore size distributions from T 2 relaxation measurements are similar to the distributions obtained from the mercury porosimetry and histomorphometry measurements. This indicates that the age-related porosity and pore size changes in human compact bone can be detected using the low-field NMR technique. Keywords: NMR, spin–spin relaxation time, microphotograph, NMR system, microphotograph system, bone, cortical porosity, pore size Ascii/Word/MST/mst157547-xsl/PAP Printed 10/10/2003 Issue no Total pages First page Last page File name mst .TEX Date req Artnum Cover date (Ed: NEIL) 1. Introduction Age-related fracture of bone is a major concern of health care for the elderly population because such fractures may Q.1 lead to a high rate of mortality and morbidity. Although the underlying mechanisms are not well understood, previous studies have shown that an increase in the porosity of bone considerably contributes to the age-related decrease of bone mechanical strength. In a comprehensive review on the porosity of bone, Martin [1] described that small changes in porosity would lead to significant changes in the stiffness and strength of both compact and spongy bone. In another study, 3 Address for correspondence: Department of Mathematics and Physical Sciences, Texas A&M International University, Laredo, TX 78041, USA. McCalden [2] reported that the capability of bone to absorb energy during fracture strongly correlates with the porosity of human bone. Since changes in bone porosity are directly related to biomechanical properties of bone [2, 3], a direct sensing technique to detect such changes in bone has been long wanted. In this paper the focus is to demonstrate that the age-related microstructural changes of the human compact (or cortical) bone can be detected by low-field nuclear magnetic resonance (NMR) relaxation techniques. In human compact bone, there are three major natural types of cavities or ‘voids’. Among them, Haversian and Volkmann’s canals play a role in accommodating longitudinal and transverse vascular vessels to transport cells, nutrients, and proteins needed for metabolism inside the bone. Besides, 0957-0233/04/000001+09$30.00 © 2004 IOP Publishing Ltd Printed in the UK 1