Bound- and Pore-Water MRI of Cortical Bone in Osteoporotic Patients
Mary Kate Manhard1, S Bobo Tanner2, Daniel F Gochberg3, Jeffry S Nyman4, and Mark D Does1

1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, 2Department of Medicine, Vanderbilt University, Nashville, TN, United States, 3Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 4Department of Orthopaedics & Rehabilitation, Vanderbilt University, Nashville, TN, United States

Synopsis

Osteoporotic fractures are a growing problem, and X-ray based methods do not always identify individuals at risk of a fracture. MRI based methods of bound and pore water in cortical bone have the potential to offer new information about fracture resistance. These methods were implemented on both osteoporotic volunteers and healthy controls in the tibia. Osteoporotic subjects had significant decreases in bound water concentration and slight increases in pore water concentration compared to healthy subjects. These promising results will allow for further investigation of changes of bound and pore water concentrations across diseases and with response to various treatment methods.

Introduction

Osteoporotic fractures are a growing problem worldwide as more individuals live longer, and current methods for evaluating fracture risk are X-ray based and do not identify many individuals who are at risk of a fracture.1 MRI based methods to evaluate and bound and pore water in cortical bone have been previously implemented in vivo2 and shown good repeatability on healthy volunteers.3,4 MRI bound and pore water concentrations can predict fracture resistance of ex vivo bone samples,5 but have not been directly assessed clinically in patients diagnosed with severe osteoporosis. The goal of this work is to evaluate bound and pore water measures acquired in the tibia from healthy volunteers and from individuals with osteoporosis.

Methods

The Adiabatic Inversion Recovery (AIR) and Double Adiabatic Full Passage (DAFP) sequences were used with 3D UTE to measure bound and pore water concentrations, respectively, in the cortical bone in the tibia of 7 healthy controls (mean age 26, 4M/3F) and 3 volunteers who were beginning drug treatment for osteoporosis (mean age 64, F). A reference marker was used in the FOV so that signal could be converted into absolute units of mol 1H/Lbone and compared across subjects. The scans were acquired at a 200 mm isotropic FOV with 1.5 mm resolution in a scan time of 14 minutes each. A B1-map was found by acquiring a T1 weighted scan twice, once using the body coil for receive and once with the knee coil for receive. The smoothed ratio of the signal was then applied to the images and bound and pore water maps were found.2 The mean bound and pore water values in the midshaft of the tibia were compared between healthy and osteoporotic subjects.

Results

Figure 1 shows a bound and pore water map overlaid on a conventional UTE image from a healthy control and the same from an osteoporotic subject. The bound/pore water concentrations are much higher/lower, respectively, in the healthy tibia compared to the osteoporotic tibia. Figure 2 shows the mean bound and pore water concentrations across both healthy and osteoporotic subjects. The healthy subjects had a mean bound/pore water concentrations of 26/9 mol 1H/Lbone. The osteoporotic subjects had a mean bound/pore water concentrations of 18/10 mol 1H/Lbone. A significant decrease in bound water and slight increase in pore water was shown in the osteoporotic subjects compared to the healthy subjects.

Discussion

These results demonstrate that MRI measures of bound and pore water using AIR and DAFP are sensitive enough to detect differences between normal and osteoporotic bone. The results show expected changes with osteoporosis, which is promising for future studies using these methods for evaluating fracture risk. The results support the hypothesis that low bound water is a marker of poor bone quality, which has been associated with low fracture resistance.6 The pore water also increases with osteoporosis as pore water is a marker of porosity and has been shown to correlate with porosity from μCT.7 Future studies will investigate bound and pore water maps of these osteoporotic patients after receiving treatment to evaluate changes in bound and pore water in response to treatment. These promising results will allow for further investigation of differences of bound and pore water measures across diseases and changes of bound and pore water with response to various treatment methods.

Acknowledgements

No acknowledgement found.

References

1. Kanis JA, Johnell O, Oden A, et al. Ten year probabilities of osteoporotic fractures according to BMD and diagnostic thresholds. Osteoporosis Int 2001;12:989–995.

2. Manhard MK, Horch RA, Harkins KD, et al. Validation of quantitative bound- and pore-water imaging in cortical bone. Magn Reson Med 2014;71:2166–2171.

3. Manhard MK, Horch RA, Gochberg DF, et al. In vivo quantitative MR imaging of bound and pore water in cortical bone. Radiology 2015;277:221–229.

4. Rajapakse CS, Bashoor-Zadeh M, Li C, et al. Volumetric cortical bone porosity assessment with MR Imaging: validation and clinical feasibility. Radiology 2015;276:526–535.

5. Horch RA, Gochberg DF, Nyman JS, et al. Non-invasive predictors of human cortical bone mechanical properties: T(2)-discriminated H NMR compared with high resolution X-ray. PLoS One 2011;6:e16359.

6. Granke M, Makowski AJ, Uppuganti S, et al. Identifying novel clinical surrogates to assess human bone fracture toughness. J Bone Min Res 2015;30:1290–300.

7. Biswas R, Bae W, Diaz E, et al. Ultrashort echo time (UTE) imaging with bi-component analysis: bound and free water evaluation of bovine cortical bone subject to sequential drying. Bone 2012;50:749–55.

Figures

Bound (top) and pore (bottom) water maps of a healthy subject (left) and an osteoporotic subject (right). The bound water concentration is higher in the healthy subject, while the pore water concentration is lower.

Mean bound water concentration significantly decreases in osteoporotic subjects compared to the healthy subjects. Mean pore water concentration increases in osteoporotic patients compared to healthy subjects.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
0177