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 vivo
2 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/L
bone
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 B
1-map
was found by acquiring a T
1 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/L
bone. The osteoporotic subjects had a mean bound/pore
water concentrations of 18/10 mol
1H/L
bone. 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
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