SAN FRANCISCO — High-resolution MRI, multidetector CT, and high-resolution peripheral quantitative CT each may be useful in assessing bone quality, according to recent data.
The three imaging modalities can produce significantly different absolute numbers compared with each other when assessing trabecular or cortical bone structure, yet all correlate reasonably well with micro-CT as a standard of reference, Dr. Thomas M. Link said at a conference sponsored by the International Society for Magnetic Resonance in Medicine.
Trabecular and cortical bone structure are key components of bone quality, an important component of bone strength according to the National Institutes of Health (JAMA 2001;285:785–95).
In one randomized, double-blind study, for example, 51 postmenopausal women with osteopenia were treated with alendronate or placebo and followed over a 2-year period by 3T MRI of the radius, tibia, and femur; high-resolution peripheral quantitative CT (hr-pQCT) of the radius and tibia; and dual x-ray absorptiometry measures of bone mineral density. Both high-resolution MRI (hrMRI), and hr-pQCT results for trabecular bone showed moderate but significant correlation with bone density as a reference, even though there was a twofold to fourfold difference between hrMRI and hr-pQCT in parameter values such as trabecular number, thickness, or separation (J. Bone Miner. Res. 2008;23:463–74).
For corticol bone imaging, a newer area of research, two 2008 studies using hr-pQCT showed substantial differences between postmenopausal women with hip or wrist fractures, compared with fracture-free women, said Dr. Link, professor of radiology at the University of California, San Francisco.
Experimentally, hrMRI and hr-pQCT are being used to assess cortical bone porosity, which affects bone stability. One recent study using hr-pQCT found significant differences among normal premenopausal women, normal postmenopausal women, and postmenopausal women with renal osteodystrophy. MRI or hr-pQCT provide high spatial resolution and produce no (or relatively little) radiation, compared with high-radiation exposure from multidetector CT. Multidetector CT allows imaging of more central skeletal sites, he said.
The hr-pQCT scanners image only peripheral sites, whereas hrMRI covers larger areas of the radius, tibia, and possibly the femur.
The CT techniques provide measures of bone densitometry. Although hrMRI gives no densitometric data, some studies suggest it may be used to analyze bone marrow composition through spectroscopy in order to assess bone stability. The three techniques appear to have similar rates of reproducibility.
MRI and hr-pQCT are expensive and prone to motion artifacts. Multidetector CT is available and requires less time for a scan. But postimage processing is challenging for MRI and CT.
Dr. Link reported receiving research funding and support from Merck & Co., which markets medication to treat osteoporosis.
The trabecular and cortical bone architecture in the distal tibia is shown in high-resolution peripheral quantitative CT (left) and high-resolution 3T MRI (right). Images courtesy Dr. Thomas M. Link
