MR phase imaging to quantify bone volume fraction: computer simulations and in vivo measurements.

Magnetic resonance phase images can be used to assess trabecular bone by measuring the standard deviation of the phases in a region of interest. The standard deviation of regional phase measurements reflects the degree of magnetic field inhomogeneity caused by susceptibility differences between bone and marrow. A 3D computer model of trabecular bone was developed and then used to explore the influence of bone volume fraction and imaging parameters such as pixel size and slice width on the standard deviation of regional phase measurements. The results from these tests show that with appropriate selection of these parameters, phase spread strongly reflects variations in trabecular bone density (a correlation of R(2) = 0.98 with bone volume fraction between 0 and 10%). The technique was then applied in vivo on the radius of 25 patients who already had a bone density scan with peripheral quantitative tomography and a correlation between phase standard deviation and trabecular bone density was found (R(2) = 0.46).