Time dependency of bone density estimation from computed tomography with intravenous contrast agent administration

Area of Science:

• Radiology and Imaging
• Bone Densitometry
• Medical Physics

Background:

• Quantitative computed tomography (QCT)-equivalent bone mineral density (BMD) values can be derived from contrast-enhanced multi-detector computed tomography (MDCT) scans.
• Previous methods utilized a density-based conversion equation for this derivation.

Purpose of the Study:

• To investigate the effect of scan delay time after intravenous (IV) contrast agent administration on BMD values derived from MDCT.
• To determine if scan timing influences the accuracy of QCT-equivalent BMD calculations.

Main Methods:

• Retrospective analysis of 198 subjects undergoing biphasic MDCT.
• Comparison of average Hounsfield unit densities in lumbar vertebrae (L1-L3) between scan phases.
• Calculation of QCT-equivalent BMD (BMDQCT) using a published conversion equation.

Main Results:

• Intravenous contrast administration significantly increased L1-L3 density by 8.6% (p < 0.0001) between scan phases.
• BMDQCT values shifted from osteoporotic to osteopenic in 4.5% and osteopenic to normal in 11.1% of subjects.
• Density increase showed a weak but statistically significant age dependency (p < 0.001).

Conclusions:

• Density-based conversion equations for deriving BMDQCT from MDCT ignore the critical variable of time dependency.
• Actual age-dependent BMD should be considered as a relevant variable for future MDCT-to-QCT conversion equations.