Chord distributions across 3D digital images of a human thoracic vertebra

Radiation dose estimates to the trabecular region of the skeleton are of pr imary importance due to recent advancements in nuclear medicine. Establishi ng methods for accurately calculating dose in these regions is difficult du e to the complex microstructure of this anatomic site and the typical range s of beta-particles in both bone and marrow tissues. At the present time, m odels of skeletal dosimetry used in clinical medicine rely upon measured di stributions of straight-line path lengths (chord lengths) through bone and marrow regions. This work develops a new three-dimensional, digital method for acquiring these distributions within voxelized images. In addition, the study details the characteristics of measuring chord distributions within digital images and provides a methodology for avoiding undesirable pixel or voxel effects. The improved methodology has been applied to a digital imag e (acquired via NMR microscopy) of the trabecular region of a human thoraci c vertebra. The resulting chord-length distributions across both bone trabe culae and bone marrow cavities were found to be in general agreement with t hose measured in other studies utilizing different methods. In addition, th is study identified that bone and marrow space chord-length distributions a re not statistically independent, a condition implicitly assumed within all current skeletal dosimetry models of electron transport. The study conclud es that the use of NMR microscopy combined with the digital measurement tec hniques should be used to further expand the existing Reference Man databas e of trabecular chord distributions to permit the development of skeletal d osimetry models which an more age and gender specific. (C) 2001 American As sociation of Physicists in Medicine.