Date of Graduation

5-2014

Document Type

Thesis (MS)

Program Affiliation

Medical Physics

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

S. Cheenu Kappadath, P. hD.

Committee Member

Dianna D. Cody, Ph. D.

Committee Member

X. John Rong, Ph. D.

Committee Member

A. Kyle Jones, Ph. D.

Committee Member

Veerabhadran Baladandayuthapani, Ph. D.

Abstract

Osteoporosis is diagnosed by assessing the bone mineral density (BMD) of the trabecular bone, and has previously been characterized with dual-energy x-ray absorptiometry (DXA) or single-energy computed tomography (SECT). Dual-energy computed tomography (DECT) is able to create two three-dimensional sets of images representing the densities of two materials in a given basis pair. DECT is theoretically capable of providing a true density measurement of trabecular bone material with the proper material basis pair.

Using the rapid kVp-switching GE HD750 scanner, the concentrations of various solutes were assessed in two-material syringe-phantoms in different experimental conditions with DECT material density images, SECT and DXA. RMS error was used to evaluate the accuracy of the DECT concentration measurements in air and regression was used to compare measurements made in other scanning conditions. The effect of anthropomorphic geometry was explored in concentric phantoms designed to model bone. The sensitivity of DECT, SECT, and DXA to change in bone composition was compared. Thecorrelation between different basis pair decompositions was evaluated. Finally, the correlation between DECT concentration measurements and DXA areal BMD (aBMD) measurements was assessed and used to develop a methodology to convert DECT concentration measurements to aBMD measurements.

The RMS error of DECT concentration measurements made in air ranged from 9-244%. Measurements of concentration made off-isocenter or with different DECT techniques were found to have a small (~5%) effect, but scattering conditions resulted in a reduction of 8-27% with similar trends observed in SECT data. In concentric phantoms, higher-attenuating material in the outer chamber increased measured values of the inner material for all measurement methods. DECT measurements had the best sensitivity (2 mg/ml K2HPO4). Different DECT basis pairs were nearly perfectly correlated (R21). This was exploited to demonstrate a strong correlation (R2 = 0.988) between measured K2HPO4 concentration and DXA aBMD for different two-material phantoms. The relationship DECT aBMD and DXA aBMD was highly correlated (R2 =0.983) but the limits of agreement (-0.16 to 0.57 g/cm2) were relatively large compared to clinical utility.

This study suggests that corrections to output DECT concentration measurements may be necessary for clinically acceptable aBMD or trabecular BMD values.

Keywords

osteoporosis, bone mineral density, dual-energy CT, material decomposition