Investigating The Coherent Normalization Method For A Bone Gadolinium X-ray Fluorescence Measurement System: A Monte Carlo Study

Abstract

Elevated gadolinium levels in patients with healthy renal function exposed to gadolinium based contrast agents (GBCA) have been confirmed by studies in the literature. Though the potential long-term effects of the retained gadolinium are still unknown, symptoms such as bone and joint pain have been reported in some subjects. As detecting the presence of gadolinium in vivo is required to diagnose toxicity related medical conditions, a 109Cd based X-ray fluorescence (XRF) bone gadolinium measurement system has been previously developed. The current method is dependent on geometrical factors and other interpatient factors, such as the size and shape of the bone and the tissue thickness overlying the measurement site, which reduces the robustness of the measurement system and causes the need for correction factors. It was previously shown that the successful use of the coherent normalization procedure can eliminate the need for such corrections and is conditional on four criteria that must be met. When detecting gadolinium two of the four criteria are not satisfied which makes further investigation of the method required. This work investigates the feasibility of the coherent normalization method to correct for the effect of varying overlying tissue thickness of an adult population through Monte Carlo simulations. The coherent normalization method was studied as a function of overlying tissue thickness (OTT) to represent varying body types. The average coherent ratio (Gd K X-ray counts/Coherent counts) was found to be 0.717 ± 0.025 and the normalization resulted in a line with a slope of -0.0053± 0.0040 which is insignificant at the 95% confidence level (p = 0.43) suggesting the validity of the method. Additionally, this thesis provides a theoretical explanation of the feasibility of the method regardless of not fulfilling all four criteria, through introducing the Secondary Fluence Fluorescence Factor (SFFF) and separating fluence components, primary and secondary, contributing to the fluorescence of gadolinium.