System for automated magnetic resonance imaging of a superheated emulsion chamber for brachytherapy dosimetry

Abstract

This manuscript describes a pressure cycling and brachytherapy source insertion/removal system developed to automate magnetic resonance imaging (MRI) of a superheated emulsion chamber (SEC), a position-sensitive radiation dosimeter. Previous MRI studies of a SEC demonstrated its efficacy for obtaining two-dimensional relative radiation dose profiles from brachytherapy sources. The SEC detector is a 0.5 l chamber containing an emulsion of highly superheated halocarbon droplets suspended in a tissue-equivalent glycerin-based gel. When irradiated by a source, the halocarbon droplets vaporize into microbubbles. Relative dose profiles are determined by mapping, via MRI, the resulting microbubble distributions. During use the SEC is repeatedly cycled through a series of steps including source insertion, exposure, and source removal, MRI data collection, and chamber pressurization and depressurization. To acquire microbubble counts sufficient to derive dose profiles having good statistics, it is necessary to collect hundreds of MRI data sets as the SEC is cycled. Clearly, automation of SEC cycling is essential for its practical use as a radiation dosimeter. The operations required to use the SEC as a radiation dosimeter have been fully automated on a commercial 3.0 T MRI scanner. The hardware and software developed to achieve automated cycling of a SEC are described. Microbubble distributions and calculated microbubble density maps generated from MRI data collected while cycling a SEC are presented to demonstrate the utility of the automated system.