Susceptibility-Based Positive-Contrast MRI for Brachytherapy Seed Identification

For a number of reasons, MRI is preferred for brachytherapy imaging. However, due to the high susceptibility of the seeds and the lack of protons, brachytherapy seeds and the surrounding tissues usually show as enlarged dark spots (negative contrast) on the MR images. Many methods have been proposed to create positive contrast in the surrounding tissues (but not in the seeds) based on the susceptibility-induced field change. This paper proposes a new method to image the brachytherapy seeds by deriving the susceptibility distribution. The method is based on an improved, sparsity-promoting, kernel deconvolution algorithm. Experimental results show the proposed method can provide localization of the seed itself, rather than the surrounding tissues, and it gives an effective positive contrast to the seeds. In addition, the proposed method is also able to identify and differentiate the seeds from other less-susceptible objects.

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