19F MRSI of capecitabine in the liver at 7T using broadband transmit-receive antennas and dual-band RF pulses

Abstract

Capecitabine (Cap) is an often prescribed chemotherapeutic agent, successfully used to cure some patients from cancer or reduce tumor burden for palliative care. However, the efficacy of the drug is limited, it is not known in advance who will respond to the drug and it can come with severe toxicity. ¹⁹F Magnetic Resonance Spectroscopy (MRS) and Magnetic Resonance Spectroscopic Imaging (MRSI) have been used to non-invasively study Cap metabolism in vivo to find a marker for personalized treatment. In vivo detection, however, is hampered by low concentrations and the use of radiofrequency (RF) surface coils limiting spatial coverage. In this work, the use of a 7T MR system with radiative multi-channel transmit-receive antennas was investigated with the aim of maximizing the sensitivity and spatial coverage of ¹⁹F detection protocols. The antennas were broadband optimized to facilitate both the ¹H (298MHz) and ¹⁹F (280MHz) frequencies for accurate shimming, imaging and signal combination. B<inf>1</inf>⁺ simulations, phantom and noise measurements showed that more than 90% of the theoretical maximum sensitivity could be obtained when using B<inf>1</inf>⁺ and B<inf>1</inf>^- information provided at the ¹H frequency for the optimization of B<inf>1</inf>⁺ and B<inf>1</inf>^- at the ¹⁹F frequency. Furthermore, to overcome the limits in maximum available RF power, whilst ensuring simultaneous excitation of all detectable conversion products of Cap, a dual-band RF pulse was designed and evaluated. Finally, ¹⁹F MRS(I) measurements were performed to detect ¹⁹F metabolites in vitro and in vivo. In two patients, at 10h (patient 1) and 1h (patient 2) after Cap intake, ¹⁹F metabolites were detected in the liver and the surrounding organs, illustrating the potential of the set-up for in vivo detection of metabolic rates and drug distribution in the body.