New synthetic reference signal injection method for absolute quantitation of metabolite concentration

Introduction The ability to quantify metabolites in vivo would improve the diagnosis of human diseases and lead to better understanding of basic physiologic processes. Noninvasive metabolite quantification can be achieved with MR spectroscopy using the synthetic signal injection method, which was previously reported by another research group[1]. The previously reported method originally claimed its feasibility for in vivo applications, but has not been successful to widely apply for in vivo measurements mainly due to significant radiofrequency (RF) radiation effects. In practice, this method is limited to in vitro applications or to small in vivo subject under an RF screening condition. We have developed novel hardware and methodology to inject a synthetic reference signal inductively using a small “tickler coil” that was specially designed and constructed to minimize RF radiation effects. We have tested our approach both in vitro and in human muscle and our results confirm the accuracy and reliability of the method. The technique is relatively straightforward and can be implemented in any MR system.