High-resolution Phosphocreatine and Creatine Mapping of Human Muscle and Brain

In this study, we aim to develop and validate a noninvasive approach for quantifying and imaging energy metabolism, without contrast agents, on widely available clinical MRI scanners. Briefly, this technique allows specific and selective imaging of the energy metabolite phosphocreatine (PCr), in vivo and non-invasively. PCr is one of the predominant high-energy phosphates present in brain and muscle and one that is altered by common diseases. Although energy metabolism and PCr play a vital role in cellular homeostasis, there currently are no routine diagnostic tests to noninvasively quantify or map the distribution of PCr with clinically acceptable spatial resolution or/and scan time. Here, we demonstrate that the exchangeable guanidinium protons of millimolar concentration PCr can be exploited to detect it via the water signal in MRI with greatly enhanced sensitivity (molar signal) using chemical exchange saturation transfer (CEST) MRI, and its concentration can be quantified using an artificial neural network (ANN). This new technique, dubbed ANNCEST, allowed us to obtain a high-resolution PCr map on human skeletal muscle within 1.5 min, on a 3T clinical MRI scanner equipped with just the standard MRI setup. To put this in a larger perspective, energy metabolism is critical for cell viability and is altered by many common acquired and inherited diseases. ANNCEST is arguably the first to use widely available MRI scanners to noninvasively image tissue energy metabolism of PCr, and thus would have appeal to a broad readership of scientists and clinicians interested in neurology, muscular dystrophies and myopathies as well as cardiology, to name a few.