title: Integrated Bloch-Siegert B₁ mapping and multislice imaging of hyperpolarized ¹³C pyruvate and bicarbonate in the heart.
abstract: Hyperpolarization of (13) C labeled substrates via dynamic nuclear polarization has been used as a method to noninvasively study real-time metabolic processes occurring in vivo. In these studies, proper calibration of radiofrequency transmit power is required to efficiently observe rapidly decaying magnetization. Conventional transmit radiofrequency field (B₁⁺) mapping methods rely on placing magnetization in a fixed, known state prior to imaging, making them unsuitable for imaging of hyperpolarized magnetization. Recently, a phase-based B(1) mapping method based on the Bloch-Siegert shift has been reported. This method uses a B(1) -dependent shift in the resonance frequency of nuclei in the presence of an off-resonance radiofrequency pulse. In this article, we investigate the feasibility of Bloch-Siegert B(1) mapping and observation of metabolism of hyperpolarized [1-¹³C] pyruvate in vivo, in a single injection. The technique is demonstrated with phantom experiments, and in normal rat and pigs in vivo. This method is anticipated to improve quantitative measurements of hyperpolarized (13) C metabolism in vivo by enabling accurate flip-angle corrections. This work demonstrates the use of Bloch-Siegert B(1) mapping under challenging out-of-equilibrium imaging conditions.
authors.affiliation: Department of Medical Biophysics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada. angus.lau@sri.utoronto.ca
authors.forename: Angus Z
authors.initials: AZ
authors.lastname: Lau
authors.forename: Albert P
authors.initials: AP
authors.lastname: Chen
authors.forename: Charles H
authors.initials: CH
authors.lastname: Cunningham
mesh_terms: D000465:Algorithms; D000818:Animals; D001639:Bicarbonates / Q000032:analysis*; D006321:Heart / Q000033:anatomy & histology; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D009206:Myocardium / Q000378:metabolism*; D019289:Pyruvic Acid / Q000032:analysis*; D051381:Rats; D011923:Rats, Nude; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D018511:Systems Integration; D014018:Tissue Distribution
chemical_list: D001639:Bicarbonates; D019289:Pyruvic Acid