³¹P magnetic resonance fingerprinting for rapid quantification of creatine kinase reaction rate in vivo

Abstract

Purpose To develop a 31P spectroscopic magnetic resonance fingerprinting (MRF) method for fast quantification of the chemical exchange rate between phosphocreatine (PCr) and ATP via creatine kinase (CK). Methods A 31P MRF sequence (CK-MRF) was developed to quantify the forward rate constant of ATP synthesis via CK ( kfCK), the T1 relaxation time of PCr ( T1PCr), and the PCr-to-ATP concentration ratio ( MRPCr). The CK-MRF sequence used a bSSFP-type excitation with ramped flip angles and a unique saturation scheme sensitive to the exchange between PCr and γATP. Parameter estimation was accomplished by matching the acquired signals to a dictionary generated using the Bloch-McConnell equation. Simulation studies were performed to examine the susceptibility of the CK-MRF method to several potential error sources. The accuracy of nonlocalized CK-MRF measurements before and after an ischemia-reperfusion (IR) protocol was compared to magnetization transfer (MT-MRS) method in rat hindlimb at 9.4 T (n=17). Reproducibility of CK-MRF was also assessed by comparing CK-MRF measurements to both MT-MRS (n=17) and four angle saturation transfer (FAST) methods (n=7). Results Simulation results showed that CK-MRF quantification of kfCK was robust with <5% error in the presence of model inaccuracies including dictionary resolution, metabolite T2 values, Pi metabolism, and B1 miscalibration. Estimation of kfCK by CK-MRF (0.38±0.02 s−1 at baseline and 0.42±0.03 s−1 post-IR) showed strong agreement with MT-MRS (0.39±0.03 s−1 at baseline and 0.44±0.04 s−1 post-IR). kfCK estimation was also similar between CK-MRF and FAST (0.38±0.02 s−1 for CK-MRF and 0.38±0.11 s−1 for FAST). The coefficient of variation from 20-s CK-MRF quantification of kfCK was 42% of that by 150-s MT-MRS acquisition and was 12% of that by 20-s FAST acquisition. Conclusion This study demonstrates the potential of a 31P spectroscopic MRF framework for rapid, accurate and reproducible quantification of chemical exchange rate of CK in vivo.

Improved MR fingerprinting for relaxation measurement in the presence of semisolid magnetization transfer

“…Therefore, MT needs to be considered because it may affect MRF signal evolution. Previously, a modified Bloch‐McConnell model was used to analyze MT in chemical exchange . In this work, the Bloch‐McConnell model was applied to analyzing the MT between bulk free water and semisolid macromolecule protons, and the results showed that there were nonnegligible biases when using 1P and 2P models (Figure A).…”

“…The measurement is then compared against a simulated dictionary to determine the best matching relaxation rates. MRF has been extended to a host of applications, including perfusion, exchange rate, chemical exchange saturation transfer measurements, and simultaneous imaging of multiple MRI contrast agents . It is worth mentioning that modeling biological tissue often involves more than 1 spin pool (i.e., the bulk tissue water, semisolid macromolecules, and/or dilute mobile proteins and peptides) .…”

Optimal Experiment Design for Magnetic Resonance Fingerprinting: Cramér-Rao Bound Meets Spin Dynamics

“…With a larger search space of acquisition parameters, we could achieve better performance, although the resulting optimization problem will be computationally more expensive. Additionally, we could optimize MR fingerprinting experiments to include other tissue parameters, such as apparent diffusion coefficients [66], magnetization transfer [67], [68], etc. Lastly, although the implementation in this paper focused on optimizing the CRB for a fixed number of TRs, there are many other design considerations (e.g., acoustic characteristics of the pulse sequence [69], SAR, total acquisition time, etc), which are important and may be worth including within the optimization framework.…”

Assessing tissue metabolism by phosphorous-31 magnetic resonance spectroscopy and imaging: a methodology review

“…Given the multi-parameter nature of 31 P MT-MRS measurements, and the similarity in measuring T 1 and the exchange-rate modulated T 1app constant in an MT-MRS experiment, an MRF-based MT-MRS method may overcome the low sensitivity and long acquisition time of the conventional 31 P MT-MRS methods. In a recent study, Wang et al developed an MRF-based acquisition strategy for quantification of CK activity (CK-MRF) in rat skeletal muscle (124). Their results showed significantly improved measurement reproducibility in 20-s data acquisition, demonstrating the potential of this new MT encoding strategy.…”