Preferably such experiments should be performed with a short TR and an appropriate FA to maximize the SNR per unit acquisition time.
Atp production full#
In addition, full relaxation requirement results in very long TR because the T 1s of the 31P metabolites are characteristically long, 20 which leads to a prohibitively lengthy total acquisition time for studies requiring higher spatial or temporal discrimination. The conventional steady-state MST experiment is inefficient in terms of signal to noise (SNR) per unit acquisition time because of the full relaxation prerequisite for both M 0 and M ss measurements. T 1 nom Method for Extremely Rapid k f Measurement and Quantification 13ĭetailed descriptions of different types of T 1 are included in the Online Data Supplement, available at. Finally, the T 1 nom method was used to measure the myocardial CK forward rate constant with transmural differentiation, demonstrating a reduction of data acquisition time by 91% as compared with a similar study using conventional saturation transfer method. The new method is verified experimentally with in vivo measurements of: (1) k f ,CK on swine heart model during the process of CK inhibition by iodoacetamide (IAA) infusion and (2) both k f ,CK and k f ,ATPase on rat brain model at rest condition. In addition, an optimization strategy for finding the best acquisition parameter range (TR and FA) used in the T 1 nom method is provided. The T 1 nom method is theoretically validated based on numeric simulation of modified Bloch–McConnell equations that govern the evolution of spin magnetizations during MST experiment. The accurate quantification of k f under such partial relaxation conditions requires only 2 spectra. In the present study, we demonstrate a novel steady-state MST method (T 1 nom) for performing extremely rapid measurements of CK and ATPase kinetics with arbitrary repetition time and flip angle (FA). 11 We have recently reported an improved MST method for measuring CK kinetics with as few as 3 spectra, 12 the method focused on minimizing the saturation time by optimizing the presaturation delay, which resulted in a significant reduction of repetition time. 11 This method was later used by Weiss et al in patients to examine the myocardial CK reaction kinetics. To compensate the lengthy data acquisition time imposed by conventional MST technique, Bottomley et al proposed a four-angle saturation transfer (FAST) method, allowing rapid in vivo measurement of CK reaction rates with 4 short-repetition time (TR) spectra. 10 In contrast, in heart it was found that CK forward flux rate was independent from the increase of cardiac workloads in response to catecholamine stimulations. 9 In addition, the CK activity in the visual cortex of human brain was increased during visual simulation. 6 – 8 The cerebral ATP metabolic rate through ATPase has been demonstrated to be tightly coupled to brain activity level in a rat model. For example, significantly lowered ATP production rates via CK have been observed in association with various heart diseases in both large animal models 4, 5 and patients. 3 – 5 Previous studies have suggested that the kinetics of the PCr↔ATP↔Pi exchange network may be associated with the pathological status of the organ. The exchange rates of CK and ATPase reactions have been extensively studied on various organs, such as heart, brain, and skeletal muscle. 1, 2 Therefore, the kinetics of PCr↔ATP↔Pi chemical exchange can be characterized by 2 forward pseudo–first-order rate constants ( k f ,CK for PCr→ATP and k f ,ATPase for Pi→ATP) and studied by 31P magnetization saturation transfer (MST) experiment, where ATPγ resonance is selectively saturated. Under most in vivo circumstances, a steady-state condition is established, resulting in equal forward and reverse fluxes for both CK and ATPase reactions. Where k f and k r are the pseudo–first-order forward and reverse rate constants for CK and ATPase reactions. PCr ⇄ k r,CK k f,CK ATP ⇄ k f,ATPase k r,ATPase Pi
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