Measurement of spin-lattice relaxation times and chemical exchange rates in multiple-site systems using progressive saturation

✍ Scribed by Craig J. Galbán; Richard G. Spencer

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 230 KB
• Volume: 58
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.21185

✦ Synopsis

Abstract

A new method for measuring spin‐lattice relaxation times and chemical exchange (CE) rate constants in multiple‐site exchanging systems is described. The method, chemical exchange and T~1~ measurement using progressive saturation (CUPS), was applied to determine T~1~s and analyze phosphorus exchange among phosphocreatine (PCr), ATP, and inorganic phosphate (Pi), mediated by creatine kinase (CK) and ATP synthase, using ^31^P‐MRS. Two‐site exchange was analyzed in vitro and in the rat leg, and three‐site exchange was analyzed in the rat heart. Data were fitted to a model of progressive saturation incorporating T~1~ relaxation and CE. For the in vitro system at 8.45T, we found T~1~(PCr) = 2.86 s and T~1~(γ‐ATP) = 1.72 s. For the rat gastrocnemius at 1.9T, we found T~1~(PCr) = 6.60 s and T~1~(γ‐ATP) = 2.06 s. For the rat heart at 9.4T, we found T~1~(PCr) = 3.35 s, T~1~(γ‐ATP) = 0.69 s, and T~1~(Pi) = 1.83 s. All of these values were within 20% of literature values. Similarly, the determined exchange rates were in the same range as published values. Using simulations, we compared CUPS with transient saturation transfer as a method for measuring T~1~s and rates. The two methods showed similar sensitivity to noise. We conclude that CUPS is a viable alternative for measuring T~1~s and CE rates in exchanging systems. Magn Reson Med 58:8–18, 2007. © 2007 Wiley‐Liss, Inc.