title: Contributions of chemical exchange to T1ρ dispersion in a tissue model.
abstract: Variations in T(1ρ) with locking-field strength (T(1ρ) dispersion) may be used to estimate proton exchange rates. We developed a novel approach utilizing the second derivative of the dispersion curve to measure exchange in a model system of cross-linked polyacrylamide gels. These gels were varied in relative composition of comonomers, increasing stiffness, and in pH, modifying exchange rates. Magnetic resonance images were recorded with a spin-locking sequence as described by Sepponen et al. These measurements were fit to a mono-exponential decay function yielding values for T(1ρ) at each locking-field measured. These values were then fit to a model by Chopra et al. for estimating exchange rates. For low stiffness gels, the calculated exchange values increased by a factor of 4 as pH increased, consistent with chemical exchange being the dominant contributor to T(1ρ) dispersion. Interestingly, calculated chemical exchange rates also increased with stiffness, likely due to modified side-chain exchange kinetics as the composition varied. This article demonstrates a new method to assess the structural and chemical effects on T(1ρ) relaxation dispersion with a suitable model. These phenomena may be exploited in an imaging context to emphasize the presence of nuclei of specific exchange rates, rather than chemical shifts.
authors: Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee 37232-2310, USA. Jared.G.Cobb@Vanderbilt.Edu
authors: Jared G
authors: JG
authors: Cobb
authors: Jingping
authors: J
authors: Xie
authors: John C
authors: JC
authors: Gore
references: J Magn Reson. 1998 Apr;131(2):191-8
references: 9571092
references: Nat Med. 2003 Aug;9(8):1085-90
references: 12872167
references: J Magn Reson B. 1996 Mar;110(3):267-77
references: 8867442
references: Magn Reson Med. 1989 Mar;9(3):325-32
references: 2709998
references: J Comput Assist Tomogr. 1985 Nov-Dec;9(6):1007-11
references: 4056129
references: Magn Reson Med. 1993 Jan;29(1):77-83
references: 8380481
references: Proc Natl Acad Sci U S A. 2001 Oct 23;98(22):12479-84
references: 11606754
references: J Magn Reson. 2004 Sep;170(1):104-12
references: 15324763
references: Proteins. 1993 Sep;17(1):75-86
references: 8234246
references: NMR Biomed. 2000 Jan;13(1):1-7
references: 10668048
references: Biochemistry. 1972 Jan 18;11(2):150-8
references: 5061873
references: Magn Reson Med. 2005 Apr;53(4):830-4
references: 15799043
references: Magn Reson Imaging. 1994;12(2):183-90
references: 8170295
references: PLoS One. 2010 Jan 05;5(1):e8565
references: 20052404
references: Magn Reson Med. 1997 Jan;37(1):53-7
references: 8978632
references: Magn Reson Med. 1996 Jan;35(1):30-42
references: 8771020
references: J Magn Reson. 2007 May;186(1):75-85
references: 17291799
references: J Magn Reson Imaging. 2003 Jan;17(1):114-21
references: 12500280
references: Magn Reson Med. 2005 Apr;53(4):790-9
references: 15799055
references: J Magn Reson. 2000 Mar;143(1):79-87
references: 10698648
references: Magn Reson Med. 1993 Jun;29(6):759-66
references: 8350718