Determination of pH using water protons and chemical exchange dependent saturation transfer (CEST)

Ward, Kathleen; Balaban, Robert S.

doi:10.1002/1522-2594(200011)44:5<799::aid-mrm18>3.0.co;2-s

Cited by 370 publications

(400 citation statements)

References 13 publications

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“…Such CEST contrast agents may prove to have some advantages over conventional T 1 -shortening agents because proton exchange is quite sensitive to temperature, pH and other physiologically related parameters, and the CEST contrast effect can be switched on and off using frequency-selective RF presaturation pulses. One disadvantage of the CEST contrast mechanism compared with typical T 1 shortening agents is that the amount of the CEST agent required to produce significant water contrast is unrealistically high (2), although later reports demonstrated that the CEST effect can be amplified using cationic diamagnetic macromolecular systems (polyamino acids and dendrimers) possessing a large number of amide-NH groups (3) or by entrapment of an aqueous shift reagent inside liposomes (4). We and others have demonstrated that the CEST effect also works in certain paramagnetic complexes where exchange between a Ln 3þ -bound water molecule and bulk water is unusually slow.…”

Section: Introductionmentioning

confidence: 99%

Catalytic effects of apoferritin interior surface residues on water proton exchange in lanthanide complexes

Vasalatiy

Zhao

Zhang

et al. 2006

Contrast Media Mol Imaging

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Section: Introductionmentioning

confidence: 99%

Catalytic effects of apoferritin interior surface residues on water proton exchange in lanthanide complexes

Vasalatiy

Zhao

Zhang

et al. 2006

Contrast Media Mol Imaging

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“…To investigate this possibility, we used chemical exchange saturation transfer (CEST) (21)(22)(23) techniques in which selective radio frequency (RF) irradiation of solute protons is detected through progressive saturation of the water signal as a function of time. Because hydroxyl protons exchange rather quickly with solvent protons [exchange rate, k Ͼ 10 3 per s, (24)], saturated hydroxyl spins on glycogen transfer rapidly to the water protons and thereby reduce the intensity of the water signal.…”

mentioning

confidence: 99%

MRI detection of glycogen in vivo by using chemical exchange saturation transfer imaging (glycoCEST)

Zijl

Jones

Ren

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

376

357

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Detection of glycogen in vivo would have utility in the study of normal physiology and many disorders. Presently, the only magnetic resonance (MR) method available to study glycogen metabolism in vivo is 13 C MR spectroscopy, but this technology is not routinely available on standard clinical scanners. Here, we show that glycogen can be detected indirectly through the water signal by using selective radio frequency (RF) saturation of the hydroxyl protons in the 0.5-to 1.5-ppm frequency range downfield from water. The resulting saturated spins are rapidly transferred to water protons via chemical exchange, leading to partial saturation of the water signal, a process now known as chemical exchange saturation transfer. This effect is demonstrated in glycogen phantoms at magnetic field strengths of 4.7 and 9.4 T, showing improved detection at higher field in adherence with MR exchange theory. Difference images obtained during RF irradiation at 1.0 ppm upfield and downfield of the water signal showed that glycogen metabolism could be followed in isolated, perfused mouse livers at 4.7 T before and after administration of glucagon. Glycogen breakdown was confirmed by measuring effluent glucose and, in separate experiments, by 13 C NMR spectroscopy. This approach opens the way to image the distribution of tissue glycogen in vivo and to monitor its metabolism rapidly and noninvasively with MRI.glucose ͉ liver ͉ water imaging ͉ noninvasive

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“…Previous research has demonstrated that the CEST effect of amide and amine groups has a complex relationship with the chemical exchange rate and acidity. 26,27) We previously showed that the CEST asymmetry of the molecules was decreased with increasing pH at 9.4T MRI. 9) The CEST asymmetry values for GABA, Glu, and Gly which contain amine groups were lowest with the highest pH which was consistent with the previous amine group studies, 9,28) which showed the decreased CEST asymmetry values with increasing pH for the amine protons.…”

Section: Cest With Aciditymentioning

confidence: 99%

Physical Modeling of Chemical Exchange Saturation Transfer Imaging

Jahng

2017

Prog Med Phys

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Chemical Exchange Saturation Transfer (CEST) imaging is a method to detect solutes based on the chemical exchange of mobile protons with water. The solute protons exchange with three different patterns, which are fast, slow, and intermediate rates. The CEST contrast can be obtained from the exchangeable protons, which are hydroxyl protons, amine protons, and amide protons. The CEST MR imaging is useful to evaluate tumors, strokes, and other diseases. The purpose of this study is to review the mathematical model for CEST imaging and for measurement of the chemical exchange rate, and to measure the chemical exchange rate using a 3T MRI system on several amino acids. We reviewed the mathematical models for the proton exchange. Several physical models are proposed to demonstrate a two-pool, three-pool, and four-pool models. The CEST signals are also evaluated by taking account of the exchange rate, pH and the saturation efficiency. Although researchers have used most commonly in the calculation of CEST asymmetry, a quantitative analysis is also developed by using Lorentzian fitting. The chemical exchange rate was measured in the phantoms made of asparagine (Asn), glutamate (Glu), γ-aminobutyric acid (GABA), glycine (Gly), and myoinositol (MI). The experiment was performed at a 3T human MRI system with three different acidity conditions (pH 5.6, 6.2, and 7.4) at a concentration of 50 mM. To identify the chemical exchange rate, the "lsqcurvefit" built-in function in MATLAB was used to fit the pseudofirst exchange rate model. The pseudo-first exchange rate of Asn and Gly was increased with decreasing acidity. In the case of GABA, the largest result was observed at pH 6.2. For Glu, the results at pH 5.6 and 6.2 did not show a significant difference, and the results at pH 7.4 were almost zero. For MI, there was no significant difference at pH 5.6 or 7.4, however, the results at pH 6.2 were smaller than at the other pH values. For the experiment at 3T, we were only able to apply 1 s as the maximum saturation duration due to the limitations of the MRI system. The measurement of the chemical exchange rate was limited in a clinical 3T MRI system because of a hardware limitation.

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Determination of pH using water protons and chemical exchange dependent saturation transfer (CEST)

Cited by 370 publications

References 13 publications

Catalytic effects of apoferritin interior surface residues on water proton exchange in lanthanide complexes

Catalytic effects of apoferritin interior surface residues on water proton exchange in lanthanide complexes

MRI detection of glycogen in vivo by using chemical exchange saturation transfer imaging (glycoCEST)

Physical Modeling of Chemical Exchange Saturation Transfer Imaging

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