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Studies of Gd‐DTPA relaxivity and proton exchange rates in tissue
Author(s) -
Donahue Kathleen M.,
Burstein Deborah,
Manning Warren J.,
Gray Martha L.
Publication year - 1994
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910320110
Subject(s) - chemistry , interstitial fluid , proton , relaxation (psychology) , perfusion , magnetization transfer , nuclear magnetic resonance , interstitial space , magnetic resonance imaging , pathology , medicine , physics , quantum mechanics , cardiology , radiology
The image intensity in many contrast agent perfusion studies is designed to be a function of bulk tissue T 1 , which is, in turn, a function of the compartmental (vascular, interstitial, and cellular) T 1 s, and the rate of proton exchange between the compartments. The goal of this study was to characterize the compartmental tissue Gd‐DTPA relaxivities and to determine the proton exchange rate between the compartments. Expressing [Gd‐DTPA] as mmol/liter tissue water, the relaxivities at 8.45 T and room temperature were: saline, 3.87 ± 0.06 (mM. s) −1 (mean ± SE; n = 29); plasma, 3.98 ± 0.05 (mM·s) −1 ( n = 6); and control cartilage (primarily an interstitium), 4.08 f 0.08 (mM·s) −1 ( n = 17), none of which are significantly different. The relexivity of cartilage did not change with compression, trypsinization, or equilibration in plasma, suggesting relaxivity is not influenced by interstitial solid matrix density, charge, or the presence of plasma proteins. T 1 relaxation studies on isolated perfused hearts demonstrated that the cellular‐interstitial water exchange rate is between 8 and 27 Hz, while the interstitial‐vascular water exchange rate is less than 7 Hz. Thus, for Gd‐DTPA concentrations, which would be used clinicallly, the T 1 relaxation rate behavior of intact hearts can be modeled as being in the fast exchange regime for cellular‐interstitial exchange but slow exchange for interstitial‐vascular exchange. A measured relaxivity of 3.82 ± 0.05 (mM·s) −1 (n = 8) for whole blood (red blood cells and plasma) and 4.16 ± 0.02 (mM·s) −1 (n = 3) for frog heart tissue (cells and interstitium) (with T 1 and Gd‐DTPA concentration defined from the total tissue water volume) supports the conclusion of fast cellular‐extracellular exchange. Knowledge of the Gd‐DTPA relaxivity and maintaining Gd‐DTPA concentration in the range so as to maintain fast cellular‐interstitial exchange allows for calculation of bulk Gd‐DTPA concentration from bulk tissue T 1 within a calculable error due to slow vascular exchange.