TY - JOUR
T1 - Influence of water based embedding media composition on the relaxation properties of fixed tissue
AU - Vučković, Ivan
AU - Nayfeh, Tarek
AU - Mishra, Prasanna K.
AU - Periyanan, Sigapriya
AU - Sussman, Caroline R.
AU - Kline, Timothy L.
AU - Macura, Slobodan
N1 - Funding Information:
This study was in part supported by the Mayo Translational Polycystic Kidney Disease Center (NIDDK P30 DK090728 ). Appendix A
PY - 2020/4
Y1 - 2020/4
N2 - Background: In MRI of formalin-fixed tissue one of the problems is the dependence of tissue relaxation properties on formalin composition and composition of embedding medium (EM) used for scanning. In this study, we investigated molecular mechanisms by which the EM composition affects T2 relaxation directly and T1 relaxation indirectly. Objective: To identify principal components of formaldehyde based EM and the mechanism by which they affect relaxation properties of fixed tissue. Methods: We recorded high resolution 1H NMR spectra of common formalin fixatives at temperatures in the range of 5 °C to 45 °C. We also measured T1 and T2 relaxation times of various organs of formalin fixed (FF) zebrafish at 7 T at 21 °C and 31 °C in several EM with and without fixative or gadolinium contrast agents. Results: We showed that the major source of T2 variability is chemical exchange between protons from EM hydroxyls and water, mediated by the presence of phosphate ions. The exchange rate increases with temperature, formaldehyde concentration in EM and phosphate concentration in EM. Depending on which side of the coalescence the system resides, the temperature increase can lead to either shortening or prolongation of T2, or to no noticeable change at all when very close to the coalescence. Chemical exchange can be minimized by washing out from EM the fixative, the phosphate or both. Conclusion: The dependence of T2 in fixed tissue on the fixative origin and composition described in prior literature could be attributed to the phosphate buffer accelerated chemical exchange among the fixative hydroxyls and the tissue water. More consistent results in the relaxation measurements could be obtained by stricter control of the fixative composition or by scanning fixed tissue in PBS without fixative.
AB - Background: In MRI of formalin-fixed tissue one of the problems is the dependence of tissue relaxation properties on formalin composition and composition of embedding medium (EM) used for scanning. In this study, we investigated molecular mechanisms by which the EM composition affects T2 relaxation directly and T1 relaxation indirectly. Objective: To identify principal components of formaldehyde based EM and the mechanism by which they affect relaxation properties of fixed tissue. Methods: We recorded high resolution 1H NMR spectra of common formalin fixatives at temperatures in the range of 5 °C to 45 °C. We also measured T1 and T2 relaxation times of various organs of formalin fixed (FF) zebrafish at 7 T at 21 °C and 31 °C in several EM with and without fixative or gadolinium contrast agents. Results: We showed that the major source of T2 variability is chemical exchange between protons from EM hydroxyls and water, mediated by the presence of phosphate ions. The exchange rate increases with temperature, formaldehyde concentration in EM and phosphate concentration in EM. Depending on which side of the coalescence the system resides, the temperature increase can lead to either shortening or prolongation of T2, or to no noticeable change at all when very close to the coalescence. Chemical exchange can be minimized by washing out from EM the fixative, the phosphate or both. Conclusion: The dependence of T2 in fixed tissue on the fixative origin and composition described in prior literature could be attributed to the phosphate buffer accelerated chemical exchange among the fixative hydroxyls and the tissue water. More consistent results in the relaxation measurements could be obtained by stricter control of the fixative composition or by scanning fixed tissue in PBS without fixative.
KW - Chemical exchange
KW - Formalin concentration
KW - Formalin fixation
KW - Labile protons
KW - Relaxation properties of formalin
KW - Tissue MRI
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U2 - 10.1016/j.mri.2019.11.019
DO - 10.1016/j.mri.2019.11.019
M3 - Article
C2 - 31821849
AN - SCOPUS:85076043405
VL - 67
SP - 7
EP - 17
JO - Magnetic Resonance Imaging
JF - Magnetic Resonance Imaging
SN - 0730-725X
ER -