Studies of 1H-NMR Relaxation Dispersion in Human Brain- tissue Samples: Implications for Magnetic Resonance Relaxation Dispersion Imaging (MARDI)

• Studies of 1H-NMR Relaxation Dispersion in Human Brain- tissue Samples: Implications for Magnetic Resonance Relaxation Dispersion Imaging (MARDI) Bertil R.R. Persson1, Lars Malmgren1,2 and Leif G. Salford3 1Medical Radiation Physics 2MAX Laboratory 3Dept. of Neurosurgery, Lund University, Lund Sweden [Bertil R.R. Persson, Lund University, Dept. of medical radiation physics, Barngatan 2, S-22185 Lund Sweden] bertil_r.persson@med.lu.se Abstract. In order to analyze the relaxation characteristics in fresh human brain tissue and blood samples we studied the proton relaxation rate dispersion in the frequency interval from 0.01 to 10 MHz. With the Field cycling method we apply, the sample is first magnetized in a relatively high magnetic fields (0.5 Tesla), which then by electronic means rapidly (10-3 s) is reduced to lower values (0.0001 - 0.5 Tesla) where the excited proton spin may relax during a time interval of about 3*T1max. Then the magnetic field is again quickly raised up to higher level for the detection of NMR-signal. In order to analyse the relaxation characteristics we applied a model with three compartments of water exchange. For each compartment we estimate a characteristic frequency by fitting the dispersion curves to a sum of Lorentz distributions. The characteristic frequencies thus obyained for various human yissuesater given in the following table. TissueFrequency n1 (low) / kHzFrequency n2 (middle) / kHzFrequency n3 (High) / kHz Whole blood285 7600 Blood plasma37 ± 4220 ± 101480 ± 40 Cerebral Spinal Fluid16 ± 42200 ± 140 Brain Gray Matter18,3 ± 0.3159 ± 21660 ± 20 Brain White Matter16 ± 1170 ± 102700 ± 100 Meningioma23 ±1190 ±102350 ±80 Studying the effect on the relaxation rate dispersion by heat treatment of blood plasma we found a breakpoint in the relaxation rate at 80 ºC The relaxation rate at low frequency 0.02 MHz gives an activation energy of 103 kJ/ mol above the breakpoint at 80 ºC and a very low value of 3.1±0.5 kJ/mol below 80 ºC. There seems to be no effect of Mn2+ after heating to 80 oC. This support the idea that paramagnetic ions has no effect on the firmly bound water in proteins. At room temperature, however, we found that paramagnetic ions (Mn2+) have a great influence on the relaxation rate dispersion in the low frequency region (10 - 20 kHz). Magnetic resonance relaxation dispersion imaging (MARDI) might be useful for imaging of reactive oxygen radicals and oxygen distribution by using paramagnetic or organic free-radical contrast agents. Keywords: field cycling, NMR, relaxation, dispersion, human brain, tissue, paramagnetic,

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

Nyckelord

field cycling

NMR

relaxation

dispersion

human brain

tissue

paramagnetic

Publikations- och innehållstyp

art (ämneskategori)

ref (ämneskategori)