The magnetic field dependence of water proton T₁ in aqueous solutions: Implications for magnetic imaging contrast media

Abstract

The magnetic field dependence of the water proton nuclear magnetic relaxation induced by a nitroxide radical both free and covalently bound to serum albumin has been measured from 0.23 mT to 0.7 T. The field dependence of the water proton 1/T1 shows only a minor dependence on the degree of radical immobilization, though the electron spin resonance (ESR) spectrum is very sensitive to the correlation time of the radical. The results and theory are described in more detail elsewhere (Journal of Chemical Physics, in press). The observed relaxation behavior arises because the long electron relaxation time of the nitroxide forces the correlation time for the magnetic interaction driving the water proton relaxation to become the correlation time for the relative translational motion of the water and the nitroxide. The relative insensitivity of the water proton relaxation to nitroxide immobilization should not change if the nitroxide is used as a contrast reagent for magnetic imaging in vivo.

Incorporating Blood Flow in Nerve Injury and Regeneration Assessment

“…One challenge for assessment is the absence of a gold-standard measurement technique to determine blood flow in the nervous system. Studies have used a variety of techniques ( Table 1 ), including intravital microscopy ( 49 ), hydrogen clearance (HC) ( 13 , 80 – 82 ), laser Doppler flowmetry ( 42 , 48 , 83 – 85 ), ultrasound ( 86 – 88 ), and numerous magnetic resonance imaging (MRI) sequences, including arterial spin labeling ( 89 , 90 ), dynamic contrast enhancement (DCE) ( 91 , 92 ), phase contrast ( 93 , 94 ), blood oxygenation level–dependent (BOLD) ( 95 , 96 ), and intravoxel incoherent motion (IVIM) ( 97 ). HC measures hydrogen gas washout via electrode probe, whereas laser Doppler and ultrasound work by measuring frequency shift from reflected light or sound from moving red blood cells; these all require close proximity or direct contact of the probe head with the nerve.…”