Abstract
Recently, there has been a renewed interest in low-field MRI. Contrast agents (CA) in MRI have magnetic behavior dependent on magnetic field strength. Therefore, the optimal contrast agent for low-field MRI might be different from what is used at higher fields. Ultra-small superparamagnetic iron-oxides (USPIOs), commonly used as negative CA, might also be used for generating positive contrast in low-field MRI. The purpose of this study was to determine whether an USPIO or a gadolinium based contrast agent is more appropriate at low field strengths. Relaxivity values of ferumoxytol (USPIO) and gadoterate (gadolinium based) were used in this research to simulate normalized signal intensity (SI) curves within a concentration range of 0-15 mM. Simulations were experimentally validated on a 0.25T MRI scanner. Simulations and experiments were performed using spin echo (SE), spoiled gradient echo (SGE), and balanced steady-state free precession (bSSFP) sequences. Maximum achievable SIs were assessed for both CAs in a range of concentrations on all sequences. Simulations at 0.25T showed a peak in SIs at low concentrations ferumoxytol versus a wide top at higher concentrations for gadoterate in SE and SGE. Experiments agreed well with the simulations in SE and SGE, but less in the bSSFP sequence due to overestimated relaxivities in simulations. At low magnetic field strengths, ferumoxytol generates similar signal enhancement at lower concentrations than gadoterate.
Highlights
Contrast agents (CAs) have been used in MRI for decades with a great use for angiographic purposes [1]
The magnetic field inhomogeneities due to the highly paramagnetic samples cause banding artefacts to appear in the balanced steady-state free precession (bSSFP) scans of the ferumoxytol samples
For ferumoxytol we found an r1 of 40.3 mM-1 s-1 and an r2 of 259.5 mM-1 s-1 at 0.25T
Summary
Contrast agents (CAs) have been used in MRI for decades with a great use for angiographic purposes [1]. Cardiovascular diseases as peripheral arterial disease, aortic aneurysms, and cardiomyopathy benefit from enhanced imaging possibilities due to CA administration with excellent signal-to-noise (SNR) ratios. Gadolinium based contrast agents (GBCAs) are used for generating positive contrast in millions of MRI examinations because of their unique magnetic properties [2]. An important characteristic of CAs in MRI is that their effect depends on the used field strength [3]. At lower magnetic field strengths the molecular tumbling rate is reduced which increases effect of a T1 CA [4].
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