Contrast agents used in cardiovascular magnetic resonance imaging: current issues and future directions

Selective magnetic resonance imaging of magnetic nanoparticles by acoustically induced rotary saturation

PURPOSE

The goal of this study was to introduce a new method to selectively detect iron oxide contrast agents using an acoustic wave to perturb the spin-locked water signal in the vicinity of the magnetic particles. The acoustic drive can be modulated externally to turn the effect on and off, allowing sensitive and quantitative statistical comparison and removal of confounding image background variations.

METHODS

We demonstrated the effect in spin-locking experiments using piezoelectric actuators to generate vibrational displacements of iron oxide samples. We observed a resonant behavior of the signal changes with respect to the acoustic frequency where iron oxide is present. We characterized the effect as a function of actuator displacement and contrast agent concentration.

RESULTS

The resonant effect allowed us to generate block-design "modulation response maps" indicating the contrast agent's location, as well as positive contrast images with suppressed background signal. We found that the acoustically induced rotary saturation (AIRS) effect stayed approximately constant across acoustic frequency and behaved monotonically over actuator displacement and contrast agent concentration.

CONCLUSION

AIRS is a promising method capable of using acoustic vibrations to modulate the contrast from iron oxide nanoparticles and thus perform selective detection of the contrast agents, potentially enabling more accurate visualization of contrast agents in clinical and research settings.

Sensing lanthanide metal content in biological tissues with magnetic resonance spectroscopy

The development and validation of MRI contrast agents consisting of a lanthanide chelate often requires a determination of the concentration of the agent in ex vivo tissue. We have developed a protocol that uses 70% nitric acid to completely digest tissue samples that contain Gd(III), Dy(III), Tm(III), Eu(III), or Yb(III) ions, or the MRI contrast agent gadodiamide. NMR spectroscopy of coaxial tubes containing a digested sample and a separate control solution of nitric acid was used to rapidly and easily measure the bulk magnetic susceptibility (BMS) shift caused by each lanthanide ion and gadodiamide. Each BMS shift was shown to be linearly correlated with the concentration of each lanthanide ion and gadodiamide in the 70% nitric acid solution and in digested rat kidney and liver tissues. These concentration measurements had outstanding precision, and also had good accuracy for concentrations ≥10 mM for Tm(III) Eu(III), and Yb(III), and ≥3 mM for Gd(III), gadodiamide, and Dy(III). Improved sample handling methods are needed to improve measurement accuracy for samples with lower concentrations.

Gadobutrol: a review of its use for contrast-enhanced magnetic resonance imaging in adults and children

Since the introduction of the first gadolinium-based contrast agent (GBCA) approximately 25 years ago, magnetic resonance imaging (MRI) using GBCAs has revolutionized diagnostic and follow-up imaging of pathological lesions, with clinical applications expanded to encompass almost all fields of medicine. Intravenous gadobutrol (Gadovist™ [EU]; Gadavist(®) [USA]) is a second-generation extracellular non-ionic macrocyclic GBCA that is used in patients undergoing diagnostic contrast-enhanced MRI for visualization of pathological lesions in the CNS and all other body regions or for contrast-enhanced magnetic resonance angiography (MRA) to evaluate perfusion and flow-related abnormalities. Its unique physicochemical profile, along with the high thermostability of macrocyclic GBCAs, means gadobutrol is formulated at twice the gadolinium ion concentration of other currently licensed GBCAs. This reduces the injection volume and provides a narrower bolus, thereby improving image enhancement. Based on extensive clinical experience in a broad range of patients, including paediatric and adult patients (younger and elderly adults), and those with moderate to severe hepatic or renal impairment or cardiovascular disorders, gadobutrol is an effective and generally well tolerated extracellular GBCA for patients undergoing diagnostic contrast-enhanced MRI and contrast-enhanced MRA. As with all macrocyclic GBCAs, the potential for gadobutrol to cause nephrogenic systemic fibrosis appears to be lower than with linear GBCAs.