Transverse relaxation rate enhancement caused by magnetic particulates

Magnetic particulates have been shown to be powerful transverse relaxation enhancers and are under consideration as an MR contrast agent for the detection of liver and spleen lesions. This work describes the magnetic properties of a commercially available magnetic particulate and a Monte Carlo simulation of the effect of these particles on the transverse relaxation rates of water protons for spin-echo experiments. From the simultations, empirical relations were developed to describe the dependence of the enhancement of particle size, and concentration as well as the diffusion constant of water and the pulse spacing of a Carr-Purcell-Meiboom-Gill pulse sequence used to measure the transverse relaxation time. The simulations are shown to agree with measurements of relaxation rates in agar samples containing the magnetic particulates.