Abstract #2516

Blockley N, Francis S, Gowland P

The dependence of the transverse relaxation rate, R2*, of blood on oxygenation and contrast agent concentration ([CA]) has been measured at 3T. A linear fit to a plot of R2* versus deoxyhaemoglobin content yielded R2*=122.0(1-Y)+7.0, although a quadratic function provided a better fit. The relaxivity of CA was found to be (-2.741.23)x10-4 s-1 M-1 (Y~0.4) for concentrations up to 1mM (i.e. R2* was observed to decrease with increasing [CA]). Additional experiments at higher oxygenation and at higher [CA] showed that the quoted relaxivity reversed at a certain [CA]. An explanation for this result is suggested.