David Thomasson, Presenter: Nothing to Disclose

Marcelino Bernardo, Abstract Co-Author: Nothing to Disclose

Andy Srikanchana, Abstract Co-Author: Nothing to Disclose

Gregory John Metzger PhD, Abstract Co-Author: Nothing to Disclose

Srirama Swaminathan PhD, Abstract Co-Author: Nothing to Disclose

Peter L. Choyke MD, Abstract Co-Author: Nothing to Disclose

Ahmed Medhat Gharib MBCHB, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Obtaining good measures of Gadolinium concentration are necessary for kinetic modeling of Dynamic Contrast Enhanced MRI “DCE-MRI” perfusion data. Simple equations using baseline T1 are accepted methods for determining the conversion of measured signal intensity to Gd-DTPA concentration but recent studies suggest simple T1 corrections to measured data does not account for changes in contrast agent relaxivity as a function of macromolecular content. It has been shown that higher concentrations of various macromolecular structures in a given substrate significantly increase Gd relaxivity that would overestimate contrast agent concentrations. Here we use MT ratios (MTR) as a separate measure of macromolecular content and then use this ratio to determine a more relevant relaxivity value.

We used a multi-vial phantom constructed of various macromolecular concentrations (milk solids) with varying concentrations of Gd-DTPA. A 3 Tesla Philips Intera whole body system is used with a multi-channel Synergy head coil. T1 data are derived using a 2 point variable flip angle 3D Spoiled Gradient Echo (T1 FFE) acquisition method. Magnetization Transfer Ratios are determined using two 3D T1-FFE acquisitions one with and one without off resonance MT pulse. All data is processed with an off-line post processing software.

Relaxivity values are calculated for each set of macromolecular samples and plotted against calculated MTR to derive a relaxivity correction table. Macromolecular samples with no Gadolinium are used as the base T1 and subsequent higher Gd concentration data is calculated with and without the corrected relaxivity data. With this method we show that using MTR correlated relaxivity values improve the calculated Gd concentration by 23% compared to using only T1 corrected data.

To get accurate Gd concentration information in in-vivo systems it is important to correct for relaxivity variability based on macromolecular content. Correction factors to relaxivity can be determined using independently correlated MTR. This method should improve measures of Gadolinium concentration for subsequent DCE-MRI kinetic analysis.

G.J.M.,S.S.: Employee Philips Medical Systems

Thomasson, D, Bernardo, M, Srikanchana, A, Metzger, G, Swaminathan, S, Choyke, P, Gharib, A, et al, , Improved Quantification of Gadolinium Contrast Agent Concentrations Using MTR Derived Relaxivity Data for DCE-MRI at 3 Tesla.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4404198.html