David Gultekin PhD, Presenter: Nothing to Disclose

Tom Raidy PhD, Abstract Co-Author: Nothing to Disclose

Purpose/Objective: Gadolinium complexes are used in-vivo as contrast agents in magnetic resonance imaging. In contrast MRI, gadolinium complexes affect the spin-lattice (T1) and spin-spin (T2) relaxation times and the effects are largely observed on T1 relaxation in-vivo when administered intravenously at prescribed doses of 0.1 mmol/kg. The mean distribution and elimination half-lives of these contrast agents are typically 0.2h and 1.6h, respectively. Currently, MR imaging and spectroscopy are being investigated for both diagnosis and monitoring of the treatment of tumors and cancer in radiation oncology. Any radiation induced changes in the MR properties of the contrast agents could affect the accuracy of these methods in oncology. It is then important to quantify the effects of radiation dose on contrast agents in MRI/MRS to assess the variations in pre and post treatment measurements. We experimentally investigate the effects of radiation on dilute aqueous solutions of two different gadolinium contrast agents (registered as Magnevist, Berlex Labs. and ProHance, Bracco Inc.) and a phantom containing metabolites using the MRI/MRS. The phantom has aqueous solution of in-vivo concentrations of N-acetylaspartate, Creatine, Choline, myo-inositol doped with 0.1% GdDPTA, Gd-diethylenetriamine pentaacetic acid. The Magnevist is a gadolinium complex of 1-deoxy-1-(methylamino)-D-glucitol dihydrogen [N,N-bis[2-[bis(carboxymethyl)amino]ethyl]-glycinato-(5-)-]gadolinate(2--)(2:1) with a molecular weight of 938 and ProHance is a gadolinium complex of 10-(2-hydroxy-propyl)- 1,4,7,10 -tetraazacyclododecane- 1,4,7 -triacetic acid with a molecular weight of 558.7. The concentrations of both gadolinium complexes are 0.5M in aqueous solutions. Materials/Methods: The aqueous solutions of 0.1% v/v concentrations of both gadolinium complexes and metabolites of in-vivo concentrations were irradiated using a Varian Clinac 21EX linear accelerator and analyzed in a head coil on a GE 1.5 Tesla MRI/S System. The radiation doses of 10, 20 and 30 Gy were delivered to the solutions using a beam energy of 6 MV. The irradiated solutions along with controls were examined in MRI/MRS with a multi-echo SE sequence (TE/TR 15,20/6000), a GRE sequence (TE/TR 3.4/300-6000, 8) and a PRESS sequence (TE/TR 35/1500, 8 phase-cycle). Results: A radiation effect was observed in solutions of complexes. MR images and spectra acquired from irradiated phantoms containing aqueous solutions of metabolites doped with gadolinium containing contrast agents changed with radiation dose. The spin-spin relaxation time, T2 and T2*, as measured by SE and PRESS sequences, respectively, decreased with increasing radiation dose in both aqueous solutions of gadolinium complexes and in phantom solutions containing metabolites and gadolinium complex. Spin echo T1-weighted MR images showed a variation in spin-lattice relaxation time, T1, in solutions of complexes with radiation dose. Conclusions: The MRI/MRS analysis showed a small variation in T1 and T2 relaxation times of dilute aqueous solutions of gadolinium complexes irradiated at dose levels up to 30 Gy using a beam energy of 6 MV.

Gultekin, D, Raidy, T, MRI/MRS of Irradiated Dilute Aqueous Solutions of Gadolinium MR Contrast Agents.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4417900.html