TO5 as a magnetization transfer contrast test object: characterization of the gels and determination of the real magnetization transfer.

Following the work of the European concerted action, "Tissue characterization by magnetic resonance spectroscopy and imaging," sets of five test objects (TO) were designed, produced, and distributed among European laboratories. The TO were designed to control the image quality of clincial magnetic resonance imaging in an independent and uniform mode. The fifth test object (TO5) was devoted to relaxation measurements and composed of 18 agarose tubes, inserted in an holder filled with a CuSO4 solution. These gels are subject to magnetization transfer (MT). The purpose of this paper is to characterize their MT parameters. An individual study of each gel was performed in a spectrometer, and an individual fit, as well as a global fit, was done on the two-pool model. The MT parameters found in each case are in agreement with the known properties of the agarose gels and given below. The real MT (transfer of magnetization from water to macromolecules) was computed, taking into account the "bleeding over" (direct saturation of the water magnetization). The maximum real MT ranges from 15 to 35% and can be obtained with almost the same saturation pulse conditions for all the gels. However, the saturating field required to reach the maximum MT is very high (46 microT) and unserviceable on a clinical device.