TISSUE CHARACTERIZATION BY MAGNETIC-RESONANCE SPECTROSCOPY AND IMAGING - RESULTS OF A CONCERTED RESEARCH-PROJECT OF THE EUROPEAN-ECONOMIC-COMMUNITY .5. IN-VIVO FIELD-DEPENDENCE OF PROTON RELAXATION-TIMES IN HUMAN BRAIN, LIVER AND SKELETAL-MUSCLE - A MULTICENTER STUDY

T1 and T2 relaxation times are fundamental parameters for signal contr ast behaviour in MRI. A number of ex vivo relaxometry studies have dea lt with the magnetic field dispersion of T1. By means of a multicenter study within the frame of the COMAC BME Concerted Action on Tissue Ch aracterization by MRI and MRS, the in vivo field dispersion of T1 and T2 has been measured in order to evaluate whether ex vivo data are rep resentative for the in vivo situation. Brain, skeletal muscle, and liv er of healthy human volunteers were studied. Fifteen MR units with a f ield strength ranging from 0.08 T to 1.5 T took part in the trial, whi ch comprised 218 volunteers. All the MR systems were tested for measur ement accuracy using the Eurospin TO5 test object. The measured relaxa tion data were subsequently corrected according to the obtained calibr ation curves. The results showed a clear field dispersion of T1, where as no significant variations were seen for T2. Our in vivo data were g enerally in reasonable agreement with proposed models based on ex vivo measurements.