Some parameters are altered by the magnetic field strength, and a different image is obtained with the same paremeter, because of the altered magnetic field strength. The contrast effect by contrast material for MRI (Gd-DTPA) differs with the magnetic field strength. We studied the T1 and T2 relaxation time of various solutions and relaxivity of Gd-DTPA with a low (0.2tesla) and high (1.5tesla) magnetic field machine, and considered the optimal sequence. T1 relaxation time is prolonged 20～40% at 1.5T compared with 0.2T. Using MnCI(2), the relaxivity of Gd-DTPA is 3.6～6.8mmo1(-1) sec(-1)1. Using albumin, the relaxivity is 5.8～12.1mmo1(-1) sec(-1)1. This difference is due to the difference in molecular size. Ti contrast, T2 contrast and signal intensity are weak with the low magnetic field machine. The signal intensity must be strengthened by changing some parameters (acquisitions, matrix, band width, etc.), and a shorter TR is suitable for T1 weighted images with a low magnetic field machine. For postcontrast T1 weighted images, shorter TR and shorter TE are useful to obtain a good contrast. More contrast material, and a longer TE is suitable for T2 weighted images wiht a low magnetic field machine.
Magnetic Field Strength
Relaxation Time Relaxivity