Magnetic Resonance Imaging (MRI) Practice Test

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Which field strength requires the shortest T1 time to suppress fat signal in MRI ankle imaging using a STIR sequence?

1.5T
3.0T
0.5T
0.7T

The correct answer is: 0.5T

To understand which field strength requires the shortest T1 time to suppress fat signal in MRI ankle imaging using a STIR sequence, it’s essential to consider the behavior of fat and water protons with varying magnetic field strengths. In MRI, T1 time, or longitudinal relaxation time, is the time it takes for protons to recover their longitudinal magnetization after being excited by a radiofrequency pulse. Fat has a shorter T1 time compared to water, which allows it to be suppressed effectively by techniques like STIR (Short Tau Inversion Recovery). At lower field strengths, such as 0.5T, the T1 relaxations of both fat and water are shorter, but the relative difference is less pronounced compared to higher field strengths. This means that at 0.5T, fat can be suppressed more effectively since the inversion time can be optimally set to target fat specifically with minimal impact on water signal. As the field strength increases, such as at 1.5T or 3.0T, while fat still has a shorter T1 time than water, the actual T1 times for both begin to increase. Thus, to effectively suppress fat using STIR, the required inversion times may lengthen, making