Magnetic Resonance Imaging (MRI) Practice Test

To produce an image based on differences in T1, the time interval between 90-degree excitation pulses should be:

1. Long

2. Short

3. Equal

4. Variable

The correct answer is: Short

To produce an image based on differences in T1 relaxation times, the time interval between 90-degree excitation pulses needs to be short. This is because T1, or longitudinal magnetization recovery time, is the time it takes for protons to return to their equilibrium state after being disturbed by a pulse. When the interval is short, not enough time is allowed for the various tissues of differing T1 values to recover. This creates contrast in the resulting images, as different tissues will recover their magnetization at different rates. Thus, a short time interval leads to significant differences in the visibility of tissues on the MRI scan, enhancing the contrast necessary for T1-weighted imaging. Longer intervals would allow for more complete recovery for all tissues, thus diminishing the differences that contribute to the image contrast being sought in T1-weighted sequences. The options indicating equal or variable intervals do not consistently support the generation of T1-weighted images, which rely on specific timing to accentuate the inherent differences in T1 relaxation among varied tissue types.