Magnetic Resonance Imaging (MRI) Practice Test

Which combination of flip angle and TR would produce a T2 weighted gradient echo?

1. 30 degree flip angle; 200 TR

2. 60 degree flip angle; 450 TR

3. 30 degree flip angle; 450 TR

4. 90 degree flip angle; 500 TR

The correct answer is: 30 degree flip angle; 450 TR

A T2-weighted gradient echo sequence is designed to highlight the differences in T2 relaxation times among various tissues. This type of imaging generally requires a short echo time (TE) and a specific choice of flip angle and repetition time (TR) to optimize contrast based on T2 relaxation. The choice of a 30-degree flip angle is particularly effective in gradient echo sequences. This smaller flip angle allows for enhanced sensitivity to T2 decay while minimizing the effect of T1 weighting. In gradient echo imaging, the flip angle also affects the longitudinal magnetization and influences the signal intensity, making 30 degrees favorable for achieving T2 weighting. Additionally, the TR of 450 milliseconds is relatively short, which helps to minimize T1 saturation effects. In T2-weighted imaging, it is important to have a TR that is not too long to increase the contribution of T2 relaxation, yet not too short to prevent excessive signal loss due to T1 effects. The chosen combination of a 30-degree flip angle and a TR of 450 milliseconds is thus well-suited for producing T2-weighted images. This combination effectively optimizes the imaging parameters to create contrast based on tissue T2 values while maintaining a gradient echo's shorter relaxation time capabilities.