Magnetic Resonance Imaging (MRI) Practice Test

Gradient echo sequences can yield T1 or T2* characteristics but are unaffected by which of the following?

1. TE value

2. Inversion time

3. TR duration

4. Field strength

The correct answer is: Inversion time

Gradient echo sequences are a type of MRI technique that can exploit the properties of both T1 and T2* relaxation times to generate images. These sequences are sensitive to certain parameters that influence image contrast and the overall acquisition process. Inversion time is a crucial element specifically associated with spin-echo sequences, where it helps to manipulate the longitudinal relaxation characteristics (T1) of the tissue being imaged. By adjusting the inversion time, one can enhance T1-weighted imaging, which is not a characteristic applicable to gradient echo sequences, since they do not utilize an inversion recovery pulse. Therefore, gradient echo sequences are unaffected by inversion time, making it the correct response. On the other hand, the echo time (TE value) and repetition time (TR duration) significantly impact the contrast and overall image quality in gradient echo sequences. The TE influences the timing of when the echo is read after the initial excitation pulse, affecting the T2* weighting of the resultant images. Similarly, TR affects the amount of time allowed for longitudinal relaxation and consequently influences the T1 weighting. Field strength also plays a role in the overall imaging characteristics by affecting the signal-to-noise ratio (SNR) and the T1 and T2 relaxation times of tissues, thus