Magnetic Resonance Imaging (MRI) Practice Test

On a T2 weighted image, edema appears bright because it has a ____ relaxation time.

1. Short T2

2. Long T1

3. Long T2

4. Short T1

The correct answer is: Long T2

On a T2 weighted image, edema appears bright because it has a long T2 relaxation time. T2 relaxation time refers to the time it takes for the transverse magnetization of protons to decay after the initial excitation pulse in MRI. Tissue with high water content, such as edema, retains its signal longer when measured on a T2 weighted image. In terms of the physiological basis, edema is characterized by the increased presence of water in tissues, which results in prolonged T2 relaxation times. This increased water content causes more protons to remain aligned longer, producing a brighter signal on T2 weighted images. In contrast, short T2 or short T1 relaxation times would result in tissues appearing darker on T2 weighted images. These are typically associated with denser tissues or those with less water content, such as muscle and fat. Long T1 relaxation time refers to a characteristic of tissues that recover their longitudinal magnetization more slowly, which does not directly relate to the brightness seen in T2 images. Thus, the presence of edema, with its long T2 relaxation time, is the reason why it appears bright in T2 weighted MRI images.