Magnetic Resonance Imaging (MRI) Practice Test

Phase contrast MRA techniques produce images in which the signal intensity within the vessel is dependent upon the?

1. Density of the tissue

2. Velocity of the flowing blood

3. Size of the vessel

4. Magnetic field strength

The correct answer is: Velocity of the flowing blood

Phase contrast MRA (Magnetic Resonance Angiography) relies on the principles of magnetic resonance to create images that highlight blood flow in vessels. In this technique, the signal intensity within the vessel is correlated with the velocity of the flowing blood. This occurs due to the phase shifts induced in the magnetic resonance signal as a result of moving protons in the blood. When protons in the bloodstream move, they experience changes in phase relative to stationary protons in surrounding tissues. The velocity of flow determines the degree of this phase shift; faster moving blood will generate a stronger signal than slower moving blood. This characteristic allows phase contrast MRA to effectively visualize the dynamics of blood flow, making it particularly useful for assessing vascular conditions. The other options do not correlate directly with the signal intensity in the same way. The density of tissue impacts overall signal but does not specifically relate to the vessel signal in terms of flow dynamics. The size of the vessel and magnetic field strength may influence image quality or resolution, but they don't directly determine the signal intensity within the vessel due to flow characteristics. Thus, the relationship between the velocity of the flowing blood and the resulting signal intensity is what makes this choice the most relevant.