Magnetic Resonance Imaging (MRI) Practice Test

What component provides spatial encoding in an MRI system?

1. Main magnet

2. Gradient system

3. RF coil

4. Receiving coil

The correct answer is: Gradient system

The gradient system is crucial for providing spatial encoding in an MRI system. It consists of multiple coils that produce varying magnetic field strengths across the imaging volume. This variation allows for precise localization of the signals being detected from different areas within the body. When the gradients are switched on, they modify the magnetic field in specific directions (typically along the x, y, and z axes). This spatially varying magnetic field enables the system to determine the location of the signals originating from each point in the imaging area, effectively allowing the MRI to convert raw signals into detailed images of internal structures. Without this capability of spatial encoding, it would not be possible to discern where in the body the signals are coming from, leading to ambiguous and non-diagnostic images. The main magnet provides a strong, uniform magnetic field necessary for aligning the protons in the body but does not contribute to spatial encoding. The RF coil is responsible for transmitting radiofrequency pulses and receiving the signals emitted by the excited protons, while the receiving coil is crucial for picking up the signals but does not influence their spatial localization.