What is the main function of gradient coils in an MRI machine?

The main function of gradient coils in an MRI machine is to produce varying magnetic fields for spatial encoding. Gradient coils are essential components that create magnetic field gradients in specific directions. These gradients allow for the encoding of spatial information within the MRI signal, enabling the machine to determine the location of protons within the body. By switching on and off at precise intervals, gradient coils alter the main magnetic field's strength, which is crucial for distinguishing between different locations in the imaging volume.

In the context of MRI, spatial encoding is fundamental to forming images accurately. Each proton in the body resonates at slightly different frequencies depending on its position within the magnetic field, and it is these variations that the imaging system captures to create detailed images. Without the effective functioning of gradient coils, it would be impossible to achieve the high spatial resolution and contrast that MRI is known for.