In what scenario must surface coils be decoupled?

Surface coils must be decoupled during transmission with the body coil to prevent interference and ensure optimal imaging performance. When surface coils are used alongside the body coil for signal transmission, they can create unwanted coupling effects that may distort the magnetic field and images. Decoupling the coils helps to minimize this interaction, allowing for clear and accurate signal reception, which is crucial for obtaining high-quality images in MRI.

The other scenarios presented in the options do not specifically require decoupling. For instance, if surface coils are used on their own, they typically function effectively without the need for decoupling. Similarly, decoupling is not relevant during image processing or when scanning small areas, as those processes do not involve simultaneous transmission interactions between multiple coils. Focused attention on decoupling during transmission with the body coil is essential for maintaining image integrity and achieving the best diagnostic outcomes.