Complex sentence: The two large magnets will be brought in on either side of the patient, they are large and looming and will sandwich the patient, but are able to precisly control the position of the electrodes that are on the end of the catheters.
Split into simpler sentences: The two large magnets are brought in on either side of the patient. They are large and looming and will sandwich the patient, but are able to precisely control the position of the electrodes that are on the end of the catheters.