It is an expensive medical procedure, due to the high cost of the equipment. Some metallic objects may distort the image, like hip, shoulder and knee replacements but the exam can still be done. Cochlear (ear) implants, some (older) aneurysm clips in the brain, and most pacemakers are not MRI compatible. Obese and severely claustrophobic patients often need sedation and/or imaging with an "open" magnet, which is much less confining. Contrast agents may or may not be indicated for some patients, and those with compromised kidney function may not be able to receive the contrast, due to a serious but rare skin reaction.