42 Tell your doctor, if:  you are feeling thirsty and/ or if you have only had small quantities or nothing to drink before the examination  you have a cardiac pacemaker or any ferromagnetic implant (vascular clips, etc.) or a metallic stent in your body  you are taking a special kind of antihypertensive medicine, i. e. a beta-blocker  you have heart disease  you suffer from epilepsy or brain lesions  you are or your child is on a controlled sodium diet If any of these apply to you, your doctor will decide whether the intended examination is possible or not.