MRI PDF

Magnetic Resonance Imaging MRI The use of magnetic fields and radio waves to obtain a mathematically reconstructed image The image receptor represents differences among various tissues of the patient in the number of the neclei and i...

Magnetic Resonance Imaging MRI The use of magnetic fields and radio waves to obtain a mathematically reconstructed image The image receptor represents differences among various tissues of the patient in the number of the neclei and in the rate at which these nuclei recover from the stimulation by radio waves in the presence of a magnetic field 1  X-ray involves the interactions with the electrons surrounding the atom, whereas MRI involves the nuclei alone. Not all nuclei respond to magnetic fields. Most imaging is preformed with hydrogen nuclei (single protons); The body is roughly 85°/o water (soft tissue) The magnet provides the powerful static magnetic field The strong magnetic field can be measured in units of Tesla Static field strengths surrounding the magnet, called fringe magnetic fields, sometimes are measured in Gauss. One Tesla equals 10,000 Gauss 2  New open MRI units are now available for those with claustrophobia but the units are slower and are restricted to basic MRI functions Contraindications Pacemakers Ferromagnetic aneurysm clips Metallic fragments in the eye Cochlear implants Starr-Edwards pre-6000 model prosthetic heart valve Internal drug infusion pumps Neurostimulators Bone growth stimulators 3  Pregnancy is often considered a contraindication in the first trimester; an informed consent should be obtained and clinically documented A pregnant patient would not be given contrast media gadolinium - DTPA Patient Preparation Remove all metal objects Remove analog watches Remove credit cards In some cases, sedation may be required 4