MRI Safety PDF

MRI SAFETY 1. What are the three effects of a static magnetic field? - Projectile or missile effect - Torque forces - medical implant malfunction 2. What happens during Projectile or missile effect? - The projectile or missile effect happens when ferromagnetic metals are dr...

MRI SAFETY 1. What are the three effects of a static magnetic field? - Projectile or missile effect - Torque forces - medical implant malfunction 2. What happens during Projectile or missile effect? - The projectile or missile effect happens when ferromagnetic metals are drawn to a magnet, which can be very dangerous and potentially fatal. 3. What happens during Torque forces? - Torque forces can cause medical implants, like coils, to move or align with the magnetic field, which can be dangerous and potentially life-threatening. 4. What happens during medical implant malfunction? - Medical implants, such as pacemakers and hearing aids, can be sensitive to magnetic fields and may be damaged by them. 5. What are the two primary causes of biological effects in MRI? -Radiofrequency and gradient fields 6. What are the 4 Effects due to RF and gradient fields? - Arise from interactions between the MR field and biological processes in the patient. - Depending on the intensity of the magnetic energy. - Have a threshold below which no response is observed. - Are deterministic in nature. 7. How do RF field effects influence tissue heating (thermal effects)?  - When the body absorbs more energy than it can lose as heat, it depends on factors like frequency, exposure time, and the mass of the object. This is measured by the Specific Absorption Rate (SAR). - The effects of RF exposure are more noticeable on the outer parts of the body and can include abnormal blood cells and cataracts. 8. What are the 3 main ways tissue heating can be increased? - Increased by: 1) Malfunctioning RF coils or improper setup 2) Conductive materials, like ECG leads 3) SAR is highest during fast imaging sequences. 9. What is Specific Absorption rate (SAR)? 1. It measures how strong the RF energy is. 2. It measures how quickly energy is absorbed by each unit of mass. 10. Why are there SAR limits? - To minimize biological effects, the exposure limits are set at 0.4 W/kg for workers and 0.08 W/kg for the public. 11. SAR tolerance depends on what? - SAR tolerance is influenced by the oxygen supply and blood flow in tissues, making areas like the eye lens more susceptible to the effects of RF energy. 12. What are the effects of the gradient field? - Create currents in conductive materials within the body. 13. What effects can gradient field currents cause? 1. Involuntary nerve stimulation – muscle twitch and pain. 2. Magnetic phosphenes – flashes of light that can be perceived with closed eyes. 3. Bone healing – especially if RF coil is placed over the fracture (Mechanism unknown). 4. Ventricular fibrillation can cause a drop in blood pressure and will stop once the induced electric current is interrupted, allowing the heartbeat to return to normal. 14. What are four additional safety concerns? 1. Emergency quenching: refers to the rapid conversion of liquid helium to gas, which can cause asphyxiation and frostbite. The sudden rise in temperature may also damage the magnet. 2. Contrast related 3. Claustrophobia 4. Hearing loss (temporary): due to the banging noise made by the gradient coils