Chapter 20: MAGNETIC RESONANCE IMAGING (MRI) Questions And Answers.

MRI uses _______________and _______________to obtain a mathematically reconstructed image. - correct answer Magnetic fields and radio waves The MRI image represents differences in the patient's tissues in the number of____________________ and the rate at which they recover from radiofrequency stimulation. - correct answer Nuclei Which nucleus is most suitable for MRI? and Why? - correct answer Hydrogen (single-proton nucleus) The large amount of hydrogen present in any organism (Hydrogen atoms are present in each water molecule, and the body is roughly 85% water.) Which component of the nucleus is affected by radio waves and static magnetic fields? - correct answer Proton Define precession by comparing it to another, more well-known phenomenon. - correct answer It is similar to the wobble of a slowly spinning top The rate of precession of a proton in a magnetic field ______________________(increases or decreases) as the strength of the magnetic field increases - correct answer increases Precession occurs as a result of _________________acting on a spinning nuclei. - correct answer An outside force (external magnetic field) The angle of precession of protons can be altered by the introduction of____________________. - correct answer Radiofrequency pulse How does an increase in the length of application time of the radio wave affect the angle of precession of the exposed nuclei? - correct answer Increase in time increases the angle of precession Timing of the radio wave frequency to the rate of the precessing nuclei is an example of the concept of________________. - correct answer Resonance The signal that is received by the antenna or the receiving coil comes from which part of the atoms in the body tissues? - correct answer Nucleus or proton The nucleus emits______________ waves because it is a tiny magnet that is also ___________________. - correct answer Radio; precessing or rotating Relaxation of the nuclei as soon as the radiofrequency pulse is turned off can be divided into two categories: ________________and _______________. - correct answer T1 relaxation and T2 relaxation T1 relaxation is known as _____________________(transverse or longitudinal), or spin-lattice, relaxation - correct answer Longitudinal T2 relaxation is known as ____________________(transverse or longitudinal), or spin-spin, relaxation. - correct answer Transverse The quantity of hydrogen nuclei per given volume of tissue is referred to as the_______________ , which is a______________ (major or minor) contributor to the appearance of the MR image - correct answer Spin (or proton) density; minor Describe the main purpose of the gradient magnetic fields (the magnetic field strengths through only specific regions or slices of body tissue) - correct answer So that the returning signal can be located (because only the precessing nuclei within these regions or slice transmit signals) What are three primary factors that determine the signal strength? - correct answer 1. Spin density 2. T1 relaxation rate 3. T2 relaxation rate list of the five MRI safety concerns: - correct answer 1.Local heating of tissues and metallic objects 2.Gradient magnetic fields (time-varying magnetic fields). 3.Potential hazards of projectiles 4.Electromechanical implants 5.Torquing of ferromagnetic objects The danger of projectiles becomes ______________(greater or less) as ferromagnetic objects are moved toward the scanner because the field strength is _______________(directly or inversely) proportional to the cube of the distance from the bore of the magnet. - correct answer Greater; directly In an emergency situation, the patient is removed from the scan room because of the danger of _______________________. - correct answer ferromagnetic objects used in emergency situations becoming projectiles Pacemakers are not allowed inside the ______________--gauss line. - correct answer 5 As a general rule, O2 tanks, IV pumps, and wheelchairs are not allowed inside the_________________-gauss line. - correct answer 5 Patients with internal drug infusion pumps and cochlear implants are not allowed inside the___________-gauss line. - correct answer 10 The most important contraindication to MRI of the brain involves torquing of_____________. - correct answer Ferromagnetic intracranial aneurysm clips What unit of measurement is used to calculate local heating of tissues? - correct answer W/kg (watts per kilogram) Which term is used to describe the amount of tissue heating delivered during an MRI procedure? - correct answer Specific absorption ratio (SAR) What is the whole-body averaged SAR permitted for a 15-minute MRI procedure with a 1.5 Tesla system? - correct answer should not exceed 3.5 W/kg for 15 minutes of scanning True/False: MR should be avoided in the first 6 months of pregnancy unless diagnosis is crucial for conditions - correct answer False