Magnetic Resonance Imaging (MRI) Practice Test

What effect do time varying magnetic fields have on patients?

1. They enhance imaging speed

2. They cause muscle contractions and cardiac arrhythmias

3. They improve image contrast

4. They reduce patient movement

The correct answer is: They cause muscle contractions and cardiac arrhythmias

Time-varying magnetic fields can induce electrical currents in conductive tissues within the body, including muscles and nerves. This phenomenon occurs due to Faraday's law of electromagnetic induction, where a change in magnetic flux through a conductor induces an electromotive force (EMF). As a result, these induced currents can lead to muscle contractions, particularly in areas where the magnetic fields fluctuate rapidly. In addition, the stimulation of cardiac tissues by time-varying magnetic fields can disrupt the normal pacemaker activity of the heart, potentially resulting in arrhythmias. This is particularly concerning in patients with pre-existing cardiac conditions or implanted devices such as pacemakers. Therefore, awareness of these risks is critical when conducting MRI scans or working with equipment that generates time-varying magnetic fields. While other choices mention potential benefits to imaging, they do not accurately reflect the direct physiological impact that time-varying magnetic fields have on patients' bodies. Enhanced imaging speed, improved image contrast, and reduced patient movement do not address the electrical and muscular effects that can arise, which is why the mentioned option regarding muscle contractions and cardiac effects is the most accurate.