Answer to Question #14004 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — MRI

The following question was answered by an expert in the appropriate field:


Sometimes a magnetic resonance imaging (MRI) technologist holds the hand of a claustrophobic patient while the patient is inside the MRI bore. I worked in MRI for about 20 years. I experienced short-term memory loss during my first job after holding the hand of a claustrophobic patient during the scan. I could not take a phone message without writing the message down. Over the years I met other MRI technologists who stated they have similar problems including slurred speech, slower response times, short-term memory loss, navigation, harder to learn new things. For me, it was like walking around in a zombie state, not depression but suppression of the nervous system. I left the field for a while. After 22 months my memory started improving. I reentered the MRI field and within six months I started having memory problems again. The term used by technologists to describe this condition is "mag lag." I recently noticed that there is now a recommendation by Dr Emanual Kanal for MRI technologists to not stay in the MRI scan room while the MRI is in progress. Why did it take 20 years for the recommendation? Where can I find information that describes this effect of magnetic fields?


Most of the normal safety effects of magnetic resonance imaging (MRI) are due to the environment inside the bore of the magnet. These include tissue heating from radiofrequency (RF field used for excitation), and transient nerve stimulation due to the rapidly switching gradient magnetic fields. Outside the magnet, the concerns are associated with the spatial field gradient of the magnet, where the magnetic field gradually becomes weaker as distance from the magnet bore is increased. This causes a time-varying magnetic field as the individual moves around the vicinity of the magnet. 

There have been some fairly limited reports on the cognitive effects of the MRI environment. The common effects reported are vertigo (dizziness) and nausea, blurred vision, and magnetophosphenes (flashes of light in the eyes). These effects mainly occur when moving through the spatial magnetic field gradient outside the bore, thus creating a time-varying magnetic field. These effects tend to occur more frequently at higher field strengths such as 7 tesla (T). These effects are transient and do not persist outside of the MRI environment There have also been a few scattered reports looking at effects on other cognition functions such as attention, ability to react, visual discrimination, hand-eye coordination, and memory. An excellent review authored by Pophof and Bix came out in 2017 that summarizes many of these studies. Unfortunately, this review is in German, but English translations are available. Another useful paper to start with is by van Nierop, Slottje, van Zandvoort, and Kromhout. At least one report showed some decreased performance on neuropsychiatric test to assess (long-term) verbal memory. None of the studies did any long-term follow up on the subjects of the study.

Thus, there are some reports of effects on cognition. None of them, however, have found the degree of effect that you report. It is also curious that the cognitive effects started to be noticed after a single session and persisted for months. 

The other factor that a person outside the magnet would experience is exposure to the loud noises produced by the MRI while scanning. Standard practice at the institution where I work is to have patients and persons within the scan room during scanning to be fitted with earplugs or headphones to attenuate the noise levels. This is usually effective in preventing hearing problems. I hope you were wearing proper ear protection while in the scan room.

As a note, it has never really been "standard practice" for technologists to stay in the room with claustrophobic patients. The standard has been if the patient cannot tolerate the scan because of claustrophobia, the exam is rescheduled with sedation prescribed to ease the anxiety. Also, having been an MRI physicist for over 35 years, I have interacted and taught many MRI technologists. In that time, I have never heard the term "mag lag," and none of the current group of techs with whom I work have heard the term. 

Dr. Kanal's recent recommendation about techs not being in the scan room is really made out of an abundance of caution, not based on any new information that has come to light.

My final comment is that it is very difficult to establish causality in cases like this. However, I advise that anyone experiencing symptoms such as these consult with a neurologist. I would say that I find it quite unlikely that these symptoms are due to exposure to the MRI environment.

Mark Brown, PhD
MR Physicist


Pophof B, Brix G. Magnetic resonance imaging: Recent studies on biological effects of static magnetic and high-frequency electromagnetic fields. German title: Magnetic Resonance Imaging: Neuere Studien zur biologischen Wirkung statischer Magnetfelder und hochfrequenter elektromagnetischer Felder. Der Radiologe. 2017 Jul;57(7):563-568

van Nierop, Slottje, van Zandvoort, Kromhout. Simultaneous exposure to MRI-related static and low-frequency movement-induced time-varying magnetic fields affect neurocongitive performance: A double-blind randomized crossover study. Magn. Reson Med 74:840–849; 2015.

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