Synopsis

Tattoos are recognised as a potential source of increased risk for MRI. Here we present the results of a prospective study designed to assess the risk of a tattoo-related adverse event occurring during MRI scanning at 3T. The study spanned a 6 year period with 573 independent scanning sessions on 319 individuals. With the inclusion criteria adopted in this study, the probability of an adverse reaction was estimated to be < 1%.

Introduction

Tattoos are recognised as a potential source of increased risk for MRI given isolated reports of adverse effects, e.g. RF-induced heating^1–3 or even pigment-specific magnetic force in the absence of scanning⁴. Despite the potential risks and increased prevalence of tattoos, guidelines remain inconsistent across sites due to the scarcity of information available on the topic, and the complexity of the situation: tattoos vary extensively across individuals making it extremely difficult to characterise, e.g. via modelling, the potential modes of interaction with the MRI environment.

An alternative approach is to quantify any increase in risk resulting from tattoos. A retrospective questionnaire-based study received two reports of potential incidents from 135 participants who had undergone MRI⁵. Retrospective approaches are limited by biased outcome reporting and not having consistent descriptors of events and exam conditions. The goal of this prospective study was to establish whether tattoos increases the risk of an adverse reaction during MRI and, if so, to identify any potential risk factors.

Methods

Volunteers were enrolled in this study if they were participating in an imaging study conducted at the Wellcome Centre for Human Neuroimaging and had at least one tattoo. All imaging was performed at 3T. To minimise potential risks, the scanner was operated in “normal” mode limiting the maximum whole-body specific absorption rate (SAR) to 2W/kg thereby limiting energy absorption. Volunteers with one or more tattoos were recruited with the following inclusion criteria:

1. no tattoo on the head, neck or genitals;
2. no thermoregulatory or skin insensitivity problems at the site of the tattoo(s);
3. longest dimension of tattoo(s) <20cm;
4. no more than 5% of the total body area was covered;
5. tattoos were at least 20cm apart (or otherwise treated as a single tattoo);
6. Informed written consent obtained.

Tattoo descriptors were recorded along with the maximum SAR reported by the scanner interface for each scanning session. Any adverse event or report of discomfort was documented and followed up if necessary.

The probability of an adverse reaction associated with having a tattoo was estimated from their frequency using a Clopper-Pearson test as implemented in Matlab.

Results

573 scanning sessions were conducted between November 2011 and October 2017 on 319 individuals. Participants were scanned on Siemens Allegra (n=17), Trio (n=551) and Prisma (n=5) systems using either a body coil (n=555) or a transmit-receive head coil (n=18) for RF transmission. A broad range of imaging data were acquired, including sequences for both functional and anatomical imaging. The maximum SAR recorded ranged from 4 to 95% (median+/-IQR = 36+/-15%).

The median age at the time of scanning was 27 years (IQR 10 years). The number of tattoos per participant ranged from 1-6, with 900 unique tattoos examined across the cohort. The tattoos were applied with black (most prominent), red, yellow, blue, white, orange, green, violet, brown, grey and turquoise inks. They ranged in size from 0.5 - 20cm and were applied primarily in Europe (547; 433 of these in the UK), but also in America, Asia, Africa and Australia.

One volunteer reported a warm and tight feeling around the tattoo that was classified as a mild tattoo-related adverse reaction. This occurred at the outset of scanning, during the localiser sequence, at which point scanning was terminated. No medical intervention was required and the event resolved naturally over the course of a day with no residual effect.

Based on the occurrence of one adverse reaction in 573, the probability of an adverse reaction was estimated to be less than 0.97% (95% confidence interval).

Discussion

This prospective study, the first of its kind, has demonstrated that the additional risk due to tattoos in the MRI environment is < 1%. It should be noted that this conclusion is drawn for the specific population studied, namely participants recruited to cognitive neuroscience studies in the first instance. It is not expected to be indicative of the UK population, but perhaps typical of a neuroimaging cohort in a large, international city such as London. Furthermore, additional safety precautions were implemented, such as limiting tattoo size, their location and their extent across the body.

It should also be borne in mind that the characteristics of the tattoo may influence the risk of an adverse effect, e.g. a wide range of inks are used, but these are not well regulated. However, our study encompassed tattoos applied in a broad range of countries.

Finally, this study has been conducted at 3T and the findings may not necessarily extrapolate to other field strengths.

Conclusion

Acknowledgements

References

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