# Displacement of intraorbital ferromagnetic foreign bodies induced by magnetic resonance imaging: Quantification using an animal model

## TL;DR

This study measures how MRI scans can move metal objects in the eye area of pig heads, showing that larger objects and multiple objects move more.

## Contribution

The study quantifies MRI-induced displacement of ferromagnetic foreign bodies in different intraorbital locations using an ex vivo animal model.

## Key findings

- MRI caused significant displacement of 2- and 4-mm ferromagnetic foreign bodies in specific intraorbital locations.
- Double ferromagnetic foreign bodies showed greater displacement than single ones in certain locations.
- 1-mm ferromagnetic foreign bodies showed no significant displacement regardless of location.

## Abstract

The presence of ferromagnetic foreign bodies in the intraorbital area, eyelids, or intraorbital fat of an examined subject represents a contraindication to magnetic resonance imaging (MRI). We sought to measure the displacement of one or two intraocular and intraorbital ferromagnetic foreign bodies in ex vivo porcine heads following 1.5 T MRI scan compared to 5-min walk test.

In this ex-vivo controlled laboratory study, a total of 48 1-, 2-, and 4-mm steel balls were surgically implanted into suprachoroidal, intraorbital fat, intrapalpebral, and intravitreal locations of 36 fresh porcine heads. Ferromagnetic foreign bodies displacement was measured by comparing computed tomography scan before and after both a 5-min walk test to simulate handling-related movement and 1.5 T MRI scan. Comparison of groups was performed using the non-parametric Mann-Whitney-Wilcoxon test.

Global median displacement after 5-min walk test was 0.8 mm. Compared to the control group, the ferromagnetic foreign bodies displacement after MRI was significant for the suprachoroidal location with single ferromagnetic foreign body (2.3 mm, p = 0.0282), and for the intravitreal location with single ferromagnetic foreign body (4.5 mm, p = 0.0282) and double ferromagnetic foreign bodies (5.0 mm, p = 0.0282). Compared to the control group, ferromagnetic foreign body displacement after MRI was significant for the double 2-mm ferromagnetic foreign bodies (2.2 mm, p = 0.0130), single 4-mm ferromagnetic foreign body (4.9 mm, p = 0.0107), and double 4-mm ferromagnetic foreign bodies (9.0 mm, p = 0.0084).

Ferromagnetic foreign body displacements after 1.5 T magnetic field exposition were not significant for extraocular intrapalpebral and intraorbital fat locations. Neither were there significant displacements for 1-mm ferromagnetic foreign body, irrespective of the location. On the other hand, the presence of two objects increased the displacement of 2- and 4-mm ferromagnetic foreign bodies.