What is the recommended imaging modality to detect a metal fragment in the face?

From the Guidelines

For detecting metal fragments in the face, a computed tomography (CT) scan is the recommended first-line imaging modality. CT scans provide excellent visualization of metallic foreign bodies with high sensitivity and can accurately determine the size, shape, and precise location of metal fragments in relation to vital facial structures 1. Plain radiographs (X-rays) may be used initially for screening but have limitations in determining exact spatial relationships, as they can be inaccurate, especially with small or fine structures, and are associated with the superimposition of adjacent anatomic structures 1. Ultrasound can be helpful for superficial foreign bodies but has limited penetration for deeper facial structures. Magnetic resonance imaging (MRI) is contraindicated when metallic fragments are suspected as the strong magnetic field could cause movement of the metal, potentially causing additional tissue damage 1.

Key Points to Consider

• CT scans offer detailed cross-sectional images that help surgeons plan removal procedures if necessary, with high image resolution and thin-section acquisitions allowing for the detection of subtle nondisplaced fractures of the facial skeleton 1.
• The radiation exposure from a facial CT is relatively low compared to the benefit of accurate localization of potentially dangerous foreign bodies that could damage nerves, blood vessels, or other critical facial structures if left untreated or if removal is attempted without precise localization.
• CT is useful as the first-line of imaging to identify penetrating foreign bodies and the subsequent determination of their trajectory and extent of the injury 1.
• Radiographic screening for metallic foreign bodies is recommended before MRI to avoid potential risks associated with metallic objects and MRI 1.

From the Research

Imaging Modalities for Detecting Metal Fragments in the Face

• Computed Tomography (CT) is a commonly used imaging modality for detecting metal fragments in the face, as it provides detailed cross-sectional images of the body 2, 3, 4, 5.
• However, metal artifacts can occur in CT images, which can obscure relevant anatomy and disease 2, 3, 4, 5.
• Metal Artifact Reduction (MAR) methods can be used to reduce artifacts from metals or metal components in CT images 3, 4.
• MAR methods can improve treatment planning quality in radiotherapy applications, but none of the investigated or proposed MAR methods was completely satisfactory for radiotherapy applications due to limitations such as the introduction of other errors or image quality degradation 3.

Techniques for Reducing Metal Artifacts in CT Images

• Using a high kilovolt peak (kVp) and high milliamperage second (mAs) exposures can help minimize beam-hardening artifacts in CT images 5.
• Positioning the examined anatomy part with metallic implants optimally and correctly in the scanner and choosing the right image reconstruction algorithm can also help reduce metal artifacts 5.
• MAR techniques such as segmentation and forward-projection can be used to remove inaccurate metal artifact pixels in CT images and exactly reconstruct the soft-tissue 2.

Alternative Imaging Modalities

• Magnetic Resonance Imaging (MRI) can be used to image patients with metallic implants, but it may produce geometric distortion and susceptibility artifacts 5, 6.
• Plain radiography can be used to detect metallic foreign bodies in the orbits, but it may not be as effective as CT in detecting metal fragments in the face 6.