Quantification of artifacts caused by fixed retainers in dental-dedicated MRI – a descriptive In vitro study

Abstract

Objectives: Magnetic Resonance Imaging (MRI) is gaining traction in the world of dental imaging and diagnostics. Major strides are being taken to explore low field MRI systems and harness their logistical and clinical advantages over the typical 1.5 Tesla (T) and 3T field strengths. One advantage is reduced susceptibility effects caused by metal dental materials. This study aimed to quantify MRI artifacts produced by a variety of common fixed lingual retainers when scanned in a dental-dedicated MRI (ddMRI) – a low field strength (0.55T) MRI scanner using a dental dedicated extraoral coil. Materials and Methods: Six common orthodontic fixed retainers were scanned in vitro using a 0.55T MRI scanner with the Orthodontic – Anatomy 3D Overview proton density (PD) pulse sequence. The artifact was measured at four different cross-sections: axial, sagittal at the midline, coronal, oblique at the canine and areas (mm2) were calculated. Artifact volumes were superimposed over an average CBCT volume to assess the extent of anatomical structures distorted by each fixed retainer. Results: Stainless steel retainers caused the largest artifacts with .0195 SS Coaxial being the biggest, followed by .030 SS Round, .0215 SS Coaxial, and Ortho Flextech SS respectively. Non stainless steel retainers, .030 Blue Elgiloy and .028 TMA artifacts were significantly smaller. .0195 SS Coaxial, .030 SS Round and .0215 SS Coaxial nearly blocked out the entire anterior oral cavity. .030 Blue Elgiloy and .028 TMA only partially blocked out the mandibular anterior crowns and leave all remaining head and neck structures unaltered. Conclusions: In a ddMRI system, fixed retainer material and style can affect the size of the metal artifacts produced. Retainers without stainless steel prove to be better at reducing artifacts, with .028 TMA being the best followed by .030 Blue Elgiloy. Clinical Relevance: Stainless steel retainers, especially .030 SS Round, and .0195 SS Coaxial and .0215 SS Coaxial will significantly obstruct viewing of adjacent oral structures and could significantly affect the ability to diagnose oral pathology. .028 TMA and Blue Elgiloy are much less likely limit diagnosis in the oral cavity but as with all artifacts, the region of interest dictates if an artifact will have a negative effect. No matter how small an artifact is, if it is present in the target area then it will have a negative impact on diagnosis.