Metallic implants and CT artefacts in the CTV area: Where are we in 2020?

Radiation therapy (RT) is one of the main modalities of cancer treatment worldwide with computed tomography (CT), as the most commonly used imaging method for treatment planning system (TPS). Image reconstruction errors may greatly affect all the radiation therapy planning process, such as target delineation, dose calculation and delivery, particularly with particle therapy. Metallic implants, such as hip and spinal implants, and dental filling significantly deteriorate image quality. These hardware structures are often very complex in geometry leading to geometric complex artefacts in the clinical target volume (CTV) area, rendering the delineation of CTV challenging. In our review, we focus on the methods to overcome artefact consequences on CTV delineation: 1- medical approaches anticipating issues associated with imaging artefacts during preoperative multidisciplinary discussions while following standard recommendations; 2- common metal artefact reduction (MAR) methods such as manually override artefact regions, ballistics avoiding beam paths through implanted materials, megavoltage-CT (MVCT); 3- prospects with radiolucent implants, MAR algorithms and various methods of dual energy computed tomography (DECT). Despite substantial and broad evidence for their benefits, there is still no universal solution for cases involving implanted metallic devices. There is still a high need for research efforts to adapt technologies to our issue: "how do I accurately delineate the ideal CTV in a metal artefact area?"

Effects of orthodontic appliances on the diagnostic capability of magnetic resonance imaging in the head and neck region: A systematic review

OBJECTIVES

Patients in active fixed orthodontic treatment or fixed retention phase may require magnetic resonance (MR) scans of the head and neck region. Orthodontists are challenged to decide whether to keep or remove orthodontic appliances prior to the scans. The aim of this study was to determine the effect of orthodontic appliances on the diagnostic capability of MR images.

METHODS

Four electronic databases were searched, with no language restrictions, from database inception to October 2016: PubMed, EMBASE, CINAHL, EBMR. A search in Google Scholar and ProQuest, as well as a manual search, were also conducted. Two independent reviewers assessed articles for inclusion. Original studies including any orthodontic appliance on human subjects were considered. Outcomes measured were development of artefacts, diagnostic quality, accuracy, and treatment outcomes. Risk of bias was assessed with the Cochrane Risk of Bias Assessment and QUADAS-2 tools.

RESULTS

Five of 1052 studies identified were included in the final qualitative synthesis. A total of 90 adult human subjects were included. Orthodontic appliances evaluated were brackets, bands, archwires, and fixed retainers. The outcomes assessed were production of artefacts, diagnostic quality and diagnostic accuracy. Detrimental effects on diagnostic quality, and subsequently diagnostic accuracy, rose with increased stainless steel (SS) and proximity to anatomic area of interest. Orthodontic appliances may render images uninterpretable and non-diagnostic.

CONCLUSIONS

There is fair evidence to suggest orthodontic appliances, mainly those with SS, cause MR artefacts. Removal of metal orthodontic appliances prior to MR scans is recommended, especially if the area of interest is near the orthodontic appliance. Additional evidence is needed to provide guidelines to clinicians.

Quality control of cardiac MRI for tetralogy of Fallot: Combination of standard measurements and physiological analysis to detect invalid examinations

BACKGROUND

Cardiac magnetic resonance imaging (MRI) is the key examination for patients with tetralogy of Fallot, but it remains challenging. The MRI report should at least mention left (L) and right (R) ventricle end-diastole volumes (V), ejection fraction (EF) and pulmonary regurgitation (PR). These variables are linked by basic physiology rules and (V × EF)L=(V × EF)R(1-PR).

AIMS

To investigate this formula as a quality control of Fallot MRI.

METHODS

A total of 98 consecutive Fallot MRI were included retrospectively. Examinations that failed the formula (with a 10% tolerance) constituted the invalid group and were compared with a control group of the same size. MRIs of both groups were randomly submitted to a senior observer for blinded reassessment. The initial and new reports were compared. The inter-observer limits of agreement were calculated for the different variables within both groups.

RESULTS

Twelve examinations failed to pass the validation formula. From the 24 reanalysed examinations (12 invalid+12 controls), four failed to pass the formula (all from the invalid group). Two examinations had significant artefacts in the aorta or pulmonary trunk due to sternal wires. The quality check detected two other patients with atypical anatomy (persistent septal defects), which were not known by the MRI physician and were not detected during the examination. The inter-observer disagreements within the invalid group concerned essentially VR (P<0.02).

CONCLUSION

The quality control detected questionable MRI examinations, in which 83% corresponded to unreliable right ventricle volumes due to questionable manual contours or unreliable output flow due to artefacts.