“Knowledge of these artifacts improves the quality of interpretation,” said Dr. Matthias Hugot, head of clinic in the medical imaging department of the Neuchâtel Hospital Network in Neuchâtel, Switzerland. AuntMinnieEurope.com August 3.
A 57-year-old patient with invasive ductal carcinoma marked with an O-Twist metal marker and treated with neoadjuvant chemotherapy underwent preoperative MRI on a Siemens 3T with T2-weighted (a), T1-weighted (b) and 3D Dixon in T1 weighting before (c) and after (d) injection of contrast product. The metallic marker is responsible for a hyposignal artifact with hyperintense peripheral halo. However, the diagnostic confidence was 3 for both readers. Despite the relatively small size of the artifact, the initial small size of the tumor (7 mm) led to uncertainty in the assessments of both readers in the presence of the metallic marker artifact. The patient was considered rCR but histology revealed the presence of residual tumor. All figures courtesy of Dr Matthias Hugot et al and European Journal of Radiology.
Hugot and his colleagues from the University Hospitals of Geneva have just published the results of a study on this subject. The results, published on July 28 in the European Journal of Radiologyshow that the diagnostic performance of preoperative MRI after neoadjuvant chemotherapy (NAC) for the prediction of pathological complete response (pCR) did not differ statistically depending on the presence or absence of metallic markers.
“Diagnostic performance for the detection of pCR at NAC was the same regardless of the presence of a marker,” they noted. “The type of metal marker, between the two broad categories studied, did not influence the diagnostic performance of readers to detect pCR. Agreement between readers was high regardless of the presence of a marker.”
The researchers included all consecutive patients who underwent preoperative breast MRI after completion of NAC (mean, 4.4 days +/- 15.9). They recorded the presence or absence of markers, the type of markers, and the size and type of artifact on each MRI sequence.
Two radiologists who were blinded to the histopathological findings and to the findings of the other assessed all MRI scans for the presence or absence of a complete response. Pathology was the reference standard. The diagnostic performance of MRI for predicting pCR in the presence or absence of markers – and also between the two most popular brands of markers (O-Twist and UltraClip) – was compared using chi-square tests or equivalent.
Ninety-three patients (mean age, 48 ± 11 years) were included in the Swiss study. Nineteen of them had no markers and 74 had 108 markers. The sensitivity and specificity of MRI for the prediction of pCR were respectively 0.73 and 0.81 for patients with and 0.67 and 0.90 for patients without markers (p
A 63-year-old patient with invasive ductal carcinoma marked with an Ultraclip metallic marker and treated with neoadjuvant chemotherapy underwent a preoperative 1.5T MRI examination with VIBE T2-weighted, T1-weighted 3D before and after injection of contrast product . The metallic marker is responsible for a hypointense artifact with a larger hyperintense halo with fat saturation than the Dixon sequences as expected. Due to this artifact, the patient was considered radiological complete response (rCR) with low diagnostic confidence from both readers, but residual tumor was detected in the final pathology results.
The authors’ hope was that the clips were not responsible for a decrease in the diagnostic accuracy of MRI, which would have challenged the interpretation of post-NAC breast MRI, Hugot explained.
“The most surprising result was to see that diagnostic confidence is affected by the presence of the clip – without however affecting diagnostic accuracy,” he noted.
Hugot admitted that there are several limitations to the study due to the retrospective nature of the research and the small number of patients in the study population. For these reasons, he believes that it is essential to conduct further research on a larger scale so that it becomes possible to generalize the group’s findings. He also thinks it’s important to test more clips from other manufacturers.
Overall, the Swiss authors report that magnetic markers are widely visible on MRI images due to the susceptibility artifact they generate.
“However, the same artifact that accounts for marker visibility may possibly mask or mimic, depending on the circumstances, residual tumor enhancement and thus reduce the diagnostic accuracy of MRI,” they wrote. “Indeed, the size and appearance of the metallic artifact in MRI depends on several factors, namely the material of the clip (in particular its magnetic susceptibility), the intensity of the magnetic field of the system and the sequence itself. (the gradient echo or the spin echo are not equally sensitive to the presence of metal).
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