"In our study, there was a relevant number of pulmonary metastases missed by PET/MRI compared with PET/CT in oncologic patients," wrote Dr. Lino Sawicki, from the department of diagnostic and interventional radiology, in an email to AuntMinnie.com.
Sawicki and colleagues retrospectively evaluated 50 patients who received both FDG-PET/CT and FDG-PET/MRI for tumor staging on the same day. Two independent readers recorded the presence, location, size, and FDG uptake for each lung nodule detected by the two hybrid modalities.
FDG-PET/MRI missed more than 40 lung nodules that were detected by FDG-PET/CT; the average size of the missed nodules was 4 mm, the researchers found.
Regarding factors that can limit the detection of small pulmonary nodules on MRI, they cited signal loss due to cardiac pulsation and respiration, susceptibility artifacts arising from multiple air-tissue interfaces, and low proton density in aerated lungs.
"Metastatic spread to the lungs commonly implies a higher tumor stage in patients suffering from malignant diseases, often requiring a change of therapy regimens and, ultimately, decreasing chances of survival," Sawicki said. "Hence, early detection of potential pulmonary metastases is essential."
Because current evidence in the field of pulmonary imaging is still limited, the researchers are evaluating FDG-PET/MRI with respect to FDG-PET/CT for a variety of lung lesions and in large-cohort trials to better understand the differences between the modalities, which remain relevant both for extended research and clinical implications.
"Furthermore, together with our team of MRI physicists, we are working on more-sensitive MR sequences in order to bring lung lesion detectability on a similar level to that of PET/CT," Sawicki said.
