Radiology: MR/PET on par with PET/CT for lung cancer staging

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MR/PET pulmonary nodule - 318.28 Kb
Superimposition of PET and anatomic images obtained in 64-year-old woman with lung cancer. Source: Radiology 2012;264:551-558

MR/PET imaging is feasible for the staging of lung cancer, with diagnostic image quality sufficient for assessment of pulmonary masses and similar lesion characterization as with PET/CT, according to a study published in the August issue of Radiology. The results indicate MR/PET could provide an alternative modality in thoracic imaging, with approximately a quarter of the radiation dose as compared with PET/CT.

Study authors Nina F. Schwenzer, MD, and colleagues from Eberhard Karls University, Tübingen, Germany, explained that while PET/CT’s strength lies in the staging of nodal and distant metastases, tumor staging can be difficult.

“Although MR imaging was considered limited for pulmonary imaging for many years, advantages in gradient systems and innovative sequences with parallel imaging offer an increasing role for MR imaging of tumors in clinical practice,” wrote the authors. They noted that in cases of chest wall infiltration, for example, MR is superior to PET/CT.

To test whether the combination of PET and MR could overcome the limitations of both modalities, Schwenzer and colleagues conducted a pilot study with ten patients in whom bronchial carcinoma was proven or clinically suspected. All patients underwent a F18 FDG PET/CT scan, immediately followed by whole-body MR/PET imaging featuring a 3T MR imager.

The authors reported that MR/PET provided good tumor delineation and diagnostic image quality in all patients. Nine out of 10 lesions showed pronounced FDG uptake, with the last lesion considered morphologically suspicious for malignancy at CT and MRI, but with no FDG uptake.

Tumor-to-liver ratios were calculated to be 8.0 for MR/PET imaging and 4.4 for PET/CT, and significant correlation was found between both imaging units, according to the authors. Liver tissue was used as a reference due to its high FDG uptake.

Seven patients had identical TNM (tumor-node-metastasis) classification scores, with differences in tumor or nodal staging “owing to modality-inherent differences in lesion size measurement.” None of the differences in tumor measurement would have resulted in a change in therapy, according to the authors.

Schwenzer et al broke down specific benefits of MR/PET imaging based on the results of the study. In one patient, infiltration of the mediastinal pleura was excluded by MR/PET, which wasn’t definitely possible with PET/CT. “This is an important finding of our study because it might indicate a potential superiority of MR imaging in determining the infiltration of surrounding structures in lung cancer. Concerning this question, the relevant information for decision making can be obtained by using the excellent soft-tissue contrast of MR imaging.”

No contrast media was used since the study was performed in an early evaluation phase of the MR/PET hybrid imager.

“The results of our study indicate the relevance of further investigation of simultaneous MR/PET imaging in therapy monitoring of pulmonary masses, especially with respect to the broad spectrum of functional MR imaging techniques,” wrote Schwenzer and colleagues.