CHICAGO - Using a 15-minute MRI protocol with PET, Swiss researchers achieved diagnostic accuracy equal to that of PET/CT for patients with non-small cell lung cancer (NSCLC).
The study results, presented on Wednesday at the RSNA annual meeting, suggest that NSCLC patients can be staged in relatively little extra time, while being exposed to less radiation than they would get from PET/CT.
For many years, PET/CT has been the standard modality for staging NSCLC patients. So, before PET/MRI can supplant it for this application, some basic clinical questions need to be addressed, said lead author Dr. Martin Huellner from University Hospital Zurich.
"One of them is if PET/MR imaging is equal to or superior to PET/CT in certain cancer entities or organs," he said during his presentation. "Second, which fast MR imaging techniques are most appropriate to achieve high diagnostic accuracy, given the shorter PET/CT image acquisition time of 10 to 15 minutes compared to PET/MRI?"
The prospective study included 40 consecutive patients (28 men, 12 women) with a mean age of 65 years (range, 35 to 85 years). All 40 patients had been referred for initial staging of suspected or biopsy-proven non-small cell lung cancer based on FDG-PET/CT.
The imaging protocol consisted of whole-body PET/CT (Discovery 690, GE Healthcare), followed by scanning on a 3-tesla MRI system (MR 750w, GE). The MRI protocol included whole-body coronal short-tau inversion recovery (STIR) for eight minutes, followed by 3D fast spoiled gradient-recalled (FSPGR) acquisition for three minutes and thoracic axial periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) imaging for five minutes. Total MRI acquisition time was 16 minutes.
The reference standard was histopathology for tumor and nodal stage in 17 patients and follow-up with imaging for 23 patients, according to the researchers.
Image results were analyzed in random order, with PET/CT and PET/MR images reviewed by two independent readers to determine tumor, node, and metastasis (TNM) staging.
When staging was correct, the researchers assigned a value of 2. Equivocal results were given a value of 1 and incorrect staging was marked as 0.
PET/MRI and PET/CT performed similarly in terms of TNM staging, Huellner and colleagues found.
| PET/MRI vs. PET/CT for NSCLC staging | ||
| PET/MRI | PET/CT | |
| Tumor | ||
| Correct | 20 patients (63%) | 22 patients (69%) |
| Equivocal | 2 patients (6%) | 1 patient (3%) |
| Incorrect | 10 patients (31%) | 9 patients (28%) |
| Node | ||
| Correct | 22 patients (69%) | 19 patients (59%) |
| Equivocal | 2 patients (6%) | 4 patients (13%) |
| Incorrect | 8 patients (25%) | 9 patients (28%) |
| Metastasis | ||
| Correct | 24 patients (75%) | 20 patients (63%) |
| Equivocal | 0 patients (0%) | 5 patients (16%) |
| Incorrect | 8 patients (25%) | 7 patients (22%) |
The reduced radiation exposure with PET/MRI versus PET/CT could benefit patients with lower-stage tumors in particular, as these patients generally have a better chance of survival and may undergo more follow-up imaging scans.
"TNM staging with PET/MR with 15-minute acquisition time has equivocal accuracy to PET/CT," Huellner concluded. "Thus, lung cancer patients may be effectively staged with PET/MR, which is not much more time-consuming than PET/CT."
