Whole-Body Magnetic Resonance Imaging/Positron Emission Tomography (MRI/PET) in the Staging of Non-Small-Cell Lung Cancer (NSCLC)

Non-small cell lung cancer (NSCLC) accounts for 75 to 80% of all lung cancers, and is currently the leading cause of tumor-related deaths (1). Optimal lung cancer treatment relies on accurate disease staging, which is based on tumor size and extent, regional nodal involvement, and the presence of metastasis. Although thoracic CT has been considered the standard modality of choice for assessing intrathoracic spread of lung cancer (2), no consensus has been reached concerning metastasis evaluation. [18F]-fluorodeoxyglucose (FDG)-positron emission tomography (PET) was introduced and developed as an integrated modality for accurate nodal staging and for metastatic lesion detection in the whole body (WB) (3-9). Currently, integrated PET/CT, by providing both morphologic and metabolic features, appears to have achieved better efficacy in staging lung cancer than CT alone or PET alone (8, 10).

Whole body magnetic resonance imaging (WB MRI) has become feasible and enables fast scan throughout the body (11-13). This technique is based on a real-time gradient-echo imaging and sliding table platform (rolling table concept, which eliminates time-consuming repositioning of patients and surface coils). MRI scanners of the latest generation use high field MRI units of > 1.5 Tesla (T), and are reported to have upgraded capabilities in terms of temporal and spatial resolution due to improved signal-to-noise ratios (SNRs) under high magnetic-field strength conditions (14, 15).

Because both integrated PET/CT and WB MRI can provide WB imaging, both modalities are used for staging in patients with a malignant condition. According to a report (16), the diagnostic efficacy of PET/CT is superior to WB MRI for T and N staging and similar to WB MRI for detecting metastases. However, according to another study (17), WB MRI showed better sensitivity than PET/CT for detecting metastatic lesions. In these studies (16, 17), in which a 1.5T MR unit was used, the regional nodal or metastatic lesions were from various types of primary malignancies with a wide range of tumor stages.

Recently we published a paper regarding the diagnostic efficacy comparison for determining TNM stages of integrated PET/CT and 3T WB MRI in patients with an NSCLC (18). In this study, we found that both PET/CT and 3T whole body MRI appear to provide acceptable accuracy and comparable efficacy for non-small cell lung cancer staging, but in M stage determination, each modality has its own advantages. Namely, WB MRI is more useful for detecting brain and hepatic metastases, whereas PET/CT for lymph node and soft-tissue metastases. Therefore, we suggested whole body MR/PET should be the future imaging modality for NSCLC staging especially for M staging.

Although PET/CT scanners have quickly become established, development of MRI/PET has been slower, due to the additional challenge of developing dual-modality systems that avoid deleterious interactions caused by the high magnetic field environment of the MRI scanner and radiofrequency (RF) interference between the PET and MRI systems. At this moment, MRI/PET is still under development and is used only in small animal study (19). Thus, the purpose of this research is to provide clinical corroborating data to show how effective future MRI/PET will be in human use especially in patients with NSCLC by providing the efficiency of side-by-side reading of WB MRI/PET as compared to PET/CT.