Purpose:To determine the value of multivoxel proton magnetic resonance spectroscopic imaging (MRSI) in distinguishing malignant skeletal tumors from benign tumors and normal bone marrow using the metabolite choline (Cho) as a marker for malignancy.
Materials and Methods:Pathologic specimens obtained from 13 patients who had undergone wide resection for skeletal tumors underwent evaluation by MRSI at 1.5 T. Coronal T1-weighted gradient-echo sequence obtained for localization purposes (TR/TE ϭ 250/1.8 msec, field of view [FOV] ϭ 18 ϫ 18), and single-slice MRSI (TR/TE ϭ 2000/ 272 msec, FOV ϭ 18 ϫ 18, 10-mm slice-thickness) were performed. Water, lipid, and Cho images were reconstructed from MRSI data. Cho signal was measured in each specimen and expressed relative to background noise level (signal-to-noise ratio [SNR]) where noise was measured between 7.0 and 9.0 ppm. Cho SNRs were compared between areas containing malignant tumor and nonmalignant tissue (benign lesion or normal bone marrow) as determined by histopathology.Results: Specimens included 13 skeletal sarcomas (seven osteosarcomas, three chondrosarcomas, one malignant fibrous histiocytoma, one fibrosarcoma, and one leiomyosarcoma). All specimens included a sample of normal bone marrow and two specimens also contained benign lesions. All sarcomas demonstrated a signal at 3.2 ppm assigned to Cho-containing metabolites in areas of malignancy. Peak Cho SNR was significantly different for areas containing histologically-proven malignancy compared to nonmalignant tissue (9.8 Ϯ 5.1 vs. 2.7 Ϯ 1.4, respectively, P Ͻ 0.002).
Conclusion:These preliminary results indicate that MRSI at 1.5 T is a promising noninvasive method of differentiating malignant skeletal tumors from nonmalignant tissue. Using MRSI, Cho can be detected in skeletal tumors and may serve as a marker for malignancy. MAGNETIC RESONANCE IMAGING (MRI) is the primary cross-sectional imaging modality used for identification and characterization of bone and soft tissue abnormalities due to the very high contrast resolution of the technique. However, although the sensitivity of MRI for malignancy is high, its specificity is low (1-3). In one study, malignancy was correctly assessed in only 55% of cases (3). As a result, there are relatively few lesions (e.g., cysts and lipomas) that are definitely characterized by conventional MRI. Gadolinium enhancement ratios with MRI have been used, but are not widely applied and are more useful for assessing treatment response (4). As a result, many lesions are indeterminate in nature, and must be biopsied or resected for definitive characterization and diagnosis. Thus, there are substantial gaps in our knowledge in the identification and classification of skeletal lesions based on MRI.Multivoxel proton magnetic resonance spectroscopic imaging (MRSI) is a new approach to the evaluation of musculoskeletal lesions. It is a means of molecular imaging with MRI that can potentially provide a noninvasive method for characterizing bone and soft tissue lesions for malignancy...