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December 23, 2003 — A new study suggests that whole-body PET/CT imaging may be more useful than whole-body MRI for determining the extent a tumor has spread, according to an article in the December 24/31 issue of The Journal of the American Medical Association.
In malignant diseases, therapeutic options as well as the patients' prognoses strongly depend on the tumor stage, according to background information in the article. Thus, accurate tumor staging encompassing the entire body is of essential importance. Magnetic resonance imaging (MRI) and a combined modality including positron emission tomography (PET) and computed tomography (CT) provide means for whole-body tumor staging in a single session. In contrast to MRI, which is mainly focused on the assessment of morphological (structural) characteristics of tissue, glucose analog [18F]-fluorodeoxyglucose-positron emission tomography (FDG-PET) provides functional information on tumor metabolism. The functional data available in whole-body scans complement morphological imaging for staging different malignancies.
PET is a medical imaging technique in which a radioactive 'tracer' is injected into a patient to help determine activity of a certain area of the body. CT imaging is the process of using digital processing to generate a three-dimensional image of an internal section of the body from a series of two-dimensional X-ray images. MRI involves application of an external magnetic field to produce three-dimensional images of body tissues.
Gerald Antoch, M.D., of the University Hospital Essen, Germany, and colleagues conducted a study to determine the staging accuracies of whole-body PET/CT and whole-body MRI for different malignant diseases and to compare these two new imaging tools.
The study included 98 patients (mean age 58 years; range, 27 to 94 years) with various cancers who underwent back-to-back whole-body PET/CT and whole-body MRI for tumor staging. The study was conducted at a university hospital from December 2001 through October 2002 and had a mean follow-up of 273 days (range, 75-515 days). The images were evaluated by two different teams. The diagnostic accuracies of the two imaging procedures were compared.
The researchers found that of the 98 patients, the overall primary tumor, regional lymph nodes, and distant metastasis (TNM) stage was correctly determined in 75 with PET/CT (77 percent) and in 53 with MRI (54 percent). "Compared with MRI, PET/CT had a direct impact on patient management in 12 patients. Results from MRI changed the therapy regimen in two patients compared with PET/CT. Separate assessment of [tumor]-stage (with pathological verification) in 46 patients revealed PET/CT to be accurate in 37 (80 percent) and MRI to be accurate in 24 (52 percent). Of 98 patients, [lymph node]-stage was correctly determined in 91 patients with PET/CT (93 percent) and in 77 patients with MRI (79 percent). Both imaging procedures showed a similar performance in detecting distant metastases," the authors write.