Whole-body MRI and PET/CT differ in their capabilities when conducting tumor, node, and metastasis (TNM) staging, with PET/CT demonstrating superior sensitivity and specificity for lymph node staging, while whole-body MRI showed strength in detecting distant metastases, according to German researchers.
The scientists conducted a prospective, blinded study of 38 patients (21 female and 17 male) ranging in age from 21 to 81 years, with a mean of 56 years, who presented with different oncological diseases. Each patient underwent an FDG-PET/CT scan (Gemini, Philips Medical Systems, Andover, MA) for tumor staging, as well as whole-body MRI (Magnetom Avanto, Siemens Medical Solutions, Malvern, PA).
The researchers than compared the accuracy in staging of various malignant tumors with whole-body MRI and PET/CT.
"The images were reviewed by two radiologists for MRI and one radiologist and one nuclear medicine physician for PET/CT," said Dr. Gerwin Schmidt, who presented the results from the Institute of Clinical Radiology at the University Hospital Munich in Germany at the 2005 RSNA conference in Chicago.
After FDG administration, the patients rested for one hour to allow uptake of the radiopharmaceutical. A CT scan was then performed for attenuation correction, a PET emission scan with a reconstruction algorithm was conducted, and a diagnostic CT scan was performed for an overall scan time of 43 minutes, according to Schmidt.
High-resolution coronal T1-weighted and STIR sequences of the whole body at five anatomical levels were performed, as well as axial T2-weighted imaging of the lung using half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, Schmidt said. In addition, contrast-enhanced dynamic and static T1-weighted sequences of the liver, brain, abdomen, and pelvis were performed, using a 32-channel whole-body MRI scanner with a total anatomic coverage of 205 cm.
"Delineation of the primary or recurrent tumor (T stage), lymph node involvement (N stage), and degree/localization of metastatic disease (M stage) were assessed using histological results and clinical-radiological follow-up within four to five months as the standard of reference," he said.
The most common primary diagnoses in the patient cohort were tumors of the gastrointestinal tract (14) and breast cancer (11), according to the researchers. They conducted a lesion-by-lesion analysis of 120 lymph nodes (60 benign and 60 malignant) and found these were detected with a sensitivity of 98% and specificity of 83% for PET/CT and 80% and 75%, respectively, for whole-body MRI.
"Borderline-size lymph nodes are sometimes hard to diagnose in MRI," Schmidt noted.
However, 268 distant lesions were identified (191 malignant and 77 benign) with a sensitivity and specificity of 82% for PET/CT and 96% and 82%, respectively, for whole-body MRI.
"MRI detected more bone lesions and liver lesions than PET/CT," Schmidt said. "MRI diagnosed nine additional brain metastases that could not be diagnosed with PET/CT properly due to the high physiological FDG uptake. PET/CT performed better in lung lesions and, surprisingly, in skin and soft-tissue lesions."
The overall accuracy for correct TNM staging was 90% for PET/CT and 86% for whole-body MRI, and the concordance of both modalities was 89%, Schmidt said. He observed that whole-body MRI's capabilities to detect additional bone and brain metastases may be ascribed to its larger field-of-view.
Rather than advocating the use of one modality over the other, the researchers believe that the two are complementary for thorough and accurate TNM staging.
"PET/CT and whole-body MRI are reliable modalities for tumor detection and metastasis screening," Schmidt said. "Whole-body MRI is highly sensitive in detecting distant metastatic diseases, especially in the bone, liver, and brain. However, PET/CT is clearly superior in lymph node staging."
By Jonathan S. Batchelor
AuntMinnie.com staff writer
January 20, 2006
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