MRI tops PET in spotting liver tumors

Contrast-enhanced MRI should be the modality of choice to check whether colon or pancreatic cancer has spread to the liver, according to a study from Massachusetts General Hospital.

The clinical literature indicates that pancreatic cancer patients who are free of metastatic disease are good candidates for curative surgery. At the same time, early detection of liver metastases bolsters survival rates in patients with colorectal cancer. If liver lesions exist, knowledge of their number, size, and location is critical, because this determines treatment, said principal investigator Dr. Dushyant Sahani, a clinical instructor of radiology at MGH.

Sahani and colleagues retrospectively reviewed the records of 34 patients with adenocarcinomas of the colon and pancreas who had undergone both mangafodipir trisodium (Mn-DPDP) MRI of the liver and whole-body FDG-PET. They found that Mn-DPDP-enhanced MRI detected more and smaller liver tumors than did FDG-PET. They published their findings in the July issue of the American Journal of Roentgenology.

Mn-DPDP MRI detected significantly more hepatic metastases than FDG-PET based on a per-lesion analysis (p = 0.016). MRI and PET showed sensitivities, positive predictive values, and accuracy rates of 81.4% and 67%, 89.8% and 81.3%, and 75.5% and 64.1%, respectively. MRI detected 100% of metastatic lesions smaller than 1 cm, whereas FDG-PET detected only 36.4% of them.

A per-patient analysis of MRI and PET showed sensitivities, positive predictive values, and accuracy rates of 96.6% and 93.3%, 100% and 90.3%, and 97.1% and 85.3%, respectively. The difference was not statistically significant (p = 0.61).

For years, CT arterial portography was the primary tool for detection and staging of patients with liver metastases. It was replaced by spiral CT. But recent studies have shown Mn-DPDP-enhanced MRI outdoes dual-phase helical CT in this realm.

FDG-PET has proved its worth for gastrointestinal cancer staging, but its role in the detection of liver metastases has not been fully established. Available data show gadolinium-enhanced MRI provides better sensitivity and specificity for detection of liver metastases compared with FDG-PET. But the MGH study was the first to weigh FDG-PET against MRI with liver-specific contrast agents such as Mn-DPDP, the researchers said.

Despite its shortcomings, FDG-PET remains a popular modality for detection of metastases. Even though the latest data tip the scales toward contrast-enhanced MRI, FDG-PET provides additional information about disease outside the liver, making both modalities complementary and necessary for a complete, accurate staging, Sahani said.

For more information from the Diagnostic Imaging archives:

Contrast and acquisition technique prove critical in liver imaging

Choices abound in contrast agents for liver MR imaging

EIron oxide contrast improves results in MR liver imaging

Newer agents contest gadolinium's dominance in contrast MR exams