MR imaging of splenic metastases: ferrite-enhanced detection in rats.

Detection of intrasplenic neoplasms using sonography, CT, and scintigraphy is limited by poor inherent tumor-spleen contrast relative to image noise. Despite the wide range of contrast parameters available for MR imaging, similar limitations have been found with this technique. Magnetopharmaceuticals have the ability to enhance tumor-spleen contrast and improve lesion detectability. In this study, a rodent model of cancer metastasized to the spleen was used to evaluate the potential of superparamagnetic ferrite particles as a tissue-specific reticuloendothelial contrast agent. Other studies have shown ferrite to have little or no toxicity. Without contrast material, metastatic adenocarcinoma of the spleen could not be distinguished from normal splenic parenchyma on in vivo MR images. At a dose of 50 mumol Fe/kg, the T2 relaxation time of spleen decreased by 77%, while tumor T2 was essentially unchanged (p less than .005). Intrasplenic tumors 4-6 mm in size became readily detectable on in vivo MR images after the administration of ferrite particles. Lesion conspicuity, quantitated by the tumor-spleen contrast-to-noise ratio, showed a 43-fold increase. Ferrite particles show great promise as a contrast agent to enhance the detection of focal splenic lesions.