Magnetic Resonance Imaging of Implanted Melanomas Before and After Chemotherapy

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Abstract
The early effects of in vivo platinum-rhodamine (PtR) chemotherapy on tumor high-energy phosphorous metabolism was investigated using phosphorus-31 (31 P) magnetic resonance spectroscopy (MRS), magnetic resonance imaging (MRI), and histologic examination in a subcutaneously implanted hamster melanoma model. PtR was chosen because of its potential antimitochondrial and antineoplastic properties. All melanomas were clearly observed on both T1- and T2-weighted images (T1WI and T2WI), with viable tumor regions generally characterized by low to intermediate intensity on T1WI and high intensity on T2WI. Necrotic regions were more variable in appearance, depending on the amount of cystic fluid and hemorrhage. No changes were detected on either T1WI or T2WI within 90 minutes of a tumoristatic dose of PtR (40 mg/kg) by visual examination, but slight differences were seen on calculations of relative signal intensities. However, this same dose of PtR caused a 50% drop in tumor ATP and phosphocreatine content (relative to Pi) measured by 31P MRS within 90 minutes of drug injection. Magnetic resonance spectroscopy appears to offer a sensitive means of detecting the earliest biochemical effects of chemotherapeutic agents that are known to affect tumor bioenergetics.