Mn-TPPS4 in the diagnosis of malignant skin tumors. In vivo assay media for high-resolution magnetic resonance tomography of melanotic melanoma

Purpose: Some authors postulate an avidity of certain porphyrin derivatives for tumors. The aim of this study was to examine the contrast enhancement of implanted melanotic melanoma after application of Mn-TPPS4 to achieve a better characterization of this malignant skin tumor. Material and method: High-resolution MR imaging (2.0 Tesla, 2.0-cm surface- coil, T1-weighted FLASH-2D-sequence) was performed on 15 mice (C57bl6) with intracutaneous implanted melanoma (B16F1), before and after intravenous ad ministration of either Gd-DTPA (Magnevist, Schering, Berlin) as a reference contrast medium, or Mn-TPPS4 (Porphyrin Products,Schering, Berlin). The im ages were evaluated quantitatively by calculating percentage enhancement, s lope of signal intensity-to-time curves, percentage increase of the signal intensity, signal-to-noise and contrast-to-noise-ratios. The qualitative ev aluation was accomplished by visual assessment of the enhancement, the dema rcation of the tumors from the surrounding tissue and the homogeneity of th e tumors. Results: Contrast medium-enhanced images showed an increased signal intensi ty from all tumors with no significant difference between the contrast medi a. Demarcation of tumors from the surrounding tissue was better following a dministration of contrast media; regressive and altered areas was more clea rly depicted. Conclusion: A specific accumulation of the metalloporphyrin Mn-TPPS4 in mel anotic melanoma could not: be proved. Based on the small and insignificant differences in the results obtained with the two contrast media, and on the side effects of the metalloporphyrin, the usefulness of Mn-TPPS4 as a cont rast medium for MRT is limited.