99mTc-Tetrofosmin SPECT for the evaluation of cerebral lesions

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Dear Sir, We read with great interest the recent article by Hellwig et al. investigating the utility of p-[I]iodo-L-phenylalanine (IPA) SPECT in differentiating between gliomas, metastases and gliotic or inflammatory lesions. The authors studied 67 cases of newly diagnosed brain lesions suspicious for gliomas. In visual interpretation all non-neoplastic lesions and metastases were negative; however, in the glioma group there were 11 false-negative cases, among them 3 high-grade tumours. On quantitative analysis a threshold tumour to background uptake ratio of 1.30 yielded an 88% sensitivity and 85% specificity for the differentiation between primary brain tumours and non-neoplastic lesions [1]. Our ongoing research deals with the usefulness of functional brain tumour imaging by SPECT. We are currently investigating the imaging properties of Tctetrofosmin (TF), a lipophilic diphosphine routinely used for myocardial perfusion imaging that also displays tumourseeking properties. We prospectively evaluated the role of Tc-TF in the characterization of intracranial spaceoccupying lesions. In a series of 106 patients with intracranial lesions and histological confirmation in nearly all patients, we found that Tc-TF SPECT can differentiate between lowgrade and high-grade gliomas with 91.3% sensitivity and 83.3% specificity. Besides that Tc-TF could reliably distinguish gliomas from non-neoplastic intra-axial tumours (p<0.0001). However, no significant difference between gliomas and metastases was found [2]. Previous studies demonstrated that Tc-TF uptake correlated with glioma aggressiveness, as assessed by Ki-67 immunohistochemistry and flow cytometry, and contrary to Tc-sestamibi was not influenced by the multidrug resistance profile of gliomas [3–5]. Compared to radiolabelled amino acids, Tc-TF uptake depends mainly on blood-brain barrier (BBB) disruption, regional blood flow and cell membrane integrity; thus, there is no tracer uptake in the normal brain parenchyma apart from aminor uptake in pituitary and choroid plexus, structures that lack BBB. Thus, tracer uptake can be easily identified. Furthermore, Tc-TF has the advantage of excellent availability and lower cost. To conclude, radiolabelled amino acids may hold promise for the characterization of brain space-occupying lesions. Nevertheless, Tc-TF seems to be a valuable alternative option. Future research could be focused on comparative studies not only among various radiotracers but also with the latest functional MR techniques such as perfusion imaging and spectroscopy. Funding: none G. A. Alexiou (*) : S. Voulgaris Department of Neurosurgery, University Hospital of Ioannina, P.O. Box 103, Neochoropoulo, Ioannina 455 00, Greece e-mail: alexiougrg@yahoo.gr