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Relevance of Image Fusion With MRI for the Interpretation of I-123 Iodo-Methyl-Tyrosine Scans in Patients With Suspected Recurrent or Residual Brain Tumor

Purpose: The aim of the study was to investigate the impact of MR/SPECT image fusion on the interpretation of I-123 iodo-methyl-tyrosine (IMT) SPECT examinations in patients with pretreated brain tumors. Material and Methods: In this retrospective study, 45 consecutive patients with suspected recurrent/residual gliomas (n = 41) or cerebral metastases (n = 4) were included. SPECT studies were performed using a triple-head gamma-camera system 10 minutes after injection of 300 to 370 MBq (8.1–10 mCi) I-123 IMT. Concerning MR, T1-, T2-, and FLAIR-weighted sequences as well as contrast-enhanced T1-weighted sequences were acquired by 1.5-T or 3.0-T scanners. For image fusion, the MPI-tool software package was used. SPECT and MR/SPECT fusion images were anonymized and then independently evaluated by 3 observers aware of the clinical data. Tumor localization and extent were evaluated and correlated with histopathology or clinical follow up, including MR imaging. Results: In 10 of 45 (22%) patients, image fusion had a significant impact on the interpretation of scans: 5 suspected SPECT findings were correctly classified as physiological or therapy-related; in another 5 patients, image fusion added relevant clinical information on tumor extent (infiltration of the contralateral hemisphere n = 3, infiltration of the brain stem n = 2). Conclusions: According to our data, image fusion is crucial for the interpretation of positive I-123 IMT SPECT findings.