Nikolaos Karatzas

SPECT imaging evaluation in movement disorders: far beyond visual assessment

Single photon emission computed tomography (SPECT) imaging with 123I-FP-CIT is of great value in differentiating patients suffering from Parkinson’s disease (PD) from those suffering from essential tremor (ET). Moreover, SPECT with 123I-IBZM can differentiate PD from Parkinson’s “plus” syndromes. Diagnosis is still mainly based on experienced observers’ visual assessment of the resulting images while many quantitative methods have been developed in order to assist diagnosis since the early days of neuroimaging. The aim of this work is to attempt to categorize, briefly present and comment on a number of semi-quantification methods used in nuclear medicine neuroimaging. Various arithmetic indices have been introduced with region of interest (ROI) manual drawing methods giving their place to automated procedures, while advancing computer technology has allowed automated image registration, fusion and segmentation to bring quantification closer to the final diagnosis based on the whole of the patient’s examinations results, clinical condition and response to therapy. The search for absolute quantification has passed through neuroreceptor quantification models, which are invasive methods that involve tracer kinetic modelling and arterial blood sampling, a practice that is not commonly used in a clinical environment. On the other hand, semi-quantification methods relying on computers and dedicated software try to elicit numerical information out of SPECT images. The application of semi-quantification methods aims at separating the different patient categories solving the main problem of finding the uptake in the structures of interest. The semi-quantification methods which were studied fall roughly into three categories, which are described as classic methods, advanced automated methods and pixel-based statistical analysis methods. All these methods can be further divided into various subcategories. The plethora of the existing semi-quantitative methods reinforces the feeling that visual assessment is still the base of image interpretation and that the unambiguous numerical results that will allow the absolute differentiation between the known diseases have not been standardized yet. Switching to a commonly agreed—ideally PC-based—automated software that may take raw or mildly processed data (checked for consistency and maybe corrected for attenuation and/or scatter and septal penetration) as input, work with basic operator’s inference and produce validated numerical results that will support the diagnosis is in our view the aim towards which efforts should be directed. After all, semi-quantification can improve sensitivity, strengthen diagnosis, aid patient’s follow-up and assess the response to therapy. Objective diagnosis, altered diagnosis in marginal cases and a common approach to multicentre trials are other benefits and future applications of semi-quantification.

Low-grade chondrosarcomas: a difficult target for radionuclide imaging. Case report and review of the literature

Bone scan with Tc-99m (technetium) diphosphonate is sensitive, but non-specific for musculoskeletal tumors. Tl-201 (thallium), Tc-99m-sestamibi, Tc-99m-tetrofosmin, and F-18-fluorodeoxyglucose (F-18-FDG) can visualize tumors more specifically and are therefore useful in orthopedic oncology. However, cartilaginous tumors are characterized by histological and biological features, which potentially impair specific radionuclide imaging. A case of a patient with a low-grade primary chondrosarcoma of the femur and a false negative Tl-201 scan is presented. Tc-99m-based tumor-localizing compounds (sestamibi, tetrofosmin), as well as metabolic and receptor-imaging radiopharmaceuticals have also been reported to fail in low-grade chondrosarcomas imaging. Low cellularity, mitochondrial specialization and the presence of an efflux membrane pump may contribute to poor imaging. A negative Tl-201 or Tc-99m-sestamibi scan should be interpreted with caution, when the possibility of a chondrosarcoma is not negligible.

Comparative evaluation of 99mtc-depreotide and 201tl chloride single photon emission tomography in the characterization of pulmonary lesions

PurposeTo compare 99mTc-depreotide and 201Tl chloride SPET in the characterization of pulmonary lesions. MethodsFifty-seven pulmonary lesions from 33 patients suspected of malignancy in computed tomography, were assessed by 99mTc-depreotide and 201Tl early and delayed SPET imaging. Images were visually assessed and the tumour-to-normal (T/N) lung activity ratio for early (ER) and delayed (DR) scans and the retention index (RI), were calculated in every lesion. A final diagnosis was reached for all lesions, based either on histology or prolonged clinical and radiological follow-up. ResultsTwenty-three lesions were characterized as malignant and 34 benign. In visual analysis, all malignant lesions accumulated both tracers resulting in sensitivity and negative predictive values of 100%. However, false positive interpretations resulted in a specificity of 64.7% and 67.6% for 99mTc-depreotide and 201Tl, respectively. ER and DR of both agents and the RI of 99mTc-depreotide were significantly higher in malignant, compared to benign lesions. In defining thresholds of abnormality from ROC analysis, a significant increase in specificity was observed for both tracers in both scan phases (91.2% for all), as compared to visual analysis (P<0.01). There was no significant difference in the diagnostic performance between 99mTc-depreotide DR and 201Tl DR, although the former provided the highest T/N ratio. ConclusionThis study demonstrates that 99mTc-depreotide and 201Tl SPET are equally effective and may be useful in the non-invasive determination of lung malignancy. The specificity of both techniques is significantly improved by quantifying radiopharmaceutical accumulation in pulmonary lesions.