Abstract
Textural analysis might give new insights into the quantitative characterization of metabolically active tumors. More than thirty textural parameters have been investigated in former F18-FDG studies already. The purpose of the paper is to declare basic requirements as a selection strategy to identify the most appropriate heterogeneity parameters to measure textural features. Our predefined requirements were: a reliable heterogeneity parameter has to be volume independent, reproducible, and suitable for expressing quantitatively the degree of heterogeneity. Based on this criteria, we compared various suggested measures of homogeneity. A homogeneous cylindrical phantom was measured on three different PET/CT scanners using the commonly used protocol. In addition, a custom-made inhomogeneous tumor insert placed into the NEMA image quality phantom was imaged with a set of acquisition times and several different reconstruction protocols. PET data of 65 patients with proven lung lesions were retrospectively analyzed as well. Four heterogeneity parameters out of 27 were found as the most attractive ones to characterize the textural properties of metabolically active tumors in FDG PET images. These four parameters included Entropy, Contrast, Correlation, and Coefficient of Variation. These parameters were independent of delineated tumor volume (bigger than 25–30 ml), provided reproducible values (relative standard deviation< 10%), and showed high sensitivity to changes in heterogeneity. Phantom measurements are a viable way to test the reliability of heterogeneity parameters that would be of interest to nuclear imaging clinicians.
Highlights
Medical imaging methods have an increasing role in cancer diagnostics and the assessment of therapy responses
The volume dependence of the heterogeneity parameters (HePs) values were limited to 25–30 ml volume range (Fig 4A)
The fourth category consisted of parameters which cannot be characterized by a simple function (Fig 4D)
Summary
Medical imaging methods have an increasing role in cancer diagnostics and the assessment of therapy responses. Computed Tomography (CT), Magnetic Resonance (MR), Single Photon Emission Computed Tomography (SPECT), and Positron Emission Tomography (PET) are the most frequently used tomographic techniques When considering these techniques overall, one of the advantages of PET imaging is that it is highly quantitative. A large number of articles have been published during the last decade to establish and reveal which SUV values and what cut off levels are the most appropriate for different tumor types in therapy monitoring and staging of cancer patients. Both the volume analysis and the SUV are confounded by the Partial Volume Effect (PVE). Any additional quantitative parameter would improve the prognostic and diagnostic capabilities of PET
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