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PVEOUT Report Summary

Project ID: QLG3-CT-2000-00594
Funded under: FP5-LIFE QUALITY
Country: Italy

Physical phantom for hybrid PET/SPET/CT/MRI use

We have realised an anthropomorphic multi-compartment phantom of the human brain suitable for PET/SPET and CT/MR imaging. No other phantom with these characteristics has either been described in the refereed literature or is currently commercially available. The phantom (which we call STEPBrain) was designed as composed by two separate compartments for grey matter (GM) and white matter (WM), which can be filled by solutions with different isotope (PET/SPET), metal (MRI), or iodine (CT) concentrations. It was built by a rapid prototyping technique applied to a digital model derived from a 1.5T MRI dataset of a 35 y.o. normal volunteer composed of 150 3mm-thick partially overlapping slices (1mm increment) covering the whole brain. For each slice location T1-, PD- and T2- weighted spin-echo images were obtained, and segmented into GM, WM and CSF using a multi-parametric technique (Magn Reson Med 1997;37:84). The subsequent processing of the segmented images by homemade and industrial software included: manual editing of the basal ganglia to ensure their connection with GM to allow proper filling; filling of the vessels located inside the parenchyma with the tissue type that occur most frequently on the surrounding pixels; final elimination of "isles" of pixels inside a tissue type not connected in 3-D with other pixels of the same type; a 5x5x3 median spatial filtering of the entire volume to smooth the boundaries of the tissues; conversion of the binary file into a vectorial representation of the surfaces; creation of the hollow of GM and WM compartments defining the separation 1.5mm-thick walls separating the three compartments; adding of tubes to allow filling of GM and WM compartments. The resulting file was used to drive a rapid prototyping machine, which, materialising the walls, provides the final phantom. GM and WM compartments are fillable with solutions with different isotope concentrations for PET/SPET scanning (i.e. 4/1 ratio simulates normal GM/WM contrast for FDG), while different paramagnetic ion concentrations can simulate different GM/WM relaxometric properties. The prototype of the phantom proved to be waterproof, with no communication between GM and WM compartments, and suitable for CT, MR, PET and SPET scanning. An important application, which is the original aim of this phantom, is the validation of different techniques for partial volume effect correction in low-resolution images. STEPBrain is currently the only anthropomorphic phantom useful for this aim. Furthermore STEPBrain can be used for NM brain study simulation better then other anthropomorphic brain phantoms, currently in use in most NM centres. The most widespread of them is the Hoffman phantom realised with shaped thin plastic levels inserted in a plastic cylinder. It comprises only one compartment simulating the brain. GM area is empty, while WM area is in part (3/4) packed by plastic levels to simulate a WM concentration of 1/4 of GM concentration. Since in STEPBrain GM and WM are two independent compartments, it can simulate any ratio of isotope concentration. The industrial cost of STEPBrain is about 1/5 of the mean price of the other anthropomorphic phantoms used in Nuclear Medicine. The potential market is very large, corresponding to all NM departments.

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Bruno ALFANO, (Research Director)
Tel.: +39-081-2203187
Fax: +39-081-2296117
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