MOD PET

The MOD-PET module automates the tests proposed by the NEMA and SFPM given below:

• Spatial resolutions¹: FWHM and FWTM (Full Width at Half Maximum and at Tenth Maximum) - intrinsic* tangential axial, central, frontal, and sagittal, at ½ and ¼ of axial FOV, of the transmission (PSF) by the PET camera of the signal coming from quasi-point sources.

• Image quality on a thorax equivalent phantom²: Contrasts obtained on hot and cold fillable spheres relative to the medium in which they are situated (background)– Over-contrast coefficients for the hot spheres, in other words the ratios of contrast measured in the image relative to the intrinsic contrast of the object given by the ratio of the radioactive concentration between the spheres and the background – Residual error in scatter and attenuation corrections in the lung insert – Noise background Signal Ratio and Background signal variability associated with hot spheres, cold spheres and the lung insert.

• Accuracy of corrections³: Control in the case of a homogeneous distribution of the radioactive concentration, of the quality of all of the corrections and of all of the calculations performed on the signal measured by the PET camera to obtain tomographic images calibrated in SUV. Thus on the CT images of a connected scanner, measurement of the average linear attenuation coefficient of water at 511 KeV, comparison to its theoretical value, study of its dispersion between slices and inside of the central slice of the cylindrical phantom. On the PET images, measurement of average SUV, comparison to its theoretical value of 1, study of its dispersion between slices and its radial distribution inside of these slices.

• Accuracy of the attenuation maps⁴: Indirect control of the quality of the corrections of attenuation originating from the scanner connected to the PET camera by measuring in the scanner images recomputed at 511 KeV by the scanner console (attenuation map), the linear attenuation coefficients (µ511)of a large range of reference materials whose coefficients are known to be 511 KeV. QUALIMAGIQ also enables you to complete this test by analysing in a similar manner the original scanner images obtained at 120 KV in order to distinguish a deviation between the measured µ and the reference µ already present in the original scanner at 120 KV from a deviation present solely in the scanner recomputed at 511 KeV. Incidentally, QUALIMAGIQ supplies based on the images of this original scanner a tracking of the stability of the conversion (Electron Density # Hounsfield units) and of the efficient energy of the X-Ray beam used to acquire the images.

• Accuracy of attenuation corrections⁵: This test is complementary to the Accuracy of the attenuation maps test on the attenuation maps produced by the scanner linked to a PET, however here QUALIMAGIQ tests whether these attenuation maps efficiently correct the attenuation of annihilation photons by verifying that the signals calibrated in raw radioactive or normalised (SUV) concentration are the same in a series of 2 to 6 test tubes containing the same radioactive concentration but different electron densities.

• Geometric alignment of the CT scanner on the PET imager⁶: Magnification deviation – Angular magnification deviations – Deviation in the position in the 3 directions of space – of a rectilinear source acquired in the 2 modalities.