Olivier Caselles PhD, Presenter: Nothing to Disclose

Delphine Serre, Abstract Co-Author: Nothing to Disclose

Th purpose of this study was to evaluate the accuracy of attenuation coefficients maps at 511 keV calculated from CT data over a wide range of densities, and to imagine a simple and reliable quality control of this calculation.

CT slices of an electron density phantom (CIRS model 062)were acquired using the routine clinical acquisition protocol (slice thickness = 3.75 mm, interval = 3.27 mm, pitch = 0.75, FOV = 50 cm, helical mode, rotation speed = 1s/t) on a Discovery ST4 PET/CT (GEMS - Milwaukee). Datasets were obtained at 80, 100,120 and 140 kV and 250 mAs.CT based attenuation correction raw data (CTAC)were reconstructed using a standard filtered back projection algorithm (Hanning filter : 7.8125 mm)to obtain attenuation maps at 511 keV in cm-1.The central transaxial image (number 23 over 47) of each dataset was analyzed by placing 18 mm diameter circular regions of interest (ROIs) over each insert. From the ROI values, a mean and standard deviation were extracted using the Artiscan CT quality control software(Aquilab - Lille, France).

No significant difference is observed between the attenuation coefficients obtained from the different datasets. The maximum deviation corresponds to high density materials (over 1.1 g/cm3), but in this case, CT attenutation coefficients obtained from a bilinear conversion model are known to be lower than theoretical ones.The results show that the quality control method we have developed is simple and reliable, and permits to obtain quickly the CTAC values.

We have developed a simple and reliable method using a commercial software to control the invariability and the accuracy of CT based attenuation coefficients, which are of main importance in quantification studies.This may be particularly relevant in case of software update, or to experiment new conversion models.

Caselles, O, Serre, D, CT-based Attenuation Correction for PET/CT: Evaluation and Quality Control.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4405618.html