Attenuation correction in whole-body FDG oncological studies: the role of statistical reconstruction

Whole-body fluorine-18 fluoro-2-D-deoxyglucose positron emission tomography (FDG-PET) is widely used in clinical centres for diagnosis, staging and th erapy monitoring in oncology. Images are usually not corrected for attenuat ion since filtered backprojection (FBP) reconstruction methods require a 10 to 15-min transmission scan per bed position on most current PET devices e quipped with germanium-68 rod transmission sources. Such an acquisition pro tocol would increase the total scanning time beyond acceptable limits. The aim of this work is to validate the use of iterative reconstruction methods , on both transmission and emission scans, in order to obtain a fully corre cted whole-body study within a reasonable scanning time of 60 min. Five min ute emission and 3-min transmission scans are acquired at each of the seven bed positions. The transmission data are reconstructed with OSEM (ordered subsets expectation maximization) and the last iteration is reprojected to obtain consistent attenuation correction factors (ACFs). The emission image is then also reconstructed with OSEM, using the emission scan corrected fo r normalization, scatter and decay together with the set of consistent ACFs as inputs. The total processing time is about 35 min, which is acceptable in a clinical environment. The image quality, readability and accuracy of u ptake quantification were assessed in 38 patients scanned for various malig nancies. The sensitivity for tumour detection was the same for the non-atte nuation-corrected (NAC-FBP) and the attenuation-corrected (AC-OSEM) images. The AC-OSEM images were less noisy and easier to interpret. The interobser ver reproducibility was significantly increased when compared with non-corr ected images (96.1% vs 81,1%, P<0.01). Standardized uptake values (SUVs) me asured on images reconstructed with OSEM (AC-OSEM) and filtered backproject ion, (AC-FBP) were similar in all body regions except in the pelvic area, w here SUVs were higher on AC-FBP images (mean increase 7.74%, P<0.01). Our r esults show that, when statistical reconstruction is applied to both transm ission and emission data, high quality quantitative whole-body images are o btained within a reasonable scanning (60 min) and processing time, making i t applicable in clinical practice.