Impact of acquisition geometry and patient habitus on lesion detectability in whole body FDG-PET: a channelized hotelling observer study

Although 3D "septaless" imaging has been shown to have advantages over 2D imaging under many conditions, it is not routinely used in the clinic in whole-body (WB) FDG-PET studies partly due to contradictory reports comparing 3D to 2D. The aim of this work was to evaluate the impact of the acquisition mode (2D vs 3D) on lesion detectability in WB FDG-PET studies for different lesion and patient sizes. Forty eight bed positions were acquired in thirty six patients, each in both 2D and 3D mode, 1-4 hours post-injection (740 MBq). Three spheres (1 cm, 1.3 cm and 1.6 cm diameter) containing FDG were also, imaged separately in air, at ten different locations corresponding to possible lesion sites in the 48 bed positions, also each in both 2D and 3D (480 tat-gets per condition). Each bed position was acquired for 7 min in 2D and 6 min in 3D and corrected for randoms. Sphere sinograms,were attenuated using the exact 2D or 3D attenuation map of the patient, after scaling 2D and 3D sinograms with identical factors to ensure marginal detectability. The resulting volumes were corrected for scatter and reconstructed using ordered subsets expectation maximization (OSEM) in 2D and Fourier rebinning (FORE)+OSEM in 3D. Next, 2D and 3D acquisition modes were compared on the basis of performance of a three-channel Hotelling observer (CHO) which incorporated internal noise in detecting the presence of a sphere of unknown size on an anatomic background. 3D imaging yielded better lesion detectability than 2D (p<0.025, two-tailed paired t-test) in patients of typical size (Body Mass Index <33). However 2D imaging yielded better lesion delectability than 3D in large patients (BMI>34) as 3D performance significantly deteriorated in large patients (P<0.05). Finally, 2D and 3D yielded similar results for different lesion sizes.