[Fundamental evaluation of segmented attenuation correction method for clinical FDG-PET studies: simulation of...

Both the segmented attenuation correction (SAC) method and post-injection transmission scanning are useful and widespread in clinical whole-body FDG-PET studies. The SAC method usually accomplishes smoothing of the transmission data. This calculation segments a micro -map into three degrees (lung, soft tissue, and bone) of attenuation coefficient. This method is used to reduce transmission scan time without deteriorating the quality of PET images. However, the SAC method has a tendency to underestimate the attenuation coefficient, resulting lower detectability for lung field mass lesions. We therefore evaluated the quantitative accuracy of the SAC method using transmission scanning and emission scanning data in a phantom study.

A dedicated 3D PET scanner, the Siemens ECAT EXACT HR+, was used to scan images of two types of phantoms, a spherical phantom (Japan Radioisotope Association phantom) and a cylindrical phantom (20 cm in diameter). We evaluated differences between transmission images ( micro -map) of the SAC method and measured attenuation correction (MAC) method, these two kinds of attenuation-corrected emission data (emission + SAC method, emission + MAC method), and emission data only (without attenuation correction).

In the micro -map, recovery coefficient (RC) values at 10 mm in diameter were 0.27 and 0.00 in the MAC and SAC methods, respectively, in the spherical hot area. For the emission data, the emission + SAC method and emission + MAC method showed almost the same RC values for all sizes of hot area diameter. The SAC method, however, resulted in 20% underestimation for all sizes of hot area diameter as compared with the MAC method.

In pulmonary mass lesions, it is necessary to correct for the partial volume effect in quantitative PET measurement. However, from our data, the SAC method is not appropriate for partial volume effect correction.