Use of segmented CT transmission map to avoid metal artifacts in PET images by a PET-CT device

Thirty oncologic patients were studied using CT and 137Cs for attenuation correction. All image data were acquired using the Gemini PET-CT scanner (Philips Medical Systems). It is an open PET-CT system that consists of the MX8000 multislice CT and the Allegro PET scanner arranged in a separable configuration. Images with ACseg+ and ACseg- were analyzed simultaneously in coronal, sagittal and transaxial planes. Two nuclear medicine physicians reviewed the image sets. Results: The image quality in the area of metal implants was better with ACseg+ than ACseg-, without metal induced artifacts generally observed in CT corrected images. Further the images with ACseg+ were qualitatively comparable to those obtained with 137Cs attenuation correction. Conclusions: In case of metal implants, PET studies corrected by CT should preferably use the ACseg+ method to avoid the image artifacts.Attenuation correction (AC) is generally applied to achieve count rate values independent from tissue densities. Transmission scanning was already suggested in 1952 by Myneord [1]. The transmission scanning was used to match anatomical contours to the radionuclide distribution measured by a rectilinear scanner [2]. Different isotopes have been used to acquire transmission data as earlier I-125, I-131, Tm-170 and later Tc-99 m, I-131, Ba-133, Cs-137 and Ge-68. With the development of SPECT and PET systems the transmission scanning was used for the purpose of AC and various methods for the use of transmission data were developed [3,4]. The PET transmission scan is ideally acquired before the radiopharmaceutical is administered, but would lead to long clinical protocols which are not suitable for routine use. Today, for PET-investigations post-injection transmission scans are performed using electronically windowed rotating rod sources as Ge-68, or rotating point sources as Cs-137 or CT in PET-CT systems. The combined PET-CT systems have the advantage to provide anatomical information while CT tr