Respiratory motion artifacts on PET emission images obtained using CT attenuation correction on PET-CT

Abstract

PET-CT scanners allow generation of transmission maps from CT. The use of CT attenuation correction (CTAC) instead of germanium-68 attenuation correction (Ge AC) might be expected to cause artifacts on reconstructed emission images if differences in respiratory status exist between the two methods of attenuation correction. The aim of this study was to evaluate for possible respiratory motion artifacts (RMA) in PET images attenuation corrected with CT from PET-CT in clinical patients. PET-CT scans were performed using a Discovery LS PET-CT system in 50 consecutive patients (23 males, 27 females; mean age 58.2 years) with known or suspected malignancy. Both CTAC and Ge AC transmission data obtained during free tidal breathing were used to correct PET emission images. Cold artifacts at the interface of the lungs and diaphragm, believed to be due to respiratory motion (RMA), that were seen on CTAC images but not on the Ge AC images were evaluated qualitatively on a four-point scale (0, no artifact; 1, mild artifact; 2, moderate artifact; 3, severe artifact). RMA was also measured for height. Curvilinear cold artifacts paralleling the dome of the diaphragm at the lung/diaphragm interface were noted on 84% of PET-CT image acquisitions and were not seen on the (68)Ge-corrected images; however, these artifacts were infrequently severe. In conclusion, RMA of varying magnitude were noted in most of our patients as a curvilinear cold area at the lung/diaphragm interface, but were not diagnostically problematic in these patients.

PET/CT imaging: Effect of respiratory motion on apparent myocardial uptake

“…This can produce a mis-registration between the CT data used to perform attenuation correction and the PET emission data which is acquired over many respiratory cycles. There have been several studies showing that this effect can cause artifacts in PET/CT reconstructions in oncology -especially at borders between the lung and soft tissue, such as the liver-lung interface [1][2][3][4][5][6]. Because the heart also has a lung-soft tissue interface, it would seem likely that there would be similar artifacts in apparent myocardial activity uptake when performing cardiac PET/CT studies.…”

Attenuation Correction Strategies for Positron Emission Tomography/Computed Tomography and 4-Dimensional Positron Emission Tomography/Computed Tomography

“…Misregistration between the CT and PET images due to respiratory motion in the thorax and abdomen was reported soon after the first commercial PET/CT was introduced in 2001 [36][37][38][39] and has been among the most researched topics in PET/CT. It has impact on radiation therapy, which relies on accurate localization of the tumor for targeted treatment.…”

“…37 However, it only impacted 2% of diagnosis in the whole-body PET/CT with 18 F-FDG 44 but caused false-positive results in 40% of the cardiac PET/CT studies with 82 Rb. 45 In whole-body PET/CT, many lesions may not be close to the diaphragm, where most misregistrations occur; and as such, the task of diagnosis may not be compromised by a misregistration between the CT and the PET data.…”

“…Pan and colleagues 42 demonstrated that registration of the CT and PET data can be improved with average CT in tumor imaging and myocardial perfusion imaging. 51 Papathanassiou and colleagues 81 and Osman and colleagues 37 showed that using the attenuation map from transmission rod sources to correct for the PET images would not produce the curvilinear cold artifacts in the PET data of PET/CT. Transmission rod source is only available in the first-generation PET/CT scanners and not available on the newer PET/CT scanners.…”

Comparative Assessment of Energy-Mapping Approaches in CT-Based Attenuation Correction for PET

“…There are several parameters that affect the quality and quantitative accuracy of PET images, including positron range [1], the limited spatial resolution and resulting partial volume effect [2], contribution from scattered photons [3], photon attenuation [4], patient motion [5], and the image reconstruction algorithm [6]. Attenuation of photons in vivo degrades the visual quality and quantitative accuracy of PET images, thereby adversely affecting interpretation and quantitation of activity concentration.…”