Assessing and accounting for the impact of respiratory motion on FDG uptake and viable volume for liver lesions in free‐breathing PET using respiration‐suspended PET images as reference

Abstract

Purpose: To assess and account for the impact of respiratory motion on the variability of activity and volume determination of liver tumor in positron emission tomography (PET) through a comparison between free-breathing (FB) and respiration-suspended (RS) PET images. Methods: As part of a PET/computed tomography (CT) guided percutaneous liver ablation procedure performed on a PET/CT scanner, a patient's breathing is suspended on a ventilator, allowing the acquisition of a near-motionless PET and CT reference images of the liver. In this study, baseline RS and FB PET/CT images of 20 patients undergoing thermal ablation were acquired. The RS PET provides near-motionless reference in a human study, and thereby allows a quantitative evaluation of the effect of respiratory motion on PET images obtained under FB conditions. Two methods were applied to calculate tumor activity and volume: (1) threshold-based segmentation (TBS), estimating the total lesion glycolysis (TLG) and the segmented volume and (2) histogram-based estimation (HBE), yielding the background-subtracted lesion (BSL) activity and associated volume. The TBS method employs 50% of the maximum standardized uptake value (SUV max ) as the threshold for tumors with SUV max ≥ 2× SUV liver-bkg , and tumor activity above this threshold yields TLG 50% . The HBE method determines local PET background based on a Gaussian fit of the low SUV peak in a SUV-volume histogram, which is generated within a user-defined and optimized volume of interest containing both local background and lesion uptakes. Voxels with PET intensity above the fitted background were considered to have originated from the tumor and used to calculate the BSL activity and its associated lesion volume. Results: Respiratory motion caused SUV max to decrease from RS to FB by −15% ± 11% (p = 0.01). Using TBS method, there was also a decrease in SUV mean (−18% ± 9%, p = 0.01), but an increase in TLG 50% (18% ± 36%) and in the segmented volume (47% ± 52%, p = 0.01) from RS to FB PET images. The background uptake in normal liver was stable, 1% ± 9%. In contrast, using the HBE method, the differences in both BSL activity and BSL volume from RS to FB were −8% ± 10% (p = 0.005) and 0% ± 16% (p = 0.94), respectively. Conclusions: This is the first time that almost motion-free PET images of the human liver were acquired and compared to free-breathing PET. The BSL method's results are more consistent, for the calculation of both tumor activity and volume in RS and FB PET images, than those using conventional TBS. This suggests that the BSL method might be less sensitive to motion blurring and provides an improved estimation of tumor activity and volume in the presence of respiratory motion.

Analysis of Prognostic Values of Various PET Metrics in Preoperative 18F-FDG PET for Early-Stage Bronchial Carcinoma for Progression-Free and Overall Survival: Significantly Increased Glycolysis Is a Predictive Factor

“…However, all of these cases would be in the low-risk category and therefore this limitation would not be as substantial for outcome prediction as it would be for therapy response assessment, if one cannot determine the baseline value. To use the background of the surrounding tissue instead of an absolute or relative cutoff also seems to be a superior approach in other organs with variable background activities, such as the liver (28). First evidence showed more stable results of BSV compared with MTV50% measurements between breath-hold and free-breathing PET.…”

“…First evidence showed more stable results of BSV compared with MTV50% measurements between breath-hold and free-breathing PET. This can be explained by the strong influence of blurring on the SUV max and consequently the selected threshold, whereas background activity of the liver is less affected by motion, therefore the tumor volume between breath-hold and free-breathing PET scans shows better correlation for BSV than MTV50% (28).…”

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

“…Multiple studies have demonstrated the benefits of 4D PET-CT in resolving the low SUV signal and decreasing the smearing effect when compared to 3D PET-CT of moving targets, which results in improved sensitivity, specificity, and accuracy in detecting malignant lung and liver lesions. [164][165][166][167][168][169][170][171] 4D PET-CT has also been shown to reduce the risk of underdosing and geographic miss of targets during treatment in comparison to 3D PET-CT. This is due to applying appropriate margins to the motion-compensated images, rather than just a generic target volume margin for 3D PET-CT. [172][173][174] Four dimensional PET-CT has also improved inter-observer agreement in target delineations for lung SBRT volumes, reiterating the benefit of avoiding a geographic miss.…”

Interventional Molecular Imaging

“…With assistance from the anesthesia team, registration issues stemming from respiratory motion may be reduced (13). Although continuous breathing during diagnostic PET acquisitions may distort lesion size or shape or create partial-volume effects, particularly along the direction of maximal respiratory motion, registration may be improved through the use of breath-holding techniques, sedation, or general anesthesia during the procedure (15,16). The use of short-breath-hold PET acquisitions (e.g., 20 s) has been shown valuable (13).…”