Abstract
BackgroundHalo artifacts from urinary catheters can occur due to inaccurate scatter correction, and the artifacts affect the tumor visibility in 18F-FDG PET/CT images. We investigated the incidence rate and the mechanisms of halo-artifact generation and explored several scatter correction techniques to prevent artifacts.MethodsWe conducted patient and phantom studies. (1) We retrospectively reviewed the cases of patients who had undergone 18F-FDG PET/CT scans. To determine the frequency of halo-artifact generation, we used the patients’ PET images with a standard scatter correction based on a tail-fitted single-scatter simulation (TF-SSS) using 4-mm voxel μ-maps (TFS 4-mm). (2) We performed phantom studies to evaluate the effects of a urine catheter and two scatter correction techniques, i.e., TF-SSS with 2-mm voxel μ-maps (TFS 2-mm) and a Monte Carlo-based single-scatter simulation (MC-SSS) using 4-mm voxel μ-maps (MCS 4-mm). The average standardized uptake values (SUVs) were measured for axial PET images. (3) Using the patients’ data, we investigated whether TFS 2-mm and MCS 4-mm can eliminate the artifacts in the clinical images.Results(1) There were 61 patients with urinary catheters; in five (8.2%), halo artifacts were observed in the TFS 4-mm PET images. (2) The phantom study clearly reproduced the halo artifacts in the TFS 4-mm PET images. The halo artifacts were generated when urine moved in the interval between the CT and PET imaging, and when the urinary catheter was placed in a circular shape. The SUVs for the TFS 4-mm and TFS-2mm PET images were underestimated at the halo-artifact regions, whereas the SUVs for the MCS 4-mm PET images were close to the true values. (3) The halo artifacts disappeared in the TFS 2-mm PET images in 4/5 patients but not 1/5 patient, whereas the halo artifacts were completely absent in the MCS 4-mm PET images in 5/5 patients.ConclusionsThese data suggest that halo artifacts are caused if the PET images do not correspond to the physical material in the μ-maps, which induces the scatter correction error. With the MC-SSS, it was possible to accurately estimate the scatter without generating halo artifacts.
Highlights
Positron emission tomography/computed tomography (PET/CT) is useful for the assessment and management of many types of cancer including their diagnosis, staging, prognosis, and therapeutic efficacy. 18F-fluorodeoxyglucose (FDG) PET/CT in particular has become an important tool for identifying new and effective therapies in cancer treatment and for its role as an imaging biomarker [1, 2].The main excretion pathway of 18F-FDG is through the kidneys, ureters, and bladder, and this makes it difficult to adequately visualize pelvic tumors by using filtered backprojection images because streak artifacts may appear in the pelvis
(2020) 7:66 (Continued from previous page). These data suggest that halo artifacts are caused if the PET images do not correspond to the physical material in the μ-maps, which induces the scatter correction error
We retrospectively evaluated the cases of patients with indwelling urinary catheters who had undergone 18F-FDG PET/CT scans, and to clarify the mechanism underlying the artifacts, we performed phantom studies simulating 18F-FDG PET/CT imaging with urinary catheters
Summary
The main excretion pathway of 18F-FDG is through the kidneys, ureters, and bladder, and this makes it difficult to adequately visualize pelvic tumors by using filtered backprojection images because streak artifacts may appear in the pelvis Such streak artifacts can be reduced by an iterative reconstruction algorithm [3], but when other radiotracers with renal excretion are used (e.g., 68Ga-labeled prostate-specific membrane antigen [PSMA]) [4], photopenic artifacts surround the kidneys and the bladder even in iterative reconstruction images [5, 6]. The possibility of the halo artifact’s appearance can be reduced by oral hydration of the imaged patient, and by suppressing the patient’s urination urge by the administration of a diuretic before PET imaging [13], and by urine drainage using an indwelling urinary catheter into the bladder This procedure is important for the identification of pelvic tumors such as colorectal and bladder cancers [14, 15]. We investigated the incidence rate and the mechanisms of halo-artifact generation and explored several scatter correction techniques to prevent artifacts
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