The Effect of Susceptibility Artifacts Related to Metallic Implants on Adjacent-Lesion Assessment in Simultaneous TOF
Hanna Svirydenka1,2, Gaspar Delso3, Felipe De Galiza Barbosa1
1Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.
Abstract:
Metalic implants may affect attenuation correction (AC) in PET/MR imaging. The purpose of this study was to evaluate the effect of susceptibility artifacts related to metallic implants on adjacent metabolically active lesions in clinical simultaneous PET/MR scanning for both time-of-flight (TOF) and non-TOF reconstructed PET images. Methods: We included 27 patients without implants but with confirmed 18F-FDG-avid lesions adjacent to common implant locations. In all patients, a clinically indicated whole-body 18F-FDG PET/MR scan was acquired. Baseline non-TOF and TOF PET images were reconstructed. Reconstruction was repeated after the introduction of artificial signal voids in the AC map to simulate metallic implants in standard anatomic areas. All reconstructed images were qualitatively and quantitatively assessed and compared with the baseline images. Results: In total, 51 lesions were assessed. In 40 and 50 of these cases (non-TOF and TOF, respectively), the detectability of the lesions did not change; in 9 and 1 cases, the detectability changed; and in 2 non-TOF cases, the lesions were no longer visible after the introduction of metallic artifacts. The inclusion of TOF information significantly reduced artifacts due to simulated implants in the femoral head, sternum, and spine (P = 0.01, 0.01, and 0.03, respectively). It also improved image quality in these locations (P = 0.02, 0.01, and 0.01, respectively). The mean percentage error was -3.5% for TOF and -4.8% for non-TOF reconstructions, meaning that the inclusion of TOF information reduced the percentage error in SUVmax by 28.5% (P < 0.01). Conclusion: Qualitatively, there was a significant reduction of artifacts in the femoral head, sternum, and spine. There was also a significant qualitative improvement in image quality in these locations. Furthermore, our study indicated that simulated susceptibility artifacts related to metallic implants have a significant effect on small, moderately 18F-FDG-avid lesions near the implant site that possibly may go unnoticed without TOF information. On larger, highly 18F-FDG-avid lesions, the metallic implants had only a limited effect. The largest significant quantitative difference was found in artifacts of the sternum. There was only a weak inverse correlation between lesions affected by artifacts and distance from the implant.
Insights
Metallic implants can cause artifacts in PET/MR imaging. Time-of-flight (TOF) reconstruction significantly reduces these artifacts, improving the detection of metabolically active lesions near implants.
Area of Science:
- Medical Imaging
- Nuclear Medicine
- Radiology
Background:
- Metallic implants can introduce susceptibility artifacts in PET/MR imaging, potentially affecting attenuation correction (AC).
- These artifacts may obscure or alter the detectability of metabolically active lesions, particularly those adjacent to implants.
- Evaluating the impact of these artifacts on lesion detectability in both time-of-flight (TOF) and non-TOF PET images is crucial for accurate diagnosis.
Purpose of the Study:
- To assess the effect of metallic implant-related susceptibility artifacts on adjacent metabolically active lesions in simultaneous PET/MR imaging.
- To compare the impact of these artifacts on both time-of-flight (TOF) and non-TOF reconstructed PET images.
- To evaluate the utility of TOF information in mitigating artifacts and improving lesion detectability.
Main Methods:
- 27 patients with 18F-FDG-avid lesions near common implant locations underwent clinical whole-body 18F-FDG PET/MR scans.
- Non-TOF and TOF PET images were reconstructed, followed by reconstructions simulating metallic implants via artificial signal voids in the AC map.
- Reconstructed images were qualitatively and quantitatively assessed and compared to baseline images.
Main Results:
- Simulated metallic implants caused artifacts that affected lesion detectability in some cases, with 2 non-TOF cases showing lesions becoming invisible.
- Time-of-flight (TOF) information significantly reduced artifacts and improved image quality near femoral head, sternum, and spine implants (P < 0.05).
- TOF reconstruction reduced the percentage error in SUVmax by 28.5% (P < 0.01) compared to non-TOF, with the largest quantitative difference in sternum artifacts.
Conclusions:
- Metallic implants significantly affect the detectability of small, moderately 18F-FDG-avid lesions near implant sites, potentially leading to missed diagnoses without TOF information.
- Time-of-flight (TOF) significantly reduces susceptibility artifacts and improves image quality in PET/MR imaging of patients with metallic implants.
- TOF information is essential for accurate assessment of metabolically active lesions in proximity to metallic implants, especially in the femoral head, sternum, and spine.
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