Summary: A new ultra-low dose imaging method using long axial field-of-view PET scanners reduces radiopharmaceutical doses by over 50 times and eliminates the need for CT scans, significantly lowering patient radiation exposure while maintaining accuracy.
Key Takeaways:
- A new ultra-low dose PET imaging method reduces radiopharmaceutical doses by over 50 times and eliminates the need for CT scans, significantly lowering patient radiation exposure.
- The method utilizes background radiation from Lutetium-176 and deep learning to generate CT-free attenuation maps, maintaining quantitative accuracy and clinically feasible scan durations.
- This advancement enhances PET scan applications, including screening, research, frequent follow-up, and pediatric scans, and involves ongoing optimizations with AI-based image enhancement.
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A new ultra-low dose PET imaging method reduces radiopharmaceutical doses by over 50 times and eliminates the need for CT scans, significantly lowering patient radiation exposure. This research was presented at the 2024 Society of Nuclear Medicine and Molecular Imaging Annual Meeting.
Balancing Radiopharmaceutical and CT Radiation Doses
PET/CT examinations expose patients to ionizing radiation in two ways: the radiation dose resulting from the administered radiopharmaceutical and from the CT scan. Increased sensitivity and high timing resolution of long axial field-of-view PET scanners have enabled significant reductions in injected dose of radiopharmaceuticals. However, the advantages of low-dose PET examinations with such scanners can be hindered by the radiation dose linked to the CT scans conducted for PET attenuation correction.
“Recently, methods have been developed to utilize the background radiation from Lutetium-176 that is found in some PET scintillators as transmission source; this is known as LSO-TX. By combining LSO-TX information with joint reconstruction- and deep learning-based methodologies, CT-free attenuation maps can be generated,” says Hasan Sari, PhD, senior research scientist at Bern University Hospital in Bern and Siemens Healthineers International AG in Zürich, Switzerland.
“In this work, we evaluated the performance of the LSO-TX-based attenuation correction method in ultra-low dose PET scans using a long axial field-of-view PET scanner,” Sari adds.
Matching CT-Based Accuracy with Less Radiation
Four subjects were administered a mean tracer activity of 7.9 MBq and underwent a 90-minute long PET scan using a long axial field-of-view PET scanner. LSO-TX data were separately acquired and enhanced using a deep-learning based method. The patients also received low-dose CT scans. CT-based and LSO-transmission-based attenuation maps were generated and used to reconstruct PET images, which were then compared across different scan durations.
A very close visual resemblance was observed between CT- and LSO-TX-based attenuation maps, as well as between PET images reconstructed with the maps. By using the LSO-TX-based attenuation correction alone (no CT), the total effective dose in these scans was reduced to approximately0.15 mSV while still preserving good quantitative accuracy and maintaining clinically feasible scan durations.
“This reduction in radiation dose is 50 times lower than the standard PET dose and is comparable to the dose received from a mammogram or a chest CT radiograph,” noted Sari. “Ultra-low-dose protocols have the potential to extend the use of PET scans beyond their current applications and could significantly enhance the utility of this modality in screening studies involving at-risk or healthy subjects, research studies, enhanced treatment response assessments with more frequent follow-up scans, and pediatric scans.”
Attenuation Maps for PET Scans
Long axial field-of-view scanners are widely available globally. The CT-free attenuation correction method uses a special research mode protocol, generating attenuation maps offline. Bern University Hospital is collaborating with Siemens Healthineers to simplify this method, with AI enhancements underway to further reduce scan durations.
Featured image: Top row: CT- and LSO-TX-based attenuation maps with their respective percentage relative change (%RC) map. Bottom row: PET images reconstructed using CT- and LSO-TX-based attenuation maps with their respective %RC map.
