New ultralow-dose PET protocol eliminates need for CT scans

por Gus Iversen, Editor in Chief | June 11, 2024
Molecular Imaging
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.
A new imaging method using long axial field-of-view PET scanners can produce images with a radiopharmaceutical dose over 50 times lower than the current standard, eliminating the need for CT scans and significantly reducing patient radiation exposure.

Traditional PET/CT exams expose patients to radiation from both the radiopharmaceutical dose and the CT scan. Long axial field-of-view PET scanners have improved sensitivity and timing resolution, allowing for lower radiopharmaceutical doses. However, the accompanying CT scan for PET attenuation correction has limited the overall reduction in radiation exposure.

"Recently, methods have been developed to use background radiation from Lutetium-176 in some PET scintillators as a transmission source, known as LSO-TX. By combining LSO-TX information with joint reconstruction and deep learning methodologies, CT-free attenuation maps can be generated," explained Hasan Sari, Ph.D., senior research scientist at Bern University Hospital and Siemens Healthineers International AG.

In the study, which was showcased at the SNMMI annual meeting in Toronto, four subjects received an average tracer activity of 7.9 MBq and underwent 90-minute PET scans with a long axial field-of-view scanner. LSO-TX data were separately acquired and enhanced using a deep learning method. Both CT-based and LSO-transmission-based attenuation maps were generated and used to reconstruct PET images, which were then compared.

The study found a close visual resemblance between CT- and LSO-TX-based attenuation maps, as well as PET images reconstructed with these maps. Using LSO-TX-based attenuation correction alone reduced the total effective dose to approximately 0.15 mSv, while maintaining good quantitative accuracy and clinically feasible scan durations.

"This reduction in radiation dose is 50 times lower than the standard PET dose and is comparable to the dose from a mammogram or chest X-ray," noted Sari. "Ultralow-dose protocols could extend PET scan applications, enhancing their use in screening studies, frequent follow-up scans, and pediatric imaging."

Long axial field-of-view scanners are commercially available with numerous installations worldwide. The CT-free attenuation correction method operates the scanner in a "research mode" and processes data offline using a research workstation.

Bern University Hospital is collaborating with Siemens Healthineers to streamline the method’s use and further optimize it with AI-based image enhancement algorithms.

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