A new PET imaging technique can greatly reduce the amount of patient radiation exposure by eliminating the need for an accompanying CT scan. Without the CT scan, the amount of radiation delivered to the patient is cut dramatically, which benefits all patients, but in particular the pediatric population and those in need of multiple scans. This research was presented at Society of Nuclear Medicine and Molecular Imaging 2022 Annual Meeting.

Long-axial field-of-view (or total-body) PET scanners allow for extremely low-dose PET scans. To aid in the localization of PET images, however, most PET scans are accompanied by an anatomical scan, such as CT. While this is helpful to obtain accurate quantitative PET images, it adds a substantial amount of radiation exposure, which makes the low-dose benefits of the PET scan irrelevant.  

To address this issue, researchers conducted a study to determine the feasibility and effectiveness of CT-less PET scans. “Most modern PET scanners use lutetium-based scintillators to detect gamma photons” said Mohammadreza Teimoorisichani, PhD, senior research scientist at Siemens Medical Imaging, Inc. “The lutetium in the scintillator contains a small amount—less than 3 percent—of the radioisotope 176Lu, which emits ‘background radiation’ during the scan. In our study, we used this background radiation as a transmission source to simultaneously reconstruct attenuation maps and quantitative PET images without the use of CT.”

PET images were reconstructed with various CT-less reconstruction techniques and compared against standard PET/CT images. The studied CT-less reconstruction algorithms showed an average organ quantitative error of 4.8 to 10 percent over the studied organs.

“This study is an important step toward practical CT-less quantitative PET imaging,” noted Teimoorisichani. “In addition to reducing patient radiation exposure, a true low-dose quantitative PET scan can have a great impact on research studies that aim to better understand human physiology at the molecular level and on research involving the development of radiopharmaceuticals. The algorithm is currently being evaluated on a large number of patients to discover its full potential.”

PHOTO CAPTION: Top: Sample coronal and sagittal slices of attenuation maps (1/cm) and PET images reconstructed with various reconstruction techniques with and without the use of CT images. Bottom: Difference image between the attenuation maps from the joint reconstruction algorithms and CT-based images (1/cm). The plot on the bottom right shows the organ quantification error from CT-less reconstructions.

Abstract 250. “Towards Quantitative CT-less Total-body PET Scan,” Mohammadreza Teimoorisichani, Vladimir Panin, Harold Rothfuss, Deepak Bharkhada, and Maurizio Conti, Siemens Medical Solutions USA Inc, Knoxville, Tennessee; Hasan Sari, Siemens Healthcare AG, Bern, Bern, Switzerland; and Axel Rominger, Inselspital, Bern, Bern, Switzerland.