Providers with the uEXPLORER total-body PET/CT scanner can perform total-body dynamic PET scans on cancer patients to detect the presence of metastatic cancer, according to a new study.

Presented this week at the Society of Nuclear Medicine and Molecular Imaging 2020 Virtual Annual Meeting, the analysis confirms that it is possible to perform total-body kinetic modeling and parametric imaging with the system — qualities which enhance visibility and characterization of metastatic cancer and allow it to be identified. It is the first to assess total-body dynamic PET imaging of cancer with uEXPLORER.

"Conventionally, a radiotracer is commonly used to measure one physiological parameter," study author Guobao Wang, associate professor and Paul Calabresi Clinical Oncology K12 Scholar in the department of radiology at the University of California (UC), Davis, told HCB News. "For example, 18F-FDG has been mainly used for assessing glucose metabolism. With tracer kinetic modeling, total-body dynamic PET not only provides the parameter of glucose metabolism (i.e., FDG influx rate Ki that is proportional to glucose metabolic rate) but also parametric images of additional physiologically important parameters, such as the fractional blood volume (vb), glucose transport rate (K1) and potentially blood flow, potentially enabling a single-tracer multiparametric imaging method. Without this technical ability from total-body dynamic PET, multiparametric imaging would otherwise need multiple radiotracers, prolonged scan time and increased imaging cost."

Static PET offers a simple snapshot of radiopharmaceutical concentration, while dynamic PET with tracer kinetic modeling generates parametric images that show how tissue behaves, enabling researchers to better detect lesions and assess responses of cancer patients to therapy. The lack of studies around the potential of these capabilities stems from the components of conventional PET scanners, which have a limited axial field-of-view and cannot perform simultaneous dynamic imaging of lesions widely separated in the body.

The method can be used with any radiotracer. For their study, Wang and his colleagues injected the tracer, 18F-FDG into a patient with metastatic renal cell carcinoma. The patient was then scanned on uEXPLORER. Static PET standardized uptake value (SUV) was calculated and kinetic modeling was performed for regional quantification in 16 areas of interest, including major organs and multiple metastases. The glucose influx rate was calculated and more kinetic modeling was used to create parametric images of the kinetic parameters. The kinetic data was then used to detect tumors and characterize them.

The researchers identified multiple metastases on the dynamic PET/CT scan. Parametric images of glucose influx rate showed improved tumor contrast over SUV in general, and specifically improved visualization of cancer lesion detection in the liver. Total-body kinetic quantification provided multi-parametric characterization of tumor metastases and organs of interest.

"Compared to the clinical standard — standardized uptake value (SUV) images — total-body dynamic PET offers parametric images of physiologically important parameters, which can (1) create higher tumor contrast, and (2) provide multiparametric characterization of tumors and organs," said Wang. "The benefit of higher tumor contrast can be translated to detect smaller liver metastases, which may change the management of patients as the presence of liver metastases can indicate poor prognosis."

He adds that "multiparametric characterization can be used to understand the behavior of both tumor metastases and organs of interest such as the spleen and bone marrow. Thus, both tumor response and therapy side effects can be assessed using the same scan."

Development of uEXPLORER began in 2016 at UC Davis where researchers sought to create the first total-body PET scanner. The final product was approved by the FDA in 2019 under the ownership of United imaging Healthcare, which partnered with UC Davis on the development of the system.

The technique can be applied to assess the severity of non-cancers, as well as organ interactions in many other systemic diseases.