Quantitative accuracy of PET for image-based kinetic analysis

It is essential to achieve quantitative accuracy of radioactivity concentrations (Bq/ml) when performing compartmental modeling and kinetic analysis of dynamic sequences of reconstructed PET images. Dynamic PET data can be acquired in list mode, and often is preferred over frame mode acquisitions due to the flexibility of reformatting the list mode data into different dynamic image sequences after the acquisition is complete. However, most PET data is acquired as static frames. It therefore is important to evaluate the quantitative accuracy of list mode or dynamic PET acquisitions prior to their use for clinical or research applications. We evaluated the quantitative accuracy of list mode acquisitions obtained with a Siemens Biograph 16 PET/CT scanner at our institution; the image data were acquired from an anthropomorphic phantom (Data Spectrum, Hillsborough, NC) filled with an aqueous solution of 18F-fluorodeoxyglucose (FDG). PET data were acquired with the phantom for the following three different configurations: (1) with nonradioactive water in the body compartment, and aqueous solution of 18F-FDG only in a fillable cylindrical insert to mimic the first few seconds of highly concentrated radioactivity within the field of view such as that in major venous or pulmonary vessels, or in the right or left cardiac ventricles, (2) with radioactivity throughout the entire body compartment and imaged within 3 min time frames in list mode, and (3) with radioactivity throughout the body compartment and imaged in list mode and reformatted into sequential time frames having intervals of 3, 10, 20, 30, 50, 67 sec, respectively (i.e., total of 180 sec). All measured concentration values were compared against values acquired from static images or against true values calculated from injected dose corrected for physical decay of 18F. These analyses demonstrated that the count rate limitation is minimal or negligible in general as long as there is no more than 370-440 MBq (10-12 mCi) radioactivity entirely within the axial FOV for 1 bed position required for dynamic PET, and the list mode acquisition provides quantitative radioactivity concentration values for all ranges of radioactivity levels. In addition, reformatting a single list mode acquisition into frame data having different time intervals retains quantitative accuracy with respect to static frame data and compared to the known radionuclide concentration in the phantom. Within these constraints, the list mode data acquired with the Biograph 16 PET/CT system is quantitatively accurate for image-based compartmental modeling and kinetic analysis.