Evaluation of whole-body parametric PET/CT image generation from high resolution high sensitivity mCT scanner

Objectives To evaluate a noninvasive whole-body parametric image generation technique with high resolution PET-CT.

Methods Patlak plot and a linear regression with spatial constraint (LRSC) algorithm was used to generate parametric images of FDG influx rate constant K_i and distribution volume V. Fifteen single-direction dynamic multi-bed (7 beds/pass) passes were performed after initial 6-min single-bed dynamic scan (with heart centered in the field of view), with 45 sec/bed as implemented on the Siemens mCT scanner. PET images were reconstructed with time of flight and spatial resolution modeling. Aorta time activity curve (TAC) was obtained for image derived input function. 8-10 venous blood samples were obtained over total 90-min scan. This is an ongoing project and 5 patients studies were collected. SUV images calculated from 70 to 90 min post FDG injection were used for comparison.

Results Using a single blood sampling at ~40 min to scale aorta TAC showed lowest variation in the ratio of aorta TACs to FDG blood activities. It was visually identified that K_i and V images appears to be improved by using the advanced mCT scanner, as compared to our previous studies. Compared to the delayed SUV images, the higher contrast K_i images improved visual detection of tumor lesions within tissues of high back ground FDG activity. The V images provided a quantitative measurements on blood volume and vascular density and function which is an important biomarker in monitoring tumor response to treatment.

Conclusions The whole-body parametric images of K_i and V generated from dynamic multi-bed FDG data by using mCT scanner and robust LRSC algorithm provided multi-functional information of normal and abnormal tissues, and higher contrast in tumor to background than SUV images . The clinical values of both Ki and V parametric images are under investigation.