Sample Research Projects

I. System Matrix Modeling for PET Reconstruction

To achieve optimal PET list-mode reconstruction, we develop a system matrix that is based on the line-of-response probability density function (LOR-PDF). Each LOR-PDF is a three-dimensional (3-D) function that describes fully the distribution of LOR’s contribution source. All the LOR-PDFs are sorted by the LOR’s incident angles to form a highly compact system matrix. The purpose of this project is to achieve optimal statistical iterative PET image reconstruction.

Fig. 1. An illustration of the 3-D LOR-PDF concept. Left: The PET detector ring is shown with image space and LOR-PDF space reference frames (x,y,z) and (r,u,d), respectively. The rectangular tube centered at the LOR is the 3-D volume of the LOR-PDF. To avoid overlapping, the origin of (x,y,z) is not shown at the CFOV. Right: A sample LOR-PDF distribution in a RU plane.



Fig. 2. Comparison of the simulated back-to-back gamma hot-rod in-air phantom reconstructed with the Component-2D (left) and the proposed LOR-PDF (right) protocols. Both images were summed over 60mm slices to minimize the effects of statistical noise. Each image is displayed by its in-plane maximum.

II. Animal SPECT Imaging on an Animal PET Scanner

Animal SPECT has become increasingly important in biomedical research. One major limiting factor, however, for the wide acceptance of animal SPECT system is its significant cost. Our group proposed a technology that would enable SPECT imaging on an existing animal PET. This technology would allow the existing animal PET owners perform animal SPECT imaging with much lower cost than investing in a new dedicated system. In addition, the dual-function imaging system would provide an ideal platform for exploring PET-SPECT dual tracer imaging applications.

Fig. 3. A 3-D diagram illustrating the composition of the animal SPECT prototype system. The detector ring of the animal PET is shown in green. The blue annulus and red octagon are tungsten septa and knife edged lead plates which are used to form multiple layers of fan-beam collimation for animal Description: Description: Description: Description: Description: Description: Description: MDP_helical_iter5_pos2.pngSPECT.

Fig. 4. The bone image of a 25 gram Balb/C normal mouse obtained with Tc-99m MDP tracer and the animal SPECT we developed.

Fig. 5. The PET and SPECT images of a mouse injected with mixed 99mTc-MDP (bone agent) and 18F-FDG (metabolism) tracers obtained from the animal PET and SPECT hybrid system.




III. Develop and support animal PET applications

Fig. 6. An example result from project “Development of the See and Treat Multifunctional Photosensitizers” (in collaboration with Drs. Munawwar Sajjad and Ravindra K. Pandey). The 18F-FDG image on the left (coronal view) was acquired first as a reference after 90 minutes post-injection of 254 µCi of activity to a tumor bearing C3H mouse. The mouse was then injected with 72 µCi 124I- labeled derivative-of-Pyropheophorbide-a, a bi-functional (imaging and photo-dynamic therapy) agent. The mouse was imaged for 30 minutes at 4.5 hours, 24 hours, 48 hours and 72 hours post-injection. The tumor (yellow circle) uptake, as relative to the rest of the body, of the bi-functional agent increased over time, indicating promising perspective of therapeutic and monitoring application of the agent. The color palette (shown on the right of the 18F image) was scaled to the min/max of the transverse slice passing through the center of the tumor site (indicated by green-bars) in each dataset. The display scheme was same for all the images. Activity was injected via tail vein.