A simulation study for the design of a prototype insert for whole-body PET scanners

Abstract

We are developing an insert device that will improve image resolution within a smaller field-of-view for clinical wholebody PET scanners. We modified SimSET (Simulation System for Emission Tomography) to simulate the insert and a PET scanner. The system consists of two detector rings. The inner ring represents an insert (r = 153 mm) with high-resolution detectors using 10 mm thick LSO. The outer ring represents a PET scanner (R = 413 mm) with 25 mm thick LSO. Events were binned into three sets of sinograms assuming a 2.4 and 6.75 mm crystal-pitch for the insert and the PET scanner, respectively. The detectors in the insert are modeled as 1, 2, or 4 layers with different offset configurations to evaluate the corresponding system resolution with the depth-ofinteraction (DOI) effect. Results show that image resolution at 1 cm radial offset is improved from 5.6 mm full-width-at-half-maximum (FWHM) of the original PET scanner to 2.0 mm with the insert. At 12 cm offset, the resolution of the original system is 5.9 and 5.5 mm for radial and tangential directions, respectively. With the insert, the radial resolution is 5.0 mm FWHM for a single-layer detector design, but improves to 2.7 and 2.2 mm for 2-and 4-layer DOI detectors, respectively. Different offsets for multi-layer detectors have negligible effect on resolution. Sensitivity of the device is, assuming the insert has a 2 cm axial extend, estimated to be 3.3%, including coincidence events from the insert-alone and insert-to-scanner sinograms. In contrast, if the insert is used as a stand-alone microPET scanner, its sensitivity is 1.3%.Index Terms-Depth of interaction (DOI), head and neck imaging, high resolution imaging, Monte Carlo simulations, pseudo pinhole positron emission tomography (PET).

Virtual-Pinhole PET

“…We have studied the potential improvement in image resolution using a full-ring insert device in a clinical whole-body PET scanner through Monte Carlo simulations (28). We are currently developing 2 PET insert systems for human and small-animal imaging applications.…”

A Feasibility Study of a Prototype PET Insert Device to Convert a General-Purpose Animal PET Scanner to Higher Resolution

“…First, the point source used in the bench system was 64 Cu in a 1-mmdiameter glass micropipette in air. The point source used in this study was a 22 Na point source (0.5-mm nominal diameter) embedded in an acrylic disk (25mm diameter). The positron range of the 64 Cu in 1-mm glass pipette surrounded by air may be smaller than the positron range of the 22 Na in a 25-mm acrylic disk.…”

“…The point source used in this study was a 22 Na point source (0.5-mm nominal diameter) embedded in an acrylic disk (25mm diameter). The positron range of the 64 Cu in 1-mm glass pipette surrounded by air may be smaller than the positron range of the 22 Na in a 25-mm acrylic disk. Second, the digitizer in our bench setup was a 12-bit analog-to-digital-converter (ADC), whereas in the microPET F-220 scanner, an 8-bit flash ADC was used.…”

“…The choice of 22 Na source was because its emission energy (E average b1 5 215 keV) is similar to that of the most widely used positron-emitting isotope 18 F (E average b1 5 250 keV); yet the long half-life of 22 Na made it much easier to perform the resolution measurement. The source was first positioned at the center of the field of view in the PET insert system.…”

“…The full width at half maximum (FWHM) and full width at tenth maximum (FWTM) were measured from the extracted profiles by linear interpolation between the 2 nearest pixels bracketing the half values and one-tenth values, respectively. Results were plotted and compared with those previously reported for the microPET F-220 scanner using the same 22 Na point source (15). Resolution results reported were not corrected for source dimension, positron range, or acolinearity of positron annihilation.…”