Effects of multiple-interaction photon events in a high-resolution PET system that uses 3-D positioning detectors
Detector system overview; shown are (a) the fully assembled system comprising two opposing and parallel detector panels, (b) individual arrays of LSO crystals covered with a reflecting polymer, (c) coupling of the arrays to PSAPDs, (d) a dual-LSO-PSAPD module, (e) a sensor card assembling many adjacent modules, and (f) a detector head/panel assembled by stacked sensor cards, which, in turn, are coupled to readout boards. In this manner, incoming photons encounter a minimum of thick LSO crystal.
Proposed analog signal multiplexing scheme (right) for the dual-LSO-PSAPD module (left) (Ref. 14).
Simulation breast slab phantom geometry with 4 cm panel separation.
Photon interaction category definitions. Note that specific “O” arrays, designating “Other crystal arrays” involved in the event, are highlighted for illustration only in defining the categories.
Edge-on irradiation of a one dual-LSO-PSAPD module. Each LSO array comprises an matrix of crystal elements.
Phantom used for reconstructed image quality and quantification study. The ratio of the activity concentration in the spheres to that of the surrounding water is 10:1, and the total activity is .
Percentage of single photon events interacting with a dual-LSO-PSAPD module at the panel corner and center (see Fig. 4) with the interaction energies summing to a 24% window about 511 keV acquired as a function of minimum energy per interaction needed to trigger an acquisition. Data plotted as a fraction of (a) all single photons that interacted at least once with the LSO detector volume and (b) events with sum of energy depositions falling within the 511 keV photopeak.
Experimental vs GRAY simulation result comparison of photon interaction categories (see Fig. 4 for the definitions, categories E and D are not applicable here for the case of edge-on irradiation of one dual-LSO-PSAPD module). Note that the vertical axis is in logarithmic scale, and 100% corresponds to all events with sum energy within a window. The statistical uncertainty in the results is shown as error bars on each bar, indicating the 90% confidence interval.
Population makeup of coincident events used in image reconstruction. The numbers inside the bars represent counts of that event type in millions. The lighter patches represent coincident photons pairs where either or both individual photon events are a MIPE.
Contrast recovery coefficient and noise of reconstructed volume over successive MLEM iterations up to a maximum of 100 iterations. Subplots (a), (b), (c), and (d) correspond to 1, 2, 4, and 8 mm diameter spheres in the phantom, respectively.
Contrast to noise ratio as a function of number of MLEM iterations. Subplots (a), (b), (c), and (d) correspond to CNR derived from 1, 2, 4, and 8 mm diameter spheres in the phantom, respectively.
Comparison of images reconstructed using (a) only single LSO array events that deposit energy within the window, (b) events used in (a) as well as MIPEs using the energy-weighted spatial mean positioning method for placing the LOR, and (c) the same event set as (b) but using the ML algorithm for estimating the initial interaction in each MIPE for positioning the LOR. (d) shows the reconstructed volume of (c) in a slice orthogonal to the panels, spanning the 4 cm panel separation. Orientation of the axes corresponds to that of Figs. 1 and 3. The sphere diameters are 1, 2, 4, and 8 mm, with mutual separation of at least twice the diameter, and have activity concentration ten times that of the surrounding medium. The total activity of the entire volume is and all images were normalized to account for system photon sensitivity nonuniformity.
(a) Contrast recovery coefficient-noise curves of images reconstructed using the single LSO array data for 100% scan time compared to those based on the MIPEs-ML method over 90% scan time. Graph shows the CRC and noise values derived from the 2 mm diameter spheres. Curves for the 4 and 8 mm diameter spheres exhibit similar behavior. (b) Contrast to noise ratio as a function of the number of MLEM iterations. Plotted are curves derived from the 2 mm diameter spheres reconstructed using the single LSO array data for the full scan time and using the MIPEs-ML method over 90% of the scan time.
Confounding factors to the MIPEs-ML LOR positioning algorithm. Note that occurrences in only two dimensions are shown for simplicity.
Frequency of occurrence of MIPEs by category.
Scatter and random fractions for the three LOR positioning algorithms.
Reconstructed image CNR and FWHM sphere size. (See Fig. 3 for the orientation of , , and .)
Article metrics loading...
Full text loading...