Article Figures & Data
Figures
- FIGURE 1.
Illustrative axial cross-section of cylindric scanner with and without slice-defining septa. Removing septa increases sensitivity by allowing detection of true coincidences that are not perpendicular to scanner axis but also increases FOV for activity that can generate random coincidences. 2D = 2-dimensional.
- FIGURE 2.
Estimated sinogram NEC rates (7) for a fully 3D patient scan centered over liver for ECAT HR+ scanner show increase in NEC rates by using a noiseless random coincidence estimation method (k = 0) relative to subtraction of delayed coincidences (k = 1).
- FIGURE 3.
Test phantom. (A) Coronal and 3 of 5 transverse planes of test phantom containing hot and cold test targets. (B) Representative total number of coincidences (T + S + R) used for 4 of the bed positions in simulations as a function of the activity level at scan start.
- FIGURE 4.
SNRI measured from simulation study as a function of activity concentration.
- FIGURE 5.
Improvement in SNR using a noiseless correction relative to an online correction. Improvement in SNR is measured in sinogram using global NEC rate (Eq. 1) and locally in image, as measured by detection of small targets.
- FIGURE 6.
Expected percent improvement in NEC by using singles-based estimation of random coincidences. (A) ECAT ART scanner: 61 patient studies. (B) ECAT HR+ scanner: 23 patient studies.
Tables
Method Comments Delayed coincidences Accurate. Higher noise (Eq. 1). Lowest processing requirements. Smoothed delayed coincidences Accurate. Lower noise (0 ≤ k ≪ 1, Eq. 1). Higher processing requirements. Calculated from single photon rates Potential for bias if scanner is not properly calibrated. Lower noise (0 ≤ k ≪ 1, Eq. 1). Low processing requirements. - TABLE 2
Count Rates Used to Simulate 5 Whole-Body Acquisitions with Different Activity Concentrations
Injected dose (MBq) Activity (kBq/cm3) Mcps True Scattered Random 74 1.1 8.1 9.9 3.5 185 3.3 21.5 26.2 24.7 370 7.0 37.0 45.0 90.0 555 11.5 47.7 58.3 197.7 777 14.7 51.7 63.2 283.4 Count levels were based on the estimated patient rates (7).
- TABLE 3
Comparison of Smoothed Delayed Coincidences and Singles-Based Random Coincidence Estimations Averaged over All Sphere Diameters
Parameter % improvement in SNR compared with delayed coincidences Smoothed delayed coincidences Singles-based estimation Background mean 2.3 1.3 Background SNRI 8.3 7.4 Hot spheres SNRI 17.4 15.4 Hot spheres CNR 9.4 3.5 Cold spheres SNRI 23.9 23.0 Cold spheres CNR 12.6 13.5 Results are expressed as the percent difference from nonsmoothed delayed coincidences.
