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SUMMARY:Collimator-Free Non-Collinear Cascade Gamma Coincidence Imaging: A
  GATE-Based Study Achieving Sub-Millimeter Resolution and High Sensitivity
DTSTART;VALUE=DATE-TIME:20260522T095000Z
DTEND;VALUE=DATE-TIME:20260522T101000Z
DTSTAMP;VALUE=DATE-TIME:20260624T055144Z
UID:indico-contribution-3845@indico.tlabs.ac.za
DESCRIPTION:Speakers: Enock Mtatiro Mwita (University of Dar es Salaam)\nT
 his study presents the GATE-based Monte Carlo model and performance evalua
 tion of a non-time-of-flight\, collimator-free tomographic medical imaging
  system based on non-collinear cascade gamma-ray Coincidence (CGC) imaging
 . A CGC imaging model was developed to reconstruct three-dimensional decay
  vertices from valid coincidence events. A custom geometric back-projectio
 n reconstruction algorithm was implemented to generate tomographic images 
 in transverse\, coronal\, and sagittal views\, enabling quantitative asses
 sment of spatial resolution\, sensitivity\, and coincidence detection effi
 ciency (CDE). The results show\, with 111In-ion point source at the center
  of field of view (FoV)\, the modeled imaging system achieved sub-millimet
 er isotropic spatial resolution of approximately 0.477 mm (FWHM) along all
  axes and demonstrated resolving capability between 1.5-2.0 mm for closely
  spaced point sources. The CGC imager achieved a coincidence efficiency of
  1.50588 × 10⁻2 and sensitivity of 15\,058.8 cps/MBq for a 111In source
  at the center of the FoV in air\, their corresponding values for source i
 n PMMA phantom were 1.25279 × 10-2 and 12\,527.9 cps/MBq\, respectively. 
 These values were significantly higher than those reported for conventiona
 l parallel-hole\, focused\, and hybrid collimator-based systems\, represen
 ting improvements of several orders of magnitude. For positional reconstru
 ction\, the analysis confirmed the reconstructed source position within ±
 16 mm transaxially and ±17 mm axially resembles to simulated position. To
  evaluate the impact of radionuclide decay characteristics on imaging perf
 ormance\, four cascade gamma emitters (43K\, 73Se\, 111In and 177Lu) were 
 simulated under identical conditions. 111In and 73Se exhibit the highest C
 DEs\, followed by 177Lu\, while 43K shows the lowest due to its extremely 
 short intermediate-state half-life of 46 ps\, which is below the detector 
 timing resolution (~0.549 ns)\, leading to missed valid coincidence events
 . The higher CDE for 111In is partly from random coincidences caused by it
 s longer half-life and wider timing window. These results emphasize that d
 etector timing resolution\, isotope selection\, and coincidence window des
 ign are critical for optimizing cascade gamma imaging performance. On the 
 other hand\, spatial resolution remained the same (~0.477 mm FWHM) across 
 radionuclides. This finding confirms that system resolution is governed by
  detector geometry and reconstruction parameters rather than decay propert
 ies. The findings demonstrate that non-collinear CGC imaging enables the s
 imultaneous achievement of both high sensitivity and sub-millimeter spatia
 l resolution. However\, experimental testing of the system should be condu
 cted to assess its practical performance.\n\nhttps://indico.tlabs.ac.za/ev
 ent/139/contributions/3845/
LOCATION:NRF-iThemba LABS\, Old Faure Road\, Cape Town Auditorium
URL:https://indico.tlabs.ac.za/event/139/contributions/3845/
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