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An accurate model base on Monte Carlo for simulation of converging collimator in nuclear medicine

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Author(s): Hamidreza Baghani | Alireza Kamali Asl

Journal: Iranian Journal of Nuclear Medicine
ISSN 1681-2824

Volume: 18;
Issue: Suppl 1;
Start page: 135;
Date: 2010;
Original page

Keywords: Converging collimator | Spatial resolution | Efficiency | Monte Carlo simulation

ABSTRACT
Introduction: Converging collimator has special application in nuclear medicine. Converging collimator are used primarily with cameras having large-area detectors to permit full utilization of the available detector area for imaging of small organs such as thyroid. Because of inherent magnification of converging collimator, it can provide higher image quality of small objects. Accurate spatial resolution and efficiency Measurement of this collimator, therefore, can have significant role in design and development of these collimators. The aim of this research is accurate modeling of converging collimator for surveying of spatial resolution and efficiency as a function of axial distance from collimator face by Monte Carlo code. Methods: A simplified model of converging collimator based on an actual model was simulated by MCNP Monte Carlo code. The spatial resolution was measured in 2cm, 5cm, 8cm and 10 cm from collimator face. The efficiency was also measured in 1cm, 2cm, 3cm, 4cm and 5cm from collimator face. Results: From the results, the spatial resolution of the system (MTF=0.1) increased from 2.15 cycle/cm at axial distance of 2 cm to 1.05 cycle/cm at axial distance of 10 cm. (1.75 and 1.4 cycle/cm at axial distances 5 and 8 cm, respectively). The efficiency of the system at mentioned axial distances increased from 8.9E-5 to 7.97E-4. In addition, the results of this simulation have acceptable accordance with prior analytic results in this field that can validate simulated system. Conclusion: From results of simulation one can deduce that spatial resolution of this collimator will decrease with increase in axial distance from collimator face. Because of magnification effect, rate of spatial resolution reduction in axial distance is lesser than parallel hole collimator. Thus, this feature of converging collimator provides better image quality in nuclear images at expense of decreased field size. The efficiency of these collimators has a direct proportion with axial distance from collimator face and improved with increasing distance. Thus, a design of a collima┬Čtor that provides both high spatial resolution and acceptable efficiency has noticeable importance.
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