Author/Authors :
Razavi, Hossein Department of Oral and Maxillofacial Radiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran , Kalantari, Faraz Department of Radiation Oncology, UT Southwestern, Medical Center, Dallas, TX, USA , Bagheri, Mahmoud Department of Medical Physics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran , Namiranian, Nasim Yazd Diabetes Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran , Nafisi-Moghadam, Reza Department of Radiology, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran , Mardanshahi, Alireza Department of Radiology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran , Emami-Ardekani, Alireza Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran , Ardekani, Mohammad Sobhan Department of Radiology, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran , Razavi-Ratki, Kazem Department of Radiology, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Abstract :
Introduction: In an ideal parallel-hole collimator, thickness of septal material should be sufficient to stop more than 95% of
incident photons. However, some photons pass the septa without interaction or experience scattering before they reach the
detector. In this study, we determined different contribution of collimator responses consist of geometrical response, septal
penetration (SP) and scattering (SC) for low, medium and high energy collimators.
Methods: A point source of activity with common energies in diagnostic nuclear medicine and three different collimators
were simulated using SIMIND Monte Carlo code.
Results: For Low Energy High Resolution (LEHR) collimator, SP was increased from 7% in 140 keV to 30% in 167keV and
more than 75% in energies higher than 296keV. SC also was increased from 4% in 98keV to more than 15% in energies higher
than 167keV and reached to its maximum (26%) in 296keV. For Medium Energy All Purpose (MEAP) collimator, SP was
suddenly increased from 6% in 186keV to 28% for 296keV and more than 50% for higher energies. SC was also increased
from 4% in energies below 186keV to 15% in 296keV and about 30% for higher energies. For High Energy (HE) collimator,
SP was about 20% for 364keV photons. SC was 15% for 364keV photons and only 65% of photons were geometrically
collimated.
Conclusion: Our results showed that even by using nominally suitable collimators, there are considerable SC and SP that
influence the quantitative accuracy of planar and SPECT images. The magnitude of geometrical response, SC and SP depend
on collimator geometric structure and photons energy.
