Assessment of X-Ray Crosstalk in a Computed Tomography Scanner with Small Detector Elements Using Monte Carlo Method

Document Type: Original Paper

Authors

1 Department of Biomedical Engineering, Faculty of Engineering, University of Isfahan, Isfahan, Iran

2 Department of Biomedical Engineering - Faculty of Engineering- University of Isfahan

3 Department of nuclear Engineering, Faculty of new science and technologies, University of Isfahan, Isfahan, Iran

Abstract

Introduction: Crosstalk is a leakage of X-ray or light produced in a matrix of X-ray detectors or array of photodiodes in one element to other elements affecting on image contrast and spatial resolution. In this study, we assessed X-ray crosstalk in a computed tomography (CT) scanner with small detector elements to estimate the effect of various parameters such as X-ray tube voltage, detector element sizes, scintillator material, impurities in the scintillator material, and the material of detector separators on X-ray crosstalk.
Materials and Methods: This study was performed using Monte Carlo simulation. In the first step, X-ray tube and its energy spectrum at the energies of 80, 100, 120, and 140 keV were simulated and validated by using SpekCalc and t-test. Then, other important parts of CT scanner, namely filters, detectors, and grids were simulated. X-ray crosstalk between CT detectors was calculated in air and in the presence of water phantom (as a simulator of human body) to compare the effect of scattered photons. Finally, the influence of some important parameters on X-ray crosstalk was evaluated.
Results: In CT scanner with small elements, when using phantom, crosstalk increases by 16-50%. Using the lowest possible energies of X-ray, decreases the crosstalk up to 43% of its initial amount. Furthermore coating a 10 or 20 µm layer of tungsten or lead on the detector separators, decreases the X-ray crosstalk significantly.
Conclusion: Choosing the proper high voltage, detectors’ material and its dimensions, scintillator impurities and septa material can decrease X-ray crosstalk.

Keywords

Main Subjects


References

 

  1. Ji F, Juntunen M , Hietanen I. Evaluation of electrical crosstalk in high-density photodiode arrays for X-ray imaging applications. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2009 Oct; 610 (1): 28-30.
    1. Budoff M. J. Computed tomography. Cardiac CT Imaging. Springer; 2016. p. 3-23.
    2. Safdari M, Karimian A. A New Method for Metal Artifact Reduction in CT Scan Images. Iranian Journal of Medical Physics. 2013 Sep ; 10(2): 139-46.
    3. Goushcha I, Tabbert B, Goushcha A. O. Optical and electrical crosstalk in PIN photodiode array for medical imaging applications. In Nuclear Science Symposium Conference Record . NSS'07. IEEE; 2007. p. 4348-53.
    4. Ikhlef A, Thrivikraman S. Crosstalk modeling of a CT detector. In Medical Imaging ; 2004. p. 906-13.
    5. Ji F, Juntunen M, Hietanen I. Electrical crosstalk in front-illuminated photodiode array with different guard ring designs for medical CT applications. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2009 Aug; 607(1): 150-3.
    6. Melnyk R , DiBianca F.A. Monte Carlo study of x-ray cross talk in a variable resolution x-ray detector. In Medical Imaging; 2003. p. 694-701.
    7. Arabi H, Kamali Asl A. R, Ay M. R, Zaidi H. Novel detector design for reducing intercell x-ray cross-talk in the variable resolution x-ray CT scanner: A Monte Carlo study. Medical physics. 2011 Mar; 38(3): 1389-96.
    8. Akbarzadeh A, Ay M. R, Ghadiri H, Sarkar S, Zaidi H. Measurement of scattered radiation in a volumetric 64-slice CT scanner using three experimental techniques. Physics in medicine and biology. 2010 Mar ;55(8): 2269-80.
    9. Ay M. R, Shahriari M, Sarkar S, Adib M, Zaidi H. Monte Carlo simulation of x-ray spectra in diagnostic radiology and mammography using MCNP4C. Physics in medicine and biology. 2004 Oct; 49(21): 4897-917.
    10. Bazalova M, Verhaegen F. Monte Carlo simulation of a computed tomography x-ray tube. Physics in medicine and biology. 2007 Sep; 52(19), 5945-55.
    11. General Electric Company. Technical Reference Manual; [updated 2017 Oct]. Available from: http://www.spectrumxray.com/sites/default/files/pdfs/GE-LightSpeed-CT.pdf.
    12. Akbarzadeh A, Ay M. R, Ghadiri H, Sarkar S. Calculation of the Scattered Radiation Profile in 64 Slice CT Scanners Using Experimental Measurement. Iranian Journal of Medical Physics. 2009 Jun; 6(2): 1-10.
    13. Ay M. R, Zaidi H. Development and validation of MCNP4C-based Monte Carlo simulator for fan-and cone-beam x-ray CT. Physics in medicine and biology. 2005 Oct ;50(20): 4863-85.
    14. Ay M. R , Ahmadian A, Ghadiri H, Maleki A, Ghafarian P, Zaidi H. The Influence of X-ray Spectra Filtration on Image Quality and Patient Dose in the GE VCT 64-Slice Cardiac CT Scanner. In Bioinformatics and Biomedical Engineering. ICBBE. 3rd International Conference on; 2009. p. 1-4.
    15. Ghafarain P, Ay M. R , Sarkar S, Ghadiri H, Zaidi H. Impact of x-ray tube voltage, field size and object thickness on scattered radiation distribution in diagnostic radiology: A Monte Carlo investigation. In Nuclear Science Symposium Conference Record. NSS'07. IEEE; 2007. p. 3830-4.
    16. Mesbahi M, Zakariaee S. Effect of anode angle on photon beam spectra and depth dose characteristics for X-RAD320 orthovoltage unit. Reports of Practical Oncology & Radiotherapy. 2013 Jun ; 18(3): 148-52.