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제안 방법
- 7. CNR results (using ROI B and ROI C in Fig. 4) for the noisy image, median filter, and proposed median filter with improved thresholding at 1, 3, and 5 cm source-to-collimator distances.
- 8. COV results (using ROI B in Fig. 4) for the noisy image, median filter, and proposed median filter with improved thresholding at 1, 3, and 5 cm source-to-collimator distances.
- Therefore, we designed a noise reduction algorithm with a median filter using an improved thresholding method, which can achieve high noise reduction ratio while retaining more details, and we confirmed the feasibility of this algorithm in a CZT pixelated semiconductor gamma camera system. For that purpose, we simulated an eV-3500 CZT pixelated semiconductor gamma camera system in GATE and evaluated the imaging performance using NNPS, CNR, and COV.
- In addition, the CNR and COV were used to evaluate the contrast, signal, and noise characteristics. The CNR and COV are calculated as follows:
- Pan [35]. In this study, an improved median filter was suggested to estimate the noise pixels and will be changed by neighboring median pixels. Fig.
- In this study, the development and implementation of a median filter using an improved thresholding method in a CZT pixelated semiconductor gamma camera system was presented and used to evaluate the noise characteristics using various evaluation parameters. Our results demonstrated that proposed median filter accomplished its goals of noise reduction in CZT gamma camera images.
- Also, although a Wiener filter helped noise stabilization in the frequency domain, this filter also suffers from loss of image details [23]. Therefore, the purpose of this study was to design an improved noise reduction algorithm with a median filter by using a thresholding method in a CZT pixelated semiconductor gamma camera system. For that purpose, we compared our proposed and conventional median filters using the Geant4 Application for Tomographic Emission (GATE) simulation.
대상 데이터
- The designed CZT pixelated semiconductor detector consisted of linear crystal arrays with 0.5 X 0.5 mm2 pixel pitch (total detector size: 128X 0.5 mm2 (5X 0.02 inch2)) and 3 mm thickness. The detection efficiency was approximately 72.
- Finally, we designed a spatial resolution phantom to assess the imaging performance using a solution of 99mTc gamma source in water with different activities and diameters, and the phantom was acquired with respect to the source-to-collimator distance (1, 3, and 5 cm). This phantom consisted of six different activities and hot-rod diameters: 9000 Bqe0.5 mm, 15,500 Bqe0.85 mm, 30,000 Bqe1.2 mm, 45,000 Bqe1.5 mm, 60,000 Bqe1.8 mm, and 90,000 Bqe2.1 mm.
이론/모형
- Among Monte Carlo simulations, Geant4 is widely used in the field of medical imaging and a tool for modelling the particle passage in the matter. In this study, we used GATE version 7.0 simulation, which is based on the open-source Geant4 software based on the Monte Carlo method [25,26]. For system modelling in the field of nuclear medicine imaging (gamma camera, single photon emission computed tomography (SPECT), and positron emission tomography (PET)), this simulation proved to be very useful in many studies [25e29].
- The improved thresholding method for noise reduction algorithm modelling can be considered as a special case of de-noising in medical imaging. The concept of this algorithm was proposed by B. Wang and Q. Pan [35]. In this study, an improved median filter was suggested to estimate the noise pixels and will be changed by neighboring median pixels.
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