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3rd International Congress 3rd International of Nuclear Congress Medicine of Nuclear & 15th Medicine Iranian Annual & 15th Iranian Congress Annual of Nuclear Congress Medicine of Nuclear Medicine Shahid Beheshti Shahid Beheshti University University of Medical Sciences of Medical 19-21 Sciences May 201119-21 May 2011 Applying interpolated projections in cardiac SPECT and its effect on lesion detectability using Hotelling Trace Mohammad Ali Askari 1 , Hossein Rajabi 1 , Armaghan Fard Esfahani 2 1 Department of Medical Physics, Tarbiat Modares University 2 Tehran University of Medical Science, Research Institute for Nuclear Medicine Introduction: Myocardial SPECT imaging is usually performed acquiring 32 views in 180 degree with equal steps of 5.625 degrees. Mathematically, increasing the number of projections can increase the image quality and decrease reconstruction artifacts. But acquiring more projections requires spending more time or injection of more activity to the patients. An idea to improve the quality of the reconstructed images without acquiring extra projections is applying interpolated data between adjacent projections. The aim of present study was using Hotelling Trace method to investigate the lesion detectability in reconstructed images with interpolated projections. Methods: Such investigation cannot be performed on real patient's data. Therefore, data were simulated using NCAT digital phantom and SimSET Monte Carlo code. The imaging was performed as usual, acquiring 32 views from right anterior oblique to left posterior oblique. The data were interpolated to construct 5 images between adjacent projections convert it into 187 projections. The simulation was performed again acquiring 187 images as the reference. The conventional, interpolated and reference data set were reconstructed and compared for improvement and degradation in quality of final images. Four methods of interpolation used, linear, cosine, cubic and hermit. The above procedure was repeated for phantoms representing different types of heart disease, different cardiac size and different count densities. Then short-axis cuts were used for Hotelling Trace analysis. Comparing Hotelling J-number would show the best method for interpolation. Results: The results showed that linear interpolation technique produces better lesion detectability comparing to other interpolation methods tested. Results also confirmed that streak artifacts decreases, signal to noise ratio and contrast increased due to increasing the number of samples. Conclusion: These results indicate that lesion detectability and the physical properties of reconstructed images improve significantly using interpolation. Keywords: Myocardial SPECT, Reconstruction, Interpolation, Image Hotelling 102
3rd International Congress of of Nuclear Medicine & & 15th 15th Iranian Annual Annual Congress of Congress of Nuclear Medicine Shahid Beheshti Shahid Beheshti University University of Medical of Medical Sciences Sciences 19-21 19-21 May May 2011 Quantification of bremsstrahlung images with respect to postradioembolization liver dosimetry Mohammad Reza Teimoori Sichani 1 , Shahram Akhalghpoor 2 , Mohammad Reza Ay 3 , Faraz Kalantari 3 , Mahasti Amoui 4 1 Islamic Azad University 2 Novin radiation medicine institute 3 Medical Physics department 4 Department of Nuclear Medicine, Shahid Beheshti University of Medical University Introduction: Evaluation of quantitative bremsstrahlung SPECT and planar images was done using phantom and patient study to calculate liver and tumor dose post radioembolization with colloidal Phosphorus-32. Material and methods: Bremsstrahlung SPECT and planar images from Jaszczak phantom and 10 patients under specific condition (MEGP collimator, Energy peak: 100keV±20%) were obtained. Due to low quality of bremsstrahlung images a method which used backscatter photons from external 99mTc sources was applied to determine body contour in SPECT images. Two small 99mTc sources on patient body were also used as landmarks. A computer program was written to calculate liver and tumor dose from raw SPECT data and CT images of patients. SPECT images were reconstructed using MLEM method. Registration of SPECT and CT images was done on a point-to-point basis using body contour and landmarks. Uniform and non-uniform attenuation maps were made from CT images. Then attenuation correction (AC) for SPECT images was done using 2 different methods, conventional Chang’s method and during an iterative reconstruction method using expectation maximization (EM) algorithm. Evaluation of both AC methods was done using SIMIND MC simulation code. VOIs for each patient were defined by user and system calibration factor is calculated using a syringe containing known activity of 32P dissolved in water. Volume and activity within each VOI are calculated using attenuation corrected images and system calibration factor. Absorbed dose within each VOI is estimated using MIRD method. Also activity and dose within liver area were calculated from planar images using Conjugate View Method (CVM). Validation of suggested methods for bremsstrahlung planar and SPECT quantification was done by phantom study and delivered dose to tumor and liver of 10 patients were estimated. Results: Phantom study reveals the most accurate method for image quantification is using attenuation corrected SPECT images using EM method and according to patient study delivered dose to livers of 80% of patients is below liver’s tolerance dose (40 Gy) while tumors receive great amount of dose. Conclusions: The study shows bremsstrahlung SPECT quantification is possible even without corrections for scatter and collimatordetector response and cumulated activity in each organ can be 103
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