Effect of post-reconstruction gaussian filtering on image quality and myocardial blood flow measurement with N-13 ammonia PET

ABSTRACT

In order to evaluate the effect of post-reconstruction Gaussian filtering on image quality and myocardial blood flow [MBF] measurement by dynamic N-13 ammonia positron emission tomography [PET], we compared various reconstruction and filtering methods with image characteristics. Dynamic PET images of three patients with coronary artery disease [male-female ratio of 21; age 57, 53, and 76 years] were reconstructed, using filtered back projection [FBP] and ordered subset expectation maximization [OSEM] methods. OSEM reconstruction consisted of OSEM_2I, OSEM_4I, and OSEM_6I with 2, 4, and 6 iterations, respectively. The images, reconstructed and filtered by Gaussian filters of 5, 10, and 15 mm, were obtained, as well as non-filtered images. Visual analysis of image quality [IQ] was performed using a 3-grade scoring system by 2 independent readers, blinded to the reconstruction and filtering methods of stress images. Then, signal-to-noise ratio [SNR] was calculated by noise and contrast recovery [CR]. Stress and rest MBF and coronary flow reserve [CFR] were obtained for each method. IQ scores, stress and rest MBF, and CFR were compared between the methods, using Chi-square and Kruskal-Wallis tests. In the visual analysis, IQ was significantly higher by 10 mm Gaussian filtering, compared to other sizes of filter [P<0.001 for both reader]. However, no significant difference of IQ was found between FBP and various numbers of iteration in OSEM [P=0.923 and 0.855 for readers 1 and 2 respectively]. SNR was significantly higher in 10 mm Gaussian filter. There was a significant difference in stress and rest MBF between several vascular territories. However CFR was not significantly different according to various filtering methods. Post-reconstruction Gaussian filtering with a filter size of 10 mm significantly enhances the IQ of N-13 ammonia PET-CT, without changing the results of CFR calculation