ABTRACT

Background: In nuclear medicine, phantoms are mainly used to evaluate the overall performance of the imaging systems and practically there is no phantom exclusively designed for the evaluation of the software performance.  In this study the Hoffman brain phantom was used for quantitative evaluation of reconstruction techniques. The phantom is modified to acquire tomographic and planar image of the same structure. The planar image may be used as the reference image to evaluate the quality of reconstructed slices using the companion software developed in MATLAB.

Methods and Materials: The designed phantom is composed of 4 independent 2D slices that may be placed juxtapose to form the 3D phantom. Each slice is composed of objects of different size and shape e.g. circle, triangle, and rectangle. Each 2D slice was imaged at the distances from 0 to 15 cm from the collimator surface. The phantom in 3D configuration was imaged acquiring 128 views of 128×128 matrix size. Reconstruction was performed using different filtering condition and the reconstructed images were compared to the corresponding planar images. The modulation transfer function, scatter fraction and attenuation map were calculated for each reconstructed image

Results: Since all the parameters of the acquisition were identical for the 2D and the 3D imaging. It was assumed that the difference in the quality of the images was exclusively due to reconstruction condition. The planar images were assumed to be the most perfect images that could be obtained with the system. Comparing the reconstructed slices to the corresponding planar images yielded the optimum reconstruction condition.  The results clearly showed that Wiener filter yields superior quality image among the entire filter tested. The extent of the improvement has been quantified in terms of universal image quality index.

Conclusion: The phantom and the accompanying software were evaluated and found to be quite useful in determining the optimum filtering condition and mathematical evaluation of the scatter and attenuation in tomographic images.