Preliminary evaluation of image reconstruction by

Authors: Jingming Bai Kunihiko Yokoyama Seigo Kinuya Kenichi Nakajima Masato Yamada Kenji Ichiyanagi Takatoshi Michigishi Norihisa Tonami

Publish Date: 2008/12/10

Volume: 17, Issue: 7, Pages: 619-

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Abstract

Objectives We observed whether clearer tumor delineation and greater tumor to nontumor T/N count ratios could be obtained using an iterative orderedsubsets expectation maximization OSEM algorithm than conventional filteredback projection algorithm FBP in the image reconstruction of thallium201 201Tl lung scintigraphyMethods In 29 patients with lung cancer and phantom studies tomograms were reconstructed using FBP and OSEM algorithms with and without a prefilter Butterworth filter BW whose cutoff frequencies were 010 cycles/pixel for FBP and 010 and 017 cycles/pixel for OSEM Visual interpretation and tumor to nontumor T/N count ratios were obtained and comparedResults Without a prefilter T/N ratios from OSEM and FBP were 189±031 early and 200±054 late for OSEM 190±033 early and 205±059 late for FBP respectively The OSEM reconstruction without prefiltering showed clearer tumor contours than FBP without a prefilter Incorporation of BW showed visually lownoised images but decreased T/N ratios in both reconstructions with BW 010 cycles/pixel No greater T/N ratios were obtained by OSEM than FBP with or without prefiltering With BW with a cutoff frequency of 017 cycles/pixel the same T/N ratios as those without BW were obtained The tumor model sized 09 cm in the phantom study was invisible in both OSEM and FBP reconstructions without a prefilter but visible with a prefilter The influence of prefiltering on T/N ratios was also observed in phantom studiesConclusions Visually improved tumor delineation could be obtained in OSEM reconstruction without a prefilter as compared to FBP reconstruction without a prefilter for tumors greater than 2 cm Prefiltering should be incorporated into OSEM reconstruction in diagnosing small tumors However the influence of prefilter BW setting on semiquantitative interpretation needs further discussion

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