Preliminary evaluation of image reconstruction by ordered-subset expectation maximization in thallium-201 lung scintigraphy.
OBJECTIVE
We observed whether clearer tumor delineation and greater tumor to non-tumor (T/N) count ratios could be obtained using an iterative ordered-subsets expectation maximization (OSEM) algorithm than conventional filtered-back projection algorithm (FBP) in the image reconstruction of thallium-201 (201Tl) lung scintigraphy.


METHODS
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 cut-off frequencies were 0.10 cycles/pixel for FBP and 0.10 and 0.17 cycles/pixel for OSEM. Visual interpretation and tumor to non-tumor (T/N) count ratios were obtained and compared.


RESULTS
Without a prefilter, T/N ratios from OSEM and FBP were 1.89 +/- 0.31 (early) and 2.00 +/- 0.54 (late) for OSEM, 1.90 +/- 0.33 (early) and 2.05 +/- 0.59 (late) for FBP, respectively. The OSEM reconstruction without prefiltering showed clearer tumor contours than FBP without a prefilter. Incorporation of BW showed visually low-noised images but decreased T/N ratios in both reconstructions with BW (0.10 cycles/pixel). No greater T/N ratios were obtained by OSEM than FBP, with or without prefiltering. With BW with a cut-off frequency of 0.17 cycles/pixel, the same T/N ratios as those without BW were obtained. The tumor model sized 0.9 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 studies.


CONCLUSIONS
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 semi-quantitative interpretation needs further discussion.
Bai
Jingming
J
Department of Biotracer Medicine, Graduate School of Medical Sciences, Kanazawa University, Japan. bjingming@nmd.m.kanazawa-u.ac.jp
Yokoyama
Kunihiko
K
Kinuya
Seigo
S
Nakajima
Kenichi
K
Yamada
Masato
M
Ichiyanagi
Kenji
K
Michigishi
Takatoshi
T
Tonami
Norihisa
N
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging / Q000379:methods; D010865:Pilot Projects; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging* / Q000473:pathology; D013793:Thallium; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D019275:Radiopharmaceuticals; C027549:thallium chloride; D013793:Thallium