Interest of the ordered subsets expectation maximization (OS-EM) algorithm in pinhole single-photon emission tomography reconstruction: a phantom study

Abstract.Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off between sensitivity and resolution for small organs located in close proximity to the pinhole aperture. This technique is hampered by artefacts in the non-central slices. These artefacts are caused by truncation and by the fact that the pinhole SPET data collected in a circular orbit do not contain sufficient information for exact reconstruction. The ordered subsets expectation maximization (OS-EM) algorithm is a potential solution to these problems. In this study a three-dimensional OS-EM algorithm was implemented for data acquired on a single-head gamma camera equipped with a pinhole collimator (PH OS-EM). The aim of this study was to compare the PH OS-EM algorithm with the filtered back-projection algorithm of Feldkamp, Davis and Kress (FDK)and with the conventional parallel-hole geometry as a whole,using a line source phantom, Picker’s thyroid phantom and a phantom mimicking the human cervical column. Correction for the angular dependency of the sensitivity in the pinhole geometrywas based on a uniform flood acquisition. The projection data were shifted according to the measured centre of rotation. No correction was made for attenuation, scatter or distance-dependent camera resolution. The resolution measured with the line source phantom showed a significant improvement with PH OS-EM as compared with FDK, especially in the axial direction. Using Picker’s thyroid phantom, one iteration with eight subsets was sufficient to obtain images with similar noise levels in uniform regions of interest to those obtained with the FDK algorithm. With these parameters the reconstruction time was 2.5 times longer than for the FDK method. Furthermore, there was a reduction in the artefacts caused by the circular orbit SPET acquisition. The images obtained from the phantom mimicking the human cervical column indicated that the improvement in image quality with PH OS-EM is relevant for future clinical useand that the improvements obtained using the OS-EM algorithm are more significant for the pinhole geometry than for the conventional parallel-hole geometry. We conclude that PH OS-EM is a practical and promising alternative for pinhole SPET reconstruction.

[1]  R J Jaszczak,et al.  A filtered backprojection algorithm for pinhole SPECT with a displaced centre of rotation , 1994, Physics in medicine and biology.

[2]  H. Tuy AN INVERSION FORMULA FOR CONE-BEAM RECONSTRUCTION* , 1983 .

[3]  P M Wanet,et al.  Physical and clinical evaluation of high-resolution thyroid pinhole tomography. , 1996, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[4]  Y W Bahk,et al.  Dual-head pinhole bone scintigraphy. , 1998, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[5]  R. Jaszczak,et al.  Cone beam collimation for single photon emission computed tomography: analysis, simulation, and image reconstruction using filtered backprojection. , 1986, Medical physics.

[6]  D R Gilland,et al.  Design and clinical utility of a fan beam collimator for SPECT imaging of the head. , 1986, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[7]  L. Feldkamp,et al.  Practical cone-beam algorithm , 1984 .

[8]  Y W Bahk,et al.  Pinhole SPECT imaging in normal and morbid ankles. , 1998, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[9]  Ronald J. Jaszczak,et al.  Single Photon Emission Computed Tomography Using Multi-Slice Fan Beam Collimators , 1979, IEEE Transactions on Nuclear Science.

[10]  K. Erlandsson,et al.  Small animal imaging with pinhole single‐photon emission computed tomography , 1994, Cancer.

[11]  R. Jaszczak,et al.  Pinhole collimation for ultra-high-resolution, small-field-of-view SPECT. , 1994, Physics in medicine and biology.

[12]  Michel Defrise,et al.  Pinhole SPECT using the ordered subsets expectation maximization (OSEM) algorithm , 1998 .

[13]  H. Atkins,et al.  Pinhole SPECT: an approach to in vivo high resolution SPECT imaging in small laboratory animals. , 1994, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.

[14]  F. Natterer The Mathematics of Computerized Tomography , 1986 .

[15]  Y. Yonekura,et al.  Ultra-high resolution SPECT system using four pinhole collimators for small animal studies. , 1995, Journal of nuclear medicine : official publication, Society of Nuclear Medicine.