David Feiglin

System matrix for OSEM SPECT with attenuation compensation in mesh domain

The purpose of this study was to develop and implement an accurate and computationally efficient method for determination of the mesh-domain ssssssystem matrix including attenuation compensation for Ordered Subsets Expectation Maximization (OSEM) Single Photon Emission Computed Tomography (SPECT). The mesh-domain system matrix elements were estimated by first partitioning the object domain into strips parallel to detector face and with width not exceeding the size of a detector unit. This was followed by approximating the integration over the strip/mesh-element union. This approximation is product of: (i) strip width, (ii) intersection length of a ray central to strip with a mesh element, and (iii) the response and expansion function evaluated at midpoint of the intersection length. Reconstruction was performed using OSEM without regularization and with exact knowledge of the attenuation map. The method was evaluated using synthetic SPECT data generated using SIMIND Monte Carlo simulation software. Comparative quantitative and qualitative analysis included: bias, variance, standard deviation and line-profiles within three different regions of interest. We found that no more than two divisions per detector bin were needed for good quality reconstructed images when using a high resolution mesh.

Implementation OSEM mesh-domain SPECT reconstruction with explicit prior information

In order to improve reconstructed image quality, we investigated performance of OSEM mesh-domain SPECT reconstruction with explicit prior anatomical and physiological information that was used to perform accurate attenuation compensation. It was accomplished in the following steps: (i) Obtain anatomical and physiological atlas of desired region of interest; (ii) Generate mesh that encodes properties of the atlas; (iii) Perform initial pixel-based reconstruction on projection dataset; (iv) Register the expected emission atlas to the initial pixel-based reconstruction and apply resulting transformation to meshed atlas; (v) Perform reconstruction in mesh-domain using deformed mesh of the atlas. This approach was tested on synthetic SPECT noise-free and noisy data. Comparative quantitative analysis demonstrated that this method outperformed pixel-based OSEM with uniform AC and is a promising approach that might lead to improved SPECT reconstruction quality.

Attenuation compensation in mesh-domain OSEM SPECT reconstruction

A new method for attenuation compensation (AC) in mesh-domain SPECT OSEM reconstruction using strip-area approximation (SAAC) is introduced and compared to single-ray AC (SRAC). SAAC uses the polygonal area of the intersection of a mesh element (ME) and a tube-of-response (TOR) for defining an effective length of photon transit and an effective attenuation coefficient. This approach to AC is compared to SRAC, which defines the effective length of photon transit as the intersection of a single ray and a ME and the effective attenuation coefficient as the mean along the ray path. Comparative quantitative and qualitative analysis demonstrated that SAAC outperformed SRAC in terms of reconstruction image accuracy and quality.

Expectation maximization SPECT reconstruction with a content-adaptive singularity-based mesh-domain image model

To improve the speed and quality of ordered-subsets expectation-maximization (OSEM) SPECT reconstruction, we have implemented a content-adaptive, singularity-based, mesh-domain, image model (CASMIM) with an accurate algorithm for estimation of the mesh-domain system matrix. A preliminary image, used to initialize CASMIM reconstruction, was obtained using pixel-domain OSEM. The mesh-domain representation of the image was produced by a 2D wavelet transform followed by Delaunay triangulation to obtain joint estimation of nodal locations and their activity values. A system matrix with attenuation compensation was investigated. Digital chest phantom SPECT was simulated and reconstructed. The quality of images reconstructed with OSEM-CASMIM is comparable to that from pixel-domain OSEM, but images are obtained five times faster by the CASMIM method.

Improved SPECT reconstruction of Tc-99m sestamibi distribution in breast tissue

This paper describes a new image reconstruction method to reduce the presence of image artifacts in scintimammography. SPECT data are mathematically modified prior to conventional image processing, followed by an inverse transform, which permits the tomographic visualization of low signals in the presence of large background intensities observed in scintimammography. Images of Tc-99m sestamibi distribution were obtained in a modeled `breast tissue, with a high activity in the `myocardium as compared to the `breast tissue (i.e. 20:1). Image reconstruction with the modified algorithm were qualitatively correct and demonstrated the regions of enhanced uptake (lesions) with no evidence of artifacts from the background counts in the heart. Comparison with MRI demonstrated that the hot regions were properly located and correlated with the MRI data. In contrast, a standard (i.e. Filtered Back Projection) reconstruction resulted in streak artifacts in place of `breast tissue which rendered them clinically useless. This new approach to scintimammography offers the prospect of significantly reducing image artifacts and improving imaging accuracy.