Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 May 7;55(9):2523-39.
doi: 10.1088/0031-9155/55/9/007. Epub 2010 Apr 14.

Regularized reconstruction in quantitative SPECT using CT side information from hybrid imaging

Yuni K Dewaraja  1 , Kenneth F Koral, Jeffrey A Fessler
Affiliations

Regularized reconstruction in quantitative SPECT using CT side information from hybrid imaging

Yuni K Dewaraja et al. Phys Med Biol. .

Abstract

A penalized-likelihood (PL) SPECT reconstruction method using a modified regularizer that accounts for anatomical boundary side information was implemented to achieve accurate estimates of both the total target activity and the activity distribution within targets. In both simulations and experimental I-131 phantom studies, reconstructions from (1) penalized likelihood employing CT-side information-based regularization (PL-CT), (2) penalized likelihood with edge preserving regularization (no CT) and (3) penalized likelihood with conventional spatially invariant quadratic regularization (no CT) were compared with (4) ordered subset expectation maximization (OSEM), which is the iterative algorithm conventionally used in clinics for quantitative SPECT. Evaluations included phantom studies with perfect and imperfect side information and studies with uniform and non-uniform activity distributions in the target. For targets with uniform activity, the PL-CT images and profiles were closest to the 'truth', avoided the edge offshoots evident with OSEM and minimized the blurring across boundaries evident with regularization without CT information. Apart from visual comparison, reconstruction accuracy was evaluated using the bias and standard deviation (STD) of the total target activity estimate and the root mean square error (RMSE) of the activity distribution within the target. PL-CT reconstruction reduced both bias and RMSE compared with regularization without side information. When compared with unregularized OSEM, PL-CT reduced RMSE and STD while bias was comparable. For targets with non-uniform activity, these improvements with PL-CT were observed only when the change in activity was matched by a change in the anatomical image and the corresponding inner boundary was also used to control the regularization. In summary, the present work demonstrates the potential of using CT side information to obtain improved estimates of the activity distribution in targets without sacrificing the accuracy of total target activity estimation. The method is best suited for data acquired on hybrid systems where SPECT-CT misregistration is minimized. To demonstrate clinical application, the PL reconstruction with CT-based regularization was applied to data from a patient who underwent SPECT/CT imaging for tumor dosimetry following I-131 radioimmunotherapy.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Images and profiles for a single noisy realization of the simulation with uniform activity spheres. (a) True activity, (b) regularization weights in the vertical direction, (c) OSEM, (d) PL-CT, (e) PL-Q, (f) PL-EP and (g) profiles across the center of the image.
Figure 2
Figure 2
Images and profiles for a single noisy realization of simulation with non-uniform activity spheres. (a) True activity, (b) OSEM, (c) PL-CT with inner and outer boundaries, (d) PL-CT with only outer boundary and (e) profiles across the center of the image.
Figure 3
Figure 3
Images and profiles for measurement with non-uniform activity spheres. (a) CT image, (b) true activity, (c) OSEM, (d) PL-CT, (e) PL-Q, (f) PL-EP and (g) profiles across the center of the image.
Figure 4
Figure 4
(a) Patient PL-CT SPECT reconstruction superimposed on CT with tumor outlines and (b) profiles across the tumor for the different reconstructions.
See this image and copyright information in PMC

References

    1. Amro H, Wilderman SJ, Dewaraja YK, Roberson PL. Methodology to incorporate biologically effective dose and equivalent uniform dose in patient-specific 3-dimensional dosimetry for non-Hodgkin lymphoma patients targeted with 131I-tositumomab therapy. J Nucl Med. 2010;51:654–9. - PMC - PubMed
    1. Boening G, Pretorius PH, King MA. Study of relative quantification of Tc-99 m with partial volume effect and spillover correction for SPECT oncology imaging. IEEE Trans Nucl Sci. 2006;53:1205–12.
    1. Bowsher JE, et al. Bayesian reconstruction and use of anatomical a priori information for emission tomography. IEEE Trans Med Imaging. 1996;15:673–86. - PubMed
    1. Comtat C, et al. Clinically feasible reconstruction of 3D whole-body PET/CT data using blurred anatomical labels. Phys Med Biol. 2002;47:1–20. - PubMed
    1. Dewaraja YK, Ljungberg M, Fessler JA. Anatomical information based partial volume compensation for I-131 SPECT imaging in radioimmunotherapy. J Nucl Med. 2006;47(Suppl 1):115.

Publication types

MeSH terms