Evaluation of collimator-detector response compensation in tumor SPECT using medium- and high-energy collimators

Tsui, B.M.W.; Zhao, Xingping; Sayeram, S.; Frey, Eric; Falen, Steven; McCartney, William

doi:10.1109/nssmic.2000.949212

Cited by 1 publication

(1 citation statement)

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“…Thus, we expect OSEM with a detector-response model to nullify the effects of background level on target activity. With I-131, the addition of a detector-response model has been said to yield "drastic improvements in clinical image quality" [18]. However, Lalush and Tsui have stated that the accuracy of results from OSEM cannot be predicted, but must be carefully verified empirically [19].…”

Section: Introductionmentioning

confidence: 99%

Determining total I-131 activity within a VoI using SPECT, a UHE collimator, OSEM, and a constant conversion factor

Koral

Yendiki

Lin

et al. 2004

IEEE Trans. Nucl. Sci.

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Accurate determination of activity within a volume of interest is needed during radiopharmaceutical therapies. Single-photon emission computed tomography(SPECT) is employed but requires a method to convert counts to activity. We use a phantom-based conversion; that is, we image an elliptical cylinder containing a sphere that has a known amount of 131-I activity inside. The regularized space alternating generalized expectation (SAGE) algorithm employing a strip-integral detector-response model was employed for reconstruction in previous patient evaluations. With that algorithm and a high-energy collimator, the estimates for sphere activity varied with changes in: 1) the level of uniform background activity in the cylinder; 2) the image resolution due to different values of the radius of rotation ; and 3) the volume of the sphere. When one used those to convert reconstructed counts within a patient tumor into an activity estimate, the resultant value may have been in error because of patient-phantom mismatch. As a potential remedy, in this paper, we use an ordered subsets expectation maximization (OSEM) algorithm with a 3-D depth-dependent detector-response model and an ultra-high-energy collimator. Results after 100 OSEM iterations and using a maximum counts registration show the estimates for sphere activity: 1) have a dependence on the level of background activity with a slope whose absolute magnitude is typically only 0.37 times that with SAGE; 2) are independent of ; and 3) are independent of sphere volume down to and including a sphere volume of 20 cm 3. We conclude that using a global-average conversion factor to relate counts to activity and no volume-based correction might be reasonable with OSEM. For a test of that conclusion, target activity is estimated for an anthropomorphic phantom containing a 100 cm 3 spherical tumor centrally located inferior to the lungs. With OSEM-based quantification, using: 1) a global-average conversion factor and 2) no volume-based correction, mean bias in the simulated-tumor activity estimate over 20 realizations is 7 37% (relative standard deviation = 5 93%). With SAGE-based quantification using: 1) the conversion factor corresponding to the experimental estimate of background and 2) volume-based correction, the mean bias is 10 7% (relative standard deviation = 2 37%). The mean bias

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Section: Introductionmentioning

confidence: 99%