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

Koral, Kenneth F.; Yendiki, Anastasia; Lin, Qiang; Dewaraja, Yuni K.; Fessler, Jeffrey A.

doi:10.1109/tns.2004.829605

Cited by 8 publications

(20 citation statements)

References 22 publications

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“…The spherical VoI that was needed to calculate total target counts was drawn on the CT image and initially located in the SPECT image by a marker-based CT-SPECT registration. Determination of the registration that finally located the VoI for each algorithm was as detailed in [10].…”

Section: Methodsmentioning

confidence: 99%

“…The reason for interest in both is that the most significant I-131 gamma-ray emission is at 364 keV (82%), but emissions at 637 keV (7.2%) and 723 keV (1.8%) also exist and penetrate the septa of a HE collimator. UHE collimation has been shown to reduce septal penetration compared to HE collimation and, therefore, to yield higher-contrast images [9], [10].…”

Section: Introductionmentioning

confidence: 99%

“…Activity-quantification results for I-131 and UHE collimation with 3-D-OSEM reconstruction have been given in a previous publication [10]. A camera-calibration curve was presented.…”

Section: Introductionmentioning

confidence: 99%

“…That mean activity estimate did not have the benefit of activity correction using recovery coefficients. The 3-D-OSEM results were compared to those from the same projection data after 1-D-SAGE reconstruction [10].…”

Section: Introductionmentioning

confidence: 99%

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Comparison of 3-D OSEM versus 1-D SAGE for focal total-activity quantification in I-131 SPECT with HE collimation

Koral

Yendiki

Lin

et al. 2005

IEEE Trans. Nucl. Sci.

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A three-dimensional (3-D) ordered-subset expectation maximization (OSEM) reconstruction algorithm used fits to the average behavior of the I-131 point-source-response function at different depths to model the detector-collimator response of a SPECT camera. The fitting function was a Gaussian, plus a single exponential to account for septal-penetration of the high-energy (HE) collimation. Results from that unregularized 3-D OSEM were compared to those with regularized one-dimensional (1-D) space-alternating generalized expectation maximization (SAGE). The latter used a simple strip integral. Each reconstruction algorithm employed attenuation correction and scatter compensation. The SPECT camera was calibrated by imaging a 200 cm 3 sphere containing a known I-131 activity. This sphere was located inside an elliptical cylinder. The water in the cylinder contained one of four I-131 activity concentrations. The ratio of background-over-target activity concentration b was used to characterize the different situations. The known activity and the reconstructed counts within the sphere at each b value yielded a counts-to-activity conversion factor, CF. After reconstruction with 3-D OSEM, CF varied much less with b than after reconstruction with 1-D SAGE. A test of activity quantification was carried out with 20 realizations of an anthropomorphic phantom with zero background activity. This phantom simulated a 100 cm 3 spherical tumor centrally located inferior to the lungs. The mean bias in the estimate of "tumor" activity was 7 3% with 3-D-OSEM-based quantification and 4 3% with 1-D-SAGE-based quantification.Recovery-coefficient-based correction was applied with both algorithms. With UHE collimation, the previously-published mean bias in the estimate of the "tumor" activity was 5 2% after adding a recovery-coefficient-based correction. For that collimation, the previously-published mean bias with 1-D-SAGE-based quantification was 10 7%. We conclude that 1) two-component fitting allowed 3-D OSEM to do a good job of compensating for the septal penetration of the HE collimation, 2) the procedure for activity quantification with 3-D OSEM was simpler than that with 1-D SAGE, and 3) activity accuracy for a test phantom had a similar quality for four situations, using 3-D OSEM-based activity quantification and 1-D-SAGE-based activity quantification and combining each with HE and UHE collimation.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Activity-quantification results for I-131 and UHE collimation with 3-D-OSEM reconstruction have been given in a previous publication [10]. A camera-calibration curve was presented.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of 3-D OSEM versus 1-D SAGE for focal total-activity quantification in I-131 SPECT with HE collimation

Koral

Yendiki

Lin

et al. 2005

IEEE Trans. Nucl. Sci.

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“…The magnitude of quantification errors has been reported by several authors for planar (conjugate view) imaging as being a few percentage points for large objects to tens or hundreds of percentage points for small objects with low source-to-background contrast (9)(10)(11)(12)(13)(14). Generally better results, with perhaps 10%-30% uncertainty for objects of various sizes, have been reported with the use of high-quality SPECT quantitative imaging (11,(15)(16)(17). Uncertainties in individual data points, however, are not always used in the fitting of the data in a regression or compartment model; often only the scatter of the data is included in reported uncertainties in the fitted parameters from a kinetic analysis.…”

Section: Biokinetic Parameters N (Or ã S )mentioning

confidence: 99%

Uncertainties in Internal Dose Calculations for Radiopharmaceuticals

Stabin¹

2008

J Nucl Med

140

111

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This paper presents a systematic analysis of the inherent uncertainty in internal dose calculations for radiopharmaceuticals. A generic equation for internal dose is presented, and the uncertainty in each of the individual terms is analyzed, with the relative uncertainty of all terms compared. The combined uncertainties in most radiopharmaceutical dose estimates will be typically at least a factor of 2 and may be considerably greater. In therapy applications, if patient-individualized absorbed doses are calculated, with attention being paid to accurate data gathering and analysis and measurement of individual organ volumes, many of the model-based uncertainties can be removed, and the total uncertainty in an individual dose estimate can be reduced to a value of perhaps 610%-20%. Radiation dose estimates for different diagnostic radiopharmaceuticals should be appreciated and considered, but small differences in dose estimates between radiopharmaceuticals should not be given too much importance when one is choosing radiopharmaceuticals for general clinical use. Diagnostic accuracy, ease of use, image quality, patient comfort, and other similar factors should predominate in the evaluation, with radiation dose being another issue considered while balancing risks and benefits appropriately.Key Words: radiobiology/dosimetry; radiopharmaceuticals; radiation safety; internal dose assessment; radiopharmaceuticals; uncertainty Radi ation dose estimates for radiopharmaceuticals are widely reported by different groups and individuals, using various modeling assumptions and computational techniques. The reported estimates are mean or median values for large populations of individuals and are sometimes reported with uncertainty estimates but usually as observed standard deviations (SD) and coefficients of variation for the group of subjects studied. In this paper, a systematic analysis of the inherent uncertainty in internal dose calculations for radiopharmaceuticals is presented. Each term of the dose equation is evaluated for its individual uncertainty, and an overall uncertainty is then evaluated (although not calculated analytically via classic error propagation, for reasons that will be explained).To evaluate the overall uncertainty in a radiation dose estimate, one must consider the uncertainty in each of the contributing terms. (Note that the generic word dose in this article may refer to a number of dose quantities, such as absorbed dose, equivalent dose, or effective dose. Most of the analysis in this paper regards the mean dose to whole organs-currently the most widely used quantity in internal dose analysis. Later, some brief discussion of the uncertainty in dose calculations at the tissue or cell level is provided, but a systematic analysis of uncertainty in these applications is not treated.) A generic equation for the average absorbed dose in a target region T (e.g., an organ or tissue with radiopharmaceutical uptake) may be shown as:where D T is mean absorbed dose (Gy or rad) to a target region of interest; Ã S...

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