The importance and implementation of accurate 3D compensation methods for quantitative SPECT

Tsui, B.M.W.; Frey, Eric; Zhao, Xingping; Lalush, David S.; Johnston, Richard; McCartney, William

doi:10.1088/0031-9155/39/3/015

Cited by 146 publications

(72 citation statements)

References 38 publications

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“…The effects of statistical noise in iterative SPECT reconstruction have been studied [2]. So too have the effects of modeling or not modeling scatter, detector response, and attenuation [1], [3]. One area that has received less attention is the consequences of incorrect modeling of imagingsystem properties.…”

Section: Introductionmentioning

confidence: 99%

The effects of incorrect modeling on noise and resolution properties of ML-EM images

Wilson

Barrett

2002

IEEE Trans. Nucl. Sci.

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The effects of incorrect compensation for collimator blur in single-photon emission computed tomography (SPECT) images are studied in terms of the noise and resolution properties of the reconstructed images. Qualitative analysis of images of the Hoffman brain phantom reconstructed using nonlinear maximum-likelihood-expectation maximization (ML-EM) show the behavior of longer noise correlations for high-pass filtered images. These qualitative observations are confirmed with more quantitative noise measures. The differences also appear in images reconstructed using linear Landweber iteration. However, the signal-to-noise ratio, in terms of the noise-equivalent quanta, remains largely unchanged. We conclude that the compensation model affects SPECT image properties, though the effect on human task performance remains to be studied.

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Section: Introductionmentioning

confidence: 99%

The effects of incorrect modeling on noise and resolution properties of ML-EM images

Wilson

Barrett

2002

IEEE Trans. Nucl. Sci.

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“…However, if optimal corrections for image degradations induced by SPECT physical phenomena such as depth-dependent blur, photon attenuation, and scatter are needed, iterative image reconstruction is to be used (1). It was shown by Gilland et al (3), Tsui et al (4,5), and Rosenthal et al (6), for example, that these corrections reduce errors for absolute quantification in SPECT. Both the availability of fast computers at low cost and advances in efficient processing allow the use of computationally expensive iterative methods in clinical routine (1).…”

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confidence: 99%

Quantitative Accuracy of Clinical ^99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction

Zeintl¹,

Vija²,

Yahil³

et al. 2010

J Nucl Med

229

185

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We present a calibration method of a clinical SPECT/CT device for quantitative 99m Tc SPECT. We use a commercially available reconstruction package including ordered-subset expectation maximization (OSEM) with depth-dependent 3-dimensional resolution recovery (OSEM-3D), CT-based attenuation correction, and scatter correction. We validated the method in phantom studies and applied it to images from patients injected with 99m Tc-diphosponate. Methods: The following 3 steps were performed to derive absolute quantitative values from SPECT reconstructed images. In step 1, we used simulations to characterize the SPECT/CT system and derive emission recovery values for various imaging parameter settings. We simulated spheres of varying diameters and focused on the dependencies of activity estimation errors on structure size and position, pixel size, count density, and reconstruction parameters. In step 2, we cross-calibrated our clinical SPECT/CT system with the well counter using a large cylinder phantom. This step provided the mapping from image counts to kBq/mL. And in step 3, correction factors from steps 1 and 2 were applied to reconstructed images. We used a cylinder phantom with variable-sized spheres for verification of the method. For in vivo validation, SPECT/CT datasets from 16 patients undergoing 99m Tc-diphosponate SPECT/CT examinations of the pelvis including the bladder were acquired. The radioactivity concentration in the patients' urine served as the gold standard. Mean quantitative accuracy and SEs were calculated. Results: In the phantom experiments, the mean accuracy in quantifying radioactivity concentration in absolute terms was within 3.6% (SE, 8.0%), with a 95% confidence interval between 219.4% and 112.2%. In the patient studies, the mean accuracy was within 1.1% (SE, 8.4%), with a 95% confidence interval between 215.4% and 117.5%. Conclusion: Current commercially available SPECT/CT technology using OSEM-3D reconstruction, scatter correction, and CT-based attenuation correction allows quantification of 99m Tc radioactivity concentration in absolute terms within 3.6% in phantoms and 1.1% in patients with a focus on the bladder. This opens up the opportunity of SPECT quantitation entering the routine clinical arena. Still, the imprecision caused by unavoidable measurement errors is a dominant factor for absolute quantitation in a clinical setup.

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“…It has been demonstrated that, with appropriate SPECT acquisition, calibration, and quantitative reconstruction, SPECT can provide accurate estimates of in vivo radioactivity distributions. [19][20][21][22] Although quantitative SPECT ͑QSPECT͒ may become the method of choice for quantifying in vivo activity distribution, it is currently difficult to implement clinically because of the more complex imaging protocol required to cover the dosimetrically important organs, the longer acquisition times conventionally used, and the need to use computationally intensive iterative reconstruction methods. In order to address some limitations of the QSPECT method, we have developed a new quantitative planar ͑QPlanar͒ method which is based on maximum-likelihood estimation of organ activities using 3D organ VOIs and a model-based projector that models image degrading effects including attenuation, scatter, and the full collimator-detector response.…”

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confidence: 99%

Effects of shortened acquisition time on accuracy and precision of quantitative estimates of organ activitya)

Frey

2010

Med. Phys.

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Purpose: Quantitative estimation of in vivo organ uptake is an essential part of treatment planning for targeted radionuclide therapy. This usually involves the use of planar or SPECT scans with acquisition times chosen based more on image quality considerations rather than the minimum needed for precise quantification. In previous simulation studies at clinical count levels ͑185 MBq 111 In͒, the authors observed larger variations in accuracy of organ activity estimates resulting from anatomical and uptake differences than statistical noise. This suggests that it is possible to reduce the acquisition time without substantially increasing the variation in accuracy. Methods: To test this hypothesis, the authors compared the accuracy and variation in accuracy of organ activity estimates obtained from planar and SPECT scans at various count levels. A simulated phantom population with realistic variations in anatomy and biodistribution was used to model variability in a patient population. Planar and SPECT projections were simulated using previously validated Monte Carlo simulation tools. The authors simulated the projections at count levels approximately corresponding to 1.5-30 min of total acquisition time. The projections were processed using previously described quantitative SPECT ͑QSPECT͒ and planar ͑QPlanar͒ methods. The QSPECT method was based on the OS-EM algorithm with compensations for attenuation, scatter, and collimator-detector response. The QPlanar method is based on the ML-EM algorithm using the same model-based compensation for all the image degrading effects as the QSPECT method. The volumes of interests ͑VOIs͒ were defined based on the true organ configuration in the phantoms. The errors in organ activity estimates from different count levels and processing methods were compared in terms of mean and standard deviation over the simulated phantom population. Results: There was little degradation in quantitative reliability when the acquisition time was reduced by half for the QSPECT method ͑the mean error changed by Ͻ1%, e.g., 0.9% -0.3% = 0.6% for the spleen͒. The magnitude of the errors and variations in errors for large organ with high uptake were still acceptable for 1.5 min scans, even though the errors were slightly larger than those for the 30 min scans ͑i.e., Ͻ2% for liver, Ͻ3% for heart͒. The errors over the ranges of scan times studied for the QPlanar method were all within 0.3% for all organs. Conclusions: These data indicate that, for the purposes of organ activity estimation, acquisition times could be reduced at least by a factor of 2 for the QSPECT and QPlanar methods with little effect on the errors in organ activity estimates. The acquisition time can be further reduced for the QPlanar method, assuming well-registered VOIs are available and the activity distribution in organs can be treated as uniform. Although the differences in accuracy and precision were statistically significant for all the acquisition times shorter than 30 min, the magnitude of the changes in accuracy and precisi...

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The importance and implementation of accurate 3D compensation methods for quantitative SPECT

Cited by 146 publications

References 38 publications

The effects of incorrect modeling on noise and resolution properties of ML-EM images

The effects of incorrect modeling on noise and resolution properties of ML-EM images

Quantitative Accuracy of Clinical ^99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction

Effects of shortened acquisition time on accuracy and precision of quantitative estimates of organ activitya)

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The importance and implementation of accurate 3D compensation methods for quantitative SPECT

Cited by 146 publications

References 38 publications

The effects of incorrect modeling on noise and resolution properties of ML-EM images

The effects of incorrect modeling on noise and resolution properties of ML-EM images

Quantitative Accuracy of Clinical 99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction

Effects of shortened acquisition time on accuracy and precision of quantitative estimates of organ activitya)

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Quantitative Accuracy of Clinical ^99mTc SPECT/CT Using Ordered-Subset Expectation Maximization with 3-Dimensional Resolution Recovery, Attenuation, and Scatter Correction