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Absolute Quantification of Regional Myocardial Uptake of ^99mTc-Sestamibi with SPECT: Experimental Validation in a Porcine Model

Department of Radiology and Cardiovascular Research Institute, University of California at San Francisco, San Francisco; and Joint Bioengineering Graduate Group, University of California at San Francisco and Berkeley, San Francisco and Berkeley, California

We have evaluated a method for absolute in vivo quantification of ^99mTc-sestamibi uptake in a porcine model of myocardial perfusion. Methods: Correlated CT and radionuclide images were obtained from eight adult pigs using a combined CT–SPECT imaging system. In each case, the CT image is used to generate an object-specific attenuation map that is incorporated into an iterative algorithm for reconstruction and attenuation correction of the radionuclide image. Anatomic information available from the correlated CT image is used to correct the radionuclide image for partial-volume errors by mathematically modeling the radionuclide imaging process. A volume of interest, or template, that approximates the geometric extent of the myocardium is defined from the CT image. Once defined, the template is assigned unit activity and is mathematically projected using a realistic physical model of the radionuclide imaging process including nonideal collimation and object-specific attenuation. The template is then reconstructed from these projections to obtain a pixel-by-pixel partial-volume correction for the myocardium in the radionuclide image. The CT image is also used to delimit the anatomic boundaries of the myocardium for quantification of the radionuclide images. The pixel intensities in the corrected radionuclide image are calibrated in units of activity concentration (MBq/g) and compared with the ex vivo activity concentration measured directly from the excised myocardium. Results: Without corrections, the measured in vivo activity concentration in the porcine myocardium was only 10% of the true value. Correcting for object-specific attenuation improved the accuracy of this measurement but resulted in values that were still only 42% of the true value. By correcting for both attenuation and partial-volume errors, we were able to achieve absolute quantification with an accuracy error near 10%. Conclusion: We have shown that, by applying object-specific attenuation corrections and suitable partial-volume corrections, absolute regional activity concentration can be measured accurately in the porcine myocardium.

Key Words: SPECT • quantification • partial-volume effects • image coregistration • myocardial perfusion

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The Road to Quantitation of Regional Myocardial Uptake of Tracer

Nagara Tamaki, Yuji Kuge, and Eriko Tsukamoto
JNM 2001 42: 780-781. [Full Text]  

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				A. K. Buck, S. Nekolla, S. Ziegler, A. Beer, B. J. Krause, K. Herrmann, K. Scheidhauer, H.-J. Wester, E. J. Rummeny, M. Schwaiger, et al. SPECT/CT J. Nucl. Med., August 1, 2008; 49(8): 1305 - 1319. [Abstract] [Full Text] [PDF]

				N. Tamaki, Y. Kuge, and E. Tsukamoto The Road to Quantitation of Regional Myocardial Uptake of Tracer J. Nucl. Med., May 1, 2001; 42(5): 780 - 781. [Full Text]