Accuracy and Precision of Radioactivity Quantification in Nuclear Medicine Images

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The ability to reliably quantify activity in nuclear medicine has a number of increasingly important applications. Dosimetry for targeted therapy treatment planning or for approval of new imaging agents requires accurate estimation of the activity in organs, tumors, or voxels at several imaging time points. Another important application is the use of quantitative metrics derived from images, such as the standard uptake value commonly used in positron emission tomography (PET), to diagnose and follow treatment of tumors. These measures require quantification of organ or tumor activities in nuclear medicine images. However, there are a number of physical, patient, and technical factors that limit the quantitative reliability of nuclear medicine images. There have been a large number of improvements in instrumentation, including the development of hybrid single-photon emission computed tomography/computed tomography and PET/computed tomography systems, and reconstruction methods, including the use of statistical iterative reconstruction methods, which have substantially improved the ability to obtain reliable quantitative information from planar, single-photon emission computed tomography, and PET images.

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Reliability of Quantitative Images

The goal of activity quantification is to enable diagnostic or therapeutic decisions based on estimates of activity in objects or regions in the body. Two criteria characterize the reliability of such estimates: accuracy and precision. Accuracy describes the deviation of an estimate of some quantity from the true value, whereas precision describes the variability of an estimate about its mean. Accuracy is often expressed in terms of the bias or relative error, whereas precision is described by

Factors Affecting Reliability of Image-Based Activity Estimates

The process of estimating activity often involves implicit or explicit modeling of the image formation process. The factors in imaging systems that result in the failure to satisfy this model are often referred to as image degrading factors. Degrading factors can be divided into the following 3 categories: effects resulting from the physics of the image formation, factors resulting from the choice of image protocol parameters, and factors resulting from biology and physiology of the patient.

Quantitative Planar Imaging

Imaging with a scintillation camera is measurement of 2D projections of a 3D activity distribution. Consequently, the source depth and extent in the direction parallel to the projection is not resolved. This complicates activity quantification because more than one organ can contribute to a particular pixel value in the projection image.

Quantitative SPECT

There have been several published reviews on quantitative SPECT. Tsui et al3 and the Society of Nuclear Medicine Computer and Instrumentation Council4 provide a taxonomy of the image degrading effects, as well as a description of compensation methods, and include some profiles that demonstrate the quantitative accuracy achievable with SPECT. Due to the theoretical advantages of statistical iterative reconstruction (IR) algorithms, in the following we confine our discussion to IR-based

Quantitative PET

PET is construed as a highly quantitative imaging modality due to the ability to calibrate PET scanners to provide image readout data directly in units of Bq/cc (μCi/cc). Calibration is performed by acquiring images on the PET scanner of a known 18F activity after uniform mixing in a cylindrical phantom of known volume. This known activity concentration in the phantom is used as the basis to convert the count density information into an activity concentration in the reconstructed, attenuation

Acknowledgments

Portions of this work have been supported by the Swedish Cancer Society. Eric Frey would like to thank Bin He, Ph.D., for comments on the manuscript and acknowledge support for portions of this work by Public Health Service grant R01-CA109234.

References (57)

  • B.M.W. Tsui et al.

    Pitfalls of attenuation compensation and their remedies in cardiac SPECT

    J Nucl Med

    (1994)
  • C.D. Stone et al.

    Effect of registration errors between transmission and emission scans on a SPECT system using sequential scanning

    J Nucl Med

    (1998)
  • C.H. Tung et al.

    A Simulation of emission and transmission noise-propagation in cardiac SPECT imaging with nonuniform attenuation correction

    Med Phys

    (1994)
  • K.J. Lacroix et al.

    Investigation of the use of X-ray CT images for attenuation compensation in SPECT

    IEEE Trans Nucl Sci

    (1994)
  • T.A. Riauka et al.

    Photon propagation and detection in single-photon emission computed-tomography—an analytical approach

    Med Phys

    (1994)
  • R.G. Wells et al.

    Analytical calculation of photon distributions in SPECT projections

    IEEE Trans Nucl Sci

    (1998)
  • F.J. Beekman et al.

    Object shape dependent PSF model for SPECT imaging

    IEEE Trans Nucl Sci

    (1993)
  • E.C. Frey et al.

    A fast projector-backprojector pair modeling the asymmetric, spatially varying scatter response function for scatter compensation in SPECT imaging

    IEEE Trans Nucl Sci

    (1993)
  • E.C. Frey et al.

    A Practical method for incorporating scatter in a projector-backprojector for accurate scatter compensation in SPECT

    IEEE Trans Nucl Sci

    (1993)
  • C.E. Floyd et al.

    Inverse monte-carlo—a unified reconstruction algorithm for SPECT

    IEEE Trans Nucl Sci

    (1985)
  • F.J. Beekman et al.

    Efficient fully 3-D iterative SPECT reconstruction with Monte Carlo-based scatter compensation

    IEEE Trans Med Imaging

    (2002)
  • B.M.W. Tsui et al.

    Implementation of simultaneous attenuation and detector response correction in SPECT

    IEEE Trans Nucl Sci NS

    (1988)
  • C.E. Metz et al.

    The geometric transfer function component for scintillation camera collimators with straight parallel holes

    Phys Med Biol

    (1980)
  • L. Geworski et al.

    Recovery correction for quantitation in emission tomography: a feasibility study

    Eur J Nucl Med

    (2000)
  • R.M. Kessler et al.

    Analysis of emission tomographic scan data: Limitations imposed by resolution and background

    J Comput Assist Tomogr

    (1984)
  • Y.K. Dewaraja et al.

    Monte Carlo evaluation of object shape effects in iodine-131 SPET tumor activity quantification

    Eur J Nucl Med

    (2001)
  • Y. Du et al.

    Partial volume effect compensation for quantitative brain SPECT imaging

    IEEE Trans Med Imaging

    (2005)
  • O.G. Rousset et al.

    Correction for partial volume effects in PET: Principle and validation

    J Nucl Med

    (1998)
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