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Degradation of myocardial perfusion SPECT images caused by contaminants in thallous (201Tl) chloride

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European Journal of Nuclear Medicine and Molecular Imaging Aims and scope Submit manuscript

Abstract

Purpose

Thallous (201Tl) chloride is a single-photon emission computed tomography (SPECT) tracer mainly used for assessing perfusion and viability of myocardial tissue. 201Tl emits X-rays around 72 keV and gammas at 167 keV, and has a half-life of 73 h. Regulations allow an intrinsic contamination up to 3-5%, which is mainly caused by 200Tl (368 keV; 26 h) and by 202Tl (439 keV; 12.2 days). Contra-intuitive to the low-level percentages in which these contaminants are present, their impact may be significant because of much higher gamma camera sensitivity for these high-energy photon emissions. Therefore, we investigate the effects of the contaminants in terms of detected fractions of photons in projections and contrast degradation in reconstructed images.

Methods

Acquisitions of a digital thorax phantom filled with thallous (201Tl) chloride were simulated with a validated Monte Carlo tool, thereby, modelling 1% of contamination by 200Tl and 202Tl each. In addition, measurements of a thorax phantom on a dual-headed gamma camera were performed. The product used was contaminated by 0.17% of 200Tl and 0.24% of 202Tl at activity reference time (ART). This ART is specified by the manufacturer, thereby, accounting for the difference in half-lives of 201Tl and its contaminants. These measurements were repeated at different dates associated with various contamination levels.

Results

Simulations showed that, with 1% of 200Tl and 202Tl, the total contamination in the 72 keV window can rise up to one out of three detected photons. For the 167keV window, the contamination is even more pronounced: more than four out of five detections in this photopeak window originate from contaminants. Measurements indicate that cold lesion contrast in myocardial perfusion SPECT imaging is at maximum close to ART. In addition to a higher noise level, relative contrast decreases 15% 2 days early to ART, which is explained by an increase in 200Tl contamination. After ART, contrast decreased by 16% when the 202Tl contamination increased to the maximal allowed limit.

Conclusions

Contra-intuitive to the low-level percentages in which they are typically present, penetration and downscatter of high-energy photons from 200Tl and 202Tl significantly contribute to thallous (201Tl) chloride images, thereby, reducing contrast and adding noise. These findings may prompt for improved production methods, for updated policies with regard to timing of usage, and they also render the usefulness of adding the high photopeak window (167 keV) questionable. A window-based correction method for this contamination is advisable.

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Acknowledgment

The authors thank Geert Ensing and Mark Konijnenberg (Tyco Healthcare/Mallinckrodt) Leonie Rijks (GE Healthcare) and Pascal Bartkowiak (Schering) for providing details on their production of thallous (201Tl) chloride. The work of S.S. is supported by the Fund for Scientific Research, Flanders (FWO). The work of T.D.W. is supported by the Dutch Science and Technology Foundation (STW) by grant UGT.6069. The work of I.L. is supported by Ghent University, and the work of F.B. is supported by the Medical Counsel of the Dutch Organization for Scientific Research by grant 917.36.335. The contents are solely the responsibility of the authors and do not necessarily represent the official view of the sponsoring agencies.

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Authors and Affiliations

  1. Department of Nuclear Medicine, Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands

    Steven G. Staelens, Tim C. de Wit & Freek J. Beekman

  2. Department of Pharmacology and Anatomy, Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, The Netherlands

    Steven G. Staelens, Tim C. de Wit & Freek J. Beekman

  3. Department of Applied Sciences, Delft University of Technology, Delft, The Netherlands

    Freek J. Beekman

  4. Department of Medical Imaging and Signal Processing, Ghent University-IBBT, Ghent, Belgium

    Steven G. Staelens & Ignace A. Lemahieu

  5. Ghent University-IBBT, IBITECH-MEDISIP, De Pintelaan 185, Block B-502a, B-9000, Ghent, Flanders, Belgium

    Steven G. Staelens

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  1. Steven G. Staelens
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  2. Tim C. de Wit
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Correspondence to Steven G. Staelens.

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Staelens, S.G., de Wit, T.C., Lemahieu, I.A. et al. Degradation of myocardial perfusion SPECT images caused by contaminants in thallous (201Tl) chloride. Eur J Nucl Med Mol Imaging 35, 922–932 (2008). https://doi.org/10.1007/s00259-008-0719-z

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  • DOI: https://doi.org/10.1007/s00259-008-0719-z

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