Physics and Technology of SPECT/CT
The introduction of combined SPECT (single-photon emission computed tomography) and X-ray CT (computed tomography) scanners has changed the practice of single-photon imaging in nuclear medicine forever. The original motivators to produce a combined SPECT/
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Physics and Technology of SPECT/CT Dale L. Bailey and Kathy P. Willowson
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SPECT/CT: Combining Form with Function
The introduction of combined SPECT (single photon emission computed tomography) and X-ray CT (computed tomography) scanners has changed the practice of single-photon imaging in nuclear medicine forever. The original motivators to produce a combined SPECT/CT system were to provide improved anatomical localisation of the distribution of the SPECT radiopharmaceutical and to improve the capability of the SPECT scanner to produce images that can be corrected for the photon scattering and attenuation that causes degradation of the image. The functional information contained in the SPECT images is complemented by the anatomical information (the ‘form’) provided by the CT scanner in numerous ways, including: • Anatomical localisation of the SPECT radiopharmaceutical distribution • Correction for photon attenuation • Correcting for scattered radiation • Ability to determine the impact of the partial volume effect (PVE) due to the limited spatial resolution of the SPECT camera • The ability to calibrate the SPECT images in absolute units of radioactivity (kBq. ml−1) • Introducing new clinical applications based on quantitative imaging in SPECT that require absolute radioactivity measures
D.L. Bailey, PhD (*) Faculty of Health Sciences, University of Sydney, Sydney, Australia Department of Nuclear Medicine, Royal North Shore Hospital, St. Leonards, Nsw. 2046, Australia e-mail: [email protected] K.P. Willowson Institute of Medical Physics, University of Sydney, Camperdon, Nsw. 2006, Australia H. Ahmadzadehfar, H.-J. Biersack (eds.), Clinical Applications of SPECT-CT, DOI 10.1007/978-3-642-35283-6_1, © Springer-Verlag Berlin Heidelberg 2014
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D.L. Bailey and K.P. Willowson
• The ability to convert the quantitative SPECT images into standardised uptake values (SUV). This chapter will concentrate on the physics and technology relevant to combined SPECT and X-ray CT imaging.
1.2
The Development of Multimodality SPECT/CT Imaging
The first multimodal imaging performed with SPECT was developed to provide more accurate attenuation correction methods. In the 1980s, a number of groups were actively producing crude CT-like measurements on the gamma camera using radionuclide transmission sources such as gadolinium-153 (Gd-153) [1–4]. The radionuclide sources were used to produce external photon beams with which the patient could be irradiated to produce a transmission image. The advantage of these measurements is that they could be performed on the gamma camera thus obviating the need for a separate second detector. When a transmission radionuclide of different photon energy to the emission radionuclide’s γ-ray energy was used, the emission and transmission measurements could be made simultaneously [3]. An example is shown in Fig. 1.1. For further discussion about these systems, the reader is referred to the review article by Bailey [6]. This technology found extensive use in SPECT myocardial perf
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