Single-Photon Emission Computed Tomography/Computed Tomography: Basic Instrumentation and Innovations
Section snippets
Software Approach to Image Fusion
Image fusion usually is performed between an anatomical imaging technique such as CT or MRI and a functional imaging technique such as positron emission tomography (PET) or SPECT. Before the introduction of dedicated PET/CT or SPECT/CT systems, considerable work had been done on the development of software algorithms for the coregistration of anatomical and functional images. It is worth briefly reviewing what has been accomplished with these techniques, particularly as we go forward and look
Development of SPECT/CT Devices
Much of the early work on the development of a combined SPECT/CT unit was performed at University of California, San Francisco, by Dr Hasegawa and colleagues. Their initial work was focused on the development of a system that could perform simultaneous CT and SPECT studies. Figure 2 shows a schematic diagram of their first system, which used an array of high-purity germanium detectors to simultaneously detect 40 to 100 keV x-rays from an external source and 140 keV gamma rays from an internally
Technical Aspects of SPECT/CT Imaging
The advantages of combining SPECT with CT are numerous and are primarily due to the anatomic referencing and the attenuation correction capabilities of CT. Whether the CT component that is used in the combined imaging approach should be a conventional MDCT scanner or the more compact, low current CT add-on used on the GE Hawkeye system is currently a matter of debate.
Sources of Error
There are several sources of error in the application of SPECT/CT, depending on the system configuration. These errors include misregistration, truncation, scatter, and beam hardening artifacts. A major issue for CT type systems is misregistration between the emission and transmission data, resulting in incorrect matching of the attenuation map to the emission data.48 This may occur for a number of reasons, including sagging of the emission table, respiratory and cardiac motion, and patient
Anatomic Referencing
Coregistration of anatomy and function is less dependent on the fidelity of the CT image than the attenuation correction algorithm. However, the accurate coregistration of the SPECT and CT data are just as important as with attenuation correction, and many of the pitfalls discussed previously, vis-à-vis table sagging, patient motion, and respiratory and cardiac motion, all apply equally to image fusion. Most vendors now include a calibration procedure to insure that, in the absence of
Planning/Siting Requirements for SPECT/CT
The space required for a SPECT/CT system depends on the type of system being installed. The GE Hawkeye or GE Hawkeye-4 only requires the same room size as conventional SPECT systems. Minimum room size for these types of units is typically 14′ × 16′. Because of the x-ray tube on these systems, some lead shielding of the room is required. The exposure rate from these systems is approximately 20 times less than that from a conventional MDCT scanner. Hence lead shielding in the walls is usually
Future Applications and Advances for SPECT/CT Technology
In addition to attenuation correction and co-registration, other possible applications for this emerging technology include patient dosimetry and radiotherapy. The development of more-sophisticated co-registration applications should permit estimation of organ or tumor volume from the anatomical data rather than the emission data. Traditional calculations of organ and tumor size from emission data are problematic, particularly for small tumors in which the limited spatial resolution of SPECT
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2020, OptikCitation Excerpt :This method is based on obtaining a cross-sectional image by acquiring projection images in various directions by rotating a gamma camera around the human body and subsequently implementing a mathematical reconstruction procedure. This is possible because physiological functional images can be acquired by injecting a radioisotope into the human body [1–5]. In particular, the SPECT scan of the brain provides a lot of information about the brain vessels and flow by imaging the distribution of a radioisotope, such as 99mTc-hexa methylene propylene amine oxime (HMPAO), by the γ-rays emitted.
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