Abstract
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Introduction: Peripheral artery disease (PAD) is a progressive circulatory disorder in which the blood flow to lower extremities is reduced due to narrowed peripheral arteries, resulting in life- and limb-threatening complications [1, 2]. PAD affects more than 200 million people worldwide and is one of the leading causes of disability among people over age 60 [3].
Multi-tracer SPECT imaging is a molecular imaging technique that shows great potential in offering novel insights into the underlying pathophysiology of PAD [1]. Considering the complex and multiple factors that contribute to the progression of PAD, the potential to assess quantitatively and simultaneously various molecular processes at the microvascular level would provide useful information in evaluating high-risk PAD patients, non-invasively monitoring their response to medical treatment, and potentially guiding therapeutic interventions.
Whereas several SPECT radiotracers are readily available in clinics for PAD applications [1], the success of multi-tracer SPECT imaging has been limited due to the relatively poor spectral resolution of current clinical SPECT instrumentation. We are developing the Dynamic Extremity SPECT (DE-SPECT) system, a stationary clinical SPECT system that offers an excellent spectral performance and sensitivity for broad-band multi-tracer imaging of the lower extremities.
Methods: The DE-SPECT system (Fig.1A) is a spectral SPECT imaging system based on two significant innovations: (1) 3D position-sensitive solid-state detectors (Fig.1C) [4], 1 cm in thickness, offering an intrinsic resolution < 0.75 mm along X-, Y-, and Z- directions and an excellent energy resolution over the 50-500 keV energy range; and (2) a tailored C-shaped system geometry equipped with interchangeable Synthetic Compound Eye (SCE) collimators [5, 6] (Fig.1B) mounted on a fast-switching mechanism for dynamic dual-field-of-view (FOV) imaging.
The detection system offers an overall active area of 838 cm2 and an angular coverage of ~303° around the gantry axis. Two sets of collimators allow the user to choose between a wide FOV (28-cm diameter) for dual-leg imaging, or a focused FOV (16-cm diameter) for high-resolution and high-sensitivity single-leg imaging, without disturbing the patient in the imaging state. The DE-SPECT system will be integrated with a pre-existing cardiac SPECT/(CT) scanner (Fig.1A), sharing the same patient bed, to perform simultaneous imaging of the lower extremities and the heart.
Results: The DE-SPECT in wide FOV configuration (peak sensitivity 0.04% at 140 keV, ~7 mm spatial resolution, Fig.1E) will acquire an initial scout image to obtain preliminary information of the radiotracers’ distributions in a broad-band energy range. The high-resolution and high-sensitivity configuration will then allow focusing on the region-of-interest and acquisition of detailed images with an improved sensitivity (peak sensitivity 0.07% at 140 keV) and a ~5 mm spatial resolution (Fig.1F). The preliminary data acquired with the CZT detectors (Fig.1D) confirm an excellent spectroscopic performance over a broad energy spectrum (<2 keV at 140 keV, 3 keV at 200 keV, 4.5 keV at 450 keV). The real-time dual-FOV SCE collimator design and the detectors’ excellent energy resolution warrant an unprecedented spectral imaging capability for simultaneous multi-tracer SPECT studies.
Conclusions: The DE-SPECT system is the first clinical spectral SPECT imaging system based on 3D position-sensitive 1-cm thick CZT detectors. Its excellent spectroscopic performance, imaging geometry, and relatively high sensitivity could potentially allow for a greatly improved spectral imaging capability in simultaneous multi-functional studies. The design phase has been completed and the DE-SPECT system is currently under construction.
Acknowledgements
We would like to acknowledge NIH/NHLBI as funding agency (R01 HL145786).
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