Intraoperative C-arm SPECT for hybrid operating room: A design study

Objectives: The cardiovascular hybrid operating room (HOR) is an emerging clinical facility where advanced medical imaging devices are integrated in a surgical suite offering the capability to perform combined image-guided procedures with minimally invasive surgery [1], such as transcatheter aortic valve replacement (TAVR), coronary artery bypass graft (CABG) and percutaneous coronary interventions (PCI) [2]. While C-arm and O-arm for 2D fluoroscopy/3D CT imaging are widely available and intraoperative MRI has been recently introduced [3], the development of intraoperative nuclear molecular imaging system such as SPECT and PET lags behind. Other groups have already presented a handheld gamma camera probe (freehandSPECT [4-5]) and a robotic single gamma camera detector [6-7] for intraoperative and radiation therapy applications. However, currently no full-size SPECT system is available to perform functional and molecular imaging in HORs. In this work, we will present the results from a design study of a C-arm SPECT system, a compact standalone SPECT system based on pixelated CZT detectors [8] and a synthetic compound-eye (SCE) gamma camera design [9] to deliver real-time, high-performance SPECT imaging capability for guiding cardiac interventions. We will discuss the results of simulation studies to estimate the system imaging performance such as spatial resolution, sensitivity, image texture and boundary distortions, considering the space and time constraints typical of a cardiovascular HOR environment.

Methods: The current SPECT-arm system design consists of six solid-state detector panels mounted on a C-arm (Fig.1A-B). Each panel consists of a high-performance array of 5×10 CZT detectors of 2×2×0.5 cm³ each (Fig.1C-D) for an overall active area of 1200 cm². Each CZT detector offers 80 × 80 square pixels of 250 μm × 250 μm pitch coupled with a specific pinhole aperture according the Synthetic Compound Eye (S-CE) Gamma Camera design [9]. The C-shaped SPECT detection system offers an angular coverage of 180° around the axis by a total of 300 independent camera elements focusing on a field-of-view (FOV) of 18 cm in diameter. This would provide a sufficient angular sampling for dynamic imaging and an excellent sensitivity to assure shorter scans necessary during surgical procedures. Moreover, the C-arm design offers additional degrees of freedom in placing the system around the surgical table such as orbit, tilt and wig-wag as well as up-down and in-out movements (Fig.1A). Finally, the system will receive the control signal from a pre-existing C-arm X-ray system, which would allow to adjust the trajectory of the SPECT C-arm during a CT image acquisition and to perform simultaneous SPECT/CT imaging (Fig.1B). Preliminary Results: In a preliminary simulation study, we used a NCAT phantom to model the human anatomy, placing the center of the 18-cm diameter FOV at the heart (Fig.1E). The distance between the center of the FOV to detector surface is 30 cm and the C-arm could be tilted for up to 45° to allow surgeons to access the surgical site. The preliminary results show that the proposed SCE gamma camera can achieve a geometrical peak sensitivity of ~0.02% (Fig.1F) while preserving a clinically relevant FOV of 18 cm and a spatial resolution between 4 and 6 mm.

Conclusions: To the best of our knowledge, the C-arm SPECT system would represent the first full-size SPECT system designed for SPECT/CT image-guided cardiac surgical intervention. It combines a state-of-art CZT detector technology with a novel synthetic compound eye (SCE) camera design to achieve a compact and maneuverable footprint while offering a substantially improved imaging performance over conventional SPECT imaging systems. The C-arm SPECT system is designed to be adaptive to the surgical procedure being carried out, and to the data acquisition protocol of a C-arm CT system for simultaneous SPECT/CT imaging, which would offer a unique addition to HORs for guiding surgical interventions.