PT - JOURNAL ARTICLE AU - Martijn Dietze AU - Britt Kunnen AU - Sandra van der Velden AU - Leo Steenbergen AU - Wilco Koppert AU - Max Viergever AU - Hugo de Jong TI - Performance of a Dual-Layer Scanner for Hybrid SPECT/CBCT DP - 2019 May 01 TA - Journal of Nuclear Medicine PG - 188--188 VI - 60 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/60/supplement_1/188.short 4100 - http://jnm.snmjournals.org/content/60/supplement_1/188.full SO - J Nucl Med2019 May 01; 60 AB - 188Purpose: Fluoroscopy guided interventional procedures involving radionuclides, such as hepatic radioembolization, would benefit from having information on both the nuclear distribution and the surrounding anatomy, since injection could be directly altered if activity is observed at an unexpected location. We have previously shown that a dual-layer detector is capable of acquiring nuclear and fluoroscopic projections simultaneously (1) and thus could be used for such radioembolization guidance. The prototype dual-layer scanner has, however, up to now only been tested using planar imaging. More complete information on the activity distribution could be obtained if a SPECT scan were performed. This study compares the obtained reconstruction quality of our prototype dual-layer scanner with that of a regular clinical SPECT/CT scanner. Methods: The proposed dual-layer scanner (see the accompanying figure) consists of a flat panel positioned in front of a gamma camera equipped with a cone beam collimator. As the x-ray tube is located in the focal spot of the collimator, x-rays and gamma photons capture the same field of view. By performing interleaved measurements, spatially overlapping fluoroscopic and nuclear projections can be acquired simultaneously. The use of a C-arm gantry results in a compact scanner that would enable seamless integration in the intervention room. An image quality phantom (spheres of the NEMA IQ phantom enclosed in a small cylinder) and an anthropomorphic phantom were scanned for 10 minutes on both the dual-layer prototype scanner and a clinical SPECT/CT scanner (Siemens Symbia T16). Whilst the prototype scanner had the dual-layer configuration, it was not yet mounted on a C-arm. The SPECT was hence made by positioning the phantom on a rotating stage. Fluoroscopic projections were sampled at 3.75 Hz during rotation, whilst nuclear counts were acquired continuously in list-mode. The fluoroscopic projections were then reconstructed into a CBCT volume, which was scaled to be used as attenuation map in the SPECT reconstruction. For the clinical scanner, the regular low-dose CT was used for attenuation correction. SPECT reconstructions were visually assessed and compared on contrast-to-noise ratio (CNR). Results: The obtained SPECT/CBCT (from the dual-layer scanner) and SPECT/CT (from the clinical scanner) of the image quality phantom can be found in the accompanying figure. Apart from the patient bed that was not present, the CBCT reconstruction compared well with the CT image. The CNR of the largest sphere in the image quality phantom of the SPECT reconstruction was 35.5 for the clinical scanner and 21.5 for the dual-layer prototype scanner. This quality deterioration was due to the change from two to one detector heads, reduced gamma sensitivity by flat panel attenuation, and increased distance of the gamma camera to the phantom. The anthropomorphic phantom (not shown) demonstrated that extrahepatic depositions can be clearly distinguished with both scanners. Conclusions: A dual-layer scanner, previously shown capable of simultaneous nuclear and fluoroscopic planar imaging, is able to acquire simultaneous SPECT/CBCT. Although reconstruction quality of the dual-layer scanner was lower in comparison with the clinical scanner, clinically relevant measures can still be extracted. The ability to perform SPECT/CBCT in the intervention room could enable more precise radionuclide injection. References: 1. Van der Velden S, Kunnen B, Koppert WJC, et al. A Dual Layer Detector for Simultaneous Fluoroscopic and Nuclear Imaging. Radiology. 2019.