Cardiac GSI Feasibility Study

The recently introduced Computed tomography (CT) scanner, Discovery CT750 HD (GE Healthcare, Milwaukee), incorporates a battery of innovations aimed at improving diagnostic image quality, evaluating perfusion and assessing for scar, in an effort to address the current shortcomings of Computed tomographic coronary angiography (CTCA) in patients with significant coronary artery disease. The new scanner will use a novel method of scanning (Cardiac Gemstone Spectral Imaging - Cardiac GSI) and image reconstruction (Adaptive Statistical Iterative Reconstruction- ASIR) as opposed to standard definition 64-slice CT Multi-detector row computed tomography(MDCT)and Filtered Back Projection (FBP) used by the conventional CT scanners. The Cardiac GSI protocol enables the scanner to acquire images at two different x-ray energies almost simultaneously, which can be post-processed to selectively reduce beam hardening artefacts and delete materials with specific attenuating properties from the images, such as coronary calcium. ASIR offsets the potential increase in radiation dose required for Cardiac GSI scanning. This will potentially result in images of higher diagnostic quality with an equivalent or perhaps lower dose of radiation compared to present technology. Furthermore, it is hypothesised that dual-energy acquisition may improve the accuracy of the assessment of perfusion. Although initial in-vitro results are encouraging, this technology has not been rigorously assessed with regards to its feasibility and diagnostic quality, limiting its applicability in routine clinical practice. This assessment will require a trial comparing the accuracy of Cardiac GSI CTCA with that of Invasive coronary angiography (ICA) for anatomical assessment of stenosis, Myocardial Perfusion Imaging with Single Photon Emission Computed Tomography (MPI-SPECT) for assessment of perfusion and Cardiac Magnetic Resonance (CMR) for assessment of myocardial scar. We have designed a pilot study in this regard which will help us assess the feasibility of the scan protocol and provide data to power a larger study to assess the diagnostic remit of Cardiac GSI scanning in the assessment of patients with high-risk of significant coronary artery disease and myocardial scar.