Hybrid cardiac imaging: More than the sum of its parts?

The constant technological developments in noninvasive cardiac imaging over the past few decades have contributed toward our pathophysiologic understanding of many conditions. Particularly in coronary artery disease (CAD), management is based on the assessment of both the presence of coronary stenoses and their hemodynamic consequences. Hence, noninvasive imaging helps guide therapeutic decisions by providing complementary information on coronary morphology and on myocardial perfusion and metabolism, using several imaging tools. This imaging includes nuclear techniques such as single-photon emission computed tomography (SPECT) or positron emission tomography (PET), computed tomography (CT) techniques such as electron-beam CT (EBCT) or multislice CT (MSCT), and cardiac magnetic resonance (CMR). Advances in image-processing software and the advent of hybrid scanners have paved the way for the fusion of image datasets from different modalities, giving rise to multimodality or hybrid imaging. This technology avoids the mental integration of functional and morphologic images, and facilitates a comprehensive interpretation of combined datasets. The interest in hybrid imaging has rapidly spread to cardiac applications, and has changed the landscape of noninvasive cardiac imaging by bringing different clinical specialties (eg, cardiology, radiology, and nuclear medicine) closer together. In addition, this interest has driven the development and production of dedicated hybrid scanners in an effort to simplify image coregistration and improve patient throughput for specialized cardiac imaging centers (ie, hardware-based image coregistration). However, given the high costs associated with such devices, an attractive alternative for hybrid imaging consists of the “offline,” software-based fusion of images obtained from nondedicated standalone scanners (software-based image coregistration). Here, we focus on comparing hardwarebased versus software-based image coregistration for cardiac hybrid imaging and their respective advantages and drawbacks.