New technical developments in nuclear cardiology and hybrid imaging

Cardiac hybrid imaging offers the ability to combine strengths of different imaging modalities in providing information on cardiac physiology along with cardiac and coronary anatomy. Hybrid images contain two data sets combined into a fused image in which both data sets contribute important information. Hybrid coronary computed tomography angiography and nuclear or magnetic resonance myocardial perfusion imaging has been shown to accurately detect coronary artery disease. Emerging clinical applications of cardiac hybrid imaging include evaluation of myocardial viability, cardiac or vascular inflammation, infection, and cardiac infiltration. Cardiac dedicated single photon emission computed tomography scanners, novel software methods for low count image reconstruction, and quantification of myocardial blood flow by positron emission tomography (PET) have potential to lower radiation dose associated with cardiac imaging while maintaining high diagnostic accuracy for the detection of coronary artery disease.

Hybrid Cardiac Imaging

Assessment of both coronary anatomy and myocardial perfusion are equally important for the appropriate treatment of patients with stable coronary artery disease. Cardiac hybrid imaging allows integration of coronary anatomy and perfusion in one all-in-one image, thereby avoiding mental integration of findings. In selected subgroups of patients, cardiac hybrid imaging has demonstrated superior diagnostic accuracy compared to single modalities. The combination of coronary anatomy and function provides incremental prognostic information and improves risk stratification of patients with suspected or known CAD. Aside from CT coronary angiography, coronary artery calcium score (CACS) scans obtained from native ECG-triggered CT are used for hybrid imaging. They are used either for attenuation correction, or can be combined with radionuclide information to improve CAD detection and risk stratification. A large number of integrated hybrid scanners are commercially available and offer advantages for cardiac hybrid imaging. However, these devices are not mandatory, and hybrid imaging is perfectly feasible from two separate datasets using appropriate image fusion software. Cardiac magnetic resonance has entered the arena of hybrid imaging and several integrated PET/MRI devices are already commercially available. Its advantages include the lack of ionizing radiation and a high spatial resolution, particularly for soft tissue structures. In research, hybrid imaging moves beyond its conventional borders of perfusion imaging to target specific molecular or biological pathways that underlie cardiac disease, a concept known as molecular imaging. The combination of radionuclide imaging with CT or MRI offers attractive features to co-localize biological signals from radiolabeled targeted compounds with microanatomical structures.