Multimodality imaging (or hybrid imaging, as it is sometimes called) is witnessing an extraordinary surge in diagnostic and therapeutic radiology for diagnosing, staging, and monitoring treatment response in complex diseases such as atherosclerosis and cancer. This trend has been made possible by the recent evolutionary developments in medical imaging instrumentation technology that allows for the identification of anatomical structures or functional processes in vivo. An elegant comprehensive review that follows the historical developments of multimodality imaging instrumentation for clinical use and its future potential has been recently published by Townsend in the first proposal to design and build a combined scanner.
In modern conformal, intensity-modulated image-guided radiotherapy (IGRT) particularly, there is noticeable value in using hybrid multimodality imaging in treatment planning, diagnosis, and staging of different cancer sites. The goal is to achieve improved target definition by incorporating information from different imaging modalities [computed tomography (CT), magnetic resonance (MR), and 3D ultrasound] as well as improved staging, disease characterization, and localization using functional and molecular imaging [positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance spectroscopy (MRS)]. In addition, onboard imaging systems [cone-beam CT (CBCT) and mega-voltage CT (MVCT)] are currently deployed in many clinics to correct patient setup and improve daily delivery of fractionated radiation treatments. Although these advanced imaging modalities have created new opportunities in radiotherapy treatment planning and delivery, they have also presented many technical challenges regarding the integration of different-modalities information, which affects visualization, delineation, and related areas.
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