Respiratory and cardiac motion correction with 4D PET imaging: shooting at moving targets

Patient motion, almost inevitable during the acquisition of medical images and radiation therapy, naturally generates artifacts and uncertainties as to the nature, delineation, and location of lesions and, hence, as to the most appropriate course of treatment. As remarked by Li et al., of the Radiation Oncology Branch, National Cancer Institute, NIH, Bethesda, MD, USA, four-dimensional (4D) medical imaging and 4D radiation therapy aim to neutralize this source of error. 4D medical imaging includes time-resolved volumetric CT, MRI, PET, PET/CT, SPECT, and US imaging [1]. To enhance the performance of these techniques, a parallel multi-detector array has been used to acquire image projections and volumetric image reconstruction has been advanced from the 2D to the 3D tomography paradigm.