This invention relates generally to imaging systems and methods and more particularly to systems and methods for retrospective internal gating.
A large source of image degradation in medical imaging can be attributed to patient motion during the image acquisition, which causes loss of detail in the resultant images. For example respiratory motion causes blurring of the torso. This blurring can be difficult to characterize, and effectively can limit detectability of details, such as small lesions or lesions with low contrasts, and might reduce the accuracy of the measurements for the lesions which are visible.
Respiratory gating in is an approach to lessen the image degradation from respiratory motion by separating the breathing cycle into different phases and generating images from data corresponding to each of these phases. In the past few years there has been much research in developing this approach to imaging, with the hope that this can increase the quality diagnostic information derived from the images. The consensus in literature is that the respiratory gating of images presents a feasible solution to the image degradation introduced by respiratory motion. Researchers have studied the use of respiratory gated PET with respect to improving image quantification, lesion detectability and artifacts, image-coregistration accuracy, and the use of gated PET/CT in radiotherapy treatment planning. A variety of methods has been presented in the above literature for characterizing patient respiratory motion including techniques utilizing cameras, pressure belts, thermometers, point sources, pneumatic sensor systems, and mechanical ventilation (in dogs).
In addition to the above work, which used hardware derived respiratory signals, several software based methods have been proposed which utilize characterization of structural movement to gate the scans.
Acquiring and using software derived respiratory signals have several advantages over hardware based methods. The algorithms are image based, and thus machine independent, and can be used with existing scans, or scanners. What's more, if the algorithm is fully automated then the gated images can be generated without any extra effort or deviation from routine clinical procedures. They come at no additional “cost”, other than processing time, and can be generated along side traditional non-gated images.
Another advantage of using image based methods is that they provide assurance of the temporal alignment of the respiratory trace and the image data.