Truly Three-Dimensional Reconstruction

If we wish to reconstruct a three-dimensional body by the methods discussed in the previous chapters, the only option available to us is to reconstruct the body cross section by cross section and then stack the cross sections to form the three-dimensional density distribution. This may cause a number of problems, the most important of which are associated with time requirements. During the time needed to collect all the data, the patient may move, causing a misalignment between the cross sections. More basically, in moving organs such as the lungs (and even more so, the heart), changes in the organ over time are unavoidable, and it is desirable (but often not possible) to collect data for all cross sections simultaneously.