The main purpose of this chapter is to give an overview of the current status of the science of 3D imaging, to identify the major challenges currently faced, and to point out the opportunities available for advancing the science. It describes schematically and systematically the main 3D imaging operations currently used and illustrates operations with medical examples. It delineates main concepts without detailing theory and algorithms and attempts to clarify some common misconceptions.
Its intended audience includes developers of 3D imaging methods and software, developers of 3D imaging applications, and clinicians interested in 3D imaging applications. The description assumes some familiarity with medical imaging modalities and a knowledge of the rudimentary concepts related to digital images.
The main purpose of 3D imaging is: given multiple multimodality images from digital radiography, computerized tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single positron emission computed tomography (SPECT), and ultrasound (US), to produce qualitative and quantitative information about an objectâobject system under study. The types of objects that are studied include rigid objects (e.g., bones), deformable objects (e.g., muscles), static objects (e.g., skull), dynamic objects (e.g., heart, joints), and conceptual entities (e.g., activity regions in PET, SPECT, functional MRI [fMRI], and isodose surfaces in radiation therapy).
Multiple dimensionalities are possible for current medical image acquisitions.
â¢ 2D: A digital radiograph, a tomographic CTâMRâPETâSPECTâUS slice.
â¢ 3D: A volume of tomographic slices of a static object.
â¢ 4D: A time sequence of 3D images of a dynamic object.
â¢ 5D: A 4D image of a dynamic object for a range of parameters (e.g., MR spectroscopic images of a dynamic object).
It is not feasible at present to acquire 4D images to truly capture dynamics. Hence, various approximations are made to capture âstop-actionâ or âgatedâ images. Five-dimensional images cannot be acquired in a routine fashion with adequate resolution, and hence are not practically feasible at present. Higher dimensional images can also be generated computationally, as we will indicate at appropriate points in the description of the various processing operations.
Among tomographic modalities, CT, MRI, and US provide structuralâanatomical information.