Functional Brain Imaging Modalities

Each imaging modality is characterized primarily as being able to render high-resolution images with good contrast resolution (anatomic imaging) or to render images that depict tissue function (functional imaging).

Anatomic (Structural) Imaging

Imaging the structure of the body has been and continues to be the major application of medical imaging, although, as described in 9.2.2, functional imaging is a very active area of research. The goal of anatomic imaging is to accurately depict the structure of the body—the size and shape of organs—and to visualize abnormalities clearly. Since the goal in anatomic imaging is to depict and understand the structure of anatomic entities accurately, high spatial resolution is an important requirement of

In recent years this ability to image function has greatly accelerated. For example, ultrasound and angiography are widely used to show the functioning of the heart by depicting wall motion, and ultrasound Doppler can image both normal and disturbed blood flow (Mehta et al. 2000). Molecular imaging (9.2.3) is increasingly able to depict the expression of particular genes superimposed on structural images, and thus can also be seen as a form of functional

In both cases it is taken as axiomatic that the functional data must be mapped to the individual subject’s anatomy, where the anatomy is extracted from structural images using techniques described in the previous sections. Once mapped to anatomy, the functional data can be integrated with other functional data from other subjects whose anatomy has been related to a template or probabilistic atlas. Techniques for generating, mapping and integrating functional data are part of the field of Functional Brain Mapping, which has become very active in the past few years, with several conferences (Organizations for Human Brain Mapping 2001) and journals (Fox 2001) devoted to the subject.

The imaging modalities described above are complex devices with many parameters that need to be specified in generating the image, and most of the parameters can have substantial impact on the following key characteristics of the final image appearance; spatial resolution, contrast resolution, and temporal resolution, all of which have substantial impact on image quality and diagnostic value of the image. These characteristics provide an objective means for comparing images formed by digital imaging