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Capítulo Dieciséis
Estudios Dinámicos

16-01 Introduccíon

he combination of MR imaging with extrinsic contrast changing agents led many researchers to try to highlight anatomical and pathological struc­tu­res and even metabolic processes which, per se, are invisible on single plain ima­­ges [⇒ Rinck 1999].

Illusion image

Image series of the same anatomical struc­ture du­ring a time pe­ri­od before and after the application of a contrast agent add an­other dimension, commonly described as per­fu­sion imaging. Per­fu­sion de­scri­bes blood delivery to tissues, usually flow on the ca­pil­la­ry level.

Perfusion imaging can be categorized into two classes: those methods mo­ni­tor­ing tar­get tis­sue sig­nal changes after the application of an ex­trin­sic con­trast agent, and those relying upon intrinsic factors such as increased blood volume or blood oxy­ge­na­tion and flow in the mi­cro-vas­cu­la­ture. The former can be vi­sua­li­zed by dy­na­mic imag­ing, the latter by functional imag­ing.

However, the individual ima­ges of a dy­na­mic se­ries will not always yield all in­­for­­ma­­tion con­­tain­­ed in them. Thus, ad­di­ti­o­nal pro­ces­sing has been sug­gest­ed (Figure 16-01).

spaceholder redThis chapter gives an overview of some of the techniques. It cannot be ex­haus­ti­ve con­si­der­ing the wide spectrum of the field. For detailed scientific treatises see Maintz and Torheim [⇒ Maintz 1998, ⇒ Torheim 1999].

Traditionally, the following methods have been applied to analyze dynamic contrast-en­hanc­ed images:

spaceholder darkbluevisual inspection of the time-intensity curves;

spaceholder darkbluevisual inspection of the time series by running the images in a movie;

spaceholder darkbluesuperposition / subtraction images.

Yet, the most intriguing and interesting way of processing the data is by the crea­tion and subsequent visualization of parametric maps: images combining parametric ima­ges derived from the information present in the image series with anatomical in­for­ma­tion (Table 16-01).

To be clinically useful, such a postprocessing method must be robust, reliable as well as automatic or semi-automatic.

Tabla 16-01:
Steps of the entire dynamic acquisition and image-processing procedure. The noise-filtering and mo­tion-correction steps are optional, but in many in­stances necessary and fairly complicated.