Biomedical Engineering Reference
In-Depth Information
FIGURE 7.22
Multiple Sclerosis: A 31-year-old female with MS: initial unenhanced (a), enhanced (b), and
registered subtraction (c) images. A repeat pre- and postenhancement scan was performed
six months later. The difference image on the unenhanced scans six months apart is shown
in (d), and the difference between the earlier ''post minus pre'' scans and the later “post minus
pre” scans is shown in (e). The enhancing lesions are see better in (c) (arrows). The ventricular
system has increased in size in (d), and there is evidence of decreased brain size. Some
lesions appear bright because they have shortened their T1 time (d). Lesions that were
enhancing in (b) now appear dark on (e); they no longer enhance (arrows).
spite of treatment. Differences in contrast enhancement were also demon-
strated by comparison of the subtracted (post-minus precontrast) images on
each examination.
In tumor regression following treatment, T1 may be decreased. This pro-
duces an increased signal on the difference image. Decreased mass effect can
also be demonstrated (Figure 7.24).
Registration may allow earlier recognition of tumor growth and response
to therapy than conventional techniques. A cohort of inoperable and par-
tially resected meningiomas has been studied to assess their rate of growth
(Figure 7.25).
T2-weighted images may also be used for registration.
11
Figure 7.26 shows
a mixed pattern of response to progression.
