Biomedical Engineering Reference
In-Depth Information
TABLE 7.2
Approach to Image Interpretation
1)
Review source images
Define any signal intensity changes and shifts.
2)
Review difference images
Define significant abnormalities (i.e., non artifactual areas of increased or decreased signal
intensity). These should fit into one or more of the four categories described in Table 7.1,
i.e., nonspecific change in signal intensity, monophasic curvilinear change, multiphasic
curvilinear change, or interplateau change.
3)
Assess interplateau shifts
For interplateau changes determine the shift direction (inplane or throughplane) by direct
reference to the source images including different slices. The shift size is equal to the
width of the full scale region on the difference image plus a fraction of the width of the
associated border zone region (see later).
4)
Assess signal intensity gradients
In the regions of other changes on the difference images, use the source images to define
the inplane contours and signal intensity gradients (which are perpendicular to the
contours), noting the direction of decreasing signal. Define the throughplane signal in-
tensity gradients in the slice of interest (these tend to be reciprocally related to the inplane
gradients). Define the throughplane signal intensity gradients between slices by compar-
ison of adjacent source images in the relevant areas.
5)
Assess border zone shifts
Determine shifts in the border zones by noting
(a) signal on the difference image is produced by a shift with a component parallel to
the maximum signal intensity gradient;
(b) the difference image signal is positive when the shift is in the direction of decreasing
gradient and vice versa;
(c) the size of the shift in the direction of the maximum gradient is equal to the width of
the change on the difference image multiplied by the average fraction of the full scale
signal intensity;
(d) local changes in signal intensity may exaggerate or minimize the signal difference
produced by a shift;
(e) profiles from source and difference may help resolve shift direction and size; and
(f) reformatting the images into a perpendicular plane may transform a nonspecific
change in signal intensity due to a throughplane shift to the curvilinear change of an
inplane shift.
6)
Assess overall pattern of shifts
Review the overall pattern of shifts for changes in brain site, shape, or size on a focal or
general basis.
7)
Assess pure changes in signal intensity
Note that with a pure change in signal intensity no shift is detectable. (A pure change
in signal intensity may, however, be accompanied by an inseparable change in lesion size).
7.8
Clinical Applications—General
There are many potential uses for this technique and the applications described
merely constitute a starting point that reflects local interest. The monitoring of
physiological changes of the brain was necessary to establish a baseline for rec-
ognition of changes in disease. The importance of radiographic positioning and
