Biomedical Engineering Reference
In-Depth Information
FIGURE 11.5
CT scan of the same subject acquired on a conventional fast scanner with breath hold (left)
and low dose CT scan on newly developed multi-modality SPECT
PET CT device acquired
over 14 seconds (GE Medical Systems, Hawkeye, right). The images demonstrate the large
differences in the body shape between the different studies. Note that the subject's arms are
resting at the side in the Hawkeye image. As the image on the right will match the corre-
sponding emission scan far more closely, this image emphasises the intrinsic difficulties in
coregistering scans from different devices under the different conditions. (Images courtesy
of Professor Ora Israel, Rambam Medical Centre, Israel).
matched. Registration in this example requires not just translations and rota-
tions but also additional degrees of freedom to take account of tissue deforma-
tion. An example of a large deformation is seen in Figure 11.5. Methods for
nonrigid registration of images are described in Chapter 13, but this remains an
area of intense investigation, especially for intermodality registration.
There is growing interest in the development of multimodality devices com-
bining structural and functional measurements. These include human scan-
ners capable of PET or SPECT with x-ray CT,
14,15
small animal scanning
20
and a functional spectroscopic device combining
PET and nuclear magnetic resonance spectroscopy (NMRS) for studying acute
changes in an isolated rat heart model.
combining PET and MRI,
21
The appeal of these devices is that
they acquire the different data at the same time, or at least in the same scanning
session, and therefore minimize the problems of tissue deformation and any
other sources of variation. When using dynamic scanning, simultaneous acqui-
sition also provides temporal registration of the image sequences, which may
be extremely difficult to achieve retrospectively. The PET-CT
14
15
and SPECT-CT
scanners for human use provide structural data from the CT scan that can be
used for attenuation and scatter correction of the emission data, resolution
recovery operations (discussed in the next section), and, of course, correlative
imaging. It has also been suggested that they will have a future role in radio-
therapy treatment planning and interventional procedures such as CT-guided
biopsy. An example of a PET-CT scan performed with a prototype dual modailty
scanner at the University of Pittsburgh is shown in Color Figure 11.6*.
Another application of image registration is in quantitative evaluation of serial
scans. PET studies using [
18
18
F]-DG) are becoming
increasingly available as PET scanners and gamma cameras modified to
F]-labeled deoxyglucose ([
* Color Figures follow page 22.
