Biomedical Engineering Reference
In-Depth Information
Fig. 3.4
Illustration of the application of hybrid PET/CT and PET/MRI on the same patient (cerebral
tumor). The combination of two imaging modalities acquired on the same hybrid device, instead
of separate studies acquired at different points in time, is illustrated here. A better identification of
tumor morphology can be observed in MRI images due to its better performance in differentiating
soft tissues and in better delineating brain anatomy. This makes the combination of PET and MRI
images more suitable than the combination of PET and CT images in this particular case
the possibility to replace CT by MRI was explored and discussed [
67
] with the
vision of exploiting the advantages that MRI offers over CT. These advantages are
a better soft tissue differentiation and an extended potential for tissue characteriza-
tion through different imaging techniques, as well as the lack of radiation exposure.
Whereas PET/CT devices have been available for over a decade, it is only recent
that the first hybrid PET/MRI scanners have become available on the market. Since
the appearance of these new hybrid scanners, the question whether PET/MRI will
replace PET/CT in the future arose, which still has not a clear answer. Since they
are based on different principles and technologies, each of them exploits different
advantages and specific values depending on the clinical application where they are
used.
In this section, some state-of-the-art devices and their clinical applications will be
summarized, without reflecting any particular ranking or judgment of performance.
SPECT/CT scanners.
The first SPECT/CT device (1996) [
68
] was composed of
a clinical SPECT gamma camera and a single slice CT scanner. In this design, the
patient was firstly imaged with the CT and then with the SPECT after injection of
the radiotracer. The data obtained from the CT scan were used for SPECT data atten-
uation correction, but the low resolution of this first device did not provide adequate
CT images for diagnostic purposes. During the last two decades, the SPECT/CT
