Biomedical Engineering Reference
In-Depth Information
concluded favorably about the integration of PET and MRI scanners; regarding PET
detector, working inside a magnetic field is not detrimental for its performance. The
MRI scanner can also be used as a standalone system for diagnostic MR procedures.
After the explanation of the main challenges that each approach offers and how they
were addressed, some key characteristics of both devices are shown in Fig.
3.7
:
3.4.2 Most Common Clinical Applications of Hybrid Imaging
(PET/CT and PET/MRI).
In the early applications of multimodal imaging in clinical practice, hybrid images
were generated by software registration of data obtained separately from different
modalities and were mostly used for the brain (its rigid character and its lack of
movement made the software registration between images easier and more repro-
ducible). Thus, earlier clinical experiences in multimodal imaging were obtained in
the field of neuroscience, being focused on the study of brain disorders and diseases
like Alzheimer or Parkinson [
73
]. With the rapid development of integrated PET/CT
and the emergence of new radiolabeled tracers for specific diseases, hybrid imaging
has gained wider adoption in a variety of clinical applications in neurodegenera-
tive diseases, in oncology and in cardiovascular diseases. Parallel to the evolution
of PET/CT technology, MRI techniques also made significant progress not only in
terms of performance, with better resolution and faster acquisition protocols, but also
in the development of new imaging algorithms, allowing for a better identification of
different body tissues and the extraction of functional parameters. The complemen-
tarity of MRI characteristics extending the diagnostic capability of PET/CT has led
to the development of combined clinical protocols for patient management where
both type of studies are often required for a given clinical situation. In fact, it is very
common that in complex situations, such as extended cancer or complex neurological
diseases, the patient needs both MRI and PET/CT studies to assert a given diagnosis.
The clear added value of better soft tissue contrast that MRI offers over CT makes
hybrid PET/MRI systems potentially more attractive than PET/CT for certain condi-
tions such as brain tumors, head and neck tumors, breast cancer and prostate cancers
[
74
,
75
]. The advantage of PET/CT remains in its ability to provide whole body scans
with much higher spatial resolution than MRI in a very short acquisition time. Today,
CT images from PET/CT scanners can be acquired in a few seconds and provide an
extended coverage of the whole body with extremely high resolution 3D data, that
can be explored in different planes and reconstructed in different ways for better
visualization and identification of local anomalies and abnormal focal tracer uptake.
Recent technological advances and software algorithms have allowed for a signifi-
cant reduction of the radiation dose from CT scans to several orders of magnitude
lower than the doses delivered by earlier scanners. While PET/MRI may not replace
PET/CT in most clinical applications, it still opens a new perspective of a single
hybrid imaging technique that can find its place in many protocols of patient workup
