Biomedical Engineering Reference
In-Depth Information
studies based on the co-registration of MRI and PET images acquired sequentially
have anticipated the potential benefits of the use of such technologies in a single
device for cardiologic diagnosis [
94
,
95
]. These benefits include the possibility for
MRI-based attenuation and partial volume corrections for improved quantification
of myocardial blood flow as well as the possibility to combine anatomy and hemody-
namic information, to improve stratification of levels of heart failure and to exactly
localize anatomical structures [
94
]. Since PET/MR hybrid scanners recently became
available for clinical use, there is still limited bibliography available about their poten-
tial applications in cardiology. Currently, some preliminary clinical experiences [
96
]
are starting to be published and are reporting interesting results, confirming the huge
potential that this technology could have in the study of cardiac disease. On the other
hand, they observe that much work has still to be done in order to make this imaging
technique fully available for daily clinical studies.
Neurology.
The highest expectations for the use of multimodal PET/MRI systems
are in the neurological field, due to the ability of MRI to perform functional imaging
of the brain (functional MRI, fMRI) and to study brain connectivity using diffusion-
imaging technique, but also because of the wide range of PET applications in neu-
rodegenerative diseases [
14
,
29
,
36
,
97
-
101
]. The complementary use of separately
acquired MRI and PET images is a widely adopted approach for the assessment
of neurological diseases. The images obtained from the two separate studies are
then fused with registration software for more convenient analysis and visualization.
However, the diagnostic accuracy of such combined studies relies on the assumption
that no remarkable changes occur between the two acquisitions, which can be mis-
leading in some neurological diseases such as strokes or migraine, as well as rapidly
evolving brain lesions. The use of hybrid scanners, which allows for simultaneous
or even sequential acquisitions with both modalities in a single session, opens a new
perspective in the assessment of the human brain and neurological diseases. A better
understanding of this organ and of its activity is also one of the most encouraging
challenges of modern medicine, and hybrid imaging could be a useful tool for this
purpose. Stand-alone CT and MRI have been employed in the assessment of mor-
phological alteration of brain structures in degenerative diseases such as dementia
and Alzheimer. Recent developments in functional MRI techniques such as perfu-
sion, diffusion, tensor imaging or fMRI may be used for studying resting-state brain
activity [
102
,
103
]. The development of new radiolabeled tracers [
104
,
105
] specif-
ically conceived to study some biological alteration in brain diseases, are expected
to bring better diagnostic accuracy, prediction and therapy monitoring of dementia
at early stages. Hybrid imaging can provide better links between MRI and PET for
the observation of multi-parametric changes in the development of such disease and
better understanding of its biological process. In acute cerebral diseases, such as
cerebral stroke, it is commonly said that “time is brain”. Due to this, although PET
methods are considered the gold standard for identifying the regions compromised
in an ischemic stroke event [
106
], CT and MRI are the modalities of choice for such
emergencies [
107
,
108
]. PET techniques that would be suitable for this goal are
logistically too complicated and they require too much time for tracer preparation
