Biomedical Engineering Reference
In-Depth Information
traditional tomographic imaging techniques, such as CT and MRI, that can pro-
vide anatomical (or structural) information of the tissue only. These latter tech-
niques are method of choice when normal anatomy is expected to be disrupted
by disease. However, there are many situations where functional changes pre-
cede anatomic changes or anatomic changes may be absent. Examples include
cancers in their early stage, and various neurodegenerative diseases such as
Alzheimer's, Huntington's, and Parkinson's diseases, epilepsy and psychiatric
disorders, [97-99], in addition to a wide variety of neuroreceptor studies [100].
Historically, clinical applications of PET were centered around neurology
and cardiology. The clinical role of PET has evolved considerably during the
past 10 years, and it is well recognized that PET has a preeminent clinical role
in oncology. Currently, oncological PET studies contribute to over 80% of clini-
cal studies performed worldwide [101]. It is well recognized that PET is useful
for monitoring patient response to cancer treatment and assessing whether le-
sions seen with CT and MRI are cancerous, and is capable of grading degree
of malignancy of tumors, detecting early developing disease, staging the extent
of disease, detecting primary site of tumor, measuring myocardial perfusion,
differentiating residual tumor or recurrence from radiation-induced necrosis
or chemonecrosis, and monitoring cancer treatment efficacy [102-107]. FDG is
the primary radiopharmaceutical used in oncological PET studies to assess glu-
cose metabolism. Improvements in instrumentation in the late 1980s overcame
the limitation of the restricted imaging aperture and enabled three-dimensional
whole-body to be imaged. Whole-body PET imaging has been proven highly ac-
curate in the detection of a number of different malignancies, particularly in
cancers of the colon, breast, pancreas, head and neck, lungs, liver, lymphoma,
melanoma, thyroid, and skeletal system, depending on the use of specific radio-
tracers. Figures 2.11 and 2.12 show examples of neuro-oncologic and whole-body
coronal FDG-PET images.
As mentioned in Section 2.3, PET offers some unique features that cannot be
found in other imaging modalities. The radiolabeled compounds used in PET are
usually carbon (
11
C), nitrogen (
13
N), oxygen (
15
O), and fluorine (
18
F), which can
be used to label a wide variety of natural substances, metabolites, and drugs,
without perturbing their natural biochemical and physiological properties. In
particular, these labeled compounds are the major elemental constituents of
the body, making them very suitable to trace the biological processes in the
body. As the measurements are obtained noninvasively using external detectors,
