Biomedical Engineering Reference
In-Depth Information
information, dynamic and functional information on biochemical and patho-
physiologic processes or organs of the human body. The importance of studying
organ functions was recognized in the middle of the nineteenth century, but the
actual relationship between physiological disturbances and anatomical lesions
was not yet elucidated. This was partly due to the concept of disease classifi-
cation, which was primarily based on anatomical lesions and causes of disease,
during that period of time.
Recent advances in basic molecular and cell biology have led to a revolu-
tionary change in our understanding of diseases. Instead of defining disease as
structural changes or histopathological abnormality, it can be defined as alter-
nations in cellular behavior that reflect functional changes. It is important to
realize that in living systems, what we call
function
is a process that evolves
over time as energy is produced during the life cycle or information is trans-
ferred and processed within cells, whereas
structure
is simply a snapshot of
function at a particular time instant. Indeed, it is very common that in many
diseases structural changes are completely absent, or physiological changes
precede structural changes. A typical example is cancer, which consists of cells
in which malfunctioning transformation has taken place owing to exposure to
some environmental factors (e.g. viruses, bacteria, irradiation, saccharin, and a
variety of chemical substances) that can cause altered membrane characteristics
and cell metabolism, deformed cell morphology, etc. as a result of alternation
in cell functions and damage in genes that control cell proliferation and migra-
tion. It was first hypothesized by Otto Warburg in 1930 that the rate of glucose
metabolism (aerobic glycolysis) in tumors increases with higher degree of ma-
lignancy when compared to normal tissue [5], and this is regarded as one of the
important indicators of tumor proliferation. If these biological characteristics
could be evaluated
in vivo
, useful information may be obtained to study the
nature of disease early in and throughout its evolution, as well as to identify and
develop effective therapies for treatment. Functional imaging makes it possible
to visualize and measure, with the use of appropriate imaging probes and agents,
these complex pathophysiologic and biochemical processes in a living system
in vivo
in multi-dimensional domains (three-dimensional spatial domains plus
a temporal domain).
There is no doubt that substantial progress has been achieved in deliver-
ing health care more efficiently and in improving disease management, and
