17
Positron Emission
Tomography
17.1 INTRODUCTION AND OVERVIEW
Positron emission tomography (PET) is a noninvasive nuclear imaging technique that
produces images of the metabolic activity of living organisms on the biochemical
level. These physiological images are detected by introducing a short-lived positronemitting radioactive tracer, or radiopharmaceutical, by either intravenous injection
or inhalation. Images are created using a process called radioactive labeling in which
one atom in a molecule is replaced by a radioactive radionucleotide.
The PET images produced help physicians identify normal and abnormal activity
in living tissue. Unlike computed tomography (CT) that primarily provides anatomical images, PET measures functional chemical changes in the tissue. Some of these
chemical changes that are typically metabolic activities occur before the resulting
abnormalities are visible on other functional imaging modalities such a regular functional magnetic resonance imaging (f MRI). The resolution of PET is far less than
that of CT and MRI, and, as a result, PET images are often registered with CT or
MRI images to superimpose the anatomical details of CT and MRI on the functional
information of PET.
Informally speaking, PET recognizes these metabolic changes by measuring the
amount of radioactive tracers distributed throughout the body. This information is
subsequently used to create a three-dimensional (3-D) image of tissue function from
the acquired decay matrix. Due to the availability of various types of radioactive
isotopes, the specific metabolic changes resulting from assorted diseases make PET
imaging particularly useful in the detection of malignancy in tumors.
In this chapter, we first describe the physical and physiological principles of PET
and then describe applications of PET in medical imaging and diagnostics. A closely
related imaging technology called single photon emission computed tomography
(SPECT) will be discussed briefly as well toward the end of the chapter. Even though
SPECT is briefly described in this chapter, this technology will be separately discussed
in Chapter 18, which is dedicated to more specialized imaging technologies.
17.2 PHYSICAL AND PHYSIOLOGICAL PRINCIPLES OF PET
The radionucleotide that is administered in the body during PET imaging contains
a specified quantity of short-lived radioactively labeled chemical substances that
are identical or closely analogous to naturally occurring substances in the body.
The radioactive substances used in PET are nucleotides in which some atoms are
replaced by their radioisotopes.
339
Positron Emission
Tomography
17.1 INTRODUCTION AND OVERVIEW
Positron emission tomography (PET) is a noninvasive nuclear imaging technique that
produces images of the metabolic activity of living organisms on the biochemical
level. These physiological images are detected by introducing a short-lived positronemitting radioactive tracer, or radiopharmaceutical, by either intravenous injection
or inhalation. Images are created using a process called radioactive labeling in which
one atom in a molecule is replaced by a radioactive radionucleotide.
The PET images produced help physicians identify normal and abnormal activity
in living tissue. Unlike computed tomography (CT) that primarily provides anatomical images, PET measures functional chemical changes in the tissue. Some of these
chemical changes that are typically metabolic activities occur before the resulting
abnormalities are visible on other functional imaging modalities such a regular functional magnetic resonance imaging (f MRI). The resolution of PET is far less than
that of CT and MRI, and, as a result, PET images are often registered with CT or
MRI images to superimpose the anatomical details of CT and MRI on the functional
information of PET.
Informally speaking, PET recognizes these metabolic changes by measuring the
amount of radioactive tracers distributed throughout the body. This information is
subsequently used to create a three-dimensional (3-D) image of tissue function from
the acquired decay matrix. Due to the availability of various types of radioactive
isotopes, the specific metabolic changes resulting from assorted diseases make PET
imaging particularly useful in the detection of malignancy in tumors.
In this chapter, we first describe the physical and physiological principles of PET
and then describe applications of PET in medical imaging and diagnostics. A closely
related imaging technology called single photon emission computed tomography
(SPECT) will be discussed briefly as well toward the end of the chapter. Even though
SPECT is briefly described in this chapter, this technology will be separately discussed
in Chapter 18, which is dedicated to more specialized imaging technologies.
17.2 PHYSICAL AND PHYSIOLOGICAL PRINCIPLES OF PET
The radionucleotide that is administered in the body during PET imaging contains
a specified quantity of short-lived radioactively labeled chemical substances that
are identical or closely analogous to naturally occurring substances in the body.
The radioactive substances used in PET are nucleotides in which some atoms are
replaced by their radioisotopes.
339