ABSTRACT
I. Introduction 60
II. SPECT Imaging 60
A. Principles of SPECT Imaging 60
B. Radionuclides Used in SPECT Imaging 62
III. PET Imaging 64
A. Principles of PET Imaging 64
B. Radionuclides Used in PET Imaging 66
IV. SPECT Imaging vs. PET Imaging 67
V. Applications of PET and SPECT Molecular Imaging 69
A. Imaging of RNA 69
B. Imaging of Endogenous Proteins and
Protein Function 71
Imaging of Intracellular Proteins 71
Imaging of Transmembrane Proteins 72
C. Imaging of Exogenous Marker Genes 76
Herpes Simplex Virus-1 Thymidine Kinase 77
Sodium Iodide Symporter 78
Somatostatin Receptor Subtype 2 79
Dopamine-2 Receptor 80
VI. Summary 80
Acknowledgments 80
References 81
I. Introduction
With the development of new molecular imaging probes, sophisticated animal
models, and small-animal imaging devices as well as advances in molecular
biology techniques, molecular imaging has become increasingly important for
understanding basic biological processes in living subjects. Molecular imaging
can be defined as the characterization of biological processes at the cellular
and molecular levels in living animals or humans using remote imaging detectors
(1). This can differ from “classical” diagnostic imaging that focuses on imaging
the end result of these biological processes (2). Molecular imaging modalities
include nuclear imaging, optical imaging, magnetic resonance imaging (MRI),
computed tomography (CT), and ultrasound. All of these modalities offer differ-
ent advantages and limitations for molecular imaging. Most of these advanta-
ges and limitations are centered on issues of spatial and temporal resolution,
sensitivity, molecular probe availability, image acquisition and analysis time,
and cost. The focus of this chapter will be on nuclear imaging, in particular
single photon emission computed tomography (SPECT) and positron emission
tomography (PET). These techniques have the advantages of having a high
sensitivity, being extremely quantitative, and having a number of probes
readily available. They are, however, relatively expensive, expose the subject
to radiation, and have lower spatial resolution than some of the other imaging
modalities. This chapter will describe the basics of SPECT and PET imaging,
describe the advantages and disadvantages of each modality, and give examples
of how each platform is used for molecular imaging applications.
