FAQ About Molecular Imaging

What is molecular imaging?

Molecular imaging is the characterization and measurement of biologic processes at the cellular and molecular level without the need for surgery. Molecular imaging has the potential to reveal the subtle differences in underlying molecular structure that often differentiate normal from diseased tissue in a relatively non-invasive manner.

Is molecular imaging new?

While many existing imaging techniques reveal something about the underlying structure of tissue and its relationship to disease, only recently have researchers begun to develop molecular probes, and associated imaging technologies, that are highly specific for detecting predetermined molecular targets in vivo in three dimensions.

What are the benefits of molecular imaging?

The imaging of molecular signatures is expected ultimately to enable earlier detection of disease. In addition, the imaging of specific proteins or pathways will allow clinicians to tailor therapies to individual patients by better drug selection and monitoring non-invasively molecular events that change medical treatment quickly. All of this will result in the creation of a molecular medicine approach to patient care.

What is a molecular probe?

A molecular probe must have two important characteristics:

1. A molecule that has a high affinity for attaching itself to a target molecule associated with a specific type of desease, e.g., breast cancer. An example is a protein or a peptide chain.
2. The ability to "tag" the molecular probe with a marker molecule that can be tracked by a suitable detector placed outside the body. This tag could be a radioactive tracer, or an optically absorbing dye.

Where do molecular probes come from?

Most molecular probes are fabricated in laboratories and injected into the blood stream in small concentrations, where they are distributed throughout the body by the cardiovascular system. In some instances, however, the body provides its own indwelling markers of molecular disease. For example, the degree of oxygen starvation (hypoxia) in blood-perfused tissue can be used to infer the presence of malignant tissue growth. The state of hypoxia can then be monitored using multi-spectral, optical-absorption techniques.

Why optical molecular imaging?

A rich history of using optically absorbing dyes (fluorescing and non-fluorescing) exists for the purpose of identifying specific cells, proteins, and other receptors in biologic tissue. Such dyes are routinely used in histological slide preparations. The use of fluorescing dyes in conjunction with optical microscopy is a well-developed field. Today, researchers are applying many of these in vitro fluorescent-imaging techniques to small animals in vivo. A particularly promising approach is to attach a fluorescent dye to a molecular probe, such as a protein, and inject it into a living animal and track its biologic distribution over time.

What is the role of mice in molecular imaging?

Most of the current molecular imaging research is being performed in mouse models. The creation of genetically homogeneous inbred strains of mice, analysis of tumor viruses and oncogenes, creation of transgenic strains carrying activated and inducible forms of oncogenes or knockouts of tumor suppressive genes have resulted in the mouse becoming the most common research platform. Mice are being used in over 90% of today’s mammalian research, and mouse models have been established for over 90% of human diseases. Over 30 million mice were used in such research in 1991 alone.

It is clear that imaging mice is an essential step in both the study of diseases and the process of therapeutic drug discovery. If a new imaging technology is to be of value for these purposes, it must be applicable to the small animal market.

Can optical molecular imaging be applied to humans?

Optical molecular imaging can certainly be applied to humans provided the tissue being studied does not lie more than 3 cm from the skin surface. In the case of the human breast, a suspicious “mass” can almost always be manipulated to lie within 1 – 3 cm of the skin surface. Non-invasive breast cancer diagnosis promises to be an ideal application of TCT imaging technology. Vascular imaging is another potential area where TCT imaging technology is likely to make an impact in the future.