Methods of registration
There are several methods for external registration of physiological and pathological processes. Some of the capabilities and drawbacks of telemetry are discussed. In addition, different registration technologies are reviewed, including transponder use and biophotonic imaging.
telemetry is a way of making physiological and behavioral measures on an animal that is free to move in its cage. Telemetry involves implanting a transmitter into the abdominal cavity of the animal. This allows prolonged registration of physiological parameters such as body temperature, heart rate, and blood pressure, outside the body, without further manipulation of the animal. Telemetry is widely used in pharmacological research. Data gathered by means of telemetry can also be used for assessing the health status of an animal and for determining a humane endpoint. Finally, it can help reduce the number of animal procedures, since an animal can be monitored over time and it can serve as its own control (see picture).
On the other hand, telemetry has drawbacks which have to be considered before one decides to set up experiments utilizing this technology. Technical possibilities combined with a desire for efficient animal use, often actually lead to an increase in the number of measurements per animal (e.g., by reusing animals), which may increase discomfort. The presence of the transmitter in the abdominal cavity and the (frequent) necessity of individual housing, can exert a negative influence on the animal's welfare and on its behavior and physiological functions.
Body temperature can also be recorded by means of a transponder, which can be implanted subcutaneously. This method relies on external induction technology, which allows the use of tiny injectable transmitters. Body temperature is read by holding a scanner close to the animal’s body.
This technology makes it possible to track microorganisms or cancerous cells inside the body (see picture). It makes use of a luciferase gene, incorporated into microorganisms or cancerous cells respectively. The luciferase gene causes photons to be emitted that can be detected outside the animal with special cameras. The resulting photographs reveal the spread of the microorganisms or the growth or metastasis of the tumor cells (see picture). Prior to biophotonic imaging the animal must be anesthetised.
In addition, we currently have many different options for non-invasive animal monitoring. These technologies include functional magnetic resonance imaging (fMRI), by which functional information , e.g. images of the beating heart or brain activity, can be gathered from a living laboratory animal.
Positron Emission Tomography (PET), PET scanning is based on the biodistribution of imaging substances. These are radio nucleotides that release positively charged particles or positrons. PET scans are used mostly to visualize biological processes in organs and tissues, and to follow them over time. A review of noninvasive or minimally invasive bioimaging technologies can be found in the ILAR Journal, Vol 49 (1) on the website of ILAR.