contamination between groups of animals, different animal species, or between animals and humans (if the device is used for both animal and human subjects) is possible because these devices may be difficult to sanitize (Klaunberg and Davis 2008; Lipman 2006). If the imaging resource is located outside the animal facility, appropriate transportation methods and routes should be developed to avoid inappropriate exposure of humans to animals in transit. If possible, animals should not be moved past offices, lunch rooms, or public areas where people are likely to be present.
As imaging may require the subject to be immobile, often for extended time periods during image acquisition, provisions should be made for delivery of anesthetics and carrier gas, the scavenging of waste anesthetic gas, and adequate animal monitoring (Balaban and Hampshire 2001). Remote storage of gas tanks is generally required in facilities where magnetic resonance (MR) scanners are used as the magnetic field requires ferrous materials to be kept a safe distance away from the magnet. Site selection of MR scanners requires special attention because of their weight, the fringe field generated (especially from unshielded magnets), and the impact of ferrous elements of the building structure or its components, especially those that are not static (e.g., elevators), as they may affect field homogeneity. Most MR scanners are superconducting and require the use of cryogens. Because cryogen boil-off can lead to asphyxiation of both personnel and animals, rooms with MR scanners or in which cryogen gases are stored must be equipped with oxygen sensors and a method for increasing room ventilation to exhaust inert gases during cryogen filling (Klaunberg and Davis 2008).
Many imaging devices, especially those designed for small animals, are self-contained and require no special physical plant considerations. Provisions should be made to locate the operating console away from imaging devices that emit ionizing or magnetic radiation. Imaging devices with components that are difficult to sanitize should be covered with a disposable or sanitizable material when not in use.
Total body irradiation of small laboratory animals may be accomplished using devices that emit either gamma- or X-rays. Devices are usually self-shielded and, because of the weight of the shielding material, may require special site considerations. Devices with gamma-emitting sources are subject to regulations that require adherence to specific security, monitoring, and personnel clearance requirements (Nuclear Regulatory Commission 2008). The site selected for irradiators should also take into account whether they are to be used for animals and biologics, as well as the source and microbial status of the animals to be irradiated. Locating them in the animal facility may require access for personnel who would normally not