Share thisBooms in the field of genetics, generous research grants, and an increase in the number of small animal laboratories have contributed to the rise in the number of imaging procedures performed each year. Concurrently, advancements in microchips and computers, imaging technology, and laboratory demands for improved image resolution have led to the design of smaller imaging systems specifically for animal research. In addition to producing conclusive information, these dedicated systems are affordable, safe to use, easy to install, and simple to operate.
The two imaging modalities most commonly used in laboratory settings are radiography and bone densitometry. These studies are primarily used to screen, track and evaluate structural and tissue changes in mice. Modern imaging equipment has revolutionized these test procedures; studies that used to take weeks are now performed in minutes. In addition, the procedures are done in vivo. Being able to preserve animals offers ethical as well as economic advantages.
Radiography
Today’s compact radiographic systems offer numerous benefits to the laboratories that use them. Unlike systems designed for human use, these freestanding units are completely self-contained eliminating the need for special lead barriers. Most notably, dedicated systems incorporate use of a micro-focus x-ray tube.
In radiographic studies, image resolution is vital. The small size, intricate skeletal structure, and low calcification of mouse bone make them difficult to radiograph. Systems designed for ultra-detailed animal images incorporate a 20-micron (0.02 mm) focal spot tube, high contrast/low kV techniques, and magnification options. (See Photo 1)
Benefits of micro-focus tubes can be explained with a brief review of radiographic physics. Recorded detail is the degree of geometric sharpness or accuracy of the structural lines actually recorded in the radiographic image. The art of radiography involves controlling the degree of unsharpness or blur.1 There are several geometric considerations that have a profound effect on the sharpness of a radiographic image: 1) the size of the focal spot on the x-ray tube, 2) source-to-image receptor distance (SID), and 3) object-to-image receptor distance (OID).2 (See Figure A)
Radiographic images consist of the image proper (umbra) and a hazy area at the edges (penumbra). The width of penumbra (unsharpness/blurring) expands as SID decreases. It also increases when the animal is placed farther from the image receptor, as in magnification studies. As the size of the focal spot decreases, the image sharpness increases because penumbra is minimized. Tubes in systems designed for human use typically have focal spot sizes of 0.6 to 1.2mm. The smaller 0.02mm focal spot used in small animal systems maximizes image resolution by increasing sharpness and detail. (See Figure B)