Ultrasound imaging is based on the reflection of high frequency sound by tissues. Sound pulses are emitted from a transducer held against the subject and the reflected signal is detected and used to construct an image. From a practical standpoint, the ultrasound can distinguish different tissues because each has its own properties of reflecting greater or lesser proportions of the emitted signal. In general, fluid-filled tissues transmit more sound than air-filled tissues, and therefore the relative water content of tissues impacts the resulting image. For most soft tissues, as the sound passes through each point in the tissues, a fraction is reflected back to the tumor, while the rest continues on. As a result, tissues far away from the transducer (i.e. at the bottom of the screen for a linear array transducer) will appear darker or black. Furthermore, the transducer itself has an optimum focal depth where the best image is acquired (in some models this can be adjusted, while in others it is fixed).
Ultrasonography is a powerful imaging modality that enables non-invasive, real time visualization of abdominal organs and tissues. This technology may be adapted for use in mice through the utilization of higher frequency transducers, allowing for extremely high resolution imaging. This technique is particularly well-suited to small animal imaging due to the ultrasonographic properties of the normal mouse tissue, easily accessible imaging planes of mouse tissue, and the comparative difficulty in imaging the mouse tissue with other technologies. A suite of measurements tools is available to characterize the normal and diseased states of tissues. Easily screened organs include all peritoneal organs (liver, stomach, intestines, kidney, pancreas, spleen, bladder, prostate, ovaries), subcutaneous ectopic xerographs, mammary tissue, melanomas, etc.. For specifics, please refer to the ultrasonic website where they offer a vast supply of applications.
Ultrasonography is a safe, non-invasive imaging modality that has found wide application in many areas of medical diagnostics, including obstetrics, cardiology, and oncology. However, it is perhaps underutilized in clinical oncology, and has only recently begun to be utilized widely in the preclinical setting. Ultrasonography is ideally suited to use in basic cancer research using small animal models since rapid, high definition and reproducible tumor imaging can be made in vivo with only minor physiological impact on the subject. Accurate quantification of tumor volumes from this technique can provide detailed information on tumor growth kinetics, which is particularly important in fields such as preclinical therapeutics, where the response of tumors to therapies may be observed in real time.