Ultrasound Biomicroscopy (UBM)
Ultrasound biomicroscopy (UBM) is a new technology that uses very high frequency ultrasound (20~55 MHz or even higher, compared to 3~15 MHz in conventional clinical ultrasound systems) to noninvasively image small animals in biological research. At the Mouse Imaging Centre, we use a Vevo 660 UBM rolling cart developed by VisualSonics, Inc. The spatial resolution of a two-dimensional image is up to ~50 μm, with penetration depth of ~20 mm. The basic function modalities of UBM include:
- B mode provides two-dimensional images of the organs, such as heart and vessels, abdominal organs, skin, eye and tumor, for the morphological and dimensional observation.
M mode displays the dynamic position change of moving structures such as left ventricle and arteries over time. It is used to measure the cardiac systolic function and arterial dimensions.
Doppler mode measures the blood flow velocity at the site of interest in the cardiovascular system.
3D reconstruction can acquire a three-dimensional volume data set of the structure of interest, measure the tissue volume, and demonstrate the surface image of the structures inside the body (Fig. 1).
EKV (ECG based Kilo-Hertz Visualization) technology can retrospectively reconstruct a two-dimensional cardiac image which equals that acquired at the frame rate of 1000 Hz. It is suitable for evaluating the left ventricular wall motion and valvular movement.
Current applications of UBM in biological research:
UBM provides a noninvasive approach for the morphological, functional and hemodynamic study on mice.
- Studies on mouse development from early embryonic period to adulthood.
- In vivo morphological and functional phenotyping of wild-type, transgenic and mutant mice and other mouse disease models. The examples are: a) Cardiovascular morphology, function and hemodynamics in wild-type and genetically altered mice; b) Tumor growth and the effects of pharmaceutical interventions.
- Image-guided interventions on mice: a) UBM-guided micro-injection for introducing genes or cells into the developing mouse embryos, and follow-up of the consequences (Fig. 2A); b) UBM-guided cardiac catheterization for perfusion-fixation for MRI and micro-CT (Fig. 2B).