![]() The 80 MHz/f 2.2 can capture the resolution of 50 microns. Therefore, a transducer of 80 MHz and f 2.2 has poorer resolution than 80 MHz/f 1.2. ![]() The lateral resolution (transverse to the direction of pulse propagation) depends on the distribution of ultrasound in the field of the transducer, which has a width at half maximum given by the product of the wavelength and the f-number. Measurement accuracy of the imaging system is dependent on the lateral and axial resolution, the stability of mechanical motion and the pixel size of the image. For example, a device with a high frequency (80 MHz) and short focal length (1.2 mm) can give a very sharp image of the cornea showing the epithelial layer at 50 microns resolution, although the deeper structures of the cornea are not shown clearly. Higher frequency and shorter focal length are usually associated with higher resolution of the images but poorer penetration. The black arrow shows the most important landmark for drainage angle measurement― scleral spurĪccording to the principles of ultrasound physics, image quality is dependent on the frequency of the ultrasound, the ratio of the focal length to the transducer diameter (f-number) and the length of the pulse. (C: Cornea AC: Anterior chamber S: Scleral spur CB: Ciliary body PC: Posterior chamber LC: Lens capsule L: Lens). Illustration of major anatomical landmarks in UBM images. In prototype models, a frequency range of 50 to 80 MHz with a field of view of 4 × 4 mm was selected because it can give a useful compromise that allows all the important structures of the anterior segment to be visualized. Only the signals returning from a 5 × 5 mm area centered at the focal depth are stored. After signal processing, ultrasound data can be converted from analog to digital format and transferred to a high speed scan converter, and eventually displayed on a video computer. ![]() The signal is amplified in proportion to the depth from which it originated using so called ‘time-gain compensation’. By moving a transducer linearly over a 5 mm image field, sonographic data are generated along each of 512 lines (8 micron between lines) ( Fig. The transducer is the critical component. The principal components of UBM are shown in Figure 1. The development of UBM equipment was made possible by advances in transducer, high-frequency signal processing and precise motion control technology. A: Ultrasound transducer and probe B: Articulated arm C: Computer monitor D: Main processing unit E: Printer The current UBM―P45 workstation (Paradigm Medical Industries, UT, USA).
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