**5. Discussion — Breaking through the speed barrier**

In contrast to conventional line-serial computer based image reconstruction as used in existing systems, it has been demonstrated that the acousto-optical hybrid scanner has the potential to provide a number of important properties. These are:


As evident from the images, the signal-to-noise ratio (SNR) of the above prototype is very high. One of the reasons for this arises from the fact that true signals are coherent and the noise signals are not. Since the image reconstruction is based on amplitude and phase of signals, this allows true signals from targets to be coherently re-constructed in the image medium while the noise and out of phase signals are being largely rejected as evident from Figure 18 below. However, just like all ultrasound equipment multiple reflections between closely spaced targets could still cause artefacts. Therefore, inclusion of selective insonification of the object medium as in item No. 2 above should enable the system to achieve even higher SNR while suppressing artefacts when imaging near-field targets.

**Figure 18.** Noise suppression

**5. Discussion — Breaking through the speed barrier**

temporal artefacts when rapidly moving targets were imaged.

the need of any dynamic focusing as in the conventional technology.

provide a number of important properties. These are:

**Figure 17.** a) - Test Block. Statically scanned images of the test block

288 Advancements and Breakthroughs in Ultrasound Imaging

scanning in conventional technology.

aperture is used for each image frame.

In contrast to conventional line-serial computer based image reconstruction as used in existing systems, it has been demonstrated that the acousto-optical hybrid scanner has the potential to

(b) (c) (d)

(a)

**•** Ultimate speed of imaging as the image reconstruction is done using acousto-optical means thus *"Breaking through the speed barrier"* of the conventional line-serial imaging technology.

**•** In axial imaging mode, a complete image frame can be produced using a single ultrasonic pulse within its time of flight thus allowing ultimate imaging speed thus eliminating

**•** In sector scanning mode image zones for each scan angle is produced allowing much higher frame-rates to be achieved, since very few scan angles are required as opposed to line serial

**•** A focused image of the whole object field is produced at the same instant of time without

**•** High lateral resolution, close to theoretical limits is achieved as the whole transducer

As evident from the images, the signal-to-noise ratio (SNR) of the above prototype is very high. One of the reasons for this arises from the fact that true signals are coherent and the noise signals are not. Since the image reconstruction is based on amplitude and phase of signals, this Another important factor as mentioned in section 2 for any imaging technique is the dynamic range. In this respect, one of the typical bottlenecks is the limited dynamic range of display equipment. The present development can provide a greater display dynamic range when images are viewed with the naked eye as the acousto-optical modulator can provide a higher display dynamic range than images captured by a camera and presented on a typical conven‐ tional VDU.
