chapter 2 8slides.pdf

Transmit/receive (T/R) The transmit/receive (T/R) switch directs the driving voltages from the pulser and pulse delays to the transducer during transmission and then directs the > returning echo voltages from the transducer to the amplifiers during reception Amplifiers Amplification is t...

Transmit/receive (T/R) The transmit/receive (T/R) switch directs the driving voltages from the pulser and pulse delays to the transducer during transmission and then directs the > returning echo voltages from the transducer to the amplifiers during reception Amplifiers Amplification is the conversion of the small voltages received from the transducer elements to larger ones suitable for further processing and storage Amplifiers increase voltage amplitudes. This increase is called gain. Gain is set subjectively so that echoes appear with appropriate brightnesses. Amplifiers The amplifiers must also compensate for the effect of attenuation on the image. Compensation (also called time gain compensation [TGC]) equalizes differences in received echo amplitudes caused by different reflector depths. Reflectors with equal reflection coefficients will not result in echoes of equal amplitude arriving at the transducer if their travel distances are different.  Two identical reflectors are located at different distances from the transducer. A, The echo at the second reflector is weaker because the incident pulse had to travel farther to get there, thereby increasing attenuation. B, The echo from the first reflector arrives at the transducer. The echo is weaker than it was in A because of attenuation on the return trip. C, The echo from the second reflector arrives at the transducer later and in a weaker form than the first one did because of the longer path to the second reflector.  Uncompensated echoes from identical structures at differing depths enter the TGC amplifier. The second (2) is weaker than the first (1) because it has come from a deeper site and has experienced more attenuation. After TGC, the amplitudes are identical. analog-to-digital converters (ADCs) An ADC (also called a digitizer) converts the voltage from analog to digital form The term analog means “proportional,” and the term digital means “in the form of discrete numbers”. Digitizers convert voltages representing echoes to numbers for digital signal processing and storage. = From the ADC, the digitalized echos voltages pass through echo delays and summer Echo Delays After amplification and digitizing, the echo voltages pass through digital delay lines to accomplish reception dynamic focus and steering functions. Summer · The final part of beamforming in ultrasound, known as the summer, integrates the signals processed by individual channels into a cohesive image. This step is crucial as it combines the focused echoes from different transducer elements, enhancing the overall image resolution and clarity by aligning and summing the received signals.