Design and development of low cost portable ultrasonic sector scanner

A diagnostic system for scanning the internal organs of human body based on ultrasound imaging techniques is being developed at CSIO, Chandigarh. It provides non-invasive, real time imaging of organs of interest in a scan area defined by a 60° sector. The heart of the system is a light weight hand held probe which consists of a piezoelectric crystal as the transducer for transmitting and receiving ultrasound. The transducer oscillates to and fro in an oil chamber at a frequency range of 10 to 15 Hz (variable) and is driven by a specialized, high torque DC motor having a clean and silent commutation. Position of the transducer at any instant is continuously and precisely monitored by a contactless potentiometer based on variable inductance principle. The front face of the probe is made of a suitable impedance matching material for coupling the ultrasound efficiently to the body and also provides the necessary mechanical protection and prevents the motor from any extra loading. The system operates in an open loop limiting the maximum displacement error within ±1% between two alternate frames. A parallelogram linkage system between the transducer and potentiometer ensures accurate position monitoring and evenly spaced lines within the sector. The crystal when excited by high voltage, short duration pulses transmits ultrasound energy at a frequency of 3.5 MHz. Echoes received from the various layers of the body are picked up by the same crystal and coupled to a high gain, low Q, radiofrequency amplifier incorporated with 3 band time gain compensation circuit. Demodulated signal after proper signal processing is fed to the digital scan converter which has a memory map of 256×256×6 bits. The picture is displayed on a gray scale monitor. The system has axial and lateral resolution of 1 mm and 3 mm respectively with 64 gray levels. During the clinical trials at PGI, Chandigarh the system was able to image most of the abdominal organs within a depth of 16 cms from the body surface