Pulsed Doppler Mode Research Articles

CW and pulse Doppler diagnostic system

In an interlaced pulse-echo and range-gated Doppler system, an ultrasound transmitter generates a train of constant repetition rate echo pulse interlaced with a Doppler pulse train of plural bursts. The time duration between each burst and the preceding range gate opening is held constant while the time to the successive range gate opening is automatically varied to provide a continuously variable PRF tracking of the console range gate depth setting. The power of the transmitted signal is internally varied in the same sense and the cutoff frequency of the receiver low pass tracking filters is varied in the opposite sense to optimize signal-to-noise ratio at various tissue inspection depths. Selectable turnable high pass filters normalized to low velocity roll-off eliminate artifact for peripheral or central vascular probes. The detection system operates in quadrature and includes a synchronous demodulator and a peak detector, and a level detector operative on peak detected signals. Transducer probes interchangeably usable in the system include within each probe a narrow band amplifier critically turned to the respective probe crystal to provide further S/N ratio improvement. The system is operable in CW or pulsed Doppler modes dependent on switch setting on the split crystal probe.

Diagnostic imaging apparatus

First Page

Surface heating of diagnostic ultrasound transducers.

Surface temperatures of a variety of transducers used with common commercial ultrasonic diagnostic equipment have been measured. Transducers operating in imaging mode, in both continuous and pulsed Doppler modes, and in mixed modes were investigated. A total of 30 transducers and scan-heads used with equipment from 10 manufacturers were examined, including a range of array types, mechanical sectors and continuous-wave Doppler transducers. Measurements were made using an infrared radiometer, or a thermocouple probe, with the transducers operating in air. Surface temperatures of 13 transducers operating in imaging mode were found to be in the range 0.0-13.1 degrees C above ambient after 5 min operation. Some transducers operating in pulsed Doppler mode reached considerably higher temperatures. The most extreme example increased the surface temperature by 36.5 degrees C after 1 min and reached a steady-state temperature of almost 80 degrees C. Transducers operating at these temperatures cannot be retained on the skin of a conscious subject without pain, and will cause skin burns within a brief period of time. A linear relationship has been demonstrated between temperature increase and spatial-average acoustic intensity. The rate of increase in air was found to be about 10 times greater for pulsed arrays than for continuous-wave Doppler transducers.

An experimental investigation of streaming in pulsed diagnostic ultrasound beams

Streaming is shown to occur in water in the focused beams produced by a number of medical pulseecho devices. The use of hot film anemometry to measure the streaming velocity is described and velocities measured in water using commercial equipment are quoted. The highest velocities occur in pulsed Doppler mode with a maximum velocity of 14 cm s−1 being observed. An experimental set-up was used to investigate the parameters affecting streaming and it was found that the harmonic content of the pulse waveform had a major effect on the streaming velocity. The time taken for a stream to become established at the focus of the acoustic beams studied was typically approximately 0.5 s.

Medium PRF for the AN/APG-66 radar

This paper discusses the medium pulse repetition frequency (PRF) pulse doppler mode of the AN/APG-66, the multimode fire control radar for the F-16A/B aircraft. This radar is currently in production and as of January 1984 over 1700 have been delivered. Included is a discussion of the three PRF types: high, low, and medium PRF, leading to the conclusion that for an airborne, look-down application the medium PRF waveform is the best choice. System tradeoffs between a high peak power and a low peak power transmitter are discussed which show that when only a medium PRF waveform is required, the high peak power transmitter yields better performance. Some system design considerations concerning the PRF selection and sidelobe clutter are also included. Finally, the radar mechanization is presented. The AN/APG-66 radar in general, and its medium PRF mode in particular, have undergone extensive operational evaluation and the results have been excellent. The radar has met or exceeded its performance design specifications and the field reliability has been outstanding. For example, for the year 1983 the MTBF was 102.9 h based on 64 204 operating hours from two operational air bases.

Neonatal cerebral blood flow velocity I. An in vitro validation of the pulsed Doppler technique.

A combined pulsed and continuous Doppler instrument was used to assess flow velocities in an in vitro model designed to simulate small deeply lying arterial vessels. Diameters of the model vessels, depth under the transducers and the pulsatile flow patterns were chosen to simulate the corresponding conditions that can be expected when cerebral blood flow velocities are measured with this technique through the anterior fontanel in newborn infants. Computer analysis of the space average velocity signal from the pulsed Doppler mode, showed that the area under this curve, which corresponds to distance, was closely correlated to true flow over a wide range of flows in vessels of different diameters. This variable is suggested to be the closest estimate of true flow, when the diameter of the vessel under study cannot be accurately measured.

Metals joining in the space age by ultrasonics: Nippes, E., and Jones, J.B. Journal of Metals, 16, No. 3, p. 244 (1964)

Streaming is shown to occur in water in the focused beams produced by a number of medical pulseecho devices. The use of hot film anemometry to measure the streaming velocity is described and velocities measured in water using commercial equipment are quoted. The highest velocities occur in pulsed Doppler mode with a maximum velocity of 14 cm s−1 being observed. An experimental set-up was used to investigate the parameters affecting streaming and it was found that the harmonic content of the pulse waveform had a major effect on the streaming velocity. The time taken for a stream to become established at the focus of the acoustic beams studied was typically approximately 0.5 s.