ECG & Pulse Doppler Systems For Cardiovascular Research on Mice
Electronics Contract R&D For Medical, Scientific, & Industrial Instrumentation

Doppler Mainframes

The 20 MHz pulsed Doppler was originally designed for measuring coronary blood flow velocity in man from a transducer mounted on the tip of a Sones coronary catheter. Subsequently, it was found to be ideal for other semi invasive applications requiring the sensing of blood flow in small vessels using miniaturized transducers. Some of these other uses have been: 1) measuring flow in the smaller vessels of acute and chronically instrumented animals using either rigid epoxy or flexible silastic cuff type probes, 2) sensing flow in small vessels near the skin surface transcutaneously, 3) sensing flow through grafts and anastomosed vessels intraoperatively in man using cuff type and miniature hand held probes, and 4) sensing cardiac and peripheral flows in mice using focussed hand-held probes. When myocardial ischemia in dogs was studied it was found desirable to measure simultaneously myocardial segment length using ultrasonic transit time and coronary blood flow using pulsed Doppler. To do this required synchronization of the ultrasound signals from the two devices, and the ultrasonic flow/dimension system was designed. It was designed in a modular package to operate both transit time and pulsed Doppler devices at ultrasonic frequencies of 5, 10, or 20 MHz and with pulse repetition rates varying from 125 kHz down to <1 kHz.

The simplest, most compact system is the single channel pulsed Doppler. This instrument is often used with catheters and in other clinical or research applications where only one velocity signal is needed. Since it is limited to one channel it is used less commonly in the animal laboratory where several flows must often be measured simultaneously. Single channel pulsed Dopplers are built standard in either 10 or 20 MHz versions with other frequencies available on special order. Standard PRF's range from 20 kHz to 125 kHz with 62.5 kHz being the most common.

Note: In addition to the analog velocity outputs, this instrument and the multichannel mainframes which follow have audio outputs which can be used with the Doppler Signal Processing Workstation for more detailed and precise analysis of Doppler velocity signals

This instrument (not pictured) allows velocity to be sensed at 8 places along the sound beam simultaneously and is used primarily for evaluating velocity profiles and detailed hemodynamics in real time. It operates at 10 or 20 MHz and provides outputs for an X Y display of velocity profiles, and separate velocity and quadrature audio outputs for each of the 8 channels. An auxiliary zero crossing interval histogram processor (a simple form of spectral analysis) is available for detecting and analyzing flow disturbances.

MULTI-CHANNEL MAINFRAMES

The 6 Channel Ultrasonic Flow/Dimension Mainframe is the standard and most widely used version and can accept any of the modules listed on the next page. It has a built in speaker for listening to a selected Doppler channel and can be connected to a high frequency oscilloscope for monitoring the ultrasonic signals from Length Gauge or Doppler Displacement modules. Recorder outputs from each channel are in the +/ 10 volt range and are suitable for connection to a strip chart recorder, FM tape recorder, computer A D input, or a physiologic monitor scope. With few limitations, all six channels can be operated simultaneously without interference. For more ambitious laboratories a 12 Channel Mainframe is available, and for more limited applications or where a more compact size is needed, a 3 Channel Mainframe is available.