Doppler Mainframe Modules

The 20MHz 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 focused 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 20MHz and with pulse repetition rates varying from 125kHz down to <1kHz.

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 20MHz versions with other frequencies available on special order. Standard PRF's range from 20kHz to 125kHz with 62.5kHz 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 20MHz 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.

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.

This module is suitable for most flow velocity measurements in smaller (20MHz) and larger (10MHz) vessels of acute and chronically instrumented animals. The output is directional with either advancing or receding flow displayed as positive. Outputs are mean velocity, phasic velocity with selectable damping, and a voltage proportional to the range gate delay. Doppler shifts up to 31.25kHz can be measured with the standard 62.5kHz pulse repetition frequency (PRF). This corresponds to a maximum velocity of 166cm/s using a 20MHz probe or 330cm/s using a 10MHz probe with a beam angle of 45°. These modules can also be used with tubing mounted probes to measure blood flow noninvasively in mice and other animals.

This module was designed to overcome the high velocity limitation of the standard module. By "unwrapping" the aliased high frequencies, it can record Doppler shifts up to 62.5kHz (~300cm/sec at 20MHz or ~600cm/sec at 10MHz) using the standard 62.5kHz PRF. Because of these extra features it is trickier to use (more critical controls to set) than the standard module. It has been found it most useful on hepatic, renal, and mesenteric arteries.

This is the standard transit-time dimension gauge (sonomicrometer) used with paired ultrasonic crystals for measuring myocardial segment length, wall thickness, and diameter and for measuring blood vessel diameter. Dimensions from 2 to 50mm can be measured from up to 4 sets of crystals (requiring 4 modules) simultaneously without interference. This module can be used with crystals ranging in frequency from 5-20MHz.

This module is used to measure ventricular thickening from a single epicardial transducer, thus eliminating the need for any intramyocardial crystals. Rather than tracking one layer, it measures thickening at a fixed depth from the epicardial surface as selected by the range gate delay. Thickening fraction is estimated by dividing the measured thickening (in mm) by the range gate depth (also in mm), which can be set to any depth from the subepicardium to the subendocardium. Although it doesn't measure absolute thickness, it is much easier to use than the two crystal method, and has been very useful in evaluating regional ventricular function in studies of ischemia and reperfusion. Resolution is 0.02mm (0.01mm) with a maximum measurable thickening of 5mm (2.5mm) at a maximum depth of 4cm (1.2cm) at 10MHz (20MHz).

This non-ultrasound module contains two standard bridge amplifiers suitable for use with pressure transducers such as those made by Gould Statham, Konigsberg, or Millar. Each amplifier is independent with input connector, balance and gain controls, and a phasic/zero/mean output selector switch. The lower amplifier has an additional mean output that is not affected by the selector switch.

This module contains a single pressure amplifier as above and also a derivative amplifier and calibrator for dP/dt measurement. Simultaneous outputs are provided for phasic pressure, mean pressure, and dP/dt. A built-in triangle wave generator is used to calibrate the dP/dt output in mmHg/s.

This module contains a differential ECG amplifier with standard lead switching, an R-wave trigger, and a rate counter. The standard lead set has four limb leads, 2 V leads, and a ground. A cable is also available for direct connection to the “Mousepad” ECG board, a simpler module with a 3-lead clip-cable and manual lead switching is also available. Outputs from each module include: ECG, heart rate, and a pulse coincident with the triggered R-wave.

This is the Temperature Controller Module that allows for automatic thermal control of the heating pad incorporated on the ECG board, while the temperature of the mouse is monitored with a rectal probe plugged into the port labeled "MOUSE" in blue (see picture to the left). The heating pad uses feedback from either the probe or the heating pad to monitor the temperature and ensure the mouse’s required body temperature is maintained.

This module is suitable for flow velocity measurements in animals larger than mice (rats, rabbits, guinea pigs, etc.). The output is directional with either advancing or receding flow displayed as positive. Outputs are mean velocity, phasic velocity with selectable PRF, and a voltage proportional to the range gate delay. Doppler shifts depend on PRF selection (low, medium, high). The low setting is ¼ of the mainframe PRF, the medium setting is ½ of the mainframe PRF, and the high setting is equal to the mainframe PRF. The mainframe PRF can be set to either 125kHz or 62.5kHz.