Pulsed Doppler Transducers

All of the transducers described below can be gas sterilized for chronic implantation or for use during sterile surgery. We often have epoxy cuffs in stock, but most probes can be built to order in two weeks.

Rigid epoxy cuffs are generally the preferred type for use in acute or chronically instrumented animals on vessels from 2 to 8mm dia. Standard sizes, are 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 7.0, and 8.0mm inside diameter. They are available with either of two methods for attaching the probe to the vessel: holes drilled near the slot for suture ties, or umbilical tape glued around the outside of the probe. Umbilical tape is usually used for chronically implanted probes which will not be reused, and sutures are best for acute or reusable probes because they are easier to replace and clean. Standard lead length is 30".

For smaller size vessels (0.5 to 2.0mm) or where a more pliable probe is required transducers made from flexible silastic are available. Silastic probes have imbedded sutures for ties and form a full circle around the vessel when closed.

For larger vessels or where a non-encircling probe is desired the ultrasonic crystal may be imbedded in a curved fabric/silastic patch for suturing to the vessel wall. This type of probe is often used on the aorta or pulmonary artery. The diameter of the curve must be specified, and it is usually better to be slightly oversized. This type of probe can be trimmed by the surgeon to fit the available exposure.

The crystals consist of 2mm discs of 5MHz material with convex diverging epoxy lenses molded to each face to spread the sound beam. A 3cm long piece of 20 gauge Teflon sleeving is placed around the leads to aid in inserting the crystal into the myocardium.

These probes are used to measure ventricular wall thickening with the displacement module. Two standard types are available: a 2mm disc or square of 10MHz material attached to a wire loop in the shape of a shamrock or clover leaf for use on large ventricles (dogs), or a similar 1mm square of 20MHz crystal for use on thin ventricles (rats). Each can be sutured to the epicardium.

These probes are used to sense flow in an exposed vessel by holding the probe against the side of the vessel. They are commonly used intraoperatively during reconstructive procedures to verify flow in anastomosed arteries and veins. They are available in 5, 6, or 7 French sizes, 4" long with 6' leads and can be used on vessels as small as 0.5mm dia. They are lighter than needle mounted probes and less likely to be damaged if dropped.

For applications where a rigid, end-mounted transducer is required, we can mount crystals to the end of a piece of tubing or needle. The smallest size is a 16 gauge needle (recess for 1mm dia 20MHz crystal), and the largest is 1/4" brass tubing (recess for 5mm dia 10MHz crystal). We can also mold epoxy lenses to the crystal face to focus the sound beam. This type of focused probe has been applied in mice to measure cardiac and peripheral blood velocity noninvasively.

Doppler catheters for research use in animals can be made as small as 3 French (1mm dia) on a custom basis. For clinical applications, standard and custom catheters operating at 10 or 20MHz are available from Millar Instruments.