V-Series Micro-Probes

Transonic Systems' V-Series probes for microcirculation with Transonic flowmeters produce repeatable high resolution volumetric blood flow measurements on vessels as small as 250 micron diameter, but also in vessels as large as 1000 microns. This designated diameter range overlaps with our 1 mm R-Series flowprobe. Choosing the appropriate series, size and style probe for your application will enhance the absolute accuracy of the flow measurement.

Accuracy Specs Physical Specs Connectors Accessories Ordering Key

Acute Protocols: V-series probes are designed to overcome the difficulties in obtaining stable, small volume measurements in vessels ranging from 250 – 900 microns diameter. Micro-vessels are positioned in the V-groove of the reflector, the position of highest sensitivity. Stainless steel handles are recommended to help stabilize the probe with a micromanipulator for lengthy acute procedures. Suitable acoustic couplant (Surgilube) is used to transmit the ultrasound.

Choosing Probe Size: Probe size should be chosen so that the full diameter of the vessel nestles within the triangle formed by the V-reflector (see diagram below). It is also important that the vessel can be isolated a sufficient length along the vessel without side-branching to fit the width of the reflector (see probe dimensions and required vessel segment lengths). For acute measurements in larger vessels (750 microns and larger) R- & S-Series probes may be used.

V-Series Reflective Path

If you look into a 90o corner consisting of two mirrors, you see a coherent picture of yourself (but flipped over, so your right ear is on the left side of the image). This is the reflective path of the V-probes; light scattered off your face first hits one mirror, then the other, before it returns to your eye. In V-probes, these rays intersect the flow four times: the incident beam intersects the flow; then, on the first reflection off the mirror surfaces, part of the beam traverses the vessel from right to left, another traverses it from left to right; the flow is sampled a fourth time when these two halves of the beam, are reflected back to the receiving transducer. This 4X sampling of the flow enhances resolution for micro-sized vessels.

Affect of Vessel Diameter on Flow Measurement Accuracy

With all Transonic probes, flow sensitivity is optimized for a specific range of vessel diameters. In V-probes, the permissible vessel diameter is small compared to the physical vessel window. Substantial errors result when the vessel fills the full probe window.

Sensitivity Flow Sensitivity Profile within V-Probe Window For proper flow readout, the vessel must be positioned within the reflector bracket's high-sensitivity triangle. For easy alignment, the preferred position is in the bottom of the V-groove.

Accurate Selection of V-Probes

Before flow measurements are made, vessel diameter must be measured in order to select the proper probe size. For instance, it is possible to fit a 1 mm diameter vessel inside a 0.5V probe. However, this would lead to erroneous measurement results since most of the vessel would be positioned outside the high intensity triangle. Optical pieces (2.5 to 4X magnification) and a calibrated microsurgical scale are necessary to do this accurately.

Probe size is selected according to the following chart.

• 250 - 500μm diameter vessels --- 0.5V
• 350 - 700μm diameter vessels --- 0.7V

V-Series Probes with Flexi-Handles

1 mm V-Probe with Flexihandle

The new flexi-handle on V-Series probes allow easier application of the V-probe on a vessel. The stainless steel handle is positioned on the cable 5 mm from the probe head.

This extra cable segment allows the probe tip to be flexible and compliant on tissues without sacrificing the stability provided by the rigid handle. Probes resist twisting and are easily mounted in a micromanipulator.

V-probes with the new flexi-handle style deter tugging on the micro-vessel and its consequent vessel spasm and shutdown. Positioned so that the probe opening faces up permits:

• better visualization of the vessel;
• easier application of acoustic gel;
• easier elimination of trapped air bubbles.

Positioning a V-Probe on a Vessel

Accurate flow measurement requires the micro-vessel is carefully positioned in the high sensitivity portion of the probe. The vessel should be "suspended" in the notch of the V-reflector, without causing a constriction of the vessel. Use of a micro-manipulator for this is helpful.

• Prefill the probe with acoustic couplant to insure that all air pockets in the probe are removed. (Transonic flowmeters will indicate good received test signal when all air bubbles are filled).
• Mount the probe handle in the micro-manipulator and position the vessel approximately in the notch of the "V". Add couplant, if necessary.
• Gently "pull" the probe into position using the micro-manipulator. If the flow reading on the flowmeter starts to decrease during this procedure, the reflector may now be constricting the vessel. Back off slightly to restore full flow.
• Verify position of vessel with the optical magnification of an eye piece or microscope.