How do I achieve optimal ultrasonic signal quality with an implantable chronic research flow probe?

One week is generally adequate time for tissue growth that will stabilize a flow probe in a chronic implant and produce adequate signal quality for flow measurements. If signal quality after one week is insufficient, consider the following:

FLOWMETER

  • What flowmeter is being used (400-series or T106 or T206)? 
  • The discontinued flowmeter models T106 and T206 will generally register lower signal levels with higher frequency probes such as the 1.5SL flow probe. 
    • The signal quality is much better with a 400-series flowmeter.

CALIBRATION KEY

  • Does the probe have a 4-pin connector?
  • Probes with a 4-pin connector require a calibration “key”. The calibration key must match the probe’s serial number. 
    • Check that the probe size is displayed on the digital display of a 400-Series meter in test mode. It will display the probe size and then NO SIG. If it displays “NO.PR.” then this may be a key from a different probe or the key is possibly bad.

EXTENSION CABLE

Is an extension cable being used?

  • The maximum extension cable length of a probe will depend on the connector type. 
    • With a 4-pin connector, the extension cable should be no more than 1.85 meters long. 
    • Longer cables may degrade the signal. 
    • If it is a 10-pin connector, the cable should be no more than 1.25 meters long.
  • Check that the extension cable is working properly with another probe. 
  • Also, check that the pins are lined up correctly with the indentation in the extension cable.

SWIVEL

Is a swivel being used for conscious measurements in animals with implanted flow probes?

  • Check that the solder connections are wired correctly and there are no loose connections.
  • Remove the swivel and check the probe with an extension cable.

ACUTE SIGNAL QUALITY

  • What was the signal quality with saline before closing the animal? 
  • How many signal bars were lit (400-series flowmeter LED display), or what was the signal strength voltage in test mode? 
    • NOTE: Signal strength will always decrease in a chronic implant over time.
  • A marginal probe signal (~.35 millivolts) may be too low for a reading. 
  • Signal should be > 0.7 volts prior to implanting.

MEDIUM ON PROBE DURING IMPLANT

  • Was any medium used on the probe when implanting?
  • QuickSil is recommended to stabilize nanoprobe positioning.
    • NOTE: Any type of medium in the probe lumen will impede signal quality.

ERROR MESSAGE

  • Is “No acoustic signal” being reported on the Flow Meter?
  • If “No flow signal” is being displayed, the probe may not be on the vessel properly or might be occluded.