Here is a selection of the questions we see asked most frequently, and our answers to them.

For the principles of Laser Doppler Flowmetry, click here.
For application notes and citations lists, click here.

For further information on our instruments or an on-site demonstration please contact us directly.

We look forward to hearing from you!
 
 

• What physiological parameters do your instruments measure?
• What makes your instruments unique?
• What are the typical applications for your instruments?
• Do I need separate instruments to measure all supported parameters?
• How do your blood perfusion instruments work?
• What are your probes made of?
• What are the advantages of fiber-optic probes?
• How small are the multi-parameter probes?
• Are your multi-parameter probes MRI-compatible?
• Do your instruments support the use of multiple probes at the same time?
• Are your multi-parameter probes supplied sterile?
• From what size range of blood vessels can you make laser-Doppler perfusion measurements?
• What is the sampling volume of your laser-Doppler probes?
• What are the units of laser-Doppler blood perfusion?
• Do you offer on-site demonstrations of your instruments?

 
What physiological parameters do your instruments measure?
The unique technology provides simultaneous parameters which represent tissue or organ vitality in real-time.  The physiological parameters most useful to the researcher are those which provide information specifically relating to oxygen balance (i.e. supply/demand) in tissues exposed to changes in oxygen supply (i.e. during ischaemia or reperfusion).  In addressing this requirement, a range of in vivo tissue monitoring instruments were developed that utilize fiber-optic micro-probes to provide real-time data for tissue oxygenation (ptO2), tissue blood perfusion (blood flow) and tissue temperature.  The simultaneous measurement of all of these parameters from a single tissue site provides the researcher with unique insights into a whole range of hypoxic and ischaemic related physiological disorders.

What makes your instruments unique?
There are several factors that make our instruments unique in the industry; for example, the ability to simultaneously obtain tissue oxygenation, blood perfusion and temperature information from a single combined probe and therefore from the same tissue micro-region; MRI-compatibility of our probes; and multi-channel ability for the simultaneous monitoring of all these physiological parameters simultaneously from up to four different tissue sites.

What are the typical applications for your instruments?
Our instruments have proved popular in applications covering such disciplines as tumour research, cerebral monitoring, free-flap/pedicle-flap transfer surgery, transplantation surgery and vital organ monitoring, pharmacology, as well as peripheral vascular disease research.

Do I need separate instruments to measure all supported parameters?
Yes, our instruments are designed as modular units for ultimate user flexibility.  We therefore manufacture two categories of instruments; (a) tissue oxygen and temperature monitors, and (b) tissue blood perfusion monitors.  These units can be used either as stand-alone devices in their own right or connected together (in a ‘stack’) to take advantage of our combined, multi-measurement parameter probes.

How do your blood perfusion instruments work?
Our instruments utilize the well-established method of laser-Doppler flowmetry (LDF) to provide a continuous measure of tissue blood perfusion.  LDF works by illuminating a small region of tissue under observation with low power laser light from a probe containing optical fiber light guides. Laser light from one fiber is directed towards the tissue and is scattered within the tissue.  Some of the scattered laser light is incident upon moving red blood cells within the tissue and this light becomes Doppler-frequency shifted as a result.  A second optical fiber collects this backscattered, Doppler shifted light from the tissue and returns it to detector within the monitor.  The photo-detected signal comprises a broad spectrum of Doppler frequency shifted signals generated as a result of the movement of red blood cells within the tissue.  Microvascular blood perfusion is electronically calculated as the product of mean red blood cell velocity and mean red blood cell concentration in the small measuring volume of tissue under illumination from the probe. 

What are your probes made of?
All our invasive microprobes probes are constructed from optical fibers with outside diameters of 125 microns or 220 microns depending on probe type.  Fibers are typically protected in PVC or silicone sleeves and can be manufactured at lengths up to 7 meters (approx. 23 feet) for MRI application.  We also manufacture a range of non-invasive surface-type probes for measuring microvascular perfusion and temperature only.

What are the advantages of fiber-optic probes?
The use of fiber-optic cables allows our probes to be minimally invasive, to be factory pre-calibrated, to offer MRI-compatibility, as well as to be lightweight and physically flexible.

How small are the multi-parameter probes?
Our most complex probe, which combines pO2, blood perfusion and integrated temperature functionality is approximately 480 microns in diameter, roughly equivalent to the outside diameter of a 24G hypodermic needle.

Are your multi-parameter probes MRI-compatible?
Yes, since our probes are based on fiber-optic technology they are intrinsically MRI-compatible.  The temperature sensor (a 60 mm diameter thermocouple) constitutes the only (non-ferrous) metallic component in our probes and in some magnets, may cause slight field interference.  For this reason, we also offer a range of probes without the temperature sensor element.

Do your instruments support the use of multiple probes at the same time?
Yes, range of instruments support up to four probes simultaneously; thereby providing physiological data from up to four different tissue sites at the same time.  This multi-channel ability is extremely useful when comparing pathological versus control tissue at the same time.  Also, the heterogeneity of tissue oxygen and blood perfusion in some (e.g. tumor) tissues can be immense and the ability to monitor from more than one tissue site at the same time provides unique possibilities for studying spatial as well as temporal changes.

Are your multi-parameter probes supplied sterile?
No.  Our multi-parameter probes are not supplied sterilized.  However, all are manufactured ‘clean’ in a class 10,000 clean room facility and are shipped in sealed Tyvec™ pouches.

From what size range of blood vessels can you make laser-Doppler perfusion measurements?
All laser-Doppler systems are primarily designed to measure microvascular blood perfusion in the microvasculature tree rather than in large, discrete blood vessels.  It is possible to measure blood flow in isolated arterioles and venules up to approximately 500um in diameter.

What is the sampling volume of your laser-Doppler probes?
For most tissues the mean sampling depth is in the region of 0.5-1.0 mm with a typical sampling volume in the region of 0.3-0.5 mm3.  These values could be higher in regions where reduced photon absorption would be expected due to depleted erythrocyte concentration.  These (unpublished) values have been obtained heuristically through many years of experience and are based on both in vitro observations and mathematical modeling of photon diffusion through ‘imaginary tissues’ using Monte-Carlo techniques.

What are the units of laser-Doppler blood perfusion?
The laser-Doppler technique for real-time blood perfusion measurement provides arbitrary, non-absolute, units for blood perfusion since the actual measurement sampling volume/depth can only be determined by identifying which erythrocytes have interacted with the light remitted from the tissue, which in turn, is principally dependant on two parameters; namely the optical scattering and the optical absorption coefficients of the tissue under observation.  Since both of these coefficients are entirely dependent on the site of observation and perfusion of the microvasculature at the time of measurement, it is impossible to determine the actual sampling volume at any tissue site and thus to express the measured component in absolute terms.  The advantage of the laser-Doppler technique lies in observing continuous and quantifiable changes relative to baseline (control) measurements.

Do you offer on-site demonstrations of your instruments?
Yes, we will be happy to arrange for an on-site demonstration of our products by an experienced product specialist.  Ideally this will involve an in vivo model of choice or a full simulation of your application in order to maximize the benefit of the demonstration to the user.  On-site demonstrations are free of charge and can typically be arranged at 2 - 4 weeks notice.