By Janet Fang
Posting in Design
To help assess burn victims and their wound healing potential, a microcirculation camera uses laser Doppler imaging to show if and how blood is flowing through the skin.
The FDA-approved, diagnostic imaging device is designed to help assess the extent and severity of burns, and it’s been trialed by burn specialists and reconstructive surgeons at CHUV University Hospital in Lausanne, Switzerland.
In particular, doctors and nurses can take instantaneous digital photos of, essentially, heart beats and the resulting changes to blood vessels – in the OR or at the bedside. This helps them decide whether to undergo surgery or not, up to 3 days sooner.
- Connected to a flexible arm, the camera can be placed over the burn area.
- On the other side, facing the picture-taker, a video screen displays color variations for differences in the intensity of circulation (pictured).
"Red means high blood flow, blue means low blood flow," explains Michael Friedrich of Aïmago, based at Ecole Polytechnique Federale de Lausanne. With this information, the user can see whether the burnt tissue still has blood supply or not; it can also determine the viability of skin tissue before it’s transferred between different body parts.
If the tissue has no blood supply, it can’t recover: “it's going to die so you need to do skin grafting,” Friedrich adds. But if the skin is perfused – with blood still flowing through – then “it's going to heal spontaneously without scarring.”
By making use of the Doppler Effect, laser Doppler imaging (LDI) tracks the movement of the red blood cells to discriminate between perfusion, concentration and average speed of the blood flow.
- The camera fires laser beams at the skin using a near-infrared laser.
- These are reflected by red blood cells in small vessels in the skin.
- The movement of red blood cells results in a tiny shift in the frequency of the light as it impacts upon the cells.
- These Doppler shifts are detected by the device and transformed into color variations on the screen.
- By delivering more than 12 images a second, the camera can detect the effect of the patient’s heart beat in the circulation images – and quickly, to limit time wounds are kept exposed.
There are a range of burn depths between a superficial and a full-thickness burn where even experienced burn clinicians will misdiagnose about a third of the time, but if you add the laser Doppler to clinical judgment, you get it right about 98% of the time.
A rival laser Doppler imager built by Moor Instruments is already in use at several UK hospitals. But it only provides static images. EasyLDI promises to be the real-time, high resolution alternative.
Sep 14, 2011