NIR Spectroscopy Produces a Handy Image of Blood Circulation

The researchers utilised two-dimensional (2D) NIR spectroscopic imaging to determine how the supply of blood to the hand is impaired in a patient suffering from systemic sclerosis (SSc).

This impairment is caused by the production of excessive amounts of collagen in those with SSc, which can damage blood vessels. Valentina Hartwig at the Italian National Research Council’s Institute of Clinical Physiology in Pisa wanted to find a non-invasive method for determining how this damage affects the blood supply to specific regions of the body. So she decided to turn to NIR spectroscopy, an analytical technique that detects specific molecules based on their absorption and reflection of light at NIR wavelengths.

NIR spectroscopy can be used to monitor blood supply and circulation by measuring the concentration of oxygenated haemoglobin in biological tissue, but conventional NIR spectroscopy can only measure these concentrations at specific points in the body. To measure the concentrations over a larger area, Hartwig took advantage of a novel NIR spectroscopic camera that irradiates samples with infrared light produced by an array of 470 light-emitting diodes.

“The recent development of NIR spectroscopic 2D imaging offers the possibility of visualising oxygenated haemoglobin distribution in large tissue areas,” explains Hartwig. “In the past, we have used this camera in experimental cardiology to map cardiac muscle tissue oxygenation during open-chest coronary by-pass surgery.”

Together with colleagues from the Institute of Clinical Physiology and the University of Florence, Hartwig used this camera to monitor blood supply in the hand of an SSc patient and a healthy control. The camera produced coloured images of the hands, with blue indicating low levels of oxygenated haemoglobin and red indicating high levels. After first monitoring the blood supply to the hands at normal, resting conditions, Hartwig and her colleagues investigated what happened when they temporarily restricted the supply of blood with a blood pressure monitor, taking an image with the camera every 10 seconds.

Even at resting conditions, Hartwig and her team found that the blood supply was lower in the hand of the SSc patient and also varied more across the hand. After restricting the blood supply to the hands for three minutes, Hartwig and her team found that it quickly returned to its resting state in the healthy control. The blood supply took much longer to return to its resting state in the hand of the SSc patient, with certain parts of the hand, such as the ring finger, returning to the resting state much later than others.

Although this study only involved two subjects, it provides an initial indication that NIR spectroscopic 2D imaging can be used to monitor the supply of blood to specific areas of the body in SSc patients. More evidence is expected to come from a larger clinical study that will begin shortly, says Hartwig.

“The camera has the potential to be employed in the clinical practice to evaluate microcirculatory impairment in systemic sclerosis,” she concludes. “We can hypothesise using the camera to assess dynamic changes after vasoactive drugs, to assess the effectiveness of treatments and to identify responses to specific therapies.”