Imaging blood circulation with NIR spectroscopy

Italian researchers have used 2D near-infrared (NIR) spectroscopic imaging to reveal poor blood circulation in a patient suffering from systemic sclerosis (SSc) — an autoimmune disease resulting in abnormal growth of connective tissue. Their study has been published in JNIRS — Journal of Near Infrared Spectroscopy.

SSc patients suffer from an excessive production of collagen, which can damage blood vessels. Valentina Hartwig, from the Italian National Research Council’s Institute of Clinical Physiology, wanted to find a non-invasive method for determining how this damage affects the blood supply to specific regions of the body.

Hartwig 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. She explained, “The recent development of NIR spectroscopic 2D imaging offers the possibility of visualising oxygenated haemoglobin distribution in large tissue areas.”

In a collaboration with the University of Florence, Hartwig and her colleagues 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, the 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, they 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 parts such as the ring finger taking much longer to return than others.

The study 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, said Hartwig.

“The camera has the potential to be employed in the clinical practice to evaluate microcirculatory impairment in systemic sclerosis,” she said. “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.”