mNIRS

  I couldn’t make it to Pavia unfortunately. For a look at what you and I missed   click here .     Fortunately for us all, we will be updating the blog with highlights over the coming months. First the meeting organiser sent me this report.   “With participants from all around the world and a programme that ranged from metabolic myopathies to intensive care, from paediatric oncology to wearable technology, mNIRS2026 confirmed that our community has never been more active. A few highlights from the science: Bruno Grassi opened with a compelling keynote on mNIRS in metabolic myopathies; Rogerio Suarez showed how the post-occlusive reperfusion slope outperforms conduit artery FMD as a marker of microvascular health; Stefan Perrey and Rebecca Re gave us a shared language for the technique's physics and limitations; Chris McManus presented McMito, a free platform for standardised mitochondrial capacity assessment; Richie Goulding reminded us that invasive validation...

Muscle near infrared spectroscopy (mNIRS) has developed enormously since Frans Jöbsis first demonstrated in 1977 that near infrared light could be used to monitor oxygen-sensitive signals in living tissue. Today there is a wide range of instruments and an equally wide range of ways in which NIRS is used to study muscle. This is a strength of the field, but it can also make it difficult to understand exactly what different instruments measure, how those measurements are obtained and, most importantly, what they tell us about muscle physiology. I’ve been working with NIRS and oxygen metabolism for many years, and I’ve created MuscleNIRS as a place to discuss some of these questions. The site has two main parts. The  Education  section contains short introductions to the measurements that can be made with mNIRS and the methods used to make them. These are intended to be relatively permanent resources and will be expanded over time. The  Blog  will be less formal and mor...

Methods other than SRS use multiple source–detector distances to estimate StO₂. While the methods vary, a shared principle is that shorter distances sample more superficial tissues, while longer distances sample deeper regions — such as the cerebral cortex or muscle tissue. These methods are sometimes loosely referred to as spatial resolution or self-calibrating approaches and, confusingly, the term spatially resolved spectroscopy is also occasionally used. Importantly, however, these methods do not use the same analytical approach as the classic SRS algorithms used in systems such as the Hamamatsu NIRO or Artinis PortaMon. Among commercial devices, the most widely used has probably been the INVOS system, now sold by Medtronic. The traditional adult sensor uses detectors placed 3 cm and 4 cm from the source. The signal from the shorter separation, which is more sensitive to superficial tissue, is used to reduce the superficial contribution to the signal measured at the longer separatio...

There are methods for measuring absolute muscle tissue oxygen saturation (StO₂) that do not require expensive time-domain or frequency-domain systems. One such method is Spatially Resolved Spectroscopy (SRS). Originally developed in the Hamamatsu NIRO systems, SRS is now best known for its implementation in devices such as the Artinis PortaMon. SRS assumes homogeneous scattering within tissue. To visualize this, imagine shining a torch into a dilute scattering solution such as milk: the light that emerges appears broadly diffused, and its brightness does not change much with small changes in viewing position. This is because scattering redirects light in many directions, creating a relatively uniform glow. If you add a chromophore to the milk, the brightness decreases with distance because of absorption. In an SRS measurement, a single light source is combined with multiple detectors placed close together relative to their distance from the source (or vice versa). The slope of the chan...

This simple approach can be applied to almost any mNIRS system. The principle is to expose the muscle to physiological conditions that produce a minimum and maximum oxygenation signal, and use these to define a 0–100% calibration range. The minimum can be produced by exercise, arterial occlusion using a pressure cuff, or a combination of the two. Exercise increases muscle oxygen consumption, whilst arterial occlusion prevents oxygen delivery, allowing tissue oxygenation to fall towards a minimum. The upper end of the calibration can also be defined in different ways. A commonly used approach is to release an arterial occlusion and use the peak oxygenation produced by the resulting reactive hyperemia as the 100% value. Earlier approaches have also used other physiological reference points. The resulting 0–100% scale is therefore a physiological calibration rather than an absolute measurement of oxygen saturation. Exactly what the 0% and 100% points represent depends upon the calibration...