Comparison of dermal vs internal light administration in human lungs using the TDLAS‐GASMAS technique—Phantom studies

Abstract

Oxygen and water vapor content, in the lungs of a 3D-printed phantom model based on CT-images of a preterm infant, is evaluated using Tunable Diode Laser Absorption Spectroscopy (TDLAS) in Gas in Scattering Media Absorption Spectroscopy (GASMAS), that is, the TDLAS-GASMAS technique. Oxygen gas is detected through an absorption line near 764 nm and water vapor through an absorption line near 820 nm. A model with a lung containing interior structure is compared to a model with a hollow lung. Compared to the model with the hollow lung, both the mean absorption path length and the transmitted intensity are found to be lower for the model with the structured lung. A new approach, where laser light is delivered internally into the model through an optical fiber, is compared to dermal light administration, that is, illumination onto the skin, for the model with structure inside the lung. The internal light administration generally resulted in larger gas absorption, and higher signal-tonoise ratios, compared to the dermal light administration. The results from the phantom measurements show great promise for the internal illumination approach and a natural next step would be to investigate it further in clinical studies. K E Y W O R D S3D-print, GASMAS, light scattering, optical phantom, oxygen evaluation, preterm infant, TDLAS

Changes in pulmonary oxygen content are detectable with laser absorption spectroscopy: proof of concept in newborn piglets

“…Likewise, calculations of oxygen concentrations were possible on a 3D phantom of a newborn infant´s torso, when applying the light source internally. 14 Autopsy of one piglet did not reveal any visually detected damage to the esophagus. However, we did not study the possible microscopic damages to the tissue from slight temperature increases or physical damage from the optical fiber probe.…”

“…This approach has successfully been used in our phantom studies. 14 We hypothesized that the GASMAS method with an external as well as an internal light source probe would detect changes in pulmonary O 2 gas concentration, including responses to induced local lung pathologies in newborn piglets.…”

Gas in scattering media absorption spectroscopy on small and large scales: Toward the extension of lung spectroscopic monitoring to adults

“…In scaling up lung monitoring from newborn to larger children or adults, internal light administration is clearly advantageous over light injection from the surface of the chest [33–35]. Internal fiber‐optical light administration would not present any major complication, since the patients mostly in need would anyway be intubated with an endotracheal tube, connected to a ventilator.…”

“…In addition, the specific gas absorption fraction of the total light received is enhanced, since all detected photons must have passed gas‐filled lung structures, and not only surrounding normal tissue. The advantages have recently been demonstrated in phantom work [34] and in a study on anesthetized piglets [35].…”

Numerical investigation of the influence of the source and detector position for optical measurement of lung volume and oxygen content in preterm infants

“…Previous study focused in advancing GASMAS for O 2 gas sensing in the lungs of pre-term neonates included theoretical modelling [26], tissue phantom measurements [27][28][29], and feasibility studies with new-born piglets [30], and healthy full-term infants [22,31,32]. Most of these studies have been conducted noninvasively with both source and detector placed on the thorax wall.…”