The influence of a clear layer on near-infrared spectrophotometry measurements using a liquid neonatal head phantom.
It is difficult to test near-infrared spectrophotometry instruments in vivo. Therefore we constructed a liquid phantom which mimics the neonatal head. It consists of a spherical 3.5 mm thick layer of silicone rubber simulating skin and bone and a 0.5 mm thick clear layer of polypropylene imitating cerebrospinal fluid. It acts as container for a liquid solution with Intralipid, 60 micromol l(-1) haemoglobin and yeast. The solution was oxygenated using oxygen and then deoxygenated by the yeast. From the instrumental (Critikon 2020) algorithm, we found that with increasing scattering (0.5%, 1%, 1.5% and 2% Intralipid concentration) the reading was increasingly offset from the expected value of 0 micromol l(-1) by 55.7, 68.6, 76.5 and 80.4 micromol l(-1) (oxyhaemoglobin) and 16.0, 24.4, 29.6 and 31.7 micromol l(-1) (deoxyhaemoglobin). This reduced the range of the oxygen saturation reading from the expected 100% to 31.5, 21.1, 14.3 and 11.5%. Haemoglobin concentration changes were increasingly underestimated by a factor of two to four. For a second algorithm based on the diffusion approximation the offsets were smaller: oxyhaemoglobin 11.4, 17.8, 22.5 and 25.1 micromol l(-1) and deoxyhaemoglobin 1.3, 3.4, 5.2 and 6.0 micromol l(-1). The range of the oxygen saturation reading was higher: 41.3, 29.2, 23.4 and 16.6%. Concentration changes were underestimated by a factor of six to ten. This study demonstrates the need to develop algorithms which take into consideration anatomical structures.
Wolf
M
M
Clinic for Neonatology, University Hospital, Zurich, Switzerland. m-wolf@physics.uiuc.edu
Keel
M
M
Dietz
V
V
von Siebenthal
K
K
Bucher
H U
HU
Baenziger
O
O
D000465:Algorithms; D002555:Cerebrospinal Fluid; D005217:Fat Emulsions, Intravenous; D006257:Head; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D007231:Infant, Newborn; D008954:Models, Biological; D010108:Oxyhemoglobins / Q000032:analysis*; D019047:Phantoms, Imaging; D011126:Polypropylenes; D013055:Spectrophotometry, Infrared / Q000379:methods*
D005217:Fat Emulsions, Intravenous; D006454:Hemoglobins; D010108:Oxyhemoglobins; D011126:Polypropylenes