Paramagnetic effect of supplemental oxygen on CSF hyperintensity on fluid-attenuated inversion recovery MR images

Abstract

Background and purpose: Oxygen has a known paramagnetic effect and increases CSF signal intensity on fluid-attenuated inversion recovery (FLAIR) MR images. The purposes of this study were to investigate the effect of supplemental oxygen on CSF signal intensity and the arterial partial pressure of oxygen and to determine the possible synergistic effect of oxygen and albumin on T1 shortening effect in vitro.

Methods: Six healthy volunteers underwent FLAIR MR imaging of the brain before and during inhalation of 10 to 15 L/min of 100% oxygen for < or = 30 min. The signal intensity was measured in the subarachnoid spaces and various tissues and correlated with estimated arterial partial pressure of oxygen and arterial carbon dioxide pressure. In vitro measurements were also obtained by using two sets of saline-filled tubes with various concentrations of albumin, one of which was exposed to increased oxygen levels. In vitro T1 relaxation times were calculated to assess the possible synergistic effect of oxygen and albumin.

Results: FLAIR images of healthy volunteers showed increased CSF signal intensity within the basal cisterns and sulci along the cerebral convexities. The CSF hyperintensity was observed immediately after the initiation of supplemental oxygen and remained stable during the oxygen administration. There was approximately a 4- to 5.3-fold increase in signal intensity with supplemental oxygen. The phantom experiments showed a T1 shortening effect of oxygen. Albumin significantly altered T1 relaxation time only at high concentrations of albumin.

Conclusion: Inhalation of increased levels of oxygen led to readily detectable CSF hyperintensity on FLAIR images of healthy volunteers. No significant synergetic effect of albumin and oxygen was noted.

Fig 1.

FLAIR images of a healthy volunteer before (upper) and after (lower) inhalation of 100% oxygen with the use of a sealed mask. CSF hyperintensity is clearly visible in the basilar cistern (left) and sulci over the cerebral convexities (right) after oxygen inhalation.

Fig 2.

Sequential signal intensity ratio change. Signal intensity of various structures normalized to white matter as a function of time after initiation of supplemental oxygen to volunteers shows that signal intensity of prepontine, ambient, and interpeduncular cisterns and sulci over the convexity increases rapidly after oxygen inhalation. No signal intensity changes are seen in the lateral ventricles, brain parenchyma, vitreous (eye), and choroid plexus. PREPON, prepontine cistern; AMBIENT, ambient cistern; INTERPED, interpeduncular cistern; LAT.VENT, lateral ventricle; CHOROID.PL, choroid plexus; CONVEX, sulci over the convexity; GRAY, gray matter; EYE, vitreous of eye; WHITE, white matter.

Fig 3.

Signal intensity to white matter ratio. Measurements of signal intensity ratios of various anatomic structures in healthy volunteers at 30 min with the use of two types of masks show that CSF hyperintensity is significantly higher with the sealed mask compared with the loose mask (P < .01). PREPON, prepontine cistern; AMBIENT, ambient cistern; INTERPED, interpeduncular cistern; LAT.VENT, lateral ventricle; CHOROID.PL, choroid plexus; CONVEX, sulci over the convexity; GRAY, gray matter; EYE, vitreous of eye; WHITE, white matter.

Fig 4.

Transcutaneous oxymetry. Measurement of transcutaneous partial pressure of oxygen (PtcO₂) and carbon dioxide (PtcCO₂) in six healthy volunteers shows markedly high transcutaneous measurement of partial pressure of oxygen (ranging from 300–500 mmHg) after inhalation of 100% oxygen at 20 min. Transcutaneous measurement of partial pressure of oxygen was substantially higher when a sealed mask was used, compared with a loose mask. Transcutaneous measurement of partial pressure of carbon dioxide remains low, and no significant difference (P = .96) was seen between the loose mask and the sealed mask.

Fig 5.

Lower concentrations of albumin did not significantly alter T1 relaxation time. A, T1 relaxation time measurement of a phantom with various degrees of albumin concentration shows marked reduction of T1 relaxation time in a set of tubes with oxygen exposure. No notable changes of T1 relaxation time are seen in a set of tubes without oxygen until the albumin concentration reaches 1250 mg/dL. B, Same data were presented as TR (R1 = 1/T1) with various degree of albumin concentration. These two graphs show nearly linear relaxivity with or without oxygen. The curves of T1 relaxation time with and without oxygen are almost parallel, suggestive of no significant synergistic effect of albumin on T1 shortening of oxygen.