Measurement of cerebrospinal fluid oxygen partial pressure in humans using MRI

Abstract

Fluid-attenuated inversion recovery (FLAIR) images obtained during the administration of supplemental oxygen demonstrate a hyperintense signal within the cerebrospinal fluid (CSF) that is likely caused by T 1 changes induced by paramagnetic molecular oxygen. Previous studies demonstrated a linear relationship between the longitudinal relaxation rate (R 1 ‫؍‬ 1/T 1 ) and oxygen content, which permits quantification of the CSF oxygen partial pressure (P csf O 2 ). In the current study, CSF T 1 was measured at 1.5 T in the lateral ventricles, third ventricle, cortical sulci, and basilar cisterns of eight normal subjects breathing room air or 100% oxygen. Phantom studies performed with artificial CSF enabled absolute P csf O 2 quantitation. Regional P csf O 2 differences on room air were observed, from 65 ؎ 27 mmHg in the basilar cisterns to 130 ؎ 49 mmHg in the third ventricle. During 100% oxygen, P csf O 2 increases of 155 ؎ 45 and 124 ؎ 34 mmHg were measured in the basilar cisterns and cortical sulci, respectively, with no change observed in the lateral or third ventricles. P csf O 2 measurements in humans breathing room air or 100% oxygen using a Cerebrospinal fluid (CSF) oxygen partial pressure (P csf O 2 ) has been proposed as a surrogate marker for brain or spinal cord tissue oxygenation, given the passive nature of oxygen diffusion (1-5). Historically, investigators have measured P csf O 2 by analyzing fluid obtained by direct cisternal or lumbar puncture, or using implanted oxygen microelectrodes. These methods are inconvenient and invasive, and are limited in terms of spatial information and repeatability. Additionally, methods that remove fluid are prone to errors introduced by exposure of CSF to room air before the analysis is performed (6). It is possible that differences exist between CSF compartments caused by local brain tissue oxygen levels, oxygen permeability-surface area product, oxygen diffusion, CSF flow, and cerebral blood flow (CBF). A noninvasive imaging method to determine P csf O 2 would permit repeated measurements with spatial sensitivity during physiological manipulations. Through these means, a more complete understanding of CSF oxygen dynamics could be obtained that might yield insights into local brain or spinal cord oxygen levels in normal and abnormal physiologic states.Normal CSF at body temperature has MR properties that are essentially identical to those of partially oxygenated water, with a well-regulated pH (7.3) and a trace amount of protein (0.15-0.45 g/L) (7,8). Using invasive means, P csf O 2 has been measured to be between 25-53 mmHg in humans, roughly 25% its room air level (160 mmHg) (2-5,9). Previous studies in humans have suggested that P csf O 2 changes occur in the setting of abnormal brain oxygen metabolism (1,4,5).It is likely that the increased CSF signal within the subarachnoid spaces of the cerebral sulci and basilar cisterns on fluid-attenuated inversion recovery (FLAIR) images in humans breathing supplemental oxygen reflects higher than normal P csf O 2 , whi...

Absence of Po2 change in fetal brain despite Po2 increase in placenta in response to maternal oxygen challenge

“…An increase in PO 2 increases R 1 (where R 1 = 1/T 1 ) due to the paramagnetism of molecular oxygen. 9 The change in this parameter DR 1 (DR 1 = 1/T 1oxygen À 1/T 1air ) has been found to be proportional to DPO 2 in water 10 and blood plasma. 11 The OE-MRI differs from BOLD, 12 which measures changes in the effective transverse relaxation time (T 2 *) related to changes in the concentration of deoxyhaemoglobin, which varies with multiple factors including SO 2 , blood flow and vessel calibre.…”

Optimizing saturation–recovery measurements of the longitudinal relaxation rate under time constraints

“…As demonstrated in a series of recent studies (1)(2)(3)(4), mapping the magnetization longitudinal relaxation rate R 1 of body fluids by MRI holds great potential to be a method of determining the oxygenation (oximetry) of the fluids in vivo. The fluids of interest, e.g., urine, vitreous humor, cerebrospinal fluid (CSF), have long relaxation time constants T 1 (T 1 = 1/R 1 ) in comparison with tissues; thus when the imaging time parameters that are optimal for relaxation measurement of tissue (T 1 ∼ 1 s) are scaled for the body fluids (T 1 ∼ 4 s), the total scan time can be too long to be clinically feasible.…”

Reduction of Oxygen-Induced CSF Hyperintensity on FLAIR MR Images in Sedated Children: Usefulness of Magnetization-Prepared FLAIR Imaging

“…13,19 The evolution of magnetization with and without magnetization preparation was simulated to determine T1-weighting and signal contrast among brain tissues. In the simulation, the imaging and sequence timing parameters used are shown in Table 2, and the tissue relaxation parameters are demonstrated in Table 3.…”

“…In the simulation, the imaging and sequence timing parameters used are shown in Table 2, and the tissue relaxation parameters are demonstrated in Table 3. 13,[21][22][23][24] Because there was no significant difference in the T2 relaxation constant between CSF and oxygenated CSF (oxy-CSF), 10,13 the T2 relaxation constant for oxy-CSF was assumed to be equal to that of the CSF. The simulation was performed with effective TE, where the T2 contrast in the pure T2-weighting sequence was equivalent to the T2 contrast in a sequence with a long refocusing train of radiofrequency with a variable flip angle.…”

“…1,2,4,5,10 Oxygen is a weak paramagnetic substance, which has 2 unpaired electrons that can cause a moderate increase in the T1 relaxation rate. 11,12 Studies have shown that the diffusional transfer of oxygen from blood to CSF and a consequent FLAIR MR signal increase depend on the inhaled oxygen concentration 1,2,4,13 and oxygen delivery methods. 3,10 3D-FLAIR imaging is based on the 3D TSE imaging technique that modulates a refocusing flip angle at the TSE echo-train to maintain relatively steady signal levels during a long train of echo signals, which can provide improved image sharpness, helpful in detecting small structures.…”