Elsevier

NeuroImage

Volume 54, Issue 1, 1 January 2011, Pages 344-349
NeuroImage

Non-invasive measurement of oxygen saturation in the spinal vein using SWI: Quantitative evaluation under conditions of physiological and caffeine load

https://doi.org/10.1016/j.neuroimage.2010.08.020Get rights and content

Abstract

Susceptibility-weighted imaging (SWI) has been used for quantitative and non-invasive measurement of blood oxygen saturation in the brain. In this study, we used SWI for quantitative measurement of oxygen saturation in the spinal vein to look for physiological- or caffeine-induced changes in venous oxygenation. SWI measurements were obtained for 5 healthy volunteers using 1.5-T MR units, under 1) 3 kinds of physiological load (breath holding, Bh; hyperventilation, Hv; and inspiration of highly concentrated oxygen, Ox) and 2) caffeine load. Oxygen saturation in the anterior spinal vein (ASV) was calculated. We evaluated changes in oxygen saturation induced by physiological load. We also evaluated the time-course of oxygen saturation after caffeine intake. For the physiological load measurements, the average oxygen saturation for the 5 subjects was significantly lower in Hv (0.75) and significantly higher in Bh (0.84) when compared with control (0.80). There was no significant difference between Ox (0.81) and control. Oxygen saturation gradually decreased after caffeine intake. The average values of oxygen saturation were 0.79 (0 min), 0.76 (20 min), 0.74 (40 min), and 0.73 (60 min), respectively. We demonstrated a significant difference in oxygen saturation at 40 and 60 min after caffeine intake when compared with 0 min.

In conclusion, we demonstrated the feasibility of using SWI for non-invasive measurement of oxygen saturation in the spinal vein. We showed changes in oxygen saturation under physiological as well as caffeine load and suggest that this method is a useful tool for the clinical evaluation of spinal cord oxygenation.

Research Highlights

►Non-invasive measurement of oxygen saturation in the spinal vein was feasible by using SWI. ►Absolute value of oxygen saturation can be calculated by using SWI. ►SWI can be a useful tool for the clinical evaluations of spinal venous oxygenation. ►Regulatory function exists in the spinal arteries as well as in the brain.

Introduction

Susceptibility-weighted imaging (SWI) is extremely sensitive to differences in local magnetic susceptibility, which can be induced by hemorrhage, iron deposit, calcification, and deoxygenated hemoglobin (deoxy-Hb) (Haacke et al., 2004). SWI has been reported to be useful for the evaluation of the intracranial veins (Koopmans et al., 2008), because SWI can clearly depict normal venous blood, utilizing the phase shift induced by paramagnetic effect of deoxy-Hb in the vein. Specifically, oxygen saturation in the vein can be measured using SWI, from the susceptibility phase difference (∆φ) between blood in the vein and surrounding tissue with an infinite cylinder approximation (Shen et al., 2007).

SWI has been reported to be useful for clinical diagnosis and for the assessment of some diseases, mainly those affecting the brain; nonetheless, SWI can also be beneficial in the assessment of conditions of the spinal cord. For example, patients with spinal arteriovenous malformations (AVM) exhibit increased oxygen saturation in the draining vein. Normalized oxygen saturation in the draining vein can be detected by SWI (Fujima et al., 2010). In the case of patients with multiple sclerosis (MS), decreased oxygen uptake leading to decreased venous vasculature in the brain was assessed by using SWI (Ge et al., 2009), and this technique can be applied to spinal MS as well. Evaluation of tumor tissue vascularization and visualization of the dilated draining vein by using SWI in patients with spinal tumors could help in the grading of gliomas (Park et al., 2009).

In healthy individuals, an auto-regulatory function maintains a constant cerebral blood flow (CBF) despite changes in blood pressure (Lassen, 1959). CBF is additionally regulated by changes in the partial arterial pressure of oxygen or carbon dioxide (Ainslie and Duffin, 2009). For example, hyperventilation leads to decreased carbon dioxide and increased oxygen levels in an artery, which promotes vasoconstriction of the cerebral artery and decreased CBF. Conversely, breath holding increases carbon dioxide and decreases oxygen in an artery, leading to increased CBF. SWI was previously used to evaluate these changes in CBF, by measuring the phase shift of a vein, which reflects venous deoxy-Hb (Fushimi et al., 2010, Sedlacik et al., 2008b). CBF was shown to be modulated by the activity of drugs such as caffeine (Cameron et al., 1990) or acetazolamide (Grossmann and Koeberle, 2000). SWI was also used to evaluate vasoconstriction in the small arteries, and decreased CBF caused by caffeine (Sedlacik et al., 2008a). However, although these studies reported a change in blood flow, they did not quantify oxygen saturation. Furthermore, all these studies were performed in the brain. To our knowledge, no such study has been performed in the spinal cord.

Since the spinal cord is an important part of the central nervous system, we elected to ask if the same mechanisms governed the regulation of oxygen saturation in the spinal cord and the brain. The main goals of our study were to use SWI to 1) quantify oxygen saturation in the spinal cord and 2) to evaluate changes in oxygen saturation and spinal blood flow after a physiological or caffeine load.

Section snippets

Subjects

Five healthy volunteers (4 males and 1 female; age range, 28–30 years; average, 29 years) were recruited for this study. None of the study participants had a past history of spinal cord diseases or symptoms. For evaluation, the subjects were asked to fill in a questionnaire that enquired about their caffeine-related habits. None of them seemed to consume large amounts of caffeine; their daily caffeine intake was 1–2 cups of coffee. Therefore, all subjects were treated as one uniform group and

Results

MR examinations were successfully performed on all study participants with no adverse events recorded before or after the examination. During breath holding, on an average, they were observed to breathe (small breath) once in 20–30 s, and this breath lasted for about 2–4 s. The ASV could be detected in all participants (Fig. 2, Fig. 3). For the physiological load measurements, the average Y values for Rc, Bh, Ox and Hv were 0.80, 0.84, 0.81, and 0.75, respectively (Fig. 4). ANOVA analysis showed

Discussion

In this study, we used SWI to non-invasively measure changes in oxygen saturation of the ASV after a physiological or a caffeine load. We showed that a physiological or caffeine load resulted in alterations in blood flow, which in turn induced changes in venous oxygenation in the spinal cord as well as in the brain. We also demonstrated the feasibility of using SWI as a non-invasive tool to detect and evaluate these changes by measuring oxygen saturation in the spinal vein.

Our results on oxygen

Acknowledgment

The authors thank the entire staff at Hokkaido University Hospital for their assistance in data collection.

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