Cerebral hemodynamics of hypoxic-ischemic encephalopathy neonates at different ages detected by arterial spin labeling imaging

Abstract

OBJECTIVE:

This study aims to investigate the application value of three-dimensional arterial spin labeling (ASL) perfusion imaging in detecting cerebral hemodynamics of neonates with hypoxic-ischemic encephalopathy (HIE).

METHODS:

Sixty normal full-term neonates and 60 HIE neonates were enrolled in this study and were respectively divided into three groups: the 1–3 days group, the 4–7 days group, and the 8–15 days group. The brains of these neonates were scanned with the 3D ASL sequence, and cerebral blood flow (CBF) images were obtained. The CBF values of the bilateral symmetrical brain regions and brain stem were measured on CBF images, and the values were averaged. The cerebral blood flow of HIE neonates in the 1–3 days group, the 4–7 days group, and the 8–15 days group was compared with normal neonates at matched ages, and the characteristics of cerebral hemodynamics in HIE neonates at different ages were summarized.

RESULTS:

The CBF values of the basal ganglia, thalamus, and brainstem in the 1–3 days HIE group were higher than normal neonates at matched ages, and the CBF value of the frontal lobe was lower than the normal group, and the differences were statistically significant (P < 0.05). The CBF values of the basal ganglia, thalamus, corona radiata, and frontal lobe in the 4–7 days HIE group were lower than the normal group, and the differences were statistically significant (P < 0.05). There were no significant differences in CBF values of different brain regions between the 8–15 days HIE and normal groups (P > 0.05).

CONCLUSION:

Early hyperperfusion of the basal ganglia and thalamus is helpful for early diagnosis and prognosis of HIE.

Keywords

Neonatal hypoxic-ischemic encephalopathy arterial spin labeling imaging magnetic resonance imaging cerebral blood flow

1 Introduction

Neonatal hypoxic-ischemic encephalopathy (HIE) is a destructive disease that mainly causes nerve and white matter damage. HIE causes great harm to the developing brain. It is one of the critical causes of infant death and the leading potential cause of epilepsy in full-term infants [1 –3]. In China, the incidence rate of neonatal HIE is 3–6/1000, and 20–30% of patients may have sequelae in varying degrees [4, 5].

Magnetic resonance imaging (MRI) has no radiation, has good spatial and temporal resolution, and is the most sensitive and specific imaging method in diagnosing neonatal HIE. A study by Baranger J et al [6] analysing methods of neonatal brain perfusion imaging suggests that ultrasound and MRI currently appear to be the imaging techniques best suited to meet the limitations and specificity of the neonate. The common areas of specific nerve injury in HIE include the basal ganglia, thalamus, white matter, limbic system, and hippocampus. Some common imaging findings can be found by non-enhanced MRI scanning. However, the detection of fine images still depends on some functional MRI methods.

Proton magnetic resonance spectroscopy (MRS) of the basal ganglia and thalamus is one of the best predictors of neurodevelopmental outcome [1]. The self-regulation damage after hypoxia-ischemia may lead to further injury [3]. A previous study revealed that early (2–4 days) hyperperfusion always exists in the brain-damaged area of neonatal HIE [4]. Perfusion weighted imaging has been proven to be able to detect blood-brain barrier hyperperfusion. Perfusion imaging of arterial spin labeling (ASL) has the advantages of non-exogenous contrast agent, non-invasion, and high repeatability, and is very suitable for neonatal cerebral perfusion imaging. The sensitivity and specificity of ASL for HIE are 100% and 95%, respectively, higher than those of diffusion-weighted imaging (DWI). The advantage of the ASL sequence is that it can evaluate the reperfusion phenomenon associated with delayed cell death. Therefore, it can be used to predict the outcome and assess neuroprotective therapy. A study has confirmed hyperperfusion in the basal ganglia and thalamus in neonates with HIE [7], which can predict the prognosis, but the impact of age on the results was not considered.

The purpose of this study was to investigate the changes in cerebral perfusion in neonates with HIE and normal neonates at different ages.

2 Materials and methods

2.1 Subjects and grouping

A total of 120 neonates born at our hospital from December 2016 to March 2018 were enrolled, with 60 cases in each group. The control group was 60 full-term normal neonates examined by non-enhanced MRI and 3D ASL scanning for other diseases. The control group included 34 boys and 26 girls aged 2–15 days, and the Apgar scores of all neonates were 10. Neonates in the control group did not have neonatal HIE, asphyxia, epilepsy, congenital heart disease, or other diseases that may affect cerebral blood flow. No medication associated with such conditions was given, and no abnormality was found on non-enhanced brain MRI scanning. The control group was divided into three groups according to their age: the 1–3 days group, 20 neonates, including 12 males and eight females; the 4–7 days group, 20 neonates, including 13 males and seven females; the 8–15 days group, 20 neonates, including 11 males and nine females.

There were 60 neonates diagnosed with HIE in the HIE group. The inclusion criteria were based on the diagnostic criteria of neonatal HIE: neonates with a history of abnormal obstetrics features and severe intrauterine fetal distress, or neonates with a history of obvious asphyxia during delivery, neonates with the presence of nervous system symptoms shortly after birth and lasting for more than 24 hours, such as changes of consciousness, muscle tension, abnormal primitive reflex, convulsions in severe cases, increased tension of anterior fontanel and brainstem signs. Exclusion criteria: neonates with convulsions caused by a birth injury, electrolyte disorder, intracranial hemorrhage, and other causes, as well as craniocerebral injury caused by genetic metabolic diseases, intrauterine infection and other congenital diseases [8]. The neonates in the HIE group were also divided into three groups according to their ages: the 1–3 days group, 20 neonates, including 13 males and seven females; the 4–7 days group, 20 neonates, including 12 males and eight females; the 8–15 days group, 20 neonates, including 12 males and eight females. None of the patients received hypothermia treatment. All patients underwent non-enhanced MRI scanning and 3D ASL sequence scanning. The Ethics Committee of our hospital approved the present study. All parents of the neonates were informed and signed the informed consent form.

2.2 Examination methods and scanning parameters

All data were collected by a GE Discovery 750B 3.0T MRI scanner, the acquisition coil adopted was a 16-channel coil. The scanning sequence included conventional T1WI, T2WI, DWI, T2-FLAIR and special 3D ASL imaging sequences. The 3D ASL sequence parameters were repetition time (TR) = 4,376 ms, echo time (TE) = 11 ms, flip angle = 111°, field of view (FOV) = 16 cm×16 cm, slice thickness = 4.0 mm, post-labeling delay (PLD) = 1,025 ms, three times of excitation. The T1WI parameters were TR = 1,750 ms, TE = 24 ms, FOV = 16×16 cm, slice thickness = 4 mm, inter-slice gap = 1.5 mm, flip angle = 111°, one time of excitation. The T2WI parameters were TR = 3,703 ms, TE = 95 ms, FOV = 16×16 cm, slice thickness = 4 mm, inter-slice gap = 1.5 mm, flip angle = 111°, one time of excitation. The T2-FLAIR parameters were TR = 9,000 ms, TE = 145 ms, FOV = 16×16 cm, slice thickness = 4 mm, inter-slice gap = 1.5 mm, flip angle = 111°, one time of excitation.

MRI was performed while the neonates were asleep. At 15–20 minutes before the scanning, pediatricians gave an intramuscular injection of phenobarbital, 5 mg/kg. After falling asleep, the neonates were taken to the MRI room for examination and placed in the supine position. The head was safely placed in the head coil for fixation, and sponge pads were put on both sides of the head to fix it further. Positioning line: coil positioning slots were attached to the eyebrow arches on both sides. Measures were taken to make sure the anatomical structure of both sides was symmetrical. During the transfer from the department to the MRI, the neonate was accompanied by a neonatal specialist or nurse, who was present during the imaging process and monitored breathing to ensure optimal care to reduce risks. If the neonate had problems during the examination (including T1, T2, T2-FLAIR, DWI, and 3D ASL sequences), the MRI scan stopped immediately.

2.3 Data post-processing

All data were uploaded to a GE AW 4.6 post-processing workstation, and the FuncTool software obtained CBF images. All measurements and film reading were performed by three experienced attending physicians or deputy chief physicians. The CBF value of the region of interest (ROI) was measured, and the size of the ROI was 55±2 mm². Each of the doctors measured once, and the average value of the three measurements was calculated and regarded as the result. Measures were taken to ensure that all neonates had the same area and shape of ROI. The area of the ROI was determined according to the anatomical landmarks to ensure that the area was consistent. A method of copying the opposite ROI was adopted to ensure that it was in a symmetrical position. The ROIs included the bilateral basal ganglia, thalamus, corona radiata, white matter of the frontal and parietal lobes, and brain stem. The average of the CBF values of the bilateral basal ganglia, thalamus, corona radiata, frontal lobe, and parietal white matter was regarded as the target values.

2.4 Statistical analysis

Data were analyzed using statistical analysis software SPSS 23.0. Continuous variables were expressed as mean±standard deviation (X±SD). The normality was tested using the Shapiro–Wilk test. The homogeneity of variance was tested using Levene’s test. Measurement data were compared between the two groups using an independent sample t-test. P < 0.05 was considered statistically significant. In the present study, all tests were two-sided tests, α= 0.05.

3 Results

1. In the 1–3 days groups, the CBF values of the basal ganglia, thalamus, and brainstem in the HIE group were higher than the control group, and the differences were statistically significant (P < 0.05). The CBF value of the frontal lobe was lower than the control group, and the difference was statistically significant (P < 0.05, Figure 1). The CBF value of the corona radiata was higher than the control group, and the CBF value of the parietal lobe was lower than the control group, and the differences were not statistically significant (P > 0.05, Table 1).

Fig. 1

Histogram of CBF value in normal group and HIE group at 1–3 days of age.

Table 1

Comparison of CBF values of neonates in normal group and HIE group at 1–3 days

Groups	Basalganglia	Thalamus	Corona radiata	Frontal white matter	Parietal white matter	Brain stem
Normal group (N = 20)	26.02±3.28	25.77±2.67	22.55±3.45	25.18±2.86	10.78±1.39	31.66±3.91
HIEgroup (N = 20)	31.53±8.82	31.6±8.64	24.43±7.44	21.42±2.57	11.34±2.32	38.2±7.54
t	–2.617	2.882	–1.026	4.374	–0.934	–3.447
P	0.015	0.009	0.312	< 0.001	0.356	0.001

2. In the 4–7 days groups, the CBF values of the basal ganglia, thalamus, corona radiata, and frontal lobe in the HIE group were lower than the control group, and the differences were statistically significant (P < 0.05, Figure 2). The CBF value of the brainstem was higher than the control group, and the difference was not statistically significant (P > 0.05). The CBF value of the parietal lobe was lower than the control group, and the difference was not statistically significant (P > 0.05, Table 2).

Fig. 2

Histogram of CBF value in normal group and HIE group at 4–7 days of age.

Table 2

Comparison of CBF values of neonates in normal group and HIE group at 4–7 days

	Basalganglia	Thalamus	Corona radiata	Frontal white matter	Parietal white matter	Brain stem
Normal group (N = 20)	30.22±6.05	28.62±6.22	24.79±4.71	25.64±5.94	10.69±1.40	31.30±6.25
HIEgroup (N = 20)	24.09±3.92	24.34±4.55	21.32±4.86	22.21±3.63	9.93±2.14	32.94±5.60
t	3.795	2.485	2.293	2.203	1.313	0.877
P	0.001	0.017	0.027	0.035	0.197	0.386

3. There were no significant differences in the CBF values of different brain regions between the 8–15 days HIE and control groups (P > 0.05, Figure 3 and Table 3).

Fig. 3

Histogram of CBF value in normal group and HIE group at 8–15 days of age.

Table 3

Comparison of CBF values of neonates in normal group and HIE group at 8–15 days

	Basalganglia	Thalamus	Corona radiata	Frontal white matter	Parietal white matter	Brain stem
Normal group (N = 20)	33.09±3.36	29.27±4.45	27.16±3.34	24.05±3.37	12.12±2.11	31.66±3.91
HIEgroup (N = 20)	31.18±4.58	28.7±4.74	25.93±3.36	23.71±3.95	12.08±1.53	38.2±7.54
t	1.506	0.387	1.108	0.299	0.078	0.571
P	0.140	0.701	0.275	0.767	0.938	0.571

4 Discussion

HIE is the most common cause of infant acquired brain injury [9]. The most common causes of hypoxic ischaemia are placental abruption, umbilical cord prolapse and uterine rupture. In addition, prenatal hypotension, severe hypoxia or infection; or postnatal shock, respiratory, or cardiac arrest can lead to ischaemic-hypoxic encephalopathy in the newborn [10]. The imaging findings are affected by the neonatal brain maturation stage, the severity and duration of ischemic injury, and other factors [11]. Predicting the neural development of the affected neonates early is vital to developing treatment interventions. It is of great significance to observe the microcirculation after neonatal HIE brain injury.

In addition to clinical attacks, at 18–24 months old, the total number of lesions, the size of lesions, and the involvement of the basal ganglia and thalamus are significantly correlated with neurodevelopmental abnormalities [12].

This study revealed that the CBF values of the basal ganglia, corona radiata, thalamus, and brainstem in the 1–3 days HIE group were higher than normal neonates at matched ages, and the difference was statistically significant, which is consistent with reports in previous literature [13, 14]. The measurement of cerebral perfusion can be adjusted according to the time of MRI scanning. Regarding the MRI scanning time points (from the first day after birth to the second week after birth), some studies revealed that HIE neonates had cerebral hyperperfusion, while others had cerebral hypoperfusion [15]. In one study [16], ASL imaging was performed twice in each asphyxiated neonate in the first week after birth. It was revealed on the first day after birth that the brain regions of neonates with hypothermia treatment had hypoperfusion subsequently and presented with MRI evidence of HIE brain damage. On the second day after birth, the brain injury areas of these neonates presented with hyperperfusion; contrary to neonates without hypothermia treatment, hyperperfusion in the basal ganglia can be seen on the first day after birth. The reason for the absence of hypoperfusion on the first day after birth in this study may be that none of the patients received hypothermia treatment. Hypoperfusion on the first day after birth may be related to hypothermia treatment, which is consistent with the above-mentioned studies. In this study, in the 1–3 days HIE group, most of the neonates who underwent MRI examination on the first day after birth underwent it 20 hours after birth; the MRI may not have been done at the best time for detecting hypoperfusion.

The pathological changes of the basal ganglia and thalamus are the markers of acute hypoxia-ischemia in full-term neonates. One month after HIE, the prognosis of neonates with atrophy of the basal ganglia and thalamus is poor [17]. Severe acute hypoxia-ischemia is related to the damage of the posterior limb of the internal capsule, brain stem, hippocampus, and cortex. Cortical gray matter damage is considered the cause of the cortex’s abnormal signal intensity, especially in the central fissure and around the insular lobe. The metabolic rate of gray matter neurons and early myelin sheath tissue is higher than that of peripheral white matter in the immature brain. In this way, although the duration of hypoxic-ischemic etiology may be relatively short, the posterior limb of the internal capsule, brainstem, hippocampus, and cerebral cortex are more susceptible to acute hypoxic-ischemic injury than white matter. The abnormal signal of the posterior limb of the internal capsule is closely related to the damage of the adjacent basal ganglia and thalamus. The absence of central gray matter (basal ganglia, thalamus) damage will not lead to extensive white matter damage. However, severe white matter damage is closely related to injuries of the basal ganglia and thalamus, indicating deep central gray matter damage in case of long-term hypoxic-ischemic injury. In this study, the neonates in the 1–3 days HIE group also had brainstem hyperperfusion. It is believed that hyperperfusion may be caused by local damage or by the interference of multiple intracranial arteries around the brainstem.

A study revealed that the changes in cerebral perfusion and cerebral blood flow of neonates were the highest 2–3 days after birth. In asphyxiated neonates, they developed into hypoxic-ischemic brain damage [18], which is consistent with the results of this study. However, Proisy revealed that [19] the CBF value of the basal ganglia was the highest on the fourth day after birth, which was one day later than in this study. Between the first and fourth days after delivery, in 9 neonatal HIE babies, the regions with decreased dispersion showed increased cerebral blood flow; in the neonate with abnormal early MRI and hyperperfusion in the cerebral cortex. This study is also the first to observe the changes of neonates with time between the first and second weeks through two consecutive scans.

At present, it remains unclear whether hyperperfusion is caused by the loss of cerebral vascular self-regulation or a metabolic driving process trying to keep pace with the increased metabolic activity of neurons. The early hyperperfusion represents the stage of reperfusion and abnormal brain self-regulation in the injured area, but the underlying mechanisms need to be better understood. Some researchers speculate that this reperfusion does not prevent infarction but may affect the formation of neovascularization and precede “new brain growth” [20]. However, this reperfusion may also be a marker of a continuous process, causing greater damage to the brain through reperfusion. Devis et al. revealed that [21] ASL did well in predicting the prognosis of HIE. The positive and negative predictive values of ASL perfusion were 100% and 96%, respectively. ASL perfusion of the basal ganglia and thalamus in the adverse outcome group was higher than in the good outcome group.

In this study, the perfusion of frontal white matter in the 1–3 days HIE group was lower than the control group. It was caused by the HIE brain damage pattern, and with the extension of hypoxia time, the compensatory mechanism was gradually lost. Finally, cerebral blood flow decreased sharply due to decreased systemic blood pressure and the impairment of cardiac function [22]. The second blood flow redistribution occurred, blood flow was reduced in both cerebral hemispheres to ensure the blood supply was restored to the most active parts of metabolism, such as the basal ganglia, thalamus, brain stem, and cerebellum. The white matter of the forehead and parietal lobe was the most vulnerable to damage. The investigators also revealed that the CBF values of the basal ganglia, thalamus, corona radiata, and frontal lobe in the 4–7 days HIE group were lower than the control group. The reason may be due to the decompensation of self-regulation of cerebral blood flow in this period. Cerebral blood flow is mainly regulated by blood pressure, and long-term hypoxia leads to decreased cardiac output and blood pressure, so cerebral perfusion decreases with time. There was no significant difference in cerebral blood flow in most brain regions between the 8–15 days HIE and control groups. Therefore, this study found the best time of ASL scanning for cerebral hemodynamic evaluation of HIE is within seven days. But in MRS, 7–14 days is significant. Decreased time-dependent concentrations of N-acetyl aspartate and creatine at 18–96 hours and 7–14 days can accurately predict adverse outcomes [23].

This study has the following limitations. (1) The number of samples was small. (2) Because of economic and other reasons, the reexamination rate of neonatal MRI was low. There was no way to make a longitudinal comparison of the same neonate at different ages. Moreover, there is a lack of contrast images before and after treatment. In future research, we will communicate with neonatal pediatricians and family members and increase reexamination after treatment. (3) Due to the limited sedation time of the same neonate, there was a lack of combined application of multiple functional imaging methods using imageomics to study neonatal HIE. In future research, we will continue to try other functional imaging methods.

5 Conclusion

Statistical analysis revealed that the CBF values of the basal ganglia, thalamus, and brainstem in the 1–3 days HIE group were higher than normal neonates at matched ages. The differences were statistically significant (P < 0.05), suggesting that there is blood flow redistribution and reperfusion injury in the central gray matter in neonates with early HIE. These areas metabolize more actively and have more oxygen demand in the immature brain.

The CBF values of frontal and parietal lobes of neonates in the 1–3 days HIE group were lower than the control group. The differences were statistically significant (P < 0.05), suggesting that cerebral blood flow in the peripheral white matter area is reduced to ensure the most active metabolism of the central gray matter area.

The CBF values of the basal ganglia, thalamus, corona radiata, and frontal lobe in the 4–7 days HIE group were lower than the control group. The differences were statistically significant (P < 0.05), suggesting that the ability of cerebral blood flow self-regulation in most brain regions is decompensated. Cerebral blood flow is mainly regulated by blood pressure, and long-term hypoxia leads to decreased cardiac output and blood pressure, so cerebral perfusion decreases with time.

There was no significant difference in cerebral blood flow of most brain regions between the 8–15 days HIE and control groups. Therefore, the best time window for cerebral hemodynamic evaluation of HIE is optimal within seven days.

Early hyperperfusion of the basal ganglia and thalamus is beneficial for early diagnosis and evaluation of the prognosis of HIE.

Funding

Hebei Medical Scientific Research Project in 2019, Health Commission of Hebei Province (No: 20190933).

Ethics approval and consent to participate

This study was conducted with approval from the Ethics Committee of Affiliated Hospital of Hebei University (No: HDFY-LL-2017-46). This study was conducted in accordance with the declaration of Helsinki.Written informed consent was obtained from all patients’ guardians.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

HZ and YTZ conceived the idea and conceptualised the study. HJL collected the data. XPY and HJLanalysed the data. JNW and JL drafted the manuscript, then JNW and JL reviewed the manuscript. All authors read and approved the final draft.

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