Changes in computed tomography perfusion parameters and maximum contrast enhancement in patients having hydrocephalus with a ventriculoperitoneal shunt: a pilot study

Background Acute hydrocephalus may decrease cerebral perfusion by increasing intracranial pressure. Computed tomography perfusion (CTP) has become a significant adjunct in evaluating regional and global cerebral blood flow (CBF). Purpose To investigate the changes in cerebral perfusion parameters and maximum contrast enhancement (MCE) in patients with hydrocephalus with ventriculoperitoneal shunt (VPS). Material and Methods We performed brain CTP in 45 patients, including those with subarachnoid hemorrhage (SAH)-induced hydrocephalus with VPS (n = 14, G1), hydrocephalus (not related to SAH) with VPS (n = 11, G2), SAH-induced hydrocephalus without VPS (n = 10, G3), and hydrocephalus (not related to SAH) without VPS (n = 10, G4). We measured the cerebral perfusion in the frontal white matter (FWM), centrum semiovale, basal ganglia (BG), and eight cortical lesions of interest and compared the differences in CTP parameters among the groups. Results Between the four groups, cerebral blood volume and MCE in the left FWM and CBF in the right FWM increased significantly in G1 and G2 who underwent VP shunt compared to G3 and G4, whereas perfusion significantly reduced in G3 and G4 who did not undergo VP shunt compared to G1 and G2. MCE in the left BG significantly increased in G2 and decreased in G3 and G4. SAH-induced hydrocephalus showed a lower perfusion than hydrocephalus (not related to SAH) in FWM. Conclusions Perfusion changes in patients with hydrocephalus after VP shunt were seen in the FWM and BG, which appears to be the result of the hydrocephalus reducing brain perfusion in the deep part of the brain. We concluded that SAH slows brain perfusion recovery.

Effects of cardiorespiratory fitness and exercise training on cerebrovascular blood flow and reactivity: a systematic review with meta-analyses

Background: We address two aims; Aim 1 (Fitness Review) compare the effect of higher cardiorespiratory fitness (CRF) (e.g. endurance athletes) with lower CRF (e.g. sedentary adults) on cerebrovascular outcomes, including middle cerebral artery velocity (MCAv) as assessed by Transcranial Doppler (TCD) or Magnetic Resonance Imaging (MRI). Aim 2 (Exercise Training Review) determine the effect of exercise training on cerebrovascular outcomes. Methods: Systematic review of studies with meta-analyses where appropriate. Certainty of evidence was assessed by Grading of Recommendations Assessment, Development and Evaluation (GRADE). Results: Twenty studies (18 using TCD) met the eligibility criteria for Aim 1 and 14 studies (8 using TCD) were included for Aim 2. There was a significant effect of higher compared with lower CRF on cerebrovascular resistance index (effect size, 95% confidence interval), (-0.54, -0.91 to -0.16) and cerebrovascular reactivity (0.98, 0.41 to 1.55). Studies including males only demonstrated a greater effect of higher CRF on cerebrovascular resistance index than mixed or female studies (male only: -0.69, -1.06 to -0.32, mixed and female studies (0.10, -0.28 to 0.49). Exercise training did not increase MCAv (0.05, -0.21 to 0.31), although there was a small improvement trending to significant in cerebrovascular reactivity (0.60, -0.08 to 1.28; p=0.09). Exercise training showed heterogeneous effects on regional, but little effect on global cerebral blood flow as measured by MRI. Conclusions: High CRF positively effects cerebrovascular function, including decreased CVRi and increased CVRCO2 however, global cerebral blood flow and MCAv is primarily unchanged following an exercise intervention in healthy and clinical populations.

Left ventricular systolic dysfunction is associated with poor functional outcomes after endovascular thrombectomy

BackgroundEndovascular thrombectomy (ET) has transformed acute ischemic stroke (AIS) therapy in patients with large vessel occlusion (LVO). Left ventricular systolic dysfunction (LVSD) decreases global cerebral blood flow and predisposes to hypoperfusion. We evaluated the relationship between LVSD, as measured by LV ejection fraction (LVEF), and clinical outcomes in patients with anterior cerebral circulation LVO who underwent ET.MethodsThis multicenter retrospective cohort study examined anterior circulation LVO AIS patients from six international stroke centers. LVSD was measured by assessment of the echocardiographic LVEF using Simpson’s biplane method of discs according to international guidelines. LVSD was defined as LVEF <50%. The primary outcome was defined as a good functional outcome using a modified Rankin Scale (mRS) of 0–2 at 3 months.ResultsWe included 440 AIS patients with LVO who underwent ET. On multivariate analyses, pre-existing diabetes mellitus (OR 2.05, 95% CI 1.24 to 3.39;p=0.005), unsuccessful reperfusion (Treatment in Cerebral Infarction (TICI) grade 0-2a) status (OR 4.21, 95% CI 2.04 to 8.66; p<0.001) and LVSD (OR 2.08, 95% CI 1.18 to 3.68; p=0.011) were independent predictors of poor functional outcomes at 3 months. On ordinal (shift) analyses, LVSD was associated with an unfavorable shift in the mRS outcomes (OR 2.32, 95% CI 1.52 to 3.53; p<0.001) after adjusting for age and ischemic heart disease.ConclusionAnterior circulation LVO AIS patients with LVSD have poorer outcomes after ET, suggesting the need to consider cardiac factors for ET, the degree of monitoring and prognostication post-procedure.

No Immediate Effects of Transcranial Direct Current Stimulation at Various Intensities on Cerebral Blood Flow in People with Multiple Sclerosis

Animal and transcranial magnetic stimulation motors have evoked potential studies suggesting that the currently used transcranial direct current stimulation (tDCS) intensities produce measurable physiological changes. However, the validity, mechanisms, and general efficacy of this stimulation modality are currently being scrutinized. The purpose of this pilot study was to investigate the effects of dorsolateral prefrontal cortex tDCS on cerebral blood flow. A sample of three people with multiple sclerosis underwent two blocks of five randomly assigned tDCS intensities (1, 2, 3, 4 mA, and sham; 5 min each) and [15O]water positron emission tomography imaging. The relative regional (i.e., areas under the electrodes) and global cerebral blood flow were calculated. The results revealed no notable differences in regional or global cerebral blood flow from the different tDCS intensities. Thus, 5 min of tDCS at 1, 2, 3, and 4 mA did not result in immediate changes in cerebral blood flow. To achieve sufficient magnitudes of intracranial electrical fields without direct peripheral side effects, novel methods may be required.

Preserved global cerebral blood flow accounts for youthful processing speed in older adults

Preserved cognitive performance is one of the key contributors to successful aging. The processing speed theory and prefrontal executive theory – are competing theories regarding the general causes of cognitive aging. Here, we used a theoretically-driven framework to investigate the neural correlates of older adults with preserved processing speed. Older adults with youth-like processing speed (SuperAgers) were compared with normal aged adults (TypicalAgers) using neuroimaging methods. Global cerebral blood flow (CBF) accounted for approximately 45% of the variance in processing speed, while neither regional CBF nor other structural measures predicted additional variance. In addition, despite having significantly cortical thinning, SuperAgers still shown comparable global CBF levels with young adults. These results support the global mechanism suggested by processing speed theory and indicate that global CBF may serve as a biomarker of cognitive aging.

Hypoglycemic thalamic activation in type 1 diabetes is associated with preserved symptoms despite reduced epinephrine

Brain responses to low plasma glucose may be key to understanding the behaviors that prevent severe hypoglycemia in type 1 diabetes. This study investigated the impact of long duration, hypoglycemia aware type 1 diabetes on cerebral blood flow responses to hypoglycemia. Three-dimensional pseudo-continuous arterial spin labeling magnetic resonance imaging was performed in 15 individuals with type 1 diabetes and 15 non-diabetic controls during a two-step hyperinsulinemic glucose clamp. Symptom, hormone, global cerebral blood flow and regional cerebral blood flow responses to hypoglycemia were measured. Epinephrine release during hypoglycemia was attenuated in type 1 diabetes, but symptom score rose comparably in both groups. A rise in global cerebral blood flow did not differ between groups. Regional cerebral blood flow increased in the thalamus and fell in the hippocampus and temporal cortex in both groups. Type 1 diabetes demonstrated lesser anterior cingulate cortex activation; however, this difference did not survive correction for multiple comparisons. Thalamic cerebral blood flow change correlated with autonomic symptoms, and anterior cingulate cortex cerebral blood flow change correlated with epinephrine response across groups. The thalamus may thus be involved in symptom responses to hypoglycemia, independent of epinephrine action, while anterior cingulate cortex activation may be linked to counterregulation. Activation of these regions may have a role in hypoglycemia awareness and avoidance of problematic hypoglycemia.

Phase contrast mapping MRI measurements of global cerebral blood flow across different perfusion states – A direct comparison with 15O-H2O positron emission tomography using a hybrid PET/MR system

Phase-contrast mapping (PCM) magnetic resonance imaging (MRI) provides easy-access non-invasive quantification of global cerebral blood flow (gCBF) but its accuracy in altered perfusion states is not established. We aimed to compare paired PCM MRI and 15O-H2O positron emission tomography (PET) measurements of gCBF in different perfusion states in a single scanning session. Duplicate combined gCBF PCM-MRI and 15O-H2O PET measurements were performed in the resting condition, during hyperventilation and after acetazolamide administration (post-ACZ) using a 3T hybrid PET/MR system. A total of 62 paired gCBF measurements were acquired in 14 healthy young male volunteers. Average gCBF in resting state measured by PCM-MRI and 15O-H2O PET were 58.5 ± 10.7 and 38.6 ± 5.7 mL/100 g/min, respectively, during hyperventilation 33 ± 8.6 and 24.7 ± 5.8 mL/100 g/min, respectively, and post-ACZ 89.6 ± 27.1 and 57.3 ± 9.6 mL/100 g/min, respectively. On average, gCBF measured by PCM-MRI was 49% higher compared to 15O-H2O PET. A strong correlation between the two methods across all states was observed (R2 = 0.72, p < 0.001). Bland–Altman analysis suggested a perfusion dependent relative bias resulting in higher relative difference at higher CBF values. In conclusion, measurements of gCBF by PCM-MRI in healthy volunteers show a strong correlation with 15O-H2O PET, but are associated with a large and non-linear perfusion-dependent difference.