Imaging the effects of oxygen saturation changes in voluntary apnea and hyperventilation on susceptibility-weighted imaging

In vivo mapping of hippocampal venous vasculature and oxygenation using susceptibility imaging at 7T

Mapping the small venous vasculature of the hippocampus in vivo is crucial for understanding how functional changes of hippocampus evolve with age. Oxygen utilization in the hippocampus could serve as a sensitive biomarker for early degenerative changes, surpassing hippocampal tissue atrophy as the main source of information regarding tissue degeneration. Using an ultrahigh field (7T) susceptibility-weighted imaging (SWI) sequence, it is possible to capture oxygen-level dependent contrast of submillimeter-sized vessels. Moreover, the quantitative susceptibility mapping (QSM) results derived from SWI data allow for the simultaneous estimation of venous oxygenation levels, thereby enhancing the understanding of hippocampal function. In this study, we proposed two potential imaging markers in a cohort of 19 healthy volunteers aged between 20 and 74 years. These markers were: 1) hippocampal venous density on SWI images and 2) venous susceptibility (Δχvein) in the hippocampus-associated draining veins (the inferior ventricular veins (IVV) and the basal veins of Rosenthal (BVR) using QSM images). They were chosen specifically to help characterize the oxygen utilization of the human hippocampus and medial temporal lobe (MTL). As part of the analysis, we demonstrated the feasibility of measuring hippocampal venous density and Δχvein in the IVV and BVR at 7T with high spatial resolution (0.25 × 0.25 × 1 mm3). Our results demonstrated the in vivo reconstruction of the hippocampal venous system, providing initial evidence regarding the presence of the venous arch structure within the hippocampus. Furthermore, we evaluated the age effect of the two quantitative estimates and observed a significant increase in Δχvein for the IVV with age (p=0.006, r2 = 0.369). This may suggest the potential application of Δχvein in IVV as a marker for assessing changes in atrophy-related hippocampal oxygen utilization in normal aging and neurodegenerative diseases such as AD and dementia.

Prominent cerebral veins on susceptibility-weighted angiography in acute meningoencephalitis

BACKGROUND AND PURPOSE

We have commonly observed prominent cerebral veins on susceptibility-weighted angiography (SWAN) in acute meningoencephalitis. This study aimed to investigate the clinical significance of these findings.

METHODS

Cerebral veins on SWAN of 98 patients with acute meningoencephalitis diagnosed from February 2016 through October 2020 were classified into three groups according to the degree of venous prominence (mild, 23; moderate, 53; and prominent, 22). Clinical variables and laboratory findings were compared between these groups. The influence of variables on the prediction of prominent cerebral veins was measured by random forest (RF) and gradient boosting machine (GBM).

RESULTS

As cerebral veins became more prominent, cerebrospinal fluid (CSF) glucose level decreased (69.61 ± 29.05 vs. 59.72 ± 22.57 vs. 48.36 ± 20.29 mg/dL, p = .01) and CSF protein level increased (100.73 ± 82.98 vs. 104.73 ± 70.99 vs. 159.12 ± 118.15 mg/dL, p = .03). The etiology of meningoencephalitis, neurological symptoms, and increased intracranial pressure (ICP) signs differed between groups (p < .05). RF and GBM demonstrated that CSF protein level was the variable with the highest power to predict the prominent cerebral vein (mean decrease in node impurity: 4.19, relative influence: 50.66).

CONCLUSION

The presence of prominent cerebral veins on SWAN in acute meningoencephalitis was significantly associated with a low CSF glucose level and a high CSF protein level, as well as ICP. Thus, the visual grade of the cerebral veins on SWAN may be utilized for the management of patients with acute meningoencephalitis.

Reduced white matter venous density on MRI is associated with neurodegeneration and cognitive impairment in the elderly

High-resolution susceptibility weighted imaging (SWI) provides unique contrast to small venous vasculature. The conspicuity of these mesoscopic veins, such as deep medullary veins in white matter, is subject to change from SWI venography when venous oxygenation in these veins is altered due to oxygenated blood susceptibility changes. The changes of visualization in small veins shows potential to depict regional changes of oxygen utilization and/or vascular density changes in the aging brain. The goal of this study was to use WM venous density to quantify small vein visibility in WM and investigate its relationship with neurodegenerative features, white matter hyperintensities (WMHs), and cognitive/functional status in elderly subjects (N = 137). WM venous density was significantly associated with neurodegeneration characterized by brain atrophy (β = 0.046± 0.01, p < 0.001), but no significant association was found between WM venous density and WMHs lesion load (p = 0.3963). Further analysis of clinical features revealed a negative trend of WM venous density with the sum-of-boxes of Clinical Dementia Rating and a significant association with category fluency (1-min animal naming). These results suggest that WM venous density on SWI can be used as a sensitive marker to characterize cerebral oxygen metabolism and different stages of cognitive and functional status in neurodegenerative diseases.

Cardiac and Respiratory Influences on Intracranial and Neck Venous Flow, Estimated Using Real-Time Phase-Contrast MRI

The study of brain venous drainage has gained attention due to its hypothesized link with various neurological conditions. Intracranial and neck venous flow rate may be estimated using cardiac-gated cine phase-contrast (PC)-MRI. Although previous studies showed that breathing influences the neck’s venous flow, this aspect could not be studied using the conventional segmented PC-MRI since it reconstructs a single cardiac cycle. The advent of real-time PC-MRI has overcome these limitations. Using this technique, we measured the internal jugular veins and superior sagittal sinus flow rates in a group of 16 healthy subjects (12 females, median age of 23 years). Comparing forced-breathing and free-breathing, the average flow rate decreased and the respiratory modulation increased. The flow rate decrement may be due to a vasoreactive response to deep breathing. The respiratory modulation increment is due to the thoracic pump’s greater effect during forced breathing compared to free breathing. These results showed that the breathing mode influences the average blood flow and its pulsations. Since effective drainage is fundamental for brain health, rehabilitative studies might use the current setup to investigate if respiratory exercises positively affect clinical variables and venous drainage.

Diagnostic utility of T2*-weighted GRE in migraine with aura attack. The cortical veins sign

OBJECTIVE

To evaluate the frequency, distribution, and clinical associations of the dilated appearance of cerebral cortical veins, termed cortical veins sign on T2*-weighted gradient recalled-echo (T2*-GRE) in the acute setting of migraine with aura attack in adult patients.

METHODS

We conducted a retrospective analysis of 60 consecutive patients admitted for acute neurological symptoms with a final diagnosis of migraine with aura (42%) or probable migraine with aura (58%) who underwent emergency brain magnetic resonance imaging and 60 non-migrainous control adults. The cortical veins sign was defined as a marked hypo-intensity and/or an apparent increased diameter of at least one cortical vein. We examined the prevalence, the spatial distribution, and the associations of cortical veins sign with clinical characteristics of migraine with aura.

RESULTS

We detected the cortical veins sign in 25 patients (42%) with migraine with aura, compared to none in the control group (p < 0.0001). The spatial distribution of cortical veins sign was characterised by the predominantly bilateral and posterior location. Presence of cortical veins sign was associated with increased severity of aura (p = 0.05), and shorter delay to MRI (p = 0.02).

CONCLUSION

In the setting of acute neurological symptoms, the presence of cortical veins sign is frequent in patients with migraine with aura and can be detected with good reliability. This imaging marker may help clinicians identify underlying migraine with aura.

Quantification of cerebral veins in patients with acute migraine with aura: A fully automated quantification algorithm using susceptibility-weighted imaging

Introduction

Susceptibility weighted imaging (SWI) is a very sensitive technique that often depicts prominent focal veins (PFV) in patients with acute migraine with aura (MwA). Interpretation of visual venous asymmetry (VVA) between brain hemispheres on SWI may help support the clinical diagnosis of MwA. Our goal was to develop an automated algorithm for segmentation and quantification of cerebral veins using SWI.

Materials and methods

Expert readers visually evaluated SWI of patients with acute MwA for VVA. Subsequently a fully automated algorithm based on 3D normalization and 2D imaging processing using SPM and MATLAB image processing software including top-hat transform was used to quantify cerebral veins and to calculate volumetric differences between hemispheres.

Results

Fifty patients with MwA were examined with SWI. VVA was present in 20 of 50 patients (40%). In 95% of patients with VVA, the fully automated calculation agreed with the side that visually harboured more PFV. Our algorithm showed a sensitivity of 95%, specificity of 90% and accuracy of 92% for detecting VVA. Patients with VVA had significantly larger vein volume on the hemisphere with more PFV compared to patients without (15.90 ± 5.38 ml vs 11.93 ± 5.31 ml; p = 0.013). The mean difference in venous volume between hemispheres in patients with VVA was larger compared to patients without VVA (16.34 ± 7.76% vs 4.31 ± 3.26% p < 1E-10). The average time between aura onset and SWI correlated negatively with venous volume of the dominant brain hemisphere (r = -0.348; p = 0.038).

Conclusion

A fully automated algorithm can accurately identify and quantify cerebral venous distribution on SWI. Absolute quantification may be useful for the future assessment of patients with suspected diseases, which may be associated with a unilateral abnormal degree of venous oxygenation.

Evaluation of renal dysfunction using texture analysis based on DWI, BOLD, and susceptibility-weighted imaging

OBJECTIVE

To explore the value of texture analysis based on diffusion-weighted imaging (DWI), blood oxygen level-dependent MRI (BOLD), and susceptibility-weighted imaging (SWI) in evaluating renal dysfunction.

METHODS

Seventy-two patients (mean age 53.72 ± 13.46 years) underwent MRI consisting of DWI, BOLD, and SWI. According to their estimated glomerular filtration rate (eGFR), the patients were classified into either severe renal function impairment (sRI, eGFR < 30 mL/min/1.73 m²), non-severe renal function impairment (non-sRI, eGFR ≥ 30 mL/min/1.73 m², and < 80 mL/min/1.73 m²), or control (CG, eGFR ≥ 80 mL/min/1.73 m²) groups. Thirteen texture features were extracted and then were analyzed to select the most valuable for discerning the three groups with each imaging method. A ROC curve was performed to compare the capacities of the features to differentiate non-sRI from sRI or CG.

RESULTS

Six features proved to be the most valuable for assessing renal dysfunction: 0.25Quantile_DWI, 0.5Quantile_DWI, Homogeneity_DWI, Entropy_BOLD, Skewness_SWI, and Correlation_SWI. Three features derived from DWI (0.25Quantile_DWI, 0.5Quantile_DWI, and Homogeneity_DWI) were smaller in sRI than in non-sRI; Entropy_BOLD and Correlation_SWI were smaller in non-sRI than in CG (p < 0.05). 0.25Quantile_DWI, 0.5Quantile_DWI, and Homogeneity_DWI showed similar capacities for differentiating sRI from non-sRI. Similarly, Entropy_BOLD and Correlation_SWI showed equal capacities for differentiating non-sRI from CG.

CONCLUSION

Texture analysis based on DWI, BOLD, and SWI can assist in assessing renal dysfunction, and texture features based on BOLD and SWI may be suitable for assessing renal dysfunction during early stages.

KEY POINTS

• Texture analysis based on MRI techniques allowed for assessing renal dysfunction. • Texture features based on BOLD and SWI, but not DWI, may be suitable for assessing renal function impairment during early stages. • SWI exhibited a similar capacity to BOLD for assessing renal dysfunction.

Decreased oxygen saturation levels in neonates with transposition of great arteries: Impact on appearance of cerebral veins in susceptibility-weighted imaging

Purpose of this study was to investigate a potential correlation between the pattern of cerebral veins (CV) on susceptibility-weighted imaging (SWI) and blood oxygen saturation, as well as preoperative brain injury, in neonates with transposition of the great arteries (TGA). Eleven neonates with TGA underwent MRI preoperatively, including SWI, T1- and T2-weighted scans. Images were retrospectively evaluated and appearance of CV was graded from 0 (normal appearance) to 3 (severe prominent appearance). White matter injuries (WMI) and strokes were analysed. Results were correlated with preductal arterial oxygen saturation. As findings one subject showed a normal CV appearance (grade 0) whereas 10 showed pathological prominent CV (grades 1–3); median 2. Mean oxygen saturation ranged between 67.5% and 89.0% (median 81.0%). CV grade and mean oxygen saturation correlated significantly (p = 0.011). WMI were absent in 5 cases, mild in 4, and moderate in 2 cases. We conclude, that SWI has the potential to be used to estimate the current hypoxic burden on brain tissue in TGA newborns by assessing the prominence of the CV.

Susceptibility-weighted imaging: current status and future directions

Susceptibility-weighted imaging (SWI) is a method that uses the intrinsic nature of local magnetic fields to enhance image contrast in order to improve the visibility of various susceptibility sources and to facilitate diagnostic interpretation. It is also the precursor to the concept of the use of phase for quantitative susceptibility mapping (QSM). Nowadays, SWI has become a widely used clinical tool to image deoxyhemoglobin in veins, iron deposition in the brain, hemorrhages, microbleeds and calcification. In this article, we review the basics of SWI, including data acquisition, data reconstruction and post-processing. In particular, the source of cusp artifacts in phase images is investigated in detail and an improved multi-channel phase data combination algorithm is provided. In addition, we show a few clinical applications of SWI for the imaging of stroke, traumatic brain injury, carotid vessel wall, siderotic nodules in cirrhotic liver, prostate cancer, prostatic calcification, spinal cord injury and intervertebral disc degeneration. As the clinical applications of SWI continue to expand both in and outside the brain, the improvement of SWI in conjunction with QSM is an important future direction of this technology. Copyright © 2016 John Wiley & Sons, Ltd.

Susceptibility-weighted Imaging in Neurovascular Disease

Susceptibility-weighted imaging (SWI) has become an important imaging sequence in the evaluation of patients with neurovascular disease. In this review, we provide a general overview of the physics of SWI and describe how image contrast is produced with this technique. We provide a general approach and differential diagnosis for 2 commonly encountered radiographic patterns seen with SWI in neurovascular disease. Finally, we discuss specific neurovascular applications of SWI, including its application in acute stroke, vascular malformations, venous thrombosis, and evaluation of cerebral microbleeds.

Reliability of cerebral vein volume quantification based on susceptibility-weighted imaging

INTRODUCTION

Susceptibility-weighted imaging (SWI) visualizes even small cerebral veins and might, therefore, be valuable in monitoring neurological diseases affecting cerebral veins. Since it is generally difficult to evaluate individual results of quantitative MRI measurements, an automatic approach would be highly appreciated to assist the diagnostic process. The aim of this study was to evaluate the rescan and reanalysis reliability using an automatic venous volumetric approach based on SWI in healthy controls.

METHODS

SWI was performed in ten healthy controls undergoing MRI examinations using a 32-channel head coil at 3 T five times on five different days. To test for rescan and reanalysis variability, the deep cerebral vein volume was quantified using ANTs and SPM8.

RESULTS

Total volumes of cerebral deep veins measured during five MRI scans in ten individuals (n = 50 scans) showed intra-individual volume changes ranging from 0.07 to 1.03 ml (mean variability = 10.2 %). Automatic reanalyses revealed exactly the same results in all scans.

CONCLUSION

Automatic SWI-based cerebral vein volumetry shows acceptable rescan-and excellent reanalyses-reliability in healthy volunteers. Therefore, this approach might be beneficial in intra-individual follow-up studies of neurological diseases affecting the cerebral venous system.

Brain venular pattern by 7T MRI correlates with memory and haemoglobin in sickle cell anaemia

Sickle cell anaemia (SCA) is a hereditary hemoglobinopathy characterised by extensive vascular dysfunction that stems from inflammation, thrombosis and occlusion of post-capillary venules. Cognitive impairment is a neurological complication of SCA whose pathogenesis is unknown. We hypothesised that cerebral venular abnormalities are linked to cognitive impairment in SCA. Thus, we employed 7T magnetic resonance imaging (MRI) to examine the association between venular density and cognitive function in homozygous SCA. We quantified the density of total, long, and short venules in pre-defined regions of interest between the frontal and occipital cornu on each hemisphere. Cognitive function was assessed using the Hopkins Verbal Learning Test - Revised (HVLT-R) test of learning and memory. Patients (n=11) were compared with race, age and gender-equated controls (n=7). Compared to controls, patients had an overall venular rarefaction, with significantly lower density of long venules and greater density of short venules which was inversely related to HVLT-R performance and haemoglobin. To our knowledge, this is the first 7T MRI study in SCA and first report of associations between cerebral venular patterns and cognitive performance and haemoglobin. Future studies should examine whether these novel neuroimaging markers predict cognitive impairment longitudinally and are mechanistically linked to severity of anaemia.