Magnetic Resonance Imaging of Acute Stroke

Clinical and imaging markers for the prognosis of acute ischemic stroke

Background and purpose

Significant differences in the outcomes observed in patients with acute ischemic stroke (AIS) have led to research investigations for identifying the predictors. In this retrospective study, we aimed to investigate the relationship of different clinical and imaging factors with the prognosis of AIS.

Materials and methods

All clinical and imaging metrics were compared between the good and poor prognosis groups according to the modified Rankin Scale (mRS) score at 90 days after discharge. Clinical factors included gender, age, NIHSS scores at admission, and other medical history risk factors. Imaging markers included the lesion's size and location, diffusion, and perfusion metrics of infarction core and peripheral regions, and the state of collateral circulation. Spearman's correlations were analyzed for age and imaging markers between the different groups. The Chi-square test and Cramer's V coefficient analysis were performed for gender, collateral circulation status, NIHSS score, and other stroke risk factors.

Results

A total of 89 patients with AIS were divided into the good (mRS score ≤ 2) and poor prognosis groups (mRS score ≥ 3). There were differences in NIHSS score at the admission; relative MK (rMK), relative MD (rMD), relative CBF (rCBF) of the infarction core; relative mean transit time (rMTT), relative time to peak (rTTP), and relative CBF (rCBF) of peripheral regions; and collateral circulation status between the two groups (p < 0.05). Among them, the rMK of infarction lesions had the strongest correlation with the mRS score at 90 days after discharge (r = 0.545, p < 0.001).

Conclusion

Perfusion and diffusion metrics could reflect the microstructure and blood flow characteristics of the lesion, which were the key factors for the salvage ability and prognosis of the infarction tissue. The characteristics of the infarction core and peripheral regions have different effects on the outcomes. Diffusion of infarction core has strong relations with the prognosis, whereas the time metrics (MTT, TTP) were more important for peripheral regions. MK had a more significant association with prognosis than MD. These factors were the primary markers influencing the prognosis of cerebral infarction patients.

Global trends and research hotspots of stroke and magnetic resonance imaging: A bibliometric analysis

BACKGROUND

In this study, we used CiteSpace and VOSviewer to create a bibliometric visualization of research papers relating to stroke and magnetic resonance imaging (MRI) between 2000 and 2022. To fully understand the trends and hotspots in MRI and stroke research and provide new perspectives for future studies.

METHODS

The Web of Science Core Collection was selected as the source of data for this paper. Using CiteSpace and VOSviewer, publications were analyzed for authors, countries, institutions, journals, references, and keywords.

RESULTS

We found 1423 papers after searching and removing duplicates, which indicated an upward trend over the previous 23 years. Fiebach J.B. is the most published author (21 publications), Hacke W. is the most cited author (213 citations), and the United States (449 publications) and Harvard University (86 publications) are the most prolific nations and institutions. Stroke is the journal with the most co-citations (1275) and the most papers (171) published. The most representative reference was the 1995 article by Marler et al, which received 115 citations and had the top 3 co-occurring keywords: stroke, magnetic resonance imaging, and MRI. The article by Nogueria et al showed the strongest citation burst at the end of 2022 (strength = 17.32). High-frequency keywords in recent years are time, association, functional connectivity, thrombectomy, and rehabilitation.

CONCLUSION

This study provides a scientific perspective on stroke and MRI research, provides valuable information for researchers to understand the current status of research, hotspots, and trends, and guides future research directions.

Direct cost analysis of rapid MRI in the emergency department evaluation of patients suspected of having acute ischemic stroke*

BACKGROUND

Abbreviated "rapid MRI" protocols have become more common for the evaluation of acute ischemic stroke (AIS). Prior research has not evaluated the effect of rapid MRIs on cost or hospital length of stay in AIS patients.

METHODS

We retrospectively identified AIS patients who presented within 6 h of acute neurologic symptom onset to an emergency department (ED) and activated a "brain attack" code. We included sequential patients from January 2012 to September 2015, before rapid MRI was available, who had CT perfusion (CTP) and compared them to patients from October 2015 to May 2018 who had a rapid MRI. We used inverse-probability-weighting (IPW) to balance the cohorts. The primary outcomes were direct cost to our healthcare system and total hospital length of stay (LOS).

RESULTS

We included 408 brain attack activations (mean ± SD age 62.1 ± 17.6 years, 47.8% male): 257 in the CTP cohort and 151 in the MRI cohort. Discharge diagnosis was ischemic stroke in 193/408 (47.3%). After patient matching, we found significant reductions for the MRI cohort in total cost (-18.7%, 95% CI -35.0, -2.4, p = 0.02) and hospital LOS (-17.0%, 95% CI -31.2, -2.8, p = 0.02), with no difference in ED LOS (p = 0.74) as compared to the CTP cohort.

CONCLUSION

Although these results are preliminary and hypothesis-generating, we found that the use of a rapid MRI protocol in emergency department brain attacks was associated with a 18.7% reduction in total direct cost and 17% reduction in hospital length of stay.

Flow augmentation STA-MCA bypass evaluation for patients with acute stroke and unilateral large vessel occlusion: a proposal for an urgent bypass flowchart

OBJECTIVE

Endovascular recanalization trials have shown a positive impact on the preservation of ischemic penumbra in patients with acute large vessel occlusion (LVO). The concept of penumbra salvation can be extended to surgical revascularization with bypass in highly selected patients. For selecting these patients, the authors propose a flowchart based on multimodal MRI.

METHODS

All patients with acute stroke and persisting internal carotid artery (ICA) or M1 occlusion after intravenous lysis or mechanical thrombectomy undergo advanced neuroimaging in a time window of 72 hours after stroke onset including perfusion MRI, blood oxygenation level-dependent functional MRI to evaluate cerebrovascular reactivity (BOLD-CVR), and noninvasive optimal vessel analysis (NOVA) quantitative MRA to assess collateral circulation.

RESULTS

Symptomatic patients exhibiting persistent hemodynamic impairment and insufficient collateral circulation could benefit from bypass surgery. According to the flowchart, a bypass is considered for patients 1) with low or moderate neurological impairment (National Institutes of Health Stroke Scale score 1-15, modified Rankin Scale score ≤ 3), 2) without large or malignant stroke, 3) without intracranial hemorrhage, 4) with MR perfusion/diffusion mismatch > 120%, 5) with paradoxical BOLD-CVR in the occluded vascular territory, and 6) with insufficient collateral circulation.

CONCLUSIONS

The proposed flowchart is based on the patient's clinical condition and multimodal MR neuroimaging and aims to select patients with acute stroke due to LVO and persistent inadequate collateral flow, who could benefit from urgent bypass.

Krizsan A, Forgács A, Berényi E, Balkay L. Effect of grey-level discretization on texture feature on different weighted MRI images of diverse disease groups

PURPOSE

Many studies of MRI radiomics do not include the discretization method used for the analyses, which might indicate that the discretization methods used are considered irrelevant. Our goals were to compare three frequently used discretization methods (lesion relative resampling (LRR), lesion absolute resampling (LAR) and absolute resampling (AR)) applied to the same data set, along with two different lesion segmentation approaches.

METHODS

We analyzed the effects of altering bin widths or bin numbers for the three different sampling methods using 40 texture indices (TIs). The impact was evaluated on brain MRI studies obtained for 71 patients divided into three different disease groups: multiple sclerosis (MS, N = 22), ischemic stroke (IS, N = 22), cancer patients (N = 27). Two different MRI acquisition protocols were considered for all patients, a T2- and a post-contrast 3D T1-weighted MRI sequence. Elliptical and manually drawn VOIs were employed for both imaging series. Three different types of gray-level discretization methods were used: LRR, LAR and AR. Hypothesis tests were done among all diseased and control areas to compare the TI values in these areas. We also did correlation analyses between TI values and lesion volumes.

RESULTS

In general, no significant differences were reported in the results when employing the AR and LAR discretization methods. It was found that employing 38 TIs introduced variation in the results when the number of bin parameters was altered, suggesting that both the degree and direction of monotonicity between each TI value and binning parameters were characteristic for each TI. Furthermore, while TIs were changing with altering binning values, no changes correlated to neither disease nor the MRI sequence. We found that most indices correlated weakly with the volume, while the correlation coefficients were independent of both diseases analyzed and MR contrast. Several cooccurrence-matrix based texture parameters show a definite higher correlation when employing the LRR discretization method However, with the best correlations obtained for the manually drawn VOI. Hypothesis tests among all disease and control areas (co-lateral hemisphere) revealed that the AR or LAR discretization techniques provide more suitable texture features than LRR. In addition, the manually drawn segmentation gave fewer significantly different TIs than the ellipsoid segmentations. In addition, the amount of TIs with significant differences was increasing with increasing the number of bins, or decreasing bin widths.

CONCLUSION

Our findings indicate that the AR discretization method may offer the best texture analysis in MR image assessments. Employing too many bins or too large bin widths might reduce the selection of TIs that can be used for differential diagnosis. In general, more statistically different TIs were observed for elliptical segmentations when compared to the manually drawn VOIs. In the texture analysis of MR studies, studies and publications should report on all important parameters and methods related to data collection, corrections, normalization, discretization, and segmentation.

Nanotheranostics for the Management of Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion injury (IRI), in which an insufficient oxygen supply followed by reperfusion leads to an inflammatory network and oxidative stress in disease tissue to cause cell death, always occurs after liver transplantations and sections. Although pharmacological treatments favorably prevent or protect the liver against experimental IRI, there have been few successes in clinical applications for patient benefits because of the incomprehension of complicated IRI-induced signaling events as well as short blood circulation time, poor solubility, and severe side reactions of most antioxidants and anti-inflammatory drugs. Nanomaterials can achieve targeted delivery and controllable release of contrast agents and therapeutic drugs in desired hepatic IRI regions for enhanced imaging sensitivity and improved therapeutic effects, emerging as novel alternative approaches for hepatic IRI diagnosis and therapy. In this review, the application of nanotechnology is summarized in the management of hepatic IRI, including nanomaterial-assisted hepatic IRI diagnosis, nanoparticulate systems-mediated remission of reactive oxygen species-induced tissue injury, and nanoparticle-based targeted drug delivery systems for the alleviation of IRI-related inflammation. The current challenges and future perspectives of these nanoenabled strategies for hepatic IRI treatment are also discussed.

Antioxidant nanomaterials in advanced diagnoses and treatments of ischemia reperfusion injuries

Organ ischemia with inadequate oxygen supply followed by reperfusion (which initiates a complex of inflammatory responses and oxidative stress) occurs in different clinical conditions and surgical procedures including stroke, myocardial infarction, limb ischemia, renal failure, organ transplantation, free-tissue-transfer, cardiopulmonary bypass, and vascular surgery. Even though pharmacological treatments protect against experimental ischemia reperfusion (I/R) injury, there has not been enough success in their application for patient benefits. The main hurdles in the treatment of I/R injury are the lack of diagnosis tools for understanding the complicated chains of I/R-induced signaling events, especially in the acute phase after ischemia, determining the affected regions of the tissue over time, and then, targeting and safe delivery of antioxidants, drugs, peptides, genes and cells to the areas requiring treatment. Besides the innate antioxidant and free radical scavenging properties, some nanoparticles also show higher flexibility in drug delivery and imaging. This review highlights three main approaches in nanoparticle-mediated targeting of I/R injury: nanoparticles (1) as antioxidants for reducing tissue oxidative stress, (2) for targeted delivery of therapeutic agents to the ischemic regions or cells, and (3) for imaging I/R injury at the molecular, cellular or tissue level and monitoring its evolution using contrasts induced by nanoparticles. These approaches can also be combined to realize so called theranostics for providing simultaneous diagnosis of ischemic regions and treatments by targeted delivery.

Arterial spin labeling perfusion magnetic resonance imaging of non-human primates

Non-human primates (NHPs) resemble most aspects of humans in brain physiology and anatomy and are excellent animal models for translational research in neuroscience, biomedical research and pharmaceutical development. Cerebral blood flow (CBF) offers essential physiological information of the brain to examine the abnormal functionality in NHP models with cerebral vascular diseases and neurological disorders or dementia. Arterial spin labeling (ASL) perfusion MRI techniques allow for high temporal and spatial CBF measurement and are intensively used in studies of animals and humans. In this article, current high-resolution ASL perfusion MRI techniques for quantitative evaluation of brain physiology and function in NHPs are described and their applications and limitation are discussed as well.

The diagnosis and clinical management of the neuropsychiatric manifestations of lupus

Neuropsychiatric (NP) involvement in Systemic Lupus Erythematosus (SLE), can be a severe and troubling manifestation of the disease that heavily impacts patient's health, quality of life and disease outcome. It is one of the most complex expressions of SLE which can affect central, peripheral and autonomous nervous system. Complex interrelated pathogenetic mechanisms, including genetic factors, vasculopathy, vascular occlusion, neuroendocrine-immune imbalance, tissue and neuronal damage mediated by autoantibodies, inflammatory mediators, blood brain barrier dysfunction and direct neuronal cell death can be all involved. About NPSLE a number of issues are still matter of debate: from classification and burden of NPSLE to attribution and diagnosis. The role of neuroimaging and new methods of investigation still remain pivotal and rapidly evolving as well as is the increasing knowledge in the pathogenesis. Overall, two main pathogenetic pathways have been recognized yielding different clinical phenotypes: a predominant ischemic-vascular one involving large and small blood vessels, mediated by aPL, immune complexes and leuko-agglutination which it is manifested with more frequent focal NP clinical pictures and a predominantly inflammatory-neurotoxic one mediated by complement activation, increased permeability of the BBB, intrathecal migration of autoantibodies, local production of immune complexes and pro-inflammatory cytokines and other inflammatory mediators usually appearing as diffuse NP manifestations. In the attempt to depict a journey throughout NPSLE from diagnosis to a reasoned therapeutic approach, classification, epidemiology, attribution, risk factors, diagnostic challenges, neuroimaging techniques and pathogenesis will be considered in this narrative review based on the most relevant and recent published data.