Prediction of infarct volume and neurologic outcome by using automated multiparametric perfusion-weighted magnetic resonance imaging in a primate model of permanent middle cerebral artery occlusion

Nonhuman Primate Models of Ischemic Stroke and Neurological Evaluation After Stroke

Nonhuman primates are closer to human beings than rodents in genetics, neuroanatomy, physiology and immunology. Nonhuman primates are therefore considered an ideal preclinical model to replicate various aspects of human stroke. Ischemia stroke models in nonhuman primates can better fit the physiological symptoms and changes in humans after cerebral ischemia. Currently, various construction methods and neurological evaluation methods have been developed and applied to stroke models of nonhuman primates, including craniectomy models, endovascular stroke models, autologous thrombus models and intraluminal filament models. Meanwhile, new innovative methods have emerged, such as the endothelin-1 model and photothrombosis model. In the past thirty years, these model studies have explored various mechanisms that are initiated in the first minutes, hours, and days after a stroke. Permanent and temporary middle cerebral artery occlusion models have been trying to simulate the complex situation of human stroke. However, a comprehensive comparison of the above methods, including their advantages and disadvantages, difficulty and application fields, is limited. Here, we introduce various modeling methods that are currently available for nonhuman primate stroke models, compare the differences between these different preparation methods, and analyze the advantages and disadvantages of the various methods and the fields of application. The imaging detection methods of nonhuman primates after cerebral ischemia and the neurological evaluation methods after stroke are also discussed briefly. Methods are sorted and compared so that scholars can choose appropriate modeling methods and evaluation methods to establish nonhuman primate stroke models.

Non-human Primate Models to Explore the Adaptive Mechanisms After Stroke

The brain has the ability to reconstruct neural structures and functions to compensate for the brain lesions caused by stroke, although it is highly limited in primates including humans. Animal studies in which experimental lesions were induced in the brain have contributed to the current understanding of the neural mechanisms underlying functional recovery. Here, I have highlighted recent advances in non-human primate models using primate species such as macaques and marmosets, most of which have been developed to study the mechanisms underlying the recovery of motor functions after stroke. Cortical lesion models have been used to investigate motor recovery after lesions to the cortical areas involved in movements of specific body parts. Models of a focal stroke at the posterior internal capsule have also been developed to bridge the gap between the knowledge obtained by cortical lesion models and the development of intervention strategies because the severity and outcome of motor deficits depend on the degree of lesions to the region. This review will also introduce other stroke models designed to study the plastic changes associated with development and recovery from cognitive and sensory impairments. Although further validation and careful interpretation are required, considering the differences between non-human primate brains and human brains, studies using brain-lesioned non-human primates offer promise for improving translational outcomes.

Encephaloduroarteriosynangiosis (EDAS) treatment of moyamoya syndrome: evaluation by computed tomography perfusion imaging

OBJECTIVE

To explore the value of computed tomography perfusion (CTP) imaging for evaluating the efficacy of encephaloduroarteriosynangiosis (EDAS) treatment of moyamoya syndrome (MMS).

METHODS

Forty-three patients with MMS (48 hemispheres) who received EDAS treatment were examined using CTP and DSA before and after surgery. CTP of the ipsilateral cortex, contralateral mirror area, and pons region were measured, and the relative cerebral blood flow (rCBF) and volume (rCBV), mean transit time (rMTT), and time-to-peak (rTTP) were calculated. Based on postoperative DSA, 48 hemispheres were apportioned to two groups based on rich (grades 2, 3) or poor (grades 0, 1) collateral vessel formation, and the pre- and post-operative differences in perfusion changes were compared. The association between clinical outcome, CTP, and the degree of DSA collateral vessels was explored.

RESULTS

rCBF and rMTT significantly improved in both the poor and rich collateral vessel formation groups (n = 21 and 27, respectively), while rTTP significantly improved only in the latter. Postoperative CTP improved in the rich and the grade 1 collateral vessel groups (p < 0.01). The clinical improvement was consistent with the improvement of CTP (p = 0.07), but less consistent with the degree of collateral angiogenesis (p = 0.003).

CONCLUSION

CTP can quantitatively evaluate the improvement of brain tissue perfusion in the operated area after EDAS. Brain tissue perfusion in operated areas improved regardless of postoperative rich or poor collateral vessel formation observed via DSA. A significant improvement in rTTP in the operated area may indicate the formation of abundant collateral vessels.

KEY POINTS

• CTP showed that brain tissue perfusion in the operated area after EDAS improved regardless of rich or poor collateral vessel formation observed via DSA. • Significant improvement of rTTP in the operated area may indicate the formation of abundant collateral vessels.

Notoginsenoside R1 for Organs Ischemia/Reperfusion Injury: A Preclinical Systematic Review

Notoginsenoside R1 (NGR1) exerts pharmacological actions for a variety of diseases such as myocardial infarction, ischemic stroke, acute renal injury, and intestinal injury. Here, we conducted a preclinical systematic review of NGR1 for ischemia reperfusion (I/R) injury. Eight databases were searched from their inception to February 23rd, 2019; Review Manager 5.3 was applied for data analysis. CAMARADES 10-item checklist and cell 10-item checklist were used to evaluate the methodological quality. Twenty-five studies with 304 animals and 124 cells were selected. Scores of the risk of bias in animal studies ranged from 3 to 8, and the cell studies ranged from 3 to 5. NGR1 had significant effects on decreasing myocardial infarct size in myocardial I/R injury, decreasing cerebral infarction volume and neurologic deficit score in cerebral I/R injury, decreasing serum creatinine in renal I/R injury, and decreasing Park/Chiu score in intestinal I/R injury compared with controls (all P < 0.05 or P < 0.01). The multiple organ protection of NGR1 after I/R injury is mainly through the mechanisms of antioxidant, anti-apoptosis, and anti-inflammatory, promoting angiogenesis and improving energy metabolism. The findings showed the organ protection effect of NGR1 after I/R injury, and NGR1 can potentially become a novel drug candidate for ischemic diseases. Further translation studies are needed.

Comparative study of MR mTI-ASL and DSC-PWI in evaluating cerebral hemodynamics of patients with Moyamoya disease

The aim of this study was to explore the correlation between multi-inversion time arterial spin labeling (mTI-ASL) and dynamic susceptibility contrast-enhanced perfusion weighted imaging (DSC-PWI) in assessment of hemodynamics of patients with Moyamoya disease (MMD).In this study, 24 MMD patients and 21 healthy subjects were enrolled between June 2017 and December 2017. The images of mTI-ASL and DSC-PWI in the week before revascularization surgery were retrospectively analyzed. The parameters of cerebral blood flow (CBF), time to peak (TTP), and bolus arrival time (BAT) were measured in regions of interest (ROIs) of lateral middle cerebral artery (MCA) territories, basal ganglia (BG), and cerebellum, and relative perfusion parameters (rCBF-ASL, rBAT-ASL, rCBF-DSC, and rTTP-DSC) were calculated by dividing by cerebellum value. One-way analysis of variance and Student-Newman-Keuls tests were performed to compare rCBF-ASL and rCBF-DSC in the MMD group and the control group. Unpaired t test was used to compare rBAT-ASL and rTTP-DSC in the MMD group and the control group. And we assessed the correlation between rCBF-ASL and rCBF-DSC and between rBAT-ASL and rTTP-DSC using Pearson correlation analysis.All the relative parameters were significantly different between the MMD group and the control group (all P<.05). Meanwhile, there was significant difference between rCBF-ASL and rCBF-DSC (P<.05), and there was strong correlation between rCBF-ASL and rCBF-DSC (r = 0.839, P<.001), and moderate correlation between rBAT-ASL and rTTP-DSC (r = 0.519, P<.001).Both mTI-ASL and DSC-PWI could be used to assess perfusion state in MMD patients before revascularization surgery effectively. As a noninvasive imaging technique, mTI-ASL could provide perfusion parameters without contrast medium injection, and the results were quite correlative with DSC-PWI.

Perfusion computed tomographic measurements of cerebral blood flow variables in live Holstein calves

OBJECTIVE To measure cerebral blood flow (CBF) and cerebral blood volume (CBV) by means of perfusion CT in clinically normal Holstein calves. ANIMALS 9 Holstein calves. PROCEDURES Each of the 9 calves (mean age, 20.2 days) was anesthetized and received an injection of iodinated contrast medium into the right jugular vein at a rate of 4.0 mL/s. Dynamic CT scanning of the head at a level that included the mandibular condyle was initiated at the time of the contrast medium injection and continued for 100 seconds. A deconvolution method was used as an analytic algorithm. RESULTS Among the 9 calves, the mean ± SD CBF in the cerebral cortex, white matter, and thalamus was 44.3 ± 10.3 mL/100 g/min, 36.1 ± 7.5 mL/100 g/min, and 40.3 ± 7.5 mL/100 g/min, respectively. The CBF in white matter was significantly lower than that in the cerebral cortex or thalamus. The mean CBV in the cerebral cortex, white matter, and thalamus was 6.8 ± 1.0 mL/100 g, 5.2 ± 1.0 mL/100 g, and 5.7 ± 0.7 mL/100 g, respectively. The CBV in the cerebral cortex was significantly higher than that in the white matter or thalamus. CONCLUSIONS AND CLINICAL RELEVANCE Measurement of CBF and CBV in clinically normal calves by means of perfusion CT was feasible. The data obtained may be useful as baseline values for use in future research or for comparison with findings from calves with CNS diseases. Investigations to determine the lower limit of blood flow at which brain function can still be restored are warranted.

Comparison of Different Post-Processing Algorithms for Dynamic Susceptibility Contrast Perfusion Imaging of Cerebral Gliomas

Purpose:

The purpose of the present study was to compare different software algorithms for processing DSC perfusion images of cerebral tumors with respect to i) the relative CBV (rCBV) calculated, ii) the cutoff value for discriminating low- and high-grade gliomas, and iii) the diagnostic performance for differentiating these tumors.

Methods:

Following approval of institutional review board, informed consent was obtained from all patients. Thirty-five patients with primary glioma (grade II, 9; grade III, 8; and grade IV, 18 patients) were included. DSC perfusion imaging was performed with 3-Tesla MRI scanner. CBV maps were generated by using 11 different algorithms of four commercially available software and one academic program. rCBV of each tumor compared to normal white matter was calculated by ROI measurements. Differences in rCBV value were compared between algorithms for each tumor grade. Receiver operator characteristics analysis was conducted for the evaluation of diagnostic performance of different algorithms for differentiating between different grades.

Results:

Several algorithms showed significant differences in rCBV, especially for grade IV tumors. When differentiating between low- (II) and high-grade (III/IV) tumors, the area under the ROC curve (Az) was similar (range 0.85–0.87), and there were no significant differences in Az between any pair of algorithms. In contrast, the optimal cutoff values varied between algorithms (range 4.18–6.53).

Conclusions:

rCBV values of tumor and cutoff values for discriminating low- and high-grade gliomas differed between software packages, suggesting that optimal software-specific cutoff values should be used for diagnosis of high-grade gliomas.

Characterization of the Molecular Mechanisms Underlying the Chronic Phase of Stroke in a Cynomolgus Monkey Model of Induced Cerebral Ischemia

Stroke is one of the main causes of mortality and long-term disability worldwide. The pathophysiological mechanisms underlying this disease are not well understood, particularly in the chronic phase after the initial ischemic episode. In this study, a Macaca fascicularis stroke model consisting of two sample groups, as determined by MRI-quantified infarct volumes as a measure of the stroke severity 28 days after the ischemic episode, was evaluated using qualitative and quantitative proteomics analyses. By using multiple online multidimensional liquid chromatography platforms, 8790 nonredundant proteins were identified that condensed to 5223 protein groups at 1% global false discovery rate (FDR). After the application of a conservative criterion (5% local FDR), 4906 protein groups were identified from the analysis of cerebral cortex. Of the 2068 quantified proteins, differential proteomic analyses revealed that 31 and 23 were dysregulated in the elevated- and low-infarct-volume groups, respectively. Neurogenesis, synaptogenesis, and inflammation featured prominently as the cellular processes associated with these dysregulated proteins. Protein interaction network analysis revealed that the dysregulated proteins for inflammation and neurogenesis were highly connected, suggesting potential cross-talk between these processes in modulating the cytoskeletal structure and dynamics in the chronic phase poststroke. Elucidating the long-term consequences of brain tissue injuries from a cellular prospective, as well as the molecular mechanisms that are involved, would provide a basis for the development of new potentially neurorestorative therapies.

Predicting Cerebral Hyperperfusion Syndrome Following Superficial Temporal Artery to Middle Cerebral Artery Bypass based on Intraoperative Perfusion-Weighted Magnetic Resonance Imaging

Moyamoya disease leads to the formation of stenosis in the cerebrovasculature. A superficial temporal artery to middle cerebral artery (STA-MCA) bypass is an effective treatment for the disease, yet it is usually associated with postoperative cerebral hyperperfusion syndrome (CHS). This study aimed to evaluate cerebral hemodynamic changes immediately after surgery and assess whether a semiquantitative analysis of an intraoperative magnetic resonance perfusion-weighted image (PWI) is useful for predicting postoperative CHS. Fourteen patients who underwent the STA-MCA bypass surgery were included in this study. An atlas-based registration method was employed for studying hemodynamics in different cerebral regions. Pre- versus intraoperative and group-wise comparisons were conducted to evaluate the hemodynamic changes. A postoperative increase in relative cerebral blood flow (CBF) at the terminal MCA territory (P = 0.035) and drop in relative mean-time-transit at the central MCA territory (P = 0.012) were observed in all patients. However, a significant raise in the increasing ratio of relative-CBF at the terminal MCA territory was only found in CHS patients (P = 0.023). The cerebrovascular changes of the patients after revascularization treatment were confirmed. Intraoperative PWI might be helpful in predicting the change in relative-CBF at MCA terminal territory which might indicate a risk of CHS.

Classification of lesion area in stroke patients during the subacute phase: a multiparametric MRI study

PURPOSE

Stroke imaging studies during the acute phase are likely to precede several vascular brain mechanisms, which have an important role in patient outcome. The aim of this study was to identify within the lesion area during the subacute phase (≥1 day) reactive tissue, which may have the potential for recovery.

METHODS

Twenty seven stroke patients from two cohorts were included. MRI performed during the subacute phase included conventional, perfusion and diffusion imaging. In cohort I, unsupervised multiparametric classification of the lesion area was performed. In cohort II threshold based classification was performed during the subacute phase, and radiological outcome was assessed at follow-up scan.

RESULTS

Three tissue classes were identified in cohort I, referred to as irreversibly damaged, intermediary, and reactive tissue. Based on threshold values defined in cohort I, the reactive tissue was identified in 11/13 patients in cohort II, and showed tissue preservation/partial recovery in 9/11 patients at follow-up scan. The irreversibly damaged tissue was identified in 7/13 patients in cohort II, and predicted tissue necrosis in all cases.

CONCLUSION

Identification of reactive tissue following stroke during the subacute phase can improve radiological assessment, contribute to the understanding of brain recovery processes and has implications for new therapeutic approaches.

Comparison of arterial spin labeling and dynamic susceptibility contrast perfusion MRI in patients with acute stroke

Background

The aim of this study was to evaluate whether arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) can reliably quantify perfusion deficit as compared to dynamic susceptibility contrast (DSC) perfusion MRI.

Methods

Thirty-nine patients with acute ischemic stroke in the anterior circulation territory were recruited. All underwent ASL and DSC MRI perfusion scans within 30 hours after stroke onset and 31 patients underwent follow-up MRI scans. ASL cerebral blood flow (CBF) and DSC time to maximum (T_max) maps were used to calculate the perfusion defects. The ASL CBF lesion volume was compared to the DSC T_max lesion volume by Pearson's correlation coefficient and likewise the ASL CBF and DSC T_max lesion volumes were compared to the final infarct sizes respectively. A repeated measures analysis of variance and least significant difference post hoc test was used to compare the mean lesion volumes among ASL CBF, DSC T_max >4–6 s and final infarct.

Results

Mean patient age was 72.6 years. The average time from stroke onset to MRI was 13.9 hours. The ASL lesion volume showed significant correlation with the DSC lesion volume for T_max >4, 5 and 6 s (r = 0.81, 0.82 and 0.80; p<0.001). However, the mean lesion volume of ASL (50.1 ml) was significantly larger than those for T_max >5 s (29.2 ml, p<0.01) and T_max >6 s (21.8 ml, p<0.001), while the mean lesion volumes for T_max >5 or 6 s were close to mean final infarct size.

Conclusion

Quantitative measurement of ASL perfusion is well correlated with DSC perfusion. However, ASL perfusion may overestimate the perfusion defects and therefore further refinement of the true penumbra threshold and improved ASL technique are necessary before applying ASL in therapeutic trials.

Initial 'TTP Map-Defect' of Computed Tomography Perfusion as a Predictor of Hemorrhagic Transformation of Acute Ischemic Stroke

Background

Hemorrhagic transformation (HT) following acute ischemic stroke is a major problem, especially for the indication of reperfusion therapy including intravenous administration of recombinant tissue plasminogen activator (IV rt-PA). The specific predictive factors of HT have not yet been established. The present study evaluated the findings of computed tomography perfusion (CTP) images as predictors of subsequent HT to identify patients with low HT risk for reperfusion therapy such as IV rt-PA.

Methods

We retrospectively reviewed 68 consecutive stroke patients (41 males; mean age 72.9 years) with steno-occlusive lesions in the major trunk, including 10 patients who underwent IV rt-PA. Each HT was detected on a follow-up T2*-weighted magnetic resonance image until 2 weeks after stroke onset and categorized into four groups [hemorrhagic infarction (HI) type 1 and 2, and parenchymal hematoma (PH) type 1 and 2] according to the European Cooperative Acute Stroke Study (ECASS) classification. We assessed clinical features and radiological findings between the HT and non-HT groups or the PH2 and non-PH2 groups. The efficacy of initial time to peak (TTP) mapping of CTP for predicting HT or PH2 was evaluated.

Results

Thirty-four patients (50%) developed subsequent HT: 18 (52.9%) had HI and 16 (47.1%) had PH, including 9 PH2 patients (13.2%). IV rt-PA was not significantly associated with HT or PH2 occurrence. Forty of the 68 patients (59%) revealed defect areas on the initial TTP mapping (TTP map-defect), and 34 of these 40 patients (85%) developed secondary HT and 9 patients (22.5%) developed PH2. Initial ‘TTP map-defect’ was significantly associated with the occurrence of HT (p < 0.0001) and PH2 (p = 0.0070). Thirty of the 34 patients (88.2%) in the HT group experienced delayed recanalization of the occluded vessels, in contrast to only 8 of the 34 patients (23.6%) in the non-HT group. All patients of the PH2 group showed recanalization (p = 0.0042). In 40 ‘TTP map-defect’-positive patients, delayed recanalization was associated with the occurrence of HT (p < 0.0001) and PH2 (p = 0.0491). All 28 patients without ‘TTP map-defect’ did not develop HT, including 8 patients (28.6%) with delayed recanalization.

Conclusions

Initial ‘TTP map-defect’ of CTP could accurately predict HT risk including PH2 risk and identify low-risk patients even in the delayed period.

Accuracy and reliability assessment of CT and MR perfusion analysis software using a digital phantom

PURPOSE

To design a digital phantom data set for computed tomography (CT) perfusion and perfusion-weighted imaging on the basis of the widely accepted tracer kinetic theory in which the true values of cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and tracer arrival delay are known and to evaluate the accuracy and reliability of postprocessing programs using this digital phantom.

MATERIALS AND METHODS

A phantom data set was created by generating concentration-time curves reflecting true values for CBF (2.5-87.5 mL/100 g per minute), CBV (1.0-5.0 mL/100 g), MTT (3.4-24 seconds), and tracer delays (0-3.0 seconds). These curves were embedded in human brain images. The data were analyzed by using 13 algorithms each for CT and magnetic resonance (MR), including five commercial vendors and five academic programs. Accuracy was assessed by using the Pearson correlation coefficient (r) for true values. Delay-, MTT-, or CBV-dependent errors and correlations between time to maximum of residue function (Tmax) were also evaluated.

RESULTS

In CT, CBV was generally well reproduced (r > 0.9 in 12 algorithms), but not CBF and MTT (r > 0.9 in seven and four algorithms, respectively). In MR, good correlation (r > 0.9) was observed in one-half of commercial programs, while all academic algorithms showed good correlations for all parameters. Most algorithms had delay-dependent errors, especially for commercial software, as well as CBV dependency for CBF or MTT calculation and MTT dependency for CBV calculation. Correlation was good in Tmax except for one algorithm.

CONCLUSION

The digital phantom readily evaluated the accuracy and characteristics of the CT and MR perfusion analysis software. All commercial programs had delay-induced errors and/or insufficient correlations with true values, while academic programs for MR showed good correlations with true values.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112618/-/DC1.

Penumbral imaging by using perfusion computed tomography and perfusion-weighted magnetic resonance imaging: current concepts

Perfusion computed tomography and perfusion-weighted magnetic resonance imaging are used to evaluate the extent of the area with ischemic penumbra; however, different parameters, algorithms, and software packages show significant discrepancies in the size of perfusion abnormalities, which should be minimized. Recently, cross-validation studies were performed using digital phantoms and have elucidated the precision and reliability of various penumbral imaging techniques. These research initiatives can promote further multicenter trials on recanalization therapies by providing accurate inclusion/exclusion criteria for appropriate patient selection.

Bayesian hemodynamic parameter estimation by bolus tracking perfusion weighted imaging

A delay-insensitive probabilistic method for estimating hemodynamic parameters, delays, theoretical residue functions, and concentration time curves by computed tomography (CT) and magnetic resonance (MR) perfusion weighted imaging is presented. Only a mild stationarity hypothesis is made beyond the standard perfusion model. New microvascular parameters with simple hemodynamic interpretation are naturally introduced. Simulations on standard digital phantoms show that the method outperforms the oscillating singular value decomposition (oSVD) method in terms of goodness-of-fit, linearity, statistical and systematic errors on all parameters, especially at low signal-to-noise ratios (SNRs). Delay is always estimated sharply with user-supplied resolution and is purely arterial, by contrast to oSVD time-to-maximum TMAX that is very noisy and biased by mean transit time (MTT), blood volume, and SNR. Residue functions and signals estimates do not suffer overfitting anymore. One CT acute stroke case confirms simulation results and highlights the ability of the method to reliably estimate MTT when SNR is low. Delays look promising for delineating the arterial occlusion territory and collateral circulation.

Large-scale transcriptome sequencing and gene analyses in the crab-eating macaque (Macaca fascicularis) for biomedical research

BACKGROUND

As a human replacement, the crab-eating macaque (Macaca fascicularis) is an invaluable non-human primate model for biomedical research, but the lack of genetic information on this primate has represented a significant obstacle for its broader use.

RESULTS

Here, we sequenced the transcriptome of 16 tissues originated from two individuals of crab-eating macaque (male and female), and identified genes to resolve the main obstacles for understanding the biological response of the crab-eating macaque. From 4 million reads with 1.4 billion base sequences, 31,786 isotigs containing genes similar to those of humans, 12,672 novel isotigs, and 348,160 singletons were identified using the GS FLX sequencing method. Approximately 86% of human genes were represented among the genes sequenced in this study. Additionally, 175 tissue-specific transcripts were identified, 81 of which were experimentally validated. In total, 4,314 alternative splicing (AS) events were identified and analyzed. Intriguingly, 10.4% of AS events were associated with transposable element (TE) insertions. Finally, investigation of TE exonization events and evolutionary analysis were conducted, revealing interesting phenomena of human-specific amplified trends in TE exonization events.

CONCLUSIONS

This report represents the first large-scale transcriptome sequencing and genetic analyses of M. fascicularis and could contribute to its utility for biomedical research and basic biology.