Perfusion Imaging In Acute Stroke Research Articles

Role of Magnetic Resonance Perfusion Imaging in Acute Stroke: Arterial Spin Labeling Versus Dynamic Susceptibility Contrast-Enhanced Perfusion.

Introduction: The role of perfusion neuroimaging in managing cases of acute ischemic stroke (AIS) is to identify ischemic penumbra and regions of hypo-perfusion, which can be salvaged. Dynamic susceptibility contrast (DSC) perfusion imaging techniques have been the main magnetic resonance imaging (MRI) perfusion techniques used to identify AIS. Arterial spin labelling (ASL) is an alternative non-invasive perfusion technique, which permits tissue perfusion measurement without any need for administration of exogenous contrast agents. The objective was to compare the diagnostic accuracy of ASL perfusion MRI versus DSC enhanced perfusion MRI in detecting perfusion-diffusion mismatch of varying volumes in acute ischemic stroke.Materials and methods: A hospital-based observational cross-sectional study was done in a tertiary care institute in Tamil Nadu between December 2018 to October 2019. Fifty-five subjects aged more than 18 years referred to the Radio-diagnosis department (less than 24 hours since the onset of weakness) for emergency assessment of suspected acute stroke were subjected to MRI stroke scan protocol. Then AIS cases were evaluated with ASL and DSC perfusion-weighted imaging. The collected data was entered in Excel (Microsoft, Redmond, WA, USA). IBM SPSS version 22 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. Receiver operating characteristic (ROC) analysis was done to assess the predictive validity of ASL in predicting DSC mismatch. The diagnostic accuracy of ASL was the primary outcome variable. P-value < 0.05 was considered statistically significant.Results: Forty-four subjects confirmed as stroke were included in the final analysis. Their mean (±SD) age was 53.84 (±10.80) years. 72.7% were males. The majority (53.8%) presented during the acute stage of cerebral infarction (53.8%). The majority (45.5%) had hemiplegia followed by aphasia (27.3%). The major vascular territory involved was the middle cerebral artery (54.5%). The sensitivity, specificity, positive predictive value, and negative predictive value of ASL (non-contrast) in predicting DSC (contrast) mismatch was found to be 71.43%, 78.57%, 83.33%, and 64.71% respectively.Conclusion: ASL MR has the potential to replace MRI DSC perfusion in the future imaging diagnostic work-up for stroke. However, further studies are required to validate its role as the first-line imaging for stroke therapy.

Post-Contrast Acute Kidney Injury after Acute Stroke-Insights from a German Tertiary Care Center.

Background: Our aim was to investigate the relationship between additional iodinated contrast medium (CM) application for acute stroke imaging and Post-Contrast Acute Kidney Injury (PC-AKI). Methods: We performed a retrospective analysis of consecutive patients with acute stroke who received a CT angiogram (CTA) with or without additional CT perfusion (CTP) at admission between 2017 and 2020. The primary endpoint was the incidence of PC-AKI. Potential causes of renal function impairment were recorded and logistic regression was performed to determine predictors of PC-AKI. Results: Of 3134 cases screened, n = 989 met the predefined inclusion criteria. PC-AKI occurred in 22 (5.4%) patients who received CTA only and 18 (3.1%) patients who received CTA and additional CTP (unadjusted OR, CI; 0.59, 0.29–1.05). In 31/40 (77.5%) patients who suffered PC-AKI, a non-CM-related cause of renal function impairment was identified. Stroke etiology (hemorrhagic vs. ischemic) and indicators of prior kidney disease were independent predictors of PC-AKI. Conclusions: Additional administration of CM for perfusion imaging in acute stroke did not show a relevant influence on the occurrence of PC-AKI. Patients with intracranial hemorrhage and/or prior kidney disease are at particular risk of developing AKI.

Magnetic Particle Imaging for Real-Time Perfusion Imaging in Acute Stroke.

The fast and accurate assessment of cerebral perfusion is fundamental for the diagnosis and successful treatment of stroke patients. Magnetic particle imaging (MPI) is a new radiation-free tomographic imaging method with a superior temporal resolution, compared to other conventional imaging methods. In addition, MPI scanners can be built as prehospital mobile devices, which require less complex infrastructure than computed tomography (CT) and magnetic resonance imaging (MRI). With these advantages, MPI could accelerate the stroke diagnosis and treatment, thereby improving outcomes. Our objective was to investigate the capabilities of MPI to detect perfusion deficits in a murine model of ischemic stroke. Cerebral ischemia was induced by inserting of a microfilament in the internal carotid artery in C57BL/6 mice, thereby blocking the blood flow into the medial cerebral artery. After the injection of a contrast agent (superparamagnetic iron oxide nanoparticles) specifically tailored for MPI, cerebral perfusion and vascular anatomy were assessed by the MPI scanner within seconds. To validate and compare our MPI data, we performed perfusion imaging with a small animal MRI scanner. MPI detected the perfusion deficits in the ischemic brain, which were comparable to those with MRI but in real-time. For the first time, we showed that MPI could be used as a diagnostic tool for relevant diseases in vivo, such as an ischemic stroke. Due to its shorter image acquisition times and increased temporal resolution compared to that of MRI or CT, we expect that MPI offers the potential to improve stroke imaging and treatment.

Timing-Invariant CT Angiography Derived from CT Perfusion Imaging in Acute Stroke: A Diagnostic Performance Study.

Timing-invariant (or delay-insensitive) CT angiography derived from CT perfusion data may obviate a separate cranial CTA in acute stroke, thus enhancing patient safety by reducing total examination time, radiation dose, and volume of contrast material. We assessed the diagnostic accuracy of timing-invariant CTA for detecting intracranial artery occlusion in acute ischemic stroke, to examine whether standard CTA can be omitted. Patients with suspected ischemic stroke were prospectively enrolled and underwent CTA and CTP imaging at admission. Timing-invariant CTA was derived from the CTP data. Five neuroradiologic observers assessed all images for the presence and location of intracranial artery occlusion in a blinded and randomized manner. Sensitivity and specificity of timing-invariant CTA and standard CTA were calculated by using an independent expert panel as the reference standard. Interrater agreement was determined by using κ statistics. We included 108 patients with 47 vessel occlusions. Overall, standard CTA and timing-invariant CTA provided similar high diagnostic accuracy for occlusion detection with a sensitivity of 96% (95% CI, 90%-100%) and a specificity of 100% (99%-100%) for standard CTA and a sensitivity of 98% (95% CI, 94%-100%) and a specificity of 100% (95% CI, 100%-100%) for timing-invariant CTA. For proximal large-vessel occlusions, defined as occlusions of the ICA, basilar artery, and M1, the sensitivity and specificity were 100% (95% CI, 100%-100%) for both techniques. Interrater agreement was good for both techniques (mean κ value, 0.75 and 0.76). Timing-invariant CTA derived from CTP data provides diagnostic accuracy similar to that of standard CTA for the detection of artery occlusions in acute stroke.

Intravoxel incoherent motion perfusion imaging in acute stroke: initial clinical experience.

Intravoxel incoherent motion (IVIM) imaging is an MRI perfusion technique that uses a diffusion-weighted sequence with multiple b values and a bi-compartmental signal model to measure the so-called pseudo-diffusion of blood caused by its passage through the microvascular network. The goal of the current study was to assess the feasibility of IVIM perfusion fraction imaging in patients with acute stroke. Images were collected in 17 patients with acute stroke. Exclusion criteria were onset of symptoms to imaging >5 days, hemorrhagic transformation, infratentorial lesions, small lesions <0.5 cm in minimal diameter and hemodynamic instability. IVIM imaging was performed at 3 T, using a standard spin-echo Stejskal-Tanner pulsed gradients diffusion-weighted sequence, using 16 b values from 0 to 900 s/mm(2). Image quality was assessed by two radiologists, and quantitative analysis was performed in regions of interest placed in the stroke area, defined by thresholding the apparent diffusion coefficient maps, as well as in the contralateral region. IVIM perfusion fraction maps showed an area of decreased perfusion fraction f in the region of decreased apparent diffusion coefficient. Quantitative analysis showed a statistically significant decrease in both IVIM perfusion fraction f (0.026 ± 0.019 vs. 0.056 ± 0.025, p=2.2 · 10(-6)) and diffusion coefficient D compared with the contralateral side (3.9 ± 0.79 · 10(-4) vs. 7.5 ± 0.86 · 10(-4) mm(2)/s, p=1.3 · 10(-20)). IVIM perfusion fraction imaging is feasible in acute stroke. IVIM perfusion fraction is significantly reduced in the visible infarct. Further studies should evaluate the potential for IVIM to predict clinical outcome and treatment response.

Real-Time Ultrasound Perfusion Imaging in Acute Stroke: Assessment of Cerebral Perfusion Deficits Related to Arterial Recanalization

We investigated whether real-time ultrasound perfusion imaging (rt-UPI) is able to detect perfusion changes related to arterial recanalization in the acute phase of middle cerebral artery (MCA) stroke. Twenty-four patients with acute territorial MCA stroke were examined with rt-UPI and transcranial color-coded duplex ultrasound (TCCD). Ultrasound studies were consecutively performed within 24 h and 72–96 h after stroke onset. Real-time UPI parameters of bolus kinetics (time to peak, rt-TTP) and of refill kinetics (plateau A and slope β of the exponential replenishment curve) were calculated from regions of interest of ischemic versus normal brain tissue; these parameters were compared between early and follow-up examinations in patients who recanalized. At the early examination, there was a delay of rt-TTP in patients with MCA occlusion (rt-TTP [s]: 13.09 ± 3.21 vs. 10.16 ± 2.6; p = 0.01) and a lower value of the refill parameter β (β [1/s]: 0.62 ± 0.34 vs. 1.09 ± 0.58; p = 0.01) in ischemic compared with normal brain tissue, whereas there were no differences of the parameters A and Axβ. At follow-up, the delay of rt-TTP was reversible once recanalization of an underlying MCA obstruction was demonstrated: rt-TTP [s], 13.09 ± 3.21 at 24 h versus 10.95 ± 1.5 at 72–96 h (p = 0.03). Correspondingly, β showed a higher slope than at the first examination: β [1/s]: 0.55 ± 0.29 at 24 h versus 0.71 ± 0.27 at 72–96 h (p = 0.04). We conclude that real-time UPI can detect hemodynamic impairment in acute MCA occlusion and subsequent improvement following arterial recanalization. This offers the chance for bedside monitoring of the hemodynamic compromise (e.g. during therapeutic interventions such as systemic thrombolysis).

Does perfusion imaging add value compared with plain parenchymal and vascular imaging?

Stroke is a leading cause of mortality and disability worldwide, with 15 million people having a stroke annually. Given that it is very difficult to distinguish an ischemic from a...

Perfusion computer tomography: imaging and clinical validation in acute ischaemic stroke

Computed tomography perfusion imaging in acute stroke requires further validation. We aimed to establish the optimal computed tomography perfusion parameters defining the infarct core and critically hypoperfused tissue. Sub-6-h computed tomography perfusion and 24-h magnetic resonance imaging were analysed from 314 consecutive patients with ischaemic stroke. Diffusion-weighted imaging lesion volume at 24 h was used to define the extent of critically hypoperfused tissue (in patients without reperfusion between acute and 24-h time points), and infarct core (in patients with major reperfusion at 24 h). Pixel-based analysis of co-registered computed tomography perfusion and diffusion-weighted imaging was then used to define the optimum computed tomography perfusion thresholds for critically hypoperfused at-risk tissue and infarct core. These optimized acute computed tomography perfusion threshold-based lesion volumes were then compared with 24-h diffusion-weighted imaging infarct volume, as well as 24-h and 90-day clinical outcomes for validation. Relative delay time >2 s was the most accurate computed tomography perfusion threshold in predicting the extent of critically hypoperfused tissue with both receiver operating curve analysis (area under curve 0.86), and the volumetric validation (mean difference between computed tomography perfusion and 24-h diffusion-weighted imaging lesions = 2 cm(2), 95% confidence interval 0.5-3.2 cm(2)). Cerebral blood flow <40% (of contralateral) within the relative delay time >2 s perfusion lesion was the most accurate computed tomography perfusion threshold at defining infarct core with both receiver operating characteristic analysis (area under curve = 0.85) and the volumetric validation. Using these thresholds, the extent of computed tomography perfusion mismatch tissue (the volume of 'at-risk' tissue between the critically hypoperfused and core thresholds) salvaged from infarction correlated with clinical improvement at 24 h (R(2) = 0.59, P = 0.04) and 90 days (R(2) = 0.42, P = 0.02). Patients with larger baseline computed tomography perfusion infarct core volume (>25 ml) also had poorer recovery at Day 90 (P = 0.039). Computed tomography perfusion can accurately identify critically hypoperfused tissue that progresses to infarction without early reperfusion, and the computed tomography perfusion cerebral blood flow infarct core closely predicts the final volume of infarcted tissue in patients who do reperfuse. The computed tomography perfusion infarct core and at-risk measures identified are also strong predictors of clinical outcome.

Systematic Review of Perfusion Imaging With Computed Tomography and Magnetic Resonance in Acute Ischemic Stroke: Heterogeneity of Acquisition and Postprocessing Parameters

Heterogeneity of acquisition and postprocessing parameters for magnetic resonance- and computed tomography-based perfusion imaging in acute stroke may limit comparisons between studies, but the current degree of heterogeneity in the literature has not been precisely defined. We examined articles published before August 30, 2009 that reported perfusion thresholds, average lesion perfusion values, or correlations of perfusion deficit volumes from acute stroke patients <24 hours postictus. We compared acquisition parameters from published studies with guidance from the Acute Stroke Imaging Research Roadmap(1). In addition, we assessed the consistency of postprocessing parameters. Twenty computed tomography perfusion and 49 perfusion-weighted imaging studies were included from 7152 articles. Although certain parameters were reported frequently, consistently, and in line with the Roadmap proposals, we found substantial heterogeneity in other parameters, and there was considerable variation and underreporting of postprocessing methodology. There is substantial scope to increase homogeneity in future studies, eg, through reporting standards.

MR Perfusion Imaging in Acute Ischemic Stroke

Magnetic resonance (MR) perfusion imaging offers the potential for measuring brain perfusion in acute stroke patients, at a time when treatment decisions based on these measurements may affect outcomes dramatically. Rapid advancements in both acute stroke therapy and perfusion imaging techniques have resulted in continuing redefinition of the role that perfusion imaging should play in patient management. This review discusses the basic pathophysiology of acute stroke, the utility of different kinds of perfusion images, and research on the continually evolving role of MR perfusion imaging in acute stroke care.

CT Perfusion Imaging in Acute Stroke

Computed tomographic perfusion (CTP) imaging is an advanced modality that provides important information about capillary-level hemodynamics of the brain parenchyma. CTP can aid in diagnosis, management, and prognosis of acute stroke patients by clarifying acute cerebral physiology and hemodynamic status, including distinguishing severely hypoperfused but potentially salvageable tissue from both tissue likely to be irreversibly infarcted ("core") and hypoperfused but metabolically stable tissue ("benign oligemia"). A qualitative estimate of the presence and degree of ischemia is typically required for guiding clinical management. Radiation dose issues with CTP imaging, a topic of much current concern, are also addressed in this review.

Establishing a Rodent Stroke Perfusion Computed Tomography Model

Brain computed tomography perfusion imaging in acute stroke may help guide therapy. However, the perfusion thresholds defining potentially salvageable (penumbra) and irreversibly injured (infarct core) tissue require further validation. The aim of this study was to validate infarct core and penumbra perfusion thresholds in a rodent stroke model by developing and optimising perfusion computed tomography imaging, performing serial scanning and correlating scans with final histology. Stroke was induced in male Wistar rats (n=17) using the middle cerebral artery thread-occlusion method. Perfusion computed tomography scans were obtained immediately pre- and postocclusion, and every 30 min for 2.5 h. Histological changes of infarction were assessed after 24 h. High-quality maps of cerebral blood flow and cerebral blood volume were generated at multiple coronal planes after optimisation of contrast injection and scanning parameters. The prestroke absolute cerebral blood flow and cerebral blood volume values (mean ± SD) were 158.2 ± 49.94 ml/min per 100 g and 5.6 ± 1.13 ml per 100 g, respectively. Cerebral blood flow was significantly lower in the infarct region of interest than the contralateral hemisphere region of interest at all time points, except the 0.5 h postocclusion time point. However, cerebral blood volume was only significantly lower in the infarct region of interest than the contralateral hemisphere region of interest at the 1 h and the 1.5 h time points (postocclusion). This study has demonstrated for the first time the feasibility of performing perfusion computed tomography in the most commonly used animal model of stroke. The model will allow definitive studies to determine optimal thresholds and the reliability of perfusion computed tomography measures for infarct core and penumbra.

MR Mismatch and Thrombolysis

Since the initial description of the ischemic penumbra 30 years ago, the concept of rapid restoration of blood flow to threatened brain tissue has been the “holy grail” of acute stroke therapy.1,2 Despite its drawbacks, MR imaging of perfusion diffusion mismatch remains the most widely used and practical means of in vivo assessment. There is accumulating evidence linking reperfusion with better clinical outcomes and attenuation of infarct growth in patients in patients with MR mismatch. However, validation that imaging effectively selects thrombolytic responders is still lacking. Both protagonists have highlighted areas of uncertainty …

Clinical application of multidetector CT angiography and perfusion imaging in acute stroke

This article illustrates clinical application of 64 Detector CT Angiography and Perfusion of the Brain in the triage of acute stroke in patients with a view to thrombolytic therapy. CTA and perfusion of the Brain is less expensive and relatively widely available compared to Magnetic Resonance Imaging. This technique is likely to be widely used in the triage of the acute stroke patient in the near future.

Blood Flow Imaging of the Brain: 50 Years Experience

Blood Flow Imaging of the Brain: 50 Years Experience

Cerebral Perfusion Imaging in Acute Stroke

Herein, the author discusses four perfusion technologies, including the diffusible tracer methods-xenon-enhanced computed tomography (CT) and single photon emission CT with various radioisotopes-and the nondiffusible tracer techniques-CT perfusion and magnetic resonance (MR) perfusion and diffusion. The methods for and important issues in the performance of each technique are presented, along with the accuracy of the data acquired with each technique, as demonstrated with experimental studies. In addition, the use of each technique in the evaluation of patients with acute stroke and their relative advantages and disadvantages are presented.

Computed tomography perfusion imaging in acute stroke.

The development of thrombolytic and neuroprotective agents for the treatment of acute stroke has created an imperative for improved imaging techniques in the assessment of acute stroke. Five cases are presented to illustrate the value of perfusion CT in the evaluation of suspected acute stroke. To obtain the perfusion data, a rapid series of images was acquired without table movement following a bolus of contrast medium. Cerebral blood flow, cerebral blood volume and mean transit time were determined by mathematically modelling the temporal changes in contrast enhancement in the brain and vascular system. Pixel-by-pixel analysis allowed generation of perfusion maps. In two cases, CT-perfusion imaging usefully excluded acute stroke, including one patient in whom a low-density area on conventional CT was subsequently proven to be tumour. Cerebral ischaemia was confirmed in three cases, one with an old and a new infarction, one with a large conventional CT abnormality but only a small perfusion defect, and one demonstrating infarct and penumbra. Perfusion CT offers the ability to positively identify patients with non-haemorrhagic stroke in the presence of a normal conventional CT, to select those cases where thrombolysis is appropriate, and to provide an indication for prognosis.