Perfusion mapping using computed tomography allows accurate prediction of cerebral infarction in experimental brain ischemia

rESWT promoted angiogenesis via Bach1/Wnt/β-catenin signaling pathway

Previous reports have established that rESWT fosters angiogenesis, yet the mechanism by which rESWT promotes cerebral angiogenesis remains elusive. rESWT stimulated HUVECs proliferation as evidenced by the CCK-8 test, with an optimal dosage of 2.0 Bar, 200 impulses, and 2 Hz. The tube formation assay of HUVECs revealed that tube formation peaked at 36 h post-rESWT treatment, concurrent with the lowest expression level of Bach1, as detected by both Western blot and immunofluorescence. The expression level of Wnt3a, β-catenin, and VEGF also peaked at 36 h. A Bach1 overexpression plasmid was transfected into HUVECs, resulting in a decreased expression level of Wnt3a, β-catenin, and VEGF. Upon treatment with rESWT, the down-regulation of Wnt3a, β-catenin, and VEGF expression in the transfected cells was reversed. The Wnt/β-catenin inhibitor DKK-1 was utilized to suppress Wnt3a and β-catenin expression, which led to a concurrent decrease in VEGF expression. However, rESWT treatment could restore the expression of these three proteins, even in the presence of DKK-1. Moreover, in the established OGD model, it was observed that rESWT could inhibit the overexpression of Bach1 and enhance VEGF and VEGFR-2 expression under the OGD environment.

The Cytoskeletal Elements MAP2 and NF-L Show Substantial Alterations in Different Stroke Models While Elevated Serum Levels Highlight Especially MAP2 as a Sensitive Biomarker in Stroke Patients

In the setting of ischemic stroke, the neurofilament subunit NF-L and the microtubule-associated protein MAP2 have proven to be exceptionally ischemia-sensitive elements of the neuronal cytoskeleton. Since alterations of the cytoskeleton have been linked to the transition from reversible to irreversible tissue damage, the present study investigates underlying time- and region-specific alterations of NF-L and MAP2 in different animal models of focal cerebral ischemia. Although NF-L is increasingly established as a clinical stroke biomarker, MAP2 serum measurements after stroke are still lacking. Therefore, the present study further compares serum levels of MAP2 with NF-L in stroke patients. In the applied animal models, MAP2-related immunofluorescence intensities were decreased in ischemic areas, whereas the abundance of NF-L degradation products accounted for an increase of NF-L-related immunofluorescence intensity. Accordingly, Western blot analyses of ischemic areas revealed decreased protein levels of both MAP2 and NF-L. The cytoskeletal alterations are further reflected at an ultrastructural level as indicated by a significant reduction of detectable neurofilaments in cortical axons of ischemia-affected areas. Moreover, atomic force microscopy measurements confirmed altered mechanical properties as indicated by a decreased elastic strength in ischemia-affected tissue. In addition to the results from the animal models, stroke patients exhibited significantly elevated serum levels of MAP2, which increased with infarct size, whereas serum levels of NF-L did not differ significantly. Thus, MAP2 appears to be a more sensitive stroke biomarker than NF-L, especially for early neuronal damage. This perspective is strengthened by the results from the animal models, showing MAP2-related alterations at earlier time points compared to NF-L. The profound ischemia-induced alterations further qualify both cytoskeletal elements as promising targets for neuroprotective therapies.

Limited reliability of computed tomographic perfusion acute infarct volume measurements compared with diffusion-weighted imaging in anterior circulation stroke

BACKGROUND AND PURPOSE

Diffusion-weighted imaging (DWI) can reliably identify critically ischemic tissue shortly after stroke onset. We tested whether thresholded computed tomographic cerebral blood flow (CT-CBF) and CT-cerebral blood volume (CT-CBV) maps are sufficiently accurate to substitute for DWI for estimating the critically ischemic tissue volume.

METHODS

Ischemic volumes of 55 patients with acute anterior circulation stroke were assessed on DWI by visual segmentation and on CT-CBF and CT-CBV with segmentation using 15% and 30% thresholds, respectively. The contrast:noise ratios of ischemic regions on the DWI and CT perfusion (CTP) images were measured. Correlation and Bland-Altman analyses were used to assess the reliability of CTP.

RESULTS

Mean contrast:noise ratios for DWI, CT-CBF, and CT-CBV were 4.3, 0.9, and 0.4, respectively. CTP and DWI lesion volumes were highly correlated (R(2)=0.87 for CT-CBF; R(2)=0.83 for CT-CBV; P<0.001). Bland-Altman analyses revealed little systemic bias (-2.6 mL) but high measurement variability (95% confidence interval, ±56.7 mL) between mean CT-CBF and DWI lesion volumes, and systemic bias (-26 mL) and high measurement variability (95% confidence interval, ±64.0 mL) between mean CT-CBV and DWI lesion volumes. A simulated treatment study demonstrated that using CTP-CBF instead of DWI for detecting a statistically significant effect would require at least twice as many patients.

CONCLUSIONS

The poor contrast:noise ratios of CT-CBV and CT-CBF compared with those of DWI result in large measurement error, making it problematic to substitute CTP for DWI in selecting individual acute stroke patients for treatment. CTP could be used for treatment studies of patient groups, but the number of patients needed to identify a significant effect is much higher than the number needed if DWI is used.

Human umbilical cord blood mesenchymal stem cell transplantation suppresses inflammatory responses and neuronal apoptosis during early stage of focal cerebral ischemia in rabbits

AIM

Human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) have been shown to ameliorate cerebral ischemia in animal models. In this study we investigated the effects of hUCB-MSCs on inflammatory responses and neuronal apoptosis during the early stage of focal cerebral ischemia in rabbits.

METHODS

Focal cerebral ischemia was induced in male New Zealand rabbits by occlusion of MCA for 2 h. The blood samples were collected at different time points prior and during MCAO-reperfusion. The animals were euthanized 3 d after MCAO, and the protein levels of IL-1β, IL-6, IL-10 and TNF-α in the serum and peri-ischemic brain tissues were detected using Western blot and ELISA, respectively. Inflammatory cell infiltration, neuronal apoptosis and neuronal density were measured morphologically. hUCB-MSCs (5 × 10(6)) were iv injected a few minutes after MCAO.

RESULTS

The serum levels of IL-1β, IL-6 and TNF-α were rapidly increased, and peaked at 2 h after the start of MCAO. hUCB-MSC transplantation markedly and progressively suppressed the ischemia-induced increases of serum IL-1β, IL-6 and TNF-α levels within 6 h MCAO-reperfusion. Focal cerebral ischemia decreased the serum level of IL-10, which was prevented by hUCB-MSC transplantation. The expression of IL-1β, IL-6, IL-10 and TNF-α in the peri-ischemic brain tissues showed similar changes as in the serum. hUCB-MSC transplantation markedly suppressed the infiltration of inflammatory cells, and increased the neuronal density around the ischemic region. Furthermore, hUCB-MSC transplantation significantly decreased the percentage of apoptosis around the ischemic region.

CONCLUSION

hUCB-MSCs transplantation suppresses inflammatory responses and neuronal apoptosis during the early stage focal cerebral ischemia in rabbits.

Window narrowing: a new method for standardized assessment of the tissue at risk-maximum of infarction in CT based brain perfusion maps

BACKGROUND

Mapping of brain perfusion using bolus tracking methods is increasingly used to assess the amount and severity of cerebral ischemia in acute stroke. Using relative perfusion maps, however, it is difficult to identify the tissue at risk-maximum (TARM) of infarction with sufficient reliability and reproducibility.

METHODS

We analysed 76 perfusion computed tomography (PCT) derived maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and time-to-peak (TTP) in 40 acute stroke patients using multidetector row technology and standard software (Somatom VolumeZoom, Siemens, Germany). 'Window narrowing' of the color maps was performed until color homogenisation of the contralateral unaffected hemisphere was reached. Tissue still depictable on the affected hemisphere after sufficient window narrowing was defined as the TARM. We analysed presence and size of the TARM on PCT maps, its relative perfusion values by comparison with contralateral, mirrored tissue, and its correlation with occurrence and final size of cerebral infarction on follow-up imaging.

RESULTS

An ischemic area was visible in 64, 58.9 and 72.6% on the conventional CBF, CBV and TTP maps, respectively. After window narrowing, a TARM was present in 56.8, 54.1 and 63.0% of slices comprising 11.9, 11.6 and 21.1% of the ipsilateral hemisphere (CBF, CBV and TTP), respectively. The relative perfusion values were 38.7 (CBF) and 43.0% (CBV) for the entire ischemic area and 11.3 (CBF) and 13.3% (CBV) for the TARM. Definite cerebral infarction was visible on 68.1% of the target slices comprising 23.7 +/- 22.9% of the ipsilateral hemisphere. The size of the TARM correlated slightly better with the final infarction size (r=0.74-0.82) than the entire ischemic area (r=0.61-0.79). With respect to the occurrence of cerebral infarction, the presence of a TARM on CBF maps showed the best positive (97.9%) and negative (72.7%) predictability.

DISCUSSION

On PCT maps, window narrowing provides a standardized display of the TARM in peracute stroke. The severely reduced values of relative CBF and CBV suggest the TARM to indicate tissue most prone to infarction.

Assessment of cerebral perfusion in post-traumatic brain injury patients with the use of ICG-bolus tracking method

The aim of this study was to verify the usefulness of the time-resolved optical method utilizing diffusely reflected photons and fluorescence signals combined with intravenous injection of indocyanine green (ICG) in the assessment of brain perfusion in post-traumatic brain injury patients. The distributions of times of flight (DTOFs) of diffusely reflected photons were acquired together with the distributions of times of arrival (DTAs) of fluorescence photons. The data analysis methodology was based on the observation of delays between the signals of statistical moments (number of photons, mean time of flight and variance) of DTOFs and DTAs related to the inflow of ICG to the extra- and intracerebral tissue compartments. Eleven patients with brain hematoma, 15 patients with brain edema and a group of 9 healthy subjects were included in this study. Statistically significant differences between parameters obtained in healthy subjects and patients with brain hematoma and brain edema were observed. The best optical parameter to differentiate patients and control group was variance of the DTOFs or DTAs. Results of the study suggest that time-resolved optical monitoring of inflow of the ICG seems to be a promising tool for detecting cerebral perfusion insufficiencies in critically ill patients.

Optimisation of vascular input and output functions in CT-perfusion imaging using 256(or more)-slice multidetector CT

OBJECTIVES

To evaluate the accuracy and reproducibility of CT-perfusion (CTP) by finding the optimal artery for the arterial input function (AIF) and re-evaluating the necessity of the venous output function (VOF).

METHODS

Forty-four acute ischaemic stroke patients who underwent non-enhanced CT, CTP and CT-angiography using 256-slice multidetector computed tomography (MDCT) were evaluated. The anterior cerebral artery (ACA), middle cerebral artery (MCA), internal carotid artery (ICA) and basilar artery were selected as the AIF. Subsequently the resulting area under the time-enhancement curve of the AIF (AUCAIF) and quantitative perfusion measurements were analysed by repeated measures ANOVA and subsequently the paired t test. To evaluate reproducibility we examined if the VOF could be deleted by comparing the perfusion measurements using versus not using the VOF (paired t test).

RESULTS

The AUCAIF and perfusion measurements resulting from the different AIFs showed significant group differences (all P < 0.0001). The ICA had the largest AUCAIF and resulted in the highest mean transient time (MTT) and lowest cerebral blood flow (CBF), whereas the basilar artery showed the lowest cerebral blood volume (CBV). Not using the VOF showed significantly higher CBV and CBF in 66 % of patients on the ipsilateral (P < 0.0001 and P = 0.007, respectively) and contralateral hemisphere (P < 0.0001 and P = 0.019, respectively).

CONCLUSION

Selecting the ICA as the AIF and continuing the use of the VOF would improve the accuracy of CTP.

KEY POINTS

• Perfusion imaging is an increasingly important aspect of multidetector computed tomography (MDCT). • Vascular input functions were evaluated for CT-perfusion using 256-slice MDCT. • Selecting different arterial input functions (AIFs) leads to variation in quantitative values. • Using the internal carotid artery for AIF provides optimal perfusion values. • Deleting the venous output function would be detrimental for validity.

Standardization of Stroke Perfusion CT for Reperfusion Therapy

With the advances in terms of perfusion imaging, the "time is brain" approach used for acute reperfusion therapy in ischemic stroke patients is slowly being replaced by a "penumbra is brain" or "imaging is brain" approach. But the concept of penumbra-guided reperfusion therapy has not been validated. The lack of standardization in penumbral imaging is one of the main contributing factors for this absence of validation. This article reviews the issues underlying the lack of standardization of perfusion-CT for penumbra imaging, and offers avenues to remedy this situation.

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.

Advanced imaging assessment of posterior circulation stroke before and after endovascular intervention

BACKGROUND

Perfusion-computed tomography (CTP) is a relatively new technique that allows rapid semiquantitative noninvasive evaluation of cerebral perfusion aiding in the diagnosis of cerebral ischemia and infarction. There is a paucity of data on its application within the posterior circulation, especially, the brainstem. We describe a case of basilar artery thrombosis with cerebellar and brainstem CTP mismatch and discuss possible future applications of CTP for acute posterior fossa circulation and infarction.

METHODS

Case report.

RESULTS

Successful use of CTP to aid in decision to proceed with neurointervention in acute basilar artery occlusion and confirm its resolution after mechanical clot retrieval.

CONCLUSION

Perfusion-computed tomography can successfully be used to define cerebral ischemia and infarction within the posterior fossa and aid in decisions to proceed with neurointervention.

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.

Arterial input function placement for accurate CT perfusion map construction in acute stroke

OBJECTIVE

The objective of our study was to evaluate the effect of varying arterial input function (AIF) placement on the qualitative and quantitative CT perfusion parameters.

MATERIALS AND METHODS

Retrospective analysis of CT perfusion data was performed on 14 acute stroke patients with a proximal middle cerebral artery (MCA) clot. Cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) maps were constructed using a systematic method by varying only the AIF placement in four positions relative to the MCA clot including proximal and distal to the clot in the ipsilateral and contralateral hemispheres. Two postprocessing software programs were used to evaluate the effect of AIF placement on perfusion parameters using a delay-insensitive deconvolution method compared with a standard deconvolution method.

RESULTS

One hundred sixty-eight CT perfusion maps were constructed for each software package. Both software programs generated a mean CBF at the infarct core of < 12 mL/100 g/min and a mean CBV of < 2 mL/100 g for AIF placement proximal to the clot in the ipsilateral hemisphere and proximal and distal to the clot in the contralateral hemisphere. For AIF placement distal to the clot in the ipsilateral hemisphere, the mean CBF significantly increased to 17.3 mL/100 g/min with delay-insensitive software and to 19.4 mL/100 g/min with standard software (p < 0.05). The mean MTT was significantly decreased for this AIF position. Furthermore, this AIF position yielded qualitatively different parametric maps, being most pronounced with MTT and CBF. Overall, CBV was least affected by AIF location.

CONCLUSION

For postprocessing of accurate quantitative CT perfusion maps, laterality of the AIF location is less important than avoiding AIF placement distal to the clot as detected on CT angiography. This pitfall is less severe with deconvolution-based software programs using a delay-insensitive technique than with those using a standard deconvolution method.

Quantitative blood flow measurements in the small animal cardiopulmonary system using digital subtraction angiography

PURPOSE

The use of preclinical rodent models of disease continues to grow because these models help elucidate pathogenic mechanisms and provide robust test beds for drug development. Among the major anatomic and physiologic indicators of disease progression and genetic or drug modification of responses are measurements of blood vessel caliber and flow. Moreover, cardiopulmonary blood flow is a critical indicator of gas exchange. Current methods of measuring cardiopulmonary blood flow suffer from some or all of the following limitations--they produce relative values, are limited to global measurements, do not provide vasculature visualization, are not able to measure acute changes, are invasive, or require euthanasia.

METHODS

In this study, high-spatial and high-temporal resolution x-ray digital subtraction angiography (DSA) was used to obtain vasculature visualization, quantitative blood flow in absolute metrics (ml/min instead of arbitrary units or velocity), and relative blood volume dynamics from discrete regions of interest on a pixel-by-pixel basis (100 x 100 microm2).

RESULTS

A series of calibrations linked the DSA flow measurements to standard physiological measurement using thermodilution and Fick's method for cardiac output (CO), which in eight anesthetized Fischer-344 rats was found to be 37.0 +/- 5.1 ml/min. Phantom experiments were conducted to calibrate the radiographic density to vessel thickness, allowing a link of DSA cardiac output measurements to cardiopulmonary blood flow measurements in discrete regions of interest. The scaling factor linking relative DSA cardiac output measurements to the Fick's absolute measurements was found to be 18.90 x CODSA = COFick.

CONCLUSIONS

This calibrated DSA approach allows repeated simultaneous visualization of vasculature and measurement of blood flow dynamics on a regional level in the living rat.

Quantitative assessment of blood volume and permeability in cerebral mass lesions using dynamic contrast-enhanced computed tomography in the dog

RATIONALE AND OBJECTIVES

To evaluate cerebral blood volume (CBV) and permeability (PS) in spontaneously occurring cerebral neoplastic and non-neoplastic lesions in dogs using dynamic contrast-enhanced computed tomography (DCE-CT).

MATERIALS AND METHODS

Dogs presenting with spontaneous intracranial lesions (n = 16) underwent DCE-CT at the level of the lesion followed by a histologically confirmed diagnosis from a CT-guided stereotactic biopsy. Data post-processing was performed with commercially available CT software (GEMS Advantage Workstation 4.2). Symmetric regions of interest (ROIs) were drawn within the lesion and unaffected areas on the contralateral side. Values were compared between lesion types and ratios of lesion-to-normal brain were calculated.

RESULTS

Dogs with extra-axial lesions (n = 3 meningiomas) had marked elevation of CBV and PS compared to normal brain. All Grade III gliomas (n = 5) had mildly elevated CBV and markedly elevated PS values. All lower Grade II gliomas (n = 2) had minimal elevation in CBV and PS. Dogs with non-neoplastic intra-axial lesions (one each necrotizing, fungal, and lymphoplasmacytic encephalitis) had elevation of PS with normal to mildly elevated CBV. Lesion-to-normal brain ratios for PS separated extra- and intra-axial neoplasms and intra-axial inflammatory/degenerative lesions from each other.

CONCLUSIONS

Low-grade gliomas do not consistently demonstrate elevated vascular parameters, whereas Grade III gliomas and non-neoplastic intra-axial lesions have elevated PS. Ratios between such lesions and normal brain may prove useful for differentiating types of lesions. These findings resemble those previously reported in similar lesions in people indicating that the dog may act as a good model for intracranial masses for the study of lesion angiogenesis and response to therapy.

Assessment of perihematomal hypoperfusion injury in subacute and chronic intracerebral hemorrhage by CT perfusion imaging

OBJECTIVE

To study alterations of perihematomal cerebral perfusion associated to subacute and chronic intracerebral hemorrhage (ICH) by means of computed tomography perfusion (CTP) imaging.

METHODS

Non-enhanced CT scan and CTP examination were performed in 12 patients with subacute and chronic supratentorial ICH. The hematoma volume was measured, and the regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), mean transit time (MTT) and time-to-peak (TTP) adjacent to hematoma were measured in 11 of 12 cases.

RESULTS

Eleven patients with mean age of 58.1 years were finally analysed. Mean time interval from symptom onset to initial CTP scanning was 18.4 days; mean hematoma volume was 26.8 ml. The gradient of hypoperfusion around the hematoma was revealed by rCBF maps in 11 cases, and by rCBV maps in ten cases. The areas of delayed TTP and MTT were showed in 11 and ten cases, respectively. The degree of reduction in rCBV correlated strongly with the hematoma volume (r(inner)=0.764, p=0.006;r(outer)=0.703, p=0.016). There was no correlation between the changes in rCBF, rCBV, MTT and TTP and the time interval from symptom onset to initial CTP examination.

CONCLUSION

We have concluded that the gradient of hypoperfusion surrounding the hematoma may still exist during the subacute and chronic phases after ICH. The alterations in rCBV correlate with the hematoma volume. We believe that the reperfusion injury marked by increased rCBV contributes to the perilesional brain injury. The quantitative CT perfusion measurements can provide valuable information in individual management and prognostic evaluation of ICH.

Multimodal Use of Computed Tomography in Early Acute Stroke, Part 2

Computed tomography (CT) scan remains the most widely technique in the cerebrovascular emergency, as it is largely available, minimally invasive, fast, cheap and reliable. Noncontrast enhanced CT (NeCT) imaging can show early signs of infarction in ischemic stroke; however, it could not show if the ischemic tissue is irreversibly damaged. CT perfusion (CTP) imaging has been shown to predict stroke location and size and can provide information about ischemic cerebral parenchyma not definitively compromised. CT angiography (CTA) could highlight stenosis or occlusion both in intracranial and extracranial vessels. By combining NeCT, CTP, and CTA the entire cerebrovascular axis can be imaged during acute stroke. Currently, the term "multimodal CT" indicates the combined use of these three techniques in order to obtain a complete picture of the extension of ischemic damage in acute stroke patients.

Utilization of dynamic CT perfusion in the study of intracranial meningiomas and their surrounding tissue

OBJECTIVE

To use CT perfusion (CTP) to assess levels of ischemia in brain areas around intracranial meningiomas.

MATERIALS AND METHODS

Fifteen patients with intracranial meningiomas were analysed preoperatively with CTP study. The cerebral blood flow (CBF), cerebral blood volume (CBV) and time to peak (TTP) were measured in the edema, peritumoral edema and in the normal areas of brain.

RESULTS

The peritumoral edema measured a mean CBF of 17.36 ml/min/100 ml (median=15.8) and the mean CBF value in the whole edema was 93.86 ml/min/100 ml (median=79.9). The mean CBV measured in the peritumoral edema was 2.7 (median=2.3) and the measured mean CBV of edema was 15 (median=13.2). In the region of the peritumoral edema, the mean CBF and CBV were lower than in the edema bed. Normal brain remote from the edema measured less CBF (mean=28.36 ml/min/100 ml, median=29.7) and CBV (mean=4.1, median=3.8) than the edema. Six patients were noted to have CBF of less than 15 ml/min/100 ml in the perilesional edema. The measured mean CBF and CBV in the normal area of brain were higher than in the peritumoral edema, while the TTP was greater in the perilesional edema (mean=11, median=10.4) when compared with areas of normal brain (mean=9.9, median=9.5) with statistically significant p values.

CONCLUSION

The values obtained elucidate the fact that perilesional edematous areas are ischemic. By subset analysis, it may be possible to identify those areas with recoverable tissue from non-recoverable tissue.

Endoplasmic reticulum in the penumbra following middle cerebral artery occlusion in the rabbit

Caspase-12 has been localized to endoplasmic reticulum (ER) and showed to involve ER stress-induced apoptosis. In the present work we investigated the temporospatial alterations of caspase-12 immunoreactivity in the penumbra following cerebral ischemia/reperfusion in rabbit. Transient cerebral ischemia was produced by intraluminal occlusion of the middle cerebral artery for 2 h followed by 1 h, 6 h, 1 day, 3 days, 7 days and 14 days of reperfusion. Caspase-12 immunohistochemistry was first increased in the penumbra 1 h after reperfusion, with a peak at day 1 to day 3, and then gradually decreased to basal level at day 14. The number of TUNEL-positive cells and ultrastructural observation of brain sections in the penumbra showed a similar change at the same time points. ER mediated by caspase-12 participated in apoptosis induced by cerebral ischemia/reperfusion injury, which may provide a new area for therapeutic intervention to ameliorate outcomes following cerebral ischemia.

CT perfusion of the neck: internal carotid artery versus external carotid artery as the reference artery

Arterial selection for reference time-enhancement curve generation in deconvolution-based perfusion CT (PCT) studies of the head and neck is under-evaluated. This study of 11 patients with confirmed head and neck squamous cell carcinoma demonstrates significant correlation (range, r = 0.85-0.95) between perfusion parameter values derived with internal carotid artery (ICA) as compared to an external carotid artery reference, supporting the use of the ICA as arterial reference in PCT studies of the neck.

Vasoreactivity and peri-infarct hyperintensities in stroke

OBJECTIVE

It is unknown if impaired cerebral vasoreactivity recovers after ischemic stroke, and whether it compromises perfusion in regions surrounding infarct and other vascular territories. We investigated the regional differences in CO2 vasoreactivity (CO2 VR) and their relationships to peri-infarct T2 hyperintensities (PIHs), chronic infarct volumes, and clinical outcomes.

METHODS

We studied 39 subjects with chronic large middle cerebral artery territory infarcts and 48 matched controls. Anatomic and three-dimensional continuous arterial spin labeling imaging at 3-Tesla MRI were used to measure regional cerebral blood flow (CBF) and CO2 VR during normocapnia, hypercapnia, and hypocapnia in main arteries distributions.

RESULTS

Stroke patients showed a significantly lower augmentation of blood flow at increased CO2 but greater reduction of blood flow with decreased CO2 than the control group. This altered vasoregulatory response was observed both ipsilateral and contralateral to the stroke. Lower CO2 VR on the stroke side was associated with PIHs, greater infarct volume, and worse outcomes. The cases with PIHs (n = 27) had lower CBF during all conditions bilaterally (p < 0.0001) compared to cases with infarct only.

CONCLUSIONS

Perfusion augmentation is inadequate in multiple vascular territories in patients with large artery ischemic infarcts, but vasoconstriction is preserved. Peri-infarct T2 hyperintensities are associated with lower blood flow. Strategies aimed to preserve vasoreactivity after an ischemic stroke should be tested for their effect on long-term outcomes.

Automated versus manual post-processing of perfusion-CT data in patients with acute cerebral ischemia: influence on interobserver variability

Introduction

The purpose of this study is to compare the variability of PCT results obtained by automatic selection of the arterial input function (AIF), venous output function (VOF) and symmetry axis versus manual selection.

Methods

Imaging data from 30 PCT studies obtained as part of standard clinical stroke care at our institution in patients with suspected acute hemispheric ischemic stroke were retrospectively reviewed. Two observers performed the post-processing of 30 CTP datasets. Each observer processed the data twice, the first time employing manual selection of AIF, VOF and symmetry axis, and a second time using automated selection of these same parameters, with the user being allowed to adjust them whenever deemed appropriate. The volumes of infarct core and of total perfusion defect were recorded. The cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT) and blood–brain barrier permeability (BBBP) values in standardized regions of interest were recorded. Interobserver variability was quantified using the Bland and Altman's approach.

Results

Automated post-processing yielded lower coefficients of variation for the volume of the infarct core and the volume of the total perfusion defect (15.7% and 5.8%, respectively) compared to manual post-processing (31.0% and 12.2%, respectively). Automated post-processing yielded lower coefficients of variation for PCT values (11.3% for CBV, 9.7% for CBF, and 9.5% for MTT) compared to manual post-processing (23.7% for CBV, 32.8% for CBF, and 16.7% for MTT).

Conclusion

Automated post-processing of PCT data improves interobserver agreement in measurements of CBV, CBF and MTT, as well as volume of infarct core and penumbra.

Theoretic basis and technical implementations of CT perfusion in acute ischemic stroke, part 1: Theoretic basis

CT perfusion (CTP) is a functional imaging technique that provides important information about capillary-level hemodynamics of the brain parenchyma and is a natural complement to the strengths of unenhanced CT and CT angiography in the evaluation of acute stroke, vasospasm, and other neurovascular disorders. CTP is critical in determining the extent of irreversibly infarcted brain tissue (infarct "core") and the severely ischemic but potentially salvageable tissue ("penumbra"). This is achieved by generating parametric maps of cerebral blood flow, cerebral blood volume, and mean transit time.

Neuroimaging of ischemic stroke with CT and MRI: advancing towards physiology-based diagnosis and therapy

Acute ischemic stroke is the third leading cause of death and the major cause of significant disability in adults in the USA and Europe. The number of patients who are actually treated for acute ischemic stroke is disappointingly low, despite availability of effective treatments. A major obstacle is the short window of time following stroke in which therapies are effective. Modern imaging is able to identify the ischemic penumbra, a key concept in stroke physiology. Evidence is accumulating that identification of a penumbra enhances patient management, resulting in significantly improved outcomes. Moreover, unexpectedly large proportions of patients have a substantial ischemic penumbra beyond the traditional time window and are suitable for therapy. The widespread availability of modern MRI and computed tomography systems presents new opportunities to use physiology to guide ischemic stroke therapy in individual patients. This article suggests an evidence-based alternative to contemporary acute ischemic stroke therapy.

Hemodynamic effects of recombinant human erythropoietin on the central nervous system after subarachnoid hemorrhage: reduction of microcirculatory impairment and functional deficits in a rabbit model

OBJECT

The authors investigated the hemodynamic effects of recombinant human erythropoietin (rhEPO) after subarachnoid hemorrhage (SAH) in rabbits.

METHODS

The authors used male New Zealand White rabbits in this study divided into the following groups: SAH plus saline (16 rabbits), SAH plus low-dose rhEPO (16 rabbits; 1500 IU/kg on Day 0 and 500 IU/kg on Days 2 and 4), SAH plus high-dose rhEPO (10 rabbits; 1500 IU/kg on Days 0, 2, 4, and 6), and sham (6 rabbits). Computed tomography perfusion studies and CT angiography were performed for 1 hour after SAH on Day 0, and once each on Days 2, 4, 7, 9, and 16 after SAH. Assessments of neurological function and tissue histology were also performed.

RESULTS

The mortality rate was significantly lower after rhEPO treatment (12%) than after saline treatment (44%) (p < 0.05). Neurological outcomes in the low-dose and high-dose rhEPO groups were better than in the saline group after SAH (p < 0.05), and the cerebral blood flow in the high-dose rhEPO group was greater than that in the saline group (p < 0.05). The mean transit time was significantly lower on Days 2 and 4 in the low-dose and high-dose rhEPO groups than in the saline group, but increased significantly on Day 7 in both groups (p < 0.05). The hematocrit increased significantly from baseline values in the high-dose and low-dose rhEPO groups on Days 4 and 7, respectively (p < 0.05).

CONCLUSIONS

Treatment with rhEPO after experimental SAH is associated with improved cerebral blood flow and microcirculatory flow as reflected by lower mean transit times. Improved tissue perfusion correlated with reduced mortality and improved neurological outcomes. Further investigation of the impact of increasing hematocrit on hemodynamic changes is needed.

Development of early cerebral swelling in surgically treated ruptured aneurysm of acute stage, its significance, and management

The present study includes 38 patients treated surgically for ruptured aneurysm manifesting subarachnoid hemorrhage without intracerebral hematoma, evaluating clinical grade at admission, secondary development and management of early cerebral swelling, subsequent complications such as cerebral infarction caused by vasospasm, and clinical outcome. Six of 32 patients treated by early surgery within 24 hours developed critical cerebral swelling in the early period after SAH. Five of these 6 patients received barbiturate therapy. Two patients died of advancing cerebral swelling. Three of 5 patients who received barbiturate therapy showed good recovery without any neurologic deficit, 1 suffered intellectual impairment, and the other 1 died. Serial computed tomography (CT), CT angiography, and dynamic CT evaluated elapsing of cerebral swelling, progression of cerebral vasospasm, and change of cerebral blood perfusion (flow) in 2 patients who suffered early cerebral swelling. In these 2 patients, progression or persistence of vasospasm was recorded for a longer period, whereas the cerebral swelling resolved within a short period. Cerebral infarction caused by vasospasm was seen in 8 of these 38 surgical cases, and hydrocephalus was seen in 15 of 38 cases. All 4 survivors after early cerebral swelling developed hydrocephalus and underwent shunting. Development of cerebral swelling in patients with ruptured aneurysm greatly affects outcome. Although barbiturate therapy is useful for the treatment of patients who suffer serious cerebral swelling, improvements in management may be required.

CT perfusion identifies increased salvage of tissue in patients receiving intravenous recombinant tissue plasminogen activator within 3 hours of stroke onset

BACKGROUND AND PURPOSE

In spite of the advent of thrombolytic therapy, CT-perfusion imaging is currently not fully used for clinical decision-making and not included in published clinical guidelines for management of ischemic stroke. We investigated whether lesion volumes on cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) maps predict final infarct volume and whether all these parameters are needed for triage to intravenous recombinant tissue plasminogen activator (rtPA). We also investigated the effect of intravenous rtPA on affected brain by measuring salvaged tissue volume in patients receiving intravenous rtPA and in controls.

MATERIALS AND METHODS

Forty-four patients receiving intravenous rtPA and 19 controls underwent CT perfusion (CTP) studies in the emergency department within 3 hours of stroke onset. Lesion volumes were measured on MTT, CBV, and CBF maps by region-of-interest analysis and were compared with follow-up CT volumes by correlation and regression analysis. The volume of salvaged tissue was determined as the difference between the initial MTT and follow-up CT lesion volumes and was compared between intravenous rtPA-treated patients and controls.

RESULTS

No significant difference between the groups was observed in lesion volume assessed from the CTP maps (P > .08). Coefficients of determination for MTT, CBF, and CBV versus follow-up CT lesion volumes were 0.3, 0.3, 0.47, with intravenous rtPA; and 0.53, 0.55, and 0.81 without intravenous rtPA. Regression of MTT on CBF lesion volumes showed codependence (R(2) = 0.98, P < .0001). Mean salvaged tissue volumes with intravenous rtPA were 21.8 +/- 17.1 and 13.2 +/- 13.5 mL in controls; these were significantly different by using nonparametric (P < .03) and Fisher exact tests (P < .04).

CONCLUSIONS

Within 3 hours of stroke onset, CBV lesion volume does not necessarily represent dead tissue. MTT lesion volume alone can be used to identify the upper limit of the size of abnormally perfused brain. More brain is salvaged in patients with intravenous rtPA than in controls.

Brain perfusion CT: principles, technique and clinical applications

The imaging of brain haemodynamics and its applications are generating growing interest. By providing quantitative measurements of cerebral blood flow (CBF) and cerebral blood volume (CBV), dynamic perfusion computed tomography (p-CT) allows visualisation of cerebral autoregulation mechanisms and represents a fast, available and reliable imaging option for assessing cerebral perfusion. Thanks to its feasibility in emergency settings, p-CT is considered most useful, in combination with CT angiography, in acute ischaemic patients, as it is able to provide a fast and noninvasive assessment of cerebral perfusion impairment. In addition, p-CT can play a diagnostic role in other types of cerebrovascular disease to assess functional reserve, and in intracranial neoplasms, where it has a role in diagnosis, grading, biopsy guidance, and follow-up during treatment. This article illustrates the principles, technique and clinical applications of p-CT cerebral perfusion studies.

Realization of reliable cerebral-blood-flow maps from low-dose CT perfusion images by statistical noise reduction using nonlinear diffusion filtering

X-ray computed tomographic perfusion (CTP) imaging, a rapid method for measuring cerebral blood flow (CBF), is an effective modality for assessment of the severity and extent of brain tissue ischemia. Low-dose scanning has been required for CTP imaging for reducing the radiation exposure to patients, because the same plane is scanned repeatedly. Low-dose CTP imaging, however, results in substantial statistical noise in the images, which may negatively impact the accuracy of CBF values. Because CBF values are calculated from the set of CTP images, it is important to reduce the statistical noise in raw CTP images to make the values reliable. Noise reduction must be performed without blurring of vessel structures, because such blurring will overestimate CBF values. For this purpose, two-dimensional nonlinear diffusion filtering (NLDF) was introduced. It was applied to CTP images of a CTP phantom for evaluating the accuracy of CBF values in low-dose CTP and to clinical low-dose CTP images for determining its effectiveness in actual CTP examinations. NLDF successfully reduced the statistical noise in the CTP images while preserving the sharp edges. This feature generated CBF values close to the reference value, producing reliable CBF maps from low-dose CT perfusion images. The CBF maps obtained with NLDF were comparable to or better than those obtained by other, commercial CTP software programs. The use of NLDF was thus effective for manipulation of low-dose CT perfusion images.

Measuring elevated microvascular permeability and predicting hemorrhagic transformation in acute ischemic stroke using first-pass dynamic perfusion CT imaging

BACKGROUND AND PURPOSE

Hemorrhagic transformation (HT) can be a devastating complication of acute ischemic stroke (AIS). The purpose of this study was to determine whether increased microvascular permeability (PS) of the blood-brain barrier was detected in early AIS by using first-pass dynamic perfusion CT (PCT) and whether PS was significantly higher in infarcts destined for HT.

MATERIALS AND METHODS

Fifty patients with AIS less than 3 hours old and evaluated by PCT were included. PS color maps were retrospectively generated from PCT data using the Patlak model. One reader analyzed each PS map by drawing 4 circular 10-mm regions of interest on any focal abnormality. The mean of these 4 regions of interest represented the PS of the infarct (PSinfarct). The mean of 4 mirror regions of interest on the nonischemic contralateral hemisphere was also obtained (PScontrol). PSinfarct and PScontrol were compared by using an exact Wilcoxon test. PSinfarct for infarcts that developed HT on follow-up (PSHT) was compared with all of the others (PSNo-HT) using an exact Mann-Whitney test.

RESULTS

Forty-four infarcts (88%) showed focal PS elevation in the region of infarct. In units of milliliters per 100 milliliters per minute, PSinfarct ranged from 0 to 13 (mean: 3.5+/-3.1) versus PScontrol of 0-0.8 (mean: 0.28+/-0.27; P<.0001). Six infarcts (12%) developed HT, all of which were within the region of PS elevation. PSHT ranged from 5.2 to 13 (mean: 9.8+/-2.9) versus PSNo-HT of 0-5.9 (mean: 2.7+/-2.0; P<.0001). Eighteen infarcts (36%) were treated with recombinant tissue plasminogen activator (rtPA). A significant difference between PSHT and PSNo-HT persisted irrespective of rtPA treatment.

CONCLUSIONS

Elevated permeability was detectable in AIS by using first-pass PCT and it predicted subsequent HT.

Perfusion CT in acute stroke: prediction of vessel recanalization and clinical outcome in intravenous thrombolytic therapy

This study evaluated perfusion computed tomography (PCT) for the prediction of vessel recanalization and clinical outcome in patients undergoing intravenous thrombolysis. Thirty-nine patients with acute ischemic stroke of the middle cerebral artery territory underwent intravenous thrombolysis within 3 h of symptom onset. They all had non-enhanced CT (NECT), PCT, and CT angiography (CTA) before treatment. The Alberta Stroke Program Early Computed Tomography (ASPECT) score was applied to NECT and PCT maps to assess the extent of ischemia. CTA was assessed for the site of vessel occlusion. The National Institute of Health Stroke Scale (NIHSS) score was used for initial clinical assessment. Three-month clinical outcome was assessed using the modified Rankin scale. Vessel recanalization was determined by follow-up ultrasound. Of the PCT maps, a cerebral blood volume (CBV) ASPECT score of >6 versus < or =6 was the best predictor for clinical outcome (odds ratio, 31.43; 95% confidence interval, 3.41-289.58; P < 0.002), and was superior to NIHSS, NECT and CTA. No significant differences in ASPECT scores were found for the prediction of vessel recanalization. ASPECT score applied to PCT maps in acute stroke patients predicts the clinical outcome of intravenous thrombolysis and is superior to both early NECT and clinical parameters.