Quantitative assessment of regional cerebral blood flows by perfusion CT studies at low injection rates: a critical review of the underlying theoretical models

Deep Learning Denoising Improves CT Perfusion Image Quality in the Setting of Lower Contrast Dosing: A Feasibility Study

BACKGROUND AND PURPOSE

Considering recent iodinated contrast shortages and a focus on reducing waste, developing protocols with lower contrast dosing while maintaining image quality through artificial intelligence is needed. This study compared reduced iodinated contrast media and standard dose CTP acquisitions, and the impact of deep learning denoising on CTP image quality in preclinical and clinical studies. The effect of reduced X-ray mAs dose was also investigated in preclinical studies.

MATERIALS AND METHODS

Twelve swine underwent 9 CTP examinations each, performed at combinations of 3 different x-ray (37, 67, and 127 mAs) and iodinated contrast media doses (10, 15, and 20 mL). Clinical CTP acquisitions performed before and during the iodinated contrast media shortage and protocol change (from 40 to 30 mL) were retrospectively included. Eleven patients with reduced iodinated contrast media dosages and 11 propensity-score-matched controls with the standard iodinated contrast media dosages were included. A residual encoder-decoder convolutional neural network (RED-CNN) was trained for CTP denoising using k-space-weighted image average filtered CTP images as the target. The standard, RED-CNN-denoised, and k-space-weighted image average noise-filtered images for animal and human studies were compared for quantitative SNR and qualitative image evaluation.

RESULTS

The SNR of animal CTP images decreased with reductions in iodinated contrast media and milliampere-second doses. Contrast dose reduction had a greater effect on SNR than milliampere-second reduction. Noise-filtering by k-space-weighted image average and RED-CNN denoising progressively improved the SNR of CTP maps, with RED-CNN resulting in the highest SNR. The SNR of clinical CTP images was generally lower with a reduced iodinated contrast media dose, which was improved by the k-space-weighted image average and RED-CNN denoising (P < .05). Qualitative readings consistently rated RED-CNN denoised CTP as the best quality, followed by k-space-weighted image average and then standard CTP images.

CONCLUSIONS

Deep learning-denoising can improve image quality for low iodinated contrast media CTP protocols, and could approximate standard iodinated contrast media dose CTP, in addition to potentially improving image quality for low milliampere-second acquisitions.

Intracerebral hemodynamic abnormalities in patients with Parkinson's disease: Comparison between multi-delay arterial spin labelling and conventional single-delay arterial spin labelling

PURPOSE

The purpose of this study was to analyze the intracerebral abnormalities of hemodynamics in patients with Parkinson's disease (PD) through arterial spin labelling (ASL) technique with multi-delay ASL (MDASL) and conventional single-delay ASL (SDASL) protocols and to verify the potential clinical application of these features for the diagnosis of PD.

MATERIALS AND METHODS

Perfusion data of the brain obtained using MDASL and SDASL in patients with PD were compared to those obtained in healthy control (HC) subjects. Intergroup comparisons of z-scored cerebral blood flow (zCBF), arterial transit time (zATT) and cerebral blood volume (zCBV) were performed via voxel-based analysis. Performance of these perfusion metrics were estimated using area under the receiver operating characteristic curve (AUC) and compared using Delong test.

RESULTS

A total of 47 patients with PD (29 men; 18 women; mean age, 69.0 ± 7.6 (standard deviation, [SD]) years; range: 50.0-84.0 years) and 50 HC subjects (28 men; 22 women; mean age, 70.1 ± 6.2 [SD] years; range: 50.0-93.0 years) were included. Relative to the uncorrected-zCBF map, the corrected-zCBF map further refined the distributed brain regions in the PD group versus the HC group, manifested as the extension of motor-related regions (PFWE < 0.001). Compared to the HC subjects, patients with PD had elevated zATT and zCBV in the right putamen, a shortened zATT in the superior frontal gyrus, and specific zCBV variations in the left precuneus and the right supplementary motor area (PFWE < 0.001). The corrected-zCBF (AUC, 0.90; 95% confidence interval [CI]: 0.84-0.96) showed better classification performance than uncorrected-zCBF (AUC, 0.84; 95% CI: 0.75-0.92) (P = 0.035). zCBV achieved an AUC of 0.89 (95% CI: 0.82-0.96) and zATT achieved an AUC of 0.66 (95% CI: 0.55-0.77). The integration model of hemodynamic features from MDASL provided improved performance (AUC, 0.97; 95% CI: 0.95-0.98) for the diagnosis of PD by comparison with each perfusion model (P < 0.001).

CONCLUSION

ASL identifies impaired hemodynamics in patients with PD including regional abnormalities of CBF, CBV and ATT, which can better be mapped with MDASL compared to SDASL. These findings provide complementary depictions of perfusion abnormalities in patients with PD and highlight the clinical feasibility of MDASL.

CTP-based estimated ischemic core: A comparative multicenter study between Olea and RAPID software

BACKGROUND AND PURPOSE

CTP is increasingly used to assess eligibility for endovascular therapy (EVT) in patients with large vessel occlusions (LVO). There remain variability and inconsistencies between software packages for estimation of ischemic core. We aimed to use heterogenous data from four stroke centers to perform a comparative analysis for CTP-estimated ischemic core between RAPID (iSchemaView) and Olea (Olea Medical).

METHODS

In this retrospective multicenter study, patients with anterior circulation LVO who underwent pretreatment CTP, successful EVT (defined TICI ≥ 2b), and follow-up MRI included. Automated CTP analysis was performed using Olea platform [rCBF < 25% and differential time-to-peak (dTTP)>5s] and RAPID (rCBF < 30%). The CTP estimated core volumes were compared against the final infarct volume (FIV) on post treatment MRI-DWI.

RESULTS

A total of 151 patients included. The CTP-estimated ischemic core volumes (mean ± SD) were 18.7 ± 18.9 mL on Olea and 10.5 ± 17.9 mL on RAPID significantly different (p < 0.01). The correlation between CTP estimated core and MRI final infarct volume was r = 0.38, p < 0.01 for RAPID and r = 0.39, p < 0.01 for Olea. Both software platforms demonstrated a strong correlation with each other (r = 0.864, p < 0.001). Both software overestimated the ischemic core volume above 70 mL in 4 patients (2.6%).

CONCLUSIONS

Substantial variation between Olea and RAPID CTP-estimated core volumes exists, though rates of overcalling of large core were low and identical. Both showed comparable core volume correlation to MRI infarct volume.

Improving pulmonary perfusion assessment by dynamic contrast-enhanced computed tomography in an experimental lung injury model

Pulmonary perfusion has been poorly characterized in acute respiratory distress syndrome (ARDS). Optimizing protocols to measure pulmonary blood flow (PBF) via dynamic contrast-enhanced (DCE) computed tomography (CT) could improve understanding of how ARDS alters pulmonary perfusion. In this study, comparative evaluations of injection protocols and tracer-kinetic analysis models were performed based on DCE-CT data measured in ventilated pigs with and without lung injury. Ten Yorkshire pigs (five with lung injury, five healthy) were anesthetized, intubated, and mechanically ventilated; lung injury was induced by bronchial hydrochloric acid instillation. Each DCE-CT scan was obtained during a 30-s end-expiratory breath-hold. Reproducibility of PBF measurements was evaluated in three pigs. In eight pigs, undiluted and diluted Isovue-370 were separately injected to evaluate the effect of contrast viscosity on estimated PBF values. PBF was estimated with the peak-enhancement and the steepest-slope approach. Total-lung PBF was estimated in two healthy pigs to compare with cardiac output measured invasively by thermodilution in the pulmonary artery. Repeated measurements in the same animals yielded a good reproducibility of computed PBF maps. Injecting diluted isovue-370 resulted in smaller contrast-time curves in the pulmonary artery (P < 0.01) and vein (P < 0.01) without substantially diminishing peak signal intensity (P = 0.46 in the pulmonary artery) compared with the pure contrast agent since its viscosity is closer to that of blood. As compared with the peak-enhancement model, PBF values estimated by the steepest-slope model with diluted contrast were much closer to the cardiac output (R2 = 0.82) as compared with the peak-enhancement model. DCE-CT using the steepest-slope model and diluted contrast agent provided reliable quantitative estimates of PBF.NEW & NOTEWORTHY Dynamic contrast-enhanced CT using a lower-viscosity contrast agent in combination with tracer-kinetic analysis by the steepest-slope model improves pulmonary blood flow measurements and assessment of regional distributions of lung perfusion.

Accuracy of Four Different CT Perfusion Thresholds for Ischemic Core Volume and Location Estimation Using IntelliSpace Portal

Computed tomography perfusion (CTP) is frequently used in the triage of ischemic stroke patients for endovascular thrombectomy (EVT). We aimed to quantify the volumetric and spatial agreement of the CTP ischemic core estimated with different thresholds and follow-up MRI infarct volume on diffusion-weighted imaging (DWI). Patients treated with EVT between November 2017 and September 2020 with available baseline CTP and follow-up DWI were included. Data were processed with Philips IntelliSpace Portal using four different thresholds. Follow-up infarct volume was segmented on DWI. In 55 patients, the median DWI volume was 10 mL, and median estimated CTP ischemic core volumes ranged from 10-42 mL. In patients with complete reperfusion, the intraclass correlation coefficient (ICC) showed moderate-good volumetric agreement (range 0.55-0.76). A poor agreement was found for all methods in patients with successful reperfusion (ICC range 0.36-0.45). Spatial agreement (median Dice) was low for all four methods (range 0.17-0.19). Severe core overestimation was most frequently (27%) seen in Method 3 and patients with carotid-T occlusion. Our study shows moderate-good volumetric agreement between ischemic core estimates for four different thresholds and subsequent infarct volume on DWI in EVT-treated patients with complete reperfusion. The spatial agreement was similar to other commercially available software packages.

Falsely normal CT perfusion ischemic core readings are common and often associated with deep infarcts

BACKGROUND

Proper identification of infarct extent is crucial for thrombectomy and prognostication. We sought to study the frequency and topographic aspects of those cases in which CT perfusion (CTP) misses a core lesion that is present on initial non-contrast CT (NCCT).

METHODS

A review was carried out of a prospectively collected database of endovascular patients with anterior circulation large vessel occlusion strokes from January 2014 to November 2018. Patients with an e-ASPECTS <10 and adequate CTP maps were included. Total missed ischemic core (TMC) was defined as a CTP core lesion (relative cerebral blood flow <30%) <1 mL with a visualized hypodensity on NCCT.

RESULTS

In total, 629 patients were analyzed of which 161 (25.6%) had a TMC. On univariate analysis, TMC was associated with isolated deep middle cerebral artery (MCA) strokes (77.6% vs 56.6%, p<0.001), lower National Institutes of Health Stroke Scale (NIHSS) score (9 (15-20) vs 17 (13-21), p=0.007) and longer times to treatment (452 (288-652) min vs 355 (236-655) min, p=0.03). After adjusting for identifiable confounders, isolated deep MCA stroke was an independent predictor of TMC (OR 2.49 (95% CI 1.63 to 3.8), p<0.001). There were no differences between patients presenting with a TMC and those not with good outcomes (modified Rankin Scale 0-2) (50.8% vs 47.6%, p=0.53) or 90-day mortality (23% vs 17.6%, p=0.17). However, TMC was associated with lower rates of any parenchymal hematomas (5.2% vs 14.6%, p=0.02; aOR 0.11 (95% CI 0.01 to 0.91), p=0.04) and smaller final infarct volumes (20.5 (11.3-42.9) mL vs 47.5 (20.3-85) mL, p<0.001).

CONCLUSIONS

CTP may completely fail to detect ischemic core in as many as 25% of cases, especially in isolated deep MCA strokes. Technical refinements of the post-processing algorithms are therefore warranted. TMC infarcts may have a lower risk of reperfusion hemorrhage, potentially due to greater preservation of the neurovascular unit structure in face of delayed recovery of cerebral blood flow.

Effects of bolus injection duration on perfusion estimates in dynamic CT and dynamic susceptibility contrast MRI

Estimates of cerebral blood flow (CBF) and tissue mean transit time (MTT) have been shown to differ between dynamic CT perfusion (CTP) and dynamic susceptibility contrast MRI (DSC-MRI). This study investigates whether these discrepancies regarding CBF and MTT between CTP and DSC-MRI can be attributed to the different injection durations of these techniques. Five subjects were scanned using CTP and DSC-MRI. Region-wise estimates of CBF, MTT, and cerebral blood volume (CBV) were derived based on oscillatory index regularized singular value decomposition. A parametric model that reproduced the shape of measured time curves and characteristics of resulting perfusion parameter estimates was developed and used to simulate data with injection durations typical for CTP and DSC-MRI for a clinically relevant set of perfusion scenarios and noise levels. In simulations, estimates of CBF/MTT showed larger negative/positive bias and increasing variability for CTP when compared to DSC-MRI, especially for high CBF levels. While noise also affected estimates, at clinically relevant levels, the injection duration effect was larger. There are several methodological differences between CTP and DSC-MRI. The results of this study suggest that the injection duration is among those that can explain differences in estimates of CBF and MTT between these bolus tracking techniques.

Advances in cerebral perfusion imaging techniques in acute ischemic stroke

The application of cerebral perfusion imaging has demonstrated significant assessment benefits and an ability to establish an appropriate triage of patients with acute ischemic stroke (AIS) and large artery occlusion (LAO) in the extended time window. Computed tomography perfusion (CTP) and magnetic resonance imaging (MRI) are routinely used to determine the ischemic core, as well as the tissue at risk, to aid in therapeutic decision-making. However, the time required to transport patients to imaging extends the door-to-reperfusion time. C-arm cone-beam CT (CBCT) is a novel tomography technology that combines 2D radiography and 3D CT imaging based on the digital subtraction angiography platform. In comparison with CT or MRI perfusion techniques, CBCT combined with catheterized angiogram or therapy can serve as a "one-stop-shop" for the diagnosis and treatment of AIS, and greatly reduce the door to reperfusion time. Here, we review the current evidence on the efficacy and theoretical basis of CBCT, as well as other perfusion techniques, with the purpose to assist clinicians to establish an effective and repaid workflow for patients with AIS and LAO in clinical practice.

Development of a computed tomography perfusion protocol to support large animal resuscitation research

BACKGROUND

Adequate cerebral perfusion is crucial for a positive neurological outcome in trauma; however, it is difficult to characterize in the acute setting with noninvasive methods. Intra-arterial computed tomography perfusion may offer a solution. The aim of this study was to develop an intra-arterial computed tomography perfusion protocol for resuscitation research.

METHODS

The study examined intra-arterial contrast administration for computed tomography perfusion (CTP) acquisition. It consisted of three phases: intra-arterial contrast dose finding, evaluation of reproducibility, and evaluation during hypotension. Blood pressure and laser Doppler flow data were collected. In phase 1, animals underwent CTPs using several intra-arterial contrast injection protocols. In phase 2, animals underwent two CTPs 7 hours apart using the 2.5 mL/s for 3-second protocol. In phase 3, animals underwent CTPs at several pressures following a computer-controlled bleed including euvolemia and at systolic pressures of 60, 40, and 20 mm Hg. Phase 1 CTPs were evaluated for contrast-to-noise ratio. In phase 2, CTPs were compared within each animal and with laser Doppler flow using linear regression. Phase 3 CTPs were graphed against systolic pressure and fitted with a nonlinear fit.

RESULTS

The protocol using 2.5mL/s for 3 seconds was optimal, demonstrating a contrast-to-noise ratio of 40.1 and a superior arterial input function curve compared with the 1 mL/s bolus. Cerebral blood flow demonstrated high concordance between baseline and end of study CTPs (R2 = 0.82, p < 0.001). Cerebral blood flow also compared moderately well against laser Doppler flow during 8 (R2 = 0.53, p = 0.03); however, laser Doppler flow did not perform well during hypovolemia, and the favorable concordance was not maintained (R2 = 0.45, p = 0.06). Cerebral blood flow was graphed against systolic blood pressure and fitted with a nonlinear fit (R2 = 0.95, p = 0.003).

CONCLUSION

Computed tomography perfusion using intra-arterial contrast injection may offer a novel alternative to traditional CTP protocols that could prove a useful additional tool in the setting of resuscitation research.

Comparative Study of Multi-Delay Pseudo-Continuous Arterial Spin Labeling Perfusion MRI and CT Perfusion in Ischemic Stroke Disease

With the aging population, stroke has gradually become the leading cause of death and disability among adults. It is necessary to verify whether multi-delay pseudo-continuous arterial spin labeling (pCASL) MRI can be used as a standard neuroimaging protocol in the patients with ischemic stroke. We aimed to investigate the clinical utility of multi-delay pCASL for evaluating cerebral perfusion in ischemic stroke disease. Twenty-one ischemic stroke patients [18 men and 3 women; median age, 62 years (age range, 37-84 years)] were enrolled in this study. All patients underwent examinations, including the multi-delay pCASL protocol (using 6 PLDs between 1,000 and 3,500 ms) and computed tomography perfusion (CTP). The cerebral blood flow (CBF) and arterial transit time (ATT) maps were obtained by the multi-delay pCASL protocol, while CBF and mean transit time (MTT) maps were derived by CTP measurements. Based on the voxel level analysis, Pearson correlation coefficients were used to estimate the associations between the two modalities in the gray matter, white matter, and whole brain of each subject. Moderate to high positive associations between ASL-CBF and CTP-CBF were acquired by voxel-level-wise analysis in the gray matter, white matter, and whole brain of the enrolled patients (all P < 0.005), and the average Pearson correlation coefficients were 0.647, 0.585, and 0.646, respectively. Highly significant positive correlations between ASL-ATT and CTP-MTT were obtained by voxel-level-wise associations in the gray matter, white matter, and whole brain (all P < 0.005), and the average Pearson correlation coefficients were 0.787, 0.707, and 0.799, respectively. In addition, significant associations between ASL and CT perfusion were obtained in the gray, white matter and whole brain, according to the subgroup analyses of patient's age and disease stage. There is a correlation between perfusion parameters from multi-delay pCASL and CT perfusion imaging in patients with ischemic stroke. Multi-delay pCASL is radiation-free and non-invasive, and could be an alternative method to CT scans for assessing perfusion in ischemic stroke disease.

Predictors of perfusion computed tomography alterations in stroke mimics attended as stroke code

BACKGROUND AND PURPOSE

Stroke mimics (SMs) account for a significant number of patients attended as stroke code (SC) with an increasing number over the years. Recent studies show perfusion computed tomography (PCT) alterations in some SMs, especially in seizures. The objective of our study was to evaluate the clinical characteristics and PCT alterations in SMs attended as SC in order to identify potential predictors of PCT alterations in SMs.

METHODS

A retrospective study was performed including all SC activations undergoing a multimodal CT study including non-enhanced computed tomography (CT), CT angiography and PCT, as part of our SC protocol, over 39 months. Patients with a final diagnosis of SM after complete diagnosis work-up were therefore selected. Clinical variables, diagnosis, PCT alteration patterns and type of map affected (T_max or time to peak, cerebral blood flow and cerebral blood volume) were registered.

RESULTS

Stroke mimics represent up to 16% (284/1761) of SCs with a complete multimodal study according to our series. Amongst SMs, 26% (74/284) showed PCT alterations. PCT abnormalities are more prevalent in seizures and status epilepticus and the main pattern is alteration of the time to peak map, of unilateral hemispheric distribution or of non-vascular territory. In our series, the independent predictors of alteration in PCT in SMs are aphasia, female sex and older age.

CONCLUSIONS

Perfusion computed tomography alterations can be found amongst almost a third of SMs attended as SC, especially older women presenting with aphasia with a final diagnosis of epileptic seizures and status epilepticus.

Imaging Ischemic and Hemorrhagic Disease of the Brain in Dogs

Strokes, both ischemic and hemorrhagic, are the most common underlying cause of acute, non-progressive encephalopathy in dogs. In effect, substantial information detailing the underlying causes and predisposing factors, affected vessels, imaging features, and outcomes based on location and extent of injury is available. The features of canine strokes on both computed tomography (CT) and magnetic resonance imaging (MRI) have been described in numerous studies. This summary article serves as a compilation of these various descriptions. Drawing from the established and emerging stroke evaluation sequences used in the investigation of strokes in humans, this summary describes all theoretically available sequences. Particular detail is given to logistics of image acquisition, description of imaging findings, and each sequence's advantages and disadvantages. As the imaging features of both forms of strokes are highly representative of the underlying pathophysiologic stages in the hours to months following stroke onset, the descriptions of strokes at various stages are also discussed. It is unlikely that canine strokes can be diagnosed within the same rapid time frame as human strokes, and therefore the opportunity for thrombolytic intervention in ischemic strokes is unattainable. However, a thorough understanding of the appearance of strokes at various stages can aid the clinician when presented with a patient that has developed a stroke in the days or weeks prior to evaluation. Additionally, investigation into new imaging techniques may increase the sensitivity and specificity of stroke diagnosis, as well as provide new ways to monitor strokes over time.

Permeability-surface area product of the penumbra as a predictor of outcome after endovascular treatment of anterior circulation acute ischemic stroke

Background

Permeability-surface product is a predictor of blood–brain barrier disruption, a condition that may be related to higher likelihoods of hemorrhagic transformations in acute stroke.

Purpose

To investigate whether permeability-surface product can be used as a parameter for predicting outcome after mechanical thrombectomy in patients with anterior circulation acute ischemic stroke.

Material and Methods

We retrospectively identified patients with acute middle cerebral artery stroke who underwent successful mechanical thrombectomy between November 2009 and July 2015. Multiple parameters (including age) and CT perfusion-related parameters (including permeability-surface product) were compared between patients with favorable (modified Rankin Scale [mRS] = 0–2) and unfavorable (mRS > 2) outcome.

Results

Thirty patients were included, 50% having favorable and 50% having unfavorable outcome. Younger age was significantly associated with favorable outcome ( P < 0.03). Other baseline characteristics, such as size of CT perfusion core infarction, perfusion abnormality, and presentation of subcortical infarction were not significantly different between groups. No significant difference was observed between groups for permeability-surface product in the ipsilateral penumbra or for the ratio between permeability-surface product penumbra value and contralateral normal brain (permeability-surface product ratio).

Conclusions

No significant difference was observed between patients with and without favorable outcome after mechanical thrombectomy for either permeability-surface product value or permeability-surface product ratio. Although permeability-surface product is a good predictor of blood–brain barrier disruption, this study revealed no evidence that either permeability-surface product value or permeability-surface product ratio is associated with future change in the penumbra.

Increased microvascular permeability and low level of low-density lipoprotein cholesterol predict symptomatic intracerebral hemorrhage in acute ischemic stroke

Symptomatic intracerebral hemorrhage is a serious potential complication of recombinant tissue-type plasminogen activator thrombolysis in acute ischemic stroke. We investigated the optimal imaging and clinical parameters to predict symptomatic intracerebral hemorrhage in acute ischemic stroke patients after recombinant tissue-type plasminogen activator therapy. We retrospectively reviewed 151 acute ischemic stroke patients with thrombolytic therapy, who were dichotomized into symptomatic intracerebral hemorrhage group and non-symptomatic intracerebral hemorrhage group. They underwent multimodal computed tomography, including the measurement of permeability surface. We compared the clinical and radiological characteristics between symptomatic intracerebral hemorrhage group and non-symptomatic intracerebral hemorrhage group, using univariate analysis. Receiver operating characteristic analysis and multivariate logistic regression analyses were then used to determine symptomatic intracerebral hemorrhage predictors. Of 151 patients, 14 patients (9.27%) developed symptomatic intracerebral hemorrhage on follow-up imaging. Relative permeability surface (infarct permeability surface/contralateral normal permeability surface) (p < 0.05) and baseline low-density lipoprotein cholesterol level (p < 0.05) were both predictors of symptomatic intracerebral hemorrhage. Receiver operating characteristic analysis of relative permeability surface revealed an optimal relative permeability surface threshold of 2.239, with an area under the curve of 0.87 (95% confidence interval, 0.732-1.0). The relative permeability surface was 2.239, the sensitivity for symptomatic intracerebral hemorrhage was 85.7%, the specificity was 94.9%, the positive predictive value was 70.6%, and the negative predictive value was 95.5%. For low-density lipoprotein cholesterol, the optimal threshold was 2.45, with an area under the curve of 0.726 (95% confidence interval, 0.586-0.867), the sensitivity for symptomatic intracerebral hemorrhage was 73.0%, the specificity was 64.3%, the positive predictive value was 67.16%, and the negative predictive value was 79.09%. Our study demonstrated that increased infarct permeability surface and low level of low-density lipoprotein cholesterol can be two predictors of symptomatic intracerebral hemorrhage. Detection of relative permeability surface and low-density lipoprotein cholesterol may help clinicians to identify acute ischemic stroke patients with the higher risk of symptomatic intracerebral hemorrhage; intravenous thrombolytic therapy should be carefully performed for patients with high relative permeability surface and low low-density lipoprotein cholesterol. We may take relative permeability surface and low-density lipoprotein cholesterol into account to refine therapeutic decision-making in acute ischemic stroke.

Advanced neuroimaging in traumatic brain injury: an overview

Traumatic brain injury (TBI) is a common condition with many potential acute and chronic neurological consequences. Standard initial radiographic evaluation includes noncontrast head CT scanning to rapidly evaluate for pathology that might require intervention. The availability of fast, relatively inexpensive CT imaging has fundamentally changed the clinician's ability to noninvasively visualize neuroanatomy. However, in the context of TBI, limitations of head CT without contrast include poor prognostic ability, inability to analyze cerebral perfusion status, and poor visualization of underlying posttraumatic changes to brain parenchyma. Here, the authors review emerging advanced imaging for evaluation of both acute and chronic TBI and include QuickBrain MRI as an initial imaging modality. Dynamic susceptibility-weighted contrast-enhanced perfusion MRI, MR arterial spin labeling, and perfusion CT are reviewed as methods for examining cerebral blood flow following TBI. The authors evaluate MR-based diffusion tensor imaging and functional MRI for prognostication of recovery post-TBI. Finally, MR elastography, MR spectroscopy, and convolutional neural networks are examined as future tools in TBI management. Many imaging technologies are being developed and studied in TBI, and some of these may hold promise in improving the understanding and management of TBI. ABBREVIATIONS ASL = arterial spin labeling; CNN = convolutional neural network; CTP = perfusion CT; DAI = diffuse axonal injury; DMN = default mode network; DOC = disorders of consciousness; DTI = diffusion tensor imaging; FA = fractional anisotropy; fMRI = functional MRI; GCS = Glasgow Coma Scale; MD = mean diffusivity; MRE = MR elastography; MRS = MR spectroscopy; mTBI = mild TBI; NAA = N-acetylaspartate; SWI = susceptibility-weighted imaging; TBI = traumatic brain injury; UHF = ultra-high field.

Automated CT perfusion imaging for acute ischemic stroke: Pearls and pitfalls for real-world use

Recent positive trials have thrust acute cerebral perfusion imaging into the routine evaluation of acute ischemic stroke. Updated guidelines state that in patients with anterior circulation large vessel occlusions presenting beyond 6 hours from time last known well, advanced imaging selection including perfusion-based selection is necessary. Centers that receive patients with acute stroke must now have the capability to perform and interpret CT or magnetic resonance perfusion imaging or provide rapid transfer to centers with the capability of selecting patients for a highly impactful endovascular therapy, particularly in delayed time windows. Many stroke centers are quickly incorporating the use of automated perfusion processing software to interpret perfusion raw data. As CT perfusion (CTP) is being assimilated in real-world clinical practice, it is essential to understand the basics of perfusion acquisition, quantification, and interpretation. It is equally important to recognize the common technical and clinical diagnostic challenges of automated CTP including ischemic core and penumbral misclassifications that could result in underestimation or overestimation of the core and penumbra volumes. This review highlights the pitfalls of automated CTP along with practical pearls to address the common challenges. This is particularly tailored to aid the acute stroke clinician who must interpret automated perfusion studies in an emergency setting to make time-dependent treatment decisions for patients with acute ischemic stroke.

Multimodal CT in Acute Stroke

PURPOSE OF REVIEW

Multimodal CT imaging (non-contrast CT, NCCT; CT angiography, CTA; and CT Perfusion, CTP) is central to acute ischemic stroke diagnosis and treatment. We reviewed the purpose and interpretation of each component of multimodal CT, as well as the evidence for use in routine care.

RECENT FINDINGS

Acute stroke thrombolysis can be administered immediately following NCCT in acute ischemic stroke patients assessed within 4.5 h of symptom onset. Definitive identification of a large vessel occlusion (LVO) requires vascular imaging, which is easily achieved with CTA. This is critical, as the standard of care for LVO within 6 h of onset is now endovascular thrombectomy (EVT). CTA source images can also be used to estimate the efficacy of collateral flow in LVO patients. The final component (CTP) permits a more accurate assessment of the extent of the ischemic penumbra. Complete multimodal CT, including objective penumbral measurement with CTP, has been used to extend the EVT window to 24 h. There is also randomized controlled trial evidence for extension of the IV thrombolysis window to 9 h with multimodal CT. Although there have been attempts to assess for responders to reperfusion strategies beyond 6 h ("late window") using collateral grades, the only evidence for treatment of this group of patients is based on selection using multimodal CT including CTP. The development of fully automated software providing quantitative ischemic penumbral and core volumes has facilitated the adoption of CTP and complete multimodal CT into routine clinical use. Multimodal CT is a powerful imaging algorithm that is central to current ischemic stroke patient care.

Comparison of three commonly used CT perfusion software packages in patients with acute ischemic stroke

Background and purpose

CT perfusion (CTP) might support decision making in patients with acute ischemic stroke by providing perfusion maps of ischemic tissue. Currently, the reliability of CTP is hampered by varying results between different post-processing software packages. The purpose of this study is to compare ischemic core volumes estimated by IntelliSpace Portal (ISP) and syngo.via with core volumes as estimated by RAPID.

Methods

Thirty-five CTP datasets from patients in the MR CLEAN trial were post-processed. Core volumes were estimated with ISP using default settings and with syngo.via using three different settings: default settings (method A); additional smoothing filter (method B); and adjusted settings (method C). The results were compared with RAPID. Agreement between methods was assessed using Bland–Altman analysis and intraclass correlation coefficient (ICC). Accuracy for detecting volumes up to 25 mL, 50 mL, and 70 mL was assessed. Final infarct volumes were determined on follow-up non-contrast CT.

Results

Median core volume was 50 mL with ISP, 41 mL with syngo.via method A, 20 mL with method B, 36 mL with method C, and 11 mL with RAPID. Agreement ranged from poor (ISP: ICC 0.41; method A: ICC 0.23) to good (method B: ICC 0.83; method C: ICC 0.85). The bias (1.8 mL) and limits of agreement (−27, 31 mL) were the smallest with syngo.via with additional smoothing (method B). Agreement for detecting core volumes ≤25 mL with ISP was 54% and 57%, 85% and 74% for syngo.via methods A, B, and C, respectively.

Conclusion

Best agreement with RAPID software is provided by syngo.via default settings with additional smoothing. Moreover, this method has the highest agreement in categorizing patients with small core volumes.

Effect of contrast medium injection rate on computed tomography-derived renal perfusion estimates obtained with the maximum slope method in healthy

OBJECTIVE To evaluate the effect of contrast medium injection rate on CT-derived renal perfusion estimates obtained with the maximum slope method in healthy small dogs. ANIMALS 6 healthy sexually intact male purpose-bred Beagles. PROCEDURES All dogs underwent CT perfusion analysis 3 times in a crossover design, receiving a different contrast medium injection rate (1.5, 3.0, and 4.5 mL/s) each time, with a 1-week interval between imaging sessions. All CT images were obtained at the level of the left renal hilus. The time to peak aortic enhancement (TPAE) and time to initial renal venous enhancement (TIRVE) were measured from time-attenuation curves. The renal CT perfusion estimates (blood flow and blood volume) were estimated by use of the maximum slope method, which assumes no venous outflow of contrast medium during CT perfusion analysis. RESULTS The TPAE occurred at or before the TIRVE at all injection rates. Median values of estimated blood flow and blood volume did not differ significantly among injection rates. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the assumption of no venous outflow of contrast medium during renal CT perfusion analysis with the maximum slope method was satisfied for all 3 contrast medium injection rates in the evaluated dogs. A low injection rate may be more practical than higher injection rates that require large catheters for CT perfusion analysis in small dogs such as Beagles.

Neuroimaging of Traumatic Brain Injury

The purpose of this article is to review conventional and advanced neuroimaging techniques performed in the setting of traumatic brain injury (TBI). The primary goal for the treatment of patients with suspected TBI is to prevent secondary injury. In the setting of a moderate to severe TBI, the most appropriate initial neuroimaging examination is a noncontrast head computed tomography (CT), which can reveal life-threatening injuries and direct emergent neurosurgical intervention. We will focus much of the article on advanced neuroimaging techniques including perfusion imaging and diffusion tensor imaging and discuss their potentials and challenges. We believe that advanced neuroimaging techniques may improve the accuracy of diagnosis of TBI and improve management of TBI.

Mechanical Thrombectomy by a Direct Aspiration First Pass Technique (ADAPT) in Ischemic Stroke: Results of Monocentric Study Based on Multimodal CT Patient Selection

Introduction

Mechanical thrombectomy with ADAP-technique of ischemic stroke has been reported as fast and effective. Aim of this study is to evaluate imaging criteria as possible predictors of stroke severity, therapeutic success, and outcome.

Materials and Methods

Patients (30) presenting from October 2015 to April 2017 with Emergent Large Vessel Occlusion of the anterior circulation were treated with ADAP-technique. 22 received also IV tPA; 8 underwent endovascular treatment only. Every patient was evaluated with noncontrast CT, multiphase angiography-CT, and perfusion CT. Clinical and radiological characteristics were measured. Good clinical outcome was an improvement of 8 points on NIHSS at discharge or a modified Rankin Scale ≤2 at discharge and at 90 days.

Results

Successful revascularization was obtained in 57% of patients, no procedural complications were witnessed, and only two hemorrhages were reported. Good outcome at discharge was obtained in 11 patients (37%) and predicted by NCCT ASPECT and TICI; outcome at 90 days was predicted by NCCT ASPECT, clot length, and premorbid mRS. Mortality was 23% at discharge and 30% at 90 days.

Conclusion

ADAPT is an effective endovascular method of stroke treatment with fast procedural times. Multimodal CT evaluation is effective in assessing stroke severity, providing important prognostic information, which is able to select patients for the appropriate treatment.

Perfusion Imaging in Acute Traumatic Brain Injury

Traumatic brain injury (TBI) is a significant problem worldwide and neuroimaging plays a critical role in diagnosis and management. Recently, perfusion neuroimaging techniques have been explored in TBI to determine and characterize potential perfusion neuroimaging biomarkers to aid in diagnosis, treatment, and prognosis. In this article, computed tomography (CT) bolus perfusion, MR imaging bolus perfusion, MR imaging arterial spin labeling perfusion, and xenon CT are reviewed with a focus on their applications in acute TBI. Future research directions are also discussed.

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.

Low-dose CT perfusion with projection view sharing

PURPOSE

CT Perfusion (CTP) is a widely used clinical imaging modality. However, CTP typically involves the use of substantial radiation dose (CTDI_vol ≥~200 mGy). The purpose of this study is to present a low-dose CTP technique using a projection view-sharing reconstruction algorithm originally developed for dynamic MRI - "K-space Weighted Image Contrast" (KWIC).

METHODS

The KWIC reconstruction is based on an angle-bisection scheme. In KWIC, a Fourier transform was performed along each projection to form a "k-space"-like CT data space, based on the central-slice theorem. As a projection view-sharing technique, KWIC preserves the spatiotemporal resolution of undersampled CTP data by progressively increasing the number of projection views shared for more distant regions of "k-space". KWIC reconstruction was evaluated on a digital FORBILD head phantom with numerically simulated time-varying objects. The numerically simulated scans were undersampled using the angle-bisection scheme to achieve 50%, 25%, and 12.5% of the original dose (288, 144, and 72 projections, respectively). The area-under-the-curve (AUC), time-to-peak (TTP), and full width half maximum (FWHM) were measured in KWIC recons and compared to fully sampled filtered back projection (FBP) reconstructions. KWIC reconstruction and dose reduction was also implemented for three clinical CTP cases (45 s, 1156 projections per turn, 1 s/turn, CTDI_vol 217 mGy). Quantitative perfusion metrics were computed and compared between KWIC reconstructed CTP data and those of standard FBP reconstruction.

RESULTS

The AUC, TTP, and FWHM in the numerical simzulations were unaffected by the undersampling/dose reduction (down to 12.5% dose) with KWIC reconstruction compared to the fully sampled FBP reconstruction. The normalized root-mean-square-error (NRMSE) of the AUC in the FORBILD head phantom is 0.04, 0.05, and 0.07 for 50%, 25%, and 12.5% KWIC, respectively, as compared to FBP reconstruction. The cerebral blood flow (CBF) and cerebral blood volume had no significant difference between FBP and 50%, 25%, and 12.5% KWIC reconstructions (P > 0.05).

CONCLUSIONS

This study demonstrates that KWIC preserves perfusion metrics for CTP with substantially reduced dose. Clinical implementation will require further investigation into methods of rapid switching of a CT x-ray source.

Overview of neuroradiology

Neuroradiology with computed tomography (CT) and magnetic resonance imaging (MRI) is essential for the initial evaluation of patients with a clinical suspicion of brain and spine disorders. Morphologic imaging is required to obtain a probable diagnosis to support the treatment decisions in pre- and perinatal disorders, vascular diseases, traumatic injuries, metabolic disorders, epilepsy, infection/inflammation, neurodegenerative disorders, degenerative spinal disease, and tumors of the central nervous system. Different postprocessing tools are increasingly used for three-dimensional visualization and quantification of lesions. Additional information is provided by angiographic methods and physiologic CT and MRI techniques, such as diffusion MRI, perfusion CT/MRI, MR spectroscopy, functional MRI, tractography, and nuclear medicine imaging methods. Positron emission tomography (PET) is now integrated with CT (PET/CT), and PET/MR scanners have recently also been introduced. These hybrid techniques facilitate the co-registration of lesions with different modalities, and give new possibilites for functional imaging. Repeated imaging is increasingly performed for treatment monitoring. The improved imaging techniques together with the neuropathologic diagnosis after biopsy or surgery allow more personalized treatment of the patient. Neuroradiology also includes endovascular treatment of aneurysms and arteriovenous malformations as well as thrombectomy in acute stroke. This catheter-based treatment has replaced invasive neurosurgery in many cases.

CT perfusion diagnoses delayed cerebral ischemia in the early stage of the time-window after aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

It has been acknowledged that delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) can be diagnosed by CT perfusion (CTP) in the DCI time-window. We evaluated the diagnostic accuracy of CTP for DCI during the early stage of the time-window.

MATERIALS AND METHODS

We prospectively enrolled patients with aneurysmal SAH. DCI was defined as both new cerebral infarction and clinical deterioration after SAH. CTP was performed by using a standardized protocol with predefined regions of interest in 4 to 6 days after SAH. We quantitatively evaluated the diagnostic accuracy of eight CTP parameters (4 for absolute parameters and 4 for relative parameters). The receiver operator characteristic (ROC) curves of all parameters were generated and the optimal threshold values were derived for the calculation of sensitivities and specificities.

RESULTS

Fifty-three patients were enrolled and 20 patients were diagnosed with DCI. In the analysis of absolute CTP parameters, CBF and MTT had areas under the curve (AUC) >0.75 and the optimal threshold value was 40.4mL/100g/min and 3.78seconds, respectively. Through the evaluation of relative CTP parameters, all 4 parameters had AUC >0.75 and the optimal threshold value was 0.9 for CBV ratio, 0.85 for CBF ratio, 0.32seconds for MTT difference and 1.31seconds for TTP difference.

CONCLUSIONS

Besides two absolute CTP parameters (CBV and TTP), all six CTP parameters can be used as good diagnostic tests for DCI in the early stage of the time-window.

Comparison of Perfusion CT Software to Predict the Final Infarct Volume After Thrombectomy

Background and Purpose—

Computed tomographic perfusion represents an interesting physiological imaging modality to select patients for reperfusion therapy in acute ischemic stroke. The purpose of our study was to determine the accuracy of different commercial perfusion CT software packages (Philips (A), Siemens (B), and RAPID (C)) to predict the final infarct volume (FIV) after mechanical thrombectomy.

Methods—

Single-institutional computed tomographic perfusion data from 147 mechanically recanalized acute ischemic stroke patients were postprocessed. Ischemic core and FIV were compared about thrombolysis in cerebral infarction (TICI) score and time interval to reperfusion. FIV was measured at follow-up imaging between days 1 and 8 after stroke.

Results—

In 118 successfully recanalized patients (TICI 2b/3), a moderately to strongly positive correlation was observed between ischemic core and FIV. The highest accuracy and best correlation are shown in early and fully recanalized patients (Pearson r for A=0.42, B=0.64, and C=0.83; P <0.001). Bland–Altman plots and boxplots demonstrate smaller ranges in package C than in A and B. Significant differences were found between the packages about over- and underestimation of the ischemic core. Package A, compared with B and C, estimated more than twice as many patients with a malignant stroke profile ( P <0.001). Package C best predicted hypoperfusion volume in nonsuccessfully recanalized patients.

Conclusions—

Our study demonstrates best accuracy and approximation between the results of a fully automated software (RAPID) and FIV, especially in early and fully recanalized patients. Furthermore, this software package overestimated the FIV to a significantly lower degree and estimated a malignant mismatch profile less often than other software.

Characteristics of Misclassified CT Perfusion Ischemic Core in Patients with Acute Ischemic Stroke

BACKGROUND

CT perfusion (CTP) is used to estimate the extent of ischemic core and penumbra in patients with acute ischemic stroke. CTP reliability, however, is limited. This study aims to identify regions misclassified as ischemic core on CTP, using infarct on follow-up noncontrast CT. We aim to assess differences in volumetric and perfusion characteristics in these regions compared to areas that ended up as infarct on follow-up.

MATERIALS AND METHODS

This study included 35 patients with >100 mm brain coverage CTP. CTP processing was performed using Philips software (IntelliSpace 7.0). Final infarct was automatically segmented on follow-up noncontrast CT and used as reference. CTP and follow-up noncontrast CT image data were registered. This allowed classification of ischemic lesion agreement (core on CTP: rMTT≥145%, aCBV<2.0 ml/100g and infarct on follow-up noncontrast CT) and misclassified ischemic core (core on CTP, not identified on follow-up noncontrast CT) regions. False discovery ratio (FDR), defined as misclassified ischemic core volume divided by total CTP ischemic core volume, was calculated. Absolute and relative CTP parameters (CBV, CBF, and MTT) were calculated for both misclassified CTP ischemic core and ischemic lesion agreement regions and compared using paired rank-sum tests.

RESULTS

Median total CTP ischemic core volume was 49.7ml (IQR:29.9ml-132ml); median misclassified ischemic core volume was 30.4ml (IQR:20.9ml-77.0ml). Median FDR between patients was 62% (IQR:49%-80%). Median relative mean transit time was 243% (IQR:198%-289%) and 342% (IQR:249%-432%) for misclassified and ischemic lesion agreement regions, respectively. Median absolute cerebral blood volume was 1.59 (IQR:1.43-1.79) ml/100g (P<0.01) and 1.38 (IQR:1.15-1.49) ml/100g (P<0.01) for misclassified ischemic core and ischemic lesion agreement, respectively. All CTP parameter values differed significantly.

CONCLUSION

For all patients a considerable region of the CTP ischemic core is misclassified. CTP parameters significantly differed between ischemic lesion agreement and misclassified CTP ischemic core, suggesting that CTP analysis may benefit from revisions.

Relation between reperfusion and hemorrhagic transformation in acute ischemic stroke

INTRODUCTION

Intravenous recombinant tissue plasminogen activator (IV-rtPA) is given in acute ischemic stroke patients to achieve reperfusion. Hemorrhagic transformation (HT) is a serious complication of IV-rtPA treatment and related to blood-brain barrier (BBB) injury. It is unclear whether HT occurs secondary to reperfusion in combination with ischemic BBB injury or is caused by the negative effect of IV-rtPA on BBB integrity. The aim of this study was to establish the association between reperfusion and the occurrence of HT.

METHODS

From the DUST study, patients were selected with admission and follow-up non-contrast CT (NCCT) and CT perfusion (CTP) imaging, and a perfusion deficit in the middle cerebral artery territory on admission. Reperfusion was categorized qualitatively as reperfusion or no-reperfusion by visual comparison of admission and follow-up CTP. Occurrence of HT was assessed on follow-up NCCT. The association between reperfusion and occurrence of HT on follow-up was estimated by calculating odds ratios (ORs) and 95 % confidence intervals (CIs) with additional stratification for IV-rtPA treatment.

RESULTS

Inclusion criteria were met in 299 patients. There was no significant association between reperfusion and HT (OR 1.2 95%CI 0.5-3.1). In patients treated with IV-rtPA (n = 203), the OR was 1.3 (95%CI 0.4-4.0), and in patients not treated with IV-rtPA (n = 96), the OR was 0.8 (95%CI 0.1-4.5). HT occurred in 14 % of the IV-rtPA patients and in 7 % of patients without IV-rtPA (95%CI of difference -1 to 14 %).

CONCLUSION

Our results suggest that the increased risk of HT after acute ischemic stroke treatment is not dependent on the reperfusion status.

Robust Low-Dose CT Perfusion Deconvolution via Tensor Total-Variation Regularization

Acute brain diseases such as acute strokes and transit ischemic attacks are the leading causes of mortality and morbidity worldwide, responsible for 9% of total death every year. "Time is brain" is a widely accepted concept in acute cerebrovascular disease treatment. Efficient and accurate computational framework for hemodynamic parameters estimation can save critical time for thrombolytic therapy. Meanwhile the high level of accumulated radiation dosage due to continuous image acquisition in CT perfusion (CTP) raised concerns on patient safety and public health. However, low-radiation leads to increased noise and artifacts which require more sophisticated and time-consuming algorithms for robust estimation. In this paper, we focus on developing a robust and efficient framework to accurately estimate the perfusion parameters at low radiation dosage. Specifically, we present a tensor total-variation (TTV) technique which fuses the spatial correlation of the vascular structure and the temporal continuation of the blood signal flow. An efficient algorithm is proposed to find the solution with fast convergence and reduced computational complexity. Extensive evaluations are carried out in terms of sensitivity to noise levels, estimation accuracy, contrast preservation, and performed on digital perfusion phantom estimation, as well as in vivo clinical subjects. Our framework reduces the necessary radiation dose to only 8% of the original level and outperforms the state-of-art algorithms with peak signal-to-noise ratio improved by 32%. It reduces the oscillation in the residue functions, corrects over-estimation of cerebral blood flow (CBF) and under-estimation of mean transit time (MTT), and maintains the distinction between the deficit and normal regions.

Evaluating CT Perfusion Deficits in Global Cerebral Edema after Aneurysmal Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Global cerebral edema is an independent predictor of mortality and poor outcomes after aneurysmal SAH. Global cerebral edema, a complex disease process, is thought to be associated with an altered cerebral autoregulatory response. We studied the association between cerebral hemodynamics and early global cerebral edema by using CTP.

MATERIALS AND METHODS

We retrospectively studied consecutive patients with aneurysmal SAH with admission CTP performed at days 0-3. Two neuroradiologists classified global cerebral edema and hydrocephalus on NCCT performed concurrently with CTP. Global cerebral edema was defined as diffuse effacement of the sulci and/or basal cisterns or diffuse disruption of the cerebral gray-white matter junction. CTP was postprocessed into CBF and MTT maps by using a standardized method. Quantitative analysis of CTP was performed by using standard protocol with ROI sampling of the cerebral cortex. The Fisher exact test, Mann-Whitney test, and independent-samples t test were used to determine statistical associations.

RESULTS

Of the 45 patients included, 42% (19/45) had global cerebral edema and 58% (26/45) did not. Patient groups with and without global cerebral edema were well-matched for demographic and clinical data. Patients with global cerebral edema were more likely to have qualitative global CTP deficits than those without global cerebral edema (P = .001) with an OR = 13.3 (95% CI, 2.09-138.63). Patients with global cerebral edema also had a very strong trend toward statistical significance, with reduced quantitative CBF compared with patients without global cerebral edema (P = .064).

CONCLUSIONS

Global perfusion deficits are significantly associated with global cerebral edema in the early phase after aneurysmal SAH, supporting the theory that hemodynamic disturbances occur in global cerebral edema.

Leptomeningeal enhancement on magnetic resonance imaging as a predictor of hemodynamic insufficiency

OBJECTIVE

The objective of this study was to evaluate the value of leptomeningeal enhancement on magnetic resonance imaging in relation to relative cerebral blood flow (rCBF) and cerebrovascular reserve.

METHODS

A retrospective analysis was performed for 31 patients with internal carotid artery or proximal middle cerebral artery occlusion without primary collateral flow, who underwent enhanced T1-weighted magnetic resonance imaging and acetazolamide-challenged perfusion computed tomography. They were graded into 3 groups in leptomeningeal enhancement on T1-weighted imaging. The rCBF and the percentage change of cerebral blood flow were obtained in the ipsilateral middle cerebral artery territory.

RESULTS

The mean percentage changes of CBF were -13.7%, 6.9%, and 23.8% in prominent (n = 11), mild (n = 11), and equivalent (n = 9) increased enhancements, respectively. The degree of leptomeningeal enhancement was significantly reverse-correlated with percentage change of CBF (P < 0.001), whereas the rCBFs were not significantly different.

CONCLUSIONS

The reverse correlation between leptomeningeal enhancement and cerebrovascular reserve suggests that increased enhancement may indicate impaired primary collaterals and hemodynamic insufficiency. Therefore, leptomeningeal enhancement degree can be used as an indicator of hemodynamic state in stroke.

Acute Stroke Imaging Part I: Fundamentals

Neuroimaging is essential to stroke diagnosis and management. To date, the non-contrast CT has served as our main diagnostic tool. Although brain parenchymal changes visible on CT do provide valuable prognostic information, they provide limited insight into the potential for tissue salvage in response to reperfusion therapy, such as thrombolysis. Newer advanced CT and MRI based imaging techniques have increased the detection sensitivity for hyperacute and chronic parenchymal changes, including ischemia and hemorrhage, permit visualization of blood vessels and cerebral blood flow. This review outlines the basic principles underlying acquisition and interpretation of these newer imaging modalities in the setting of acute stroke. The utility of advanced brain parenchymal and blood flow imaging in the context of acute stroke patient management is also discussed. Part II in this series is a discussion of how these techniques can be used to rationally select appropriate patients for thrombolysis based on pathophysiological data.

Cost-effectiveness of CT angiography and perfusion imaging for delayed cerebral ischemia and vasospasm in aneurysmal subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Delayed cerebral ischemia and vasospasm are significant complications following SAH leading to cerebral infarction, functional disability, and death. In recent years, CTA and CTP have been used to increase the detection of delayed cerebral ischemia and vasospasm. Our aim was to perform comparative-effectiveness and cost-effectiveness analyses evaluating CTA and CTP for delayed cerebral ischemia and vasospasm in aneurysmal SAH from a health care payer perspective.

MATERIALS AND METHODS

We developed a decision model comparing CTA and CTP with transcranial Doppler sonography for detection of vasospasm and delayed cerebral ischemia in SAH. The clinical pathways were based on the "Guidelines for the Management of Aneurysmal Subarachnoid Hemorrhage: A Guideline for Healthcare Professionals from the American Heart Association/American Stroke Association" (2012). Outcome health states represented mortality and morbidity according to functional outcomes. Input probabilities of symptoms and serial test results from CTA and CTP, transcranial Doppler ultrasound, and digital subtraction angiography were directly derived from an SAH cohort by using a multinomial logistic regression model. Expected benefits, measured as quality-adjusted life years, and costs, measured in 2012 US dollars, were calculated for each imaging strategy. Univariable, multivariable, and probabilistic sensitivity analyses were performed to determine the independent and combined effect of input parameter uncertainty.

RESULTS

The transcranial Doppler ultrasound strategy yielded 13.62 quality-adjusted life years at a cost of $154,719. The CTA and CTP strategy generated 13.89 quality-adjusted life years at a cost of $147,097, resulting in a gain of 0.27 quality-adjusted life years and cost savings of $7622 over the transcranial Doppler ultrasound strategy. Univariable and multivariable sensitivity analyses indicated that results were robust to plausible input parameter uncertainty. Probabilistic sensitivity analysis results yielded 96.8% of iterations in the right lower quadrant, representing higher benefits and lower costs.

CONCLUSIONS

Our model results suggest that CTA and CTP are the preferred imaging strategy in SAH, compared with transcranial Doppler ultrasound, leading to improved clinical outcomes and lower health care costs.

The role of imaging in acute ischemic stroke

Neuroimaging has expanded beyond its traditional diagnostic role and become a critical tool in the evaluation and management of stroke. The objectives of imaging include prompt accurate diagnosis, treatment triage, prognosis prediction, and secondary preventative precautions. While capitalizing on the latest treatment options and expanding upon the "time is brain" doctrine, the ultimate goal of imaging is to maximize the number of treated patients and improve the outcome of one the most costly and morbid disease. A broad overview of comprehensive multimodal stroke imaging is presented here to affirm its utilization.

Improvement of image quality and radiation dose of CT perfusion of the brain by means of low-tube voltage (70 KV)

OBJECTIVES

To investigate the feasibility of 70 kV cerebral CT perfusion by comparing image quality and radiation exposure to 80 kV.

METHODS

Thirty patients with suspected cerebral ischemia who underwent dual-source CT perfusion were divided into group A (80 kV, 150 mAs) and group B (70 kV, 150 mAs). Quantitative comparisons were used for maximum enhancement, signal-to-noise index (SNI), and values of cerebral blood flow (CBF), cerebral blood flow (CBV), mean transit time (MTT) on CBF, CBV, and MTT images, and radiation dose from these two groups. Qualitative perfusion images were assessed by two readers.

RESULTS

Maximum enhancement for group B was higher than group A (P < 0.05). There were no significant differences between the two groups for SNI on CBF and CBV maps (P = 0.06 - 0.576), but significant differences for MTT when SNI was measured on frontal white matter and temporo-occipital white matter (P < 0.05). There were no differences among values of CBF, CBV, and MTT for both groups (P = 0.251-0.917). Mean image quality score in group B was higher than group A for CBF (P < 0.05), but no differences for CBV (P = 0.542) and MTT (P = 0.962). Radiation dose for group B decreased compared with group A.

CONCLUSIONS

70 kV cerebral CT perfusion reduces radiation dose without compromising image quality.

KEY POINTS

• Radiation dose is a key concern with the increased using cerebral CT perfusion. Cerebral CT perfusion of 70 kV reduces radiation dose without compromising image quality. • A 70-kV protocol could be used for cerebral CT perfusion.

Whole-brain adaptive 70-kVp perfusion imaging with variable and extended sampling improves quality and consistency while reducing dose

BACKGROUND AND PURPOSE

Despite common use of CTP to assess cerebral hemodynamics in the setting of ischemia, concerns over radiation exposure remain. Our aim was to evaluate the efficacy of an adaptive 70-kVp (peak) whole-brain CTP protocol with variable sampling intervals and extended duration against an established fixed-sampling, limited-period protocol at 80 kVp.

MATERIALS AND METHODS

A retrospective analysis of 37 patients with stroke scanned with conventional (n = 17) and variant-protocol (n = 20) whole-brain CTP was performed. We compared radiation dose, parametric map quality, and consistency of full-contrast circulation capture between a modified 70-kVp protocol, with 20 whole-brain passes at variable sampling intervals over an extended sampling period, and a conventional 80-kVp CTP examination with 24 passes at fixed-sampling intervals and a more limited scanning window. Mann-Whitney U test analysis was used to compare both protocols.

RESULTS

The 70-kVp CTP scan provided superior image quality at a 45% lower CT dose index volume and 13% lower dose-length product/effective dose compared with the conventional 80-kVp scan. With respect to the consistency of contrast-passage capture, 95% of the adaptive, extended protocol continued through the venous return to baseline, compared with only 47% by using the conventional limited-length protocol. Rapid sampling during the critical arterial arrival and washout period was accomplished in nearly 95% with both the variable and fixed-sampling-interval protocols.

CONCLUSIONS

Seventy-kilovolt (peak) CTP with variable and extended sampling produces improved image quality at lower radiation doses with greater consistency of full contrast passage capture.

Multi-modal CT scanning in the evaluation of cerebrovascular disease patients

Ischemic stroke currently represents one of the leading causes of severe disability and mortality in the Western World. Until now, angiography was the most used imaging technique for the detection of the extra-cranial and intracranial vessel pathology. Currently, however, non-invasive imaging tool like ultrasound (US), magnetic resonance (MR) and computed tomography (CT) have proven capable of offering a detailed analysis of the vascular system. CT in particular represents an advanced system to explore the pathology of carotid arteries and intracranial vessels and also offers tools like CT perfusion (CTP) that provides valuable information of the brain's vascular physiology by increasing the stroke diagnostic. In this review, our purpose is to discuss stroke risk prediction and detection using CT.

Normal range and regional heterogeneity of myocardial perfusion in healthy human myocardium: assessment on dynamic perfusion CT using 128-slice dual-source CT

Information about myocardial perfusion in healthy hearts is essential for evaluating patients with ischemic heart disease. The purpose of this study was to determine the range and regional variability of myocardial perfusion in normal volunteers on dynamic perfusion computed tomography (CT). Myocardial perfusion was assessed in 19 healthy volunteers (age 33-60 years; 11 men) at rest and during adenosine-induced hyperemia using a 128-slice dual-source CT scanner. Data were quantified as cc/cc/min for the transmural myocardium based on a 17-segment American Heart Association model. Mean myocardial blood flows (MBF) were 1.73 ± 0.33 cc/cc/min during adenosine-induced hyperemia, 0.83 ± 0.21 cc/cc/min at rest, and perfusion reserve was 2.20 ± 0.53. Regional variability was 17 ± 5% for hyperemic perfusion, 18 ± 7% for resting, and 21 ± 6 % for perfusion reserve. Although statistically insignificant, perfusion in the septum was lower at rest and during hyperemia than in other regions. Women tended to have lower perfusion during hyperemia (1.65 ± 0.40 vs. 1.79 ± 0.28 cc/cc/min, P = 0.40), and higher perfusion at rest than men (0.91 ± 0.27 vs. 0.77 ± 0.15 cc/cc/min, P = 0.23), resulting in lower perfusion reserve (1.86 ± 0.31 vs. 2.45 ± 0.53, P = 0.11). This small cohort of healthy volunteers study reveals normal myocardial perfusion parameter on dynamic perfusion CT as follows: mean MBF is 1.73 ± 0.33 cc/cc/min during hyperemia, 0.83 ± 0.21 cc/cc/min at rest, and perfusion reserve is 2.20 ± 0.53. And the study also demonstrates considerable regional heterogeneity of the myocardial perfusion.

Multi-delay arterial spin labeling perfusion MRI in moyamoya disease--comparison with CT perfusion imaging

OBJECTIVES

To present a multi-delay pseudo-continuous ASL (pCASL) protocol that offers simultaneous measurements of cerebral blood flow (CBF) and arterial transit time (ATT), and to study correlations between multi-delay pCASL and CT perfusion in moyamoya disease.

METHODS

A 4 post-labeling delay (PLD) pCASL protocol was applied on 17 patients with moyamoya disease who also underwent CT perfusion imaging. ATT was estimated using the multi-delay protocol and included in the calculation of CBF. ASL and CT perfusion images were rated for lesion severity/conspicuity. Pearson correlation coefficients were calculated across voxels between the two modalities in grey and white matter of each subject respectively and between normalized mean values of ASL and CT perfusion measures in major vascular territories.

RESULTS

Significant associations between ASL and CT perfusion were detected using subjective ratings, voxel-wise analysis in grey and white matter and region of interest (ROI)-based analysis of normalized mean perfusion. The correlation between ASL CBF and CT perfusion was improved using the multi-delay pCASL protocol compared to CBF acquired at a single PLD of 2 s (P < 0.05).

CONCLUSIONS

There is a correlation between perfusion data from ASL and CT perfusion imaging in patients with moyamoya disease. Multi-delay ASL can improve CBF quantification, which could be a prognostic imaging biomarker in patients with moyamoya disease.

KEY POINTS

• Simultaneous measurements of CBF and ATT can be achieved using multi-delay pCASL. • Multi-delay ASL was compared with CT perfusion in patients with moyamoya disease. • Statistical analyses showed significant associations between multi-delay ASL and CT perfusion. • Multi-delay ASL can improve CBF quantification in moyamoya disease.