Applicability of tableside flat panel detector CT parenchymal cerebral blood volume measurement in neurovascular interventions: preliminary clinical experience

Feasibility of FDCT Early Brain Parenchymal Blood Volume Maps in Predicting Short-Term Prognosis in Patients With Aneurysmal Subarachnoid Hemorrhage

Purpose

Aneurysmal subarachnoid hemorrhage (SAH) is accompanied by cerebral perfusion changes. We aimed to measure the parenchymal blood volume (PBV) maps acquired by C-arm flat-panel detector CT (FDCT) to assess the cerebral blood volume at an early stage in aneurysmal SAH and to explore the correlation with the outcomes at discharge.

Methods

Data of 66 patients with aneurysmal SAH who underwent FDCT PBV examination were retrospectively analyzed. The PBV of regions of interest, including the cortices of the bilateral frontal lobe, the parietal lobe, the occipital lobe, and the cerebral hemisphere, as well as the basal ganglia, were measured and quantitatively analyzed. The clinical and imaging data of the patients were also collected, and logistic regression analysis was performed to explore the correlation between the perfusion parameters and outcomes at discharge.

Results

The favorable and poor outcomes at discharge were found in 37 (56.06%) and 29 (43.94%) patients, respectively. The whole-brain PBV was significantly correlated with the Hunt-Hess grades (p < 0.005) and the WFNSS grades (p < 0.005). The whole-brain PBV of the poor prognosis was significantly higher than that of the favorable prognosis (35.17 ± 7.66 vs. 29.78 ± 5.54, p < 0.005). The logistic regression analysis showed that the PBV of the parietal lobe at the bleeding side (OR = 1.10, 95%CI: 1.00-1.20, p = 0.04) was an independent risk factor predicting the short-term prognosis.

Conclusions

Parenchymal blood volume (PBV) maps could reflect the cerebral blood volume throughout the brain to characterize its perfusion status at an early stage in aneurysmal SAH. It enables a one-stop imaging evaluation and treatment in the same angio-suite and may serve as a reliable technique in clinical assessment of aneurysmal SAH.

Endovascular thrombectomy for acute ischemic stroke

This review describes the evolution of endovascular treatment for acute ischemic stroke, current state of the art, and the challenges for the next decade. The rapid development of endovascular thrombectomy (EVT), from the first attempts into standard of care on a global scale, is one of the major achievements in modern medicine. It was possible thanks to the establishment of a scientific framework for patient selection, assessment of stroke severity and outcome, technical development by dedicated physicians and the MedTech industry, including noninvasive imaging for patient selection, and radiological outcome evaluation. A series of randomized controlled trials on EVT in addition to intravenous thrombolytics, with overwhelmingly positive results for anterior circulation stroke within 6 h of onset regardless of patient characteristics with a number needed to treat of less than 3 for any positive shift in outcome, paved the way for a rapid introduction of EVT into clinical practice. Within the "extended" time window of 6-24 h, the effect has been even greater for patients with salvageable brain tissue according to perfusion imaging with a number needed to treat below 2. Even so, EVT is only available for a small portion of stroke patients, and successfully recanalized EVT patients do not always achieve excellent functional outcome. The major challenges in the years to come include rapid prehospital detection of stroke symptoms, adequate clinical and radiological diagnosis of severe ischemic stroke cases, enabling effective recanalization by EVT in dedicated angiosuites, followed by personalized post-EVT stroke care.

Limitations of Current Near-Infrared Spectroscopy Configuration in Detecting Focal Cerebral Ischemia During Cardiac Surgery: An Observational Case-Series Study

Cerebral oximetry using near-infrared spectroscopy (NIRS) allows for continuous monitoring of cerebral perfusion and immediate treatment of hemodynamic perturbations. In configurations used in current clinical practice, NIRS optodes are placed on the patient`s forehead and cerebral oxygen saturation (ScO₂ ) is determined in bilateral frontal cortical samples. However, focal cerebral ischemic lesions outside of the NIRS field of view may remain undetected. The objective of this observational case-series study was to investigate ScO₂ measurements in patients with acute iatrogenic stroke not located in the frontal cortical region. Adult patients undergoing cardiac surgery with cardiopulmonary bypass or interventional cardiology procedures and suffering stroke in the early postoperative period were identified from the Bernese Stroke Registry and analyzed for their intraoperative ScO₂ values and brain imaging data. Main outcome measures were the ScO₂ values, computed tomography and magnetic resonance imaging findings. In six patients, the infarct areas were localized in the vascular territories of the posterior and/or dorsal middle cerebral arteries. One patient had watershed stroke and another one excellent collaterals resulting in normal cerebral blood volume and only subtle decrease of cerebral blood flow in initially critically perfused watershed brain areas. Intraoperative ScO₂ values were entirely unremarkable or nonindicative for brain damage. Our results indicate that uneventful intraoperative NIRS monitoring does not exclude severe cerebral ischemia due to the limited field of view of commercially available NIRS devices. False negative NIRS may occur as a consequence of stroke localized outside the frontal cortex.

Implication of cerebral circulation time in intracranial stenosis measured by digital subtraction angiography on cerebral blood flow estimation measured by arterial spin labeling

PURPOSE

Arterial spin labeling (ASL) magnetic resonance imaging to assess cerebral blood flow (CBF) is of increasing interest in basic research and in diagnostic applications, since ASL provides similar information to positron emission tomography about perfusion in vascular territories. However, in patients with steno-occlusive arterial disease (SOAD), CBF as measured by ASL might be underestimated due to delayed bolus arrival, and thus increased spin relaxation. We aimed to estimate the extent to which bolus arrival time (BAT) was delayed in patients with SOAD and whether this resulted in underestimation of CBF.

METHODS

BAT was measured using digital subtraction angiography (DSA) in ten patients with high-grade stenosis of the middle carotid artery (MCA). Regional CBF was assessed with pseudocontinuous ASL.

RESULTS

BATs were nonsignificantly prolonged in the stenotic hemisphere 4.1±2.0 s compared with the healthy hemisphere 3.3±0.9 s; however, there were substantial individual differences on the stenotic side. CBF in the anterior and posterior MCA territories were significantly reduced on the stenotic hemisphere. Severe stenosis was correlated with longer BAT and lower quantified CBF.

CONCLUSION

ASL-based perfusion measurement involves a race between the decay of the spins and the delivery of labeled blood to the region of interest. Special caution is needed when interpreting CBF values quantified in individuals with altered blood flow and delayed circulation times. However, from a clinician's point of view, an accentuation of hypoperfusion (even if caused by underestimation of CBF due to prolonged BATs) might be desirable since it indexes potentially harmful physiologic deficits.

Feasibility of Flat Panel Detector CT in Perfusion Assessment of Brain Arteriovenous Malformations: Initial Clinical Experience

The different results from flat panel detector CT in various pathologies have provoked some discussion. Our aim was to assess the role of flat panel detector CT in brain arteriovenous malformations, which has not yet been assessed. Five patients with brain arteriovenous malformations were studied with flat panel detector CT, DSC-MR imaging, and vessel-encoded pseudocontinuous arterial spin-labeling. In glomerular brain arteriovenous malformations, perfusion was highest next to the brain arteriovenous malformation with decreasing values with increasing distance from the lesion. An inverse tendency was observed in the proliferative brain arteriovenous malformation. Flat panel detector CT, originally thought to measure blood volume, correlated more closely with arterial spin-labeling-CBF and DSC-CBF than with DSC-CBV. We conclude that flat panel detector CT perfusion depends on the time point chosen for data collection, which is triggered too early in these patients (ie, when contrast agent appears in the superior sagittal sinus after rapid shunting through the brain arteriovenous malformation). This finding, in combination with high data variability, makes flat panel detector CT inappropriate for perfusion assessment in brain arteriovenous malformations.

Evaluation of Cerebral Hyperperfusion After Carotid Artery Stenting Using C‑Arm CT Measurements of Cerebral Blood Volume

PURPOSE

Hyperperfusion syndrome (HPS) after carotid artery stenting (CAS) causes serious symptoms; therefore, early evaluation after CAS is considered to be important. Measurement of cerebral blood volume using C‑arm computed tomography (C-arm CBV) has recently become possible. Here, the usefulness of C‑arm CBV for the evaluation of hyperperfusion was investigated.

METHODS

C-arm CBV was measured before and immediately after CAS in 30 patients. The regions of interest (ROI) were set in the bilateral middle cerebral artery perfused regions, and the affected/healthy side ratio of measured C‑arm CBV (CBV ratios) was determined to evaluate cerebral perfusion. For comparing values before and after CAS, the CBV ratio increase rate (postoperative CBV ratios/preoperative CBV ratios) was also determined.

RESULTS

C-arm CBV was successfully measured in 30 patients. Intracerebral hemorrhage (ICH) was detected in 3 patients, and no other patient had hyperperfusion syndrome. In the patients who developed ICH, postoperative C‑arm CBV on the affected side was high, and a marked increase was confirmed in the postoperative CBV ratios. Postoperative CBV ratios were 1.03 ± 0.40 and 1.45 ± 0.68 in the non-ICH and ICH groups, and CBV ratio increase rates were 2.7 ± 24.0% and 28.5 ± 26.7% in the non-ICH and ICH groups, respectively; these differences were statistically significant (P < 0.01).

CONCLUSION

C-arm CT allows CBV measurements immediately after CAS without requiring transport of the patient out of the angiography room, and it may enable the evaluation of hyperperfusion before and after CAS.

Flat-detector computed tomography PBV map in the evaluation of presurgical embolization for hypervascular brain tumors

BACKGROUND

Preoperative embolization of hypervascular brain tumors is frequently used to minimize intraoperative bleeding.

OBJECTIVE

To explore the efficacy of embolization using flat-detector CT (FDCT) parenchymal blood volume (PBV) maps before and after the intervention.

MATERIALS AND METHODS

Twenty-five patients with hypervascular brain tumors prospectively received pre- and postprocedural FDCT PBV scans using a biplane system under a protocol approved by the institutional research ethics committee. Semiquantitative analysis, based on region of interest measurements of the pre- and post-embolization PBV maps, operating time, and blood loss, was performed to assess the feasibility of PBV maps in detecting the perfusion deficit and to evaluate the efficacy of embolization.

RESULTS

Preoperative embolization was successful in 18 patients. The relative PBV decreased significantly from 3.98±1.41 before embolization to 2.10±2.00 after embolization. Seventeen patients underwent surgical removal of tumors 24 hours after embolization. The post-embolic tumor perfusion index correlated significantly with blood loss (ρ=0.55) and operating time (ρ=0.60).

CONCLUSIONS

FDCT PBV mapping is a useful method for evaluating the perfusion of hypervascular brain tumors and the efficacy of embolization. It can be used as a supplement to CT perfusion, MRI, and DSA in the evaluation of tumor embolization.

Voxel-Based Sensitivity of Flat-Panel CT for the Detection of Intracranial Hemorrhage: Comparison to Multi-Detector CT

Objectives

Flat-panel CT (FPCT) allows cross-sectional parenchymal, vascular and perfusion imaging within the angiography suite, which could greatly facilitate acute stroke management. We hypothesized that FPCT offers equal diagnostic accuracy compared to multi-detector CT (MDCT) as a primary tool to exclude intracranial hemorrhage.

Methods

22 patients with intracranial hematomas who had both MDCT and FPCT performed within 24 hours were retrospectively identified. Patients with visible change in hematoma size or configuration were excluded. Two raters independently segmented hemorrhagic lesions. Data sets and corresponding binary lesion maps were co-registered to compare hematoma volume. Diagnostic accuracy of FPCT to detect hemorrhage was calculated from voxel-wise analysis of lesion overlap compared to reference MDCT.

Results

Mean hematoma size was similar between MDCT (16.2±8.9 ml) and FPCT (16.1±8.6 ml), with near perfect correlation of hematoma sizes between modalities (ρ = 0.95, p<0.001). Sensitivity and specificity of FPCT to detect hemorrhagic voxels was 61.6% and 99.8% for intraventricular hematomas and 67.7% and 99.5% for all other intracranial hematomas.

Conclusions

In this small sample containing predominantly cases with subarachnoid hemorrhage, FPCT based assessment of hemorrhagic volume in brain yields acceptable accuracy compared to reference MDCT, albeit with a limited sensitivity on a voxel level. Further assessment and improvement of FPCT is necessary before it can be applied as a primary imaging modality to exclude intracranial hemorrhage in acute stroke patients.

Reproducibility of Parenchymal Blood Volume Measurements Using an Angiographic C-arm CT System

RATIONALE AND OBJECTIVES

Intra-procedural measurement of hepatic perfusion following liver embolization continues to be a challenge. Blood volume imaging before and after interventional procedures would allow identifying the treatment end point or even allow predicting treatment outcome. Recent liver oncology studies showed the feasibility of parenchymal blood volume (PBV) imaging using an angiographic C-arm system. This study was done to evaluate the reproducibility of PBV measurements using cone beam computed tomography (CBCT) before and after embolization of the liver in a swine model.

MATERIALS AND METHODS

CBCT imaging was performed before and after partial bland embolization of the left lobe of the liver in five adult pigs. Intra-arterial injection of iodinated contrast with a 6-second x-ray delay was used with a two-sweep 8-second rotation imaging protocol. Three acquisitions, each separated by 10 minutes to allow for contrast clearance, were obtained before and after embolization in each animal. Post-processing was carried out using dedicated software to generate three-dimensional (3D) PBV maps. Two region-of-interest measurements were placed on two views within the right and left lobe on each CBCT 3D PBV map. Variation in PBV for scans acquired within each animal was determined by the coefficient of variation and intraclass correlation. A Wilcoxon signed-rank test was used to test post-procedure reduction in PBV.

RESULTS

The CBCT PBV maps showed mean coefficients of variation of 7% (range: 2%-16%) and 25% (range:  13%-34%) for baseline and embolized PBV maps, respectively. The intraclass correlation for PBV measurements was 0.89, demonstrating high reproducibility, with measurable reduction in PBV displayed after embolization (P = 0.007).

CONCLUSIONS

Intra-procedural acquisition of 3D PBV maps before and after liver embolization using CBCT is highly reproducible and shows promising application for obtaining intra-procedural PBV maps during locoregional therapy.

A novel reconstruction tool (syngo DynaCT Head Clear) in the post-processing of DynaCT images to reduce artefacts and improve image quality

BACKGROUND

Latest generations of flat detector (FD) neuroangiography systems are able to obtain CT-like images of the brain parenchyma. Owing to the geometry of the C-arm system, cone beam artifacts are common and reduce image quality, especially at the periphery of the field of view. An advanced reconstruction algorithm (syngo DynaCT Head Clear) tackles these artifacts by using a modified interpolation-based 3D correction algorithm to improve image quality.

MATERIALS AND METHODS

Eleven volumetric datasets from FD-CT scans were reconstructed with the standard algorithm as well as with the advanced algorithm. In a two-step data analysis process, two reviewers compared dedicated regions of the skull and brain in both reconstruction modes using a 5-point scale (1, much better; 5, much worse; advanced vs standard algorithm). Both reviewers were blinded to the reconstruction mode. In a second step, two additional observers independently evaluated image quality of the 3D data (non-comparative evaluation) in dedicated regions also using a 5-point scale (1, not diagnostically evaluable; 5, good quality, perfectly usable for diagnosis) for both reconstruction algorithms.

RESULTS

Both in the comparative evaluation of dedicated brain regions and in the independent analysis of the FD-CT datasets the observers rated a better image quality if the advanced algorithm was used. The improvement in image quality was statistically significant at both the supraganglionic (p=0.018) and the infratentorial (p=0.002) levels.

CONCLUSIONS

The advanced reconstruction algorithm reduces typical artifacts in FD-CT images and improves image quality at the periphery of the field of view.

Whole brain C-arm computed tomography parenchymal blood volume measurements

INTRODUCTION

C-arm flat detector computed tomography (FDCT) parenchymal blood volume (PBV) imaging in the neuro-interventional suite is a new technique for which detailed whole brain measurements have not been previously reported. This study aims to create a catalogue of PBV measurements for various anatomical regions encompassing the whole brain, using a three-dimensional volume-of-interest (3D-VOI) analysis.

METHODS

We acquired and analysed 30 C-arm FDCT datasets from 26 patients with aneurysmal subarachnoid haemorrhage (SAH), as part of a prospective study comparing C-arm computed tomography (CT) PBV with magnetic resonance perfusion-weighted imaging (MR-PWI). We calculated the PBV values for various brain regions with an automated analysis, using 58 pre-defined atlas-based 3D-VOIs encompassing the whole brain. VOIs partially or completely overlapping regions of magnetic resonance diffusion weighted imaging (MR-DWI) abnormality or magnetic resonance cerebral blood flow (MR-CBF) asymmetry were excluded from the analysis.

RESULTS

Of the 30 C-arm CT PBV datasets, 14 (54%; 12 patients) had areas of restricted diffusion, the majority of which were focal. The PBV values for the cerebral cortex and cerebral white matter were 4.01 ± 0.47 (mean ± SD) and 3.01 ± 0.39 ml per 100 ml. Lobar PBV values were: frontal lobe 4.2 ± 0.8, temporal lobe 4.2 ± 0.9, parietal lobe 3.9 ± 0.7 and occipital lobe 4.3 ± 0.8 ml/100 ml. The basal ganglia and brainstem PBV values were 3.4 ± 0.7 and 4.6 ± 0.6 ml/100 ml, respectively.

CONCLUSIONS

Compared with the typical reference cerebral blood volume (CBV) values reported in the literature for Positron Emission Tomography (PET), the PBV values were relatively high for the white matter and relatively low for the cortical grey matter. The reported catalogue of PBV values for various brain regions would be useful to inform future studies and could be used in clinical practice, when interpreting PBV maps.

C-arm flat detector computed tomography parenchymal blood volume imaging: the nature of parenchymal blood volume parameter and the feasibility of parenchymal blood volume imaging in aneurysmal subarachnoid haemorrhage patients

INTRODUCTION

C-arm flat detector computed tomography (FDCT) parenchymal blood volume (PBV) measurements allow assessment of cerebral haemodynamics in the neurointerventional suite. This paper explores the feasibility of C-arm computed tomography (CT) PBV imaging and the relationship between the C-arm CT PBV and the MR-PWI-derived cerebral blood volume (CBV) and cerebral blood flow (CBF) parameters in aneurysmal subarachnoid haemorrhage (SAH) patients developing delayed cerebral ischemia (DCI).

METHODS

Twenty-six patients with DCI following aneurysmal SAH underwent a research C-arm CT PBV scan using a biplane angiography system and contemporaneous MR-PWI scan as part of a prospective study. Quantitative whole-brain atlas-based volume-of-interest analysis in conjunction with Pearson correlation and Bland-Altman tests was performed to explore the agreement between C-arm CT PBV and MR-derived CBV and CBF measurements.

RESULTS

All patients received medical management, while eight patients (31%) underwent selective intra-arterial chemical angioplasty. Colour-coded C-arm CT PBV maps were 91% sensitive and 100% specific in detecting the perfusion abnormalities. C-arm CT rPBV demonstrated good agreement and strong correlation with both MR-rCBV and MR-rCBF measurements; the agreement and correlation were stronger for MR-rCBF relative to MR-rCBV and improved for C-arm CT PBV versus the geometric mean of MR-rCBV and MR-rCBF. Analysis of weighted means showed that the C-arm CT PBV has a preferential blood flow weighting (≈ 60% blood flow and ≈ 40% blood volume weighting).

CONCLUSIONS

C-arm CT PBV imaging is feasible in DCI following aneurysmal SAH. PBV is a composite perfusion parameter incorporating both blood flow and blood volume weightings. That PBV has preferential (≈ 60%) blood flow weighting is an important finding, which is of clinical significance when interpreting the C-arm CT PBV maps, particularly in the setting of acute brain ischemia.

Mechanical thrombectomy using a combined CT/C-arm X-ray system

Background

Mechanical thrombectomy (MT) using stent-retrievers has been proven to be a safe and effective treatment in acute ischemic stroke (AIS), particularly in large vessel occlusion. Other than patient characteristics, time to recanalization is the most important factor linked to outcome. MT is usually performed in a dedicated angiography suite using a floor- and/or ceiling-mounted biplane angiographic system. Here we report our first experience of MT with a new combined CT and mobile C-arm X-ray device setup.

Methods

Patients with AIS underwent stroke imaging (non-contrast enhanced CT, CT perfusion, and CT angiography) using a commercially available 64-slice CT scanner which was modified for combined use with a C-arm system. In patients with large vessel occlusion, MT was conducted without further patient transfer within the CT imaging suite using a mobile C-arm X-ray device equipped with a 30×30 cm (12×12 inch), 1.5×1.5 k full-view flat detector which was positioned between the gantry and patient table. The safety and feasibility of this new system was assessed in preliminary patients.

Results

Angiographic imaging quality of the mobile C-arm was feasible and satisfactory for diagnostic angiography and MT. Using this setup, time between stroke imaging and groin puncture (picture-to-puncture time) was reduced by up to 35 min (including time for preparation of the patient such as intubation).

Conclusions

MT using a combined CT/C-arm system is safe and feasible. The potential advantages, particularly time saving and ensuing improvement in patient outcome, need to be assessed in a larger study.

Use of cone-beam computed tomography angiography in planning for gamma knife radiosurgery for arteriovenous malformations: a case series and early report

BACKGROUND

The effectiveness of Gamma Knife radiosurgery (GKR) for cerebral arteriovenous malformations (AVMs) is predicated on inclusion of the entire nidus while excluding normal tissue. As such, GKR may be limited by the resolution and accuracy of the imaging modality used in targeting.

OBJECTIVE

We present the first case series to demonstrate the feasibility of using ultrahigh-resolution C-arm cone-beam computed tomography angiography (CBCT-A) in AVM targeting.

METHODS

From June 2009 to June 2013, CBCT-A was used for targeting of all patients with AVMs treated with GKR at our institution. Patients underwent Leksell stereotactic head frame placement followed by catheter-based biplane 2-dimensional digital subtraction angiography, 3-dimensional rotational angiography, as well as CBCT-A. The CBCT-A dataset was used for stereotactic planning for GKR. Patients were followed at 1, 3, 6, and 12 months and then annually thereafter.

RESULTS

CBCT-A-based targeting was used in 22 consecutive patients. CBCT-A provided detailed spatial resolution and sensitivity of nidal angioarchitecture enabling treatment. The average radiation dose to the margin of the AVM nidus corresponding to the 50% isodose line was 15.6 Gy. No patient had treatment-associated hemorrhage. At early follow-up (mean, 16 months), 84% of patients had a decreasing or obliterated AVM nidus.

CONCLUSION

CBCT-A-guided radiosurgery is feasible and useful because it provides sufficient detailed resolution and sensitivity for imaging brain AVMs.

Superior performance of cone-beam CT angiography in characterization of intracranial atherosclerosis

Object

Intracranial atherosclerotic disease (ICAD) carries a high risk of stroke. Evaluation of ICAD has focused on assessing the absolute degree of stenosis, although plaque morphology has recently demonstrated increasing relevance. The authors provide the first report of the use of ultra-high-resolution C-arm cone-beam CT angiography (CBCT-A) in the evaluation of vessel stenosis as well as plaque morphology.

Methods

Between August 2009 and July 2012, CBCT-A was used in all patients with ICAD who underwent catheter-based angiography at the authors' institution (n = 18). Lesions were evaluated for maximum degree of stenosis as well as plaque morphological characteristics (ulcerated, calcified, dissected, or spiculated) via digital subtraction angiography (DSA), 3D-rotational angiography (3DRA), and CBCT-A. The different imaging modalities were compared in their assessment of absolute stenosis as well as their ability to resolve different plaque morphologies.

Results

Lesions were found to have similar degrees of stenosis when utilizing CBCT-A compared with 3DRA, but both 3DRA and CBCT-A differed from DSA in their assessment of the absolute degree of stenosis. CBCT-A provided the most detailed resolution of plaque morphology, identifying a new plaque characteristic in 61% of patients (n = 11) when compared with DSA and 50% (n = 9) when compared with 3DRA. CBCT-A identified all lesion characteristics visualized on DSA and 3DRA.

Conclusions

CBCT-A provides detailed spatial resolution of plaque morphology and may add to DSA and 3DRA in the evaluation of ICAD. Further prospective study is warranted to determine any benefit CBCTA-A may provide in clinical decision making and risk stratification over existing conventional imaging modalities.

Use of time attenuation curves to determine steady-state characteristics before C-arm CT measurement of cerebral blood volume

INTRODUCTION

Cerebral blood volume (CBV) measurement by flat panel detector CT (FPCT) in the angiography suite seems to be a promising tool for patient management during endovascular therapies. A steady state of contrast agent distribution is mandatory during acquisition for accurate FPCT CBV assessment. To the best of our knowledge, this was the first time that steady-state parameters were studied in clinical practice.

METHODS

Before the CBV study, test injections were performed and analyzed to determine a customized acquisition delay from injection for each patient. Injection protocol consisted in the administration of 72 mL of contrast agent material at the injection rate of 4.0 mL/s followed by a saline flush bolus at the same injection rate. Peripheral or central venous accesses were used depending on their availability. Twenty-four patients were treated for different types of neurovascular diseases. Maximal attenuation, steady-state length, and steady-state delay from injection were derived from the test injections' time attenuation curves.

RESULTS

With a 15 % threshold from maximum attenuation values, average steady-state duration was less than 10 s. Maximum average steady-state duration with minimal delay variation was obtained with central injection protocols.

CONCLUSION

With clinically acceptable contrast agent volumes, steady state is a brief condition; thus, fast rotation speed acquisitions are needed. The use of central injections decreases the variability of steady-state's delay from injection. Further studies are needed to optimize and standardize injection protocols to allow a larger diffusion of the FPCT CBV measurement during endovascular treatments.

Clinical application of perfusion computed tomography in neurosurgery

OBJECT

Currently, perfusion CT (PCT) is a valuable imaging technique that has been successfully applied to the clinical management of patients with ischemic stroke and aneurysmal subarachnoid hemorrhage (SAH). However, recent literature and the authors' experience have shown that PCT has many more important clinical applications in a variety of neurosurgical conditions. Therefore, the authors share their experiences of its application in various diseases of the cerebrovascular, neurotraumatology, and neurooncology fields and review the pertinent literature regarding expanding PCT applications for neurosurgical conditions, including pitfalls and future developments.

METHODS

A pertinent literature search was conducted of English-language articles describing original research, case series, and case reports from 1990 to 2011 involving PCT and with relevance and applicability to neurosurgical disorders.

RESULTS

In the cerebrovascular field, PCT is already in use as a diagnostic tool for patients suspected of having an ischemic stroke. Perfusion CT can be used to identify and define the extent of the infarct core and ischemic penumbra core, and thus aid patient selection for acute reperfusion therapy. For patients with aneurysmal SAH, PCT provides assessment of early brain injury, cerebral ischemia, and infarction, in addition to vasospasm. It may also be used to aid case selection for aggressive treatment of patients with poor SAH grade. In terms of oncological applications, PCT can be used as an imaging biomarker to assess angiogenesis and response to antiangiogenetic treatments, differentiate between glioma grades, and distinguish recurrent tumor from radiation necrosis. In the setting of traumatic brain injury, PCT can detect and delineate contusions at an early stage. In patients with mild head injury, PCT results have been shown to correlate with the severity and duration of postconcussion syndrome. In patients with moderate or severe head injury, PCT results have been shown to correlate with patients' functional outcome.

CONCLUSIONS

Perfusion CT provides quantitative and qualitative data that can add diagnostic and prognostic value in a number of neurosurgical disorders, and also help with clinical decision making. With emerging new technical developments in PCT, such as characterization of blood-brain barrier permeability and whole-brain PCT, this technique is expected to provide more and more insight into the pathophysiology of many neurosurgical conditions.

A prospective, multicenter pilot study investigating the utility of flat detector derived parenchymal blood volume maps to estimate cerebral blood volume in stroke patients

Purpose

Newer flat panel angiographic detector (FD) systems have the capability to generate parenchymal blood volume (PBV) maps. The ability to generate these maps in the angiographic suite has the potential to markedly expedite the triage and treatment of patients with acute ischemic stroke. The present study compares FP-PBV maps with cerebral blood volume (CBV) maps derived using standard dynamic CT perfusion (CTP) in a population of patients with stroke.

Methods

56 patients with cerebrovascular ischemic disease at two participating institutions prospectively underwent both standard dynamic CTP imaging followed by FD-PBV imaging (syngo Neuro PBV IR; Siemens, Erlangen, Germany) under a protocol approved by both institutional review boards. The feasibility of the FD system to generate PBV maps was assessed. The radiation doses for both studies were compared. The sensitivity and specificity of the PBV technique to detect (1) any blood volume deficit and (2) a blood volume deficit greater than one-third of a vascular territory, were defined using standard dynamic CTP CBV maps as the gold standard.

Results

Of the 56 patients imaged, PBV maps were technically adequate in 42 (75%). The 14 inadequate studies were not interpretable secondary to patient motion/positioning (n=4), an injection issue (n=2), or another reason (n=8). The average dose for FD-PBV was 219 mGy (median 208) versus 204 mGy (median 201) for CT-CBV. On CT-CBV maps 26 of 42 had a CBV deficit (61.9%) and 15 (35.7%) had a deficit that accounted for greater than one-third of a vascular territory. FD-PBV maps were 100% sensitive and 81.3% specific to detect any CBV deficit and 100% sensitive and 62.9% specific to detect any CBV deficit of greater than one-third of a territory.

Conclusions

PBV maps can be generated using FP systems. The average radiation dose is similar to a standard CTP examination. PBV maps have a high sensitivity for detecting CBV deficits defined by conventional CTP. PBV maps often overestimate the size of CBV deficits. We hypothesize that the FP protocol initiates PBV imaging prior to complete saturation of the blood volume in areas perfused via indirect pathways (ie, leptomeningeal collaterals), resulting in an overestimation of CBV deficits, particularly in the setting of large vessel occlusion.

C-arm CT measurement of cerebral blood volume and cerebral blood flow using a novel high-speed acquisition and a single intravenous contrast injection

BACKGROUND AND PURPOSE

Assessment of perfusion parameters is important in the selection of patients who are most likely to benefit from revascularization after an acute ischemic stroke. The aim of this study was to evaluate the feasibility of measuring cerebral perfusion parameters with the use of a novel high-speed C-arm CT acquisition in conjunction with a single intravenous injection of contrast.

MATERIALS AND METHODS

Seven canines had experimentally induced focal ischemic regions confirmed by CT perfusion imaging. Four hours after ischemic injury creation, each subject underwent cerebral perfusion measurements with the use of standard perfusion CT, immediately followed by the use of C-arm CT. Cerebral blood flow and cerebral blood volume maps measured by C-arm CT were quantitatively and qualitatively compared with those measured by perfusion CT for 6 of the 7 canine subjects.

RESULTS

Results from independent observer evaluations of perfusion CT and C-arm perfusion maps show strong agreement between observers for identification of ischemic lesion location. Significant percentage agreement between observers for lesion detection and identification of perfusion mismatch between CBV and CBF maps indicate that the maps for both perfusion CT and C-arm are easy to interpret. Quantitative region of interest-based evaluation showed a strong correlation between the perfusion CT and C-arm CBV and CBF maps (R(2) = 0.68 and 0.85). C-arm measurements for both CBV and CBF were consistently overestimated when compared with perfusion CT.

CONCLUSIONS

Qualitative and quantitative measurements of CBF and CBV with the use of a C-arm CT acquisition and a single intravenous injection of contrast agent are feasible. Future improvements in flat detector technology and software algorithms probably will enable more accurate quantitative perfusion measurements with the use of C-arm CT.

Toward the era of a one-stop imaging service using an angiography suite for neurovascular disorders

Transportation of patients requiring multiple diagnostic and imaging-guided therapeutic modalities is unavoidable in current radiological practice. This clinical scenario causes time delays and increased risk in the management of stroke and other neurovascular emergencies. Since the emergence of flat-detector technology in imaging practice in recent decades, studies have proven that flat-detector X-ray angiography in conjunction with contrast medium injection and specialized reconstruction algorithms can provide not only high-quality and high-resolution CT-like images but also functional information. This improvement in imaging technology allows quantitative assessment of intracranial hemodynamics and, subsequently in the same imaging session, provides treatment guidance for patients with neurovascular disorders by using only a flat-detector angiographic suite-a so-called one-stop quantitative imaging service (OSIS). In this paper, we review the recent developments in the field of flat-detector imaging and share our experience of applying this technology in neurovascular disorders such as acute ischemic stroke, cerebral aneurysm, and stenoocclusive carotid diseases.

Impact of a new metal artefact reduction algorithm in the noninvasive follow-up of intracranial clips, coils, and stents with flat-panel angiographic CTA: initial results

INTRODUCTION

Flat-panel angiographic CT after intravenous contrast agent application (ivACT) is increasingly used as a follow-up examination after coiling, clipping, or stenting. The purpose of this study was to evaluate the feasibility of a new metal artefact reduction algorithm (MARA) in patients treated for intracranial aneurysms and stenosis.

METHODS

IvACT was performed on a flat-panel detector angiography system after intravenous application of 80 ml contrast media. The uncorrected raw images were transferred to a prototype reconstruction workstation where the MARA was applied. Two experienced neuroradiologists examined the corrected and uncorrected images on a commercially available workstation.

RESULTS

Artefacts around the implants were detected in all 16 uncorrected cases, while eight cases showed remaining artefacts after correction with the MARA. In the cases without correction, there were 11 cases with "extensive" artefacts and five cases with "many" artefacts. After correction, seven cases showed "few" and only one case "many" artefacts (Wilcoxon test, P < 0.001). Parent vessels were characterized as "not identifiable" in 62% of uncorrected images, while the delineation of parent vessels were classified as "excellent" in 50% of the cases after correction (Wilcoxon test, P = 0.001).

CONCLUSIONS

Use of the MARA in our study significantly reduced artefacts around metallic implants on ivACT images and allowed for the delineation of surrounding structures.

Does preinterventional flat-panel computer tomography pooled blood volume mapping predict final infarct volume after mechanical thrombectomy in acute cerebral artery occlusion?

PURPOSE

Decreased cerebral blood volume is known to be a predictor for final infarct volume in acute cerebral artery occlusion. To evaluate the predictability of final infarct volume in patients with acute occlusion of the middle cerebral artery (MCA) or the distal internal carotid artery (ICA) and successful endovascular recanalization, pooled blood volume (PBV) was measured using flat-panel detector computed tomography (FPD CT).

MATERIALS AND METHODS

Twenty patients with acute unilateral occlusion of the MCA or distal ACI without demarcated infarction, as proven by CT at admission, and successful Thrombolysis in cerebral infarction score (TICI 2b or 3) endovascular thrombectomy were included. Cerebral PBV maps were acquired from each patient immediately before endovascular thrombectomy. Twenty-four hours after recanalization, each patient underwent multislice CT to visualize final infarct volume. Extent of the areas of decreased PBV was compared with the final infarct volume proven by follow-up CT the next day.

RESULTS

In 15 of 20 patients, areas of distinct PBV decrease corresponded to final infarct volume. In 5 patients, areas of decreased PBV overestimated final extension of ischemia probably due to inappropriate timing of data acquisition and misery perfusion.

CONCLUSION

PBV mapping using FPD CT is a promising tool to predict areas of irrecoverable brain parenchyma in acute thromboembolic stroke. Further validation is necessary before routine use for decision making for interventional thrombectomy.