The role of dual energy CT in differentiating between brain haemorrhage and contrast medium after mechanical revascularisation in acute ischaemic stroke

Carotid artery assessment in dual-source photon-counting CT: impact of low-energy virtual monoenergetic imaging on image quality, vascular contrast and diagnostic assessability

PURPOSE

Preliminary dual-energy CT studies have shown that low-energy virtual monoenergetic (VMI) + reconstructions can provide superior image quality compared to standard 120 kV CTA series. The purpose of this study is to evaluate the impact of low-energy VMI reconstructions on quantitative and qualitative image quality, vascular contrast, and diagnostic assessability of the carotid artery in patients undergoing photon-counting CTA examinations.

MATERIALS AND METHODS

A total of 122 patients (67 male) who had undergone dual-source photon-counting CTA scans of the carotid artery were retrospectively analyzed in this study. Standard 120 kV CT images and low-keV VMI series from 40 to 100 keV with an interval of 15 keV were reconstructed. Quantitative analyses included the evaluation of vascular CT numbers, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). CT number measurements were performed in the common, external, and internal carotid arteries. Qualitative analyses were performed by three board-certified radiologists independently using five-point scales to evaluate image quality, vascular contrast, and diagnostic assessability of the carotid artery.

RESULTS

Mean attenuation, CNR and SNR values were highest in 40 keV VMI reconstructions (HU, 1362.32 ± 457.81; CNR, 33.19 ± 12.86; SNR, 34.37 ± 12.89) followed by 55-keV VMI reconstructions (HU, 736.94 ± 150.09; CNR, 24.49 ± 7.11; SNR, 26.25 ± 7.34); all three mean values at these keV levels were significantly higher compared with the remaining VMI series and standard 120 kV CT series (HU, 154.43 ± 23.69; CNR, 16.34 ± 5.47; SNR, 24.44 ± 7.14) (p < 0.0001). The qualitative analysis showed the highest rating scores for 55 keV VMI reconstructions followed by 40 keV and 70 keV VMI series with a significant difference compared to standard 120 kV CT images series regarding image quality, vascular contrast, and diagnostic assessability of the carotid artery (all comparisons, p < 0.01).

CONCLUSIONS

Low-keV VMI reconstructions at a level of 40-55 keV significantly improve image quality, vascular contrast, and the diagnostic assessability of the carotid artery compared with standard CT series in photon-counting CTA.

The value of quantitative dual-energy CT parameters in predicting delayed haemorrhage after thrombectomy in acute ischaemic stroke

OBJECTIVE

This study investigates the predictive value of dual-energy CT Rho/Z quantitative parameters for delayed hemorrhage post-thrombectomy in patients with acute ischemic stroke MATERIALS AND METHODS: A retrospective analysis was conducted on 80 patients who underwent dual-energy CT after thrombectomy for acute ischemic stroke. Patients were divided into delayed hemorrhage/no delayed hemorrhage, symptomatic intracranial hemorrhage/asymptomatic intracranial hemorrhage and cerebral parenchymal hematoma/no cerebral parenchymal hematoma groups RESULTS: The quantitative parameters significantly associated with delayed hemorrhage are DEI and Zeff (p < 0.001), with the optimal cutoff values for DEI and Zeff being 0.045 and 9.355, respectively. The quantitative parameters significantly associated with symptomatic intracranial hemorrhage are DEI and Zeff (p < 0.001), with the optimal cutoff values being 0.064 and 9.422, respectively. The parameters significantly associated with cerebral parenchymal hematoma are DEI and Zeff (p < 0.001), with the optimal cutoff values for DEI and Zeff being 0.058 and 9.09, respectively CONCLUSION: The DEI and Zeff parameters derived from dual-energy CT Rho/Z analysis are valuable in predicting delayed hemorrhage, symptomatic intracranial hemorrhage, and cerebral parenchymal hematoma in patients with acute ischemic stroke following thrombectomy.

Impact of post-thrombectomy isolated subarachnoid hemorrhage on neurological outcomes in patients with anterior ischemic stroke - a retrospective single-center observational study

PURPOSE

We aimed to investigate the impact of post-thrombectomy isolated subarachnoid hemorrhage (i-SAH) and other types of intracranial hemorrhage (o-ICH) on patient's neurological outcomes.

METHODS

Stroke data from 2018 to 2022 in a tertiary care center were retrospectively analyzed. Patients with large vessel occlusion from ICA to M2 branch were included. Post-thrombectomy intracranial hemorrhages at 24 h were categorized with Heidelberg Bleeding Classification. Neurological impairment of patients was continuously assessed at admission, at 24 h, 48 h and 72 h, and at discharge. Predictors of i-SAH and o-ICH were assessed.

RESULTS

297 patients were included. i-SAH and o-ICH were found in 12.1% (36/297) and 11.4% (34/297) of patients. Overall, NIHSS of i-SAH patients at discharge were comparable to o-ICH patients (median 22 vs. 21, p = 0.889) and were significantly higher than in non-ICH patients (22 vs. 7, p < 0.001). i-SAH often resulted in abrupt deterioration of patient's neurological symptoms at 24 h after thrombectomy. Compared to non-ICH patients, the occurrence of i-SAH was frequently associated with worse neurological outcome at discharge (median NIHSS increase of 4 vs. decrease of 4, p < 0.001) and higher in-hospital mortality (41.7% vs. 23.8%, p = 0.022). Regardless of successful reperfusion (TICI 2b/3), the beneficial impact of thrombectomy appeared to be outweighed by the adverse effect of i-SAH. Incomplete reperfusion and shorter time from symptom onset to admission were associated with higher probability of i-SAH, whereas longer procedure time and lower baseline ASPECTS were predictive for o-ICH occurrence.

CONCLUSION

Post-thrombectomy isolated subarachnoid hemorrhage is a common complication with significant negative impact on neurological outcome.

Real-time diagnosis of intracerebral hemorrhage by generating dual-energy CT from single-energy CT

Real-time diagnosis of intracerebral hemorrhage after thrombectomy is crucial for follow-up treatment. However, this is difficult to achieve with standard single-energy CT (SECT) due to similar CT values of blood and contrast agents under a single energy spectrum. In contrast, dual-energy CT (DECT) scanners employ two different energy spectra, which allows for real-time differentiation between hemorrhage and contrast extravasation based on energy-related attenuation characteristics. Unfortunately, DECT scanners are not as widely used as SECT scanners due to their high costs. To address this dilemma, in this paper, we generate pseudo DECT images from a SECT image for real-time diagnosis of hemorrhage. More specifically, we propose a SECT-to-DECT Transformer-based Generative Adversarial Network (SDTGAN), which is a 3D transformer-based multi-task learning framework equipped with a shared attention mechanism. In this way, SDTGAN can be guided to focus more on high-density areas (crucial for hemorrhage diagnosis) during the generation. Meanwhile, the introduced multi-task learning strategy and the shared attention mechanism also enable SDTGAN to model dependencies between interconnected generation tasks, improving generation performance while significantly reducing model parameters and computational complexity. In the experiments, we approximate real SECT images using mixed 120kV images from DECT data to address the issue of not being able to obtain the true paired DECT and SECT data. Extensive experiments demonstrate that SDTGAN can generate DECT images better than state-of-the-art methods. The code of our implementation is available at https://github.com/jiang-cw/SDTGAN.

Prognostic implications of intracranial haemorrhage on dual-energy CT immediately following endovascular treatment for acute ischemic stroke

OBJECTIVE

To describe the incidence, risk factors, and prognostic relevance of intracranial haemorrhage (ICH) immediately after endovascular treatment (EVT) for ischaemic stroke in the anterior circulation.

METHODS

EVT records from 2010 to 2019 were screened. Included patients underwent DECT within 3h post-EVT. Virtual native reconstructions were evaluated for ICH according to the Heidelberg criteria and grouped into Heidelberg classes (HCs): [HC1] haemorrhagic infarction (HI)1, HI2 and parenchymal haematoma (PH)1; [HC2] PH2; [HC3] i.a. intraventricular and subarachnoid haemorrhage. If ICH corresponding to multiple HCs was observed, we assumed that the (largest) parenchymal ICH would have the greatest prognostic impact. Hence, a single HC was attributed by the following order of severity: HC2, HC1, HC3. The primary outcome was the modified Rankin Scale (mRS) at 90 days. The effect of asymptomatic ICH (aICH) and symptomatic ICH (sICH) of (1) HC1 or HC2 and (2) HC3 on patient outcomes was evaluated with multivariable regression after multiple imputation.

RESULTS

Out of 651 records, 498 patients were included. Eighty-one (16%) patients showed ICH on post-EVT DECT, of which 19 were classified as HC1 (21% symptomatic), 6 as HC2 (100% symptomatic), and 56 as HC3 (14% symptomatic). ICH development was mainly associated with unfavourable procedural characteristics. Both aICH and sICH of HC1 or HC2 were associated with the mRS (aICH: adjusted [a]cOR 4.92, 95%CI [1.48-16.35]; sICH: acOR 12.97, 95%CI [2.39-70.26]) and mortality (aICH: aOR 10.08, 95%CI [2.48-40.88]; sICH: aOR 9.92, 95%CI [1.48-66.31]). Likewise, sICH of HC3 was associated with the mRS and mortality (acOR 19.91, 95%CI [4.03-98.35], and aOR 13.23, 95%CI [2.27-77.18], respectively). aICH of HC3 was not significantly associated with the mRS or mortality (acOR 0.87, 95%CI [0.48-1.57], and cOR 0.84, 95%CI [0.32-2.20], respectively).

CONCLUSIONS

Immediate post-EVT ICH is a frequent finding. Except for aICH of HC3, any ICH is associated with poor long-term clinical outcomes.

Dual-Energy Computed Tomography in the Evaluation and Management of Subarachnoid Hemorrhage, Intracranial Hemorrhage, and Acute Ischemic Stroke

Dual-energy computed tomography (DECT) has emerged as a valuable imaging modality in the diagnosis and management of various cerebrovascular pathologies, including subarachnoid hemorrhage, intracranial hemorrhage, and acute ischemic stroke. This article reviews the principles of DECT and its applications in the evaluation and management of these conditions. The authors discuss the advantages of DECT over conventional computed tomography, as well as its limitations, and provide an overview of current research and future directions in the field.

Procedural Blood Pressure and Intracranial Hemorrhage on Dual-Energy Computed Tomography After Endovascular Stroke Treatment

PURPOSE

Optimal systolic blood pressure (SBP) management during endovascular treatment (EVT) for acute ischemic stroke remains a topic of debate. Though BP is associated with worse functional outcome, the relationship between BP and post-procedural intracranial hemorrhage (ICH) is less well-known. We aimed to investigate the association between BP during EVT and post-procedural ICH on dual-energy CT (DECT).

METHODS

We included all patients who underwent EVT for an anterior circulation large vessel occlusion between 2010 and 2019, and received DECT < 3 h post-EVT. All BP measurements during the EVT procedure were used to calculate mean arterial pressure (MAPmean), mean SBP (SBPmean), and SBPmax-min (highest minus lowest). ICH was assessed using virtual post-procedural unenhanced DECT reconstructions and classified as intraparenchymal or extraparenchymal. Symptomatic ICH was scored according to the Heidelberg criteria. The association between different BP parameters and ICH was assessed using multivariable logistic regression.

RESULTS

We included 478 patients. Seventy-six patients (16%) demonstrated ICH on DECT, of which 26 (34%) were intraparenchymal. Symptomatic intraparenchymal and extraparenchymal ICH occurred in 10 (38%) and 4 (8%) patients. SBPmax, SBPmean, and MAPmean were associated with intraparenchymal ICH with an adjusted odds ratio of 1.19 (95%CI, 1.02-1.39), 1.22 (95%CI, 1.03-1.46), and 1.40 (95%CI, 1.09-1.81) per 10 mmHg, while BP was not significantly associated with extraparenchymal ICH. BP did not differ between asymptomatic and symptomatic ICH.

CONCLUSION

Procedural BP is associated with intraparenchymal ICH on post-EVT DECT but not with extraparenchymal ICH. Future studies should evaluate whether individual procedural BP management reduces post-EVT ICH and improves clinical outcome.

Quantification of ischemic brain edema after mechanical thrombectomy using dual-energy computed tomography in patients with ischemic stroke

Net water uptake (NWU) is a quantitative imaging biomarker used to assess cerebral edema resulting from ischemia via Computed Tomography (CT)-densitometry. It serves as a strong predictor of clinical outcome. Nevertheless, NWU measurements on follow-up CT scans after mechanical thrombectomy (MT) can be affected by contrast staining. To improve the accuracy of edema estimation, virtual non-contrast images (VNC-I) from dual-energy CT scans (DECT) were compared to conventional polychromatic CT images (CP-I) in this study. We examined NWU measurements derived from VNC-I and CP-I to assess their agreement and predictive value in clinical outcome. 88 consecutive patients who received DECT as follow-up after MT were included. NWU was quantified on CP-I (cNWU) and VNC-I (vNWU). The clinical endpoint was functional independence at discharge. cNWU and vNWU were highly correlated (r = 0.71, p < 0.0001). The median difference between cNWU and vNWU was 8.7% (IQR: 4.5-14.1%), associated with successful vessel recanalization (mTICI2b-3) (ß: 11.6%, 95% CI 2.9-23.0%, p = 0.04), and age (ß: 4.2%, 95% CI 1.3-7.0%, p = 0.005). The diagnostic accuracy to classify outcome between cNWU and vNWU was similar (AUC:0.78 versus 0.77). Although there was an 8.7% median difference, indicating potential edema underestimation on CP-I, it did not have short-term clinical implications.

Diagnostic accuracy of dual-energy computed tomography in the diagnosis of neurological complications after endovascular treatment of acute ischaemic stroke: a systematic review and meta-analysis

OBJECTIVES

To investigate dual-energy computed tomography's (DECT) diagnostic performance in detecting neurological complications following endovascular therapy (EVT) of acute ischaemic stroke (AIS).

METHODS

We performed the literature search using Web of Science, Scopus, PubMed, EBSCO, and Science Direct databases for published related studies. The selected studies estimated the validity of DECT in the detection of neurological complications after EVT for AIS. Study quality assessment was performed utilizing the Quality of Diagnostic Accuracy Studies-2 Tool. Our meta-analysis calculated the pooled sensitivity, negative likelihood ratio, specificity, and positive likelihood ratio for each detected complication. The summary receiver operating characteristics (sROC) curve was utilized to estimate the area under the curve (AUC).

RESULTS

Of 22 studies, 21 were included in the quantitative synthesis. In the detection of intracerebral haemorrhage (ICH), DECT pooled overall sensitivity and specificity were 69.9% (95% CI, 44.5%-86.8%) and 100% (95% CI, 92.1%-100%); whereas, in the detection of ischaemia, they were 85.9% (95% CI, 80.4%-90%) and 90.7% (95% CI, 87%-93.5%), respectively. On the sROC curve, AUC values of 0.954 and 0.952 were recorded for the detection of ICH and ischaemia, respectively.

CONCLUSIONS

DECT demonstrated high accuracy and specificity in the detection of neurological complications post-endovascular treatment of AIS. However, further prospective studies with a standardized reference test and a larger sample size are recommended to support these findings.

ADVANCES IN KNOWLEDGE

DECT is a rapid and valid imaging tool for the prediction of ICH and cerebral ischaemia after the EVT of AIS.

Determinants and Clinical Relevance of Iodine Contrast Extravasation after Endovascular Thrombectomy: A Dual-Energy CT Study

BACKGROUND AND PURPOSE

Iodine contrast extravasation (ICE) is common in patients with acute ischemic stroke (AIS) after endovascular-thrombectomy (EVT). The aim of our study was to evaluate the incidence of ICE assessed by dual-energy CT (DECT), its determinants, and associations with clinical outcome.

MATERIALS AND METHODS

We retrospectively examined imaging parameters and clinical factors from consecutive patients with AIS treated with EVT who had a DECT 24 hours thereafter, identified at a single academic center. Associations between ICE, clinical, imaging, and procedural parameters, as well as clinical outcome were explored by using univariable and multivariable models.

RESULTS

A total of 197 consecutive patients were included (period 2019-2020), of which 53 (27%) demonstrated ICE that was pure ICE in 30/53 (57%) and mixed with intracranial hemorrhage (ICH) in 23/53 (43%). Low initial-ASPECTS, high per-procedural-contrast volume injected, and high admission-glycemia were independently associated with ICE (respectively, OR = 0.43, 95% CI, 0.16-1.13, P = .047; OR = 1.02, 95% CI, 1.00-1.04, P = .003; OR = 8.92, 95% CI, 0.63-125.77, P = .043). ICE was independently associated with ICH (P = .047), but not with poorer clinical outcome (6-month mRS >2, P = .223). Univariate analysis demonstrated that low ADC, higher ischemic volume, ICA occlusion, mass effect, longer procedure duration, combined thrombectomy technique, higher number of device passes, and lower recanalization rate were associated with ICE (respectively, P = .002; <.001; .002; <.001; .002; 0.011; <0.001; 0.015).

CONCLUSIONS

ICE evaluated with DECT is a relatively frequent finding after EVT, present in almost one-third of patients. Lower admission ASPECTS, higher glycemia, and high contrast volume injected per procedure were associated with ICE. We also found an association between ICE and ICH, confirming blood-brain barrier alteration as a major determinant of ICH.

[Usefulness of Electron Density Calculated from Dual Energy CT in Differential Diagnosis between Hepatocellular Carcinoma and Hepatic Hemangioma]

PURPOSE

The aim of this study were to compare electron density (ED), obtained by dual energy computed tomography (DECT), between hepatocellular carcinoma (HCC) and hemangioma, and to assess the differential diagnostic performance of ED between HCC and hemangioma.

METHODS

A total of 46 patients (27 men and 19 women; mean age, 65.7±14.0 years) diagnosed with HCC or hemangioma who underwent upper abdominal DECT between October 2021 and December 2022 were included. ED of each lesion was measured. Relative ED (rED), which is normalized by the ED of background liver parenchyma, was calculated. ED and rED of HCC and hemangioma were statistically analyzed.

RESULTS

The HCC group showed significantly higher ED (48.1±5.2) and rED (80.0±7.3) than the hemangioma group (43.7±4.1, 69.7±7.2, respectively) (p<0.01). The area under the curve of rED was greater than that of ED, but no significant difference was found (p=0.153).

CONCLUSION

ED may help in the differential diagnosis between HCC and hemangioma.

Early antithrombotic therapy in patients with postinterventional cerebral hyperdensity reduces early neurological deterioration after mechanical thrombectomy

BACKGROUND

Initiation of early antithrombotic therapy after acute ischemic stroke (AIS) is crucial. We aimed to investigate whether early antithrombotic therapy influences early neurological deterioration (END) in AIS patients with postinterventional cerebral hyperdensity (PCHD) immediately after mechanical thrombectomy (MT).

METHODS

We retrospectively analyzed 108 consecutive anterior circulation AIS patients with PCHD immediately after MT. All patients were divided into END group and non-END group and END was defined as an increase of four points or more on the postinterventional National Institutes of Health Stroke Scale (NIHSS) score within the first 72 h after MT. Early antithrombotic therapy was defined as patients with PCHD who received antithrombotic therapy within 24 h after MT. Statistical analyses were performed to evaluate the association between early antithrombotic therapy and the risk of END.

RESULTS

Among 108 patients, 27 (25%) patients developed END. Multivariate regression analysis revealed that early use of antithrombotic therapy (OR = 0.229, 95%CI = 0.083-0.626, P = 0.004) was an independent protector of END and postinterventional low density shadow exceeding 1/3 of the vascular territory (OR = 4.000, 95%CI = 1.157-13.834, P = 0.029) was an independent risk factor for END.

CONCLUSION

Antithrombotic therapy within 24 h after MT maybe associated with the reduced risk of END in anterior circulation AIS patients with PCHD.

Occult contrast retention post-thrombectomy on 24-h follow-up dual-energy CT: Associations and impact on imaging analysis

BACKGROUND

Following reperfusion treatment in ischemic stroke, computed tomography (CT) imaging at 24 h is widely used to assess radiological outcomes. Even without visible hyperattenuation, occult angiographic contrast may persist in the brain and confound Hounsfield unit-based imaging metrics, such as net water uptake (NWU).

AIMS

We aimed to assess the presence and factors associated with retained contrast post-thrombectomy on 24-h imaging using dual-energy CT (DECT), and its impact on the accuracy of NWU as a measure of cerebral edema.

METHODS

Consecutive patients with anterior circulation large vessel occlusion who had post-thrombectomy DECT performed 24-h post-treatment from two thrombectomy stroke centers were retrospectively studied. NWU was calculated by interside comparison of HUs of the infarct lesion and its mirror homolog. Retained contrast was quantified by the difference in NWU values with and without adjustment for iodine. Patients with visible hyperdensities from hemorrhagic transformation or visible contrast retention and bilateral infarcts were excluded. Cerebral edema was measured by relative hemispheric volume (rHV) and midline shift (MLS).

RESULTS

Of 125 patients analyzed (median age 71 (IQR = 61-80), baseline National Institutes of Health Stroke Scale (NIHSS) 16 (IQR = 9.75-21)), reperfusion (defined as extended-Thrombolysis-In-Cerebral-Infarction 2b-3) was achieved in 113 patients (90.4%). Iodine-subtracted NWU was significantly higher than unadjusted NWU (17.1% vs 10.8%, p < 0.001). In multivariable median regression analysis, increased age (p = 0.024), number of passes (p = 0.006), final infarct volume (p = 0.023), and study site (p = 0.021) were independently associated with amount of retained contrast. Iodine-subtracted NWU correlated with rHV (rho = 0.154, p = 0.043) and MLS (rho = 0.165, p = 0.033) but unadjusted NWU did not (rHV rho = -0.035, p = 0.35; MLS rho = 0.035, p = 0.347).

CONCLUSIONS

Angiographic iodine contrast is retained in brain parenchyma 24-h post-thrombectomy, even without visually obvious hyperdensities on CT, and significantly affects NWU measurements. Adjustment for retained iodine using DECT is required for accurate NWU measurements post-thrombectomy. Future quantitative studies analyzing CT after thrombectomy should consider occult contrast retention.

Dual-Energy Computed Tomography to Photon Counting Computed Tomography: Emerging Technological Innovations

Computed tomography (CT) has seen remarkable developments in the past several decades, radically transforming the role of imaging in day-to-day clinical practice. Dual-energy CT (DECT), an exciting innovation introduced in the early part of this century, has widened the scope of CT, opening new opportunities due to its ability to provide superior tissue characterization. The introduction of photon-counting CT (PCCT) heralds a paradigm shift in CT scanner technology representing another significant milestone in CT innovation. PCCT offers several advantages over DECT, such as improved spectral resolution, enhanced tissue characterization, reduced image artifacts, and improved image quality.

Low Levels of Low-Density Lipoprotein Cholesterol Increase the Risk of Post-Thrombectomy Delayed Parenchymal Hematoma

PURPOSE

Low levels of low-density lipoprotein cholesterol (LDL-C) have been suggested to increase the risk of hemorrhagic transformation (HT) following acute ischemic stroke. However, the literature on the relationship between LDL-C levels and post-thrombectomy HT is sparse. The aim of our study is to investigate the association between LDL-C and delayed parenchymal hematoma (PH) that was not seen on immediate post-thrombectomy dual-energy computed tomography (DECT).

MATERIALS AND METHODS

A retrospective analysis was conducted on all patients with anterior circulation large vessel occlusion who underwent thrombectomy at a comprehensive stroke center from 2018-2021. Per institutional protocol, all patients received DECT immediately post-thrombectomy and magnetic resonance imaging or CT at 24 hours. The presence of immediate hemorrhage was assessed by DECT, while delayed PH was assessed by 24-hour imaging. Multivariable analysis was performed to identify predictors of delayed PH. Patients with hemorrhage on immediate post-thrombectomy DECT were excluded to select only those with delayed PH.

RESULTS

Of 159 patients without hemorrhage on immediate post-thrombectomy DECT, 18 (11%) developed delayed PH on 24-hour imaging. In multivariable analysis, LDL-C (odds ratio [OR], 0.76; P=0.038; 95% confidence interval [CI], 0.59-0.99; per 10 mg/dL increase) independently predicted delayed PH. High-density lipoprotein cholesterol, triglyceride, and statin use were not associated. After adjusting for potential confounders, LDL-C ≤50 mg/dL was associated with an increased risk of delayed PH (OR, 5.38; P=0.004; 95% CI, 1.70-17.04), while LDL-C >100 mg/dL was protective (OR, 0.26; P=0.041; 95% CI, 0.07-0.96).

CONCLUSION

LDL-C ≤50 mg/dL independently predicted delayed PH following thrombectomy and LDL-C >100 mg/dL was protective, irrespective of statin. Thus, patients with low LDL-C levels may warrant vigilant monitoring and necessary interventions, such as blood pressure control or anticoagulation management, following thrombectomy even in the absence of hemorrhage on immediate post-thrombectomy DECT.

Prognostic value of contrast staining on dual-energy CT after endovascular therapy in acute ischemic stroke: a meta-analysis

BACKGROUND

Contrast staining (CS) on dual-energy CT (DECT) is common after endovascular therapy (EVT) in acute ischemic stroke (AIS). We performed a meta-analysis to investigate the prognostic significance of CS detected by DECT after EVT in AIS.

METHOD

MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science and Scopus databases were searched from inception to July 2023 for publications on the prognostic significance of CS on DECT after EVT in patients with AIS. Prognostic outcomes were hemorrhage transformation (HT) and poor functional outcome (modified Rankin Scale [mRS] Score of 3-6 at the 90-day follow-up). Data are presented as odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

Eleven studies including 1123 cases of AIS were included. Pooled results indicated a higher risk of HT in patients with CS than in those without CS (OR = 2.22; 95% CI 1.41-3.51, P = 0.001; I2 = 45.4%). No association between CS and symptomatic HT was observed (OR = 2.10; 95% CI 0.64-6.95, P = 0.223; I2 = 67.3%). Moreover, there was also higher odds of poor functional outcome in patients with CS than in those without CS (OR = 2.76; 95% CI 1.53-4.97, P = 0.001; I2 = 44.9%).

CONCLUSIONS

The presence of contrast staining on DECT after EVT is associated with a higher risk of hemorrhage transformation and poor functional outcome. However, further high-quality studies with standardized processes are required to confirm these results.

The clinical utility of dual-energy CT in post-thrombectomy care: Part 2, the predictive value of contrast density and volume for delayed hemorrhagic transformation

OBJECTIVES

Dual-energy CT allows differentiation between blood and iodinated contrast. This study aims to determine the predictive value of contrast density and volume on post-thrombectomy dual-energy CT for delayed hemorrhagic transformation and its impact on 90-day outcomes.

MATERIALS AND METHODS

A retrospective analysis was performed on patients who underwent thrombectomy for anterior circulation large-vessel occlusion at a comprehensive stroke center from 2018-2021. Per institutional protocol, all patients underwent dual-energy CT immediately post-thrombectomy and MRI or CT 24 hours afterward. The presence of hemorrhage and contrast staining was evaluated by dual-energy CT. Delayed hemorrhagic transformation was determined by 24-hour imaging and classified into petechial hemorrhage or parenchymal hematoma using ECASS III criteria. Univariable and multivariable analyses were performed to determine predictors and outcomes of delayed hemorrhagic transformation.

RESULTS

Of 97 patients with contrast staining and without hemorrhage on dual-energy CT, 30 and 18 patients developed delayed petechial hemorrhage and delayed parenchymal hematoma, respectively. On multivariable analysis, delayed petechial hemorrhage was predicted by anticoagulant use (OR,3.53;p=0.021;95%CI,1.19-10.48) and maximum contrast density (OR,1.21;p=0.004;95%CI,1.06-1.37;per 10 HU increase), while delayed parenchymal hematoma was predicted by contrast volume (OR,1.37;p=0.023;95%CI,1.04-1.82;per 10 mL increase) and low-density lipoprotein (OR,0.97;p=0.043;95%CI,0.94-1.00;per 1 mg/dL increase). After adjusting for potential confounders, delayed parenchymal hematoma was associated with worse functional outcomes (OR,0.07;p=0.013;95%CI,0.01-0.58) and mortality (OR,7.83;p=0.008;95%CI,1.66-37.07), while delayed petechial hemorrhage was associated with neither.

CONCLUSION

Contrast volume predicted delayed parenchymal hematoma, which was associated with worse functional outcomes and mortality. Contrast volume can serve as a useful predictor of delayed parenchymal hematoma following thrombectomy and may have implications for patient management.

Dual-energy computed tomography material decomposition improves prediction accuracy of hematoma expansion in traumatic intracranial hemorrhage

OBJECTIVE

The angiographic spot sign (AS) on CT angiography (CTA) is known to be useful for predicting expansion in intracranial hemorrhage, but its use is limited due to its relatively low sensitivity. Recently, dual-energy computed tomography (DECT) has been shown to be superior in distinguishing between hemorrhage and iodine. This study aimed to evaluate the diagnostic performance of hematoma expansion (HE) using DECT AS in traumatic intracranial hemorrhage.

METHODS

We recruited participants with intracranial hemorrhage confirmed via CTA for suspected traumatic cerebrovascular injuries. We evaluated AS on both conventional-like and fusion images of DECT. AS is grouped into three categories: intralesional enhancement without change, delayed enhancement (DE), and growing contrast leakage (GL). HE was evaluated by measuring hematoma size on DECT and follow-up CT. Logistic regression analysis was used to evaluate whether AS on fusion images was a significant risk factor for HE. Diagnostic accuracy was calculated, and the results from conventional-like and fusion images were compared.

RESULTS

Thirty-nine hematomas in 24 patients were included in this study. Of these, 18 hematomas in 13 patients showed expansion on follow-up CT. Among the expanders, AS and GL on fusion images were noted in 13 and 5 hematomas, respectively. In non-expanders, 10 and 1 hematoma showed AS and GL, respectively. In the logistic regression model, GL on the fusion image was a significant independent risk factor for predicting HE. However, when AS was used on conventional-like images, no factors significantly predicted HE. In the receiver operating characteristic curve analysis, the area under the curve of AS on the fusion images was 0.71, with a sensitivity and specificity of 66.7% and 76.2%, respectively.

CONCLUSIONS

GL on fusion images of DECT in traumatic intracranial hemorrhage is a significant independent radiologic risk factor for predicting HE. The AS of DECT fusion images has improved sensitivity compared to that of conventional-like images.

Early post-endovascular treatment contrast extravasation on dual-energy CT is associated with clinical and radiological stroke outcomes: A 10-year single-centre experience

OBJECTIVE

To determine the association between early post-endovascular treatment (EVT) contrast extravasation (CE) on dual-energy CT (DECT) and stroke outcomes.

METHODS

EVT records in 2010-2019 were screened. Exclusion criteria included the occurrence of immediate post-procedural intracranial haemorrhage (ICH). Hyperdense areas on iodine overlay maps were scored according to the Alberta Stroke Programme Early CT Score (ASPECTS), thus forming a CE-ASPECTS. Maximum parenchymal iodine concentration and maximum iodine concentration relative to the torcula were recorded. Follow-up imaging was reviewed for ICH. The primary outcome measure was the modified Rankin Scale (mRS) at 90 days.

RESULTS

Out of 651 records, 402 patients were included. CE was found in 318 patients (79%). Thirty-five patients developed ICH on follow-up imaging. Fourteen ICHs were symptomatic. Stroke progression occurred in 59 patients. Multivariable regression showed a significant association between decreasing CE-ASPECTS and the mRS at 90 days (adjusted (a)cOR: 1.10, 95% CI: 1.03-1.18), NIHSS at 24-48 h (aβ: 0.57, 95% CI: 0.29-0.84), stroke progression (aOR: 1.14, 95% CI: 1.03-1.26) and ICH (aOR: 1.21, 95% CI: 1.06-1.39), but not symptomatic ICH (aOR 1.19, 95% CI: 0.95-1.38). Iodine concentration was significantly associated with the mRS (acOR: 1.18, 95% CI: 1.06-1.32), NIHSS (aβ: 0.68, 95% CI: 0.30-1.06), ICH (aOR: 1.37, 95% CI: 1.04-1.81) and symptomatic ICH (aOR: 1.19, 95% CI: 1.02-1.38), but not stroke progression (aOR: 0.99, 95% CI: 0.86-1.15). Results of the analyses with relative iodine concentration were similar and did not improve prediction.

CONCLUSIONS

CE-ASPECTS and iodine concentration are both associated with short- and long-term stroke outcomes. CE-ASPECTS is likely a better predictor for stroke progression.

Dual Source Photon-Counting Computed Tomography-Part II: Clinical Overview of Neurovascular Applications

Photon-counting detector (PCD) is a novel computed tomography detector technology (photon-counting computed tomography-PCCT) that presents many advantages in the neurovascular field, such as increased spatial resolution, reduced radiation exposure, and optimization of the use of contrast agents and material decomposition. In this overview of the existing literature on PCCT, we describe the physical principles, the advantages and the disadvantages of conventional energy integrating detectors and PCDs, and finally, we discuss the applications of the PCD, focusing specifically on its implementation in the neurovascular field.

Spectral CT in Emergency

Spectral CT technology is based on the acquisition of CT images with X-ray at 2 different energy levels which makes possible to distinguish between materials with different atomic numbers using their energy-dependent attenuation, even if those materials have similar density at conventional CT. This kind of technology has gained wide application due to the innumerable uses of their post-processing techniques, including virtual non-contrast images, iodine maps, virtual mono-chromatic images or mixed images without increasing radiation dose. There are several applications of spectral CT in Emergency Radiology that help in the detection, diagnosis and management of various pathologies such as differentiate haemorrhage from the underlaying causative lesion, diagnosis of pulmonary embolisms, demarcation of abscess, characterization of renal stones or reduction of artifacts. The purpose of this review is to provide the emergency radiologist a brief description of the main indications for spectral CT.

A Novel Dual-Energy CT Method for Detection and Differentiation of Intracerebral Hemorrhage From Contrast Extravasation in Stroke Patients After Endovascular Thrombectomy : Feasibility and First Results

PURPOSE

Dual-energy computed tomography (DECT) has been shown to be able to differentiate between intracranial hemorrhage (ICH) and extravasation of iodinated contrast media (contrast staining [CS]). TwinSpiral DECT is a recently introduced technique, which allows image acquisition at two different energy levels in two consecutive spiral scans. The aim of this study was to evaluate the feasibility and accuracy of TwinSpiral DECT to distinguish between ICH and CS after endovascular thrombectomy (EVT) in patients with acute ischemic stroke.

METHODS

This retrospective single-center study conducted between November 2019 and July 2020 included non-contrast TwinSpiral DECT scans (tube voltages 80 and 150Sn kVp) of 39 ischemic stroke patients (18 females, 21 males, mean age 69 ± 11 years) within 48-72 h after endovascular thrombectomy. Parenchymal hyperdensity was assessed for the presence of ICH or/and CS by two board certified and fellowship-trained, blinded and independent neuroradiologists using standard mixed images and virtual non-contrast (VNC) images with corresponding iodine maps from TwinSpiral DECT. Follow-up examinations (FU; CT or MRI) were used as a standard of reference. Sensitivity, specificity, and accuracy for the detection of ICH as well as the inter-reader agreement were calculated.

RESULTS

Parenchymal hyperdensities were detected in 17/39 (44%) patients. Using DECT, they were classified by both readers as ICH in 9 (53%), CS in 8 (47%), and mixture of both in 6 (35%) cases with excellent agreement (κ = 0.81, P < 0.0001). The sensitivity, specificity, and accuracy for the detection of ICH in DECT was 90% (95% confidence interval [CI]: 84-96%), 100% (95% CI 94-100%) and 95% (95% CI 89-100%), and in mixed images 90% (95% CI 84-96%), 86% (95% CI 80-92%) and 88% (95% CI 82-94%), respectively. Inter-reader agreement for detecting ICH on DECT compared to the mixed images was κ = 1.00 (P < 0.0001) vs. κ = 0.51 (P = 0.034).

CONCLUSION

TwinSpiral DECT demonstrates high accuracy and excellent specificity for differentiating ICH from CS in patients after mechanical thrombectomy due to acute ischemic stroke, and improves inter-reader agreement for detecting ICH compared to the standard mixed images.

Virtual versus true non-contrast images of the brain from spectral detector CT: comparison of attenuation values and image quality

BACKGROUND

Prior studies focused on utilization of dual-energy computed tomography (DECT) to better detect intracranial pathology and to reduce artifacts. It is still unclear whether virtual non-contrast (VNC) images of DECT can replace true non-contrast (TNC) images.

PURPOSE

To compare attenuation values and image quality of VNC images to TNC images of the brain, obtained using spectral detector CT (SDCT).

MATERIAL AND METHODS

We retrospectively evaluated patients that underwent head CT with and without contrast material, on a SDCT scanner at our institution (n = 33). The attenuation values of different brain structures were obtained from TNC images, the conventional images of the post-contrast exams (n = 16) or the CT angiography (CTA) (n = 17), and the derived VNC images. In total, 591 regions of interest were obtained, including white and gray matter. Two neuroradiologists independently evaluated the image quality of the VNC and TNC images, using a 5-point Likert scale.

RESULTS

The mean difference between the attenuation values on the VNC versus the TNC images was <4 HU for almost all the structures. The difference reached statistical significance (P < 0.05) for the deep gray structures but not for the white matter. The image quality score of the TNC images was 5 in all the patients (excellent gray-white matter differentiation). The scores of the VNC images differed between post-contrast and CTA examinations, with means of 4.9 ± 0.3 (excellent) and 3.2 ± 0.4 (fair), respectively (P < 0.001).

CONCLUSION

Our results show minor differences between attenuation values of different brain structures on VNC versus TNC images of SDCT.

Smart Visualization of Medical Images as a Tool in the Function of Education in Neuroradiology

The smart visualization of medical images (SVMI) model is based on multi-detector computed tomography (MDCT) data sets and can provide a clearer view of changes in the brain, such as tumors (expansive changes), bleeding, and ischemia on native imaging (i.e., a non-contrast MDCT scan). The new SVMI method provides a more precise representation of the brain image by hiding pixels that are not carrying information and rescaling and coloring the range of pixels essential for detecting and visualizing the disease. In addition, SVMI can be used to avoid the additional exposure of patients to ionizing radiation, which can lead to the occurrence of allergic reactions due to the contrast media administration. Results of the SVMI model were compared with the final diagnosis of the disease after additional diagnostics and confirmation by neuroradiologists, who are highly trained physicians with many years of experience. The application of the realized and presented SVMI model can optimize the engagement of material, medical, and human resources and has the potential for general application in medical training, education, and clinical research.

Quantitative Intracerebral Iodine Extravasation in Risk Stratification for Intracranial Hemorrhage in Patients with Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Intracerebral hemorrhage poses a severe threat to the outcomes in patients with postthrombectomy acute stroke. We aimed to compare the absolute intracerebral iodine concentration and normalized iodine concentration ratio in predicting intracerebral hemorrhage in patients postthrombectomy.

MATERIALS AND METHODS

Patients with acute anterior circulation large-vessel occlusion who underwent mechanical thrombectomy and had successful recanalization were retrospectively included in the study. Dual-energy CT was performed within 1 hour after mechanical thrombectomy. Postprocessing was performed to measure the absolute intracerebral iodine concentration and the normalized iodine concentration ratio. The correlation between the absolute intracerebral iodine concentration and the normalized iodine concentration ratio was analyzed using the Spearman rank correlation coefficient. We compared the area under the receiver operating characteristic curve of the absolute intracerebral iodine concentration and the normalized iodine concentration ratio using the DeLong test.

RESULTS

We included 138 patients with successful recanalization. Of 43 patients who did not have parenchymal contrast staining on postthrombectomy dual-energy CT, 5 (11.6%) developed intracerebral hemorrhage. Among patients (95/138, 68.8%) with parenchymal contrast staining, 37 (38.9%, 37/95) developed intracerebral hemorrhage. The absolute intracerebral iodine concentration was significantly correlated with the normalized iodine concentration ratio (ρ = 0.807; 95% CI, 0.718-0.867; P < .001). The cutoffs of the normalized iodine concentration ratio and absolute intracerebral iodine concentration for identifying patients with intracerebral hemorrhage development were 222.8%, with a sensitivity of 67.6% and specificity of 76.4%, and 2.7 mg I/mL, with a sensitivity of 75.7% and specificity of 65.5%, respectively. No significant difference was found between the areas under the receiver operating characteristic curve for the absolute intracerebral iodine concentration and the normalized iodine concentration ratio (0.753 versus 0.738) (P = .694).

CONCLUSIONS

The hemorrhagic transformation predictive power of the normalized iodine concentration ratio is similar to that of the absolute intracerebral iodine concentration in patients with successful recanalization.

Detection of Early Ischemic Changes with Virtual Noncontrast Dual-Energy CT in Acute Ischemic Stroke: A Noninferiority Analysis

BACKGROUND AND PURPOSE

Dual-energy virtual NCCT has the potential to replace conventional NCCT to detect early ischemic changes in acute ischemic stroke. In this study, we evaluated whether virtual NCCT is noninferior compared with standard linearly blended NCCT, a surrogate of conventional NCCT, regarding the detection of early ischemic changes with ASPECTS.

MATERIALS AND METHODS

Adult patients who presented with suspected acute ischemic stroke and who underwent dual-energy NCCT and CTA and brain MR imaging within 48 hours were included. Standard linearly blended images were reconstructed to match a conventional NCCT. Virtual NCCT images were reconstructed from CTA. ASPECTS was evaluated on conventional NCCT, virtual NCCT, and DWI, which served as the reference standard. Agreement between CT assessments and the reference standard was evaluated with the Lin concordance correlation coefficient. Noninferiority was assessed with bootstrapped estimates of the differences in ASPECTS between conventional and virtual NCCT with 95% CIs.

RESULTS

Of the 193 included patients, 100 patients (52%) had ischemia on DWI. Compared with the reference standard, the ASPECTS concordance correlation coefficient for conventional and virtual NCCT was 0.23 (95% CI, 0.15-0.32) and 0.44 (95% CI, 0.33-0.53), respectively. The difference in the concordance correlation coefficient between virtual and conventional NCCT was 0.20 (95% CI, 0.01-0.39) and did not cross the prespecified noninferiority margin of -0.10.

CONCLUSIONS

Dual-energy virtual NCCT is noninferior compared with conventional NCCT for the detection of early ischemic changes with ASPECTS.

Process of cerebral edema in the infarct core after reperfusion: A case report

RATIONALE

It is generally believed that cerebral infarction shows hypoattenuation on computed tomography (CT) scans 12 to 24 hours after onset. Cerebral edema affects the occurrence of hypoattenuation, originating from the inner edge of the infarct and extending to the core. When reperfusion occurs in the infarct, the process of cerebral edema changes significantly, affecting the imaging of cerebral infarction on CT scans. This article focused on the mechanism of cerebral edema to provide a new perspective for understanding the impact of reperfusion on cerebral infarction.

PATIENT CONCERNS

We describe the case of a 77-year-old man who presented with an acute onset of right limb weakness with speech difficulties 10 hours before the visit. He had been diagnosed with atrial fibrillation 4 months ago. During the acute phase of infarction, the central area of the hypoattenuated infarct appears as isodensity on CT scans in this case.

DIAGNOSES

The patient was diagnosed with acute cerebral infarction, cardiogenic cerebral embolism, and spontaneous recanalization of left middle cerebral artery occlusion.

INTERVENTIONS

Metoprolol was given to control the ventricular rate. The patient received blood pressure control, symptomatic management, and rehabilitation treatments.

OUTCOMES

Finally, the patient became alert.

LESSONS

Cerebral edema originating directly in the infarct core after reperfusion could lead to a significantly accelerated edema process and imaging evolution, causing more severe cerebral damage. In such a case, the patient should not receive antiplatelet and anticoagulant therapy in order to prevent bleeding conversion.

The Assessment of Endovascular Therapies in Ischemic Stroke: Management, Problems and Future Approaches

Ischemic stroke accounts for over 80% of all strokes and is one of the leading causes of mortality and permanent disability worldwide. Intravenous administration of recombinant tissue plasminogen activator (rt-PA) is an approved treatment strategy for acute ischemic stroke of large arteries within 4.5 h of onset, and mechanical thrombectomy can be used for large arteries occlusion up to 24 h after onset. Improving diagnostic work up for acute treatment, reducing onset-to-needle time and urgent radiological access angiographic CT images (angioCT) and Magnetic Resonance Imaging (MRI) are real problems for many healthcare systems, which limits the number of patients with good prognosis in real world compared to the results of randomized controlled trials. The applied endovascular procedures demonstrated high efficacy, but some cellular mechanisms, following reperfusion, are still unknown. Changes in the morphology and function of mitochondria associated with reperfusion and ischemia-reperfusion neuronal death are still understudied research fields. Moreover, future research is needed to elucidate the relationship between continuously refined imaging techniques and the variable structure or physical properties of the clot along with vascular permeability and the pleiotropism of ischemic reperfusion lesions in the penumbra, in order to define targeted preventive procedures promoting long-term health benefits.

CT-based radiomics for differentiating intracranial contrast extravasation from intraparenchymal haemorrhage after mechanical thrombectomy

OBJECTIVE

To develop a nonenhanced CT-based radiomic signature for the differentiation of iodinated contrast extravasation from intraparenchymal haemorrhage (IPH) following mechanical thrombectomy.

METHODS

Patients diagnosed with acute ischaemic stroke who underwent mechanical thrombectomy in 4 institutions from December 2017 to June 2020 were included in this retrospective study. The study population was divided into a training cohort and a validation cohort. The nonenhanced CT images taken after mechanical thrombectomy were used to extract radiomic features. The maximum relevance minimum redundancy (mRMR) algorithm was used to eliminate confounding variables. Afterwards, least absolute shrinkage and selection operator (LASSO) logistic regression was used to generate the radiomic signature. The diagnostic performance of the radiomic signature was evaluated by the area under the curve (AUC), accuracy, specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV).

RESULTS

A total of 166 intraparenchymal areas of hyperattenuation from 101 patients were used. The areas of hyperattenuation were randomly allocated to the training and validation cohorts at a ratio of 7:3. The AUC of the radiomic signature was 0.848 (95% confidence interval (CI) 0.780-0.917) in the training cohort and 0.826 (95% CI 0.705-0.948) in the validation cohort. The accuracy of the radiomic signature was 77.6%, with a sensitivity of 76.7%, a specificity of 78.9%, a PPV of 85.2%, and a NPV of 68.2% in the validation cohort.

CONCLUSIONS

The radiomic signature constructed based on initial post-operative nonenhanced CT after mechanical thrombectomy can effectively differentiate IPH from iodinated contrast extravasation.

KEY POINTS

• Radiomic features were extracted from intraparenchymal areas of hyperattenuation on initial post-operative CT scans after mechanical thrombectomy. • The nonenhanced CT-based radiomic signature can differentiate IPH from iodinated contrast extravasation early. • The radiomic signature may help prevent unnecessary rescanning after mechanical thrombectomy, especially in cases where contrast extravasation is highly suggestive.

Comparative Studies of Cerebral Reperfusion Injury in the Posterior and Anterior Circulations After Mechanical Thrombectomy

Cerebral reperfusion injury is the major complication of mechanical thrombectomy (MT) for acute ischemic stroke (AIS). Contrast extravasation (CE) and intracranial hemorrhage (ICH) are the key radiographical features of cerebral reperfusion injury. The aim of this study was to investigate CE and ICH after MT in the anterior and posterior circulation, and their effect on functional outcome. This is a retrospective study of all consecutive patients who were treated with MT for AIS at University of California Irvine Medical Center between January 1, 2014, and December 31, 2017. Patient characteristics, clinical features, procedural variables, contrast extravasation, ICH, and outcomes after MT were analyzed. A total of 131 patients with anterior circulation (AC) stroke and 25 patients with posterior circulation (PC) stroke underwent MT during the study period. There was no statistically significant difference in admission NIHSS score, blood pressure, rate of receiving intravenous tPA, procedural variables, contrast extravasation, and symptomatic ICH between the 2 groups. Patients with PC stroke had a similar rate of favorable outcome (mRS 0–2) but significantly higher mortality (40.0% vs. 10.7%, p < 0.01) than patients with AC stroke. Multivariate regression analysis identified initial NIHSS score (OR 1.1, CI 1.0–1.2, p = 0.01), number of passes with stent retriever (OR 2.1, CI 1.3–3.6, p < 0.01), and PC stroke (OR 9.3, CI 2.5–35.1, p < 0.01) as independent risk factors for death. There was no significant difference in functional outcomes between patients with and without evidence of cerebral reperfusion injury after MT. We demonstrated that AC and PC stroke had similar rates of cerebral reperfusion injury and favorable outcome after MT. Cerebral reperfusion injury is not a significant independent risk factor for poor functional outcome.

Quantitative X-ray phase contrast computed tomography with grating interferometry : Biomedical applications of quantitative X-ray grating-based phase contrast computed tomography

The ability of biomedical imaging data to be of quantitative nature is getting increasingly important with the ongoing developments in data science. In contrast to conventional attenuation-based X-ray imaging, grating-based phase contrast computed tomography (GBPC-CT) is a phase contrast micro-CT imaging technique that can provide high soft tissue contrast at high spatial resolution. While there is a variety of different phase contrast imaging techniques, GBPC-CT can be applied with laboratory X-ray sources and enables quantitative determination of electron density and effective atomic number. In this review article, we present quantitative GBPC-CT with the focus on biomedical applications.

Early Prediction of Malignant Edema After Successful Recanalization in Patients with Acute Ischemic Stroke

BACKGROUND

Postinterventional cerebral hyperdensities are common on non-contrast-enhanced computed tomography (CT) after endovascular thrombectomy in patients with acute ischemic stroke, which may reflect blood-brain barrier damage. The disruption of the blood-brain barrier may lead to malignant brain edema. The relationship between the extent of postinterventional cerebral hyperdensities and malignant brain edema is unclear.

METHODS

Patients with middle cerebral artery territory infarction and successful recanalization were consecutively enrolled. Postinterventional non-contrast-enhanced CT was performed to evaluate postinterventional cerebral hyperdensities within 24 h after endovascular thrombectomy. On the basis of the areas of the Alberta Stroke Program Early CT Score, we devised the Hyperdensity on CT Score to evaluate the extent of postinterventional cerebral hyperdensities. The primary outcome was malignant brain edema, defined as the development of clinical signs of herniation (including a decrease in consciousness and/or anisocoria), accompanied by imaging evidence of brain swelling. The component of postinterventional cerebral hyperdensities was divided into contrast staining and hemorrhage on the basis of persistency.

RESULTS

Three hundred sixty patients were included (50.6% male, mean age 67.9 years), of whom 247 (68.6%) developed postinterventional cerebral hyperdensities and 66 (18.3%) developed malignant brain edema. After adjustment for confounders, including the component of postinterventional cerebral hyperdensities, the extent of postinterventional cerebral hyperdensities assessed by the Hyperdensity on CT Score was significantly associated with malignant brain edema (odds ratio 1.46, 95% confidence interval 1.20-1.77, p < 0.001). A Hyperdensity on CT Score greater than 3 had a sensitivity of 0.73 and a specificity of 0.87 for predicting malignant brain edema.

CONCLUSIONS

The extent of postinterventional cerebral hyperdensities on postinterventional non-contrast-enhanced CT was associated with malignant brain edema. The Hyperdensity on CT Score could be used to predict malignant brain edema regardless of the component of postinterventional cerebral hyperdensities.

Risk factors of contrast extravasation and subsequent hemorrhagic transformation after thrombectomy

Objective

The risk factors associated with iodine contrast extravasation immediately after endovascular thrombectomy (EVT) and subsequent hemorrhagic transformation within 24 hours remain unclear.

Methods

Mixed images, iodine overlay maps, and virtual non-contrast images were reconstructed from 106 consecutive acute ischemic stroke patients who underwent dual energy computed tomography immediately and 24 hours after EVT. Multivariate analyses of clinical and radiological data were performed to explore independent predictors of iodine contrast extravasation and hemorrhagic transformation.

Results

Sixty-eight (64.2%) patients exhibited pure iodine contrast extravasation after EVT; 30.9% developed hemorrhagic transformation within 24 hours after EVT. The number of stent retriever passes was independently associated with both iodine contrast extravasation (odds ratio 1.608; 95% confidence interval (CI) 1.047–2.469) and subsequent hemorrhagic transformation (odds ratio 1.477; 95% CI 1.003–2.175). Patients with more than two stent retriever passes were more likely to exhibit iodine contrast extravasation (sensitivity = 68.2%, specificity = 81.5%), while those with more than three stent retriever passes more often exhibited hemorrhage after iodine contrast extravasation (sensitivity = 64.6%, specificity = 87.2%).

Conclusions

The number of stent retriever passes was an independent predictor for both iodine contrast extravasation and subsequent hemorrhagic transformation.

Image Quality of Virtual Monochromatic Reconstructions of Noncontrast CT on a Dual-Source CT Scanner in Adult Patients

RATIONALE AND OBJECTIVES

To evaluate the image quality of virtual monochromatic images (VMI) reconstructed from dual-energy dual-source noncontrast head CT with different reconstruction kernels.

MATERIALS AND METHODS

Twenty-five consecutive adult patients underwent noncontrast dual-energy CT. VMI were retrospectively reconstructed at 5-keV increments from 40 to 140 keV using quantitative and head kernels. CT-number, noise levels (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) in the gray and white matter and artifacts using the posterior fossa artifact index (PFAI) were evaluated.

RESULTS

CT-number increased with decreasing VMI energy levels, and SD was lowest at 85 keV. SNR was maximized at 80 keV and 85 keV for the head and quantitative kernels, respectively. CNR was maximum at 40 keV; PFAI was lowest at 90 (head kernel) and 100 (quantitative kernel) keV. Optimal VMI image quality was significantly better than conventional CT.

CONCLUSION

Optimal image quality of VMI energies can improve brain parenchymal image quality compared to conventional CT but are reconstruction kernel dependent and depend on indication for performing noncontrast CT.

Principles and Applications of Dual Energy Computed Tomography in Neuroradiology

Dual-energy computed tomography (DE CT) is a promising tool with many current and evolving applications. Available DE CT scanners usually consist of one or two tubes, or use layered detectors for spectral separation. Most DE CT scanners can be used in single energy or dual-energy mode, except for the layered detector scanners that always acquire data in dual-energy mode. However, the layered detector scanners can retrospectively integrate the data from two layers to obtain conventional single energy images. DE CT mode enables generation of virtual monochromatic images, blended images, iodine quantification, improving conspicuity of iodinated contrast enhancement, and material decomposition maps or more sophisticated quantitative analysis not possible with conventional SE CT acquisition with an acceptable or even lower dose than the SE CT. This article reviews the basic principles of dual-energy CT and highlights many of its clinical applications in the evaluation of neurological conditions.

ASPECTS estimation using dual-energy CTA-derived virtual non-contrast in large vessel occlusion acute ischemic stroke: a dose reduction opportunity for patients undergoing repeat CT?

PURPOSE

Recent studies have shown the feasibility of dual-energy CT (DECT) virtual non-contrast (VNC) for determining infarct extent. In this study, patients presenting with large-vessel occlusion (LVO) acute ischemic stroke (AIS), we assess whether ASPECTS on DECTA-VNC differs from non-contrast CT (NCCT).

METHODS

After IRB approval, LVO-AIS patients undergoing NCCT and DECTA between October 2016 and September 2018 were retrospectively reviewed. DECTA-VNC images were derived using Syngo.via (Siemens, Erlangen, Germany). ASPECTS was scored by two blinded neuroradiologists. Square-weighted kappa statistic, diagnostic performance, Wilcoxon signed-rank tests between groups, and CT doses were calculated.

RESULTS

Fifty-one patients met inclusion criteria, with median age of 76 (IQR 67-82); 26/51 (51%) were female. Median time between last-known-well and CT was 120 min (IQR 60-252). DECTA-VNC ASPECTS score differed by ≤ 1 from consensus NCCT in 49/51 (96%) patients for reader 1 and in 46/51 (90%) for reader 2. ASPECTS on DECTA-SI and consensus NCCT differed by ≤ 1 in 45/51 (88%) for both readers. On a per ASPECTS-region basis, DECTA-VNC had 87% sensitivity, 95% specificity, 0.82% PPV, and 0.96% NPV. ASPECTS inter-rater agreement was highest for DECTA-VNC (κ = 0.71), DECTA-SI (κ = 0.48), and NCCT (κ = 0.40). NCCT median CTDIvol was 63.7 mGy (IQR 60.7-67.2); DLP was 1060.0 mGy·cm (IQR 981.0-1151.5). DECTA-VNC dose was lower: median CTDIvol was 20.9 mGy (IQR 19.8-22.2); DLP was 804.1 (IQR 691.6-869.4), p < 0.0001.

CONCLUSION

DECTA-derived VNC yielded similar ASPECTS scores as NCCT and is therefore non-inferior in early ischemia-related low attenuation edema/infarct detection in acute LVO-AIS patients. Further evaluation of the role of DECTA-VNC in AIS imaging is warranted.

Application of Flat-Panel Volume Computed Tomography to Evaluate Cerebral Hemorrhage After Mechanical Thrombectomy of Acute Embolic Stroke of the Anterior Circulation

OBJECTIVE

The aim of the study was to evaluate cerebral hemorrhage (CH) and contrast media leakage (CML or commonly synonymous with "contrast staining") differentiation on flat-panel volume computed tomography (FPVCT) after intra-arterial mechanical thrombectomy.

METHODS

We evaluated patients with hyperattenuation on FPVCT after intra-arterial mechanical thrombectomy between 2018 and 2021 by multiple parameters on CT angiography, FPVCT, CT, and/or magnetic resonance imaging.

RESULTS

The CH (n = 43) versus CML (n = 24) groups revealed: (1) regional anatomical characteristics (preserved and distorted): 7 of 43 (9.6%) and 36 of 43 (83.7%) versus 22 of 24 (91.7%) and 2 of 24 (8.3%, P < 0.001); (2) thrombus in proximal two-thirds versus distal one-thirds M1 segment of middle cerebral artery (preserved and distorted): 17 of 21 (81.0%) and 4 of 21 (19.0%) versus 5 of 11 (45.5%) and 6 of 11 (54.5%, P = 0.040); and (3) average density ratio: 1.83 ± 0.65 versus 1.35 ± 0.13 (P = 0.004).

CONCLUSIONS

Contrast media leakage can be differentiated from CH by preserved regional anatomical characteristics and relatively low average density ratio on FPVCT. Patients with CML who have embolism in proximal two thirds of M1 segment are more likely to develop hyperattenuation with preserved regional anatomy.

Diagnostic accuracy of dual-energy computed tomography to differentiate intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke: systematic review and meta-analysis

OBJECTIVES

To assess whether dual-energy computed tomography (DECT), using conventional computed tomography or magnetic resonance imaging as a reference standard, is sufficiently accurate to differentiate intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke.

METHODS

On January 20, 2021, we searched the PubMed Medline, Embase, Web of Science, and Cochrane Library databases. QUADAS-2 was used to assess the risk of bias and applicability. Meta-analyses were performed using a bivariate random-effects model. To explore sources of heterogeneity, meta-regression analyses were performed. Deeks' funnel plot asymmetry test was used to assess publication bias.

RESULTS

A total of 7 studies (269 patients, 269 focal areas) were included. The pooled mean sensitivity, specificity, and accuracy of DECT in identifying intracerebral hemorrhage from contrast extravasation after mechanical thrombectomy for acute ischemic stroke were 0.77 (95% confidence interval (CI) 0.29 to 0.96), 1 (95% CI 0.86 to 1), and 0.99 (95% CI 0.98 to 1), respectively. This evidence was of moderate certainty due to the risk of bias. Higgin's I-squared for study heterogeneity was observed for the pooled sensitivity (I² = 78.88%) and pooled specificity (I² = 82.12%). Moreover, Deeks' funnel plot asymmetry test revealed no publication bias (p = 0.38).

CONCLUSION

DECT shows excellent accuracy and specificity in differentiating intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke. Nevertheless, there was substantial and moderate heterogeneity among the studies. Future large-scale, prospective cohort studies are warranted to validate our findings.

KEY POINTS

• Dual-energy computed tomography shows excellent accuracy and specificity in differentiating intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke. • Via meta-regression analysis, we found various possible covariates, including the publication date, image analysis, index test time, time of follow-up imaging, and reference standard judgment, that had an important effect on the heterogeneity. • There were no concerns regarding applicability in any of the included studies.

Prediction of Intracerebral Hemorrhage After Endovascular Treatment of Acute Ischemic Stroke: Combining Quantitative Parameters on Dual-Energy CT with Clinical Related Factors

OBJECTIVES

To evaluate the predictive value of dual-energy CT (DECT) quantitative parameters and clinical influence factors for intracerebral hemorrhage (ICH) complications after endovascular treatment in patients with acute ischemic stroke (AIS).

METHODS

Seventy-two consecutive patients who underwent brain DECT immediately after endovascular treatment for AIS from November 2017 to October 2019 were included. Retrospectively, the volume of brain parenchymal hyperdensity area (HDA), the maximum iodine concentration, and maximum CT value on DECT images was evaluated and measured by two radiologists blinded to any clinical information independently. Follow-up CT imaging (24-72 h) were used to assess the development of ICH complications. DECT parameters and clinical influence factors were analyzed by Chi-square test or Fisher's exact test and Mann-Whitney U test. Receiver operating characteristic curves were generated for continuous variables.

RESULTS

Follow-up CT images confirmed that forty of 72 patients (55.6%) developed ICH. The volume of HDA, median maximum iodine concentration and maximum CT value between ICH group and non-ICH group were significantly different (P < 0.001). Combining the DECT quantitative parameters with clinical predictors, receiver operating characteristic analysis revealed an area under the curve of 0.985, for identifying patients developing ICH with sensitivity, specificity, positive predictive value and negative predictive value were 90%, 100%, 100% and 88.9%, respectively.

CONCLUSIONS

Three quantitative parameters of DECT and clinical predictors showed great predictive performance in identifing ICH complications in patients with brain parenchyma HDA after endovascular therapy, which may contribute to better clinical decision-making.

Value of Dual-Energy Dual-Layer CT After Mechanical Recanalization for the Quantification of Ischemic Brain Edema

Background and Purpose: Ischemic brain edema can be measured in computed tomography (CT) using quantitative net water uptake (NWU), a recently established imaging biomarker. NWU determined in follow-up CT after mechanical thrombectomy (MT) has shown to be a strong predictor of functional outcome. However, disruption of the blood-brain barrier after MT may also lead to contrast staining, increasing the density on CT scans, and hence, directly impairing measurements of NWU. The purpose of this study was to determine whether dual-energy dual-layer CT (DDCT) after MT can improve the quantification of NWU by measuring NWU in conventional polychromatic CT images (CP-I) and virtual non-contrast images (VNC-I). We hypothesized that VNC-based NWU (vNWU) differs from NWU in conventional CT (cNWU). Methods: Ten patients with middle cerebral artery occlusion who received a DDCT follow-up scan after MT were included. NWU was quantified in conventional and VNC images as previously published and was compared using paired sample t-tests. Results: The mean cNWU was 3.3% (95%CI: 0-0.41%), and vNWU was 11% (95%CI: 1.3-23.4), which was not statistically different (p = 0.09). Two patients showed significant differences between cNWU and vNWU (Δ = 24% and Δ = 36%), while the agreement of cNWU/vNWU in 8/10 patients was high (difference 2.3%, p = 0.23). Conclusion: NWU may be quantified precisely on conventional CT images, as the underestimation of ischemic edema due to contrast staining was low. However, a proportion of patients after MT might show significant contrast leakage resulting in edema underestimation. Further research is needed to validate these findings and investigate clinical implications.

Clinical Significance of Hyperdense Area after Endovascular Therapy in Patients with Acute Ischemic Stroke: A Systematic Review and Meta-Analysis

OBJECTIVE

We performed a systematic review and meta-analysis to investigate the clinical significance of hyperdense area after thrombectomy in patients with acute ischemic stroke (AIS).

METHODS

We searched Ovid MEDLINE(R) and Epub Ahead of Print, In-Process and other Non-Indexed, Cochrane Library Clinical Controlled Trials and Embase from inception to September 2020 and collected the cohort and case-control studies about the clinical significance of hyperdense area on different types of computed tomography (CT) after thrombectomy in patients with AIS. Outcomes were poor functional outcome (modified Rankin Scale [mRS] Score 3-6 at discharge or 90-day), mortality and subtypes of hemorrhage according to the European Cooperative Acute Stroke Study (ECASS).

RESULTS

1,999 patients from 16 studies were included in this meta-analysis. Pooled results indicated higher risk of symptomatic intracerebral hemorrhage (odds ratio [OR] = 3.02; 95% confidence interval [CI] 1.84-4.95; p < 0.0001, I2 = 0%) in patients with hyperdense area, and the subtype of parenchymal hematoma as well. There was also higher odds of poor functional outcome based on the mRS 3-6 at discharge or 90-day (OR = 1.92; 95% CI 1.35-2.73; p = 0.0003, I2 = 31%) and mortality (OR = 2.06; 95% CI 1.41-3.02; p = 0.0002, I2 = 0%) in patients with hyperdense area after thrombectomy compared with those without hyperdense area.

CONCLUSIONS

Our results indicated that the presence of hyperdense area on CT after thrombectomy was associated with high risk of symptomatic intracerebral hemorrhage, poor functional outcome, as well as mortality in patients with AIS. However, further studies were needed to confirm these results. The meta-analysis was conducted in adherence with the PRISMA Statement and was registered at the International Prospective Register of Systematic Reviews (CRD42020164165). To the best of our knowledge, this study is the first meta-analysis investigating the effect of hyperdense area after endovascular therapy in patients with AIS.

Initial experience with dual-layer detector spectral CT for diagnosis of blood or contrast after endovascular treatment for ischemic stroke

PURPOSE

To determine whether spectral detector CT (SDCT) with a plain non-enhanced monochromatic CT, a water-weighted image after iodine removal, an iodine map, and Mono energetic images changes the diagnosis and classification of intracranial hemorrhage based on single energy CT after endovascular treatment (EVT) for ischemic stroke.

METHODS

Two readers evaluated single energy and SD CT data collected from 63 patients within one week after EVT. They diagnosed ICH or contrast staining, and graded ICH according to the Heidelberg and Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST) classification. Differences in diagnosis between single energy and SD CT were tested with Pearson's chi-squared test. Diagnostic values of single energy CT were calculated. Interrater agreement was based on Cohen's Kappa.

RESULTS

When spectral data were added to single energy CT, the diagnosis of ICH changed in 8 CT scans (13%): in 4, the diagnosis of ICH was rejected and in 4, initially undetected ICH was diagnosed. In an additional 3 patients, the ICH grade was modified. CT alone had 88% sensitivity, 87% specificity, 88% positive diagnostic value, 87% negative diagnostic value, and 87% overall accuracy for ICH compared to SDCT. Interreader agreement on the presence of ICH was 0.84 (95% CI 0.51-0.86) for spectral CT and 0.84 (95% CI 0.73-0.97) for single energy CT.

CONCLUSION

SD CT after endovascular treatment contributes to the distinction between intracranial hemorrhage and contrast staining.

Use of dual-energy computed tomography post endovascular treatment of cerebral aneurysm

Background:

Along with surgical clipping, endovascular management is one of the mainstay treatment options for cerebral aneurysms. However, immediate post procedural imaging is often hard to interpret due to the presence of contrast material. Dual-energy computed tomography (CT) allows differentiation between contrast extravasation and intracranial hemorrhage and this case illustrates the importance of this following endovascular treatment of an unruptured cerebral aneurysm.

Case Description:

A patient presented with acute ophthalmoplegia secondary to mass effect from an intracavernous ICA fusiform aneurysm. The patient underwent an endovascular flow diverting stent to treat this aneurysm. Post procedure, the patient had a reduced level of consciousness and underwent a conventional CT showing diffuse subarachnoid hyperdensity of the left hemisphere. Dual-energy CT allowed accurate differentiation and illustrated diffuse contrast material extravasation, allowing patient to continue on dual antiplatelets and therapeutic anticoagulation to reduce the risk of ischemic injury post endovascular stent.

Conclusion:

Use of dual-energy CT in the setting of endovascular management of intracranial aneurysms allows accurate diagnosis of any postoperative complications. Specifically, differentiating between subarachnoid hemorrhage and contrast extravasation is vital in these patients due to the significant consequences to their ongoing management in regard to continuation or cessation of antiplatelets or anticoagulation. With increasing access to this technology, its use should become standard practice in the post-operative investigation of these patients undergoing endovascular treatment.

Potential of dual-layer spectral CT for the differentiation between hemorrhage and iodinated contrast medium in the brain after endovascular treatment of ischemic stroke patients

BACKGROUND

One possible complication after mechanical thrombectomy is hemorrhage. In conventional CT it is often difficult to differ between extravasation of iodinated contrast medium and blood. This differentiation, however, is essential for treatments with anticoagulants and antiplatelets.

PURPOSE

To evaluate dual-layer spectral Computed Tomography (DLSCT) for the differentiation between intracranial hemorrhage and iodinated contrast medium in ischemic stroke patients after mechanical thrombectomy.

MATERIALS AND METHODS

First, in vitro experiments were performed. Then, head CT images of 47 patients after mechanical thrombectomy were analyzed. Virtual non-contrast (VNC) images and iodine density maps (IDM) were calculated and evaluated. Region of interests (ROIs) analyses were performed. Sensitivity and specificity as well as ROC curves were calculated.

RESULTS

IDM and VNC images enabled clear differentiation between blood and iodine and reliable quantification of different iodine concentrations in vitro. A total of 23 hyperdense areas were detected in 13 patients, classified as hemorrhage (n = 7), iodinated contrast medium (n = 4) and a mixture of both (n = 12). Sensitivity and specificity for the detection of blood was 100%.

CONCLUSION

DLSCT enables differentiation between intracranial hemorrhage and iodinated contrast medium in patients after mechanical thrombectomy and might improve diagnostic imaging in post-interventional stroke patients.

Utilizing dual energy CT to distinguish blood from contrast leakage following middle meningeal artery embolization for chronic subdural hematomas

BACKGROUND

Recently, middle meningeal artery (MMA) embolization has emerged as a potential alternative treatment option for chronic subdural hematomas (SDH). Imaging following MMA embolization often shows high density material in the subdural space, usually representing contrast leakage through the dura or, less commonly, hemorrhage. These cannot be reliably differentiated on conventional CT. Dual energy CT (DECT) provides the ability to differentiate materials that otherwise appear similar on conventional CT such as blood and iodine.

METHODS

A retrospective review was conducted to evaluate patients who underwent MMA embolization for SDH between May 2019 and April 2020. Post-procedural head CT performed on an IQon Elite Spectral CT detector-based DECT scanner enabled two-material decomposition to separate iodine from blood. The dual energy reconstructions used included the virtual non-contrast and iodine no-water images.

RESULTS

Four representative illustrative cases were selected to highlight the ability of DECT to characterize new hyperdensity on head CT following MMA embolization as blood, contrast or a combination.

CONCLUSIONS

DECT allows objective differentiation of contrast leakage from blood following MMA embolization. This technology can obviate the need for additional follow-up scanning and prolonged patient observation, which in turn can result in reduced costs and radiation exposure to patients.

Early diagnosis and prediction of intracranial hemorrhage using dual-energy computed tomography after mechanical thrombectomy in patients with acute ischemic stroke

PURPOSE

This study assesses the clinical value of dual-energy computed tomography (DECT) in the early diagnosis of intracranial hemorrhage and evaluates the risk of hemorrhagic transformation in patients with acute ischemic stroke (AIS) after mechanical thrombectomy.

METHODS

Patients with AIS who have undergone thrombectomy with Solitaire stent and DECT within one hour after surgery were prospectively enrolled. Linear mixed energy images, virtual non-contrast (VNC) image, and iodine overlay map (IOM) were obtained. Routine CT scan was performed 24 h postoperatively. The sensitivity, specificity, positive and negative predictive values, and accuracy of DECT in the early diagnosis of intracranial hemorrhage was evaluated. The iodine concentration of intracranial lesions was measured by IOM with the follow-up results taken as reference. Receiver operating characteristic (ROC) analysis was performed to obtain the threshold of hemorrhagic transformation and increased bleeding.

RESULTS

Among the 44 patients enrolled in this study, 25 (56.8 %) were diagnosed with simple extravasation of iodinated contrast agent, and 19 (43.2 %) showed intracranial hemorrhage in DECT. Compared with the follow-up CT 24 h after surgery, early diagnosis of postoperative intracranial hemorrhage using DECT demonstrated a sensitivity of 90.5 %, specificity of 100 %, positive predictive rate of 100 %, negative predictive rate of 92.0 %, and accuracy of 95.5 %. Among the 86 intracranial lesions that underwent iodine concentration measurement, 19 were diagnosed with hemorrhagic transformation or increased bleeding, and 67 were diagnosed without the aforementioned conditions. The sensitivity and specificity for differentiating the two groups were 73.7 % and 92.5 %, respectively, with a cut-off value of 2.7 mg/mL.

CONCLUSION

DECT is clinically valuable in early diagnosis and prediction of intracranial hemorrhage after mechanical thrombectomy in AIS patients.