4D-CTA in neurovascular disease: a review

Imaging of Intracranial Aneurysms: A Review of Standard and Advanced Imaging Techniques

The treatment of intracranial aneurysms is dictated by its risk of rupture in the future. Several clinical and radiological risk factors for aneurysm rupture have been described and incorporated into prediction models. Despite the recent technological advancements in aneurysm imaging, linear length and visible irregularity with a bleb are the only radiological measure used in clinical prediction models. The purpose of this article is to summarize both the standard imaging techniques, including their limitations, and the advanced techniques being used experimentally to image aneurysms. It is expected that as our understanding of advanced techniques improves, and their ability to predict clinical events is demonstrated, they become an increasingly routine part of aneurysm assessment. It is important that neurovascular specialists understand the spectrum of imaging techniques available.

Nonrigid temporal registration of multiphase CT pulmonary angiography using low-kV and low contrast: a feasibility study with dual-source CT

AIM

This study aimed to compare the nonrigid temporal registration of multiphase computed tomography pulmonary angiography (CTPA) with single-phase CTPA in terms of radiation dose, contrast agent usage, objective and subjective image quality.

MATERIALS AND METHODS

Consecutive patients suspected of acute pulmonary embolism were prospectively included in this study, and randomly received multiphase or single-phase CTPA. Regarding the contrast media, 15 mL was applied in the multiphase CTPA in comparison with 40 mL applied in the single-phase CTPA. Temporal registration was performed for multiphase CTPA during post-processing. Two experienced radiologists independently evaluated the image quality (IQ) based on objective measurements, subjective impression and diagnostic confidence. Patient demographics, scan parameters and image quality were compared between the two groups.

RESULTS

A total of 72 patients were analysed (37 multiphase CTPA and 35 single-phase CTPA). Positive pulmonary embolism was confirmed in five and seven patients, respectively. The two patient groups had similar demographics besides older age in those who underwent single-phase CTPA. Radiation dose and the contrast-to-noise ratio (CNR) were also similar between groups except for the CNR in the right main pulmonary artery. Both readers rated the multiphase CTPA with a statistically superior subjective IQ over the single-phase CTPA. The diagnostics confidence of the two CTPA protocols was similarly rated by one reader and slightly different according to the second reader.

CONCLUSION

The nonrigid temporal registration of multiphase CT pulmonary angiography could offer similar or even better image quality than the single-phase protocol and significantly reduce the amount of contrast usage.

Application of deep learning reconstruction combined with time-resolved post-processing method to improve image quality in CTA derived from low-dose cerebral CT perfusion data

BACKGROUND

To assess the effect of the combination of deep learning reconstruction (DLR) and time-resolved maximum intensity projection (tMIP) or time-resolved average (tAve) post-processing method on image quality of CTA derived from low-dose cerebral CTP.

METHODS

Thirty patients underwent regular dose CTP (Group A) and other thirty with low-dose (Group B) were retrospectively enrolled. Group A were reconstructed with hybrid iterative reconstruction (R-HIR). In Group B, four image datasets of CTA were gained: L-HIR, L-DLR, L-DLRtMIP and L-DLRtAve. The CT attenuation, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and subjective images quality were calculated and compared. The Intraclass Correlation (ICC) between CTA and MRA of two subgroups were calculated.

RESULTS

The low-dose group achieved reduction of radiation dose by 33% in single peak arterial phase and 18% in total compared to the regular dose group (single phase: 0.12 mSv vs 0.18 mSv; total: 1.91mSv vs 2.33mSv). The L-DLRtMIP demonstrated higher CT values in vessels compared to R-HIR (all P < 0.05). The CNR of vessels in L-HIR were statistically inferior to R-HIR (all P < 0.001). There was no significant different in image noise and CNR of vessels between L-DLR and R-HIR (all P > 0.05, except P = 0.05 for CNR of ICAs, 77.19 ± 21.64 vs 73.54 ± 37.03). However, the L-DLRtMIP and L-DLRtAve presented lower image noise, higher CNR (all P < 0.05) and subjective scores (all P < 0.001) in vessels than R-HIR. The diagnostic accuracy in Group B was excellent (ICC = 0.944).

CONCLUSION

Combining DLR with tMIP or tAve allows for reduction in radiation dose by about 33% in single peak arterial phase and 18% in total in CTP scanning, while further improving image quality of CTA derived from CTP data when compared to HIR.

Intraoperative Fast Adaptive Focus Tracking Robotic OCT Enables Real-Time Tumor Grading and Large-Area Microvascular Imaging in Human Spinal Cord Surgery

Current surgical procedures for spinal cord tumors lack in vivo high-resolution multifunctional imaging systems, hindering precise tumor resection. This study introduces the fast adaptive focus tracking robotic optical coherence tomography (FACT-ROCT) system, which provides real-time, artifact-free imaging during surgery, addressing motion artifacts and resolution degradation. Imaging occurs in 22 patients, including 13 with gliomas (WHO grade I-IV). This represents the first in situ OCT imaging of human spinal cord tumors, enabling the differentiation of tumor types in real-time. The standard deviation of the attenuation coefficient serves as a physical marker, achieving 90.2%  ±  2.7% accuracy in distinguishing high- from low-grade gliomas intraoperatively at a threshold of 0.75  ±  0.01 mm-1. FACT-ROCT also enables microvascular imaging, covering areas of 70 mm × 13 mm × 10 mm within 2 min and revealing greater vascular tortuosity in higher-grade tumors. This extensive imaging capability provides critical information that guides surgical strategies, enhancing surgical outcomes. Overall, FACT-ROCT represents a significant advancement in intraoperative imaging, offering high-resolution, high-speed, and comprehensive insights into spinal cord tumor structure and vasculature.

Evaluation of Image Quality of Temporal Maximum Intensity Projection and Average Intensity Projection of Adaptive 4D-Spiral CT Scans: A Phantom Study

Adaptive four-dimensional (4D) spiral computed tomography (CT) scans facilitate the acquisition of volume perfusion data for organs or long-range vessels; however, optimizing image quality and reducing noise while minimizing radiation doses remains challenging. Thus, image-processing techniques such as temporal maximum intensity projection (MIP) and average intensity projection (AIP) are crucial in this context. This ex vivo study aimed to compare the image noise, spatial resolution, and measurements of temporal MIP and AIP images generated from low radiation dose 4D CT scans data with those of conventional CT images using phantoms. Three phantoms were scanned with equivalent radiation doses using single helical and adaptive 10-phase 4D spiral scans using a third-generation dual-source CT scanner. Temporal MIP and AIP images of 4D CT scans were generated by summing varying numbers of phases, incorporating automatic motion correction with non-rigid registration and noise reduction algorithm. The CT values and image noise of the temporal MIP and AIP images were compared to conventional CT images. The task transfer function (TTF) was calculated using static phantoms. Vessel diameters of the phantoms for each image dataset were evaluated using motion phantoms. Temporal AIP images showed comparable CT values with those of the reference image. In contrast, the CT values of the temporal MIP images were significantly higher than those of the reference images (p<0.01). The image noise of temporal AIP images with six or more phases was equal to or lower than that of the reference images. In contrast, temporal MIP images exhibited consistently high noise levels regardless of the number of summed phases. The TTF of temporal AIP images was comparable to that of the reference CT images. However, the TTF of temporal MIP images gradually decreased as the number of summed phases increased. No significant differences were observed in vessel diameter measurements among the three groups or with varying numbers of summed phases (p>0.05). In conclusion, temporal MIP and AIP images generated from low radiation dose 4D CT scans could effectively reduce noise while preserving measurement reliability in the motion phantom, achieving performance comparable to conventional CT images.

Image Follow-Up After Flow Diverter Treatment Using Only Ultra-High Resolution CT Angiography with Model-Based Iterative Reconstruction: A Case Report

Follow-up examinations using magnetic resonance imaging or digital subtraction angiography are mandatory after flow diverter treatment of cerebral aneurysms. However, flow diverter features metal artifacts on magnetic resonance imaging and ischemic complications with digital subtraction angiography. Ultra-high-resolution computed tomography systems have recently become available in clinical practice. The combined use of ultra-high-resolution computed tomography and a reconstruction technique called model-based iterative reconstruction is expected to replace follow-up magnetic resonance imaging and digital subtraction angiography of flow diverter placement. Here, we report a case of ultra-high-resolution computed tomography with model-based iterative reconstruction after flow diverter treatment.

Contrast enhancement boost improves the image quality of CT angiography derived from 80-kVp cerebral CT perfusion data

RATIONALE AND OBJECTIVE

To investigate the impact of the contrast enhancement boost (CE-boost) technique on the image quality of CT angiography (CTA) derived from 80-kVp cerebral CT perfusion (CTP) data, and to compare it with conventional CTApeak as well as other currently employed methods for enhancing CTA images, such as CTAtMIP and CTAtAve extracted from CTP.

MATERIALS AND METHODS

The data of forty-seven patients who underwent CTP at 80 kVp were retrospectively collected. Four sets of images: CTApeak, CTAtMIP, CTAtAve, and CE-boost images. The CTApeak image represents the arterial phase at its peak value, captured as a single time point. CTAtMIP and CTAtAve are 4D CTA images that provide maximum density projection and average images from the three most prominent time points. CE-boost is a postprocessing technique used to enhance contrast in the arterial phase at its peak value. We compared the average CT value, standard deviation (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the internal carotid artery (ICA) and basilar artery (BA) among the four groups. Image quality was evaluated using a 5-point scale.

RESULTS

The CE-boost demonstrated and CNR in the ICA and BA (all p < 0.001). Compared with the other three CTA reconstructed images, the CE-boost images had the best subjective image quality, with the highest scores of 4.77 ± 0.43 and 4.87 ± 0.34 for each reader (all p < 0.001).

CONCLUSION

Compared with other currently used techniques,CE-boost enhances the image quality of CTA derived from 80-kVp CTP data, leading to improved visualization of intracranial arteries.

Noninvasive Treatment of Venous Pulsatile Tinnitus with an Internal Jugular Vein Compression Collar

OBJECTIVE

The study was conducted to evaluate the safety and efficacy of mild internal jugular (IJV) compression via an FDA approved compression collar for symptomatic treatment of venous pulsatile tinnitus.

METHODS

This is a prospective study that recruited 20 adult patients with venous pulsatile tinnitus. Participants completed the Tinnitus Handicap Inventory (THI), were fitted with the collar, and rated symptom intensity on a 10-point tinnitus intensity scale before and during collar use. Once weekly for 4 weeks, they answered a survey quantifying days used, average tinnitus intensity before and after wearing the collar each day of use, and any safety concerns. Lastly, they completed an exit interview. The primary outcome was symptomatic relief, with secondary outcomes of safety, effect of treatment setting, effect of time, and quality of life assessed via nonparametric testing.

RESULTS

18 participants completed the study, and 276 paired daily before use/during use intensity scores were submitted. The median symptom intensity without the collar was 6 (IQR 4, 7), whereas with the collar it was 3 (IQR 2, 5), for a median symptomatic relief of 50%. The collar had a significant effect in reducing symptom intensity (p < 0.0001) and burden of illness via the THI (p < 0.0001). There was no effect of setting, frequency, or time on symptomatic relief with the collar. There were no adverse safety events reported aside from minor discomfort upon initial application.

CONCLUSIONS

Venous compression collars offer acute symptom relief for patients with venous pulsatile tinnitus. Further study is needed to assess safety and efficacy of longitudinal use.

LEVEL OF EVIDENCE

4 Laryngoscope, 134:3342-3348, 2024.

Depiction rate of feeding arteries of renal cell carcinoma on four-dimensional computed tomography angiography

PURPOSE

To retrospectively evaluate the depiction rate of feeding arteries in biopsy-proven clear cell renal cell carcinoma (CCRCC) on four-dimensional computed tomography angiography (4D-CTA) images.

MATERIALS AND METHODS

This study included 22 patients with 22 CCRCC and 30 feeding arteries treated with transcatheter renal artery embolization. The depiction rate of the feeding arteries on preprocedural 4D-CTA was evaluated. Images were acquired by 320-row multi-detector computed tomography (CT) 15‒36 s after starting to inject a contrast agent (600 mg/kg iodine) intravenously into patients at 2.1 s intervals (11 phases). Two board-certified radiologists retrospectively assessed the feeder depiction rate in all 11 phases with reference to the procedural images as the gold standard. Discrepancies were resolved by consultation with a third radiologist.

RESULTS

Among the feeders, 11 (36.7%) were segmental or lobar, and 19 (63.3%) were interlobar or arcuate arteries. The feeder depiction rate was the highest (25 [83.3%] of 30) in the 5th phase (delay, 23.4 s) where the gap in contrast enhancement between the renal artery and cortex was the largest. This was followed by the 6th (23 [76.7%] of 30), 4th (22 [73.3%] of 30]), and 7th (21 [70.0%] of 30) phases. The overall rate of depicting feeding arteries in the 11 phases of 4D-CTA was 28 (93.3%) of 30.

CONCLUSIONS

The depiction rate of CCRCC feeding arteries including lobar or smaller artery branches by 4D-CTA was favorable. The feeding arteries were optimally visualized during the phase with the largest contrast gap between the renal artery and cortex.

The novel imaging methods in diagnosis and assessment of cerebrovascular diseases: an overview

Cerebrovascular diseases, including ischemic strokes, hemorrhagic strokes, and vascular malformations, are major causes of morbidity and mortality worldwide. The advancements in neuroimaging techniques have revolutionized the field of cerebrovascular disease diagnosis and assessment. This comprehensive review aims to provide a detailed analysis of the novel imaging methods used in the diagnosis and assessment of cerebrovascular diseases. We discuss the applications of various imaging modalities, such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and angiography, highlighting their strengths and limitations. Furthermore, we delve into the emerging imaging techniques, including perfusion imaging, diffusion tensor imaging (DTI), and molecular imaging, exploring their potential contributions to the field. Understanding these novel imaging methods is necessary for accurate diagnosis, effective treatment planning, and monitoring the progression of cerebrovascular diseases.

Deep learning-assisted diagnosis of large vessel occlusion in acute ischemic stroke based on four-dimensional computed tomography angiography

Purpose

To develop deep learning models based on four-dimensional computed tomography angiography (4D-CTA) images for automatic detection of large vessel occlusion (LVO) in the anterior circulation that cause acute ischemic stroke.

Methods

This retrospective study included 104 LVO patients and 105 non-LVO patients for deep learning models development. Another 30 LVO patients and 31 non-LVO patients formed the time-independent validation set. Four phases of 4D-CTA (arterial phase P1, arterial-venous phase P2, venous phase P3 and late venous phase P4) were arranged and combined and two input methods was used: combined input and superimposed input. Totally 26 models were constructed using a modified HRNet network. Assessment metrics included the areas under the curve (AUC), accuracy, sensitivity, specificity and F1 score. Kappa analysis was performed to assess inter-rater agreement between the best model and radiologists of different seniority.

Results

The P1 + P2 model (combined input) had the best diagnostic performance. In the internal validation set, the AUC was 0.975 (95%CI: 0.878-0.999), accuracy was 0.911, sensitivity was 0.889, specificity was 0.944, and the F1 score was 0.909. In the time-independent validation set, the model demonstrated consistently high performance with an AUC of 0.942 (95%CI: 0.851-0.986), accuracy of 0.902, sensitivity of 0.867, specificity of 0.935, and an F1 score of 0.901. The best model showed strong consistency with the diagnostic efficacy of three radiologists of different seniority (k = 0.84, 0.80, 0.70, respectively).

Conclusion

The deep learning model, using combined arterial and arterial-venous phase, was highly effective in detecting LVO, alerting radiologists to speed up the diagnosis.

Relationships between irregular pulsation and variations in morphological characteristics during the cardiac cycle in unruptured intracranial aneurysms by 4D-CTA

Background and purpose

Irregular pulsation of the aneurysmal wall has been suggested as a novel predictor for aneurysm rupture. Aneurysm volume variations during the cardiac cycle and the association between irregular pulsation and morphological features have been discussed, but the clinical significance remains unclear. The purpose of this study was to quantify changes in morphological characteristics over the cardiac cycle and examine their correlation with irregular pulsation to facilitate comprehension of aneurysm dynamics.

Materials and methods

Fourteen unruptured intracranial aneurysms (UIAs) from 11 patients were included in this study, and each of them underwent 4D-CTA after diagnosis by DSA. The R-R intervals were divided into 20-time phases at 5% intervals to determine whether an aneurysm had irregular pulsation throughout the cardiac cycle. CT images from the 20-time phases were used to reconstruct 3D aneurysm models, measure 14 morphological parameters, and quantify each parameter's absolute change and relative rates of change during the cardiac cycle.

Results

Seven of 14 UIAs exhibited irregular pulsation over the cardiac cycle by 4D-CTA, 5 of which were small aneurysms (< 7 mm). The UIAs with irregular pulsation exhibited greater changes in morphological characteristics. As aneurysm size increased, the absolute change in aneurysm volume increased (p = 0.035), but the relative rates of change in aneurysm size (p = 0.013), height (p = 0.014), width (p = 0.008), height-to-width ratio (p = 0.009), dome-to-neck ratio (p = 0.019) and bottleneck factor (p = 0.012) decreased.

Conclusion

Although the larger the aneurysm, the greater the amplitude of its volumetric variation, small aneurysms are prone to irregular pulsation during the cardiac cycle and have more pronounced and dramatic morphological changes during the cardiac cycle that may increase the risk of rupture. This proof-of-concept study could help to explain the importance of dynamic changes using 4D-CTA in assessing the rupture risk of UIAs.

The Predictive Value of Cerebral Veins on Hemorrhagic Transformation After Endovascular Treatment in Acute Ischemic Stroke Patients: Enhanced Insights From Venous Collateral Circulation Analysis Using Four-Dimensional CTA

RATIONALE AND OBJECTIVES

A significant complication of endovascular treatment (EVT) is hemorrhagic transformation (HT), which can worsen the outcomes of patients with acute ischemic stroke (AIS). This study aimed to evaluate the predictive value of venous collateral circulation on HT in patients with AIS undergoing EVT.

MATERIALS AND METHODS

We retrospectively analyzed 126 patients with AIS who received EVT. The four-dimensional computed tomography angiography-based venous collateral score (4D-VCS) and arterial collateral circulation score (4D-ACS) were used to assess venous and arterial collaterals, respectively. Significant variables were identified using the least absolute shrinkage and selection operator algorithm. Logistic regression analysis, receiver operating characteristic (ROC) analysis, and DeLong's test were conducted.

RESULTS

HT occurred in 41.3% (52/126) of patients. Higher clot burden score (CBS; odds ratio [OR]: 0.82, 95% confidence interval [CI]: 0.71-0.95, p = 0.009), better arterial collateral circulation (OR: 0.59, 95% CI: 0.42-0.83, p = 0.003), and better venous collateral circulation (OR: 0.85, 95% CI: 0.73-0.97, p = 0.020) were significantly associated with reduced HT risk. The area under the curve (AUC) values for CBS, 4D-ACS, and 4D-VCS were 0.730, 0.772, and 0.795, respectively. Model 1 (4D-VCS+CBS) achieved AUC of 0.820, significantly improving over CBS alone (p = 0.0133). Model 2 (4D-VCS+4D-ACS) had an AUC of 0.829, significantly higher than 4D-ACS alone (p = 0.0271). Model 3 (4D-ACS+CBS) had an AUC of 0.790. Model 4 (4D-VCS+4D-ACS+CBS) showed highest AUC of 0.851. Significant correlations were found between 4D-VCS and ischemic core volume (r = -0.684, p < 0.001) and between 4D-VCS and mismatch ratio (r = 0.558, p < 0.001).

CONCLUSION

Evaluating venous collateral circulation using 4D-VCS could improve HT risk prediction in patients with AIS after EVT. When combined with other predictors, 4D-VCS may potentially enhance diagnostic performance, which suggests the potential role of venous collateral circulation in predicting HT risk.

Dynamic Computed Tomography Angiography for capturing vessel wall motion: A phantom study for optimal image reconstruction

BACKGROUND

Reliably capturing sub-millimeter vessel wall motion over time, using dynamic Computed Tomography Angiography (4D CTA), might provide insight in biomechanical properties of these vessels. This may improve diagnosis, prognosis, and treatment decision making in vascular pathologies.

PURPOSE

The aim of this study is to determine the most suitable image reconstruction method for 4D CTA to accurately assess harmonic diameter changes of vessels.

METHODS

An elastic tube (inner diameter 6 mm, wall thickness 2 mm) was exposed to sinusoidal pressure waves with a frequency of 70 beats-per-minute. Five flow amplitudes were set, resulting in increasing sinusoidal diameter changes of the elastic tube, measured during three simulated pulsation cycles, using ECG-gated 4D CTA on a 320-detector row CT system. Tomographic images were reconstructed using one of the following three reconstruction methods: hybrid iterative (Hybrid-IR), model-based iterative (MBIR) and deep-learning based (DLR) reconstruction. The three reconstruction methods where based on 180 degrees (half reconstruction mode) and 360 degrees (full reconstruction mode) raw data. The diameter change, captured by 4D CTA, was computed based on image registration. As a reference metric for diameter change measurement, a 9 MHz linear ultrasound transducer was used. The sum of relative absolute differences (SRAD) between the ultrasound and 4D CTA measurements was calculated for each reconstruction method. The standard deviation was computed across the three pulsation cycles.

RESULTS

MBIR and DLR resulted in a decreased SRAD and standard deviation compared to Hybrid-IR. Full reconstruction mode resulted in a decreased SRAD and standard deviations, compared to half reconstruction mode.

CONCLUSIONS

4D CTA can capture a diameter change pattern comparable to the pattern captured by US. DLR and MBIR algorithms show more accurate results than Hybrid-IR. Reconstruction with DLR is >3 times faster, compared to reconstruction with MBIR. Full reconstruction mode is more accurate than half reconstruction mode.

Deep Learning Reconstruction Improves the Image Quality of CT Angiography Derived From 80-kVp Cerebral CT Perfusion Data

RATIONALE AND OBJECTIVE

To investigate the impact of the deep learning reconstruction (DLR) technique on the image quality of CT angiography (CTA) derived from 80-kVp cerebral CT perfusion (CTP) data and compare it with hybrid-iterative reconstruction (HIR).

MATERIALS AND METHODS

Thirty-three patients underwent CTP at 80 kVp were prospectively enrolled. CTP data were reconstructed with HIR and DLR. Four image datasets were reconstructed: HIRpeak and DLRpeak were single arterial phase images derived from the time point showing the peak value, HIRtMIP and HIRtAve were time-resolved maximum intensity projection image and time-resolved average image derived from three time points with the greatest enhancement of HIR. The mean CT values, standard deviation, signal-to-noise ratio, and contrast-to-noise ratio of the internal carotid artery and basilar artery were compared among the four image dataset. Image quality was performed using a five-point rating scale. Arterial stenosis was evaluated.

RESULTS

DLRpeak had the highest CT value and contrast-to-noise ratio in the internal carotid artery and basilar artery (all p < 0.001). DLRpeak showed the best subjective image quality and had the highest score (4.93 ± 0.4) compared to the other three HIR CTA images (all p < 0.001). The degree of vascular stenosis was consistent among the four evaluated sequences (HIRtAve, HIRpeak, and HIRtMIP DLRpeak).

CONCLUSION

For CTA derived from 80-kVp cerebral CTP data, images reconstructed with deep learning showed better image quality and improved intracranial artery visualization than those processed with HIR and other currently used techniques.

Accuracy Verification of Four-Dimensional CT Analysis of Knee Joint Movements: A Pilot Study Using a Knee Joint Model and Motion-Capture System

Objective This study aimed to use the optical motion-capture method to verify the accuracy of four-dimensional computed tomography (4D-CT) analysis of knee joint movement. Methods One static CT and three 4D-CT examinations of the knee joint model were obtained. The knee joint model was passively moved in the CT gantry during 4D-CT acquisitions. 4D-CT and static CT examinations were matched to perform 3D-3D registration. An optical-motion capture system recorded the position-posture of the knee joint model simultaneously with the 4D-CT acquisitions. Reference axes (X, Y, and Z directions) were defined based on static CT and applied to 4D-CT and the optical-motion capture system. Using the position-posture of the motion capture system as a reference standard, the position-posture measurements using 4D-CT were compared to these values, and the accuracy of the 4D-CT analysis of knee joint movements was quantitatively assessed. Results The position-posture measurements obtained from 4D-CT showed a similar tendency to those obtained from the motion-capture system. In the femorotibial joint, the difference in the spatial orientation between the two measurements was 0.7 mm in the X direction, 0.9 mm in the Y direction, and 2.8 mm in the Z direction. The difference in angle was 1.9° in the varus/valgus direction, 1.1° in the internal/external rotation, and 1.8° in extension/flexion. In the patellofemoral joint, the difference between the two measurements was 0.9 mm in the X direction, 1.3 mm in the Y direction, and 1.2 mm in the Z direction. The difference in angle was 0.9° for varus/valgus, 1.1° for internal/external rotation, and 1.3° for extension/flexion. Conclusions 4D-CT with 3D-3D registration could record the position-posture of knee joint movements with an error of less than 3 mm and less than 2° when compared with the highly accurate optical-motion capture system. Knee joint movement analysis using 4D-CT with 3D-3D registration showed excellent accuracy for in vivo applications.

Evaluating diploic vein blood flow using time-resolved whole-head computed tomography angiography and determining the positional relationship between typical craniotomy approaches and diploic veins in patients with meningioma

BACKGROUND

Diploic veins may act as collateral venous pathways in cases of meningioma with venous sinus invasion. Diploic vein blood flow should be preoperatively evaluated to consider preserving the veins. In this study, we evaluated the use of time-resolved whole-head computed tomography angiography (4D-CTA)-which is less patient-intensive than digital subtraction angiography (DSA)-for assessing diploic vein blood flow and the positional relationship between typical craniotomy approaches and diploic veins.

METHODS

We retrospectively examined 231 patients who underwent surgery for intracranial meningioma. We performed contrast-enhanced magnetic resonance imaging (MRI) to evaluate diploic vein pathways and compared the visualization rates of diploic vein blood flow assessed using 4D-CTA and DSA. Subsequently, we evaluated the rates of the diploic veins transected during craniotomy by comparing the pre- and postoperative contrast-enhanced MRI.

RESULTS

The diagnostic performance of 4D-CTA was assessed in 45 patients. Of the 320 diploic veins identified in these patients, blood flow in 70 (21.9%) diploic veins was identified by 4D-CTA and DSA, and both results were consistent. To assess the transection rates of the diploic veins, 150 patients were included. A trend towards a high transection rate of the diploic vein in the basal interhemispheric, frontotemporal, orbitozygomatic, combined transpetrosal, and convexity craniotomy approaches was observed.

CONCLUSIONS

In patients with meningiomas, both 4D-CTA and DSA are useful in evaluating diploic vein blood flow. In meningiomas with venous sinus invasion, determining the extent of craniotomy after understanding the pathways and blood flow of diploic veins is recommended.

BNP on Admission Combined with Imaging Markers of Multimodal CT to Predict the Risk of Cardioembolic Stroke

Background

The aim of the study was to find the potential roles of B-type natriuretic peptide (BNP) and imaging markers on distinguishing cardioembolic (CE) stroke from non-CE stroke, so as to provide useful information for making individualized endovascular treatment (EVT) plan for the patients with acute ischemic stroke (AIS).

Methods

The patients with unilateral anterior circulation large vessel occlusion who underwent EVT between March 2016 and December 2021 were analyzed in this study, retrospectively. The risk factors, laboratory test indicators, imaging parameters, and other factors were compared between the CE group and non-CE group. Logistic regression was used to analyze the risk factors of CE stroke. ROC curves were used to assess the values of different parameters on distinguishing CE stroke from non-CE stroke. The relationships between BNP and imaging parameters were assessed using the Spearman correlation analysis.

Results

160 patients were enrolled in the study and divided into the CE group (n = 66) and non-CE group (n = 94). BNP (odds ratio (OR) = 1.004; 95% CI, 1.001-1.009; p = 0.038), MMR (OR = 0.736; 95% CI, 0.573-0.945; p = 0.016), NIHSS (OR = 1.150; 95% CI, 1.022-1.294; p = 0.020), and AF (OR = 556.968; 95% CI, 51.739-5995.765; p < 0.001) were the independent predictive factors of CE stroke. The area under the curve (AUC) of BNP and mismatch ratio (MMR) were 0.846 (95% CI (0.780-0.898), p < 0.001) and 0.636 (95% CI (0.633-0.779), p < 0.001), respectively. The cut-off value of BNP was 249.23 pg/mL with the sensitivity of 74.24% and the specificity of 82.98%. BNP combined with MMR improved the predictive value for CE stroke. The AUC of the combination was 0.858 with the sensitivity of 84.85% and the specificity of 73.40%. BNP was correlated with 4D CTA collateral score, MMR, clot burden score, final infarct volume, infarct core volume, and ischemic penumbra volume (all, p < 0.05).

Conclusion

BNP on admission combined with MMR is valuable for the risk prediction of CE stroke, which will promote the further screening of the high-risk patients with CE stroke and provide more diagnostic information for clinicians.

Cerebral proliferative angiopathy depicted by four-dimensional computed tomographic angiography: A case report

Cerebral proliferative angiopathy is a rare cerebrovascular disorder characterized by diffuse abnormal vessels with intermingled brain parenchyma fed by many arteries and draining into many veins without high-flow arteriovenous shunts, which is usually confirmed by conventional digital subtraction angiography. However, dilution of the contrast medium due to the markedly increased blood flow and volume in cerebral proliferative angiopathy leads to low-contrast angiography. We report a 53-year-old man with cerebral proliferative angiopathy who underwent CT, MR imaging, MR angiography, digital subtraction angiography and 4D-CTA. The 4D-CTA exhibited abnormal vessels without early venous filling between the atrophic brain parenchyma in higher contrast than the angiography due to high spatial and time resolution, whereas the left external carotid angiography visualized the characteristic transdural supply more clearly than the 4D-CTA due to high vascular selectivity. Therefore, novel 4D-CTA and conventional angiography plays a complementary role in the accurate diagnosis of cerebral proliferative angiopathy. Taking invasiveness into account, 4D-CTA may be advantageous for the diagnosis of cerebral proliferative angiopathy based on the characteristic imaging findings.

Digital subtraction angiography in cerebrovascular disease: current practice and perspectives on diagnosis, acute treatment and prognosis

Digital Subtraction Angiography (DSA) is the gold-standard imaging modality in acute cerebrovascular diagnosis. The role of DSA has become increasingly prominent since the incorporation of endovascular therapy in standards of care for acute ischemic stroke. It is used in the assessment of cerebral vessel patency; however, the therapeutic role of DSA from a prognostic standpoint merits further investigation. The current paper provides an update on current practice on diagnostic, therapeutic and prognostic use of DSA in acute cerebrovascular diseases and various indications and perspectives that may apply, or limit its use, in ongoing surveillance or prognosis. Pre-clinical and clinical studies on the aspects, including but not limited to the morphology of cerebrovasculature in acute ischaemic stroke, are required to delineate and inform its prognostic role.

Imaging Modalities for Intracranial Aneurysm: More Than Meets the Eye

Intracranial aneurysms (IA) are often asymptomatic and have a prevalence of 3 to 5% in the adult population. The risk of IA rupture is low, however when it occurs half of the patients dies from subarachnoid hemorrhage (SAH). To avoid this fatal evolution, the main treatment is an invasive surgical procedure, which is considered to be at high risk of rupture. This risk score of IA rupture is evaluated mainly according to its size and location. Therefore, angiography and anatomic imaging of the intracranial aneurysm are crucial for its diagnosis. Moreover, it has become obvious in recent years that several other factors are implied in this complication, such as the blood flow complexity or inflammation. These recent findings lead to the development of new IA imaging tools such as vessel wall imaging, 4D-MRI, or molecular MRI to visualize inflammation at the site of IA in human and animal models. In this review, we will summarize IA imaging techniques used for the patients and those currently in development.

Evaluation of Modified Calcium Removal Algorithm in dual energy CT of Internal Carotid Artery

PURPOSE

To evaluate the performance of a dual-energy (DE) calcium removal software based on a modified three-material decomposition algorithm in assessing the stenosis of the internal carotid artery (ICA) in comparison with mixed images using digital subtraction angiography (DSA) as the reference standard.

METHODS

Forty-six patients (38 men; 67±8 years old), including 154 calcified ICA segments C1-C2 (59), C3-C5 (63), C6 (24), and C7 (8), were recruited in this retrospective study. Mixed images and virtual non-calcium (VNCa) images using the modified dual-energy computed tomography (DECT) algorithm were reconstructed. The differences between VNCa and DSA images vs. mixed and DSA images of degree of stenosis were compared. The intraclass correlation coefficient (ICC) was used for assessing the agreement between VNCa, mixed images, and DSA.

RESULTS

The degree of stenosis differed significantly between mixed and DSA images in the C3-C5 (30%±17.9% vs. 23.0%±16.9%, p = 0.026) and C6 (38.3%±15.4% vs. 28.5%±13.3%, p = 0.023) segments. The stenosis of VNCa images showed no significant difference with DSA images in all segments (all p > 0.05). The ICCs between VNCa and DSA images (0.86-0.97) were higher than those between the mixed and DSA images (0.68-0.96) in all segments.

CONCLUSION

The performance of a modified three-material decomposition DECT algorithm for calcium removal in ICA stenosis evaluation, particularly for the C3-C5 and C6 ICA segments, was promising.

Bilateral carotid cavernous fistula after trauma: a case report and literature review

BACKGROUND

Carotid cavernous fistula is a rare complication that is typically associated with head trauma and skull base fractures. The traumatic bilateral carotid cavernous fistula are significantly rarer.

CASE PRESENTATIONS

We report a case of a 61-year-old man presenting with unilateral exophthalmos, swollen eyelids, conjunctival congestion, and edema etiologically associated with severe trauma. Thereafter, the patient demonstrated symptoms of contralateral oculomotor nerve injury caused by skull base fracture, such as ptosis of eyelid, dilated pupils, and eye movement disorder, and was diagnosed with bilateral carotid cavernous fistula.

CONCLUSIONS

The patient recovered after undergoing endovascular embolization of bilateral cavernous sinus fistulas. The patient demonstrated the classic symptoms of an extremely rare condition known as bilateral carotid cavernous fistula, in only one eye. Reporting and analyzing this case will help us elucidate the underlying mechanisms of this disease.

Diagnostic accuracy of shuttle CT angiography (CTA) and helical CTA in the diagnosis of vasospasm

PURPOSE

To evaluate the diagnostic accuracy of computed tomography angiography (CTA) acquired with shuttle technique (CTAs) and helical CTA (CTAh) for vasospasm, using digital subtraction angiography (DSA) obtained within 24 h as reference standard.

METHODS

Thirty-six patients with suspected vasospasm in the setting of aneurysmal subarachnoid hemorrhage (ASAH, 30/36) or acute inflammatory/infectious conditions (6/36) who underwent CTAs (17/36) or CTAh (19/36) followed by DSA within 24 h were identified retrospectively. Presence of vasospasm in the proximal cerebral arterial segments was assessed qualitatively and semi-quantitatively on CTA and subsequent DSA. Sensitivity, specificity, and receiver operating characteristic (ROC) curves were calculated. Inter-rater variability was assessed using Cohen's kappa.

RESULTS

On CTAs, 35% of patients had low and 65% had high vasospasm burden. On CTAh, 37% had low and 63% had high vasospasm burden. ROC analysis demonstrated an AUC of 0.87 for CTAs (95%CI 0.67-1.00, p = 0.015) and 0.88 for CTAh (0.72-1.00, p = 0.028). Cohen's kappa was 0.843 (95%CI 0.548-1.000). Thresholding with Youden's J index, CTAs had a sensitivity of 85.71% (95%CI 48.69 to 99.27) and specificity of 66.67% (35.42 to 87.94). CTAh had sensitivity of 100% (56.55 to 100.00) and specificity of 78.57% (52.41 to 92.43).

CONCLUSION

CTAs and CTAh yielded similar sensitivity, specificity, and AUC values on ROC analysis for the detection of vasospasm using DSA as reference standard. Our findings suggest that CTAs is a promising alternative to CTAh especially in patients requiring serial imaging, given its potential advantages of decreased radiation exposure, contrast dose, and cost-effectiveness.

Detecting causes of pulsatile tinnitus on CT arteriography-venography: A pictorial review

Pulsatile tinnitus (PT) can be a mild or debilitating symptom. Following clinical examination and otoscopy, when the underlying aetiology is not apparent, radiological imaging can be used to evaluate further. CT arteriography-venography (CT A-V) of the head and neck has recently been introduced as a single 'one catch' modality for identifying the many causes of PT including those which are treatable and potentially serious whilst also providing reassurance through negative studies or studies with benign findings. CT A-V is performed as a single phase study allowing both arterial and venous assessment, hence limiting radiation exposure. Additional multiplanar reformats and bone reconstructions are desirable. Understanding the limitations of CT A-V is also required, with an awareness of the scenarios where other imaging modalities should be considered. The causes of PT can be divided into systemic and non-systemic categories. Non-systemic aetiologies in the head and neck should be carefully reviewed on CT A-V and include a variety of vascular causes (arteriovenous malformations/fistulas, venous or arterial aetiologies) and non-vascular causes (tumours and bony dysplasias). Venous causes (dominant, aberrant, stenosed or thrombosed venous vessels) are more common than arterial aetiologies (aberrant or stenosed internal carotid artery, aneurysms or a persistent stapedial artery). Glomus tumours that are not visible on otoscopy and osseous pathologies such as bony dehiscence and otospongiosis should also be excluded. Careful assessment of all the potential vascular and non-vascular causes should be reviewed in a systematic approach, with correlation made with the clinical history. A structured reporting template for the reporting radiologist is provided in this review to ensure all the potential causes of PT are considered on a CT A-V study. This will help in providing a comprehensive radiological evaluation, hence justifying the radiation dose and for patient assessment and prognostication.

Advances in imaging acute ischemic stroke: evaluation before thrombectomy

Recent advances in neuroimaging have demonstrated significant assessment benefits and appropriate triage of patients based on specific clinical and radiological features in the acute stroke setting. Endovascular thrombectomy is arguably the most important aspect of acute stroke management with an extended time window. Imaging-based physiological information may potentially shift the treatment paradigm from a rigid time-based model to a more flexible and individualized, tissue-based approach, increasing the proportion of patients amenable to treatment. Various imaging modalities are routinely used in the diagnosis and management of acute ischemic stroke, including multimodal computed tomography (CT) and magnetic resonance imaging (MRI). Therefore, these imaging methods should provide information beyond the presence or absence of intracranial hemorrhage as well as the presence and extent of the ischemic core, collateral circulation and penumbra in patients with neurological symptoms. Target mismatch may optimize selection of patients with late or unknown symptom onset who would potentially be eligible for revascularization therapy. The purpose of this study was to provide a comprehensive review of the current evidence about efficacy and theoretical basis of present imaging modalities, and explores future directions for imaging in the management of acute ischemic stroke.

The feasibility of low iodine dynamic CT angiography with test bolus for evaluation of lower extremity peripheral artery disease

OBJECTIVE

This study aims to determine if low iodine dynamic computed tomography angiography performed after a fixed delay or test bolus acquisition demonstrates high concordance with clinical computed tomography angiography (using a routine amount of iodinated contrast) to display lower extremity peripheral arterial disease.

METHODS

After informed consent, low iodine dynamic computed tomography angiography examination (using either a fixed delay or test bolus) using 50 ml of iodine contrast media was performed. A subsequent clinical computed tomography angiography using standard iodine dose (115 or 145 ml) served as the reference standard. A vascular radiologist reviewed dynamic and clinical computed tomography angiography images to categorize the lumen into "not opacified", "<50% stenosis", " 50 ̶70% stenosis", ">70% stenosis", and "occluded" for seven arterial segments in each lower extremity. Concordance between low iodine dynamic computed tomography angiography and the routine iodine reference standard was calculated. The clinical utility of 4D volume-rendered images was also evaluated.

RESULTS

Sixty-eight patients (average age 66.1 ± 12.3 years, male; female = 49: 19) were enrolled, with 34 patients each undergoing low iodine dynamic computed tomography angiography using fixed delay and test bolus techniques, respectively. One patient assigned to the test bolus group did not undergo low iodine computed tomography angiography due to unavailable delayed time. The fixed delay was 13 s, with test bolus acquisition resulting in a mean variable delay prior to image acquisition of 19.5 s (range; 8-32 s). Run-off to the ankle was observed using low iodine dynamic computed tomography angiography following fixed delay and test bolus acquisition in 76.4% (26/34) and 100% (33/33) of patients, respectively (p = 0.005). Considering extremities with run-off to the ankle and without severe artifact, the concordance rate between low iodine dynamic computed tomography angiography and the routine iodine reference standard was 86.8% (310/357) using fixed delay and 97.9% (425/434) using test bolus (p < 0.001). 4D volume-rendered images using fixed delay and test bolus demonstrated asymmetric flow in 57.7% (15/26) and 58.1% (18/31) (p = 0.978) of patients, and collateral blood flow in 11.5% (3/26) and 22.6% (7/31) of patients (p = 0.319), respectively.

CONCLUSION

Low iodine dynamic computed tomography angiography with test bolus acquisition has a high concordance with routine peripheral computed tomography angiography performed with standard iodine dose, resulting in improved run-off to the ankle compared to dynamic computed tomography angiography performed after a fixed delay. This method is useful for minimizing iodine dose in patients at risk for contrast-induced nephropathy. 4D volume-rendered computed tomography angiography images provide useful dynamic information.

Quick evaluation of lower leg ischemia in patients with peripheral arterial disease by time maximum intensity projection CT angiography: a pilot study

Background

The purpose of this study is to evaluate a new method involving time maximum intensity projection (t-MIP) postprocessed from dynamic computed tomographic angiography (dyn-CTA) in diagnosing peripheral arterial disease (PAD).

Methods

A population of 34 patients with known PAD was examined with a combined CTA protocol consisting of a standard CTA (s-CTA) scan of the lower extremities and a dyn-CTA scan of the calves. For each lower leg, t-MIP images consisting of the MIP₀ (sagittal MIP), MIP_+θ (45° lateral MIP), and MIP_−θ (− 45° lateral MIP) were automatically generated from dyn-CTA. An objective evaluation of the vascular CT attenuation of the best enhancement phase of dyn-CTA and t-MIP was measured; a subjective evaluation of vessel stenosis and occlusion was performed, assigning a score for t-MIP and s-CTA. The CT attenuation of t-MIP and dyn-CTA was compared, as were the runoff scores of t-MIP and s-CTA.

Results

The CT attenuation of t-MIP CTA of three vascular segments from 68 lower extremities was higher than that of the best enhancement phase of dyn-CTA and s-CTA, with statistically significant differences at the posterior tibial artery and fibular artery (all p < 0.05). There were strong correlations (r ≥ 0.75, p < 0.05) of the runoff scores between t-MIP and s-CTA.

Conclusions

There is potential clinical applicability of t-MIP in assisting with the diagnosis of lower leg vascular stenosis in dyn-CTA with reliable diagnostic accuracy and convenient immediacy.

Current and novel non-invasive imaging modalities in vascular neurosurgical practice

Radiological investigations are a powerful tool in the assessment of patients with intracranial vascular anomalies. 'Visual' assessment of neurovascular lesions is central to their diagnosis, monitoring, prognostication and management. Computed tomography and magnetic resonance imaging are the two principal non-invasive imaging modalities used in clinical practice for the assessment of the cerebral vasculature, but these techniques continue to evolve, enabling clinicians to gain greater insights into neurovascular pathology and pathophysiology. This review outlines both established and novel imaging modalities used in modern neurovascular practice and their clinical applications.

Injection of contrast media using a large-bore angiography catheter with a guidewire in place: Physical factors influencing injection pressure in cerebral angiography

BACKGROUND

We have used a contrast injection scheme termed as "guided catheterization method (guided method)." By using a large-bore 5-Fr catheter and 0.032-in guidewire, a contrast medium could be injected without removing the guidewire. Using a neurovascular phantom, we studied the influence of leaving the guidewire on the contrast injection pressure. Image quality was compared with that obtained using a 4-Fr regular angiography catheter (conventional method).

METHODS

Actual contrast injection pressure, flow rate, flow volume, and several variables from the time-density curve (TDC) were obtained using the guided method and the conventional method. Catheterization parameters included flow rate, the viscosity of a contrast medium (CM), and catheter length. The pressure limit of a contrast injector was set as 1200 psi. Digital subtraction angiography (DSA) images on the neurovascular phantom were acquired. The DSA images were processed, and TDC on a specific region of interest was obtained. Variables from TDC were calculated and compared between the different catheters.

RESULTS

The ranges of actual contrast injection pressure with the conventional and the guided method were 138-299 psi and 184-451 psi, respectively. A minimal reduction of the actual flow rate was found under some conditions with the guided method. Comparable opacifications in DSA images were achieved in all conditions. Although peak intensity was different by flow rate or CM, all TDC variables did not differ based on the catheter. There were no significant harmful events during the 90 experiments.

CONCLUSIONS

With adjustment of the pressure limit, cerebral angiography using the 5-Fr, large-bore catheter without removal of the guidewire is feasible, safe, and expected to provide image quality comparable to that of the 4-Fr regular catheter.

Four-dimensional computed tomography angiography analysis of internal carotid arteries opacification at the skull base to detect delayed cerebral ischemia: a feasibility study

PURPOSE

Delayed cerebral ischemia represents a significant cause of poor functional outcome for patients with vasospasm after subarachnoid hemorrhage. We investigated whether delayed cerebral ischemia could be detected by the arterial opacification of internal carotid artery at the level of the skull base.

METHODS

In this exploratory, nested retrospective cohort diagnostic accuracy study, patients with clinical and/or transcranial Doppler suspicion of vasospasm who underwent four-dimensional computed tomography angiography were included. They were split into two groups for the main endpoint analysis, according to the actually adopted morphological (cerebral infarction) and clinical criteria (neurologic deterioration) of delayed cerebral ischemia. Opacification with a temporal resolution of 0.15 s of both internal carotid arteries at the skull base level was obtained through a semi-automated segmentation method based on skeletonization, and analyzed by a wavelet transform (rbio2.2, level 1). The results obtained by k-means clustering were analyzed with regard to the state of delayed cerebral infarction.

RESULTS

Over ten patients included and analyzed, five patients presented a delayed cerebral ischemia, two of them in both side. The semi-automated processing and analysis clustered two different types of opacification curves. The obtaining of a nonlinear opacification pattern was associated (p < 0.001) with delayed cerebral ischemia.

CONCLUSIONS

The analysis of arterial opacification of internal carotid arteries at skull base by the proposed processing is feasible and leads to cluster two types of opacification that may help to early detect and prevent delayed cerebral ischemia, in particularly when examinations are artifacted by aneurysm treatment materials.

Cerebral Artery and Vein Segmentation in Four-dimensional CT Angiography Using Convolutional Neural Networks

Purpose

To implement and test a deep learning approach for the segmentation of the arterial and venous cerebral vasculature with four-dimensional (4D) CT angiography.

Materials and Methods

Patients who had undergone 4D CT angiography for the suspicion of acute ischemic stroke were retrospectively identified. A total of 390 patients evaluated in 2014 (n = 113) or 2018 (n = 277) were included in this study, with each patient having undergone one 4D CT angiographic scan. One hundred patients from 2014 were randomly selected, and the arteries and veins on their CT scans were manually annotated by five experienced observers. The weighted temporal average and weighted temporal variance from 4D CT angiography were used as input for a three-dimensional Dense-U-Net. The network was trained with the fully annotated cerebral vessel artery-vein maps from 60 patients. Forty patients were used for quantitative evaluation. The relative absolute volume difference and the Dice similarity coefficient are reported. The neural network segmentations from 277 patients who underwent scanning in 2018 were qualitatively evaluated by an experienced neuroradiologist using a five-point scale.

Results

The average time for processing arterial and venous cerebral vasculature with the network was less than 90 seconds. The mean Dice similarity coefficient in the test set was 0.80 ± 0.04 (standard deviation) for the arteries and 0.88 ± 0.03 for the veins. The mean relative absolute volume difference was 7.3% ± 5.7 for the arteries and 8.5% ± 4.8 for the veins. Most of the segmentations (n = 273, 99.3%) were rated as very good to perfect.

Conclusion

The proposed convolutional neural network enables accurate artery and vein segmentation with 4D CT angiography with a processing time of less than 90 seconds.© RSNA, 2020.

CT for Treatment Selection in Acute Ischemic Stroke: A Code Stroke Primer

CT is the primary imaging modality used for selecting appropriate treatment in patients with acute stroke. Awareness of the typical findings, pearls, and pitfalls of CT image interpretation is therefore critical for radiologists, stroke neurologists, and emergency department providers to make accurate and timely decisions regarding both (a) immediate treatment with intravenous tissue plasminogen activator up to 4.5 hours after a stroke at primary stroke centers and (b) transfer of patients with large-vessel occlusion (LVO) at CT angiography to comprehensive stroke centers for endovascular thrombectomy (EVT) up to 24 hours after a stroke. Since the DAWN and DEFUSE 3 trials demonstrated the efficacy of EVT up to 24 hours after last seen well, CT angiography has become the operational standard for rapid accurate identification of intracranial LVO. A systematic approach to CT angiographic image interpretation is necessary and useful for rapid triage, and understanding common stroke syndromes can help speed vessel evaluation. Moreover, when diffusion-weighted MRI is unavailable, multiphase CT angiography of collateral vessels and source-image assessment or perfusion CT can be used to help estimate core infarct volume. Both have the potential to allow distinction of patients likely to benefit from EVT from those unlikely to benefit. This article reviews CT-based workup of ischemic stroke for making tPA and EVT treatment decisions and focuses on practical skills, interpretation challenges, mimics, and pitfalls.^©RSNA, 2019.

Evaluation of Intracranial Vascular Status in Patients with Acute Ischemic Stroke by Time Maximum Intensity Projection CT Angiography: A Preliminary Study

RATIONALE AND OBJECTIVES

To describe the application of time maximum intensity projection CTA (t-MIP CTA) in acute ischemic stroke and compare t-MIP CTA and single-phase CTA (sCTA) in assessing collateral circulation and predicting prognosis.

MATERIALS AND METHODS

Twenty-nine acute ischemic stroke patients who underwent one-stop CT angiography (CTA)-CT perfusion scan were reviewed retrospectively. sCTA and t-MIP CTA were developed by CT perfusion scanning data. Image quality and collateral circulation were compared between the sCTA and t-MIP CTA groups. CT attenuation values, image noise, signal to noise , contrast to noise, and subjective image quality were obtained and compared between these two groups. The correlations of clinical prognosis and infarct volume with collateral status on t-MIP CTA and sCTA were analyzed, separately. Receiver operating characteristic curve was used to reveal the sensitivity and specificity of t-MIP CTA and sCTA in predicting outcome.

RESULTS

All images exhibited good quality for diagnosis. In objective evaluation, the noise level of t-MIP CTA was significantly lower than that of sCTA (p < 0.001). Vascular attenuation (signal to noise and contrast to noise) of t-MIP were higher than those of sCTA (all, p < 0.001). The collateral status on t-MIP CTA and sCTA were both negatively correlated with modified Rankin Scale scores (t-MIP CTA, r = -0.709, p < 0.001; sCTA, r = -0.551, p = 0.024) and the final infarction volume (t-MIP CTA, r = -0.716, p = 0.001; sCTA, r = -0.629, p = 0.003). t-MIP CTA was better for predicting prognosis (AUC, 0.956; sensitivity, 0.917; specificity, 0.941; p < 0.001) than sCTA (AUC, 0.824; sensitivity, 0.500; specificity, 0.941; p = 0.003).

CONCLUSION

In comparison with sCTA, t-MIP images showed higher image quality of intracranial vascularity and MIP could reveal vascular occlusion and evaluate collateral circulation more accurately. It was speculated that t-MIP could predict the prognosis more precisely.

Traumatic Middle Meningeal Arteriovenous Fistula of Non-fractured Site Detected by Four-dimensional Computed Tomography Angiography: A Case Report

Middle meningeal arteriovenous fistula (MMAVF) of a non-fractured site is extremely rare, and the clinical characteristics are still unclear. We report a case of delayed onset of venous infarction due to an MMAVF following a fall accident. A 69-year-old man sustained multiple trauma due to a fall accident. Head computed tomography (CT) showed traumatic subarachnoid hemorrhage, a left subdural hematoma, and skull fracture in his right temporal bone, all of which were managed conservatively. Five days after his admission, he suddenly exhibited total aphasia and right hemiparesis. Emergent CT revealed sporadic low-density areas in his left cerebral hemisphere, and four-dimensional CT angiography (4D-CTA) showed dilatation of the left middle meningeal artery and early venous drainage in the cavernous sinus and anterior temporal diploic vein (ATDV). A series of hemodynamics of 4D-CTA revealed early venous filling of ATDV interrelated with retrograde upward flow to high convexity in the venous phase. The MMAVF was successfully obliterated by transarterial coil embolization. We herein describe this case of MMAVF in which 4D-CTA was useful for the diagnosis.

CT angiography with 15 mL contrast material injection on time-resolved imaging for endovascular abdominal aortic aneurysm repair

PURPOSE

To assess the utility of whole-aorta CT angiography (CTA) with 15 mL contrast material (CM) on time-resolved imaging for endovascular abdominal aortic repair (EVAR).

METHODS

Twenty-six patients with a high-risk of post-contrast acute kidney injury (PC-AKI) underwent CTA with 15 mL CM using temporal maximum intensity projection (tMIP-CTA) generated from time-resolved imaging. The aortoiliac CT values were measured. Two observers measured the arterial diameters in unenhanced CT and tMIP-CTA images, and image quality was evaluated on a 5-point scale. The presence of the accessory renal artery, inferior mesenteric artery (IMA) occlusion, and instructions for use (IFU) of EVAR were evaluated.

RESULTS

CT examinations were successfully performed, and no patients developed PC-AKI. The mean CT values of the whole aorta were 267.5 ± 51.4 HU, which gradually decreased according to the distal levels of the aorta. Bland-Altman analysis revealed excellent agreement for the external arterial diameter measurements between unenhanced CT and tMIP-CTA. Excellent interobserver agreement was achieved for the measurements of the external (ICCs, 0.910-0.992) and internal arterial diameters (ICCs, 0.895-0.993). Excellent or good overall image quality was achieved in 24 (92 %) patients. The presence of the accessory renal artery, IMA occlusion and the assessment of IFU were in 100 % agreement. Multivariate analysis revealed aortic volume as the most significant independent factor associated with strong aortic enhancement (p = 0.004).

CONCLUSIONS

Whole-aorta tMIP-CTA on time-resolved imaging is useful for maintaining contrast enhancement and image quality for EVAR planning, and can substantially reduce the amount of CM.

Quantitative Analysis of Lower Leg Muscle Enhancement Measured From Dynamic Computed Tomographic Angiography for Diagnosis of Peripheral Arterial Occlusive Disease

OBJECTIVES

The purpose of this study was to evaluate whether quantitative analysis of lower leg muscle enhancement measured from dynamic computed tomographic angiography (dyn-CTA) could be used for diagnosis of peripheral arterial occlusive disease.

METHODS

Patients (N = 35) with known peripheral arterial occlusive disease underwent the dyn-CTA of calves first. Five minutes later, standard CTA of the peripheral runoff from the diaphragm to the toes was performed. A runoff score was assigned by radiologists as a reference standard for each of 4 lower leg artery segments. The lower leg muscle enhancement measured from the dyn-CTA was analyzed by using quantitative kinetic parameters, including initial enhancement (E1), peak enhancement (Epeak), and enhancement ratio (ER) calculated from average time attenuation curves. In addition, histogram of lower leg muscle enhancement was evaluated by using the first enhanced phase images.

RESULTS

Lower extremities were diagnosed as a normal group (n = 22) with each vessel segment score equals to 1 or lower and runoff score, 7 or lower, and otherwise as an ischemia group (n = 48). Average ± SD E1 is 91.4% ± 8.5% and 82.3% ± 10.7%, Epeak is 122.7% ± 10.4% and 115.6% ± 11.1%, and ER is 0.75 ± 0.05 and 0.72 ± 0.09 for normal and ischemia group, respectively. Statistical analysis showed that average E1 and Epeak for the ischemia group were significantly lower (P < 0.05) than the normal group. The histogram analysis demonstrated that mean and median of muscle enhancement in the ischemia group were significantly smaller (P < 0.05), and coefficient of variation (CV) was significantly larger (P < 0.05) than the normal group. There were weak negative correlations (r = -0.42, P < 0.05) between runoff scores and E1 and Epeak, and weak positive correlation (r = 0.40, P < 0.05) between runoff scores and CV. The receiver operating characteristics analysis between the 2 groups had area under the curve of 0.77 and 0.76 for E1 and CV, respectively.

CONCLUSIONS

Lower leg muscle enhancement measured from the dyn-CTA could be assessed quantitatively to assist diagnosis of ischemia in clinical practice.

Color-Mapping of 4D-CTA for the Detection of Cranial Arteriovenous Shunts

BACKGROUND AND PURPOSE

4D CT angiography is increasingly used in clinical practice for the assessment of different neurovascular disorders. Optimized processing of 4D-CTA is crucial for diagnostic interpretation because of the large amount of data that is generated. A color-mapping method for 4D-CTA is presented for improved and enhanced visualization of the cerebral vasculature hemodynamics. This method was applied to detect cranial AVFs.

MATERIALS AND METHODS

All patients who underwent both 4D-CTA and DSA in our hospital from 2011 to 2018 for the clinical suspicion of a cranial AVF or carotid cavernous fistula were retrospectively collected. Temporal information in the cerebral vasculature was visualized using a patient-specific color scale. All color-maps were evaluated by 3 observers for the presence or absence of an AVF or carotid cavernous fistula. The presence or absence of cortical venous reflux was evaluated as a secondary outcome measure.

RESULTS

In total, 31 patients were included, 21 patients with and 10 without an AVF. Arterialization of venous structures in AVFs was accurately visualized using color-mapping. There was high sensitivity (86%-100%) and moderate-to-high specificity (70%-100%) for the detection of AVFs on color-mapping 4D-CTA, even without the availability of dynamic subtraction rendering. The diagnostic performance of the 3 observers in the detection of cortical venous reflux was variable (sensitivity, 43%-88%; specificity, 60%-80%).

CONCLUSIONS

Arterialization of venous structures can be visualized using color-mapping of 4D-CTA and proves to be accurate for the detection of cranial AVFs. This finding makes color-mapping a promising visualization technique for assessing temporal hemodynamics in 4D-CTA.

Management of a wake-up stroke

Current national guidelines advocate intravenous thrombolysis to treat patients with acute ischaemic stroke presenting within 4.5 hours from symptom onset, and thrombectomy for patients with anterior circulation ischaemic stroke from large vessel occlusion presenting within 6 hours from onset. However, a substantial group of patients presents with acute ischaemic stroke beyond these time windows or has an unknown time of onset. Recent studies are set to revolutionise treatment for these patients. Using MRI diffusion/FLAIR (fluid-attenuated inversion recovery) mismatch, it is possible to identify patients within 4.5 hours from onset and safely deliver thrombolysis. Using CT perfusion imaging, it is possible to identify subjects with a middle cerebral artery syndrome who have an extensive area of ischaemic brain but as yet have only a small area of infarction who may benefit from urgent thrombectomy in up to 24 hours. Here, we highlight the recent advances in late window stroke treatment and their potential contribution to clinical practice.

Thick Clot in the Inferior Limiting Sulcus on Computed Tomography Image as an Indicator of Sylvian Subpial Hematoma in Patients with Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

Sylvian subpial hematoma (SSH) is occasionally observed in aneurysm subarachnoid hemorrhage (aSAH) when accompanied with the thick clot in the inferior limiting sulcus (ILS). We aimed to determine whether the thickness of the clot in the ILS (TCILS) was an indicator of SSH.

METHODS

Data from 150 consecutive patients with aSAH were retrospectively analyzed. The relationship between TCILS on axial computed tomography (CT) image and intraoperatively confirmed SSH was reviewed. In patients without SSH, the average of the clot thickness in the bilateral ILS was used. The primary outcome was SSH.

RESULTS

The median TCILS of the SSH group (n = 18, 12%) was larger than that of the non-SSH group (n = 132, 88%) (21 vs. 2.1 mm, respectively; P < 0.001). The intraclass correlation coefficients for clot thickness in the right and left ILS between 2 observers were 0.97 (P < 0.001) and 0.85 (P < 0.001). The TCILS threshold of ≥6.0 mm was associated with SSH, with a sensitivity of 89% and specificity of 99%. The unadjusted and adjusted odds ratios of the SSH of clot thickness in the affected ILS ≥6 mm relative to clot thickness in the affected ILS <6 mm were 263 (95% confidence interval [CI], 46-5063) and 137 (95% CI, 19-3029), respectively.

CONCLUSIONS

The clot thickness in the ILS on CT image was easily measured and could be a marker of SSH. SSH assessment could be useful in helping us predict the clinical course in patients with aSAH.

Applications and development of permeability imaging in ischemic stroke

Brain permeability imaging techniques are specific for the assessment of blood-brain barrier integrity. The present review article primarily focuses on the application of permeability imaging in cases of ischemic stroke. The permeability maps may be used to predict future hemorrhagic transformation in patients following acute ischemic stroke, that have been treated with tissue plasminogen activator (tPA) or recanalization therapy. The permeability imaging would help make the clinical decision to administer tPA following acute ischemic stroke or not, which is not only due to the current 3-4.5 h time window. Additionally, permeability imaging may also be used to evaluate the collateral circulation in the perfusion and permeability of the ischemic area of the brain.

Diagnostic accuracy of emergency CT angiography for presumed tandem internal carotid artery occlusion before acute endovascular therapy

BACKGROUND

Extracranial internal carotid artery (ICA) occlusion can be overestimated on emergent single phase CT angiography (CTA) of stroke patients with isolated intracranial ICA occlusion. We aimed to measure the ability of identifying the extracranial site of presumed tandem ICA occlusions on pre-procedural CTA relative to catheter angiography during acute endovascular stroke therapy.

METHODS

Retrospective study of patients with intracranial ICA occlusion, with or without extracranial ICA occlusion, who underwent single phase CTA before acute endovascular treatment. Two neuroradiologists reviewed CTA images for the presence or absence of extracranial ICA occlusion, blinded to the catheter angiography results. The sensitivity, specificity, and predictive values of presumed extracranial ICA occlusions on CTA were calculated in reference to catheter angiography.

RESULTS

91 stroke patients with acute intracranial ICA occlusion met the inclusion criteria for the study. 24% of patients (22/91) had tandem ICA occlusion confirmed on catheter angiography. Single phase CTA had a sensitivity of 95.5% (95% CI 77.2 to 99.9%) and a specificity of 69.6% (95% CI 57.3 to 80.1%) for concomitant extracranial ICA occlusion (false positive rate 30.4%). The positive and negative predictive values of single phase CTA for extracranial ICA occlusion in the presence of a distal ICA occlusion were 50% (95% CI 34.2 to 65.8%) and 98% (95% CI 89.1 to 100%), respectively.

CONCLUSIONS

Emergency single phase CTA is highly sensitive but has reduced specificity to identify extracranial ICA occlusion in patients with intracranial ICA occlusion, which may confound planning for acute endovascular stroke therapy and cause over exclusion of patients with isolated ICA terminus occlusion from clinical trials.

Gamma Knife Radiosurgery for Arteriovenous Malformations Using a Four-Dimensional Dynamic Volume Computed Tomography Angiography Planning System as an Alternative to Traditional Catheter Angiogram

Background Gamma knife radiosurgery (GKRS) remains a critical intervention in the long-term management of arteriovenous malformations (AVMs). For planning a treatment, identification of the nidus is essential, and it is dependent on high-resolution blood flow imaging, usually in the form of a traditional angiogram. The development of dynamic 320-slice computed tomography (CT) angiography has offered a noninvasive alternative to intra-arterial fluoroscopic imaging, and it is capable of providing equivalent temporal resolution. In this study, we describe the feasibility of using four-dimensional CT angiography (4D-CTA) in GKRS planning for AVM treatment and a comparative analysis with a traditional angiogram. Methods A retrospective review was performed on AVM patients treated via GKRS with a 4D-CTA prior to the day of treatment, on the day of treatment, or with a day-of-treatment angiogram. Treatment times, along with total times in the Leksell® coordinate frame G, were obtained from the medical records. The frame-on time was calculated by subtracting the treatment time from the total time starting from application to removal, and the statistical analysis was performed across groups using analysis of variance (ANOVA). All treatments were performed on the Perfexion™ model with a dynamic flow imaging procured via a 320-slice CT scanner or traditional angiography platform. Results Some 27 patients underwent a total of 29 GKRS procedures for AVM treatment at our institution between September 2011 and January 2017. Mean age at the time of treatment was 35.5 (6-65) years, and male:female ratio was 5:4. Some 12 patients had 4D-CTA performed prior to the day of treatment, eight patients had the same CTA completed after frame placement on the day of treatment, while seven patients underwent traditional angiography. The mean frame-on times of each group were 190, 336, and 426 minutes, respectively (p < 0.0001). No procedures were aborted based on the image quality. Conclusions 4D-CTA is an effective tool in identifying the AVM nidus for GKRS planning. These studies can be performed prior to the day of treatment, allowing for a significant reduction in frame-on time and eliminating the risk of angiogram complication on the day of GKRS.

Clinical applications of dynamic CT angiography for intracranial lesions

BACKGROUND

Dynamic CT angiography (dCTA) augments traditional CTA with temporal resolution and has been demonstrated to influence operative planning in skull base surgery.

METHODS

Three hundred twenty-five dynamic CTA cases from a single institution were reviewed for indication of study, findings, and comparison to other modalities of imaging.

RESULTS

The most frequent application of dCTA was pre-operative surgical planning (59.4%); resection of skull base tumors represented the majority of these pre-operative studies (93.3%). It was also used to evaluate new neurological symptoms (20.9%). Of these, the most common symptoms prompting a dCTA study included headache (22.1%) and visual field deficit (11.8%). The most commonly visualized vascular lesions were partial (22.9%) and complete vascular occlusions (9.0%). Dynamic CTA has also been useful in post-operative imaging for vascular malformations (9.5%) and tumors (2.5%). Finally, dCTA was employed to evaluate ambiguous abnormal findings observed on other imaging modalities (7.7%). Cerebral dCTA ruled out inconclusive abnormal vascular findings visualized on other imaging modalities (64.0%) more frequently than it confirmed them (32.0%), and was inconclusive in a singular case (4.0%).

CONCLUSIONS

Cerebral dCTA is an evolving new technology with a diverse spectrum of potential applications. In addition to its role in guiding pre-operative planning for skull base surgical cases, dynamic CTA offers excellent spatial and temporal resolution for assessment of vascular lesions.

Circle of Willis Collateral Flow in Carotid Artery Occlusion Is Depicted by 4D-CTA

BACKGROUND

In case of carotid artery occlusion, the risk and extent of ischemic cerebral damage are highly dependent on the pathways of collateral flow including the anatomy of the circle of Willis. In this report, cases are presented to illustrate that 4-dimensional computed tomography angiography (4D-CTA) can be considered as a noninvasive alternative to digital subtraction angiography for the evaluation of circle of Willis collateral flow.

CASE DESCRIPTION

Five patients with unilateral internal carotid artery (ICA) occlusion underwent 4D-CTA for the evaluation of intracranial hemodynamics. Next to a visual evaluation of 4D-CTA, temporal information was visualized using a normalized color scale on the cerebral vasculature, which enabled quantification of the contrast bolus arrival time. In these patients, 4D-CTA demonstrated dominant middle cerebral artery blood supply on the side of ICA occlusion originating from either the contralateral ICA or posterior circulation via the communicating arteries.

CONCLUSIONS

Temporal dynamics of collateral flow in the circle of Willis can be depicted with 4D-CTA in patients with a unilateral carotid artery occlusion.