Imaging Intracranial Aneurysms in the Endovascular Era: Surveillance and Posttreatment Follow-up

CTA-based deep-learning integrated model for identifying irregular shape and aneurysm size of unruptured intracranial aneurysms

BACKGROUND

Artificial intelligence can help to identify irregular shapes and sizes, crucial for managing unruptured intracranial aneurysms (UIAs). However, existing artificial intelligence tools lack reliable classification of UIA shape irregularity and validation against gold-standard three-dimensional rotational angiography (3DRA). This study aimed to develop and validate a deep-learning model using computed tomography angiography (CTA) for classifying irregular shapes and measuring UIA size.

METHODS

CTA and 3DRA of UIA patients from a referral hospital were included as a derivation set, with images from multiple medical centers as an external test set. Senior investigators manually measured irregular shape and aneurysm size on 3DRA as the ground truth. Convolutional neural network (CNN) models were employed to develop the CTA-based model for irregular shape classification and size measurement. Model performance for UIA size and irregular shape classification was evaluated by intraclass correlation coefficient (ICC) and area under the curve (AUC), respectively. Junior clinicians' performance in irregular shape classification was compared before and after using the model.

RESULTS

The derivation set included CTA images from 307 patients with 365 UIAs. The test set included 305 patients with 350 UIAs. The AUC for irregular shape classification of this model in the test set was 0.87, and the ICC of aneurysm size measurement was 0.92, compared with 3DRA. With the model's help, junior clinicians' performance for irregular shape classification was significantly improved (AUC 0.86 before vs 0.97 after, P<0.001).

CONCLUSION

This study provided a deep-learning model based on CTA for irregular shape classification and size measurement of UIAs with high accuracy and external validity. The model can be used to improve reader performance.

Ultra-high resolution CT angiography for the assessment of intracranial stents and flow diverters using photon counting detector CT

BACKGROUND

The patency of intracranial stents may not be reliably assessed with either CT angiography or MR angiography due to imaging artifacts. We investigated the potential of ultra-high resolution CT angiography using a photon counting detector (PCD) CT to address this limitation by optimizing scanning and reconstruction parameters.

METHODS

A phantom with different flow diverters was used to optimize PCD-CT reconstruction parameters, followed by imaging of 14 patients with intracranial stents using PCD-CT. Images were reconstructed using three kernels based on the phantom results (Hv56, Hv64, and Hv72; Hv=head vascular) and one kernel to virtually match the resolution of standard CT angiography (Hv40). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements were calculated. Subjective image quality and diagnostic confidence (DC) were assessed using a five point visual grading scale (5=best, 1=worst) and a three point grading scale (1=best, 3=worst), respectively, by two independent neuroradiologists.

RESULTS

Phantom images demonstrated the highest image quality across dose levels for 0.2 mm reconstructions with Hv56 (4.5), Hv64 (5), and Hv72 (5). In patient images, SNR and CNR decreased significantly with increasing kernel sharpness compared with control parameters. All reconstructions showed significantly higher image quality and DC compared with the control reconstruction with Hv40 kernel (P<0.001), with both image quality and DC being highest with Hv64 (0.2 mm) and Hv72 (0.2 mm) reconstructions.

CONCLUSION

Ultra-high resolution PDC-CT angiography provides excellent visualization of intracranial stents, with optimal reconstructions using the Hv64 and the Hv72 kernels at 0.2 mm.

REGISTRATION

BASEC 2021-00343.

Impact of Patient Head Posture on Lens Radiation Exposure During Cerebral Angiography

BACKGROUND AND PURPOSE

Cerebral angiography remains crucial for detailed characterization and preoperative assessments for intracranial aneurysm. Despite its diagnostic importance, cerebral angiography poses challenges due to its invasiveness, the risk of neurologic complications, and radiation exposure. To investigate the impact of head posture on lens radiation exposure during cerebral angiography, this study focused on the correlation between radiation doses to the eye lens, head flexion angles, and head size.

MATERIALS AND METHODS

A retrospective analysis was performed on 20 patients who underwent cerebral angiography for unruptured intracranial aneurysms between October and November 2022. Radiation doses to the lens, which were measured in a prior prospective study by using photoluminescent glass dosimeters, were analyzed alongside head flexion angles, anterior-posterior (AP) head diameters, and kerma-area product (KAP) to evaluate their correlation with lens radiation exposure. The lateral radiation source is located on the left side of the patients.

RESULTS

The cohort consisted of 20 patients (60% women, mean age: 62.3 ± 9.9 years). The radiation dose to the left eye (the eye closer to the x-ray source) was 2.8 times higher than that to the right eye (9.18 ± 3.31 mGy versus 3.3 ± 0.60 mGy, P < .001). A strong positive correlation was observed between the left eye lens dose and head flexion angle (R = 0.815, P < .001). While the AP head diameter correlated significantly with the flexion angle, it showed no significant correlation with lens dose. The KAP was inversely correlated with both the left lens dose (R = -0.597, P = .005) and the flexion angle (R = -0.689, P < .001).

CONCLUSIONS

Our findings underscore the meaningful impact of head posture on lens radiation exposure during cerebral angiography. Adjusting head positioning may provide a practical approach to reduce radiation exposure to the lens. Furthermore, it is worth noting that the left lens received more radiation than the right, likely due to the x-ray source being on the left side of the patient.

Endovascular treatment of high-flow carotid-cavernous fistula secondary to rupture of a carotid-cavernous aneurysm post-flow diverter stent placement

Carotid-cavernous aneurysms (CCAs) have the potential for growth, and their risk of rupture can lead to severe complications. Treatment is typically recommended to prevent these complications, with endovascular therapy being the preferred approach due to the challenging surgical access. This case presents a rare instance of rupture of a CCA that had been previously treated with a flow-diverting stent, which resulted in the development of a carotid-cavernous fistula, requiring venous access endovascular treatment. Our patient experienced persistent neurological deficits following treatment, specifically paralysis of the IV cranial nerve and palpebral ptosis, underscoring the complex nature of such cases and the potential for lasting complications despite intervention.

Special Considerations for Cross-Sectional Imaging in the Child with Neurovascular Disease

Pediatric neurovascular diseases are a complex group of disorders associated with significant morbidity and mortality. Given their heterogeneous clinical manifestations, ranging from emergent presentations (eg, acute neurologic deficits) to chronic neurocognitive or developmental issues, cross-sectional imaging modalities play a key role in accurate diagnosis and direct further management. However, imaging pediatric patients is associated with logistical and technical issues. This article provides an overview of the cross-sectional findings of common pediatric neurovascular diseases and discusses the imaging techniques used for their diagnosis.

Aneurysmal Wall Enhancement of Non-Ruptured Intracranial Aneurysms after Endovascular Treatment Correlates with Higher Aneurysm Reperfusion Rates, but Only in Large Aneurysms

INTRODUCTION

Aneurysmal wall enhancement (AWE) of non-ruptured sacular intracranial aneurysms (IA) after endovascular treatment (ET) is a frequently observed imaging finding using AWE-sequences in brain magnetic resonance imaging (MRI). So far, its value remains unclear. We aimed to investigate the effect of AWE on aneurysm reperfusion rates in a longitudinal cohort.

METHODS

This is a retrospective MRI study over the timespan of up to 5 years, assessing the correlation of increased AWE of non-ruptured IAs and events of aneurysm reperfusion and retreatment, PHASES Score and grade of AWE. T1 SPACE fat saturation (FS) and T1 SE FS blood suppression sequences after contrast administration were used for visual interpretation of increased AWE. The IAs' sizes were assessed via the biggest diameter. The grade of enhancement was defined in a grading system from grade 1 to grade 3.

RESULTS

127 consecutive non ruptured IA-patients (58.9 ± 9.0 years, 94 female, 33 male) who underwent elective aneurysm occlusion were included. AWE was observed in 40.2% of patients (51/127) after ET, 6 patients already showed AWE before treatment. In large IAs (which were defined as a single maximum diameter of over 7.5 mm), AWE was significantly associated with aneurysm reperfusion in contrast to large aneurysm without AWE). All grades of AWE were significantly associated with reperfusion.

CONCLUSIONS

Our data suggests that in patients with initially large IAs, AWE is correlated with aneurysm reperfusion.

Intracranial cerebrovascular lesions on T2-weighted magnetic resonance imaging

Magnetic resonance imaging (MRI) of the brain has been implemented to evaluate multiple intracranial pathologies. Non-contrast T2-weighted images are a routinely acquired sequence in almost all neuroimaging protocols. It is not uncommon to encounter various cerebrovascular lesions incidentally on brain imaging. Neuroradiologists should evaluate the routine T2-weighted images for incidental cerebrovascular lesions, irrespective of the primary indication of the study. Vascular structures typically demonstrate a low signal flow-void on the T2-weighted images. In our experience, large cerebrovascular abnormalities are easily visible to a typical neuroradiologist. In this article, we present the spectrum of the characteristic imaging appearance of various intracranial cerebrovascular lesions on routine non-contrast T2-weighted MRI. These include aneurysm, arteriovenous malformation, arterial occlusion, capillary telangiectasia, cavernous malformation, dural arteriovenous fistula, moyamoya, proliferative angiopathy, and vein of Galen malformation.