DWI lesions after intracranial aneurysm treatment with contour or WEB-does the device matter?

OBJECTIVE: In this study, we report our experience with the occurrence of diffusion-weighted imaging (DWI) lesions following aneurysm treatment with Woven EndoBridge (WEB) device and Contour Neurovascular System in elective settings. We compared both techniques in a retrospective single-center analysis, to investigate whether there are significant differences in the incidence of microemboli depending on the device used. MATERIALS AND METHODS: Sixty-two cases treated with Contour were retrospectively compared with 84 WEB cases. Postinterventional MRI was performed in all patients within five days after the angiographic procedure. Only DWI lesions in the dependent vascular territory of the treated aneurysm were considered. Data on occurrence of DWI lesions, device implantation times as well as device change or repositions maneuvers were compared. RESULTS: A total of 146 patients were included in this study. Postinterventional DWI lesions were detected in 33 of the 62 (53.2%) Contour cases and in 36 of the 84 (42.8%) WEB cases with an average lesion number of 1.70 ± 3.45 in our WEB group and 1.68 ± 2.53 in our Contour cohort. Neither periinterventional device changes nor device reposition maneuvers had a significant impact on the occurrence of DWI lesions. Although four patients experienced transient neurological deterioration, the DWI lesions were not clinically relevant at the time of discharge, as the patients' NIHSS remained stable compared to the preintervention NIHSS in the entire cohort. There was no statistically significant difference between the implantation times of WEB and Contour, although Contour could be implanted slightly faster. CONCLUSION: Aneurysm treatment with WEB or Contour results in a comparable numbers of procedure-related DWI lesions. This effect was consistent after adjustment for other demographic or technical variables.

Non-invasive follow-up for intracranial aneurysms treated with contour neurovascular system-comparison of digital subtraction angiography (DSA) to magnetic resonance imaging (MRI) and spectral computed tomography angiography (CTA) in vitro.

PURPOSE: The contour neurovascular system (CNS) is an intrasaccular flow-disrupting device designed for the treatment of intracranial wide-necked bifurcation aneurysms. Metal artifacts limit magnetic resonance imaging (MRI) accessibility after implantation. The purpose of this in vitro study was to evaluate non-invasive imaging alternatives to digital subtraction angiography (DSA). MATERIAL AND METHODS: Three aneurysms of patients originally treated with CNS were three-dimensional (3D)-printed (one at the basilar tip and two at the middle cerebral artery bifurcation). CNS devices were implanted under fluoroscopic control into the 3D models. Post-implantation two-dimensional-DSA, flat panel computed tomography angiography (CTA), MRI, and spectral CTA were performed. RESULTS: Time of flight angiography and T1 weighted sequences showed large susceptibility artifacts at the detachment zone of the devices. A thin-sliced T2 weighted sequence in cross-sectional orientation to the aneurysm allowed visualization of the aneurysm dome, but the aneurysm neck and parent vessel could not be assessed. Focused spectral CTA, especially a 40 keV reconstruction with a metal artifact reduction algorithm (orthopedic metal artifact reduction (OMAR)), showed only minor artifacts at the detachment zone. This approach achieved a very similar result to DSA and flat panel computed tomography, enabling the assessment of the device structure, aneurysm perfusion, and parent vessel perfusion. DISCUSSION AND CONCLUSION: For non-invasive follow-up of CNS, focused 40 keV CTA with OMAR seems to be a valuable option. MRI can be valuable for larger aneurysms to assess the aneurysm dome, but was not suitable for evaluating the parent vessels and aneurysm neck after CNS implantation in this study.

Detecting optic nerve lesions in multiple sclerosis patients with a 1,5 T MRI: Evaluation of a 3D DIR sequence compared to a 2D STIR sequence.

OBJECTIVES: Optic neuritis is a common clinical presentation in patients suffering from multiple sclerosis (MS). Even though optic neuritis is not part of the MS diagnostic criteria, the diagnosis and consideration of differential diagnoses are important in clinical routine. For the evaluation of the optic nerves with MRI, T2-weighted images with fat suppression, known as short tau inversion recovery sequences (STIR), are often used. Besides that, double inversion recovery (DIR) sequences are being used increasingly in MS patients, especially to determine cortical lesions. The Aim of this study was to evaluate the 3D-DIR for the detection of lesions in the optic nerves in MS patients. METHODS: MR examinations of 45 MS-patients containing both STIR and DIR images were independently assessed by two neuroradiologic experienced radiologists, blinded to clinical data. A third neuroradiologic, an experienced radiologist, evaluated the images together, also considering clinical data. These results were considered ground truth and statistically compared to the results of the single readings. To objectify our findings, ROI measurements of affected and unaffected optic nerve segments were made, and a contrast ratio (CR) was calculated. RESULT: DIR images are statistically equivalent to STIR images concerning the detection of lesions in the optic nerve (p < 0.001). The sensitivity of DIR images (84.7 %) and STIR images (77 %), as well as the specificity (92.2 % and 91.2 %), are comparable. The interrater reliability was substantial for both sequences (κ = 0,73) as well as separated for the STIR images (κ = 0.744) and the DIR images (κ = 0.707). The objective analysis revealed significantly higher CRs in DIR images (p < 0.001). CONCLUSION: 3D DIR images showed similar sensitivity and specificity for detecting optic nerve lesions in comparison to dedicated 2D images of the optic nerve. When 3D DIR images are part of the routine scan protocol for evaluating MS patients, additional 2D imaging of the optic nerve is no longer necessary.

AI supported detection of cerebral multiple sclerosis lesions decreases radiologic reporting times.

PURPOSE: Multiple Sclerosis (MS) is a common autoimmune disease of the central nervous system. MRI plays a crucial role in diagnosing as well as in disease and treatment monitoring. Therefore, evaluation of cerebral MRI of MS patients is part of daily clinical routine. A growing number of companies offer commercial software to support the reporting with automated lesion detection. Aim of this study was to evaluate the effect of such a software with AI supported lesion detection to the radiologic reporting. METHOD: Four radiologist each counted MS-lesions in MRI examinations of 50 patients separated by the locations periventricular, cortical/juxtacortical, infrantentorial and unspecific white matter. After at least six weeks they repeated the evaluation, this time using the AI based software mdbrain for lesion detection. In both settings the required time was documented. Further the radiologists evaluated follow-up MRI of 50 MS-patients concerning new and enlarging lesions in the same manner. RESULTS: To determine the lesion-load the average reporting time decreased from 286.85 sec to 196.34 sec (p > 0.001). For the evaluation of the follow-up images the reporting time dropped from 196.17 sec to 120.87 sec (p < 0.001). The interrater reliabilities showed no significant differences for the determination of lesion-load (0.83 without vs. 0.8 with software support) and for the detection of new/enlarged lesions (0.92 without vs. 0.82 with software support). CONCLUSION: For the evaluation of MR images of MS patients, an AI-based support for image-interpretation can significantly decreases reporting times.

Automatic lesion detection at Multiple Sclerosis patients - Comparison of 2D- and 3D-FLAIR-datasets.

BACKGROUND: Multiple Sclerosis (MS) is a common autoimmune inflammatory disease of the central nervous system (CNS). Magnetic Resonance Imaging (MRI) allows a sensitive assessment of the CNS and is established for diagnostic, prognostic and (therapy-) monitoring purposes. Especially lesion counting in T2- or Fluid Attenuated Inversion Recovery (FLAIR)-weighted images plays a decisive role in clinical routine. Software-packages allowing an automatic evaluation of image data are increasingly established aiming a faster and improved workflow. These programs allow e.g. the counting, spatial attribution and volumetry of MS-lesions in FLAIR-weighted images. Research has shown that 3D-FLAIR-sequences are superior to 2D-FLAIR-sequences in visual evaluation of lesion burden in MS. An influence on the automatic analysis is expectable but not yet systematically studied. This work will therefore investigate the influence of 2D- and 3D datasets on the results of an automatic assessment. MATERIAL AND METHODS: In this prospective study, 80 Multiple Sclerosis patients underwent a clinically indicated routine MRI examination. The clinical routine protocol already including a 3D-FLAIR sequence was adapted by an additional 2D-FLAIR sequence also conform to the 2021 MAGNIMS-CMSCNAIMS consensus recommendations. To obtain a quantitative analysis for assessment of amount, dissemination and volume of the lesions, the acquired MR images were post-processed using the CE-certified Software mdbrain (mediaire, Berlin, Germany). The resulting data were statistically analysed using the paired t-test for normally distributed data and the Wilcoxon-signed-rank-test for not normally distributed data respectively. Demographic data and data such as the subtype, duration, severity and therapy of the disease were collected, pseudonymized and evaluated. RESULTS: There is a significant difference concerning the total number and lesion volume with more lesions being detected (2D: 29.7, +/- 20.22 sd; 3D: 40.1 +/- 31.67 sd; p < 0.0001) but lower total volume (2D: 6.24 +/- 6.11 sd; 3D: 5.39 +/- 6.37 sd; p < 0.0001) when using the 3D- sequence. Especially significantly more small lesions in the unspecific white matter and infratentorial region were detected by using the 3D-FLAIR sequence (p < 0.0001) compared to the 2D-FLAIR image. Main reason for the lower total volume in the 3D-FLAIR sequence was the calculated volume for periventricular lesions which was significantly beneath the calculated volume from the 2D-FLAIR sequence (p < 0.0001). CONCLUSION: Automatic lesion counting and volumetry is feasible with both 2D- and 3D-weightend FLAIR images. Still, it leads to partly significant differences even between two sequences that both are conform to the 2021 MAGNIMS-CMSCNAIMS consensus recommendations. This study contributes valuable insights into the impact of using different input data from the same patient for automated MS lesion evaluation.

Assessment of intracranial aneurysm neck deformation after contour deployment.

PURPOSE: The contour neurovascular system (CNS) is a novel device to treat intracranial wide-necked bifurcation aneurysms, with few studies assessing its long-term effects. Particularly its impact on aneurysm morphology has not been explored yet. We present a preliminary study to explore this impact for the first time, focusing on the neck curve and ostium of the aneurysm. METHODS: We investigated seven aneurysms treated with the CNS to assess ostium deformation after CNS deployment by comparing models extracted from in vivo medical pre-treatment and follow-up scans via morphological analysis. Time between pre- and follow-up scans was ten months on average. Size and shape indices like area, neck diameter, ellipticity index, undulation index, and more were assessed. RESULTS: Ostium size was reduced after treatment. On average, ostium area was reduced at a rate of - 0.58 (± 4.88) mm2 per year, from 15.52 (± 3.51) mm2 to 13.30 (± 2.27) mm2, and ostium width from 5.01 (± 0.54) mm to 4.49 (± 0.45) mm, with an average reduction of - 0.59 (± 0.87) mm. This shrinking positively correlated with time passing. Shape deformation was low, though notably mean ellipticity index was reduced by 0.06 (± 0.15) on average, indicating ostia were less elongated after treatment. CONCLUSION: We interpret the shrinking of the ostium as part of the healing process. Shape changes were found to be small enough to conclude no shape deformation of the ostium from CNS deployment, but the analysis of more cases with more parameters and information is necessary.

Perivascular spaces and where to find them - MR imaging and evaluation methods. / Perivaskuläre Räume und wo sie zu finden sind ­ MR-Bildgebung und Auswertungsmethoden.

BACKGROUND: Perivascular spaces (synonym: Virchow-Robin spaces) were first described over 150 years ago. They are defined as the fluid-filled spaces surrounding the small penetrating cerebral vessels. They gained growing scientific interest especially with the postulation of the so-called glymphatic system and their possible role in neurodegenerative and neuroinflammatory diseases. METHODS: PubMed was used for a systematic search with a focus on literature regarding MRI imaging and evaluation methods of perivascular spaces. Studies on human in-vivo imaging were included with a focus on studies involving healthy populations. No time frame was set. The nomenclature in the literature is very heterogeneous with terms like "large", "dilated", "enlarged" perivascular spaces whereas borders and definitions often remain unclear. This work generally talks about perivascular spaces. RESULTS: This review article discusses the morphologic MRI characteristics in different sequences. With the continual improvement of image quality, more and tinier structures can be depicted in detail. Visual analysis and semi or fully automated segmentation methods are briefly discussed. CONCLUSION: If they are looked for, perivascular spaces are apparent in basically every cranial MRI examination. Their physiologic or pathologic value is still under debate. KEY POINTS: · Perivascular spaces can be seen in basically every cranial MRI examination.. · Primarily T2-weighend sequences are used for visual analysis. Additional sequences are helpful for distinction from their differential diagnoses.. · There are promising approaches for the semi or fully automated segmentation of perivascular spaces with the possibility to collect more quantitative parameters.. CITATION FORMAT: · Seehafer S, Larsen N, Aludin S et al. Perivascular spaces and where to find them - MRI imaging and evaluation methods. Fortschr Röntgenstr 2024; 196: 1029 - 1036.

Contour device implantation for treatment of intracranial aneurysms in the basilar tip.

INTRODUCTION: Treatment of basilar apex aneurysms will remain challenging regarding the nobility of the parent vessel and their often wide-necked configuration. With endovascular techniques being the treatment approach of choice, novel intrasaccular flow-disruption devices constitute an endovascular embolization option. In this research, we report our experiences in embolizing basilar tip aneurysms with the novel Contour device. MATERIAL AND METHODS: Retrospective analysis of eight patients after Contour implantation into a basilar apex aneurysm. Periprocedural data on intervention times, radiation dose, procedural success and complications were gathered. All patients received follow-up digital subtraction angiography after six months. Further follow-up examination results were analysed given their availability. RESULTS: Contour implantation was successful in all patients. The mean device instrumentation time was 18.8 ± 7.7 min with a mean full intervention time of 100 ± 65.8 min. The mean full procedure radiation dose was 1917 (421-5107) cGy/cm2. After six months, six aneurysms were occluded (Raymond Roy Scale (RRS) 1/2), one showed perfusion inside the device (RRS 3a) and one patient had undergone reintervention due to progression. The aneurysm with constant perfusion at six months was seen to be occluded after 24 months. CONCLUSION: Contour device implantation is a promising feasible alternative endovascular method for embolization of intracranial aneurysms located in the basilar tip with short intervention times and low radiation dosages. Short- and medium-term follow-ups show promising results concerning aneurysm occlusion and reinterventions, however further research is needed to show long-term stability.

In vitro and in silico assessment of flow modulation after deploying the Contour Neurovascular System in intracranial aneurysm models.

BACKGROUND: The novel Contour Neurovascular System (Contour) has been reported to be efficient and safe for the treatment of intracranial, wide-necked bifurcation aneurysms. Flow in the aneurysm and posterior cerebral arteries (PCAs) after Contour deployment has not been analyzed in detail yet. However, this information is crucial for predicting aneurysm treatment outcomes. METHODS: Time-resolved three-dimensional velocity maps in 14 combinations of patient-based basilar tip aneurysm models with and without Contour devices (sizes between 5 and 14 mm) were analyzed using four-dimensionsal (4D) flow MRI and numerical/image-based flow simulations. A complex virtual processing pipeline was developed to mimic the experimental shape and position of the Contour together with the simulations. RESULTS: On average, the Contour significantly reduced intra-aneurysmal flow velocity by 67% (mean w/ = 0.03m/s; mean w/o = 0.12m/s; p-value=0.002), and the time-averaged wall shear stress by more than 87% (mean w/ = 0.17Pa; mean w/o = 1.35Pa; p-value=0.002), as observed by numerical simulations. Furthermore, a significant reduction in flow (P<0.01) was confirmed by the neck inflow rate, kinetic energy, and inflow concentration index after Contour deployment. Notably, device size has a stronger effect on reducing flow than device positioning. However, positioning affected flow in the PCAs, while being robust in effectively reducing flow. CONCLUSIONS: This study showed the high efficacy of the Contour device in reducing flow within aneurysms regardless of the exact position. However, we observed an effect on the flow in PCAs, which needs to be investigated further.

Intra-cranial aneurysm treatment with contour or WEB - a single center comparison of intervention times and learning curves.

BACKGROUND AND PURPOSE: Treating aneurysms with intra-saccular flow disruption is a feasible alternative to coil-embolization. Besides the established WEB device, the novel Contour Neurovascular System has emerged as a potentially easier alternative regarding sizing and deployment. We report the learning curve experienced at our center from the first 48 patients treated with Contour and compared it with 48 consecutive WEB cases. METHODS: Both groups were compared concerning intervention time, sizing failures leading to device changes and radiation dose. Additionally, we analyzed potential learning effects by comparing the first 24 Contour cases with our last 24 Contour cases and WEB cases respectively. RESULTS: Patient demographics, acute vs. incidental cases and aneurysm localization were comparable in both groups. The deployment time was faster in our 48 Contour cases (median: 22.0 ± 17.0 min), than in the WEB group (median: 27.5 ± 24.0 min). Total intervention time was similar for Contour (median: 68.0 ± 46.9 min) and WEB cases (median: 69.0 ± 38.0 min). Device implantation times in our WEB cases were slightly shorter in the later cases (median: 25.5 ± 24.1 min) than in the earlier (median: 28.0 ± 24.4 min) cases. In the Contour cohort, deployment times were similar for the first 24 cases (median: 22.0 ± 14.5 min) and the final 24 (median: 22.0 ± 19.4 min). Radiation dose was lower in the Contour group (1469.0 ± 1718 mGy*cm2 vs. 1788.0 ± 1506 mGy*cm2 using the WEB device). Less intra-procedural device changes were performed in the Contour cohort (6 of 48 cases, 12.5%), than in the WEB group (8 of 48 cases, 16.7%). CONCLUSION: Aneurysm occlusion times and consequently radiation doses, as well as the amount of device changes were lower in the Contour group. Occlusion times did not differ in the first and last 24 Contour cases, leading to the assumption that the handling of Contour does not require extended training. A short training effect in occlusion times was noted, however, between the first and last WEB cases as shorter procedure times were seen in the latter cases.

Spectral cardiac CT in acute stroke patients.

Cardiac CT obtained in acute ischemic stroke patients can facilitate timely detection of cardiac sources of embolism and guide secondary prevention strategies. Spectral CT exploiting the simultaneous acquisition of separate higher-energy and lower-energy photon spectrum datasets has the potential to improve contrast between thrombi and cardiac structures. This study aimed to investigate the diagnostic value of spectral cardiac CT compared to conventional CT for the detection of cardiac thrombi in acute stroke patients. Patients with acute ischemic stroke undergoing spectral cardiac CT were retrospectively included. Conventional CT images, virtual 55 keV monoenergetic (monoE55), z-effective (zeff), and iodine density images were evaluated for the presence of thrombi. Diagnostic certainty was rated on a 5-point Likert scale. Contrast ratios were calculated for all reconstructions. 63 patients with 20 thrombi were included. Four thrombi were missed on conventional images but detected on spectral reconstructions. MonoE55 achieved the highest scores for diagnostic certainty. Contrast ratios were highest on iodine density images, followed by monoE55, conventional and zeff (p < 0.005). Spectral cardiac CT adds diagnostic benefit for the detection of intra-cardiac thrombi in acute ischemic stroke patients compared to conventional CT.

Contour device implantation versus coil embolization for treatment of narrow neck intracranial aneurysms.

The novel Contour device is an intrasaccular flow disruption device designed for treatment of intracranial wide-neck bifurcation aneurysms. Outside its original purpose, Contour implantation can be used to treat aneurysms with a higher dome-to-neck ratio which would be suitable for conventional unassisted coil embolization. We compared both techniques in a retrospective single-center analysis. A total of 42 aneurysms from 42 patients with a dome-to-neck ratio of 1.6 or higher were included in this study. Data on technical success, implantation times, radiation dosages, procedural complications, reinterventions and recurrences were gathered and compared. Technical success was achieved in all cases with both techniques. Aneurysm embolization was achieved significantly faster in the Contour group compared to coiling (Overall p = 0.0002; r = 0.580; acute setting: p = 0.005, r = 0.531; elective setting: p = 0.002, r = 0.607). Significantly less radiation dosage was applied in the Contour group (Overall p = 0.002; r = 0.478; acute group p = 0.006; r = 0.552; elective group p = 0.045; r = 0.397). The number of complications was higher in the coiling group compared to the Contour group (Coiling 7/21 (33,3%); Contour 3/21 (14.3%). There was a higher rate of reinterventions in the coiling group (7.6% vs 21.4%). Outside its original intention, the Contour device seems to be a safe and fast alternative to coil embolization for the treatment of narrow-neck-aneurysms.

The effect of the size of the new contour neurovascular device for altering intraaneurysmal flow.

BACKGROUND: Recently, a novel intrasaccular device (contour neurovascular system, contour) was introduced to treat intracranial aneurysms. Contour is placed at thе aneurysm neck and reduces the intraaneurysmal blood inflow. Contour comes in a range of sizes to target different aneurysms. The efficiency of altering flow with contour and the effect of device size have not yet been investigated. Therefore, we studied the effect of the device size with patient-based aneurysm models using 2D digital subtraction angiography (DSA). METHODS: Three patient-based aneurysm models with necks ranging from 2.7 to 9.7 mm were produced, providing standardized testing conditions. Contours with diameters of 5, 11, and 14 mm were implanted into the models, four of each size. 2D DSA images were acquired before and after implanting contour (15 frames/s, manual contrast injection). After injecting angiographic contrast agent, the DSA signal was recorded over time to calculate the contrast washout time (WOT), which is a measure of flow diversion efficiency. RESULTS: All contour devices caused contrast agent stasis and increased WOT in aneurysm sac (p-value = 0.0005). The median relative WOT was largest for 5-mm contour (6.6 ± 3.2) and similar for 11-mm contour (3.4 ± 2.6) and 14-mm contour (3.2 ± 3.8). The implantation procedure might affect WOT values even for contours of the same size; the overall relative WOT ranged between 1.5 and 10.89. CONCLUSION: The 5-mm contour showed the longest WOT value in our study, while no apparent difference between 11-mm contour and 14-mm contour was found.

Deep learning-based semantic vessel graph extraction for intracranial aneurysm rupture risk management.

PURPOSE: Intracranial aneurysms are vascular deformations in the brain which are complicated to treat. In clinical routines, the risk assessment of intracranial aneurysm rupture is simplified and might be unreliable, especially for patients with multiple aneurysms. Clinical research proposed more advanced analysis of intracranial aneurysm, but requires many complex preprocessing steps. Advanced tools for automatic aneurysm analysis are needed to transfer current research into clinical routine. METHODS: We propose a pipeline for intracranial aneurysm analysis using deep learning-based mesh segmentation, automatic centerline and outlet detection and automatic generation of a semantic vessel graph. We use the semantic vessel graph for morphological analysis and an automatic rupture state classification. RESULTS: The deep learning-based mesh segmentation can be successfully applied to aneurysm surface meshes. With the subsequent semantic graph extraction, additional morphological parameters can be extracted that take the whole vascular domain into account. The vessels near ruptured aneurysms had a slightly higher average torsion and curvature compared to vessels near unruptured aneurysms. The 3D surface models can be further employed for rupture state classification which achieves an accuracy of 83.3%. CONCLUSION: The presented pipeline addresses several aspects of current research and can be used for aneurysm analysis with minimal user effort. The semantic graph representation with automatic separation of the aneurysm from the parent vessel is advantageous for morphological and hemodynamical parameter extraction and has great potential for deep learning-based rupture state classification.

Geometric uncertainty in intracranial aneurysm rupture status discrimination: a two-site retrospective study.

OBJECTIVES: Assessing the risk associated with unruptured intracranial aneurysms (IAs) is essential in clinical decision making. Several geometric risk parameters have been proposed for this purpose. However, performance of these parameters has been inconsistent. This study evaluates the performance and robustness of geometric risk parameters on two datasets and compare it to the uncertainty inherent in assessing these parameters and quantifies interparameter correlations. METHODS: Two datasets containing 244 ruptured and unruptured IA geometries from 178 patients were retrospectively analysed. IAs were stratified by anatomical region, based on the PHASES score locations. 37 geometric risk parameters representing four groups (size, neck, non-dimensional, and curvature parameters) were assessed. Analysis included standardised absolute group differences (SADs) between ruptured and unruptured IAs, ratios of SAD to median relative uncertainty (MRU) associated with the parameters, and interparameter correlation. RESULTS: The ratio of SAD to MRU was lower for higher dimensional size parameters (ie, areas and volumes) than for one-dimensional size parameters. Non-dimensional size parameters performed comparatively well with regard to SAD and MRU. SAD was higher in the posterior anatomical region. Correlation of parameters was strongest within parameter (sub)groups and between size and curvature parameters, while anatomical region did not strongly affect correlation patterns. CONCLUSION: Non-dimensional parameters and few parameters from other groups were comparatively robust, suggesting that they might generalise better to other datasets. The data on discriminative performance and interparameter correlations presented in this study may aid in developing and choosing robust geometric parameters for use in rupture risk models.

Influence of Spatial Resolution and Compressed SENSE Acceleration Factor on Flow Quantification with 4D Flow MRI at 3 Tesla.

Four-dimensional (4D) flow MRI allows quantifying flow in blood vessels-non invasively and in vivo. The clinical use of 4D flow MRI in small vessels, however, is hampered by long examination times and limited spatial resolution. Compressed SENSE (CS-SENSE) is a technique that can accelerate 4D flow dramatically. Here, we investigated the effect of spatial resolution and CS acceleration on flow measurements by using 4D flow MRI in small vessels in vitro at 3 T. We compared the flow in silicon tubes (inner diameters of 2, 3, 4, and 5 mm) measured with 4D flow MRI, accelerated with four CS factors (CS = 2.5, 4.5, 6.5, and 13) and three voxel sizes (0.5, 1, and 1.5 mm3) to 2D flow MRI and a flow sensor. Additionally, the velocity field in an aneurysm model acquired with 4D flow MRI was compared to the one simulated with computational fluid dynamics (CFD). A strong correlation was observed between flow sensor, 2D flow MRI, and 4D flow MRI (rho > 0.94). The use of fewer than seven voxels per vessel diameter (nROI) resulted in an overestimation of flow in more than 5% of flow measured with 2D flow MRI. A negative correlation (rho = -0.81) between flow error and nROI were found for CS = 2.5 and 4.5. No statistically significant impact of CS factor on differences in flow rates was observed. However, a trend of increased flow error with increased CS factor was observed. In an aneurysm model, the peak velocity and stagnation zone were detected by CFD and all 4D flow MRI variants. The velocity difference error in the aneurysm sac did not exceed 11% for CS = 4.5 in comparison to CS = 2.5 for all spatial resolutions. Therefore, CS factors from 2.5-4.5 can appear suitable to improve spatial or temporal resolution for accurate quantification of flow rate and velocity. We encourage reporting the number of voxels per vessel diameter to standardize 4D flow MRI protocols.

Luminal enhancement in intracranial aneurysms: fact or feature?-A quantitative multimodal flow analysis.

PURPOSE: Intracranial aneurysm (IA) wall enhancement on post-contrast vessel wall magnetic resonance imaging (VW-MRI) is assumed to be a biomarker for vessel wall inflammation and aneurysm instability. However, the exact factors contributing to enhancement are not yet clarified. This study investigates the relationship between luminal enhancement and intra-aneurysmal flow behaviour to assess the suitability of VW-MRI as a surrogate method for determining quantitative and qualitative flow behaviour in the aneurysm sac. METHODS: VW-MRI signal is measured in the lumen of three patient-specific IA flow models and compared with the intra-aneurysmal flow fields obtained using phase-contrast magnetic resonance imaging (PC-MRI) and computational fluid dynamics (CFD). The IA flow models were supplied with two different time-varying flow regimes. RESULTS: Overall, the velocity fields acquired using PC-MRI or CFD were in good agreement with the VW-MRI enhancement patterns. Generally, the regions with slow-flowing blood show higher VW-MRI signal intensities, whereas high flow leads to a suppression of the signal. For all aneurysm models, a signal value above three was associated with velocity values below three cm/s. CONCLUSION: Regions with lower enhancements have been correlated with the slow and high flow at the same time. Thus, further factors like flow complexity and stability can contribute to flow suppression in addition to the flow magnitude. Nevertheless, VW-MRI can qualitatively assess intra-aneurysmal flow phenomena and estimate the velocity range present in the corresponding region.

Diagnostic Accuracy of Dual-Layer Spectral CT Using Electron Density Images to Detect Post-Traumatic Prevertebral Hematoma of the Cervical Spine.

PURPOSE: To investigate the diagnostic value of dual-layer spectral detector computed tomography (SDCT) in detecting posttraumatic prevertebral hematoma of the cervical spine by including electron density images. METHODS: 38 patients with post-traumatic imaging of the cervical spine were included in this study and received both SDCT and MRI examinations. MRI was set as the reference and combined conventional/electron density (C + ED) images were compared to conventional CT (CCT) images alone. RESULTS: A total of 18 prevertebral hematomas were identified. Reader 1 identified 14 of 18 and reader 2 15 of 18 prevertebral hematomas by using C + ED reconstructions. Readers 1 and 2 detected 6 and 9 of 18 hematomas on CCT, respectively. CCT showed a sensitivity of 33-50 % and a specificity of 75-80 %, while for C + ED reconstructed images the sensitivity was 77-83 % and the specificity was 85-90 %. Accuracy increased from 55-66 % to 84 % by using C + ED images. The minimum thickness for detecting hematoma on C + ED images was 3 mm. The sizes of prevertebral hematoma on CCT/C + ED were not significantly under- or overestimated compared to the MRI reference. There was a significant difference between the two readers for measuring hematoma sizes on CCT (p = 0.04). Readers showed an excellent inter-rater reliability (kappa = 0.82) for C + ED images and a moderative inter-rater reliability (kappa = 0.44) for CCT. CONCLUSION: With SDCT, the diagnostic accuracy for detecting post-traumatic prevertebral hematoma is improved by using combined conventional and electron density reconstructions compared to conventional images alone. KEY POINTS: · SDCT has a high potential for detecting post-traumatic prevertebral hematomas of the cervical spine by using combined conventional and electron density images.. · Prevertebral hematomas with a thickness of less than 3 mm cannot be reliably identified by SDCT.. · There is no discernible value of conventional SDCT images for diagnosing prevertebral hematoma.. CITATION FORMAT: · Sedaghat S, Langguth P, Larsen N et al. Diagnostic Accuracy of Dual-Layer Spectral CT Using Electron Density Images to Detect Post-Traumatic Prevertebral Hematoma of the Cervical Spine. Fortschr Röntgenstr 2021; 193: 1445 - 1450.