Postinterventional Assessment after Stent and Flow-Diverter Implantation Using CT: Influence of Spectral Image Reconstructions and Different Device Types

BACKGROUND AND PURPOSE

CTA provides a noninvasive alternative technique to DSA in the follow-up after endovascular aneurysm treatment to evaluate aneurysm occlusion and exclude intraluminal narrowing after stent or flow-diverter implantation; however, assessability may be impeded by stent material artifacts. The objective of this in vitro study was to compare the visual assessability of different conventional stents and flow diverters as well as different reconstructions of dual-layer CT images.

MATERIALS AND METHODS

Four conventional intracranial stents and 4 flow diverters were implanted in identical aneurysm phantoms. Conventional and monoenergetic images (40, 50, 60, 90, 120, 180 keV) were acquired to evaluate attenuation alteration, visible lumen diameter, and SNR. Image quality was rated subjectively by 2 independent radiologists using a 4-point Likert scale.

RESULTS

Low kiloelectron volt (40-60 keV) monoenergetic reconstructions showed an improved SNR and an improved lumen density ratio compared with high kiloelectron volt reconstructions (90-180 keV) and conventional reconstructions, however without reaching significance compared with the latter. Assessment of the adjacent aneurysm and subjective evaluation was not affected by the imaging technique and stent type. Artifact susceptibility varied with the device used and increased among flow diverters.

CONCLUSIONS

Low kiloelectron volt reconstructions improved the assessment of the stent lumen in comparison with high kiloelectron volt reconstructions. No significant improvement in image quality could be shown compared with conventional images. For some devices, iodine-specific reconstructions led to severe artifacts and are therefore not recommended. There was no relevant improvement in the assessability of the adjacent aneurysm.

Development of a skull phantom for the assessment of implant X-ray visibility

The paper presents the development and test of a skull phantom, which can be used for the assessment of the radiographic visibility of neurovascular implants. State of the art methods are based on specimens of the human skull. These are highly individual and not suitable for comparison of different radiographic data sets. The development process of the skull phantom is described from data generation to image processing, design and manufacturing using 3D printing. An experimental setup is recommended to generate reproducible data sets for implant visibility assessment with bone mimicking structures of the phantom. The model is evaluated by qualitative comparison with equivalent data sets of the original human skull model. The results show, that contrast characteristics of the phantom and the human skull model are similar. X-ray attenuation of the human bone is higher than the polymeric phantom material. The introduced phantom allows the determination of X-ray attenuation characteristics of different neurovascular implants for medical approval and testing processes.

Radiopacity assessment of neurovascular implants

An experimental method for radiopacity evaluation of neurovascular implants is presented. State of the art methods are described for cardiovasular implants. To extend the methods to neurovascular devices, imaging parameters were determined from clinical radiography data sets and protocols. To reduce background noise, a thresholding method is introduced. This method is evaluated on a setup with four different laser cut and braided stents. The results are compared to current evaluation methods without filtering. It is shown that unfiltered methods underestimate the radiopacity by 0.89 mm ± 0.21 mm (aluminum equivalent). The introduced method is highly repeatable and uses modern clinical imaging technology. Thus an image evaluation under realisitc conditions is possible. Slightly visible vascular devices and implants can be compared with high accuracy.

Inside-Out access strategy using new trans-vascular catheter approach

Image guided minimal invasive treatment can have large benefits for patient recovery and is lowering hospitalisation costs. But an access path, minimizing patient’s risk, is needed to reach the target structure inside of the body. Beside the use of natural orifices like oral, vaginal or anal cavities, a percutaneous puncture is common to enter the body. Also an interstitial path can be selected but if the pathological structure is situated in the deep, a long accesses path is required. Thereby the risk of additional damage and affecting organ functionality is increased. A possible option to come closer to the target structure with less organ damage is by using the vascular system. Entering the vessel from an uncritical point, the vasculature can be used as “highway” to the target structures. For the treatment of these nearby structures, the vessel has to be punctured and occluded afterwards by a save procedure. We propose an Inside-Out access strategy using a new trans-vascular catheter approach.