High-Definition Zoom Mode, a High-Resolution X-ray Microscope for Neurointerventional Treatment Procedures

Abstract

Introduction

Fluoroscopically-guided endovascular intervention has become the preferred treatment modality for most intracranial aneurysms. The constantly evolving design of neuroendovascular devices and recent development of new technologies such as flow diversion, intrasaccular, and bifurcation devices now offer neurointerventionists a variety of treatment options. The quality of visualization of such devices in the region of interest during the treatment procedure can be critical for optimal placement and deployment, contributing to the success of the intervention.

The commercial x-ray imaging systems in most angiographic and fluoroscopy suites utilize flat-panel detectors (FPDs) during neuroendovascular interventions. These detectors consist of an array of square pixels based on thin-film transistor (TFT) technology with sizes varying from 140μm to 200μm.¹ The larger pixel sizes afford the FPDs an advantage of larger fields-of-view (FOV) ranging from 30 cm×30cm to 15cm×15cm at a typical display resolution of 1k×1k. However, any further display magnification for smaller FOVs is achieved using digital interpolation techniques (or digital zoom). Due to larger pixel sizes, the resulting image after digital zoom may not have sufficient resolution and image quality to properly visualize stents and other treatment devices.

The new true 2-resolution imaging x-ray detector system from Canon Medical Systems Corporation, Tochigi, Japan (https://global.medical.canon/products/angiography/alphenix/neurology) has a 194μm pixel conventional FPD mode and a 76μm pixel, high-resolution, high-definition (Hi-Def) zoom mode in one detector panel. The Hi-Def mode was developed for use in interventional procedures that require superior image quality over a small FOV. In this work, we report the successful use of this imaging system in the treatment of intracranial aneurysms in 2 patients at our institute: 1 patient was treated with a Pipeline embolization device (PED; Medtronic, Dublin, Ireland),² which is a flow-diverter stent, and the other patient was treated with “low-profile visualized intramural support” (LVIS Blue; MicroVention-Terumo, Somerset, New Jersey)³ stent-assisted coiling.

METHODS

Benchtop Testing

To demonstrate the improvement in resolution, a line pair (lp) object was imaged using the two detector modes (Figure 1 left and right). To reduce the blurring effect of the finite focal spot, the lp object was placed on the detector entrance surface. Due to the larger pixel sizes of the FPD mode, only up to 2.5 lp/mm can be visualized without any aliasing. In the Hi-Def mode, due to the smaller pixel sizes, up to 6.3 lp/mm can be visualized without any aliasing or loss of information. Line pairs give an indication of how well the imaging system can resolve the spatial frequency content information of the image. The higher the lp/mm being visualized, the sharper and better the image quality (especially the edges). To demonstrate the improvement in visualization of the treatment devices, images of a PED deployed in a neurovascular phantom were acquired using both modes of the detector (Figure 2 left and right). The higher resolution of the Hi-Def mode resulted in much improved visualization of the PED structure.

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Figure 1:

Images of a line pair (lp) object acquired using the standard-resolution 194 μm pixel flat-panel detector (FPD) mode (left) and high-resolution 76 μm high-definition (Hi-Def) mode (right). Due to the larger pixel sizes of the FPD mode, only up to 2.5 lp/mm can be visualized without any aliasing. In the Hi-Def mode, due to the smaller pixel sizes, up to 6.3 lp/mm can be visualized without any aliasing or loss in information. Note: the reader is advised to zoom the display to better appreciate the comparison.

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Figure 2:

Images of a Pipeline embolization device (Medtronic, Dublin, Ireland) deployed inside a neurovascular phantom acquired using both detector modes, high-definition (Hi-Def) and flat-panel detector (FPD). Due to higher resolution, the Hi-Def mode images are sharper (left). Structural details of the stent, especially the individual stent struts, are more easily resolved and visible in the Hi-Def images compared to the FPD images (right). Note: the reader is advised to zoom the display to better appreciate the comparison.

RESULTS

Case 1

History and Diagnostic Imaging

A 64-year-old man with a medical history of pancreatic cancer, hypertension, and prostate cancer presented to the emergency department with syncope. The patient’s cardiac evaluation was unremarkable. A diagnostic cerebral angiogram revealed a 13mm×7mm left paraclinoid internal carotid artery (ICA) aneurysm and a small, 1.5 mm×2 mm petrocavernous ICA aneurysm (Figure 3A). Given its size and irregular morphology, the paraclinoid aneurysm was believed to be at high risk of rupture and, after discussion with the patient, he opted for endovascular treatment.

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Figure 3.

Case 1: Pretreatment digital subtraction angiography images. A) Image of a 13mm×7mm left paraclinoid internal carotid artery (ICA) aneurysm and a small (1.5 mm×2mm) petrocavernous ICA aneurysm acquired using flat-panel detector mode, 15cm×15cm field-of-view (FOV). Only the paraclinoid aneurysm was treated. B) Image of the same aneurysms acquired using high-definition [Hi-Def]) mode, 5.8cm×5.8cm FOV. C) Hi-Def image showing minimal contrast flow stasis inside the paraclinoid aneurysm at a later arterial phase than in B.

Procedure

With the patient under conscious sedation, a micropuncture kit was used to access the right common femoral artery. An 8-French sheath was introduced into the vessel using a modified Seldinger technique. Using the 20cm×20cm large FOV FPD mode for image guidance, a Neuron Max guide catheter (Penumbra, Inc., Alameda, California) was advanced into the aortic arch over a Vitek Select catheter (Cook Medical, Bloomington, Indiana) and a 0.038 inch exchange length Glide wire (MicroVention-Terumo, Somerset, New Jersey). The left common carotid artery was selected, and the Neuron Max guide catheter was advanced into the distal common carotid artery. Roadmaps were obtained. A Phenom Plus intermediate catheter (Medtronic) placed over a Phenom 27 microcatheter (Medtronic) with a Synchro 2 microwire (Stryker Neurovascular, Fremont, California) was used for navigation into the petrous ICA. The Synchro 2 and Phenom 27 were then removed, and a Supracore exchange wire (Abbott Vascular, Abbott Park, Illinois) was used inside the Phenom Plus to provide more stability to help navigate the Neuron Max guide catheter to the skull base. Under roadmap guidance, the Phenom 27 microcatheter was steered into the distal M1 segment of the middle cerebral artery. Image acquisition was switched to Hi-Def mode with an FOV of 5.8cm×5.8cm. Contrast digital subtraction angiography (DSA) was performed (Figure 3B and ​andC).C). A 4.25mm×25mm PED was delivered and unsheathed to cover the ostium of the paraclinoid artery aneurysm. Deployment of the device was viewed under Hi-Def mode (Figure 4A–D, Video 1). Postdeployment DSA contrast injections were performed to check the apposition of the PED to the parent vessel wall and changes in the pattern of contrast flow through the parent vessel and within the aneurysm (Figure 5A and ​andB).B). The image acquisition mode was switched back to large FOV FPD mode. The catheters were retrieved, and the arterial access site was closed with an 8F Angio-Seal device (MicroVention-Terumo). The patient remained neurologically intact.

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Figure 4.

Case 1: Left paraclinoid internal carotid artery aneurysm. Different stages of the deployment of a Pipeline embolization device (PED; Medtronic, Dublin, Ireland) using a 0.27 inch Phenom microcatheter (Medtronic) and a Phenom Plus intermediate catheter (Medtronic) under high-definition 5.8cm×5.8cm zoom mode. A) Distal end of the PED opening. B) PED deployed halfway. The cone-like structure of the partially deployed PED device can be easily seen. C) PED fully deployed. D) The deployment wire and Phenom microcatheter were drawn into the intermediate catheter and then retracted from the body.

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Figure 5.

Case 1: Left paraclinoid artery aneurysm. Digital subtraction angiography images after Pipeline embolization device (Medtronic, Dublin, Ireland) deployment. Images were acquired using high-definition mode, 5.8cm×5.8cm field-of-view. A) Contrast flow in an arterial phase similar to that in Figure 3B. Notice the flow of contrast material outside the stent walls. B) Contrast flow in a phase similar to that in Figure 3C. There is a higher degree of contrast flow stasis inside the aneurysm compared to that in Figure 3C.

The patient’s entrance skin dose (Figure 6A and ​andB)B) for the entire procedure (from patient on the table to patient off the table) was monitored in real time using a dose-tracking system (DTS);⁴ Canon Medical Systems USA, Inc.; Tustin, California). The peak skin dose for the entire procedure was 1150 milligray (mGy).

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Figure 6.

Case 1: A cumulative patient entrance skin dose distribution map for the entire procedure was calculated using a real-time dose tracking system (Canon Medical Systems USA, Inc., Tustin, California) during treatment. The peak skin dose for the entire procedure was 1150 milligray (mGy). A) and B) show 2 different views of the dose distribution. CRA, cranial; LAO, left anterior oblique; RAO, right anterior oblique.

Case 2

History and Diagnostic Imaging

A patient with no remarkable medical history presented to the emergency room with the worst headache of her life. Magnetic resonance angiography (MRA) demonstrated a right carotid cavernous aneurysm measuring 11mm×7mm. Lumbar puncture and head CT scan were negative for subarachnoid hemorrhage. The aneurysm size and location were confirmed with diagnostic cerebral angiography.

Procedure

With the patient under general anesthesia, the right common femoral artery puncture site was prepared and draped in a sterile manner. Using a micropuncture kit, the right common femoral artery was accessed; using a modified Seldinger technique, a 6F sheath was placed into the right common femoral artery. Under large 20cm×20cm FOV FPD mode, a Benchmark guide catheter (Penumbra, Inc. Alameda, California) over a Berenstein select catheter (Boston Scientific, Natick, Massachusetts) and over a 0.035 inch Glide wire was introduced into the aortic arch and used to selectively catheterize the right common carotid artery and right ICA, and the Benchmark catheter was placed in the distal cervical ICA. A DSA contrast injection was performed to locate and confirm the aneurysm location (Figure 7). The patient was fully heparinized to a therapeutic activated coagulation time of 250 seconds.

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Figure 7.

Case 2: Digital subtraction angiography contrast run using large (20cm×20cm) field-of-view flat-panel detector mode showing a right carotid cavernous aneurysm measuring 11mm×7mm.

Under small (5.8cm×5.8cm) FOV Hi-Def mode roadmap guidance, a Headway 21 microcatheter (MicroVention-Terumo) over a Synchro 2 (Stryker Neurovascular, Fremont, California) microwire was introduced and placed in the distal M1 segment on the right. An SL-10 microcatheter (Stryker Neurovascular) with a 45-degree angle was introduced concomitantly over the Synchro 2 microwire to cannulate the aneurysm neck. Under Hi-Def magnification, a single 9mm×33mm coil (MicroVention) was partially deployed into the aneurysm dome. Subsequently, a 4.5×23 mm LVIS Blue stent was introduced into the Headway 21 and deployment was started just distal to the aneurysm neck. Under Hi-Def magnification, deployment showed good wall apposition throughout the curve of the cavernous carotid artery (Figure 8A–C). The partially deployed coil was fully deployed, followed by a second 5×20 mm coil (MicroVention) (Figure 8D). After the second coil deployment, DSA contrast runs were obtained and showed stasis in the aneurysm dome (Figure 9A).

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Figure 8.

Case 2: A–C) Different stages of low-profile visualized intramural support (LVIS) Blue (MicroVention-Terumo, Somerset, New Jersey) deployment using a Headway 21 microcatheter (MicroVention) in small (5.8cm×5.8 cm) field-of-view (FOV) high-resolution high-definition (Hi-Def) mode. A) Distal end of the stent outside the SL-10 microcatheter (Stryker Neurovascular, Fremont, California). B) LVIS Blue partially deployed. C) LVIS Blue completely deployed. D) Deployment of the second (final) 5mm×20mm coil (MicroVention) using the SL-10 microcatheter in small FOV high-resolution Hi-Def mode.

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Figure 9.

Case 2: Digital subtraction angiography images after low-profile visualized intramural support Blue and coil deployments A) acquired using small (5.8cm×5.8 cm) field-of-view (FOV) high-definition mode and B) acquired using large (20cm×20cm) FOV flat-panel detector mode.

The imaging mode was switched to large FOV, and a DSA contrast run was obtained to make sure the distal circulation was patent post treatment (Figure 9B). Under large FOV FPD mode guidance, microcatheters and guide catheter were withdrawn. The arterial access site was closed with a 6F Angio-Seal device. The patient was extubated and remained neurologically intact. The entrance skin dose to the patient for every radiation event of the entire procedure was recorded using the DTS. The peak skin dose for the entire procedure was 815mGy (Figure 10).

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Figure 10.

Case 2: Cumulative patient entrance skin dose distribution map for the entire procedure was calculated using a real-time dose tracking system (Canon Medical Systems USA, Inc., Tustin, California) during treatment of the right carotid cavernous aneurysm. The peak skin dose for the entire procedure was 815 milligray (mGy).

DISCUSSION

The quality of imaging during critical stages of endovascular interventions, such as during microcatheterization or stent or coil deployment, directly affects the safety and effectiveness of neurointerventional procedures. In this work, we are the first to describe the clinical application of the Hi-Def mode for the treatment of intracranial aneurysms with devices that have finite struts.

To improve imaging quality during neurointerventions, a high-resolution microangiographic fluoroscope (MAF) with a pixel size of 35 μm^5,6 was previously developed and used in clinical cases. Use was reported in 2 cases of intracranial aneurysm coiling⁷ and 1 case of coil embolization of a very small (2 mm) ruptured aneurysm.⁸ Both reports indicated that the MAF improved visualization during the treatment procedure without adding any additional time to the procedure. However, the MAF detector was a separate system attached to the C-arm using a specially designed changer mechanism. When high-quality imaging was needed, the detector was deployed mechanically into the active FOV using the changer mechanism. In addition, the MAF was limited to a single small FOV of 3.8cm×3.8cm.

The new detector system introduced in this work has a conventional large FOV FPD mode and a small FOV high-resolution Hi-Def zoom mode available in 1 system. The 2 modes can be switched electronically without any mechanical motion, unlike the previous MAF system. As mentioned, the Hi-Def mode has FOVs ranging from 8.5cm×8.5cm to 3.8cm×3.8cm. With conventional FPD systems, such small FOVs can be achieved using image interpolation techniques (digital zoom); however, the resulting image is still suboptimal and poor in resolution due to the larger pixel sizes of the FPD.

The improvement in resolution in Hi-Def mode was demonstrated in Figure 1 with up to 6.3 lp/mm visualized in Hi-Def mode without any aliasing or loss of information. The improvement in visualization in Hi-Def mode due to higher resolution was demonstrated in Figure 2. Structural details of the PED were easily visualized in Hi-Def mode compared to FPD. An earlier preclinical investigation⁹ compared the visualization of PED deployment in 6cm×6cm FOV Hi-Def zoom mode and 6cm×6cm FOV interpolated FPD mode images in a neurovascular 3-dimensional printed vascular phantom with bone and simulated tissue attenuation. The Hi-Def images were rated by well experienced neurointerventionists as similar, better, much better, or substantially better than the FPD images. From a total of 60 image comparisons of PED deployments performed on the 3D-printed phantom, 2 raters selected Hi-Def images with a frequency of at least 95% each and on an average with a frequency of 73% as much better than the FPD images. The expectation that the Hi-Def zoom mode could improve visualization of treatment procedures was realized in the clinical investigation reported here.

In both cases, the catheter systems and devices were guided from the femoral artery access site to the proximity of the treatment area under the large FOV FPD mode. During the critical stages of the treatment, when superior imaging quality of solely the treatment area was required, image acquisition was immediately switched to the small FOV high resolution Hi-Def mode. This is analogous to the use of a surgical microscope during critical stages when a magnified view of the operative field is required.

In the first case, the PED was deployed under Hi-Def mode guidance. Structural changes to the PED due to minute manipulations of the catheter and wire during different stages of deployment were easily visualized in real time under Hi-Def imaging (Video 1). Post-deployment visualization of positions with suboptimal opening of the stent was significantly improved with Hi-Def, compared to FPD mode, especially at the distal end of the device as it was initially unsheathed from the microcatheter. Consequently, the intermediate catheter was “bumped” against the proximal end of the stent to change its structure and ensure optimal opening.

In the second case, structural changes to the LVIS Blue stent due to minute manipulation of the catheter and wire during different stages of deployment were easily visualized in real-time under the Hi-Def mode. Magnified visualization of the aneurysm site was critical in guiding the coiling microcatheter safely into the aneurysm dome prior to stent deployment. During coil deployment, enhanced visualization of the position of the microcatheter tip within the coil mass and its movement allowed the interventionists to better delineate coil apposition to the stent tines. During deployment of the second coil, feedback about catheter redundancy and kickback was more clearly visualized within the coil mass with Hi-Def when compared to FPD.

Preliminary comments from the senior attending neurosurgeon suggested that the Hi-Def views offered a sharper image and allowed for easier and safer deployment of the stents and coils than the existing FPD system. From a training point of view, the fellows indicated that it was critical for them to easily visualize structural changes in devices, such as a PED, and correlate them to the changes in applied forces on the microcatheter and wire. Both the surgeon and fellows indicated that the new system had a minimal learning curve.

The skin dose maps were calculated in real-time and updated for every x-ray exposure. When using the Hi-Def mode, the FOV is limited to the treatment area. This has 2 main advantages: first, it reduces the radiation received by the patient to only the region of interventional activity, thus resulting in a lower integral dose. Secondly, with real-time feedback from the dose maps, the C-arm angles can be changed by only a few degrees due to the small FOVs to enable the dose to be spread without overlap, thus minimizing the potential for damage to the patient’s skin. With the real-time DTS display, which showed the peak skin dose to be substantially below the threshold for skin effects (2000 mGy for temporary skin erythema), dose spreading was not necessary in these 2 cases; and the Hi-Def projections were relatively stationary throughout the intervention.

In this work, we present our initial clinical experience and feedback on the use of the new dual-resolution imaging detector during neurovascular interventions. In the 2 cases presented, the Hi-Def mode was shown to be an important tool in improving the accuracy with which neurointerventionists can perform certain intracranial procedures. Studies with larger patient cohorts and statistical analysis to evaluate the impact of the improved imaging with the Hi-Def mode are in progress.

The Hi-Def zoom mode was developed for use in neurointerventional procedures when superior image quality over a small FOV is required. We report the adjunctive use of the new imaging system during the treatment of 2 aneurysm cases at our institute. Using the Hi-Def tool, the neurointerventionists could appreciate the nuances of the cases described here. The system has been easily incorporated into routine clinical practice.

Supplementary Material

Acknowledgments and Disclosures

REFERENCES