Stent Lumen Research Articles

Stent imaging on a clinical dual-source photon-counting detector CT system-impact of luminal attenuation and sharp kernels on lumen visibility.

To assess the impact of scan modes and reconstruction kernels using a novel dual-source photon-counting detector CT (PCD-CT) on lumen visibility and sharpness of different stent sizes. A phantom containing six balloon-expandable stents (2.5 to 9 mm diameter) in silicone tubing was scanned on a PCD-CT with standard (0.6 mm and 0.4 mm thicknesses) and ultra-high-resolution (0.2 mm thickness) modes. With the use of increasing contrast medium concentrations, densities of 0, 200, 400, and 600 HU were achieved. Standard-resolution scans were reconstructed using increasing sharpness kernels, using both polyenergetic quantitative soft tissue "conventional" ((Qr40c(0.6 mm), Qr40c(0.4 mm), Qr72c(0.2 mm)) and vascular (Bv) virtual monoenergetic reconstructions (Bv44m(0.4 mm), Bv60m(0.4 mm)) at 70 keV. In-stent lumen visibility, sharpness (max. ΔHU of the stent measured in profile plots), and in-stent noise (standard deviation of HU) were measured. In-stent lumen visibility was highest for Qr72c(0.2 mm) (86.5 ± 2.8% to 88.3 ± 2.6%) and in Bv60m(0.4 mm) reconstructions (77.3 ± 2.9 to 82.7 ± 2.5%). Lumen visibility was lowest in the smallest stent (2.5 mm) ranging from 54.1% in Qr40c(0.6 mm) to 74.1% in Qr72c(0.2 mm) and highest in the largest stent (9 mm) ranging from 93.8% in Qr40c(0.6 mm) to 99.1% in the Qr72c(0.2 mm) series. Lumen visibility decreased by 2.1% for every 200-HU increase in lumen attenuation. Max. ΔHU between stents and stent lumen was highest in Qr72c(0.2 mm) (ΔHU 892 ± 504 to 1526 ± 517) and Bv60m(0.4 mm) series (ΔHU 480 ± 357 to 1030 ± 344). Improvement of lumen visibility and sharpness in UHR and Bv60m(0.4 mm) series was strongest in smaller stent sizes. UHR acquisition mode and sharp reconstruction kernels on a novel PCD-CT system significantly improve in-stent lumen visibility and sharpness-especially for smaller stent sizes. • In-stent lumen visibility and sharpness of stents significantly improve using sharp reconstruction kernels (Bv60) and ultra-high-resolution mode in photon-counting detector computed tomography. • The observed improvement of stent-lumen visibility was highest in smaller stent sizes.

Abstract 10054: Super Resolution Deep Learning Reconstruction for Detection of In-Stent Restenosis

Introduction: Evaluation of in-stent-restenosis (ISR), especially of small stents, remains a challenge for computed tomography (CT) angiography. Hypothesis: To quantitatively define stent strut thickness and lumen vessel diameter at the stent site by deep learning reconstruction and compare this with conventional reconstruction strategies. Methods: We employed ultra-high-resolution CT (URCT) data to train a super resolution neural network (Precise IQ engine, or PIQE) and apply the network to current standard resolution CT (Forward projected model-based Iterative Reconstruction SoluTion, FIRST). We examined 166 stents in 85 consecutive patients who underwent CT and invasive coronary angiography (ICA) within three months of each other from 2019-2021 after percutaneous coronary intervention with coronary stent placement. The diagnostic accuracy for the presence of ISR was defined as percent diameter stenosis > 50% on ICA. All images were reconstructed with PIQE and FIRST and assessed by two blinded cardiovascular imagers. Results: Compared to FIRST, the full width at half maximum of the lumen was larger, and that of the strut was smaller in PIQE. Image quality score was significantly better in PIQE than in FIRST (4.2±1.1 vs. 2.7±1.2, P <0.01). The sensitivity, specificity, PPV, NPV, and accuracy for detection of ISR in PIQE were better than the FIRST (86.1, 89.5, 50.0, 98.1, and 89.2 vs. 80.6, 77.4, 30.2, 97.0, and 77.7, respectively); the differences were particularly pronounced in a group with < 3.0 mm stent diameter. Conclusions: PIQE provides superior image quality and diagnostic accuracy for ISR, even in stents with < 3.0 mm diameter.

Contrast-enhanced US Evaluation of Endoleaks after Endovascular Stent Repair of Abdominal Aortic Aneurysm.

Ruptured abdominal aortic aneurysm (AAA) carries high morbidity and mortality. Elective repair of AAA with endovascular stent-grafts requires lifetime imaging surveillance for potential complications, most commonly endoleaks. Because endoleaks result in antegrade or retrograde systemic arterialized flow into the excluded aneurysm sac, patients are at risk for recurrent aneurysm sac growth with the potential to rupture. Multiphasic CT has been the main imaging modality for surveillance and symptom evaluation, but contrast-enhanced US (CEUS) offers a useful alternative that avoids radiation and iodinated contrast material. CEUS is at least equivalent to CT for detecting endoleak and may be more sensitive. The authors provide a general protocol and technical considerations needed to perform CEUS of the abdominal aorta after endovascular stent repair. When there are no complications, the stent-graft lumen has homogeneous enhancement, and no contrast material is present in the aneurysm sac outside the stented lumen. In patients with an antegrade endoleak, contrast material is seen simultaneously in the aneurysm sac and stent-graft lumen, while delayed enhancement in the sac is due to retrograde leak. Recognition of artifacts and other potential pitfalls for CEUS studies is important for examination performance and interpretation. Online supplemental material is available for this article. ©RSNA, 2022.

Fluid mechanical performance of ureteral stents: The role of side hole and lumen size.

Ureteral stents are indispensable devices in urological practice to maintain and reinstate the drainage of urine in the upper urinary tract. Most ureteral stents feature openings in the stent wall, referred to as side holes (SHs), which are designed to facilitate urine flux in and out of the stent lumen. However, systematic discussions on the role of SH and stent lumen size in regulating flux and shear stress levels are still lacking. In this study, we leveraged both experimental and numerical methods, using microscopic-Particle Image Velocimetry and Computational Fluid Dynamic models, respectively, to explore the influence of varying SH and lumen diameters. Our results showed that by reducing the SH diameter from to the median wall shear stress levels of the SHs near the ureteropelvic junction and ureterovesical junction increased by over , even though the flux magnitudes through these SH decreased by about . All other SHs were associated with low flux and low shear stress levels. Reducing the stent lumen diameter significantly impeded the luminal flow and the flux through SHs. By means of zero-dimensional models and scaling relations, we summarized previous findings on the subject and argued that the design of stent inlet/outlet is key in regulating the flow characteristics described above. Finally, we offered some clinically relevant input in terms of choosing the right stent for the right patient.

Stent-in-stent technique under fluoroscopy for removal of embedded esophageal stent: a retrospective case series

Treatment of complications after esophageal stent placement and methods for removal of stents need to be improved. The purpose of this study was to evaluate the safety and efficacy of stent-in-stent (SIS) removal of esophageal stent under fluoroscopy. This study analyzed the clinical data of consecutive patients undergoing esophageal stent removal by the SIS technique under fluoroscopy. The procedure was performed under local anesthesia on conscious sedated patients. Under fluoroscopy, a second esophageal stent was released within the lumen of the first esophageal stent. The second stent was larger than the first, with both ends protruding 1-2 cm beyond the ends of the first stent. Four weeks later, both esophageal stents were removed by the SIS technique under fluoroscopy. All procedures were performed by the same interventional radiologist (with >10 years of experience). A total of 25 patients were treated by the SIS removal technique. In 23 patients, the first esophageal stent was easily removed by the SIS technique; in the other 2 patients, stent fracture occurred, and some residual nitinol wire had to be removed endoscopically. No serious complications occurred in any patient. The SIS removal technique appears to be a safe and effective method for removal of embedded esophageal metallic stents.

Magnetic resonance imaging of invitro urine flow in single and tandem stented ureters subject to extrinsic ureteral obstruction.

To quantify the relative volumetric flows in stent and ureter lumina, as a function of stent size and configuration, in both unobstructed and externally obstructed stented ureters. Magnetic resonance imaging was used to measure flow in stented ureters using a phantom kidney model. Volumetric flow in the stent and ureter lumina were determined along the stented ureters, for each of four single stent sizes (4.8F, 6F, 7F, and 8F), and for tandem (6F and 7F) configurations. Measurements were made in the presence of a fully encircling extrinsic ureteral obstruction as well as in benchmark cases with no extrinsic ureteral obstruction. Under no obstruction, the relative contribution of urine flow in single stents is 1-10%, while the relative contributions to flow are ~6 and ~28% for tandem 6F and 7F, respectively. In the presence of an extrinsic ureteral obstruction and single stents, all urine passes within the stent lumen near the extrinsic ureteral obstruction. For tandem 6F and 7F stents under extrinsic ureteral obstruction, relative volumetric flows in the two stent lumina are ~73% and ~81%, respectively, with the remainder passing through the ureter lumen. Magnetic resonance imaging demonstrates that with no extrinsic ureteral obstruction, minimal urine flow occurs within a stent. Stent lumen flow is significant in the presence of extrinsic ureteral obstruction, in the vicinity of the extrinsic ureteral obstruction. For tandem stents subjected to extrinsic ureteral obstruction, urine flow also occurs in the ureter lumen between the stents, which can reduce the likelihood of kidney failure even in the case of both stent lumina being occluded.

Imaging and Chemical Analysis of External and Internal Ureteral Stent Encrustation.

IntroductionUreteral stents are effective in alleviating flow disruptions in the urinary tract, whether due to ureteral stones, strictures or extrinsic ureteral obstruction. However, significant stent encrustation on the external and/or internal stent lumen walls can occur, which may interfere with stent functioning and/or removal. Currently, there is only limited, generally qualitative, information on the distribution, mineral structure, and chemical content of these deposits, particularly in terms of stent lumen encrustation.ObjectiveTo quantify, in an initial investigation, external and internal encrustation in representative, intact ureteral stents. The study investigates possible correlations between patterns of external and internal encrustation, determines mineral structure and chemical composition, and examines the potential for stent lumen obstruction even in the absence of external stent wall encrustation.Study DesignHigh-resolution, laboratory micro-computed tomography (micro-CT) was used to non-destructively image external and internal stent encrustation in four representative stents. X-ray diffractometry (XRD) and scanning electron microscopy–energy dispersive x-ray spectroscopy (SEM-EDS) enabled parallel analysis of mineral structure and chemical content of samples collected from external and internal encrusted material along the distal, proximal and mid-ureteral stent regions.ResultsExtensive stent lumen encrustation can occur within any region of a stent, with only incidental or minor external encrustation, along the entire length of the stent. External and internal encrusted materials in a given stent are generally similar, consisting of a combination of amorphous (mostly organic) and crystalline mineral deposits.ConclusionMicro-CT demonstrates that significant stent lumen encrustation can occur, which can lead to partial or full stent lumen occlusion, even when the exterior stent wall is essentially free of encrusted material.

CFD study on vesicoureteral reflux in the urinary tract with double J stent

ObjectiveThis study investigates the effects of vesicoureteral reflux (VUR) in the upper and lower urinary tracts with and without ureteral stenosis and with a double J stent (DJS). MethodsThe entire length of the urinary tract with an implanted DJS was modeled. To assess the possibility of VUR, the measured values were used as boundary conditions for the baseline, the maximum cystometric bladder capacity (MCBC) during the filling phase, and maximum vesical pressure during the voiding phase were computed. The flow rates, flow patterns, wall shear stress (WSS) distribution, impact force induced by reflux urination, and helicity of the bladder were investigated for the urinary system. ResultsThe flow from the bladder to the renal pelvis was detected at maximum vesical pressure (75 cmH2O) during the voiding phase, and a small amount (1.09 mL/s) of VUR was noted at the MCBC during the filling phase. The WSS increased when the reflux was large. Helicity within the bladder varied with the stenosis as well as opening and closing of the urethra. The reflux within the stent was reduced by 40% by inserting a ball into the stent. ConclusionThe main VUR factor was the opening and closing of the vesicoureteric junction by the detrusor muscle. The largest urine reflux (11.7 mL/s) to the kidney occurred when the detrusor muscle was relaxed. SignificanceUreteral stenosis affected the VUR and reduced urine reflux. Ball insertion in the stent reduced urine reflux through the stent lumen.

Urethral stenting in a dog due to compression and invasion by a liposarcoma

AbstractAn approximately 10‐year‐old, mixed breed, entire male dog was referred for acute onset of urethral obstruction. Abdominal ultrasound was unremarkable, complete blood count, serum biochemical analysis and urine analysis were all unremarkable. A retrograde urethrogram demonstrated narrowing of the urethral lumen caudal to the ischiadic arc. Urethral stenting with a self‐expanding nitinol stent was performed and the patient was without symptoms over a 6‐month period. After that time, ingrowth of tissue into the stent lumen could be seen via a new retrograde urethrogram; therefore, a covered stent was placed into the previously placed uncovered stent. Clinical signs resolved immediately. Another contrast study 4 months later demonstrated almost complete obstruction at the distal end of the stent. Scrotal ablation with perineal urethrostomy was performed and tissue samples submitted for histopathology. Liposarcoma was diagnosed. The patient was urinating without problems, but suddenly died at home 1 week after the last surgery.

Ultrastructural analysis of explanted CyPass microstents and correlation with clinical findings

PurposeThe purpose of this study was to obtain insight into cellular processes after CyPass microstent implantation into the supraciliary space. With this knowledge, we expected to find some reason for surgical failure.MethodsNine CyPass microstents of 8 patients with primary open-angle glaucoma (n = 1), pseudoexfoliation glaucoma (n = 5), uveitic glaucoma (n = 1), and posttraumatic open-angle glaucoma (n = 1) were explanted due to recurrence of IOP elevation, corneal decompensation, or persistent hypotony. The explants were processed for light and transmission electron microscopy.ResultsFibrotic material, consisting of collagen fibrils, microfibrils, pseudoexfoliation fibrils produced by activated fibroblasts, was detected in the stent lumen of 4/5 pseudoexfoliation glaucoma patients and also in posttraumatic open-angle glaucoma. Fibrotic material was also present on the outer surface and within fenestrations of the majority of stents. Complete absence of fibrotic reaction was noticed in 3 of 9 microstents.ConclusionAlthough MIGS is known to be less invasive than conventional surgery, implants placed in the suprachoroidal space may be adversely affected by a fibrotic tissue reaction resulting in implant failure. Understanding mechanisms and risk factors leading to fibrotic scarring following antiglaucomatous surgery may help to develop novel strategies that improve surgical outcome.

Percutaneous Endoluminal Radiofrequency Ablation of Occluded Biliary Metal Stent in Malignancy Using Monopolar Technique: A Feasibility Study.

To prove feasibility and safety of percutaneous endoluminal radiofrequency ablation (eRFA) using a monopolar approach in treatment of occluded biliary stent in malignancy. The study included 11 patients with occluded biliary metal stent that had been implanted due to malignant biliary obstruction. All underwent metal stent recanalization by percutaneous eRFA in monopolar setting. Sixteen eRFA procedures were performed under fluoroscopic guidance with an EndoHPB 8F radiofrequency ablation catheter. The effect of stent recanalization was assessed based upon change from pre- to post-procedural diameter of the patent lumen of the metal stent (Wilcoxon test), primary and secondary stent patency (compared by log-rank test), catheter-free period, and overall survival. Adverse events were evaluated according to Common Terminology Criteria for Adverse Events (CTCEA) 4.0. Recanalization of the metal stent by monopolar radiofrequency ablation was successful in all 11 patients. Diameter of the patent lumen of the stent significantly widened after the eRFA inside the stent (median 2 vs. 7mm, p = 0.003). Grade 1 complications were observed in one-third of procedures. Median stent patency after recanalization by eRFA was non-inferior to primary metal stent patency (154 vs. 161days, p = 0.27). Median catheter-free survival and overall survival after stent recanalization were 149 and 210days, respectively. Endoluminal radiofrequency ablation in monopolar setting was shown to be a feasible and safe method for recanalization of occluded biliary metal stents. Level 4, Case Series.

A Novel Method for Urinary Tract Reconstruction in Transplanted Embryonic Kidneys Using the Hybrid Stent: A Pig Study.

A Novel Method for Urinary Tract Reconstruction in Transplanted Embryonic Kidneys Using the Hybrid Stent: A Pig Study.

Endoscopic stenting for stenosing cancer and digestive canal structures

Background. The purpose of the work was to evaluate the effectiveness of the endoscopic stenting method in stenosing cancer and strictures of the digestive tract. Materials and methods. Since January 2015, endoscopic stenting has been performed in 12 patients using self-expanding nitinol stents with/without polymer coating manufactured by Boston Scientific, Ltd (USA) and uncoated nitinol stents manufactured by Garson (Korea). The study included 8 men (66.7 %) and 4 women (33.3 %) aged 51–80 years, (63.0 ± 4.2) years on average. Stenosing esophageal cancer was diagnosed in 5 patients, stenosing cancer of the gastric outlet— in 3, stenosing duodenal cancer — in one, esophageal stricture — in 3 people. In all patients, the indication for stenting was impaired patency of the digestive tract due to the underlying di-sease. Results. Nutrition was restored in all patients. In the group of stenosing esophageal cancer, the 30-day mortality rate was 20%, the median survival rate was 9 months. Recurrence of dysphagia was diagnosed in one person, recanalization of the stent lumen was performed. In the group with stenosing cancer of the gastric outlet and duodenum, the 30-day mortality rate was 33.3%, the median survival rate was 11 months. Impaired gastric emptying was detected in one patient, repeated stent-to-stent stenting was performed. In the group with esophageal stricture, one individual had stent migration, so the stent was repositioned. Conclusions. Endoscopic stenting with self-expanding nitinol stents in incurable patients with malignant stenoses of the esophagus, stomach, duodenum and in those with benign esophageal strictures is the surgery of choice, a safe and effective method that allows you to restore and continue natural nutrition and thereby improve the quality of life in incurable cases. Complications arising in the late period after stenting were found in 25 % of patients, and were corrected endoscopically.

3D Printed Bioinspired Stents with Photothermal Effects for Malignant Colorectal Obstruction.

Stent placement is an effective palliation therapy for malignant colorectal obstruction. However, recurrent obstruction is a common severe complication caused by tumor ingrowth into the stent lumen. Conventional covered stents play a part in preventing the tumor from growing inward but at the expense of significantly increasing the risk of stent migration. Therefore, there is an urgent demand to develop stents with sustained antitumor and antimigration abilities. Herein, we propose a facile method for fabricating multifunctional bioinspired colorectal stents using 3D printing technology. Inspired by high-adhesion biological structures (gecko feet, tree frog toe pads, and octopus suckers) in nature, different types of bioinspired colorectal stents are designed to reduce migration. After functionalization with graphene oxide (GO), bioinspired colorectal stents show excellent and controllable photothermal performance, which is validated by effective ablation of colon cancer cells in vitro and tumors in vivo. Besides, the bioinspired colorectal stents demonstrate the feasibility of transanal placement and opening of the obstructed colon. More importantly, the facile manufacturing process of multifunctional bioinspired colorectal stents is appealing for mass production. Hence, the developed multifunctional bioinspired colorectal stents exhibit a highly promising potential in clinical applications.

First In-Human Results of Computed Tomography Angiography for Coronary Stent Assessment With a Spectral Photon Counting Computed Tomography.

ObjectivesThe aim of this study is to compare the image quality of in vivo coronary stents between an energy integrating detectors dual-layer computed tomography (EID-DLCT) and a clinical prototype of spectral photon counting computed tomography (SPCCT).Materials and MethodsIn January to June 2021, consecutive patients with coronary stents were prospectively enrolled to undergo a coronary computed tomography (CT) with an EID-DLCT (IQon, Philips) and an SPCCT (Philips). The study was approved by the local ethical committee and patients signed an informed consent. A retrospectively electrocardiogram-gated acquisition was performed with optimized matching parameters on the 2 scanners (EID-DLCT: collimation, 64 × 0.625 mm; kVp, 120, automatic exposure control with target current at 255 mAs; rotation time, 0.27 seconds; SPCCT: collimation, 64 × 0.275 mm; kVp, 120; mAs, 255; rotation time, 0.33 seconds). The injection protocol was the same on both scanners: 65 to 75 mL of Iomeron (Bracco) at 5 mL/s. Images were reconstructed with slice thickness of 0.67 mm, 512 matrix, XCB (Xres cardiac standard) and XCD (Xres cardiac detailed) kernel, iDose 3 for EID-DLCT and 0.25-mm slice thickness, 1024 matrix, Detailed 2 and Sharp kernel, and iDose 6 for SPCCT. Two experienced observers measured the proximal and distal external and internal diameters of the stents to quantify blooming artifacts. Regions of interest were drawn in the lumen of the stent and of the upstream coronary artery. The difference (Δ S-C) between the respective attenuation values was calculated as a quantification of stent-induced artifacts on intrastent image quality. For subjective image quality, 3 experienced observers graded with a 4-point scale the image quality of different parameters: coronary wall before the stent, stent lumen, stent structure, calcifications surrounding the stent, and beam-hardening artifacts.ResultsEight patients (age, 68 years [interquartile range, 8]; all men; body mass index, 26.2 kg/m2 [interquartile range, 4.2]) with 16 stents were scanned. Five stents were not evaluable owing to motion artifacts on the SPCCT. Of the remaining, all were drug eluting stents, of which 6 were platinum-chromium, 3 were cobalt-platinum-iridium, and 1 was stainless steel. For 1 stent, no information could be retrieved. Radiation dose was lower with the SPCCT (fixed CT dose index of 25.7 mGy for SPCCT vs median CT dose index of 35.7 [IQ = 13.6] mGy; P = 0.02). For 1 stent, the internal diameter was not assessable on EID-DLCT. External diameters were smaller and internal diameters were larger with SPCCT (all P < 0.05). Consequently, blooming artifacts were reduced on SPCCT (P < 0.05). Whereas Hounsfield unit values within the coronary arteries on the 2 scanners were similar, the Δ S-C was lower for SPCCT-Sharp as compared with EID-DLCT-XCD and SPCCT-Detailed 2 (P < 0.05). The SPCCT received higher subjective scores than EID-DLCT for stent lumen, stent structure, surrounding calcifications and beam-hardening for both Detailed 2 and Sharp (all P ≤ 0.05). The SPCCT-Sharp was judged better for stent structure and beam-hardening assessment as compared with SPCCT-Detailed 2.ConclusionSpectral photon counting CT demonstrated improved objective and subjective image quality as compared with EID-DLCT for the evaluation of coronary stents even with a reduced radiation dose.

Magnetic particle imaging for artifact-free imaging of intracranial flow diverter stents: A phantom study.

Magnetic Particle Imaging (MPI) is a new, background- and radiation-free tomographic imaging method that enables near real-time imaging of superparamagnetic iron-oxide nanoparticles (SPIONs) with high temporal and spatial resolution. This phantom study aims to investigate the potential of MPI for visualization of the stent lumen in intracranial flow diverters (FD). Nitinol FD of different dimensions (outer diameter: 3.5mm, 4.0mm, 5.5mm; total length: 22-40mm) were scanned in vascular phantoms in a custom-built MPI scanner (in-plane resolution: ~ 2mm, field of view: 65mm length, 29mm diameter). Phantoms were filled with diluted (1:50) SPION tracer agent Ferucarbotran (10µmol (Fe)/ml; NaCL). Each phantom was measured in 32 different projections (overall acquisition time per image: 3200ms, 5averages). After image reconstruction from raw data, two radiologists assessed image quality using a 5-point Likert scale. The signal intensity profile was measured using a semi-automatic evaluation tool. MPI visualized the lumen of all FD without relevant differences between the stented vessel phantom and the reference phantom. At 3.5mm image quality was slightly inferior to the larger diameters. The FD themselves neither generated an MPI signal nor did they lead to relevant imaging artifacts. Ratings of both radiologists showed no significant difference, interrater reliability was good (ICC 0.84). A quantitative evaluation of the signal intensity profile did not reveal any significant differences (p>0.05) either. MPI visualizes the lumen of nitinol FD stents in vessel phantoms without relevant stent-induced artifacts.

Influence of Single Stent Size and Tandem Stents Subject to Extrinsic Ureteral Obstruction and Stent Occlusion on Stent Failure.

Background and Purpose: Drainage of obstructed kidney attributable to extrinsic ureteral obstruction (EUO), required to prevent renal damage, is often achieved using Double-J ureteral stents. However, these stents fail frequently, and there is considerable debate regarding what stent size, type, and configuration offer the best option for sustained drainage. In this study, we examine the impact of stent diameter and choice of single/tandem configuration, subject to EUO and various degrees of stent occlusion, on stent failure. Materials and Methods: Computational fluid dynamics simulations and an in vitro ureter-stent experiment enabled quantification of flow behavior in stented ureters subject to EUO and stent occlusions. Various single and tandem stents under EUO were considered. In each simulation and experiment, changes in renal pressure were monitored for different degrees of stent lumen occlusion, and onset of stent failure as well as simulated distributions of fluid flow between stent and ureter lumina were determined. Results: For an encircling EUO that completely obstructs the ureter lumen, with or without partial stent occlusion, the choice of stent size/configuration has little effect on renal pressure. The pressure increases significantly for ∼90% stent lumen occlusion, with failure at >95% occlusion, independent of stent diameter or a tandem configuration, and with little influence of occlusion length along the stent. Conclusions: Stent failure rate is independent of stent diameter or single/tandem configuration, for the same percentage of stent lumen occlusion, in this model. Stent failure incidence may decrease for larger diameter stents and tandem configurations, because of the larger luminal area.

Efficacy of intravascular ultrasound-guided rotational atherectomy combined with cutting balloon for pretreatment of severe coronary artery calcified lesions

To investigate the efficacy and safety of intravascular ultrasound (IVUS)-guided rotational atherectomy (RA) combined with cutting balloon for pretreatment of severe calcified lesions in the coronary artery before stent placement. A total of 120 patients with severe coronary artery calcifications detected by IVUS that required percutaneous coronary intervention (PCI) were recruited from our hospital between January, 2016 to January, 2019. The patients were randomized into two groups for pretreatment of the lesions with semicompliant balloon (SB group, 60 cases) or RA combined with CB (RA+CB group, 60 cases), and drug-eluting stents were implanted after the procedure. The immediate success rate of PCI, vascular parameters detected by IVUS after PCI, and the rates of residual stenosis < 10% were compared between the two groups. The incidences of intraoperative complications and major adverse cardiac events (MACE) within 24 months after the surgery were also observed in the two groups. The immediate success rate was significantly higher in RA+CB group than in SB group (P=0.032). After pretreatment and stent placement, the minimum stent lumen diameter (P=0.035), minimum stent lumen cross-sectional area (P=0.029), immediate lumen acquisition, immediate lumen cross-sectional area acquisition and the rate of residual stenosis < 10% were all significantly higher in RA+CB group than in SB group (P < 0.001). The patients in RA+ CB group showed obviously less residual stenosis of lumen cross-sectional area than those in SB group after the surgery (χ2= 7.859, P=0.005). The incidences of intraoperative complications (χ2=5.997, P=0.014) and MACE within 24 months after the operation (χ2=4.285, P=0.038) were significantly lower in RA+CB group than in SB group. For patients with severe coronary artery calcifications eligible for PCI, RA combined with CB angioplasty can significantly improve the success rate of immediate PCI, expand the lumen diameter and cross-sectional area of the stent after PCI, enhance immediate lumen gain, and reduce the incidence of intraoperative complications and MACE after the operation.

Rescue of Failed XEN-45 Gel Implant by Nd:YAG Shock Wave to Anterior Chamber Tip to Dislodge Hidden Intraluminal Occlusion.

Purpose:The purpose of this study was to inform ophthalmic surgeons in a timely manner of the hidden problem of clear intraluminal cellular debris as a cause for XEN-45 failure and to describe low energy neodymium-doped yttrium aluminum garnet (Nd:YAG) laser revision with periluminal anterior chamber tip shockwave treatment to improve flow to the bleb.Patients and Methods:Six patients with visibly patent stent lumen post XEN-45 surgery. These eyes developed rising intraocular pressure (IOP) with a history of excellent prior bleb formation and were treated successfully with Nd:YAG laser shockwave therapy to disperse assumed intraluminal cellular debris. The laser was aimed just anterior and axial to the intracameral tip of the gel stent through a gonioscopy lens.Results:Six patients with an average age of 75 years (60 to 90 y), preoperative IOP of 30 mm Hg (16 to 52 mm Hg) on an average of 2 antiglaucoma medications (0 to 4) underwent periluminal anterior chamber tip shock wave at an average of 12 months (1 to 38 mo) from XEN-45 surgery. The IOP was immediately reduced to an average of 15 mm Hg (8 to 23 mm Hg) and last IOP averaged 15 mm Hg (10 to 23 mm Hg) on 1.5 medications (0 to 4) at 4 months post periluminal anterior chamber tip shock wave.Conclusion:Nd:YAG laser revision of hidden blockage of a XEN-45 gel implant with periluminal anterior chamber tip shockwave treatment can disperse invisible intraluminal cellular debris and improve flow in a failing XEN-45 microstent, especially when distal fibrosis is not excessive.

Failure of ureteral stents subject to extrinsic ureteral obstruction and stent occlusions

To quantify the occurrence of stent failure and the dynamic behavior of urine flow in ureter-stent systems, including the relative flow in the ureter and stent lumina, subject to various degrees of ureter and stent blockage. Numerical simulations based on computational fluid dynamics (CFD) were used to quantify urine flow behavior in stented ureters, in the presence of extrinsic ureteral obstruction (EUO) and stent occlusions. Two stented ureter configurations were considered, one with circumferential occlusion of the ureter and the second with pressure on one side of the ureter wall. The pressure within the renal unit for different degrees of ureter closure and stent lumen occlusion was determined systematically. Onset of stent failure and the distribution of urine flow between stent and ureter lumina were determined. In the case of EUO completely encircling the ureter, causing 100% obstruction of the ureter lumen, pressure in the renal unit is essentially unaffected until the stent lumen reaches ~ 90% occlusion, and fails only with > 95% occlusion. Occlusions of 50% in stent side holes in the vicinity of the EUO only alter local flow patterns but have no significant influence on renal unit pressure. For EUO deforming and compressing the ureter from one side, with ~ 50% reduction in ureter lumen, urine drainage proceeds with negligible increase in renal pressure even with 100% occlusion in the stent lumen. CFD simulations show that stent failure under EUO tends to occur suddenly, only when both ureter and stent lumina become almost fully blocked.