Andrew England

Observations on surveillance imaging after endovascular sealing of abdominal aortic aneurysms with the Nellix system.

Purpose: To describe and interpret the findings of computed tomography images acquired before and after endovascular aneurysm sealing (EVAS) with the Nellix endoprosthesis and consider the potential implications of these findings on EVAS planning and performance. Methods: A retrospective review was performed of perioperative imaging from 30 consecutive patients (median age 79 years; 19 men) undergoing elective EVAS at our center between December 2013 and November 2014. The images were systematically reviewed specifically looking for endobag collapse, aortic thrombus compression, and aortic wall disruption according to definitions set a priori. Results: There was no perioperative mortality or endoleak after the EVAS procedure. Endobag collapse, which could potentially result in type II endoleak if occurring near a patent side branch, was seen in the endobags of 12 patients. Aortic thrombus compression, which affects the accuracy of preoperative volume measurements in predicting the amount of polymer needed to perform EVAS, was seen in 15 patients. There was one aortic wall disruption, which could potentially result in intraoperative hemorrhage, though this did not occur in this case. Conclusion: These observations and their potential implications should help clinicians in planning and performing EVAS, as well as in interpreting postoperative imaging.

ChEVAS: Combining Suprarenal EVAS with Chimney Technique

Endovascular sealing with the Nellix® endoprosthesis (EVAS) is a new technique to treat infrarenal abdominal aortic aneurysms. We describe the use of endovascular sealing in conjunction with chimney stents for the renal arteries (chEVAS) in two patients, one with a refractory type Ia endoleak and an expanding aneurysm, and one with a large juxtarenal aneurysm unsuitable for fenestrated endovascular repair (EVAR). Both aneurysms were successfully excluded. Our report confirms the utility of chEVAS in challenging cases, where suprarenal seal is necessary. We suggest that, due to lack of knowledge on its durability, chEVAS should only been considered when more conventional treatment modalities (open repair and fenestrated EVAR) are deemed difficult or unfeasible.

Virtual reality, ultrasound-guided liver biopsy simulator: Development and performance discrimination

OBJECTIVES The aim of this article was to identify and prospectively investigate simulated ultrasound-guided targeted liver biopsy performance metrics as differentiators between levels of expertise in interventional radiology. METHODS Task analysis produced detailed procedural step documentation allowing identification of critical procedure steps and performance metrics for use in a virtual reality ultrasound-guided targeted liver biopsy procedure. Consultant (n=14; male=11, female=3) and trainee (n=26; male=19, female=7) scores on the performance metrics were compared. Ethical approval was granted by the Liverpool Research Ethics Committee (UK). Independent t-tests and analysis of variance (ANOVA) investigated differences between groups. RESULTS Independent t-tests revealed significant differences between trainees and consultants on three performance metrics: targeting, p=0.018, t=-2.487 (-2.040 to -0.207); probe usage time, p = 0.040, t=2.132 (11.064 to 427.983); mean needle length in beam, p=0.029, t=-2.272 (-0.028 to -0.002). ANOVA reported significant differences across years of experience (0-1, 1-2, 3+ years) on seven performance metrics: no-go area touched, p=0.012; targeting, p=0.025; length of session, p=0.024; probe usage time, p=0.025; total needle distance moved, p=0.038; number of skin contacts, p<0.001; total time in no-go area, p=0.008. More experienced participants consistently received better performance scores on all 19 performance metrics. CONCLUSION It is possible to measure and monitor performance using simulation, with performance metrics providing feedback on skill level and differentiating levels of expertise. However, a transfer of training study is required.

Changes in Aortic Volumes Following Endovascular Sealing of Abdominal Aortic Aneurysms With the Nellix Endoprosthesis

Purpose: To investigate the effects on aortic volumes of endovascular aneurysm sealing (EVAS) with the Nellix device. Methods: Twenty-five consecutive patients (mean age 78±7 years; 17 men) with abdominal aortic aneurysms containing thrombus were treated with EVAS. Their pre- and post-EVAS computed tomography (CT) scans were reviewed to document volume changes in the entire aneurysmal aorta, the lumen, and the intraluminal thrombus. The changes are reported as the mean and 95% confidence interval (CI). Results: Total aortic volume was greater on postoperative scans by a mean 17 mL (95% CI 10.0 to 23.5, p<0.001). The volume occupied by the endobags was greater than the preoperative lumen volume by a mean 28 mL (95% CI 24.7 to 31.7, p=0.002). Postoperatively, the aortic volume occupied by thrombus had decreased by a mean 11 mL (95% CI 4.7 to 18.2, p<0.001). There were good correlations between changes in aneurysm and thrombus volumes (r=0.864, p<0.001), between the planning CT/EVAS time interval and the change in aneurysm volume (r=0.640, p=0.001), and between the planning CT/EVAS time interval and the change in thrombus volume (r=0.567, p=0.003). Conclusion: There are significant changes in aortic volumes post EVAS. These changes may be a direct consequence of the technique and have implications for the planning and performance of EVAS.

Intra- and interobserver variability of target vessel measurement for fenestrated endovascular aneurysm repair.

Purpose: To evaluate intra- and interobserver agreement of target vessel measured from computed tomography (CT) scans with 2 measuring techniques used in planning fenestrated endovascular aneurysm repairs (FEVAR): multiplanar reconstruction (MPR) and semi-automated central lumen line (CLL). Methods: CT datasets from 25 FEVAR patients were independently analyzed by 2 experienced observers according to a standardized protocol using the MPR (Leonardo workstation) and CLL (Aquarius workstation) techniques for each patient. Longitudinal vessel separation and clock-face position of the visceral aortic branches were measured twice. The repeatability coefficient (RC) was calculated using the Bland and Altman method to measure intra- and interobserver variability. Differences between groups were examined by paired t test (continuous data) or chi-squared analysis (categorical). Clock-face discrepancy >30 minutes was considered significant. Results: Intraobserver mean difference was insignificant regardless of the measurement technique: the observer and workstation-specific RCs varied between 3.9 and 4.9 mm. Paired measurements differed by >3 mm in 8%. Interobserver variability was greater: observer and workstation-specific RC varied between 5.6 and 7.4 mm, with a tendency toward consistency using MPR, although the mean difference was insignificant. Paired measurements differed by >3 mm in 18%. There was no significant intraobserver variation in clock-face measurement, while interobserver variation was significant in 12% of measurements using the Aquarius workstation and 6% using the Leonardo workstation (p=0.19). Conclusion: Subjective interpretation of anatomical landmarks is more important than measurement techniques or workstations used in the generation of measurement inconsistencies. Introduction of consensus regarding interpretation of anatomical detail and development of fenestrated stent-grafts tolerant of measurement errors might ameliorate some of the problems encountered in FEVAR.

Type IIIb Endoleak and Relining A Mathematical Model of Distraction Forces

Purpose: To examine the changes in distraction force following relining of a conventional abdominal aortic stent-graft with a type IIIb endoleak using the Nellix endovascular sealing device compared to a unilateral stent-graft. Methods: Relining is often used to repair type IIIb endoleaks, but the consequences to graft stability are unknown. A mathematical model was constructed based on pressure and volume flow through the stent-grafts, incorporating recognized distraction force equations. Steady flow was presumed at peak systolic pressures to calculate the maximum distraction force, with gravity ignored. Distraction forces for 28- to 36-mm-diameter stent-graft bodies with 16-mm limbs were calculated and compared to forces following relining with single and double Nellix devices or the Renu unilateral device. Results: Distraction forces for the 28-, 32-, and 36-mm stent-grafts prior to relining were 5.99, 10.21, and 14.99 N, respectively. Similar forces were reported after relining with bilateral Nellix devices (5.86, 10.08, and 14.86 N, respectively). However, use of a unilateral Nellix increased the distraction forces to 9.92, 14.14, and 18.92 N, respectively. These were comparable to the increase observed after relining with a Renu unilateral stent-graft (9.87, 14.09, and 18.86 N, respectively). The proportional increase in distraction force for a unilateral relining ranged from 26% to 66%, with the greatest increase noted in the smaller diameter main bodies. Conclusion: Relining a stent-graft with a type IIIb endoleak using bilateral Nellix devices does not increase the distraction force. However, a unilateral Nellix device or the Renu system could theoretically increase the distraction force by up to 66%, potentially risking migration and type Ia endoleak. In clinical practice, these results suggest that a relining with bilateral Nellix may have benefits over the Renu unilateral stent-graft.

Endovascular Aneurysm Sealing Is Associated With Reduced Radiation Exposure and Procedure Time Compared With Standard Endovascular Aneurysm Repair

Purpose: To compare indirect measures of radiation exposure and operating time between endovascular aneurysm sealing (EVAS) and endovascular aneurysm repair (EVAR) for the treatment of abdominal aortic aneurysm (AAA). Methods: The study compared 32 consecutive patients (mean age 78 years; 21 men) with AAA who underwent standard EVAS with 32 consecutive patients (mean age 78 years; 25 men) treated with EVAR between November 2013 and May 2015. Electronic medical records and image archiving databases were interrogated to retrieve relevant information and scans. Screening time and dose area product (DAP) were the primary outcome measures. Data are presented as median and interquartile range (IQR). Correlations were tested with the Spearman rank coefficient (ρ). Results: The screening time was shorter in EVAS than in EVAR [16 (IQR 14, 20) vs 32 (IQR 26, 38) minutes; p<0.001]. DAP was lower in EVAS than in EVAR [54 (IQR 42, 77) vs 111 (IQR 75, 157) Gy∙cm2; p<0.001]. Digital subtraction angiography delivered 20% (IQR 15%, 28%) of the DAP in EVAS compared with 14% (IQR 11%, 19%) in EVAR (p<0.001), but the absolute time used on digital subtraction was marginally lower in EVAS than in EVAR [1.07 (IQR 0.52, 1.23) vs 1.19 (IQR 0.70, 1.39) minutes; p=0.037]. The operating time was shorter for EVAS [121 (IQR 105, 146) vs 162 (IQR 145,186) minutes; p<0.001]. There was a moderate correlation between DAP and screening time (ρ=0.597, p<0.001), fluoroscopy time (ρ=0.595, p<0.001), digital subtraction time (ρ=0.301, p=0.015), and operating time (ρ=0.512, p<0.001). Conclusion: EVAS is associated with reduced radiation exposure and operating room usage compared with EVAR, which may have safety and financial implications.

Radiologist variability in assessing the position of the cavoatrial junction on chest radiographs

OBJECTIVE To assess the variability in identifying the cavoatrial junction (CAJ) on chest X-rays (CXRs) amongst radiologists. METHODS 23 radiologists (13 consultants and 10 trainees) assessed 25 posteroanterior erect CXRs (including 8 duplicates) and marked the positions of the CAJ. Differences in the CAJ position both within and between observers were evaluated and reported as limits of agreement (LOA), repeatability coefficients (RCs) and intraclass correlation coefficients and were displayed graphically with Bland-Altman plots. RESULTS The mean difference for within-observer assessments was -0.2 cm (95% LOA, -1.5 to +1.1 cm) and between observers, it was -0.3 cm (95% LOA, -2.5 to +1.8 cm). Intraobserver RCs were marginally lower for consultants than for trainees (1.1 vs 1.5). RCs between observers were comparable (2.1 vs 2.2) for consultants and trainees, respectively. CONCLUSION This study detected a large interobserver variability of the CAJ position (up to 4.3 cm). This is a significant finding considering that the length of the superior vena cava is reported to be approximately 7 cm. We conclude that there is poor consensus regarding the CAJ position amongst radiologists. ADVANCES IN KNOWLEDGE No comparisons exist between radiologists in determining CAJ position from CXRs. This report provides evidence of the large observer variability amongst radiologists and adds to the discussion regarding the use of CXRs in validating catheter tip location systems.

Development and validation of a visual grading scale for assessing image quality of AP pelvis radiographic images

OBJECTIVE The aim of this article was to apply psychometric theory to develop and validate a visual grading scale for assessing the visual perception of digital image quality anteroposterior (AP) pelvis. METHODS Psychometric theory was used to guide scale development. Seven phantom and seven cadaver images of visually and objectively predetermined quality were used to help assess scale reliability and validity. 151 volunteers scored phantom images, and 184 volunteers scored cadaver images. Factor analysis and Cronbachs alpha were used to assess scale validity and reliability. RESULTS A 24-item scale was produced. Aggregated mean volunteer scores for each image correlated with the rank order of the visually and objectively predetermined image qualities. Scale items had good interitem correlation (≥0.2) and high factor loadings (≥0.3). Cronbachs alpha (reliability) revealed that the scale has acceptable levels of internal reliability for both phantom and cadaver images (α = 0.8 and 0.9, respectively). Factor analysis suggested that the scale is multidimensional (assessing multiple quality themes). CONCLUSION This study represents the first full development and validation of a visual image quality scale using psychometric theory. It is likely that this scale will have clinical, training and research applications. ADVANCES IN KNOWLEDGE This article presents data to create and validate visual grading scales for radiographic examinations. The visual grading scale, for AP pelvis examinations, can act as a validated tool for future research, teaching and clinical evaluations of image quality.

Multicenter retrospective investigation into migration of fenestrated aortic stent grafts

OBJECTIVE Fenestrated stent grafts are subject to the same hemodynamic forces that have resulted in migration of standard infrarenal stent grafts. Outcome data for fenestrated endovascular aneurysm repair consist of short-term and midterm efficacy studies where migration was generally poorly investigated. This study investigated the migration of fenestrated stent grafts in patients treated by fenestrated endovascular aneurysm repair in the United Kingdom. METHODS A total of 154 patients were retrospectively enrolled from nine sites across the United Kingdom. Patients had been treated with a Zenith fenestrated endograft (Cook Medical, Bloomington, Ind) between 2003 and 2010. Patients were required to have a baseline (first) postoperative computed tomography (CT) scan and at least one additional CT scan available. Measurements from the proximal stent graft to the superior mesenteric artery and from the distal stent graft to the iliac bifurcation were performed on the first postoperative CT scan. These measurements were repeated on all subsequent CT scans, and differences between the baseline and subsequent CT scans for the same anatomical location were suggestive of device migration. Migration was defined as cranial (-) or caudal (+) movement of the stent graft of ≥4 mm. RESULTS Proximal migration (median, +6.0 mm; range, +4.1 to +10.0 mm) was evident in 33 patients (21%). The probability of being free from proximal migration at 12, 24, and 36 months was estimated as 82% (95% confidence interval [CI], 75%-89%), 77% (95% CI, 70%-85%), and 77% (95% CI, 70%-85%), respectively. Of 259 limbs assessed, 34 (13%) showed evidence of cranial migration (median, -6.1 mm; range, -21.3 to -4.1 mm). The observed probability of being free from any iliac limb migration at 12, 24, and 36 months was 85% (95% CI, 79%-92%), 82% (95% CI, 75%-90%), and 65% (95% CI, 52%-80%), respectively. CONCLUSIONS Proximal migration occurs in approximately one-third of patients by 4 years, all migration was caudal in direction, with 60% <6.0 mm in length. Clinical sequelae were infrequent, with no statistically significant differences in the number of complications or reinterventions in patients with and without proximal migration.