Comparison of Three Workstations For Abdominal Aortic Aneurysm Sizing: Impact in Decision Making and Graft Selection

PURPOSE

The aim of this study was to assess the agreement of multiplanar reconstruction (MPR) and semiautomated central lumen line (CLL) analysis of abdominal aortic aneurysms (AAA), with 3 different software workstations (WS1, WS2, WS3) and 2 experienced practitioners as well as to analyze its eventual impact in graft selection.

MATERIALS AND METHODS

Twenty computed tomography (CT) angiography data sets were randomly chosen from a series of 100 consecutive studies. Measurements were performed twice by each reader, in random order, and included 8 parameters (5 diameters and 3 lengths). Each observer performed a complete set of 60 studies. Intra-observer and interobserver variability for every WS was assessed. Measurements were evaluated using Bland-Altman analysis, correlation coefficients (r), and concordance correlation coefficients (CCC [95% confidence interval (CI)]).

RESULTS

A high overall agreement between repeated measurements for both observers was obtained (r=0.989; CCC=0.988 [0.982-0.992] and r=0.998; CCC=0.996 [0.994-0.997], for observers 1 and 2, respectively). However, reproducibility for individual parameters was excellent for observer 2 and only moderate for observer 1. A high overall agreement was obtained for interobserver concordance (r=0.987; CCC=0.986 [0.982-0.989]). When analyzing for individual parameters, greatest interobserver differences were found at CLL measurement of the diameter of aortic neck (WS2) and bifurcation (WS1 and WS2) as well as iliac diameter in all 3 WS for both CLL and MPR. Similar differences were observed in paired comparison between WS when involving these parameters. Careful inspection of Bland-Altman charts revealed some cases of disagreement between WS and observers that would affect decision making on graft selection, changing the neck diameter to a different size, in 2 cases when measuring with WS1, and iliac diameter in 4 cases (2 of them with WS1 and 2 with WS2). Greatest discordance was observed regarding ipsilateral iliac length affecting 7 measurements that would lead to change the length of the selected limb graft (2 with WS1, 3 with WS2, and 2 with WS3).

CONCLUSIONS

Although a high agreement between different observers using different WS for AAA measurements is to be expected, small differences may lead to the selection of a different graft size. The use of a single software by experienced users, and double check by a different one, may be advisable.

CLINICAL IMPACT

Influence of inter and intraobserver variability in CT measurements during planning of endovascular aneurysm repair (EVAR) has been extensively reviewed. However, its impact in graft selection (final choose of diameter and lengths) has been scarcely analyzed. The results of this study suggest that, although a high agreement between different observers using different workstations for AAA measurements is to be expected, small differences may lead to the selection of a different graft size. The use of a single software by experienced users, and double check by a different one, may be advisable.

Fully automated guideline-compliant diameter measurements of the thoracic aorta on ECG-gated CT angiography using deep learning

Background

Manually performed diameter measurements on ECG-gated CT-angiography (CTA) represent the gold standard for diagnosis of thoracic aortic dilatation. However, they are time-consuming and show high inter-reader variability. Therefore, we aimed to evaluate the accuracy of measurements of a deep learning-(DL)-algorithm in comparison to those of radiologists and evaluated measurement times (MT).

Methods

We retrospectively analyzed 405 ECG-gated CTA exams of 371 consecutive patients with suspected aortic dilatation between May 2010 and June 2019. The DL-algorithm prototype detected aortic landmarks (deep reinforcement learning) and segmented the lumen of the thoracic aorta (multi-layer convolutional neural network). It performed measurements according to AHA-guidelines and created visual outputs. Manual measurements were performed by radiologists using centerline technique. Human performance variability (HPV), MT and DL-performance were analyzed in a research setting using a linear mixed model based on 21 randomly selected, repeatedly measured cases. DL-algorithm results were then evaluated in a clinical setting using matched differences. If the differences were within 5 mm for all locations, the cases was regarded as coherent; if there was a discrepancy >5 mm at least at one location (incl. missing values), the case was completely reviewed.

Results

HPV ranged up to ±3.4 mm in repeated measurements under research conditions. In the clinical setting, 2,778/3,192 (87.0%) of DL-algorithm's measurements were coherent. Mean differences of paired measurements between DL-algorithm and radiologists at aortic sinus and ascending aorta were -0.45±5.52 and -0.02±3.36 mm. Detailed analysis revealed that measurements at the aortic root were over-/underestimated due to a tilted measurement plane. In total, calculated time saved by DL-algorithm was 3:10 minutes/case.

Conclusions

The DL-algorithm provided coherent results to radiologists at almost 90% of measurement locations, while the majority of discrepent cases were located at the aortic root. In summary, the DL-algorithm assisted radiologists in performing AHA-compliant measurements by saving 50% of time per case.

New indicators for systematic assessment of aortic morphology: a narrative review

In order to prevent the occurrence of aortic adverse events in ascending thoracic aortic aneurysm patients, preventive surgery is the sole option in case of large aneurysm. Identifying high-risk patients timely and accurately requires effective predictive indicators of aortic adverse events and accurate risk stratification thresholds. Absolute diameter measured after a single imaging examination, which has been used as the predictive indicator for decades, has been proved to be ineffective for risk stratification in moderately dilated aorta. Previously, new indicators combining absolute diameters with personalized parameters have been reported to show better predictive power of aortic adverse events than absolute diameters by correcting the effect of these parameters on the diameters. Meanwhile, combining three-dimensional parameters to formulate risk stratification thresholds not only may characterize the aortic risk morphology more precisely, but also predict aortic adverse events more accurately. These new indicators may provide more systematic assessment methods of patients’ risk, formulate more personalized intervention strategies for ascending thoracic aortic aneurysm patients, and also provide a basis for researchers to develop more accurate and effective risk thresholds. We also highlight that the algorithm obtained by combining multiple indicators may be a better choice compared with single indicator, but this still requires the support of more evidence. Due to the particularity of syndromic aortic disease, whether these new indicators can be used for its risk stratification is still uncertain. Therefore, the scope of this manuscript does not include this kind of disease.

Combined automated 3D volumetry by pulmonary CT angiography and echocardiography for detection of pulmonary hypertension

OBJECTIVES

To assess the diagnostic accuracy of automated 3D volumetry of central pulmonary arteries using computed tomography pulmonary angiography (CTPA) for suspected pulmonary hypertension alone and in combination with echocardiography.

METHODS

This retrospective diagnostic accuracy study included 70 patients (mean age 66.7, 48 female) assessed for pulmonary hypertension by CTPA and transthoracic echocardiography with estimation of the pulmonary arterial systolic pressure (PASP). Gold standard right heart catheterisation with measurement of the invasive mean pulmonary arterial pressure (invasive mPAP) served as the reference. Volumes of the main, right and left pulmonary arteries (MPA, RPA and LPA) were computed using automated 3D segmentation. For comparison, axial dimensions were manually measured. A linear regression model was established for prediction of mPAP (predicted mPAP).

RESULTS

MPA, RPA and LPA volumes were significantly increased in patients with vs. without pulmonary hypertension (all p < 0.001). Of all measures, MPA volume demonstrated the strongest correlation with invasive mPAP (r = 0.76, p < 0.001). Predicted mPAP using MPA volume and echocardiographic PASP as covariates showed excellent correlation with invasive mPAP (r = 0.89, p < 0.001). Area under the curves for predicting pulmonary hypertension were 0.94 for predicted mPAP, compared to 0.90 for MPA volume and 0.92 for echocardiographic PASP alone. A predicted mPAP > 25.8 mmHg identified pulmonary hypertension with sensitivity, specificity, positive and negative predictive values of 86%, 93%, 95% and 81%, respectively.

CONCLUSIONS

Automated 3D volumetry of central pulmonary arteries based on CTPA may be used in conjunction with echocardiographic pressure estimates to noninvasively predict mPAP and pulmonary hypertension as confirmed by gold standard right heart catheterisation with higher diagnostic accuracy than either test alone.

KEY POINTS

• This diagnostic accuracy study derived a regression model for noninvasive prediction of invasively measured mean pulmonary arterial pressure as assessed by gold standard right heart catheterisation. • This regression model using automated 3D volumetry of the central pulmonary arteries based on CT pulmonary angiography in conjunction with the echocardiographic pressure estimate predicted pulmonary arterial pressure and the presence of pulmonary hypertension with good diagnostic accuracy. • The combination of automated 3D volumetry and echocardiographic pressure estimate in the regression model provided superior diagnostic accuracy compared to each parameter alone.

Preoperative Measurements and Planning Sheet for an Endograft With 3 Inner Branches to Repair Aortic Arch Pathologies

Purpose: To present a methodology for aortic arch anatomy measurement to plan and size an arch endograft with 3 inner branches. Technique: The arch endograft is custom manufactured with 3 inner side branches. Computed tomography angiography should be used to measure the clock position, the distances between the supra-aortic vessels, and the length and diameter of the proximal and distal landing zones. On the planning sheet, the vertical axis on the grid represents the spiral stabilizing wire at the 12 o’clock position; the horizontal baseline at 0 mm represents the idealized proximal margin of the innominate artery (IA). The first inner branch for the IA would be at 12:30 clock position and −20 mm from the horizontal baseline, while the second inner branch would be at the 11:30 clock position and at 0 mm. The third inner branch would vary among the different potential positions. Conclusion: Preoperative measurements of aortic arch anatomy can be made using a standard methodology to plan the size and position of inner branches. Future studies will show the potential applicability of a standard 3-inner-branch arch endograft using the planning sheet.

Unplanned stents in thoracic endovascular aortic repair for type B aortic dissection: A 16-year single-center report

Background

Unplanned stents in thoracic endovascular aortic repair mean additional stents implantation beyond the preoperative planning to achieve operation success. This study aimed to reveal the prevalence and consequences of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection and explore the reasons, risk factors and solutions for unplanned stents.

Methods

Retrospectively analysis consecutive patients diagnosed as type B aortic dissection with initial tear originating distal from the left subclavian artery and underwent thoracic endovascular aortic repair from September 1998 to June 2014 in our center.

Results

Under the criteria, this study enrolled 322 patients, with 83 (25.8%) patients in unplanned group. The incidence rate of unplanned stents in thoracic endovascular aortic repair for type B aortic dissection in each year demonstrates as a bimodal curve. The curve showed that, 2003 and, 2004 was the first and highest peak and 2007 was the second peak. There was no difference in five-year survival rate between planned and unplanned patients (log-rank test, p = 0.994). The unplanned group had higher hospitalization expenses (142,699.08 ± 78,446.75 yuan vs. 175,238.58 ± 34,838.01 yuan; p = 0.019), longer operation time (104.50 ± 93.24 min vs. 179.08 ± 142.47 min; p < 0.001) and hospitalization time (17.07 ± 16.62 d vs. 24.00 ± 15.34 d; p = 0.001). The reasons for unplanned stents were type Ia endoleak (46 patients, 55.4%), bird beak (25 patients, 30.1%), and inappropriate shaping of stent (9 patients, 10.8%). Asymptomatic aortic dissection patients had higher incidence of unplanned stents. Short proximal neck length (2.66 ± 0.59 mm vs. 2.50 ± 0.51 mm; p = 0.016), short stent coverage length (154.62 ± 41.12 mm vs. 133.60 ± 44.33 mm; p = 0.002), and large distal stent oversize (75.44±10.77% vs. 82.68±15.80%; p <0.001) were risk factors for unplanned stents in thoracic endovascular aortic repair.

Conclusion

There are some special risk factors and reasons for unplanned stents in thoracic endovascular aortic repair for type B aortic dissection. Knowing these can we reduce the utilization of unplanned stents with appropriate methods.

Cluster analysis of acute ascending aortic dissection provides novel insight into mechanisms of distal progression

Background

Whether primary tear size impacts extent of type A dissection is unclear. Using statistical groupings based on dissection morphology, we examined its relationship to primary tear area.

Methods

We retrospectively reviewed 108 patients who underwent acute ascending dissection repair from 2000-2016. Dissection morphology was characterized using 3-dimensional (3D) reconstructions of computed tomography (CT) scan images. Two-step cluster analysis was performed to group the dissections by examining the true lumen area as a fraction of the total aortic area at various levels.

Results

Cluster analysis defined two distinct categories. This first grouping corresponds to DeBakey type I (n=71, 65.7%) with a dissection extending from the ascending aorta to the aortic bifurcation. The second grouping conforms more closely to DeBakey type II dissection (n=37, 34.3%). It differs however from the classic type II definition as the dissection may extend up to the distal arch from the ascending aorta. Compared to type I, this "extended" DeBakey type II had no malperfusion (P<0.05), a larger primary tear area (6.6 vs. 3.7 cm², P=0.009), and a greater burden of atherosclerotic coronary artery disease (P<0.05). A smaller aortic valve annulus (P=0.025) and a smaller root false lumen area (P=0.017) may explain less aortic valve insufficiency (P<0.05) in extended type II dissections. No differences in complications or survival were seen.

Conclusions

In this series, limited distal extension of DeBakey type II dissections appears to be related to a larger primary tear area and greater atherosclerotic disease burden. It is also associated with less malperfusion and aortic valve insufficiency.

How Precise Are Preinterventional Measurements Using Centerline Analysis Applications? Objective Ground Truth Evaluation Reveals Software-Specific Centerline Characteristics

PURPOSE

To evaluate different centerline analysis applications using objective ground truth from realistic aortic aneurysm phantoms with precisely defined geometry and centerlines to overcome the lack of unknown true dimensions in previously published in vivo validation studies.

METHODS

Three aortic phantoms were created using computer-aided design (CAD) software and a 3-dimensional (3D) printer. Computed tomography angiograms (CTAs) of phantoms and 3 patients were analyzed with 3 clinically approved and 1 research software application. The 3D centerline coordinates, intraluminal diameters, and lengths were validated against CAD ground truth using a dedicated evaluation software platform.

RESULTS

The 3D centerline position mean error ranged from 0.7±0.8 to 2.9±2.5 mm between tested applications. All applications calculated centerlines significantly different from ground truth. Diameter mean errors varied from 0.5±1.2 to 1.1±1.0 mm among 3 applications, but exceeded 8.0±11.0 mm with one application due to an unsteady distortion of luminal dimensions along the centerline. All tested commercially available software tools systematically underestimated centerline total lengths by -4.6±0.9 mm to -10.4±4.3 mm (maximum error -14.6 mm). Applications with the highest 3D centerline accuracy yielded the most precise diameter and length measurements.

CONCLUSION

One clinically approved application did not provide reproducible centerline-based analysis results, while another approved application showed length errors that might influence stent-graft choice and procedure success. The variety and specific characteristics of endovascular aneurysm repair planning software tools require scientific evaluation and user awareness.

Measurements After Image Post-processing Are More Precise in the Morphometric Assessment of Thoracic Aortic Aneurysms: An Intermodal and Intra-observer Evaluation

OBJECTIVES

Precise pre-procedural anatomical analysis of aneurysmal anatomy is essential for successful thoracic endovascular aortic repair (TEVAR). Since surgeons and radiologists have to perform multiple measurements in the same patient, high intra-observer reliability of any imaging method is mandatory. Commercially available three dimensional (3D) post-processing techniques are expected to be superior to conventional two dimensional multiplanar reconstructions (MPRs) derived from computed tomography angiograms (CTAs). However, few data exist to support this view. This study aims to evaluate the intermodal and intra-observer differences using 3D software (3surgery) in descending thoracic aortic aneurysms (dTAAs).

METHODS

Pre-operative CTAs (performed between 2004 and 2010) of 30 dTAAs (mean maximum diameter 61.4 ± 13 mm) were assessed by three independent investigators with different experience in the measurement of aortic pathologies. Intra-observer reliability and intermodal differences (3D vs. 2D) were investigated using pre-specified measurement points (distances of total length, maximum diameter, proximal and distal landing zones). Statistical analyses were performed using the Bland-Altman method and a mixed regression model.

RESULTS

Intermodal comparison showed that 2D measurements significantly underestimate the measured distances (maximum diameter 3.7 mm [95% CI -5.3 to -2.1] and landing zone maximum 1.4 mm [95% CI -2.0 to -0.2] shorter with 2D, p < .05). In almost all 3D measurements, all investigators showed lower variability comparing the intra-observer differences, most notably in the measuring point total length (reduction of the SD up to 7.9 mm).

CONCLUSIONS

These data show that both techniques led to significant measurement disparity. This occurs especially at the point of indication (maximum diameter) and the total length of the aneurysm (important for correct stent graft selection). But overall the variability is reduced with the 3D technique, which also tends to measure greater distances. The use of post-processing software therefore leads to more precise device selection for TEVAR in TAA.

Impact of Oversizing on the Risk of Retrograde Dissection After TEVAR for Acute and Chronic Type B Dissection

Purpose: To find a suitable rate of thoracic stent-graft oversizing by exploring its association with the occurrence of retrograde type A dissection (RTAD) after thoracic endovascular aortic repair (TEVAR) for type B aortic dissection. Methods: From January 2013 to June 2014, 203 patients (mean age 55 years; 167 men) with type B aortic dissection underwent TEVAR. The mean rate of oversizing at the proximal landing zone was 10% (range 0%–32%). Patients were stratified into 2 groups based on the degree of oversizing: ≤5% (n=105, mean 1.2%±1.5%) and >5% (n=98, mean 18.5%±2.8%). TEVAR-related complications, including RTAD, stent migration, and type I endoleaks, were analyzed. Results: There were no significant differences in the preoperative proximal landing zone diameters between the groups (31.1 mm for the ≤5% group vs 31.8 mm for the >5% group, p=0.229). The incidence of type I endoleaks over a mean follow-up 15.1±6.4 months was 5.4% [6 (5.7%) in the ≤5% group vs 5 (5.1%) in the >5% group, p=0.847]. The stent migration rate was low in both groups (1% vs 2%, respectively; p=0.521). The occurrence of RTAD [0 in the ≤5% group vs 11 (11.2%) in the >5% group] was significantly associated with the rate of oversizing (p<0.001). Conclusion: The early and midterm outcomes of this study demonstrate that ≤5% oversizing may be a suitable option for thoracic endografts used to treat type B dissection. The smaller rate of oversizing can lower the incidence of RTAD without increasing stent migration or type I endoleak rates.

A Robotic Ultrasound Scanner for Automatic Vessel Tracking and Three-Dimensional Reconstruction of B-Mode Images

Locating and evaluating the length and severity of a stenosis is very important for planning adequate treatment of peripheral arterial disease (PAD). Conventional ultrasound (US) examination cannot provide maps of entire lower limb arteries in 3-D. We propose a prototype 3D-US robotic system with B-mode images, which is nonionizing, noninvasive, and is able to track and reconstruct a continuous segment of the lower limb arterial tree between the groin and the knee. From an initialized cross-sectional view of the vessel, automatic tracking was conducted followed by 3D-US reconstructions evaluated using Hausdorff distance, cross-sectional area, and stenosis severity in comparison with 3-D reconstructions with computed tomography angiography (CTA). A mean Hausdorff distance of 0.97 ± 0.46 mm was found in vitro for 3D-US compared with 3D-CTA vessel representations. To evaluate the stenosis severity in vitro, 3D-US reconstructions gave errors of 3%-6% when compared with designed dimensions of the phantom, which are comparable to 3D-CTA reconstructions, with 4%-13% errors. The in vivo system's feasibility to reconstruct a normal femoral artery segment of a volunteer was also investigated. These results encourage further ergonomic developments to increase the robot's capacity to represent lower limb vessels in the clinical context.

A 3-D ultrasound imaging robotic system to detect and quantify lower limb arterial stenoses: in vivo feasibility

The degree of stenosis is the most common criterion used to assess the severity of lower limb peripheral arterial disease. Two-dimensional ultrasound (US) imaging is the first-line diagnostic method for investigating lesions, but it cannot render a 3-D map of the entire lower limb vascular tree required for therapy planning. We propose a prototype 3-D US imaging robotic system that can potentially reconstruct arteries from the iliac in the lower abdomen down to the popliteal behind the knee. A realistic multi-modal vascular phantom was first conceptualized to evaluate the system's performance. Geometric accuracies were assessed in surface reconstruction and cross-sectional area in comparison to computed tomography angiography (CTA). A mean surface map error of 0.55 mm was recorded for 3-D US vessel representations, and cross-sectional lumen areas were congruent with CTA geometry. In the phantom study, stenotic lesions were properly localized and severe stenoses up to 98.3% were evaluated with -3.6 to 11.8% errors. The feasibility of the in vivo system in reconstructing the normal femoral artery segment of a volunteer and detecting stenoses on a femoral segment of a patient was also investigated and compared with that of CTA. Together, these results encourage future developments to increase the robot's potential to adequately represent lower limb vessels and clinically evaluate stenotic lesions for therapy planning and recurrent non-invasive and non-ionizing follow-up examinations.

Functional lengths of the lower limb arterial tree measured by CT angiography centreline analysis: implications for catheter lengths in peripheral angioplasty

PURPOSE

Lower limb angioplasty is a common procedure. However, arterial lengths have not been well studied and there is no evidence base for the optimum catheter lengths required for the various applications of femoral or distal below-the-knee angioplasty. The industry standard catheter measures 80 cm.

METHOD

Fifty CT angiograms were post-processed using vessel tracking and centreline analysis tools and lengths were measured from the ipsilateral first segment of the femoral artery (FSFA) (common femoral artery) to the contralateral FSFA and on to the second segment of the femoral artery (superficial femoral artery) and popliteal arteries down to the posterior tibial (PT) artery at the ankle. This allowed clinically meaningful lengths for 'cross-over' and 'antegrade' angioplasty to be calculated.

RESULTS

Mean cross-over length to the second segment of the femoral artery as it crossed the femoral cortex was 72.3 cm, and the mean cross-over length to the popliteal artery at the knee joint was 83.8 cm, and the length from the FSFA to the PT was 85.1 cm.

CONCLUSION

Selection of a standard length catheter can result in a situation where the catheter is too short. Optimum catheter length for a particular task will reduce the need for catheter exchanges and use of multiple balloons and therefore reduce complications, procedure time, radiation dose and cost.

Accuracy and variability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR

OBJECTIVES

This study aims to test whether inter-observer variability and time of diameter measurements for thoracic endovascular aortic repair (TEVAR) are improved by semiautomatic centerline analysis compared to manual assessment.

METHODS

Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 males) were retrospectively analysed by two blinded experts in vascular radiology. Maximum aortic diameters at three positions relevant to TEVAR were assessed (P1, distal to left common carotid artery; P2, distal to left subclavian artery; and P3, proximal to coeliac trunk) using three measurement techniques: manual axial slices (axial), manual double-oblique multiplanar reformations (MPRs) and semiautomatic centerline analysis.

RESULTS

Diameter measurements by both centerline analysis and the axial technique did not significantly differ from MPR (p = 0.17 and p = 0.37). Total deviation index for 0.9 was for P1 2.7 mm (axial), 3.7 mm (MPR), 1.8 mm (centerline); for P2 2.0 mm (axial), 3.6 mm (MPR), 1.8 mm (centerline); and for P3 3.0 mm (axial), 3.5 mm (MPR), 2.5 mm (centerline). Measurement time using centerline analysis was significantly shorter than for assessment by MPR.

CONCLUSIONS

Centerline analysis provides the least variable and fast diameter measurements in TEVAR patients with the same accuracy as the current reference standard MPR.

Proximal thoracic aortic diameter measurements at CT: repeatability and reproducibility according to measurement method

AIM

To determine the variability in CT measurements of proximal thoracic aortic diameters obtained using double-oblique short axis and semiautomatic centerline analysis techniques. Institutional review board approval, with waiver of informed consent, was obtained for this HIPAA-compliant, retrospective study. Cardiac gated thoracic aortic CT scans were evaluated in 25 patients. Maximum aortic diameter measurements at the annulus, sinuses, sinotubular junction and ascending aorta were generated using double-oblique short axis and semiautomatic centerline analysis techniques. Intraobserver and interobserver variability and variability between techniques were assessed using the Wilcoxon signed rank test, Spearman's correlation coefficients and Bland-Altman plots. Mean intraobserver diameter differences using double oblique views ranged from -0.3 to 0.6 mm. The 95 % confidence interval for difference in diameters was ±2.4 to ±5.1 mm for radiologist #1 and ±2.6 to ±5.2 mm for radiologist #2, depending on location. Mean intraobserver diameter differences using centerline analysis ranged from 0.2 to 2.3 mm, and the 95 % confidence interval for difference in diameters was ±2.0 to ±4.6 mm, depending on location. Significant interobserver differences were seen for both double oblique views and centerline analysis. Measurements obtained using the two methods were strongly correlated (r = 0.81-0.99), although they were consistently larger using centerline analysis (95 % confidence interval, ±1.8 to ±3.2 mm). Although measurement variability of the proximal thoracic aorta was generally low using double oblique and centerline analysis techniques, differences of up to approximately 5 mm in diameter occurred within the 95 % confidence interval. Neither technique was clearly more reliable than the other.

Development of in vivo quantitative geometric mapping of the aortic arch for advanced endovascular aortic repair: feasibility and preliminary results

PURPOSE

To evaluate whether quantitative characterization of aortic arch geometry including its branches is feasible based on in vivo computed tomography (CT) angiography and magnetic resonance (MR) angiography data in healthy and diseased aortic arches.

MATERIALS AND METHODS

Ten healthy volunteers, 10 patients with abdominal aortic disease, and 10 patients with aortic arch disease underwent MR angiography (10 volunteers) or CT angiography (20 patients). Commercial software was used for individual segmentation of supraaortic arteries. In-house software was developed for segmentation of aortic arch landmarks based on standardized multiplanar reformations (MPRs) and for subsequent aortic arch mapping.

RESULTS

Supraaortic arteries and aortic arch landmarks were successfully segmented in all 30 subjects for CT angiography and MR angiography data. Significant tapering within the first centimeter was observed in all supraaortic arteries (P < .001). The three supraaortic arteries showed significantly different vessel diameters and areas (P < .001). The software developed in-house allowed detailed aortic arch mapping with quantitative definitions of the positional relationships between each supraaortic artery and the aorta. Distances between supraaortic arteries were less than 5 mm in 77.6% (mean 4.1 mm ± 3.8). The brachiocephalic trunk tended to be positioned on the right side of the aortic arch, and the left subclavian and left common carotid arteries tended to be positioned on the left side of the aortic arch.

CONCLUSIONS

The feasibility and application of a postprocessing method allowing quantification of geometry of supraaortic arteries and aortic arch mapping were successfully demonstrated. Validation and evaluation of clinical implications are warranted.

In vitro validation of flow measurements in an aortic nitinol stent graft by velocity-encoded MRI

PURPOSE

To validate flow measurements within an aortic nickel-titanium (nitinol) stent graft using velocity-encoded cine magnetic resonance imaging (VEC MRI) and to assess intraobserver agreement of repeated flow measurements.

MATERIALS AND METHODS

An elastic tube phantom mimicking the descending aorta was developed with the possibility to insert an aortic nitinol stent graft. Different flow patterns (constant, sinusoidal and pulsatile aortic flow) were applied by a gear pump. A two-dimensional phase-contrast sequence was used to acquire VEC perpendicular cross-sections at six equidistant levels along the phantom. Each acquisition was performed twice with and without stent graft, and each dataset was analysed twice by the same reader. The percental difference of the measured flow volume to the gold standard (pump setting) was defined as the parameter for accuracy. Furthermore, the intraobserver agreement was assessed.

RESULTS

Mean accuracy of flow volume measurements was -0.45±1.63% without stent graft and -0.18±1.45% with stent graft. Slightly lower accuracy was obtained for aortic flow both without (-2.31%) and with (-1.29%) stent graft. Accuracy was neither influenced by the measurement position nor by repeated acquisitions. There was significant intraobserver agreement with an intraclass correlation coefficient of 0.87 (without stent graft, p<0.001) and 0.80 (with stent graft, p<0.001). The coefficient of variance was 0.25% without stent graft and 0.28% with stent graft.

CONCLUSION

This study demonstrated high accuracy and excellent intraobserver agreement of flow measurements within an aortic nitinol stent graft using VEC MRI. VEC MRI may give new insights into the haemodynamic consequences of endovascular aortic repair.

Endografting in the aortic arch - does the proximal landing zone influence outcome?

OBJECTIVES

To analyse early and midterm results of thoracic aortic endografting (TEVAR) in the aortic arch.

METHODS

Between January 1997 and February 2009 178 patients received TEVAR in the aortic arch at our institution. This population was subdivided into four groups according to the proximal landing zone (LZ) classification in the aortic arch by Ishimaru et al. and a retrospective analysis regarding perioperative mortality, morbidity and endoleak formation was performed.

RESULTS

The overall 30-day mortality rate was 14% with no statistical significant difference between LZ's 0-3 (p=0.274). Renal insufficiency (hazard ratio (HR) 2.5; p=0.0119), age >75 years (HR 3.1; p=0.0019) and emergency procedures (HR 8.9; p < 0.0001) were independent predictors of death. There was no significant difference regarding type I (p=0.07) or type III (p=0.49) endoleaks between the proximal LZs, but a significant difference regarding the development of type II endoleaks (p=0.01).

CONCLUSIONS

The present study showed no influence of the proximal LZ on perioperative mortality and morbidity rate. Furthermore it did not influence relevant (type I/III) endoleak formation.