Aortic neck diameter assessment method according to the current standard.

<p>The average of long (left) and short (right) axis provide the diameter of the corresponding circle.</p

Endograft Sizing for Endovascular Aortic Repair and Incidence of Endoleak Type 1A

<div><p>Objective</p><p>In endovascular aortic aneurysm repair (EVAR), proximal type 1A endoleaks can occur as a result of hostile neck anatomy or over- or undersizing of the endograft. As the current standard is based on the diameter or average of the short and long axes in a central lumen reconstruction image, it can falter in irregularly shaped aortic necks. An alternative method is circumference-based, therefore minimizing the measurement error. In this study we aimed to assess the degree of discrepancy between both methods and the association of this discrepancy with the occurrence of endoleak type 1A.</p><p>Methods</p><p>All patients with early (<30 days post-operative) endoleak type 1A after elective EVAR at our center between 2004 and 2016 were identified for a retrospective case-control study. Control patients were matched based on hostile neck anatomy, such as calcification, thrombus, reverse taper, and β-angulation. The aortic neck diameter was measured using the traditional, diameter-based method as well as an alternative method, based on the circumference of the aortic neck.</p><p>Results</p><p>In 482 EVAR patients, 18 early endoleak type 1A cases were found (3.9%). After exclusion, 12 cases remained and 48 matching controls were found. No significant differences were found between the two measuring methods at any level below the renal arteries. The inter-observer variability was significant for the D(mean) (0.4 ± 1.69 mm, P = .02) and was larger than the D(circ) method (-0.1 ± 1.03 mm, P = .35). In only four out of 12 cases the endograft size was 10–20% larger than the D(mean) and D(circ) measurements. The differences between the diameter of the D(mean) and D(circ) and the chosen endograft were smaller for the case group (-8 ± 25.6% and -7 ± 24%) than for the control group. (-12.4 ± 12.4% and -11 ± 10.7%).</p><p>Conclusion</p><p>The difference between the D(mean) and D(circ) methods for aortic neck measurement was not large enough to play a significant role in the incidence of endoleak type 1A. Inadequate oversizing and considerable β-angulation of the aortic neck may have been the cause of endoleak type 1A in this population. Robust and well-investigated sizing methods are paramount for accurate endograft sizing and prevention of endoleak type 1A. Therefore the lack of studies in this field and a sizeable inter-observer variability do not justify the widespread reliance on the traditional diameter-based methods for endograft sizing.</p></div

Computed tomography image of the abdominal aorta.

<p>In Roman numerals the infra renal distances are portrayed. I: 0 mm, II: 7.5 mm, and III: 15 mm. To provide a standardized method for measuring the distances as mentioned above, first the midline of the aortic neck is chosen. The perpendicular line is then placed at the point where the lowest renal artery branches from the aorta. In the caudal direction from this point (I) and parallel to the midline, a distance of 7.5 and of 15 mm is measured to identify point II and III, respectively.</p

Case group neck measurements, endograft size, and comparisons.

<p>Case group neck measurements, endograft size, and comparisons.</p

Characteristics and treatment of endoleak type 1A in the case group.

<p>Characteristics and treatment of endoleak type 1A in the case group.</p

Bland-Altman plot of the differences between D(mean) and D(circ) measurements of both observers.

<p>Bland-Altman plot of the differences between D(mean) and D(circ) measurements of both observers.</p

Demographic characteristics of case and control groups.

<p>Demographic characteristics of case and control groups.</p

Population selection in this study.

<p>Of the 482 patients with AAA who were selected for EVAR treatment, 23 received acute intervention and were excluded. EL1A was found in 18 patients, two of which received custom made endografts and in four cases the CTA images were missing. These were therefore excluded. Of the 441 remaining EVAR, 48 controls were selected based on matching for hostile neck anatomy. AAA: abdominal aortic aneurysm. EVAR: endovascular aneurysm repair. EL1A: endoleak type 1A. CTA: computed tomography angiography.</p

Quantification of abdominal aortic calcification: Inherent measurement errors in current computed tomography imaging

<div><p>Objective</p><p>Quantification software for coronary calcification is often used to measure abdominal aortic calcification on computed tomography (CT) images. However, there is no evidence substantiating the reliability and accuracy of these tools in this setting. Differences in coronary and abdominal CT acquisition and presence of intravascular contrast may affect the results of these tools. Therefore, this study investigates the effects of CT acquisition parameters and iodine contrast on automated quantification of aortic calcium on CT.</p><p>Methods</p><p>Calcium scores, provided in volume and mass, were assessed by automated calcium quantification software on CT scans. First, differences in calcium scores between the abdominal and coronary CT scanning protocols were assessed by imaging a thorax phantom containing calcifications of 9 metrical variations. Second, aortic calcification was quantified in 50 unenhanced and contrast-enhanced clinical abdominal CT scans at a calcification threshold of 299 Hounsfield Units (HU). Also, the lowest possible HU threshold for calcifications was calculated per individual patient and compared to a 130 HU threshold between contrast-enhanced and unenhanced CT images, respectively.</p><p>Results</p><p>No significant differences in volume and mass scores between the abdominal and the coronary CT protocol were found. However, volume and mass of all calcifications were overestimated compared to the physical volume and mass (volume range: 0–649%; mass range: 0–2619%). In comparing unenhanced versus contrast-enhanced CT images showed significant volume differences for both thresholds, as well as for mass differences for the 130 vs patient-specific threshold (230 ± 22.6 HU).</p><p>Conclusion</p><p>Calcification scoring on CT angiography tends to grossly overestimate volume and mass suggesting a low accuracy and reliability. These are reduced further by interference of intravascular contrast. Future studies applying calcium quantification tools on CT angiography imaging should acknowledge these issues and apply corrective measures to ensure the validity of their outcomes.</p></div

Histogram of the HU levels of the non-enhanced and contrast-enhanced CT scans of one patient.

<p>The arrows show the selected thresholds. Purple arrow: static threshold (299 HU). Green arrow: patient specific threshold. HU: Hounsfield Units.</p