3D ultrasound applied to abdominal aortic aneurysm: preliminary evaluation of diameter measurement accuracy Poster No.: C-0493 Congress: ECR 2011 Type: Authors: Keywords: DOI: Scientific Paper A. LONG 1, L. Rouet 2, R. Ardon 2, A. Wolak 1, E. Allaire 3 ; 1 Reims/ FR, 2 Suresnes/FR, 3 Creteil/FR Arteries / Aorta, Vascular, Ultrasound, Computer Applications-3D, Aneurysms 10.1594/ecr2011/C-0493 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 13
Purpose Follow-up of abdominal aortic aneurysm (AAA) consists in monitoring its maximal diameter with 2D ultrasound (2D U/S). But this technique has limits : 1. The choice of the optimal diameter is not standardized. Both anteroposterior diameter and maximal diameter perpendicular to the blood flow are used (1-3). 2. 2D U/S mode provides a limited number of slices. Their content and quality depends on the skill of the operator. Once the 2D slices are acquired, it is no longer possible to image other planes. 3. Reproducibility of measurements between successive exams may be comparable to the amount of aneurysm growth. An original protocol for 3D U/S analysis of AAA including U/S volume acquisitions and software prototype was developed with the purpose to overcome the above limitations. This protocol allows : 3D visualization of the AAA geometry in space, navigation in the volume along axial, sagittal and coronal, planes and diagnostic review at any time, automatic and manual selections of the cross-section of interest, automatic extraction of quantification parameters. Its accuracy was evaluated for AAA diameter measurements. Methods and Materials Patients This study included 13 patients with native AAA. AAA standard diameter from 2D acquisition, body mass index and aneurismal depth were collected. Ultrasound protocol U/S volume acquisitions were performed with a 3D convex mechanical abdominal probe. Page 2 of 13
Two volumes were acquired per patient (Fig. 1) : - Angular scanning in the cranio-caudal provided axial volume. - Angular scanning in the transverse direction provided longitudinal volume. Sequences were transferred to a dedicated PC with the prototype software. Sequences analysis included (Fig. 2): 1. semi-automatic segmentation of the AAA, 2. centerline determination, 3. cross-section extraction, 4. automatic diameter extraction. Navigation in the interface allowed to show different views of the AAA (Fig. 3). For each cross-section normal to centerline, the prototype extracted 3 parameters (4): 1. real maximum diameter corresponding to the maximum distance between any couple of points on a cross-section, 2. major diameter corresponding to the long axis length obtained from an elliptic model fitting, 3. the corresponding minor diameter of the ellipse. For each AAA, maximum value of real and major diameters were reported (Fig. 4 and 5). Statistical analysis Agreement : Bland-Altman assessment for agreement was used to compare parameters between axial and longitudinal volumes. Limits of agreement (LOA) were defined as mean difference ± 2SD. Clinically acceptable LOA was ± 5mm. Correlation : Correlation between agreement and body mass index, aneurysm depth, and standard diameter was studied. Images for this section: Page 3 of 13
Fig. 1: Volume scanning of the AAA. Angular scanning in the cranio-caudal direction (top) and in the transverse direction (bottom). Red arrow indicates probe array tilting. Page 4 of 13
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Fig. 2: Steps for image processing. Top : Semi-automatic segmentation of the AAA Middle : Centerline. Red point : cranial extremity; blue point : caudal extremity Bottom : Cross-sections extraction Page 6 of 13
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Fig. 3: Different views of the AAA. Top : Lateral Middle : Caudo-cranial Bottom : Superior Fig. 4: Automatic quantification : the blue circle identifies the maximum real diameter Fig. 5: Automatic quantification interface showing longitudinal quantification of AAA Page 8 of 13
Results Each AAA could be segmented. Bland-Altman plots for the 3 diameters are reported in Fig. 1 to 3. The LOA were clinically acceptable for real diameter, and almost acceptable for major and minor diameters (table below). Diameter Mean Difference Limits of agreement (mm) (mm) Real maximum 0.20-4.53 to 4.92 Major 0.25-5.02 to 5.52 Minor -0.56-5.93 to 4.80 There was no correlation between real maximum diameter agreement and : body mass index (r = 0.05, p = 0.88) aneurismal depth (r = 0.07, p = 0.81) 2D standard diameter (r = - 0.35, p = 0.24) Images for this section: Page 9 of 13
Fig. 1: Bland-Altman plot for Real Maximum diameter (Axial versus longitudinal volumes) Fig. 2: Bland-Altman plot for corresponding major diameter (Axial versus longitudinal volumes) Page 10 of 13
Fig. 3: Bland-Altman plot for corresponding minor diameter (Axial versus longitudinal volumes) Page 11 of 13
Conclusion A rotation of 90 of the 3D probe incidence (axial or longitudinal scanning) has low influence on evaluated parameters. 3D ultrasound analysis of AAA is independent from body mass index, aneurismal depth or size. The present protocol is expected to reduce operator dependency. References 1) The UK Small Aneurysm Trial Participants Mortality results for randomised controlled trial of early elective surgery or ultrasonographic surveillance for small abdominal aortic aneurysms. The Lancet 1998 ; 352 : 1649-55. 2) Lederle FA, Wilson SE, Johnson GR, Littooy FN, Acher C, Messina LM, Reinke DB, Ballard DJ, for the ADAM VA Cooperative Study Group Design of the abdominal aortic Aneurysm Detection and Management Study. J Vasc Surg 1994 ; 20 : 296-303. 3) Sprouse LR, Meier GH, Parent FN, DeMasi RJ, Glickman MH, Barber GA. Is ultrasound more accurate than computed tomography for determination of maximal abdominal aortic aneurysm? Eur J Vasc Endovasc Surg 2004 ; 28 : 28-35. 4) L Rouet, R Ardon, JM Rouet, B Mory, A Long. Semi-automatic abdominal aortic aneurysms geometry assessment based on 3D ultrasound imaging. IEEE. Accepted for publication. Page 12 of 13
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