**8. Evaluation of morphologic measurements**

European population showed statistically significantly longer neck of the aneurysm. With the premise that the length of the neck of 15 mm is the minimal infrarenal distance needed for graft insertion, this study showed that 31,7% patients in the Asian populaion had contraindication for EVAR, e. g. length of the neck of the AAA shorter than 15 mm. Furthermore, the mean length of the anuerysmatic neck in this population is 18,49 mm. Analyzing the subgroup of the Asian population with the neck length < 15 mm, we found that in 8 of 11 patients this length was < 10 mm, 9 mm on average.

The neck of AAA is the place of the proximal insertion of the graft, and in most cases there is a small distance between the normal and pathologic structures of aortic wall. The largest number of EVAR complications, of endoleak type, occur in this proximal part of graft insertion (43). CT aortography (CT fluoroscopy), as a dynamic analysis, enables monitoring of contrast agent flow along the aorta, or the region of interest established in examination protocol. More accurately, due to small slice thickness (0,625 mm), high spatial and temporal resolution, possibility of retroreconstruction in postprocessing at the distance of 0,2 mm and other technical features of this exam, it is possible to analyze CT exam as continuous video-recording in various visualization extensions. Also, "film" can be stoppped and paused in every moment to analyze the segment in 3D and 4D projetions, in all planes and projections.

Valuable advantage of these possibilities is that aorta, AAA and graft can be evaluated in all morphologic features, from the lateral aspects and also as ortogonally isolated transverse projections, a feature which cannot be performed using conventional aortography. These visualization possibilities favour MDCT over conventional aortography or catheter aortography. Beside the fact that it is a non-invasive procedure, additional advantage is that more diagnostic information on the early complications, such as proximal endoleak, can be obtained. Exceptional software features in standard postprocessing alow measuring of the contrast flow rate above the insertion place, inside the graft and distally, as well as different features of AAA before theraputic procedure. Critical moment for the development of proximal endoleak is physical contact of the contrast (blood) with graft contours. As it advances in cranio-caudal direction, contrast flow rate changes as a function of age, constitutional and hemodynamic cardiovascular parameters (stroke volume, width of aorta, degree of sclerotic changes, tortuosity, dilatation, etc.), but usually varies in range of 20-40 cm/sec. If the length of AAA neck is at the critical value (10-20 cm) this contact occurs in the place where vessel wall is already weakened, and its contractility, elasticity and histology are changed. Proximal endoleak can occur anywhere in the upper circumference of the graft, can be minimal, discrete and without clinical manifestations. Also, it can remain minimal in a long period of time, but usually there is a certain degree of progression, dilatation and degradation of the graft function.

Due to physical contact and strike of contrast flow onto the upper edge of the graft, the speed with which blood continues to flow, decreases gradually. Presumption is that the velocity gradient directly influences the possibility of proximal endoleak occurrence. Developing this hypothesis, in the sense of possible clinical implications and technical advances, study offered the idea that the first contact of contrast and graft occurs suprarenally, e. g. 2-3 cm cranially of the insertion place. As a consequence, in last 10 years, fenestrated grafts with suprarenal insertions have become comercially available (44,45). In this tudy, a new design of graft for AAA treatment is proposed, for patients with short aneurysmatic neck. Inovation is the annular extension of existing graft that is continuous with the basic graft on the back side, while it is opened on the front and lateral sides, where is also the orifice of renal arteries. If the force of contrast stroke at MDCT exam is marked as F1 in the common concept of insertion place, and as F2 in the proposed graft design with suprarenal insertion, we could say that F2>F1 and that blood, distally from the suprarenal insertion flows continuously with lower speed (29).

128 Aneurysm

patients with AAA (OR=0.65, 0.60-0.70, p<0.001)(30). 3 referring studies found decreased

European population showed statistically significantly longer neck of the aneurysm. With the premise that the length of the neck of 15 mm is the minimal infrarenal distance needed for graft insertion, this study showed that 31,7% patients in the Asian populaion had contraindication for EVAR, e. g. length of the neck of the AAA shorter than 15 mm. Furthermore, the mean length of the anuerysmatic neck in this population is 18,49 mm. Analyzing the subgroup of the Asian population with the neck length < 15 mm, we found

The neck of AAA is the place of the proximal insertion of the graft, and in most cases there is a small distance between the normal and pathologic structures of aortic wall. The largest number of EVAR complications, of endoleak type, occur in this proximal part of graft insertion (43). CT aortography (CT fluoroscopy), as a dynamic analysis, enables monitoring of contrast agent flow along the aorta, or the region of interest established in examination protocol. More accurately, due to small slice thickness (0,625 mm), high spatial and temporal resolution, possibility of retroreconstruction in postprocessing at the distance of 0,2 mm and other technical features of this exam, it is possible to analyze CT exam as continuous video-recording in various visualization extensions. Also, "film" can be stoppped and paused in every moment to analyze the segment in 3D and 4D projetions, in

Valuable advantage of these possibilities is that aorta, AAA and graft can be evaluated in all morphologic features, from the lateral aspects and also as ortogonally isolated transverse projections, a feature which cannot be performed using conventional aortography. These visualization possibilities favour MDCT over conventional aortography or catheter aortography. Beside the fact that it is a non-invasive procedure, additional advantage is that more diagnostic information on the early complications, such as proximal endoleak, can be obtained. Exceptional software features in standard postprocessing alow measuring of the contrast flow rate above the insertion place, inside the graft and distally, as well as different features of AAA before theraputic procedure. Critical moment for the development of proximal endoleak is physical contact of the contrast (blood) with graft contours. As it advances in cranio-caudal direction, contrast flow rate changes as a function of age, constitutional and hemodynamic cardiovascular parameters (stroke volume, width of aorta, degree of sclerotic changes, tortuosity, dilatation, etc.), but usually varies in range of 20-40 cm/sec. If the length of AAA neck is at the critical value (10-20 cm) this contact occurs in the place where vessel wall is already weakened, and its contractility, elasticity and histology are changed. Proximal endoleak can occur anywhere in the upper circumference of the graft, can be minimal, discrete and without clinical manifestations. Also, it can remain minimal in a long period of time, but usually there is a certain degree of progression, dilatation and

prevalence of DM in patients with AAA (17,18,20).

all planes and projections.

degradation of the graft function.

**8. Evaluation of morphologic measurements** 

that in 8 of 11 patients this length was < 10 mm, 9 mm on average.

The angle between aneurysm and sagittal plane of aorta in Asian population was significantly larger than in Caucasian. Also, in Asian population there were no patients with contraindication for EVAR (considering mean angle and standard deviation), while in Caucasian population, this number was not statistically significant.

On the contrary to the length of infrarenal aorta, a.i.c. in control group of Caucasian population was statistically significantly longer than in Asian. The mean length of both femoral arteries in white race population was about 14 mm higher than in yellow race, which was statistically significant. There was no significant difference in the length of infrarenal aorta between Asian and Caucasian population, but the linear distance between lower renal artery and bifurcation was significantly higher in European patient group (mean value was about 20 mm longer). This result can be explained by variations in the angle of AAA. Compared to the Hong Kong authors, this study found that linear distance in the white race patients was twice longer (40).

Transverse CT measurements considering flow diameter were performed in advanced CT aortography postprocessing programme, after transverse visualizations in graphic tool "Xsection". This software tool enables contouring flow diameter along complete length and is used for differentiating contrast agent from intraluminal and intramural calcifications, while it enables continuity and accuracy in measuring in each segment.

There was significant difference between the study populations at the level of largest and smallest flow diameter below main trunks of renal arteries (F.d. a.a. 1-2) as well as total diameter of aneurysm with the vessel wall structures at the level of maximum width of aneurysm (R.d. a.a. 3-4). Especially significant was the difference between diameters R.d. a.a. 3-4. To the best of our knowledge, there are no similar results published in literature, nor have these measurements been performed in populations of different races. CT aortographic measurements performed in this study were inspired by problems that doctors who perform EVAR encountered due to incompatibility of the comercially available grafts for the patients of yellow race.

Infrarenal segment of aorta in patients with AAA is a nondilated part. However, the fact that infrarenal segment of aorta in all the subject of Asian population was significantly wider than transverse diameter of control subjects, and additionally, that it is related to the neck which is not dialated in transverse diameter, leads to conclusion that AAA patients in general have wider aneurysmatic neck than infarenal segment of control subjects (with discrete aortic dilatation or normal findings). Furthermore, the width of this segment may be disposing factor for the development of AAA or/and vice versa, that the development of AAA leads to dilatation of the aneurysmatic neck.

Most of the studies showed that the diameter of abominal aorta aneurysm grows for 0,08 cm annually, so the most accurate conclusions could be obtained by comparing subjects of the same age (29,40).

Asian population with the presence of aneurysm had significanty higher following diameters F.d. a.i.c. 2-6 i R-d. a.i.c. 1-6. compared to controls, while in F.d. a.i.c 1 there was no significant difference. The most prominent result was found in the transverse diameters F.d. a.c.i 1 of patients and controls. This was the only parameter where there was no difference in patients and controls of the Asian population, while in Caucasian there was a border-line difference. The exact place is just above the bifurcation, where depending on the bifurcation angle, there is a different flow gradient that correlates with the angle of bifurcation, which is lower in the population of yellow race. Additionally, there is a subtle difference between the blood flow velocity of the aorta and proximal parts of iliac arteries. The changes in the vessel wall, as well as propagation of the aneurysm from aorta to iliac arteries, have no direct impact on Fd diameter.
