Fig 1.
Diameter assessment in three control aortas using (a) Long Axis MMode, (b) Short Axis MMode, and (c) Short Axis BMode.
For each case, the images on the right show either diameters (MMode) or circumferences (BMode) at three timepoints during systole and three timepoints during diastole. Tracing was performed using the built-in Vevo 2100 software. For the MMode cases (a and b), the arrows in the left images indicate the placement of the MMode measurement line. Diameter values for the BMode view were derived from the perimeter assuming a circular shape. In all cases, the median diameter from each set of three measurements was used. Branches are labeled in the Long Axis MMode (CA: Coeliac Artery, MA: Mesenteric artery. SC: Supraceliac. PV: Paravisceral), but cannot be visualized in the same field of the view during Short Axis measurements."
Fig 2.
Diameter assessment in dissecting AAAs.
a. Long axis view taken at the level of the intramural hematoma and false channel, where the abdominal aorta is not visible. b. Long axis view taken at the level of the tear in the tunica media, showing a dissecting flap. The image in MM2 shows how the inner layer (tunica media) is more distensible than the dissected outer layer (tunica adventitia), while the tunica media is not visible when measuring at MM3. c. Long axis view taken at the level of the aortic lumen, the false channel is not visible, and the intramural hematoma seems much smaller than in reality. d. 3D visualization of dissecting AAA based on PCXTM scans. Image taken from [42] for visualization purposes. The ultrasound images shown in panels a-c (LA MMode) and d-f (SA MMode) do not correspond to the actual 3D geometry shown on the top panels, but were taken at locations that were similar to the indicated lines. IH: Intramural Hematoma. FC: False Channel. CA: Celiac Artery. MA: Mesenteric Artery. RRA: Right Renal Artery. AA: Abdominal Aorta. e. Short axis view showing an intramural hematoma that is located on the anterior side of the aortic lumen. f. Short axis view showing an intramural hematoma that is located on the left side of the abdominal aorta. g. Short axis view taken at the level of the false channel. h. Short axis MMode circumferential strain in matched pairs (n = 19) where both a dissected adventitia and tunica media could be measured simultaneously (cfr. MM2). The inner, medial layer is more distensible than the outer, adventitial layer. Since the pulse wave travels over the innermost layer, this will influence the PWV value obtained with transit time methods.
Fig 3.
PWV assessment in controls and dissecting AAAs.
a. Global, ultrasound-based transit time PWV (Eq (3)). Descending and distal abdominal pulsed Doppler waveforms were obtained sequentially, the foot-to-foot time lag is obtained from averaged waveforms. The distance between both measurement locations is measured externally with tape. b. Regional, pressure-based transit time PWV (Eq (4)). Pressure waveforms are obtained simultaneously, and the foot-to-foot time lag from beat-to-beat waveforms. The distance between both pressure sensors is fixed on 0.02m. c. Local PWV assessed from aortic distensibility (Eqs (5) and (6)). Invasive pressure waveforms and non-invasive, raw-frequency MMode diameter waveforms are obtained simultaneously. No distance measurement is needed. d. Top: schematic representation depicting how in some cases the inserted pressure probe entered into the false channel at the level of the tear in the tunica media. IH: Intramural Hematoma. FC: False Channel. AA: Abdominal Aorta. P: Pressure probe. Since further insertion of the probe was not possible, no transit time PWV could be obtained in these cases. Middle: In vivo long axis BMode image showing how the pressure probe gets stuck within the intramural hematoma of a dissecting AAA. Bottom: In vivo long axis BMode image of the pressure probe inserted inside a normal aorta without dissecting AAA.
Fig 4.
Increase of aortic diameters and decrease of circumferential strains over time.
a. Aortic diameters are shown for 3 different methods, measured at paravisceral and supra-celiac regions and showing systolic as well as diastolic values. All methods show low standard deviations at baseline but not at later time points. All methods find a highly signficant difference (p<0.001, indicated by **) between diameters at baseline and day 14. Short axis BMode and MMode find a highly significant difference between diameters at days 14 and 28, but long axis MMode does not. b. Circumferential strains are shown for 3 different methods, measured at paravisceral and supra-celiac regions. All methods show high standard deviations at all time points. All methods find a highly significant difference between diameters at baseline and day 14. Short axis and long axis MMode find a highly significant difference between strains at days 14 and 28, but BMode does not.
Fig 5.
Comparison of diameters assessed with short axis BMode to long axis or short axis MMode.
a. High correlation between short axis MMode and BMode diameters. b. Bland-Altman plot shows low dispersion between short axis MMode and BMode diameters, no bias. a. Poor correlation between long axis MMode and BMode diameters. b. Bland-Altman plot shows high dispersion between long axis MMode and BMode diameters, no bias, larger dispersion for later time points.
Table 1.
Diameters and circumferential strains obtained with three techniques at three different time points and two different aortic locations.
Fig 6.
Comparison of circumferential strains assessed with short axis MMode to short axis BMode or long axis MMode.
a. Poor correlation between BMode and short axis MMode circumferential strains. b. Bland-Altman shows high dispersion between short axis BMode and short axis MMode circumferential strains, no bias, larger dispersion for earlier time points. c. Poor correlation between long axis and short axis MMode circumferential strains. d. Bland-Altman shows high dispersion between long axis MMode and short axis MMode circumferential strains, no bias, larger dispersion for earlier time points.
Fig 7.
Comparison of different methods to assess aortic PWV in vivo.
a. Standard deviations in control animals are highest for ultrasound-based transit time and lowest for the pressure-diameter method. Ultrasound nor pressure-based transit time methods can differentiate in PWV between controls and AAAs, while the pressure-diameter method detects a significant difference. b. Poor correlation between ultrasound-based and pressure-based transit time methods for PWV assessment. In only 4/8 AAAs a pressure transit time could be obtained (Fig 3d).