Vascular Deformation Mapping (VDM) of Thoracic Aortic Enlargement in Aneurysmal Disease and Dissection

Figures

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  Figure 1.. Vascular deformation mapping (VDM) workflow: computed tomography angiography (CTA) images undergo digital image processing and analysis that involves segmentation of the contrast-enhancing aortic blood volume followed by nonrigid coregistration between baseline and follow-up sessions. 3D maps of the determinant of the spatial Jacobian are then generated using the final optimized transform. These values are subsequently mapped to the 3D surface of the aortic segmentation, essentially allowing for visualization of the aortic wall deformation rate between imaging sessions. Expansion can be visualized as red (VDM > 1), compression as blue (VDM < 1), and no deformation as green (VDM = 0).

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  Figure 2.. Progressive enlargement of an aortic aneurysm of the descending aorta in a 76-year-old patient with history of prior surgical repair of the ascending aorta. Aortic enlargement is noted at all intervals, but increases in rate and extent over time. Aortic lumen area (in square millimeter) measured at a single level (black line) in the distal descending aorta was used to corroborate a focal region of enlargement in the distal descending aorta seen on the VDM map. VDM values for replaced ascending aorta are not displayed owing to artifact.

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  Figure 3.. VDM analysis shows no areas of high-intensity wall expansion in a 66-year-old woman with a mild dilated ascending aorta (4.1 cm maximally). Although aortic dimensions were stable by clinical diameter assessment, low-intensity areas of potential aortic enlargement were noted at the sinotubular junction and in the region of the innominate artery, suggesting the possibility of limited growth in these regions.

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  Figure 4.. Overall stable aortic dimensions in a 56-year-old man with a history of surgical repair of the ascending aorta for type A dissection with residual dissection flap in the aortic arch and descending aorta. Small areas of apparent aortic expansion at the aortic root and distal descending aorta are likely because of mild coregistration artifact (*).

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  Figure 5.. VDM analysis of a 52-year-old man with a history of type B dissection shows interval expansion of the false lumen (red) with interval compression of the true lumen (blue) over a short interval of 6 months. Clinical diameter measurements suggested 1–2 mm increase in maximal dimensions, but no definite enlargement was described because the diameter change was within the range of measurement error. Cardiac motion artifact in the ascending aorta results in a wavy aortic wall contour and areas of high- and low-VDM values on opposite sides of the aortic wall.

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  Figure 6.. Progressively enlarging aortic dimensions in a 76-year-old man with a history of type B aortic dissection over 3 intervals with the rate of enlargement noted to progressively decrease during follow-up. The highest-intensity regions of enlargement were at the level of the proximal and distal descending aorta levels corresponding to the location of entry tears in the dissection flap. Clinical diameter assessment detected a 4-mm interval growth at the second interval in the distal arch, but no definite enlargement was noted at the first or third intervals. VDM values for replaced ascending aorta are not displayed because of artifact.

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  Figure 7.. Diagram of sources of measurement variability with maximal diameter and VDM measurement techniques. Variability in diameter measurements arises from 3 potential user-specific inputs: placement of the near-wall caliper (green error bar), placement of the far-wall caliper (red error bar), and sight differences in radial position of diameter measurement in noncircular aortic segments (blue error bar). The nonrigid image registration techniques used in the VDM analysis are reported to have submillimeter precision (purple error bar), and coregister all points in 3D space along the circumference and length of the aorta, making detection of local regions of nonmaximal growth possible (gray area of wall bulging).

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  Figure 8.. Color 3D-printed model of the thoracic aorta produced from the VDM results of a patient with progressively enlarging descending aortic aneurysm presented in Figure 2, interval 2. The superimposition of pathophysiologic VDM data on a 3D-anatomic model represents a novel application of medical 3D printing and be valuable in operative planning.