Synchrotron Radiation-based X-ray phase-contrast imaging of the aortic walls in acute aortic dissection

Synchrotron radiation-based X-ray phase-contrast tomography (XPCT) imaging is an innovative modality for the quantitative analysis of three-dimensional morphology. XPCT has been used in this study to evaluate ascending aorta specimens from patients with acute type A aortic dissection (ATAAD) and to analyze the morphologic structure of the aortic wall in patients with this condition.

Aortic specimens from 12 patients were obtained during repairs for ATAAD and were fixed with formalin. Five patients had Marfan syndrome (MFS), and seven did not. In addition, six normal aortas were obtained from autopsies. Using XPCT (effective pixel size, 12.5 μm; density resolution, 1 mg/cm³), the density of the tunica media (TM) in each sample was measured at eight points. The specimens were subsequently analyzed pathologically.

The density of the TM was almost constant within each normal aorta (mean, 1.081 ± 0.001 g/cm³). The mean density was significantly lower in the ATAAD aortas without MFS (1.066 ± 0.003 g/cm³; P < .0001) and differed significantly between the intimal and adventitial sides (1.063 ± 0.003 vs 1.074 ± 0.002 g/cm³, respectively; P < .0001). The overall density of the TM was significantly higher in the ATAAD aortas with MFS than those without MFS (1.079 ± 0.008 g/cm³; P = .0003), and greater variation and markedly different distributions were observed in comparison with the normal aortas. These density variations were consistent with the pathologic findings, including the presence of cystic medial necrosis and malalignment of the elastic lamina in the ATAAD aortas with and without MFS.

XPCT exhibited differences in the structure of the aortic wall in aortic dissection specimens with and without MFS and in normal aortas. Medial density was homogeneous in the normal aortas, markedly varied in those with MFS, and was significantly lower and different among those without MFS. These changes may be present in the TM before the onset of aortic dissection.