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Figure 11.13. Intramural hematoma (IMH) is diagnosed on the unenhanced CT scans on the basis of the identification of a crescent-shaped area of attenuation in the aortic wall, corresponding to the hematoma, such as in this example of type A IMH ((a), axial scan, arrows). This area does not show contrast enhancement after contrast material injection ((b), axial scan), and no intimal tears are visualized. Therefore, the unenhanced scans are required for the diagnosis.

Figure 11.13. Intramural hematoma (IMH) is diagnosed on the unenhanced CT scans on the basis of the identification of a crescent-shaped area of attenuation in the aortic wall, corresponding to the hematoma, such as in this example of type A IMH ((a), axial scan, arrows). This area does not show contrast enhancement after contrast material injection ((b), axial scan), and no intimal tears are visualized. Therefore, the unenhanced scans are required for the diagnosis.

Figure 11.14. The penetrating atherosclerotic plaque of the thoracic aorta is visualized as an ulcerlike area of contrast enhancement outside the aortic lumen ((a), axial scan, arrow). The corresponding aortic wall can be thickened ((b), MPR reconstruction in sagittal plane, arrow).

Figure 11.14. The penetrating atherosclerotic plaque of the thoracic aorta is visualized as an ulcerlike area of contrast enhancement outside the aortic lumen ((a), axial scan, arrow). The corresponding aortic wall can be thickened ((b), MPR reconstruction in sagittal plane, arrow).

ogy of the wall, status of the lumen, flow, and functional properties of the vessel. For these reasons, MRI has been proposed for the evaluation of acute aortic diseases, such as aortic dissection, intramural hematoma, as well as for chronic diseases such as aneurism and inflammatory diseases69-73.

MRI has several advantages (such as the use of nonionizing radiations, and the use of nonnephrotoxic contrast agents) and, similar to CT, it has the capability of producing two- and three-dimensional images with a panoramic field of view. Spatial resolution is lower than both TEE and CT; however, it remains high enough to allow an excellent diagnostic accuracy, higher than TEE and superimposeable to CT18,66-69. Beyond the crude anatomical information, MRI allows a finer depiction of histopathologic components of the vessel wall, such as the presence of edema, fat, and hemorrhage. A great advantage of MRI is the possibility of quantitatively evaluating the flow inside the vessel and, eventually, in the presence of a dissection, of evaluating the relative flow in both the true and the false lumen. Finally, similar to TEE, MRI easily offers the possibility of evaluating the morphology and functionality of the aortic valve and the presence of valvular, perivalvular regurgitation, which has relevant clinical and therapeutical implications.

With respect to the other techniques, MRI has some disadvantages, such as the reduced availability of scanners and higher cost. It also is more demanding both for the operator and the patient: claustrophobia affects 5% of patients, and patients have to be clinically and hemodynamically stable. However, in specialized centers the availability of qualified personnel who are able to manage unstable patients inside the scanner and of vital-signs monitors, which can be used inside the magnet room, reduces the number of patients who cannot be studied with MRI, if clinically indicated66.

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