Adequate diagnosis of aortic dissection is still a challenge, not because of difficulties in imaging depiction but because of the need to rapidly achieve diagnosis, given that the outcome of patients decreases tremendously with time in cases of acute type A dissection. Furthermore, additional information on the localization and extent of the dissection, on entries and re-entries as well as on the involvement of other vessels or paravascular hemorrhage is needed in order to satisfactorily plan therapeutic strategy.
CT and CTA represent widely available and rapid imaging modalities for the diagnosis of acute aortic dissection. Sensitivity and specificity values between 83% and 94%, and 87% and 100%, respectively, have been achieved with these techniques . With the application of helical CT scans, further improvements in diagnostic accuracy have been achieved especially in type A dissection in which sensitivity was previously below 80% [22,23]. Unfortunately, CT is disadvantaged by the need for radiation and iodinated contrast material as well as by decreased soft tissue resolution.
In comparison, MR imaging is able to achieve sensitivities and specificities of 95 to 100% for the diagnosis of aortic dissection [7,19,20,24,25].Ac-cordingly, this technique represents the imaging modality of choice for both elective examination of suspicious aortic dissection and for follow up studies. Apart from not requiring radiation and potentially nephrotoxic iodinated contrast agents, MR imaging permits a free choice of image orientation and increased soft tissue resolution. Disadvantages, however, are longer examination times, the lack of immediate and widespread availability of scanners and a restriction of monitoring capabilities and patient access due to narrow gantry tubes. However, these limitations will improve with further developments in hardware and software.
Another quick and widely available imaging modality is transesophageal echography (TEE) which permits accurate diagnosis of aortic dissection with a specificity from 63% to 96% and a sensitivity of up to 98% [20,26,27]. Clear advantages are the bed-side performance in unstable patients and the possibility to evaluate paravascular hemorrhage, blood flow, dissection membrane and heart with a one-stop-shop approach. Limitations of TEE are the strong dependence on investigator experience, the small field of view and the relative invasiveness of the procedure.
With aortography, which was formerly considered an imaging modality of choice, sensitivities of 86 to 88% and specificities of 75 to 94% have been reached for the diagnosis of aortic dissection [20,28,29]. However, due to the invasiveness of the procedure aortagraphy is seldom used as primary diagnostic tool. On the other hand, pre-surgical evaluation of the coronary arteries often requires invasive aorto- and coronarography.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.