Pitfalls Limitations

Due to the sometimes tremendous mobility of the ascending aorta and aortic arch, especially in patients with Marfan's syndrome, it is occasionally possible to observe blurring of the ascending aorta and even depiction of artifacts which might be misinterpreted as aortic dissection.

In cases in which diagnosis of aortic dissection is suspected from contrast enhanced MRA images, conventional ECG-gated cross-sectional images should also be acquired to confirm the diagnosis. Sometimes this can also be accomplished by means of CINE imaging.

Another pitfall in imaging of the thoracic aorta especially in patients with advanced atherosclerotic disease and elongation with increased tortuosity of the thoracic aorta is incomplete coverage of the anatomy. As mentioned above, in some patients elongation and tortousity of the thoracic aorta may be so extreme as to necessitate slab orientation in the sagittal plane in order to completely cover the aorta. In general to avoid this kind of pitfall one should perform extensive localizer imaging before finally positioning the slab for the contrast enhanced 3D MRA study. Similarly, a preliminary unenhanced scan should be reviewed to look for aliasing or incomplete coverage of the thoracic aorta.

Another important issue in imaging of the thoracic aorta is ringing or stripe artifacts. These artifacts in the lumen of the aorta are caused by incorrect timing of the contrast agent bolus. If the contrast agent bolus arrives too late the central parts of k-space are acquired at a time when the maximum Gd concentration has not yet been reached. If a significantly higher Gd concentration in the area of interest is then found during the acquisition of the peripheral parts of k-space, artificial longitudinal dark stripes within the aortic lumen may occur which can simulate the presence of aortic dissection in a similar manner to that found in patients with increased mobility of the ascending aorta and aortic arch.

To avoid or compensate for this kind of artifact a second acquisition of a 3D dataset should be performed immediately after the first, bolus-timed acquisition. If these dark longitudinal lines are only found on the first dataset, a diagnosis of aortic dis section can be excluded. Conversely, if these lines also appear on the second dataset, a diagnosis of aortic dissection is likely.

Finally, periaortic inflammation may be misdi-agnosed in cases of pneumonia adjacent to the aorta or in cases in which the surrounding lung parenchyma is atelectatic due to dilatation of the aorta. In these cases strong enhancement of the lung tissue is observed which should not be mistaken for inflammation of the aortic wall.

In general to avoid the pitfalls in thoracic 3D CE MRA accurate planning of the examination is necessary and imaging should be performed in conjunction with conventional cross-sectional imaging or CINE imaging. Using this approach in the majority of cases images should be diagnostic and interpretation should be unequivocal.

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Essentials of Human Physiology

Essentials of Human Physiology

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