Thoracic aorta anatomy is complex, variable and the blood flow can be fast or slow. As a result, no single protocol will be suitable for all patients. It is necessary to customize the exam based upon the indication, age, cardiovascular status and anatomy.
In general pediatric patients and young adults have very fast flow which allows the aorta to be well seen on spin echo and time-of-flight sequences. In these patients the black blood, T1 weighted spin echo sequences with EKG gating may be sufficient. Use at least a minimum full echo and no gradient moment nulling (no flow compensation) to achieve suffcient "black blood" effect. Older adult patient generally fall into one of two categories. The first category are those with know aortic aneurysm or dissection and the only clinical issue is to determine if the aneurysm or false lumen is increasing in size. To measure aortic diameter, a simple protocol including Coronal T1, Axial T1 and Sagittal oblique T1 spin echo sequences is adequate. The second category are all the other patients where more precise vascular anatomy and lumenal detail involving both aorta and branch vessels must be imaged. For this second category of patients, 3D Gd:MRA is essential.
Sagittal 3D Gd:MRA: If you have a slow scanner and only the only the aorta and proximal great vessels need to be imaged, consider a sagittal 3D Gd:MRA.The sagittal acquisition eliminates the problem of wrap-around artifact from the arms along side the patient and allows coverage of the aorta with fewer slices. With sagittal acquistion you can speed up the scan by using rectangular FOV or you can reduce the FOV to maximize resolution.
Coronal 3D Gd:MRA: But if you need to image the subclavian or renal arteries, a coronal acquistion for the 3D Gd:MRA is preferred. This requires a state-of-the-art scanner with fast gradients to cover the anatomy with sufficient resolution within a breath hold. Start with a Sagittal spin echo locator, then axial T1, then coronal 3D Gd:MRA followed by axial 2D TOF post gadolinium. If the renal arteries are an issue (especially in patients with hypertension) then 3D phase contrast of the renal arteries can be added on at the end to take advantage of the extra SNR from the gadolinium that was administered
In general pediatric patients and young adults have very fast flow which allows the aorta to be well seen on spin echo and time-of-flight sequences. In these patients the black blood, T1 weighted spin echo sequences with EKG gating may be sufficient. Use at least a minimum full echo and no gradient moment nulling (no flow compensation) to achieve suffcient "black blood" effect. Older adult patient generally fall into one of two categories. The first category are those with know aortic aneurysm or dissection and the only clinical issue is to determine if the aneurysm or false lumen is increasing in size. To measure aortic diameter, a simple protocol including Coronal T1, Axial T1 and Sagittal oblique T1 spin echo sequences is adequate. The second category are all the other patients where more precise vascular anatomy and lumenal detail involving both aorta and branch vessels must be imaged. For this second category of patients, 3D Gd:MRA is essential.
Sagittal 3D Gd:MRA: If you have a slow scanner and only the only the aorta and proximal great vessels need to be imaged, consider a sagittal 3D Gd:MRA.The sagittal acquisition eliminates the problem of wrap-around artifact from the arms along side the patient and allows coverage of the aorta with fewer slices. With sagittal acquistion you can speed up the scan by using rectangular FOV or you can reduce the FOV to maximize resolution.
Coronal 3D Gd:MRA: But if you need to image the subclavian or renal arteries, a coronal acquistion for the 3D Gd:MRA is preferred. This requires a state-of-the-art scanner with fast gradients to cover the anatomy with sufficient resolution within a breath hold. Start with a Sagittal spin echo locator, then axial T1, then coronal 3D Gd:MRA followed by axial 2D TOF post gadolinium. If the renal arteries are an issue (especially in patients with hypertension) then 3D phase contrast of the renal arteries can be added on at the end to take advantage of the extra SNR from the gadolinium that was administered
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