Normal Cardiac Anatomy









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    Knowledge of the anatomy of the heart and in particular the three-dimensional (3D) relationships of the various normal structures is essential.


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    The heart lies at an oblique and variable angle within the chest, and standard cardiovascular magnetic resonance (CMR) imaging planes are relative to the long axis of the heart rather than the body. Standard image planes relative to body position (e.g., coronal, transaxial) can provide useful anatomic information, but it should be made clear how the image plane was positioned to avoid confusion.


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    Three-dimensional spatial awareness is important in appreciating normal cardiac anatomy. Because of the oblique nature of many cardiac structures and the two-dimensional plane of a single CMR image slice, it is possible to “slice” through a structure at an oblique angle, which may appear abnormal. Further imaging in different planes (often perpendicular to the one with the apparent abnormality) is recommended to fully appreciate the nature of the anatomy and determine whether it is normal or abnormal.


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    Modification of the image position may be required if the initial image is not ideal. Do not be afraid of repeating the sequence, having moved the image plane slightly or obtained other image slices to better position the image slice.


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    Optimization of the sequence to each patient is important for obtaining the highest-quality images (e.g., the trade-off between spatial and temporal resolution may have to be adjusted individually). If the initial image is of poor quality, repeat with better parameters as necessary.


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    For many images, cine imaging is recommended because of the continuously moving heart, because this provides a better appreciation of the anatomy in motion.


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    Spin-echo images provide good contrast between tissues containing adipose tissue (e.g., pericardial fat) and tissues with high water content (e.g., myocardium) or fibrous tissue (e.g., pericardium).


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    Beware of partial volume effects. The relatively thick slice thickness of CMR images (5 to 8 mm) can include parts of two structures combined in one image plane.



KEY POINTS





Figure 1-1


Transverse views from HASTE sequence in upper thorax, from superior ( A ) to inferior ( D ). Black-blood sequence, with adipose tissue appearing bright (high signal), air and flowing blood appearing dark (low signal), and most other tissues of mid-gray intensity (intermediate signal); slice thickness = 7 mm. In ( A ), the great vessel origins can be seen-innominate/brachiocephalic artery (innom), left common carotid artery (LCC), left subclavian artery (LSA), and superior vena cava (SVC), in addition to the trachea (Tr). The esophagus (Eso) is located posterior to the Tr, but is normally compressed when lying flat, and is difficult to visualize; it can be seen lower down in ( C ). The aortic arch (Ao arch) and SVC appear in ( B ). Just below the aortic arch in ( C ), the left pulmonary artery (LPA) can be seen along with the right (RMB) and left (LMB) main bronchi, highlighted against the mediastinal fat. Lower still in ( D ), the main pulmonary artery/trunk (PA) and right pulmonary artery (RPA) and left upper pulmonary vein (LUPV) are visible between the ascending and descending (Desc Ao) limbs of the thoracic aorta. The pulmonary veins are often better visualized on coronal imaging because of their thin wall and angulated course but ideally imaged with magnetic resonance (MR) contrast angiography. The azygous vein (Az V) can also be seen just anterior to the spine on the right side.





Figure 1-2


Transverse views from HASTE sequence in lower thorax, from superior ( A ) to inferior ( D ). The sequence characteristics are as for Figure 1-1 . A , The superior aspects of the heart are now in plane, aortic root (Ao root), right ventricular outflow tract (RVOT) and left atrium (LA) visible, along with the SVC. The very top of the left ventricle (LV) can also be seen adjacent to the RVOT, although is better appreciated in the slightly lower slices. B , The aortic sinuses (Ao sinuses) and LV are visible, and the circumflex artery (Circ) is highlighted as a small circular black void within the fat in the left atrioventricular groove. The origin of the right coronary artery (RCA) can be seen arising from the right coronary cusp. C , The RCA is further seen, highlighted in a similar fashion to the circumflex, within the right atrioventricular groove. The main cardiac chambers are also seen–LA, LV, right atrium (RA), right ventricle (RV), and the dome of the diaphragm. At the lowest thoracic level ( D ), the liver can be seen because of the more superior position of the right diaphragm, along with the inferior vena cava (IVC). The Eso can be seen again adjacent to the descending aorta (Desc Ao), because both penetrate the diaphragm on entering the abdomen.





Figure 1-3


Coronal views from HASTE sequence, from anterior ( A ) to posterior ( F ). The sequence characteristics are as for Figure 1-1 . A, Slice through the clavicles, with the ascending aorta (Asc Ao), PA, RA, and LV visible. B, The SVC and the innominate artery (innom) arising from the AO arch can be seen. D, In the mid-mediastinum, the RPA, LA, and LSA can be seen (Hep V, hepatic vein; IVC, IVC). E, The bifurcation of the Tr into the left main bronchus (LMB) and right main bronchus (RMB) can be seen, crossing the left pulmonary artery (LPA). F, The most posterior slice shows the Desc Ao and the retroperitoneal abdominal organs.

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Feb 1, 2019 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Normal Cardiac Anatomy

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