Normal Radiographic Findings
Standard chest radiography includes posteroanterior and lateral projections. This method provides a general overview of heart size, great vessel contours, and pulmonary parenchyma status. For example, analysis of the pulmonary vasculature plays a key role in determining the severity of heart failure, while the detection of calcifications helps suspect valvular heart disease.
Normal radiographs demonstrate the characteristic contours of the cardiovascular silhouette. The superior vena cava (v. cava superior) and right atrium (atrium dextrum) are visualized on the right. On the left, one can distinguish the aortic arch (the so-called "knob"), the left pulmonary artery in the region of the lung root, and the left ventricle (ventriculus sinister).
In the lateral projection, the anterior contour is formed by the right ventricle (ventriculus dexter) and its outflow tract. The posterior contour is represented superiorly by the left atrium (atrium sinistrum) and inferiorly by the left ventricle, which forms a relative bulge compared to the inferior vena cava line.
Cardiac Magnetic Resonance Imaging (MRI)
MRI has several advantages over echocardiography. First, the method allows free selection of scanning planes and does not depend on acoustic windows. This is particularly important for evaluating the right ventricle, whose geometry and function are difficult to study on ultrasound due to its crescent shape.
Additionally, the unlimited field of view in tomography provides a detailed look at extracardiac structures and large vessels.
To obtain high-quality dynamic images (cine mode), data acquisition is synchronized with the R wave on the electrocardiogram. There are two types of gating:
- Prospective — scanning is triggered based on a predefined expected heart rate.
- Retrospective — the scanner acquires data continuously while recording the ECG, and frame reconstruction by cardiac cycle phases occurs after data collection is complete.
A critically important condition is the patient's ability to hold their breath. Slices are usually obtained during a single breath-hold, which is recommended to be performed at end-expiration because this chest position is the most stable and reproducible.
Main MRI Sequences
To differentiate cardiac structures, various contrast weightings between the myocardium and blood are used:
- Bright-blood images (bright-blood). Blood within the cavities produces a bright signal, while the heart muscle appears dark. This is the ideal option for visualizing endocardial and epicardial borders, as well as for quantifying ventricular volumes and function. Steady-state free precession (SSFP) sequences are most commonly used.
- Dark-blood images (black-blood). Based on double inversion recovery spin-echo with fat suppression. They allow the acquisition of high-resolution static slices for detailed morphological assessment.
Additional techniques, such as T2-weighted scans or gadolinium-based contrast enhancement, are used for myocardial tissue characterization.
Scanning Planes
Standard MRI slices are planned along the axes of the heart and correspond to projections used in other imaging modalities. Fast scans or real-time modes are used for planning.
- Vertical Long Axis (VLA): passes through the apex and the middle of the mitral valve.
- Horizontal Long Axis (HLA): planned using the VLA, also intersecting the apex and the mitral valve.
- Short Axis (SA): a series of slices parallel to the mitral valve annulus, covering the entire left ventricle.
- Two-Chamber Projection: constructed perpendicularly to the anterior and inferior walls of the left ventricle, allowing evaluation of the left atrium and mitral valve.
- Four-Chamber Projection: visualizes the interventricular and interatrial septa, the lateral wall of the left ventricle, the free wall of the right ventricle, and both atrioventricular valves.
- Three-Chamber Projection: optimal for assessing the left ventricular outflow tract, aortic valve, and anteroseptal wall.
The standard function evaluation protocol must include short-axis slices and 2-, 3-, and 4-chamber projections, allowing the analysis of all 17 segments of the left ventricle.
Briefly: answers to topical questions
Which structures form the cardiac waist on a posteroanterior chest radiograph?
The cardiac waist on a straight radiograph is formed by a deep notch on the left contour of the cardiac silhouette. The following structures participate in the formation of this anatomical region:
- Aorta (aorta) — forms the 1st arch of the left contour.
- Left ventricle (ventriculus sinister) — forms the 4th arch of the left contour.
It is precisely between these two arches that an accentuated waist is visualized in the aortic configuration, arising from the simultaneous dilation of the aorta and enlargement of the left ventricle.
What radiographic signs indicate pulmonary venous hypertension in heart failure?
In left-sided heart failure, the radiographic picture is driven by extravascular fluid accumulation and pulmonary edema. The main findings detected are:
- Interlobular septa — visualized as Kerley B lines (30–60 mm long in subpleural regions) and Kerley A lines (up to 80–100 mm long, directed toward the lung root).
- Intralobular septa (intralobular septa) — their smooth thickening.
- Ground-glass opacification (ground-glass opacification) — mild hazy attenuation of the lung tissue.
Thickened edematous septal lines become visible due to their distension by fluid.
Which MRI sequences and techniques are used to detect a post-infarction scar or myocardial fibrosis?
Tissue characterization techniques are used to detect fibrosis and scarring in the myocardium. The main MRI sequences used are:
- Late gadolinium enhancement (Late gadolinium enhancement, LGE) — detects areas of fibrosis as hyperintense foci.
- T1 mapping (T1 mapping) — used to assess diffuse fibrosis, which may not be apparent on standard LGE images due to the absence of healthy reference myocardium.
T2-weighted images are also used for comprehensive tissue assessment and differential diagnosis of acute injury.
Class and exam questions
What are bright-blood images used for?
In this mode, blood produces a bright signal while the myocardium appears dark. This creates the high contrast necessary to accurately define the boundaries of the cardiac chambers and calculate their volumes.
Which cardiac structures form the left contour on a posteroanterior radiograph?
From top to bottom, the left contour is formed by the aortic arch ("knob"), the left pulmonary artery, and the left ventricular contour.
What else to study on this topic
- Principles of Left Ventricular Myocardial Segmentation (17 Segments)
- Pathophysiology of Pulmonary Pattern Changes in Heart Failure
- Specifics of Using Gadolinium-Based Contrast Agents
- Evaluation of the Valvular Apparatus: Calcifications and Valvular Disease on Radiographs
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