What is the normal cardiothoracic ratio?

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Multiple Choice

What is the normal cardiothoracic ratio?

The concept being tested is how to gauge heart size relative to the chest on imaging, using the cardiothoracic ratio (CTR). The CTR is the width of the heart measured from the inner borders of the right and left heart outlines, divided by the widest width of the chest (thoracic diameter) on a radiograph. A normal CTR is about one third of the chest width, roughly 0.3. That means the heart takes up about one third of the thoracic diameter. So, the best answer is one third. If the ratio were around two thirds or three quarters, the heart would be disproportionately large for the chest, indicating cardiomegaly or another abnormal finding. A value around one quarter is smaller than typical normal in most contexts, and is less commonly cited as the standard normal benchmark.

The concept being tested is how to gauge heart size relative to the chest on imaging, using the cardiothoracic ratio (CTR). The CTR is the width of the heart measured from the inner borders of the right and left heart outlines, divided by the widest width of the chest (thoracic diameter) on a radiograph. A normal CTR is about one third of the chest width, roughly 0.3. That means the heart takes up about one third of the thoracic diameter.

So, the best answer is one third. If the ratio were around two thirds or three quarters, the heart would be disproportionately large for the chest, indicating cardiomegaly or another abnormal finding. A value around one quarter is smaller than typical normal in most contexts, and is less commonly cited as the standard normal benchmark.

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