Q. What do you know about Cardiothoracic ratio?

The cardiothoracic ratio (CTR) shown in figure is the transverse cardiac diameter (the horizontal distance between the most rightward and leftward borders of the heart seen on a PA chest radiograph) divided by the transverse chest diameter (measured from the inner rib margin at the widest point above the costophrenic angles on a PA chest film).

A cardiothoracic ratio of more than 50 per cent is generally considered abnormal in an adult. It may be upto 55 per cent in blacks and Asians and 60 per cent in neonates and the elderly. The cardiac diameter alone can also be measured. It is less than 13.5 cm in 90 per cent of males and 12.5 cm in 90 per cent of females. A change in diameter of greater than 1.5 cm between two radiographs is considered significant.