Cardio-thoracic ratio

Cardio-thoracic ratio is the "transverse diameter of the heart, as determined by x-ray examination, compared with that of the thoracic cage, used to help determine enlargement of the heart." These diameters are taken from PA chest x-rays using the widest point of the chest and measuring as far as the lung pleura, not the lateral skin margins. If the cardiac thoracic ratio is greater than 50%, pathology is suspected, assuming the x-ray has been taken corectly. The measurement was first proposed in 1919 to screen military recruits. A newer approach to using these x-rays for evaluating heart health, takes the ratio of heart area to chest area and has been called the two-dimensional cardiothoracic ratio.