However, there is no previous research that demonstrates the impact of lung size or the phase of respiration on the CTR. Interestingly, a large change in the CTR between inspiration and expiration has been described in a textbook of pediatric radiology; and this phenomenon was suggested as a confoundable finding in the evaluation of congenital heart diseases, since infants or children cannot hold their breath during CT scanning [12 ].
Source: wiktionary