Limitations of cardiothoracic ratio derived from chest radiographs to predict real heart size: comparison with magnetic resonance imaging

ConclusionsCTR correlates weakly with true chamber size assessed by gold standard cardiac MRI and has a weak discriminatory power. Thus, clinical decisions based on intermediate CTRs (45 –55%) should be avoided. Large CTRs (>  55%) are likely indicative of true heart chamber enlargement. Low CTRs (<  45%) are likely indicative of normal heart size.
Source: Insights into Imaging - Category: Radiology Source Type: research