Calculation of the Cardiothoracic Ratio from Portable Anteroposterior Chest Radiography

Abstract

Cardiothoracic ratio (CTR), the ratio of cardiac diameter (CD) to thoracic diameter (TD), is a useful screening method to detect cardiomegaly, but is reliable only on posteroanterior chest radiography (chest PA). We performed this cross-sectional 3-phase study to establish reliable CTR from anteroposterior chest radiography (chest AP). First, CDChest PA/CDChest AP ratios were determined at different radiation distances by manipulating chest computed tomography to simulate chest PA and AP. CDChest PA was inferred from multiplying CDChest AP by this ratio. Incorporating this CD and substituting the most recent TDChest PA, we calculated the 'corrected' CTR and compared it with the conventional one in patients who took both the chest radiographies. Finally, its validity was investigated among the critically ill patients who performed portable chest AP. CDChest PA/CDChest AP ratio was {0.00099 × (radiation distance [cm])} + 0.79 (n = 61, r = 1.00, P < 0.001). The corrected CTR was highly correlated with the conventional one (n = 34, difference: 0.00016 ± 0.029; r = 0.92, P < 0.001). It was higher in congestive than non-congestive patients (0.53 ± 0.085; n = 38 vs 0.49 ± 0.061; n = 46, P = 0.006). Its sensitivity and specificity was 61% and 54%. In summary, reliable CTR can be calculated from chest AP with an available previous chest PA. This might help physicians detect congestive cardiomegaly for patients undergoing portable chest AP.

Determination of the theoretical personalized optimum chest compression point using anteroposterior chest radiography

“…4). 21 In contrast to chest_PA, which is obtained at a fixed distance of 180 cm with the heart located posteriorly, chest_AP is obtained at shorter and variable distances with the heart located anteriorly. Besides the derivation and validation set, we collected a convenience sample of 30 patients to perform a chest_AP in the emergency department.…”

Cardiothoracic area ratio for evaluation of ejection fraction in patients

“…The size of the heart can be estimated from a PA chest radiograph by the CTR. Clinicians continue to use the CTR because a quick decision is required under urgent situations, especially in the emergency department [12]. The upper limit for CTR measurement is generally considered to be 50% but different studies suggest different cut-off points for CTR [13].…”

Diagnostic accuracy of cardiothoracic ratio on admission chest radiography to detect left or right ventricular systolic dysfunction: a retrospective study

“…This significantly calls into question their findings, as their inclusion criteria of radiological signs of cardiac failure overlap with the test variable of interest; namely the cardiothoracic ratio. More recently, Chon et al 26 attempted to compare erect antero-posterior films with supine computed tomography chest measurements and tried to 'correct' for the differences in projection based on variable film to detector distances. They validated their method by comparing 18 patients with echocardiographic evidence of heart failure with 17 patients with normal echocardiograms and found a sensitivity of 61% and a specificity of 54% based on a 'corrected cardiothoracic ratio' of !0.5.…”