Editorial for: “Right/Left Ventricular Blood Pool T2 Ratio as an Innovative Cardiac MRI Screening Tool for the Identification of Left‐to‐Right Shunts in Patients with Right Ventricular Disease”

Editorial for: “Right/Left Ventricular Blood Pool T2 Ratio as an Innovative Cardiac MRI Screening Tool for the Identification of Left-to-Right Shunts in Patients with Right Ventricular Disease” Congenital heart diseases (CHD) may occur due to interventricular or interatrial septal defects, valve abnormalities, and aplasia or hypoplasia of one of the cardiac chambers. It has been reported that 1 in 100 newborns is affected, including those with mild lesions. Severe shunt disease causes cyanosis and requires surgery during childhood. However, mild cases are difficult to diagnose and remain asymptomatic until adolescence and are discovered incidentally during a routine health check-up. Therefore, a noninvasive clinical investigation that can be performed routinely is considered important for the early detection of symptoms of CHD. Generally, when a left-to-right (L-R) shunt is suspected due to heart murmur or right-sided volume overload, pulmonary to systemic flow ratios (Qp/Qs) and blood oxygen saturation are measured. These are cardiac catheterization-derived parameters that are measured invasively and are considered the reference standard for shunt disease. In contrast, echocardiography or cardiovascular magnetic resonance imaging (CMR) analyzes the blood flow volume of the pulmonary artery and aorta noninvasively. Echocardiography-derived Qp/Qs is widely measured in daily clinical practice owing to its simplicity. However, the limited field of view remains an issue of echocardiography. In particular, echocardiographic measurements in CHD may be inaccurate because the diverse anatomical structures of the heart cause difficulty in setting appropriate echocardiographic cross sections. Therefore, CMR can be expected to provide accurate measurements of blood flow volume without field of view and slice angle setting restrictions. However, setting the Qp/Qs cross sections in CMR requires multiple image acquisition processes, which is a complicated method that requires proficiency. Thus, a simple and highly accurate measurement using CMR is required for diagnosing L-R shunt. The authors presented a new noninvasive method for estimating blood oxygen saturation in patients with shunt disease. This method uses T2 mapping that is used in comprehensive cardiac investigations and does not require complicated slice settings or additional image acquisitions. It is expected that clinicians will be able to perform this method easily and accurately in daily clinical practice. The authors have demonstrated that L-R shunt can be detected using T2 ratio. Estimation of blood oxygen saturation using magnetic resonance imaging (MRI) utilizes the strong paramagnetic property of deoxyhemoglobin, which decreases the MRI signal. Previously, T2*-weighted imaging has been used to image changes in blood flow dynamics related to brain activity and quantify myocardial oxygen metabolism in patients with heart failure. In reference to this study, Wright et al reported the relationship between T2 value and blood oxygen saturation. The clinical application of estimation of oxygen saturation using MRI is increasing. This study investigated a total of 100 individuals, including 52 healthy participants, 27 patients with L-R shunt, and 21 patients with right ventricular (RV) disease without shunt. To evaluate the shunt, short-axis T2 mapping was acquired, and the RV/left ventricle (LV) T2 ratio was calculated. A cutoff value of 0.78 on the receiver operating characteristic curve for the detection of patients with shunt had sensitivity, specificity, and area under the curve [AUC] of 100%, 73.9%, and 0.965, respectively. A T2 ratio > 0.83 was able to detect clinically relevant shunts (Qp/Qs > 1.5) with a sensitivity of 100%, specificity of 95.4%, and AUC of 0.99 and indicated the need for surgery. It was reported that the RV/LV T2 ratio is not only useful for the diagnosis of L-R shunt but may also indicate disease severity. There are some limitations to the proposed method. First, because the ventricular septal defect is a high-pressure system, it may be difficult to estimate the distribution and dynamics of blood flow across the L-R shunt and to the