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Dual Source CT is an established technology with a high number of benefits. These benefits are relevant for all “standard” cardiac fields, whether it be coronary artery disease, structural heart disease or congenital heart disease. But is there still something new to explore? For example, why not use Dual Source CT for specific applications instead of MRI or transesophageal echo-cardiography (TEE)? Or even use Dual Source CT images to plan leaflet repair for tricuspid regurgitation?
Let’s deep-dive into some potential future topics our customer recently explored.
Myocardial extracellular volume assessment with Dual Source CT
Cardiomyopathy is the third leading cause of heart failure in the United States and it is associated with muscular or electrical dysfunction of the heart. Myocardial fibrosis is an important indicator of myocardial damage. It is quite common to evaluate myocardial fibrosis with non-invasive techniques like MRI or CT perfusion.
The assessment of myocardial extracellular volume (ECV) fraction has been studied as a new approach, as increased ECV can be associated with fibrosis.
Here, the reference standard for non-invasive assessment of ECV is cardiac MRI. However, it is not available everywhere and is contraindicated, e.g., in for patients with metal implants. One alternative here could be Dual Source CT. It has the potential to save examination time. Cardiac MRI typically requires long examination times (45–60 min) and whole-heart ECV by cardiac MRI requires 18–20 breath-holds. On the other hand, the examination time for cardiac CT is relatively short (15–30 min) and whole-heart ECV estimation by cardiac CT requires only a few breath-holds.
Studies have shown that ECV can be successfully measured with single-energy computed tomography (SECT) and dual-energy CT (DECT). These results showed a good correlation between ECV measurements derived from CT and equilibrium MRI [,35].
Recently, Abadia et al. demonstrated that ECV can be assessed using a DECT approach with only one delayed iodine-enhanced acquisition. They reported that this approach provides similar results when compared to multi phase SECT . Furthermore, Dual Source CT has the potential to lower the radiation dose by replacing a true non-contrast scan with a virtual non-contrast DECT reconstruction. That is possible because the Dual Source system can be operated at different tube potentials, leading to maximum spectral separation, which results in an optimal material differentiation.
In can be concluded that with Dual Source CT it is feasible to reliably assess myocardial extracellular volume fraction because dedicated benefits (e.g., high temporal resolution) can be assured. Furthermore, limiting factors known from MRI (e.g., metal implants or claustrophobia) do not apply, which make this approach feasible for the clinical routine.
Use of Dual Source CT to plan of leaflet repair for tricuspid regurgitation
Although minimally invasive interventions of the tricuspid valve are not yet fully established, transcatheter tricuspid valve interventions are rapidly evolving. Therefore, the need for appropriate imaging solutions (e.g., CT) is increasing to accurately assess the anatomy of the valve and the right ventricular function, especially in patients with a high surgical risk [,].
Because the assessment of the tricuspid valve poses new challenges, like complexity of the geometry, and so forth, the quality of the CT image that is used for pre-procedural planning highly depends on the temporal resolution of the available CT scanner.
Furthermore, patients who undergo tricuspid valve repair (TTVr)/replacement often suffer from a high heart rate and atrial fibrillation, which can cause image blurring.
Lopez et al. recently investigated the usage of Dual Source CT systems in this context. The authors came to the conclusion that with high native temporal resolution and specific contrast protocols for image acquisition, this CT imaging technique will play an important role. It allows for accurate assessment of the tricuspid valve anatomy as well as the comprehensive functional assessment of right ventricular function and remodeling (pre- and post-TTVr).
In addition, smooth opacification of the right heart together with the advantages of the scanner will allow for outstanding image quality of the tricuspid valve; the results from Lopez et al. were perfect.
Although guidelines promote TEE as the imaging modality to assess tricuspid regurgitation (TR) severity, Hashimoto et al. indicated in a recent publication that TEE can lead to an underestimation of the true extent of right heart disease. Additionally, complex right ventricle (RV) geometry often leads to incomplete and inadequate visualization of the entire RV by 2D TTE. As 46% of patients undergoing tricuspid valve surgery suffer from postoperative RV dysfunction, which is associated with high in-hospital mortality, the authors investigated if pre-operative CT cardiac assessment could provide essential information for predicting postoperative RV dysfunction. They found that in addition to functional and remodeling quantification, cardiac CT can provide information regarding the mechanism of TR, TV/leaflet anatomy, motion and visualization of the valve gap with the best fluoroscopic angles to help define the correct therapy strategy.
Detection of left atrial appendage (LAA) thrombi with Dual Source CT instead of TEE
In patients with atrial fibrillation, one side effect is the development of a thromboembolism, which can be associated with morbidity and increased mortality [38]. This potential risk needs to be considered prior to catheter ablation because navigating the catheter inside the left atrium may dislodge the thrombus and cause thrombo-embolic complications. Today TEE is the gold standard prior to catheter ablation to exclude the presence of thrombi in the left atrium or left atrial appendage. But this imaging modality is semi-invasive, time-consuming and uncomfortable for patients, and studies indicate that it bears potential risks, such as esophageal lesions [38].
Li et al. investigated the diagnostic performance of DECT-derived iodine concentration (mg/ml) compared to conventional enhancement measurements (Houns-field Units (HU)) and the reference standard TEE to detect left atrial appendage (LAA) thrombi and differentiate thrombi from circulatory stasis in atrial fibrillation (AF) patients referred for catheter ablation. The comparisons of the diagnostic accuracy of the different modalities showed that DECT-derived iodine concentration was associated with improved diagnostic accuracy [38].
The authors reported radiation doses (2.45 ± 0.54 mSv) in DECT using a third-generation Dual Source CT system which are well below the dose (7.5 mSv) that results in DNA damage [38]. The reason for that is that third-generation Dual Source CT systems are equipped with Stellar detectors, which are more sensitive to electron influx and hence more dose-efficient.
The pre-condition here again is that the scanner provide both a high native temporal resolution (≤ 83 ms) and the ability to significantly reduce dose while keeping image quality high. Otherwise the interpretation of the images can cause false-positive/false-negative readings.
The authors are convinced that dual-energy cardiac CT may be clinically useful for detecting and ruling out intra-cardiac thrombi in AF patients and should be understood as an alternative diagnostic tool to TEE.
Read the article online: https://www.siemens-healthineers.com/en-ca/computed-tomography/technologies-and-innovations/dual-source-ct/dsct-cardiac-imaging
References:
Abadia AF, van Assen M, Martin SS, Vingiani V, Griffith LP, Giovagnoli DA, et al. Myocardial extracellular volume fraction to differentiate healthy from cardiomyopathic myocardium using dual-source dual-energy CT. J Cardiovasc Comput Tomogr. 2019;(September).
Hashimoto G, Fukui M, Sorajja P, Cavalcante JL. Essential roles for CT and MRI in timing of therapy in tricuspid regurgitation. Prog Cardiovasc Dis. 2019;62(6):459–62.
BC Lopez B, Sorajja P, Hashimoto G, Fukui M, Du Y, Ahmed A, et al. Early Effects of Transcatheter Edge-to-Edge Leaflet Repair for Tricuspid Regurgitation: First-in-Human Experience with Computed Tomography. J Cardiovasc Comput Tomogr. 2020;(July):1–3.
Li W, Yu F, Zhu W, Zhang W, Jiang T. Detection of left atrial appendage thrombi by third-generation dualsource dual-energy CT: Iodine concentration versus conventional enhancement measurements. Int J Cardiol [Internet]. 2019;292:265–70. Available from: https://doi.org/10.1016/j.ijcard.2019.04.079