Benefits of photon-counting technology
for cardiac CT
siemens-healthineers.com/naeotom-alpha
Trends in cardiac CT
Chest pain guidelines published in 2021 by various cardiac professional organizations (ACC, AHA and SCCT) [1] have put CT imaging at the forefront of the assessment of patients with stable chest pain with no known coronary artery disease (CAD – defined here as a minimum of calcified plaques), regardless of their risk levels. Coronary CT angiography (CCTA) was identified in guidelines as a class 1 strength of recommendation with the highest evidence of being clinically effective, and coronary artery calcium scoring (CACS) as group 2a with moderate recommendation for usefulness. In the recent DISCHARGE multicenter trial of over 3500 patients comparing CT with invasive coronary angiography (ICA) as an initial diagnostic imaging strategy for guiding the treatment of patients with stable chest pain who were clinically referred for ICA, the frequency of major procedure-related complications was lower with an initial CT strategy [2].
Furthermore, recent European Society of Cardiology (ESC) guidelines [3] recommend CCTA as first line test to evaluate the presence and extent of CAD, while also suggesting CCTA as a highly valuable tool to exclude significant CAD in patients with newly diagnosed dilated cardiomyopathy. The guidelines also suggest CCTA as an alternative to ICA in patients with newly diagnosed reduction of ejection fraction to establish the presence and extent of CAD and evaluate clinical indication to myocardial revascularization. In addition, CACS is a well-established method for early detection and prevention of adverse cardiovascular events, as a decision-aiding tool for initiation of preventative therapy, and as a negative risk factor for excluding cardiovascular risk in symptomatic and asymptomatic patients [4]. Updated CAD-RADS 2.0 guidelines [5] state that plaque burden should be estimated whenever present and can be accomplished using either an evaluation of the amount of calcium (i.e., CACS), a segment involvement score (SIS), or a visual assessment leading to a category of total plaque burden from P1–P4 (mild, moderate, severe, extensive).
With this prominence of cardiac CT in clinical guidelines in both diagnosis and disease stratification and the increased growth in the use of CCTAs of up to 355% in a decade [6], accurate quantification of CT imaging biomarkers of relevant pathophysiology is of utmost importance in efficient patient management. Parallel to CT use in CCTAs, the field of transcatheter valve and structural interventions has seen rapid growth and maturation over the last decade and represents a rapidly growing area of cardiology, especially as the number of devices to address valvular and nonvalvular heart disease continues to increase. CT imaging is thus a critical component for many aspects of structural heart treatment, from disease assessment and patient selection, to device selection and sizing, as well as procedural risk prediction.
Cardiac imaging with NAEOTOM Alpha® represents a major paradigm shift in cardiac CT, with unparalleled* ability to assist clinicians in the classification and quantification of disease using breakthrough technological advancements developed by Siemens Healthineers. This white paper aims to demonstrate the improved imaging potential for cardiac imaging brought about by the introduction of NAEOTOM Alpha.
CT is an increasingly pivotal tool to assist the physician in the diagnosis of cardiovascular disease and for the preprocedural planning for structural intervention and for device implantation.
Technical advancements of NAEOTOM Alpha for cardiac CT
Accurate imaging of the millimeter size of epicardial coronary arteries and the structure of the heart have been a great challenge for CT imaging because rapid cardiac motion and patient breathing may cause image blurring. Because of this, cardiac imaging requires both excellent temporal and spatial resolution to create adequate visualization of the vessels. Dual Source CT (DSCT) scanning technology from Siemens Healthineers improved routine temporal resolution to below 100 ms. New detector designs with the use of submillimeter collimations also deliver better spatial resolution along the z-axis. The pioneering development of high-performance X-ray tubes, such as the Vectron®, enabled the delivery of sufficient photon flux to maintain image quality at all kV levels for patients of all sizes, especially those who are obese.
With the launch of NAEOTOM Alpha and the implementation of photon-counting CT technology in a Dual Source, whole-body, routine capable CT scanner, a quantum leap over conventional CT imaging has been achieved. Benefits include ultra-high spatial resolution due to smaller detector elements, improved contrast to noise ratio (CNR) through equal weighting of low and high energy photons, elimination of electronic noise due to thresholding of electrical pulses, and intrinsic spectral sensitivity. Further, building on the successful high-end dual-source CT architecture, NAEOTOM Alpha uniquely combines ultra-high resolution, spectral capabilities, and industry-leading temporal resolution of up to 66 ms* without compromises. This in many cases allows a cardiac CT acquisition without the use of beta blockers to control heart rate. These and other benefits have been highlighted and summarized in the NAEOTOM Alpha – CT redefined white paper [7] and are briefly described in Figure 1.
When imaging the heart, these technical benefits lead to clinical imaging improvements such as a reduction of calcium blooming, in-stent imaging, visualization of small arteries, highly detailed plaque imaging, and detailed prosthetic valve/endograft imaging.
Figure 1. Benefits of using QuantaMax detectors demonstrating four technological benefits of smaller detector pixels, the removal of electronic noise, equal energy weighting of high and low energy photons, and spectral sensitivity.
Figure 2: Workflow of the Quantum PURE Lumen
& Quantum PURE Calcium algorithms and how
spectral data is utilized to produce the final datasets.
* data on file
** PURE Lumen (Vascular Calcium Removal [VCR]) can be used to measure vessel (e.g., coronary) stenoses by removing
the contributions of calcium from images; based on a phantom evaluation (Allmendinger T. et al., Invest Radiol. 2022;57(6):399-405)