Spectral imaging and advanced spectral reconstructions
The ability to fully integrate spectral capabilities in cardiac CT without compromises in temporal or spatial resolution makes it possible to selectively detect and differentiate iodine and calcium through material decomposition (Figure 2). In NAEOTOM Alpha, this has translated into two new applications: Quantum PURE Lumen** in which calcifications are spectrally removed by a dedicated material-based decomposition enabling the unobstructed visibility of the vessel lumen; and Quantum PURE Calcium in which the contribution of iodine is removed from contrast-enhanced images while calcium is aimed to be left unmodified. This feature enables quantitative calcium scoring evaluations.
Quantum PURE Lumen – Seeing through calcifications
In conventional CT imaging, calcified plaques can appear larger than they actually are due to partial volume effects (commonly known as “blooming”), in turn potentially leading to overestimation of arterial stenoses. The Quantum PURE Lumen algorithm removes calcifications, enabling highly accurate stenosis quantifications as the impact of calcium blooming is negated, revealing the accurate lumen underneath (Figure 3).
Figure 3. The use of Quantum PURE Lumen* to reveal the underlying reality of the pathology due to the virtual removal of calcifications from the result image. Severe calcifications in CAD mask the pathology and distort the severity of the stenosis (i.e., no clinical value is delivered). Quantum PURE Lumen reveals the underlying reality of the pathology and can guide the radiologists and cardiologists with non-invasive imaging in advanced CAD. Courtesy of Centre Cardio-Thoracique, Monte Carlo, Monaco.
* 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).
Quantum PURE Calcium – Removing iodine contributions
Of note, the key difference between virtual non-iodine images of Quantum PURE Calcium with other Siemens Healthineers applications that provide virtual-unenhanced images such as DE Virtual Unenhanced (VUE), is the use of different basis materials for decomposition. Quantum PURE Calcium uses iodine, calcium and water as basis materials; while VUE uses iodine, water and air. While the VUE algorithm has been shown to be very successful at removing iodine, it does not maintain the original calcium contribution due to the selected material base and reduces the calcium contribution in the final image, making it unsuitable for quantitative calcium scoring.
The Quantum PURE Calcium algorithm leverages the advanced spectral capabilities of NAEOTOM Alpha to virtually remove iodine material from CT images while selectively preserving calcifications. The resulting virtual non-iodine images reflect the information found in non-contrast CT examinations, such as CACS examinations.
It has already been demonstrated [8] that comparable information to a non-contrast CACS was acquired by leveraging the Quantum PURE Calcium algorithm without the need of an additional examination. Eliminating the non-contrast scan would result in workflow savings of scan time and radiation dose. Agatston score estimates from Quantum PURE Calcium scans strongly correlate with estimates from conventional scans using 120 kV, demonstrating accurate removal of the iodine contrast [8] (Figure 4).