On NAEOTOM Alpha, in the cardiovascular domain, UHR is known as Quantum HD Cardiac. With typical size of coronary vessels of around 1 to 4 mm, Quantum HD Cardiac may benefit the accurate assessment of such small vasculature. Additionally, it may facilitate observing even smaller plaques and calcifications or evaluating stent patency not previously possible. Since calcium blooming is related to the partial volume effect, enabling high resolution reconstruction capabilities is an alternative non-spectral approach to solve this critical clinical challenge.
Coronary stenosis
In evaluating coronary stenosis, many studies [24]–[27] have reported a downgrading or reclassification of Coronary Artery Disease Reporting and Data System (CAD-RADS) scores due to Quantum HD Cardiac’s ability to provide “sharper images of coronary arteries, a superior coronary plaque delineation, a reduction of partial volume effects, and fewer blooming artifacts,” [26] compared to conventional EID-CT.
Specifically, it has been demonstrated that Quantum HD Cardiac “allowed for a reclassification of 54% of patients toward a lower Coronary Artery Disease Reporting and Data System category compared with standard spatial resolution,” [27].
This regrading of CAD-RADS for patients undergoing coronary evaluation can also be seen in Figure 22, where Quantum HD Cardiac provided a downgrading of CAD-RADS from grade 3 to grade 2, which “altered the care plan” for this [28].
On a larger scale, an 812-patient study reported that “in patients who underwent CCTA with PCCT the number of subsequent ICAs (Invasive Coronary Angiography) was lower as compared to patients who were scanned with EID-CT. This difference was greater in patients with extensive coronary calcification,” which suggests that “PCCT improves clinical efficacy, as the number of invasive examinations could be decreased” [28].
The corresponding axial slices, perpendicular to the vessel centerlines at the stenosis, are shown in the left lower corners. The blooming effect of the calcified plaques affecting the visualization of the vessel lumen and the stenosis grading is clearly reduced in the UHR images.
An invasive catheter coronary angiography (Fig. 22c) confirmed a mild stenosis in the proximal RCA (arrow) consistent with the result from the UHR image evaluation.
Figure 22: Curved MPR images (Figs. 22a & 22b) show a proximal RCA stenosis caused by calcified plaques (arrows). Images are reconstructed at 0.6 mm with kernel Bv40 (Fig. 22a) and at 0.2 mm with kernel Bv60 (Fig. 22b). Courtesy of University Hospital Zurich, Zurich, Switzerland.
Stent patency
Quantum HD Cardiac can also play a role in evaluating stent patency. The presence of heavy calcifications in a stented segment may exacerbate any artifacts due to the stent material itself. The small pixel sizes associated with Quantum HD Cardiac, however, may reduce the partial volume effects and therefore calcium blooming (Figure 23).
In one study evaluating coronary artery segments, it was shown that out of 1080 evaluated coronary segments in 60 patients, 85% had “excellent or very good image quality”, suggesting that “UHR PCCT can play an essential role in the evaluation of coronary stents and in-stent restenosis” [29] (see Figure 23). The patient underwent coronary stent implantation multiple times and had 8 stents implanted in total in the left and right coronary arteries. The orange arrow shows a focal, severe in-stent restenosis at the ostium of the LAD.
Figure 23: Stent imaged in Quantum HD Cardiac mode (Bv72, 1024 × 1024, QIR 4, 0.2 mm slice thickness) on NAEOTOM Alpha, demonstrating in-stent restenosis. MPR 0.2 mm (Fig. 23a) | Cinematic VRT (Fig. 23b) | Bv56 | 140 kV | CTDIvol 22.5 mGy. Cinematic VRT MPR | 0.2 mm | Bv60 In-stent restenosis in LAD. Courtesy of Semmelweiss University Hospital, Budapest, Hungary.
Plaque Quantification
Due to calcium blooming, it can be difficult to accurately assess calcified lesions. A high coronary calcium burden may lead to an overestimation of the degree of stenosis and a false-positive diagnosis. In such cases, Quantum HD Cardiac, employing a sharp vascular kernel, may improve the visualization of these highly calcified plaques (Figure 24).
In this high-risk population, “UHR photon-counting CCTA provided high diagnostic accuracy in the detection of CAD … including subjects with severe coronary calcification” [30].
Figure 24: Coronary CTA using Quantum HD Cardiac in patient with calcium score of 1758. Curved MPR 0.2 mm (Fig. 24a–c) | Cinematic VRT (Fig. 24d) | Bv56 | 120 kV | CTDIvol 19.6 mGy. Courtesy of Semmelweis University, Budapest, Hungary.
The Future: New Quantum HD Cardiac features and AI-tools
Motion artifacts from patient breathing or movement can adversely influence cardiac assessment and diagnosis. This can manifest as discontinuities along the range of acquisition (e.g., for sequential ECG-gated scanning this may appear as a stair step at the image stack transition).
ZeeFree, a new reconstruction-stage algorithm, can mitigate the appearance of these misalignments. Quantum HD may be paired with ZeeFree. CT Quantum HD with the NAEOTOM …
Another recent technological advancement in Quantum HD Cardiac is the optional inclusion of spectral information. This allows for the reconstruction of both UHR and spectral image volumes from a single acquisition. Stent evaluation may benefit from this feature.
Finally, tools for semi-automatic and automatic coronary vessel and plaque assessment are firmly established in the cardiac imaging community. However, these AI tools have been trained and evaluated on conventional EID-CT data. It will be exciting to see what effect the introduction of Quantum HD Cardiac will have on this technology. CT Quantum HD with the NAEOTOM …
“At our institution we expect to send fewer patients to the cath lab for diagnostic imaging and do a photon-counting CT instead.”
Richard Bayer, MD · Cardiologist MUSC, Charleston, SC, USA