History
A 76-year-old male patient, complaining of palpitations and chest tightness, was presented to the hospital. Fourteen years ago, the patient had undergone coronary stenting, with 3 overlapping stents placed in the left main (LM) and left anterior descending artery (LAD) and a single stent in the circumflex (Cx). A follow-up coronary CT angiography (CCTA), performed 11 years later with an energy-integrating detector (EID) CT, showed satisfactory results with no indication for further interventions. The patient was then treated with pharmacotherapy. Now, an ECG-triggered sequential ultra-high resolution (UHR) CCTA with a dual source photon-counting detector (PCD) CT, NAEOTOM Alpha®, was performed to assess the coronary arteries and the patency of the stents.
Diagnosis
CCTA images showed 3 overlapping stents in the LM, proximal and mid LAD, and a single stent in the proximal Cx. All stents were patent, except for the one in the Cx, where a non-calcified plaque was present in the distal stent, causing severe stenosis (>70%). Another non-calcified plaque, with high-risk plaque (HRP) features of spotty calcifications and positive remodeling in the mid right coronary artery (RCA), was also seen causing mild stenosis (<50%). Multiple calcified plaques were seen in the LM, proximal LAD, mid RCA, and proximal Cx, causing no significant stenosis. CT findings were classified as CAD-RADS 4/P2/HRP/S. The patient was recommended to undergo interventional coronary angioplasty, he however refused and continued with pharmacotherapy.
Fig. 1: Curved MPR images of the LM and LAD show a comparison of different reconstructions: 0.2 mm with kernel Bv72 (Fig. 1a, PCD-CT), 0.2 mm with kernel Bv60 (Fig. 1b, PCD-CT), 0.6 mm with kernel Bv48 (Fig. 1c, PCD-CT) and 0.75 mm with kernel Bv49 (Fig. 1d, EID-CT). The patency of the stents is clearly visualized in the image reconstructed at 0.2 mm with a kernel of Bv72.
Fig. 2: Curved MPR images of the Cx show a comparison of different reconstructions in the same sequence as in Fig. 1. The non-calcified plaque in the distal stent, causing a severe stenosis (Fig. 2a, arrow), is clearly shown in the image reconstructed at 0.2 mm with a kernel of Bv72.
Fig. 3: Curved MPR images of the RCA show a comparison of different reconstructions in the same sequence as in Fig. 1 & 2. The HRP with spotty calcification and positive remodelling in the mid RCA (arrow), causing mild stenosis, is clearly seen in the image reconstructed at 0.2 mm with a kernel of Bv72.
Fig. 4: Curved MPR images of the Cx (Fig. 4a) and the RCA (Fig. 4b) show an enlarged view of a severe in-stent stenosis, caused by a non-calcified plaque, in the distal Cx stent (Fig. 4a, arrow), and a non-calcified plaque, with HRP features of spotty calcifications and positive remodelling, in the mid RCA (Fig. 4b, dotted arrow). Images are reconstructed at 0.2 mm with a kernel of Bv72.
Fig. 5: Cinematic VRT images show a three-dimensional view of the coronary arteries. The stents and the calcified plaques are highlighted. The axial images used were reconstructed at 0.2 mm with a kernel of Bv72.
Comments
Coronary stenting is commonly performed for coronary revascularization to improve the blood flow in the myocardium. The long-term clinical outcome depends upon the patency of the stents. It has been recognized in the guidelines of American Heart Association that CCTA assessment for the patency of coronary stents (≥3mm in diameter) has its value. [1] However, blooming artifacts caused by severely calcified plaques or the stent struts impair the visualization of the coronary lumen, posing a diagnostic challenge. Numerous advances in CT technology, such as improvements in the temporal resolution from the dual source CT principle, optimization of scan protocols and refined iterative reconstruction algorithms, have been made, aiming at increasing the diagnostic accuracy of CCTA for stent imaging. The introduction of a dual source PCD-CT with UHR mode has shown further improvements in this area. A recent study using the UHR mode of PCD-CT achieved a 100% negative predictive value for coronary stent patency evaluation against invasive angiography as the reference standard. [2] The PCD-CT provides energy-resolved CT data at increased spatial resolution without electronic noise. [3] The photon-counting detectors do not require optical crosstalk to be prevented by separating layers between the individual detector elements. Therefore, they can be more finely structured than scintillation detectors. [4] An electric field, instead of physical separation, is applied to define smaller sub-pixels which are read out separately to increase the spatial resolution. This approach also improves the geometrical dose efficiency of the detector. The combination of the increased spatial resolution and the high temporal resolution (66 ms) effectively overcomes the blooming artifacts [5].
In this case, the patency of the stents, the in-stent restenosis caused by a non-calcified plaque and the HRP are successfully evaluated by the clinician using the UHR mode, providing essential information for the physicians to outline an appropriate treatment and follow-up plan within the given situation.
Examination Protocol