History
A 60-year-old male patient, complaining of intermittent chest pain and shortness of breath for the past month, came to the hospital for a check-up. He had suffered a myocardial infarction four years ago and had undergone coronary stenting of the left anterior descending artery (LAD) using two interconnected stents (3.5 mm x 20 mm and 3.0 mm x 38 mm). A year later, he was diagnosed with lung cancer and has been treated with chemotherapy. A follow-up coronary CT angiography (CCTA) performed six months ago, with a conventional energy-integrating detector (EID) CT, resulted in no remarkable findings other than a left ventricular apical aneurysm. Now, another CCTA was requested to assess the coronaries and the stent patency. A prospectively ECG triggered sequential CCTA, using an ultra-high resolution (UHR) mode, was performed with a dual-source photon-counting detector (PCD) CT, NAEOTOM Alpha®.
Diagnosis
CCTA images showed two interconnected stents in the LAD, both clearly identified as patent. A noncalcified plaque was seen proximal to the stent, causing mild stenosis (<50%). Further two mixed plaques, with high-risk plaque (HRP) features of spotty calcifications and positive remodeling in the mid Cx and RCA, were also seen causing mild stenoses. Two non-calcified plaques, distal to the HRP in the RCA, were seen, causing mild stenoses. Multiple calcified plaques were present in the left main (LM), proximal and middle LAD, circumflex (Cx) as well as right coronary artery (RCA), these causing no significant stenoses. The left ventricle was enlarged and an apical aneurysm was evident. The coronary system was right dominant. CT findings were classified as CADRADS 2/P2/HRP/S. No further invasive workup was considered. The patient continued pharmacotherapy for his coronary artery disease (CAD) and chemotherapy for lung cancer. A short-term clinical follow-up was recommended.
Fig. 1: Curved MPR images of the LAD show a comparison of the details in the stent patency and in a non-calcified plaque (arrow) proximal to the stent causing mild stenosis. The axial images, acquired from PCD-CT, are reconstructed at 0.2 mm with a kernel of Bv72 (Fig. 1a) and an enlarged view (Fig. 1c). Axial images, acquired from a conventional EID-CT, are reconstructed at 0.625 mm with a standard kernel (Fig. 1b).
Fig. 2: Curved MPR images show a comparison of a HRP (arrow) details in the mid Cx. The axial images, acquired from PCD-CT, are reconstructed at 0.2 mm with a kernel of Bv72 (Fig. 2a) and an enlarged view (Fig. 2c). Axial images, acquired from a conventional EID-CT, are reconstructed at 0.625 mm with a standard kernel (Fig. 2b).
Fig. 3: Curved MPR images show a comparison of the details of a HRP (arrow) and two non-calcified plaques (dotted arrows) distal to the HRP in the mid RCA causing mild stenoses. The axial images, acquired from PCD-CT, are reconstructed at 0.2 mm with a kernel of Bv72 (Fig. 3a) and an enlarged view (Fig. 3c). Axial images, acquired from a conventional EID-CT, are reconstructed at 0.625 mm with a standard kernel (Fig. 3b).
Fig. 4: Cinematic VRT images show a three-dimensional view of the coronary arteries, the enlarged left ventricle with an apical aneurysm. The stents and the calcified plaques are highlighted in green.
Comments
CCTA assessment for the patency of coronary stents, using conventional CT, has been challenged by blooming artifacts caused by stent struts. In the American Heart Association guidelines, it is limited to a borderline of 3 mm stent diameter for patients who experience symptomatic changes despite guideline-directed management and therapy. [1] HRP, associated with a higher risk of future acute coronary syndrome (ACS) and lesion specific ischemia, has been incorporated as a modifier in the CAD-RADS recommendations, which suggests that the identification of the HRP would signify the need for more aggressive preventive therapies, even if the lesion is nonobstructive. [2] Studies have shown that half of culprit plaques causing major adverse cardiovascular events (MACE), have previously caused a stenosis < 50%. [3]
CCTA assessment of coronary stent patency and HRP posts a technical challenge, requiring a combination of high spatial and temporal resolution. Potential improvement has been shown with the introduction of a dual-source PCD-CT, NAEOTOM Alpha. The UHR mode with PCD-CT works differently from that of conventional EID-CT. Smaller detector pixels are not defined by physical separation as in EID-CT, causing reduced geometrical dose efficiency, but an electric field is applied to define smaller sub-pixels which are read out separately to increase the spatial resolution. A recent study using this mode achieved a 100% negative predictive value for coronary stent patency evaluation against invasive angiography as the reference standard. [4] The identification of the HRP features also benefits from the improved spatial resolution of the UHR mode and the high temporal resolution of 66 ms through the dual-source principle. [5] This combination can effectively minimize the blooming interference caused by calcified plaques and stent struts.
In this case, the stent patency is assessed and the HRP is identified successfully by the clinician using the UHR mode. As no further invasive coronary angiography is deemed necessary, the associated costs and risks could be spared for this patient.
Examination Protocol
