History
Diagnosis
Fig. 1: A curved MPR image (Fig. 1a) shows three interconnected stents in the LM and LAD without evidence of ISR. The stent struts and the components of calcified and mixed plaques outside the stents are visually well distinguished. A single stent in the proximal Cx (Fig. 1b) is seen with signs of intimal hyperplasia in the mid portion (arrow), causing a less than 50% narrowing of the lumen. Multiple calcified plaques in the proximal and distal Cx and the RCA (Fig. 1c), as well as two mixed plaques (dotted arrows) in the mid RCA are present, causing mild stenosis.
Fig. 2: Curved MPR images, reconstructed with standard images (Fig. 2a) and UHR images (Fig. 2b), show an imaging comparison of the stent in the proximal Cx. In standard image, the intimal hyperplasia in the mid portion of the stent appears to cause an ISR, while in UHR image, a less than 50% narrowing of the lumen is clearly shown, ruling out an ISR.
Fig. 3: A cinematic VRT image rendered with UHR images shows a three-dimensional view of the coronary tree with the stents and the calcified plaques highlighted in blue.
Comments
Coronary ISR is defined as a higher than 50% re-narrowing of the previously stented arterial lumen, requiring revascularization. It is frequently encountered, due to stent-related, procedure-related and biological factors. Intracoronary imaging, such as angiography, intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have been performed to identify and characterize the underlying mechanisms and substrate of ISR and to guide clinical management. [1] CCTA assessment for the patency of coronary stents, using conventional energy-integrating detector (EID) CT, has been limited to a borderline of 3 mm stent diameter in the American Heart Association guidelines, due to the challenge of blooming artifacts caused by stent struts. [2] Potential improvement has been shown with the introduction of a UHR scan mode provided by a dual source PCD-CT, NAEOTOM Alpha. In the PCD, an electric field, instead of physical separation as in an EID, is applied to define smaller detector sub-pixels which are read out separately to increase the spatial resolution while retaining geometrical dose efficiency. In the dual source PCD-CT, UHR data acquisition is achieved at a temporal resolution of 66 ms. A recent study using this mode achieved a 100% negative predictive value for coronary stent patency evaluation against invasive angiography as the reference standard. [3]
In this case, an ISR is ruled out in the UHR images (0.2 mm, kernel Bv72), as the hypodense intimal hyperplasia causing a less than 50% narrowing of the lumen, is clearly visualized. However, when images are reconstructed at 0.6 mm with a kernel of Bv48, simulating a standard image reconstruction in CCTA with an EID-CT, an ISR could have been diagnosed leading to the necessity of further invasive work-up. The combination of high spatial and temporal resolution provided by PCD-CT effectively improves the visualization of coronary stents, minimizing the blooming interference caused by calcified plaques and stent struts.[4] This helps the physicians to make a confident assessment of the stent patency and the appropriate decision on patient management.
Examination Protocol