History
A 62-year-old female patient presented to the institutional chest pain unit with typical angina and an extensive cardiovascular risk profile. The combination of the new onset of symptoms, normal Troponin levels and ECG, as well as a history of arterial hypertension, hyperlipidemia and obesity (BMI 35.6 kg/m2) led to an intermediate pre-test probability for coronary artery disease (CAD). To assess or rule-out CAD, a coronary CT angiography (cCTA) was performed using a dual source photon-counting detector (PCD) CT in ultra-high resolution (UHR) mode.
Diagnosis
A calcium score scan demonstrated a severe coronary plaque burden (P3), with calcifications in all three coronary territories (calcium volume 795 mm3, Agatston score 993). cCTA images revealed a CAD-RADS 3 (moderate stenosis, 50%–69%) lesion in the left anterior descending coronary artery (LAD), combined with the clinical presentation, triggered an invasive coronary angiography (ICA) with fractional flow reserve (FFR) and optical coherence tomography (OCT). The lesion in the LAD showed no hemodynamic relevance on invasive FFR. Alongside this lesion, there was diffuse coronary sclerosis, however no further relevant stenosis. Interestingly, using UHR reconstructions (0.2 mm, kernel Bv64), a fibrous cap was visualized on top of the calcified plaque in the distal segment 3 of the right coronary artery (RCA), with a minimal lumen area of 2.2 mm2, which could not be depicted in standard resolution reconstructions (0.6 mm, kernel Bv40) from the same examination, with a minimum lumen area of 1.6 mm2. OCT confirmed a fibro-fatty lesion with a fibrous cap beneath the calcification and a minimal luminal area of 2.3 mm2, in good agreement with the UHR-reconstruction. Angiographic findings led to the initiation of an intensified medical therapy with statins for secondary prevention.
Fig. 1: In the image reconstructed with standard resolution (Bv40, 0.6 mm) (Fig. 1a), only calcified plaques are visible in the distal segment 3 of the RCA. In the UHR image (Bv64, 0.2 mm) (Fig. 1b), a fibrous cap beneath the calcified plaque is visualized, due to reduced calcium blooming. OCT correlation (Fig. 1c) of the same plaque confirms the plaque composition.
Comments
CAD is the leading cause of morbidity and mortality in the western world. cCTA has emerged into one of the most clinically used diagnostic procedures for the workup of patients with stable angina and suspected CAD due to its excellent sensitivity and negative predictive value. However, conventional cCTA examinations suffer from moderate specificity and positive predictive value. This is mainly due to calcium blooming, an artifact which is caused by high density structures such as calcified plaques and metallic objects, which appear larger than their true size. Beside the effect on the stenosis grading, calcium blooming also suppresses accurate plaque characterization. Hence, small, but relevant components of plaques such as fibro-fatty lesions and/or fibrous caps may be not recognizable in conventional cCTA examinations because of limited spatial resolution and blooming artifacts. UHR PCD-cCTA offers improved spatial resolution and may be a promising technical development to overcome these limitations as demonstrated in this case report. The fibro-fatty lesion with a fibrous cap was verified by invasive OCT as ground truth. Since invasive coronary angiography with functional testing did not reveal flow-limiting disease, and a high Agatston Score (993) as well as a high blood cholesterol level (248 mg/dL) were present, the patient was put on an intensified medical therapy with statins.
Examination Protocol