M R Dweck

Recommendations for the imaging assessment of prosthetic heart valves: a report from the European Association of Cardiovascular Imaging endorsed by the Chinese Society of Echocardiography, the Inter-American Society of Echocardiography, and the Brazilian Department of Cardiovascular Imaging †

Prosthetic heart valve (PHV) dysfunction is rare but potentially life-threatening. Although often challenging, establishing the exact cause of PHV dysfunction is essential to determine the appropriate treatment strategy. In clinical practice, a comprehensive approach that integrates several parameters of valve morphology and function assessed with 2D/3D transthoracic and transoesophageal echocardiography is a key to appropriately detect and quantitate PHV dysfunction. Cinefluoroscopy, multidetector computed tomography, cardiac magnetic resonance imaging, and to a lesser extent, nuclear imaging are complementary tools for the diagnosis and management of PHV complications. The present document provides recommendations for the use of multimodality imaging in the assessment of PHVs.

004 Diagnostic performance of myocardial blood flow quantification in coronary artery disease by magnetic resonance

Background Mathematical modelling of magnetic resonance (MR) perfusion imaging data allows myocardial blood flow (MBF) quantification and can potentially improve the diagnosis and prognostication of obstructive coronary artery disease (CAD). The diagnostic performance of distributed parameter (DP) modelling in detecting obstructive CAD has not yet been assessed. A model assessment in per vessel against per patient analysis has not been fully assessed yet in a single MR study. This work compares the diagnostic performance of DP modelling against the standard Fermi modelling, for the detection of obstructive CAD, in per vessel against per patient analysis. Methods After informed consent, a pilot cohort of 28 subjects with known or suspected CAD underwent adenosine stress-rest magnetic resonance perfusion imaging at 3T. Data were analysed using Fermi and DP modelling against invasive coronary angiography and fractional flow reserve, acquired in all subjects. Obstructive CAD was defined as luminal stenosis of ≥70% alone, or luminal stenosis ≥50% and fractional flow reserve ≤0.80. Results On ROC analysis, the diagnostic performance of all methods was improved in per patient analysis. DP modelling outperformed the standard Fermi model, in per vessel and per patient analysis. In per patient analysis, DP modelling-derived MBF at stress demonstrated the highest sensitivity and specificity (0.96, 0.92) in detecting obstructive CAD, against Fermi modelling (0.78, 0.88) and visual assessments (0.79, 0.88), respectively. Conclusions DP modelling consistently outperformed Fermi modelling and showed that it may have merit for robustly stratifying patients with at least one vessel with obstructive CAD.

Positron Emission Tomography Evaluation of Aortic Stenosis

Positron Emission Tomography is an emerging non-invasive imaging techniques which allows the activity of specific biochemical processes to be studied within even small structures in the body. PET has recently been applied to patients with aortic stenosis providing some key insights to the pathological processes underlying this condition. In the chapter we will review the principles of PET and how this imaging modality can be applied to heart and specifically the aortic valve.

Assessing the reliability of DP and Fermi estimates in single and dual bolus cardiac MR perfusion imaging

Background MR dual bolus (DB) perfusion imaging has been effectively shown to eliminate signal saturation of the arterial input function (AIF) and allow more reliable quantification of myocardial (Myo) blood flow (MBF). Single bolus (SB) protocols are prone to AIF signal saturation but have been widely used in clinical studies. The Fermi model has been well established for MBF quantification. The distributed parameter (DP) model has been implemented in a recent study to measure additional physiological parameters (PP) such as intravascular (vb) and extravascular-extracellular space (ve) of the coronary arteries (CAs). Our study aims to a) validate absolute values, correlations and differences between SB versus DB estimates and b) assess which model more reliably fits SB data.

B Assessment of valvular calcification and inflammation by positron emission tomography

Background The pathophysiology of aortic stenosis is incompletely understood and the relative contributions of valvular calcification and inflammation to disease progression are unknown. Methods Patients with aortic sclerosis and mild, moderate and severe stenosis were prospectively compared to age and sex-matched control subjects. Aortic valve severity was determined by echocardiography. Calcification and inflammation in the aortic valve were assessed by sodium 18-fluoride (18F-NaF) and 18-fluorodeoxyglucose (18F-FDG) uptake using positron emission tomography. Histological analysis was performed on the valves of five patients who subsequently underwent aortic valve replacement. Results 121 subjects (20 controls; 20 aortic sclerosis; 25 mild, 33 moderate and 23 severe aortic stenosis) were administered both 18F-NaF and 18F-FDG. Quantification of tracer uptake within the valve demonstrated excellent inter-observer repeatability with no fixed or proportional biases and limits of agreement of ±0.21 (18F-NaF) and ±0.13 (18F-FDG) for maximum tissue-to-background ratios. Activity of both tracers was higher in patients with aortic stenosis than control subjects (18F-NaF: 2.87±0.82 vs 1.55±0.17; 18F-FDG: 1.58±0.21 vs 1.30±0.13; both p<0.001). 18F-NaF uptake displayed a progressive rise with valve severity (r2=0.540, p<0.001) and colocalised to osteocalcin staining on histology. Uptake was observed both in the presence and absence of underlying calcium on CT with the latter predominating. 18F-FDG displayed a more modest increase in activity with valve severity (r2=0.218; p<0.001) and mapped to areas of macrophage accumulation. Among patients with aortic stenosis, 91% had increased 18F-NaF (>1.97) and 35% increased 18F-FDG (>1.63) uptake. A weak correlation between the activities of these tracers was observed (r2=0.174, p<0.001) and while 18F-NaF activity was higher in the aortic valve than aortic atheroma (2.68±0.84 vs 2.07±0.30; p<0.001) the reverse was true for 18F-FDG (1.56±0.21 vs 1.80±0.25; p<0.001). Conclusions Positron emission tomography is a novel, feasible and repeatable approach to the evaluation of valvular calcification and inflammation in patients with aortic stenosis. Calcification appears to be the predominant process that is particular to the valve and disproportionate to the degree of inflammation, indicating it to be a more attractive target for therapeutic intervention.

D Uptake of ultrasmall superparamagnetic particles of iron oxide predicts growth in abdominal aortic aneurysms: a Pilot Study

Background Prediction of abdominal aortic aneurysm (AAA) expansion and rupture is challenging and currently relies on serial measurements of maximum aneurysm diameter. Using ultrasmall superparamagnetic particles of iron oxide (USPIO) and MRI, we aimed to assess whether areas of cellular inflammation correlated with the rate of abdominal aortic aneurysm expansion. Methods and Results An image acquisition and data analysis algorithm for the detection of focal USPIO accumulation in tissues was developed. Patients (n=29; 27 male; aged 70±5 years) with asymptomatic AAA (4.0–6.6 cm) were recruited from an outpatient surveillance programme and underwent 3T MRI before and 24–36 h after administration of USPIO. The change in T2* value on T2*-weighted imaging was used to detect accumulation of USPIO within the abdominal aortic aneurysm. Histology of aortic wall tissue samples confirmed co-localisation and uptake of USPIO in areas with macrophage infiltration. Patients were classified into one of three groups on the basis of imaging findings (Abstract D Figure 1). Group 1: periluminal USPIO uptake only. Group 2: USPIO uptake throughout the thrombus. Group 3: USPIO uptake in the aortic wall. Patients in group 3 with distinct mural uptake of USPIO had a threefold higher growth rate (n=13; 0.66 cm/yr; p=0.020) than those with no (Group 1; n=7; 0.22 cm/yr) or non-specific USPIO uptake (Group 2; n=9; 0.24 cm/yr) despite having similar aneurysm diameters (5.4±0.6, 5.1±0.5 and 5.0±0.5 cm respectively; p>0.05) and patient characteristics (p>0.05). In one patient with an inflammatory aneurysm, USPIO uptake and inflammation extended beyond the aortic wall into surrounding tissues.Abstract D Figure 1 Conclusion USPIO uptake in the aortic wall detects cellular inflammation in patients with AAA and appears to predict more rapidly progressive AAA expansion. This technique therefore holds major promise as a new method of risk-stratifying patients with AAA that extends beyond the simple anatomical measure of aneurysm diameter.Abstract D Figure 2