Ullrich Ebersberger

In vivo molecular imaging of angiogenesis, targeting αvβ3 integrin expression, in a patient after acute myocardial infarction

A 35-year-old Caucasian male presented with chest pain and nausea in the emergency room. The initial ECG displayed sinus-rhythm with ST elevation in I, aVL, V1–5, ST-depression in III, and aVR and pathological Q waves in V1–5. The laboratory results showed severely elevated cardiac enzymes. Percutaneous coronary intervention (PCI) with stenting of the completely occluded proximal left anterior descending (LAD) was performed without complications. Two weeks after the myocardial infarction and PCI, the patient underwent MRI and PET/CT evaluation …

Conformational Pulsatile Changes of the Aortic Annulus: Impact on Prosthesis Sizing by Computed Tomography for Transcatheter Aortic Valve Replacement

OBJECTIVES This study sought to investigate pulsatile changes of the aortic annulus and their impact on prosthesis selection by computed tomography (CT). BACKGROUND Precise noninvasive prosthesis sizing is a prerequisite for transcatheter aortic valve replacement. METHODS A total of 110 patients with severe aortic stenosis (mean age: 82.9 ± 8 years, mean aortic valve area: 0.69 ± 0.18 cm(2)) underwent electrocardiogram-gated CT. Aortic annulus dimensions were planimetrically quantified as area-derived diameter (D(A) = 2 ×✓(CSA/π), where CSA is the cross-sectional area) and perimeter-derived diameter (D(P) = P/π, where P is the length of the perimeter) in 5% increments of the RR interval. Hypothetical prosthesis sizing was based on D(A) and D(P) (23-mm prosthesis for <22 mm; 26 mm: 22 to 25 mm; 29 mm: >25 mm) and compared between maximum and traditional cardiac CT reconstruction phases at 35% and 75% of RR. Agreement for prosthesis selection was calculated by κ statistics. RESULTS D(A) and D(P) were increased and eccentricity was reduced during systole, with D(A-MAX) and D(P-MAX) most often observed at 20% of RR. D(P) was consistently larger than D(A). Average net differences were 2.0 ± 0.6 mm and 1.7 ± 0.5 mm by D(A-MIN) versus D(A-MAX) and D(P-MIN) versus D(P-MAX). Agreement for prosthesis sizing was found in 93 of 110 patients (κ = 0.75) by D(A-75%) and in 80 of 110 patients (κ = 0.53) by D(A-MAX) compared with D(A-35%); and in 94 of 110 patients (κ = 0.73) by D(P-75%) and in 93 of 110 patients (κ = 0.73) by D(P-MAX) compared with D(P-35%). With sizing by D(A-75%) or D(P-75%), nominal prosthesis diameter was smaller than D(A-MAX) or D(P-MAX) in 15 and 6 patients respectively. CONCLUSIONS Aortic annulus morphology exhibits conformational pulsatile changes throughout the cardiac cycle due to deformation and stretch. These changes affect prosthesis selection. Prosthesis selection by diastolic perimeter- or area-derived dimensions harbors the risk of undersizing.

Dual-Energy CT of the Heart

OBJECTIVE Interest in dual-energy CT (DECT) for evaluating the myocardial blood supply, as an addition to coronary artery assessment, is increasing. Although it is still in the early clinical phase, assessment of myocardial ischemia and infarction by DECT constitutes a promising step toward comprehensive evaluation of coronary artery disease with a single noninvasive modality. CONCLUSION Compared with dynamic CT approaches, DECT has advantages regarding radiation dose and clinical applicability. In this review, the literature on DECT of the heart is discussed.

Iterative Image Reconstruction Techniques for CT Coronary Artery Calcium Quantification: Comparison with Traditional Filtered Back Projection in Vitro and in Vivo

PURPOSE To investigate in vitro and in vivo the use of image-based and raw data-based iterative reconstruction algorithms for quantification of coronary artery calcium by using the Agatston score and subsequent cardiac risk stratification. MATERIALS AND METHODS In vitro data were obtained by using a moving anthropomorphic cardiac phantom containing calcium inserts of different concentrations and sizes. With institutional review board approval and HIPAA compliance, coronary calcium imaging data of 110 consecutive patients (mean age ± standard deviation, 58.2 years ± 9.8; 48 men) were reconstructed with filtered back projection (FBP), iterative reconstruction in image space (IRIS), and sinogram-affirmed iterative reconstruction (SAFIRE). Image noise was measured and the Agatston score was obtained for all reconstructions. Assignment to Agatston scores and percentile-based cardiac risk categories was compared. Statistical analysis included the Cohen κ coefficient and Friedman and Wilcoxon testing. RESULTS In vitro, mean Agatston scores ± standard deviation for FBP (638.9 ± 9.6), IRIS (622.7 ± 15.2), and SAFIRE (631.4 ± 17.6) were comparable (P = .30). The smallest phantom calcifications were more frequently detected when iterative reconstruction techniques were used. The Agatston scores in the patient cohort were not significantly different among FBP, IRIS, and SAFIRE in paired comparisons (median Agatston score [25th and 75th percentiles]: 76.0 [20.6, 243.9], 76.4 [22, 249.3], and 75.7 [21.5, 49.1], respectively; P = .20 each). Comparison of categorization based on Agatston score percentiles showed excellent agreement for both IRIS and SAFIRE with FBP (κ = 0.975 [0.942-1.00] and κ = 0.963 [0.922-1.00], respectively). The mean effective dose was 1.02 mSv ± 0.51. Mean image noise was significantly (P < .001) higher with FBP than that with iterative reconstructions. CONCLUSION In comparison with FBP, iterative reconstruction techniques do not have a profound effect on the reproducible quantification of coronary calcium according to Agatston score and subsequent cardiac risk classification, although risk reclassification may occur in a small subset of subjects.

Monoenergetic extrapolation of cardiac dual energy CT for artifact reduction

Background Monoenergetic extrapolation of cardiac dual-energy computed tomography (DECT) could be useful in artifact reduction in clinical practice. Purpose To evaluate the potential of monoenergetic extrapolation of cardiac DECT data for reducing artifacts from metal and high iodine contrast concentration. Material and Methods With IRB approval and in HIPAA compliance, 35 patients (22 men, 61 ± 12 years) underwent cardiac DECT with dual-source CT (100 kVp and 140 kVp). Contrast material injection protocols were adapted to the patient’s weight using non-ionic low-osmolar 370 mgI/mL iopromide. Datasets were transferred to a stand-alone workstation and dedicated monoenergetic analysis software was used for postprocessing. Reconstructions with the following five photon energies were generated: 40 keV, 60 keV, 80 keV, 100 keV, and 120 keV. Artifact severity was graded on a 5-point Likert scale (0, massive artifact; 5, absence of artifact). The size of artifact and image noise (expressed as HU) in anatomic structures adjacent to the artifact were measured. Quantitative and subjective image quality was compared using Friedman and Wilcoxon tests. Results We observed artifacts arising from densely concentrated contrast material in the superior vena cava (SVC) in 18 patients, from sternal wires in 14, from bypass clips in eight, and from coronary artery stents in seven. Artifact size in monoenergetic reconstructions from 40 to 120 keV decreased from 21.3 to 19 mm for the SVC (P < 0.001), from 8.4 to 2.6 mm for sternal wires (P < 0.001), from 6.4 to 2.2 mm for bypass clips (P < 0.001), and from 5.9 to 2.7 mm for stents (P < 0.001), respectively. The quality score changed from 0.2 to 3.8 for the SVC (P < 0.001), from 0.1 to 4 for sternal wires (P < 0.001), from 0 to 3.9 for bypass clips (P < 0.001), and from 0 to 3.9 for stents (P < 0.001). Lowest noise in adjacent structures was found at 80 keV for the SVC (39.1 HU), for sternal wires (33.3), for bypass clips (26.9), and for stents (33.9). Conclusion A significant reduction of high-attenuation artifacts can be achieved by use of higher monoenergetic energy levels with cardiac DECT. However, image noise in anatomic structures affected by artifacts is lowest at 80 keV, which suggests an evaluation approach that makes use of multiple energy levels for a complete diagnosis.

Global Quantification of Left Ventricular Myocardial Perfusion at Dynamic CT: Feasibility in a Multicenter Patient Population

OBJECTIVE The purpose of this study was to determine the feasibility of global quantitative measurements of left ventricular myocardial perfusion derived from stress dynamic CT myocardial perfusion imaging. MATERIALS AND METHODS The coronary CT angiographic and CT myocardial perfusion imaging datasets of 146 patients were visually evaluated for the presence of coronary artery stenosis and perfusion defects. For the quantitative analysis, volumes of interest were defined over the entire left ventricular myocardium to obtain global myocardial blood flow (MBF), myocardial blood volume (MBV), and volume transfer constant (K(trans)). RESULTS In patients without anatomically significant coronary stenosis or perfusion defects, the mean value of global MBF was 137.9 ± 28.8 mL/100 mL/min; MBV, 19.5 ± 2.3 mL/100 mL; and K(trans), 85.8 ± 15.2 mL/100 mL/min. In patients with perfusion defects in one, two, or three vessels, the mean global MBF values were 132.6 ± 29.2, 117.4 ± 4.9, and 92.5 ± 11.2 mL/100 mL/min; MBV, 17.9 ± 3.2, 16.1 ± 3.1, and 12.8 ± 1.7 mL/100 mL; and K(trans), 80.4 ± 12.9, 76.6 ± 13.8, and 72.6 ± 15.5 mL/100 mL/min. In patients with significant (> 50%) stenosis in one, two, or three vessels at coronary CT angiography, the mean global MBF values were 129.2 ± 28.3, 120.5 ± 24.2, and 119.4 ± 33.5 mL/100 mL/min; MBV, 17.8 ± 3.3, 17.2 ± 3.2, and 14.7 ± 4.1 mL/100 mL; and K(trans), 80.3 ± 12.9, 76.0 ± 14.7, and 77.6 ± 13.2 mL/100 mL/min. CONCLUSION Global quantitative assessment of left ventricular perfusion with stress dynamic CT myocardial perfusion imaging is feasible, and the findings correlate with the visual assessment of perfusion and the presence of coronary artery stenosis at coronary CT angiography. The potential clinical utility of this technique as a diagnostic tool for differentiating normal from globally reduced myocardial perfusion or as a prognostic marker merits further investigation.

Magnetic resonance myocardial perfusion imaging at 3.0 Tesla for the identification of myocardial ischaemia: comparison with coronary catheter angiography and fractional flow reserve measurements

AIMS To assess image quality and diagnostic performance of 3.0 Tesla (3T) cardiac magnetic resonance (CMR) myocardial perfusion imaging with a dual radiofrequency source to detect functional relevant coronary artery disease (CAD), using coronary angiography and invasive pressure-derived fractional flow reserve (FFR) as reference standard. METHODS AND RESULTS We included 116 patients with suspected or known CAD, who underwent 3T adenosine myocardial perfusion CMR (resolution 2.97 × 2.97 mm) and coronary angiography plus FFR measurements in intermediate lesions. Image quality of myocardial perfusion CMR was graded on a 4-point scale (1 = poor to 4 = excellent). Diagnostic accuracy was assessed by ROC analyses using a 16-myocardial segment-based summed perfusion score (0 = normal to 3 = transmural perfusion defect) and by determining sensitivity, specificity, positive and negative predictive value on the coronary vessel territory and the patient level. Diagnostic image quality was achieved for all stress myocardial perfusion CMR studies with an average quality score of 2.5, 3.1, and 3.0 for LAD, LCX, and RCA territories. The ability of the myocardial perfusion CMR perfusion score to detect significant coronary artery stenosis yielded an area under the curve of 0.93 on ROC analysis. Values for sensitivity, specificity, positive and negative predictive value on a vessel territory level and the patient level were 89, 95, 87, 96% and 85, 87, 77, 92%, respectively. CONCLUSION In patients with suspected or known significant CAD, 3T myocardial perfusion CMR with standard perfusion protocols provides consistently high image quality and an excellent diagnostic performance.

Iterative image reconstruction: a realistic dose-saving method in cardiac CT imaging?

Iterative techniques are a valuable computed tomography image reconstruction alternative to filtered back projection. In repetitive cycles, iterative algorithms reduce image noise virtually independently of spatial resolution. In light of substantially decreased image noise, tube voltage or current reductions are enabled, resulting in significant radiation dose savings while preserving image quality. Moreover, iterative reconstruction techniques have the advantage of minimizing calcium blooming and metal artifacts. Iterative reconstruction may therefore lead to more exact coronary artery evaluation at constant x-ray tube settings and appears beneficial in clinically challenging scenarios such as overly obese patients, calcified coronary arteries and presence of iatrogenic hardware. For cardiac computed tomography, iterative reconstruction represents a promising and readily available tool.

CT Evaluation of Small-Diameter Coronary Artery Stents: Effect of an Integrated Circuit Detector with Iterative Reconstruction

PURPOSE To use suitable objective methods of analysis to assess the influence of the combination of an integrated-circuit computed tomographic (CT) detector and iterative reconstruction (IR) algorithms on the visualization of small (≤3-mm) coronary artery stents. MATERIALS AND METHODS By using a moving heart phantom, 18 data sets obtained from three coronary artery stents with small diameters were investigated. A second-generation dual-source CT system equipped with an integrated-circuit detector was used. Images were reconstructed with filtered back-projection (FBP) and IR at a section thickness of 0.75 mm (FBP75 and IR75, respectively) and IR at a section thickness of 0.50 mm (IR50). Multirow intensity profiles in Hounsfield units were modeled by using a sum-of-Gaussians fit to analyze in-plane image characteristics. Out-of-plane image characteristics were analyzed with z upslope of multicolumn intensity profiles in Hounsfield units. Statistical analysis was conducted with one-way analysis of variance and the Student t test. RESULTS Independent of stent diameter and heart rate, IR75 resulted in significantly increased xy sharpness, signal-to-noise ratio, and contrast-to-noise ratio, as well as decreased blurring and noise compared with FBP75 (eg, 2.25-mm stent, 0 beats per minute; xy sharpness, 278.2 vs 252.3; signal-to-noise ratio, 46.6 vs 33.5; contrast-to-noise ratio, 26.0 vs 16.8; blurring, 1.4 vs 1.5; noise, 15.4 vs 21.2; all P < .001). In the z direction, the upslopes were substantially higher in the IR50 reconstructions (2.25-mm stent: IR50, 94.0; IR75, 53.1; and FBP75, 48.1; P < .001). CONCLUSION The implementation of an integrated-circuit CT detector provides substantially sharper out-of-plane resolution of coronary artery stents at 0.5-mm section thickness, while the use of iterative image reconstruction mostly improves in-plane stent visualization.

In Vivo Assessment of Aortic Aneurysm Wall Integrity Using Elastin-Specific Molecular Magnetic Resonance Imaging

Background—The incidence of abdominal aortic aneurysms (AAAs) has increased during the last decades. However, there is still controversy about the management of medium-sized AAAs. Therefore, novel biomarkers, besides aneurysmal diameter, are needed to assess aortic wall integrity and risk of rupture. Elastin is the key protein for maintaining aortic wall tensile strength and stability. The progressive breakdown of structural proteins, in particular, medial elastin, is responsible for the inability of the aortic wall to withstand intraluminal hemodynamic forces. Here, we evaluate the usefulness of elastin-specific molecular MRI for the in vivo characterization of AAAs. Methods and Results—To induce AAAs, ApoE–/– mice were infused with angiotensin-II. An elastin-specific magnetic resonance molecular imaging agent (ESMA) was administered after 1, 2, 3, and 4 weeks of angiotensin-II infusion to assess elastin composition of the aorta (n=8 per group). The high signal provided by ESMA allowed for imaging with high spatial resolution, resulting in an accurate assessment of ruptured elastic laminae and the compensatory expression of elastic fibers. In vivo contrast-to-noise ratios and R1-relaxation rates after ESMA administration were in good agreement with ex vivo histomorphometry (Elastica van Gieson stain) and gadolinium concentrations determined by inductively coupled plasma mass spectroscopy. Electron microscopy confirmed colocalization of ESMA with elastic fibers. Conclusions—Changes in elastin content could be readily delineated and quantified at different stages of AAAs by elastin-specific molecular magnetic resonance imaging. ESMA-MRI offers potential for the noninvasive detection of the aortic rupture site prior to dilation of the aorta and the subsequent in vivo monitoring of compensatory repair processes during the progression of AAAs.