Axel Küttner

Performance evaluation of a multi-slice CT system with 16-slice detector and increased gantry rotation speed for isotropic submillimeter imaging of the heart.

Background: 4-slice CT scanners have shown limitations in clinical application for noninvasive coronary CT angiography (CTA). We evaluate advances in ECG-gated scanning of the heart and the coronary arteries with recently introduced 16-slice CT equipment (SOMATOM Sensation 16, Siemens, Forchheim, Germany). Materials and Methods: The technical principles of ECG-gated cardiac scanning, scan parameters, and detector design of the new scanner are presented. ECG-gated scan and image reconstruction techniques and ECG-controlled dose modulation (“ECG pulsing”) for a reduction of the patient dose are described, key parameters for image quality and simulation results presented, and phantom studies and initial patient experience discussed. The impact of reduced gantry rotation time (0.42 s) on temporal resolution and initial estimations of the patient dose are presented. Results: Extensions of ECG-gated reconstruction algorithms used for 4-slice CT provide adequate image quality for up to 16 slices. For each detector collimation different slice widths are available for retrospective reconstruction with well-defined slice sensitivity profiles (SSPs). For coronary CTA the heart can be covered with 0.75 mm collimation within a 20-s breathhold. The best possible spatial resolution is 0.5 × 0.5 × 0.6 mm. For 0.42 s gantry rotation time, temporal resolution reaches its optimum (105 ms) at a heart rate of 81 bpm. Effective patient dose for coronary CTA is 4–5 mSv using ECG-pulsed acquisition. Conclusion: The clinical performance of coronary CTA by means of spatial resolution, temporal resolution and scan time is substantially improved with the evaluated 16-slice CT scanner. Also, display of smaller coronary segments and instent visualization are substantially improved.Hintergrund: Die Einführung der Mehrschicht-CT im Jahr 1998 stellte einen Durchbruch der mechanischen CT in der nichtinvasiven Bildgebung des Herzens dar. Klinische Studien zeigten jedoch Limitationen gängiger 4-Schicht-CT-Geräte, welche die breite klinische Anwendung der Methode einschränken. Material und Methoden: Die neue Generation von Mehrschicht-CT-Geräten bietet gleichzeitige Aufnahme von bis zu 16 Submillimeter-Schichten und verbesserte Zeitauflösung für Herzuntersuchungen durch Verringerung der Gantry-Rotationszeit auf 0,42 s. Diese Arbeit stellt die technischen Grundlagen und mögliche Applikationen dieser neuen Technologie in der Untersuchung des Herzens und der Koronargefäße am Beispiel eines neuartigen 16-Schicht-CT-Gerätes dar (SOMATOM Sensation 16, Siemens AG, Forchheim). Das neue Systemkonzept, Detektordesign und Dosiseffizienz sowie Datenaufnahme- und Bildrekonstruktionstechniken für die EKG-synchronisierte Untersuchung des Herzens werden diskutiert. Ergebnisse: Die Erweiterung gängiger Rekonstruktionstechniken von 4- auf 16-Schicht-Detektoren liefert eine diagnostisch adäquate Bildqualität. Die neuen Verfahren sind in der Lage, für jede kollimierte Schichtdicke Schichten verschiedener Dicke mit gut definierten Schichtempfindlichkeitsprofilen zu rekonstruieren. Basierend auf einer kollimierten Schichtdicke von 0,75 mm kann eine hochaufgelöste CT-Angiographie (CTA) des Herzens und der Koronargefäße in einer 20-sekündigen Atempause durchgeführt werden. Die bestmögliche räumliche Auflösung beträgt 0,5 × 0,5 × 0,6 mm. Mit einer Rotationszeit des Messsystems von 0,42 s wird die bestmögliche zeitliche Auflösung von 105 ms bei einer Herzfrequenz von 81 Schlägen/min erreicht. Unter Verwendung einer EKG-synchronisierten Röhrenstrommodulation ist für eine CTA des Herzens und der Herzkranzgefäße mit einer effektiven Patientendosis von 4–5 mSv zu rechnen. Schlussfolgerung: Mit den neuen 16-Schicht-CT-Systemen lassen sich bei reduzierter Untersuchungszeit sowohl die räumliche als auch zeitliche Auflösung für die CTA des Herzens und der Koronargefäße deutlich verbessern. Auch die Darstellung kleinerer Koronarsegmente und die In-Stent-Visualisierung werden ermöglicht.

CT imaging in acute pulmonary embolism: diagnostic strategies

Computed tomography pulmonary angiography (CTA) has increasingly become accepted as a widely available, safe, cost-effective, and accurate method for a quick and comprehensive diagnosis of acute pulmonary embolism (PE). Pulmonary catheter angiography is still considered the gold standard and final imaging method in many diagnostic algorithms. However, spiral CTA has become established as the first imaging test in clinical routine due to its high negative predictive value for clinically relevant PE. Despite the direct visualization of clot material, depiction of cardiac and pulmonary function in combination with the quantification of pulmonary obstruction helps to grade the severity of PE for further risk stratification and to monitor the effect of thrombolytic therapy. Because PE and deep venous thrombosis are two different aspects of the same disease, additional indirect CT venography may be a valuable addition to the initial diagnostic algorithm—if this was positive for PE—and demonstration of the extent and localization of deep venous thrombosis has an impact on clinical management. Additional and alternate diagnoses add to the usefulness of this method. Using advanced multislice spiral CT technology, some practitioners have advocated CTA as the sole imaging tool for routine clinical assessment in suspected acute PE. This will simplify standards of practice in the near future.

Inhibition of smooth muscle cell proliferation after local drug delivery of the antimitotic drug paclitaxel using a porous balloon catheter

Abstract Percutaneous transluminal coronary angioplasty is an accepted treatment for coronary artery disease. The major limitation, however, is the high incidence of restenosis which limits the long-term benefit of this intervention. Paclitaxel is a new antiproliferative agent that has generated considerable scientific interest since it was introduced in clinical trials in the early 1980s. Recent in vitro studies have shown that paclitaxel has considerable antiproliferative activity in human coculture systems. In the present study the efficacy of paclitaxel was investigated after development of an intimal plaque by electrical stimulation and additional cholesterol diet and subsequent balloon angioplasty in 63 New Zealand White rabbits. Local drug delivery of paclitaxel was accomplished in 30 rabbits with a porous balloon catheter (35 holes, hole diameter 75 μm, 2.5 mm catheter diameter). Paclitaxel was administered locally with 4 ml (solution 10−5 mol/L) using an injection pressure of 2 atm. To study the extent of restenosis and morphological changes, the animals were sacrificed 7, 28 or 56 days after intervention. After staining procedures quantification of SMC proliferation, intimal macrophages and morphological analyses were performed. Paclitaxel plasma concentrations were measured using HPLC technique. One week after balloon angioplasty the arteries treated with local paclitaxel delivery showed an insignificant trend towards a reduction in intimal smooth muscle cell proliferation (untreated 8.4 ± 4.9 % vs paclitaxel treated 2.4 ± 2.4 %, p = NS). However, this resulted in a significant reduction of stenosis degree of 66 % 8 weeks after intervention compared to the untreated group (untreated 41 ± 18 % vs paclitaxel treated 14 ± 11 %, p = 0.005). In conclusion, locally delivered paclitaxel prevented neointimal thickening in the rabbit carotid artery after balloon angioplasty. Local paclitaxel treatment may therefore be a clinical option for the prevention of restenosis after coronary interventions. However, further preclinical studies have to prove long-term efficacy and safety.

Non-invasive coronary angiography with 16-slice spiral computed tomography: image quality in patients with high heart rates

The purpose of this study was to assess segment image quality at high heart rates using 16-slice computed tomography and differential reconstruction for major coronary vessels. According to the following protocol, 16-slice CT coronary angiography in 46 patients with a mean heart rate of 86.3±11.8 was reconstructed. At three transverse planes, preview series were obtained and motion artifacts evaluated in 5% increments from 0-95% within the cardiac cycle. Relying on image quality in the previews, reconstructions were performed at three z-positions for each patient. Segment image quality was assessed in terms of artifacts and visibility. The effects of heart rate and trigger delay on image quality were analyzed. Optimal image quality was achieved at 25 to 35% of the cardiac cycle for the left circumflex (CX) and right coronary artery (RCA) or 30 to 40% for the left main (LM) and left anterior descending artery (LAD). Sixteen-slice CT and differential reconstruction produced good image quality with a low percentage of motion-degraded proximal and middle segments (8.8%). Grades were 1.5 for the LM, 1.9 for the LAD, 2.0 for the CX and 2.3 for the RCA. At high heart rates, good image quality of the coronary arteries is achieved by 16-slice CT and a sophisticated reconstruction strategy at peak to late systole.

MDCT: cardiology indications.

In the past 2 years mechanical multidetector-row CT (MDCT) systems with simultaneous acquisition of four slices and half-second scanner rotation have become widely available. Data acquisition with these scanners allows for considerably faster coverage of the heart volume compared with single-slice scanning. This increased scan speed can be used for retrospective gating together with 1-mm collimated slice widths and allows coverage of the entire cardiac volume in one breath hold. Initial results from studies in correlation with intracoronary ultrasound suggest that MDTC technology not only offers the possibility to visualize intracoronary stenoses non-invasively but also to differentiate plaque morphology. This is especially the case with the next generation of 16-row multidetector CT. An increased number of simultaneously acquired slices and sub-millimeter collimation for cardiac applications allows true isotropic scanning with high temporal resolution. Contrast-enhanced MDTC is a promising non-invasive technique for the detection, visualization, and characterization of stenotic artery disease. It could act as a gate keeper prior to cardiac catherization and finally replace conventional diagnostic modalities.

Visualization and comparison of drug effects after local paclitaxel delivery with different catheter types

AbstractBackground: The microtubule stabilizing compound paclitaxel has proved to have potent antiproliferative effects on smooth muscle cells both in vitro and in vivo. It induces cellular modifications that result in reduced proliferation, migration and signal transduction by shifting the cellular microtubule equilibrium towards assembly. We therefore reasoned that a visualization of the altered cytoskeleton could enable an evaluation of the drug effects following local drug delivery. Methods and results: 3 catheters – the porous balloon, the microporous balloon and the double balloon catheter – were chosen for this study representing the spectrum from passive to active, pressure-driven delivery. After the induction of a defined plaque in the right carotid arteries of 40 New Zealand rabbits by electrical stimulation, 32 animals underwent balloon dilatation and 8 animals served as pre-interventional control group with electrostimulation only. In 24 animals (n = 8 in each group) subsequent local paclitaxel delivery (10 μmol/L) was performed. 8 animals served as control with angioplasty only. Vessels were excised 1 week following intervention. Immunohistochemistry with antibodies against bromodeoxyuridine, alpha-actin, macrophages, von Willebrand factor and α-tubulin was performed. Cytoskeletal changes were analyzed by electron microscopy. Tubulin staining and electron microscopy revealed changes with distinct staining patterns for the different catheters. Specific catheter-induced injuries could be identified for the porous and double balloon catheter. Intimal proliferation, percentage of macrophages and extent of injury favor the double balloon catheter for local paclitaxel delivery. Conclusions: The alterations of the cytoskeleton induced by paclitaxel allowed for the detection of drug action by staining of tubulin and electron microscopy. This enables an evaluation of transfer, distribution and drug effects directly in the vasculature without marker substances. The double balloon catheter appears to be best suited for local paclitaxel therapy.

Contrast-enhanced MDCT of the thorax.

The introduction of multidetector-row computed tomography (MDCT) into clinical radiology has revolutionized the spectrum of thoracic imaging. The current generation of MDCT scanners with simultaneous acquisition of up to 16 slices enables scan speeds which are 45 times faster than single-slice CT. The most important difference compared with conventional spiral CT is the conceptual change of acquiring a volume of data rather than individual sections [1]. This has also affected the techniques and protocols of contrast injection for various applications. After some technical remarks, we concentrate in this article on various applications of contrast-enhanced thoracic imaging. The main focus is on imaging of the thoracic aorta, the pulmonary arteries, and the pulmonary veins.

Cardiac and vascular MDCT: thoracic imaging

The current generation of multi-detector row CT (MDCT) with simultaneous acquisition of up to 16 slices enables scan speeds which are 45 times faster compared with single-slice CT [1, 2]. The scan speed translates into the ability to scan the entire thorax in just one breath hold of not more than 10 s [3, 4]. Despite submillimeter resolution, this scan speed allows motion-free images even in the most critically ill patients; however, the most important difference compared with conventional spiral CT is the conceptual change of acquiring a volume of data rather than individual sections [5]. This has also affected the techniques and protocols for contrast injection for various applications. After some technical remarks, we concentrate, in this article, on various applications of contrast-enhanced thoracic imaging. The main focus is on imaging of the thoracic aorta, the pulmonary arteries, and the pulmonary veins. Examination techniques

Virtual bronchoscopy: comparison of different surface rendering models.

The aim of this study was to compare different representation models of surface-rendered virtual bronchoscopy. 10 consecutive patients with inoperable primary lung tumors underwent thin-section spiral computed tomography. The structures of interest, the tracheobronchial system and anatomical and pathological thoracic structures were segmented using an interactive threshold interval volume-growing segmentation algorithm and visualized with the aid of a color-coded surface rendering method. For virtual bronchoscopy, the tracheobronchial system was visualized using a triangle-surface rendering model, a shaded-surface rendering model and a transparent shaded-surface rendering model. The triangle-surface rendering model allowed optimum detailed spatial representation of the dimensions of extraluminal anatomical and pathological mediastinal structures. As the lumen of the tracheobronchial system was less well defined, the rendering model was of limited use for depiction of the airway surface. The shaded-surface rendering model facilitated an optimum assessment of the airway surface, but the mediastinal structures could not be depicted. The transparent shaded-surface rendering model provides simultaneous adequate to optimum visualization and assessment of the intraluminal airway surface and the extraluminal mediastinal structures as well as a quantitative assessment of the spatial relationship between these structures. Fast data acquisition with a multi-slice detector spiral computed tomography scanner and the use of virtual bronchoscopy with the transparent shaded-surface rendering model obviate the need for time consuming detailed analysis and presentation of axial source images by providing improved the diagnostic imaging of endotracheal and endobronchial diseases and offering a useful alternative to fiberoptic bronchoscopy.

Funktionale Darstellung des Herzens

Derzeit gibt es keine evidenzbasierte Indikation, eine retrospektiv EKG-gegatete Mehrschicht-Spiral-CT (Mehrschicht-CT) alleine zur Untersuchung der Herzfunktion durchzufuhren. Funktionsbildgebung einschlieslich Funktionsanalyse stammen also aus Untersuchungen der Mehrschicht-CT Koronarangiographie und morphologischen Untersuchungen des Herzens. Diese erlauben die Beurteilung der Herzfunktion wie folgt: 1. Bestimmung der allgemeinen Funktion des linken Ventrikels: Enddiastolisches Volumen (EDV) Endsystolisches Volumen (ESV) Schlagvolumen (SV) Ejektionsfraktion (EF) Herzzeitvolumen (Cardiac output, CO) Peak filling rate (PFR) Peak ejection rate (PER) Zeit bis zur PER Zeit vom Ende der Systole bis zur PFR Myokardiale Masse Regionale Bewegungsanalyse der Herzwand