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S Achenbach

Publications and source records attributed to S Achenbach.

81 records · Page 5Linked to original sources
PubMed1995

Coronary artery stenoses: three-dimensional imaging with electrocardiographically triggered, contrast agent-enhanced, electron-beam CT.

PURPOSE: To compare electron-beam computed tomography (CT) and coronary angiography for depiction of coronary artery stenoses. MATERIALS AND METHODS: In 27 patients (age range, 50-70 years), electrocardiographically triggered axial electron-beam CT scans of the heart were obtained during breath hold and intravenous administration of contrast agent. Coronary arteries were reconstructed three-dimensionally. Electron-beam CT and angiographic results were compared. RESULTS: Significant enhancement within the vessel lumen (P < .001) permitted selective reconstruction of the inner coronary artery lumen. Nine of 11 high-grade stenoses and all five occlusions in the proximal left anterior descending artery and three of five high-grade right coronary artery stenoses were clearly identified. Recognition of stenosis of the left circumflex artery was not reliable. Success after percutaneous transfemoral coronary angioplasty was documented in five of five patients by visualizing the increase in vessel diameter at repeat investigation. CONCLUSION: Contrast-enhanced electron-beam CT yields promising results concerning the visualization of coronary artery stenoses.

Aged↗
PubMed1994

Biomagnetic localization of electrical current sources in the human heart with realistic volume conductors using the single-current-dipole model.

The boundary element method was applied in order to investigate the localization accuracy for focal sources measured from MCG data. Various homogeneous volume conductor models were composed: the individually shaped torso, a scaled standard torso, an unscaled standard torso, a scaled cuboid and a scaled ellipsoid. We implemented these models in single-dipole inverse solution techniques. High resolution multichannel data were analysed from two patients showing ventricular extrasystoles and two patients suffering from Wolff-Parkinson-White syndrome. Moreover, we report the localization of shallow- and deep-lying catheters (depth 9 cm and depth 17.5 cm below the measurement grid). Using an individually shaped homogeneous torso yields a localization error of less than 3 cm even for the deepest sources (mean error 2.4 cm). Probability-based dipole localization shows that the remaining error could only partly be explained by data noise statistics. Therefore it seems to be due to either inner inhomogeneities or the inadequacy of the single current dipole or a combination of the two. Thus clinically useful localization accuracy in the millimetre range requires more sophisticated volume conductor and source models. The evaluation of measurement data and simulation study shows that a scaled cuboid model can provide nearly the same localization accuracy as the individually shaped torso model. Single dipole reconstruction with this model is computationally faster than that with the individually shaped model of the human body and is fast enough for use in clinical applications.

Arrhythmias, Cardiac↗
PubMed1991

[Magnetocardiography. Biomagnetic localization of impulse development and transmission of the heart].

Magnetocardiography is a non-invasive biomagnetic technique for measuring magnetic fields produced at the surface of the body when the heart is stimulated to beat. The measurement is contact-free and is independent of tissue resistance. For the first time, magnetocardiography employing multi-channel systems permits the accurate, non-invasive localization of accessory conduction pathways and ectopic ventricular activity.

Cardiac Complexes, Premature↗
PubMed1991

Clinical magnetocardiography: experience with a biomagnetic multichannel system.

The magnetic fields caused by the human heart's electrical activity were coherently recorded with a biomagnetic multichannel system (KRENIKON) during 1 to 10 minutes in 49 patients. 31 to 37 magnetic channels were recorded simultaneously with the ECG and respiration. Comparison of a magnetic index and the Sokolow-Lyon index to echocardiographic findings in the quantification of left ventricular hypertrophy demonstrated the superiority of the magnetocardiogram (MCG) as compared to the ECG. The magnetocardiographic investigation of patients with WPW-Syndrome, ventricular extrasystoles, ventricular tachycardia, and paced ventricular beats demonstrated that multichannel magnetocardiography permits the non-invasive three dimensional localization of arrhythmogenic tissue with high spatial accuracy.

Action Potentials↗
PubMed1991

Biomagnetic localization of ventricular arrhythmias.

The magnetic fields caused by electrical activity of the human heart can be coherently measured with a highly sensitive, multichannel, superconducting quantum interference-device system and can enable noninvasive localization of the underlying electrical activity. The magnetocardiograms (MCGs) of 10 patients with spontaneous premature ventricular complexes (PVCs), three patients with ventricular tachycardia (VT), and four healthy subjects with induced paced beats were recorded for 2-15 minutes. After correction for superimposed repolarization activity, the site of origin of the arrhythmias was localized from the magnetic field distribution at the onset of the ectopic beats. The localization results of paced beats showed an error of a few millimeters in relation to the position of the catheter tip. The results of spontaneous PVC and VT were confirmed with endocardial mapping or associated with ischemic lesions. The authors conclude that multichannel magnetocardiographic studies enable the completely noninvasive localization of ventricular arrhythmias.

Adult↗
PubMed1990

Elimination of electronic offset and physiological background activity in magnetocardiographic localization.

A method has been developed to eliminate disturbing magnetic signals in the biomagnetic localization of arrhythmogenic sources in the heart. The procedure consists of two steps: Superimposed background activity of the heart is eliminated by subtraction of a template of pure background activity. Systematic and electronic offset is subsequently eliminated by baseline-correction during periods of zero activity. The method was applied to several kinds of arrhythmias. It was demonstrated that elimination of background activity is the prerequesite for exact localization and that the proposed procedure yields correct results.

Algorithms↗
PubMedDate not supplied

Feasibility of C-arm-supported CT fluoroscopy in percutaneous abscess drainage procedures.

PURPOSE: Evaluation of C-arm-supported CT fluoroscopy to facilitate percutaneous abscess drainage procedures. METHODS: Prospectively, 40 percutaneous drainage procedures were performed either with C-arm-supported CT fluoroscopy or with CT fluoroscopy alone. Hybrid imaging was performed on the CT couch after complementing a CT fluoroscopy scanner with a C-arm fluoroscopy unit. Procedure times, drainage revisions during follow-up, and postinterventional drainage periods were analyzed. RESULTS: When compared with exclusive CT fluoroscopic guidance, a median procedure time of 9 +/- 3.7 min versus 14.8 +/- 7.3 min was required for C-arm-supported CT fluoroscopy (p < 0.005, t-test). During follow-up, eight drainage catheters had to be revised within the exclusive CT fluoroscopy group, while only two revisions were necessary within the C-arm-supported CT fluoroscopy group. With C-arm-supported CT fluoroscopy, postinterventional drainage periods were reduced (median 13 vs 19 days; p < 0.001, t-test). CONCLUSION: Compared with exclusive cross-sectional image guidance, C-arm-supported CT fluoroscopy seems to improve placement of abscess drainage catheters to possibly reduce procedure times, drainage catheter revisions, and postinterventional drainage periods.

Abscess↗
PubMedDate not supplied

Overlapping cross-sections significantly improve the reproducibility of coronary calcium measurements by electron beam tomography: a phantom study.

PURPOSE: We conducted phantom studies to investigate whether overlapping cross-sections and volumetric scoring would significantly improve interscan reproducibility of electron beam tomography (EBT) for coronary artery calcium quantification. METHOD: Fifteen phantoms simulating various amounts of coronary calcification were scanned in five different positions with a slice thickness of 3.0 mm and a table feed of 3.0, 2.5, and 2.0 mm. For the conventional "Agatston score" and a "volume score" (total volume of calcified lesions), interscan variabilities were compared between the three image acquisition protocols. RESULTS: Agatston score variability was significantly lower for the 2.0 mm table feed than for the 3.0 or 2.5 mm table feed (3.0 mm: 22.9 +/- 10.3%; 2.5 mm: 13.6 +/- 8.2%; 2.0 mm: 8.9 +/- 5.5%). Volume score variability was significantly lower for 2.5 and 2.0 mm table feed than for 3.0 mm table feed (3.0 mm: 21.7 +/- 11.0%; 2.5 mm: 10.9 +/- 5.9%; 2.0 mm: 9.8 +/- 5.9%). CONCLUSION: Overlapping cross-sections, especially in combination with volumetric scoring, significantly improved interscan reproducibility of EBT calcium quantification in a phantom study.

Aged↗