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Biomedical subjects

S Achenbach

Publications and source records attributed to S Achenbach.

At least 73 records · Page 4Linked to original sources
PubMed1998

Curved multiplanar reconstructions for the evaluation of contrast-enhanced electron beam CT of the coronary arteries.

OBJECTIVE: We investigated the applicability of curved multiplanar reconstructions for the evaluation of contrast-enhanced electron beam CT scans of the coronary arteries. SUBJECTS AND METHODS: Thirty-two patients (43-72 years old; mean age, 58 years old) underwent electron beam CT. After injection of i.v. contrast medium, 40 axial cross sections of the heart were acquired, triggered to the ECG during breath-hold (3-mm slice thickness, 1-mm overlap). Curved multiplanar reconstructions were obtained separately for each coronary artery. The reconstructions were independently evaluated by two investigators for the presence of high-grade stenoses and occlusions. The results were then compared with coronary angiography results, of which the two investigators had been unaware. RESULTS: Because of degraded image quality, 15 (12%) of the 128 vessels (left main, left anterior descending, left circumflex, and right coronary arteries in 32 patients) were excluded from evaluation. In the remaining 113 vessels, 16 (89%) of 18 high-grade stenoses and occlusions were correctly detected (89% sensitivity). Absence of significant stenosis was correctly detected in 87 (92%) of 95 vessels (92% specificity). The negative and positive predictive values were 98% and 67%, respectively. CONCLUSION: Curved multiplanar reconstructions are useful in the evaluation of contrast-enhanced electron beam CT scans of coronary arteries.

Adult↗
PubMed1997

Detection of high-grade restenosis after PTCA using contrast-enhanced electron beam CT.

BACKGROUND: Contrast-enhanced electron beam computed tomography (EBCT) has been shown to permit noninvasive visualization of the coronary arteries. We determined the value of EBCT to noninvasively detect high-grade restenosis after percutaneous transluminal coronary angioplasty (PTCA). METHODS AND RESULTS: Fifty patients (37 to 68 years of age), were investigated by EBCT at a mean interval of 9 months after PTCA of coronary artery stenoses. Forty axial cross-sections of the heart (3-mm slice thickness, 1-mm overlap) were acquired triggered to the ECG after intravenous injection of contrast agent. Three-dimensional reconstructions of the coronary arteries were rendered with a lower threshold of 80 HU to selectively visualize the contrast-enhanced vessel lumen. EBCT results were compared with conventional quantitative coronary angiography (QCA) performed within 1 week. In 6 patients, the PTCA segment could not be evaluated because of impaired image quality. Sixteen of the remaining 44 patients had high-grade restenoses in QCA (>70% diameter reduction), which was correctly detected by EBCT in 15 cases (94% sensitivity). There were 5 false-positive EBCT results of high-grade restenosis (82% specificity). CONCLUSIONS: EBCT with intravenous injection of contrast agent permits the noninvasive diagnosis of restenosis after PTCA, with high sensitivity and sufficient specificity.

Adult↗
PubMed1997

Usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings > or = 50% in diameter in native coronary arteries and in aortocoronary bypass conduits.

Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with navigator echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (> or = 50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.

Adult↗
PubMed1997

Noninvasive, three-dimensional visualization of coronary artery bypass grafts by electron beam tomography.

Electron beam tomography (EBT, ultrafast computed tomography [CT], cine CT) combines unique temporal and high spatial resolution and is especially well suited for cardiac imaging. We established and evaluated a protocol for the noninvasive visualization and assessment of aortocoronary artery bypass grafts. Twenty-five patients with 56 bypass grafts were studied by EBT. Forty contiguous cross-sectional images were acquired triggered to the electrocardiogram during breathhold and intravenous injection of contrast agent. Three-dimensional reconstructions of the heart and bypass grafts were performed and compared with selective angiography of the bypass grafts. In 1 patient with 2 bypass grafts, a technically inadequate EBT examination was obtained. In the remaining patients (54 grafts), all 13 bypass occlusions were diagnosed with a sensitivity and specificity of 100%. Evaluation for hemodynamically relevant stenosis was possible in 84% of cases (36 of 43 patent grafts) and yielded a sensitivity of 100% (5 of 5 high-grade stenoses correctly detected) and specificity of 97% (1 false-positive diagnosis of high-grade graft stenosis). The main reasons for impaired ability to evaluate the scans were breathing artifacts and misplacement of the imaging volume, causing parts of the bypass grafts to be cut off. EBT permits noninvasive determination of bypass graft occlusion and relevant stenosis with high accuracy.

Coronary Artery Bypass↗
PubMed1997

[Non-invasive coronary diagnosis with EBT (electron beam tomography). Population screening for coronary heart disease--reliability imaging of coronary stenoses].

Electron beam tomography (EBT) is currently the fastest high resolution imaging procedure available. A modern non-invasive method, it provides an accurate spatial representation of the heart including the coronary arteries. Enabling the quantitative detection of microcalcifications in the coronary arteries--a reliable parameter of early-stage CAD-EBT now makes it possible to screen large population strata. In addition, the direct, non-invasive representation of coronary arteries and coronary arterial stenoses has now become possible. Although at present, EBT will probably not completely replace invasive coronary angiography, in specific areas such as evaluating the long-term results of coronary angioplasty (PTCA) or coronary bypass, the method could make invasive diagnostic procedures superfluous.

Adult↗
PubMed1997

[Teleteaching with CONRAD. From collected cases to interactive learning system].

Radiological teaching files on the Internet suffer from certain restrictions such as limited user interactivity. The Internet teaching project CONRAD (computer online network for radiological didactics) circumvents these restrictions by using a new database structure that also reflects the development of a diagnosis over time. The cases are presented in the internet with different HTML-based teaching programs. To support interactivity, CONRAD offers the building of online learning groups over the internet.

Computer Communication Networks↗
PubMed1997

[Noninvasive coronary angiography with electron beam tomography: methods and clinical evaluation in post-PTCA follow-up].

Electron beam tomography (EBT) is a computed tomography technique with unique spatial and temporal resolution. The aim of the study was to establish and evaluate a protocol for the non-invasive visualization and detection of stenoses of the coronary arteries. Following phantom studies, 103 patients were investigated. Among these, 25 patients after coronary angioplasty (PTCA) were included in a prospective, blinded comparison to coronary angiography. After injection of contrast agent in a peripheral vein, 40 axial cross sections of the heart were acquired, triggered to the ECG (slice thickness 3 mm, 1 mm overlap, pixel size 0.29 x 0.29 mm). Three-dimensional reconstructions of the heart and coronary arteries were performed in the form of "shaded surface display," the results were compared to coronary angiography. In the reconstructions, the proximal and mid section of the LAD was visualized in 94% and 85%, image quality was reduced for the right coronary artery (89%/64%) and left circumflex (74%/54%), mainly due to movement artifacts. EBT displayed a sensitivity of 100% (9/9) for the detection of occlusions and high-grade restenoses in patients after PTCA, due to one false-positive result, specificity was 92% (12/13). Three PTCA patients could not be evaluated due to respiration artifacts. Contrast-enhanced electron beam tomography (EBT) permits the visualization of coronary arteries and the detection of stenoses and occlusions with high sensitivity and specificity.

Adult↗
PubMed1997

Effects of magnetic resonance imaging on cardiac pacemakers and electrodes.

In phantom studies we investigated the effects of magnetic resonance imaging (MRI) on pacemakers and electrodes. Twenty-five electrodes were exposed to MRI in a 1.5T scanner with continuous registration of the temperature at the electrode tip. Eleven pacemakers (five single chamber and six dual chamber) were exposed to MRI. Pacemaker output was monitored to detect malfunction in VOO/DOO and VVI/DDD modes. A temperature increase at the electrode tip of up to 63.1 degrees C was observed during 90 seconds of scanning. In seven electrodes the temperature increase exceeded 15 degrees C. Although no pacemaker malfunctions were observed in asynchronous pacing mode (VOO/DOO), inhibition and rapid pacing were observed during spin-echo imaging if the pacemakers were set to VVI or DDD mode. Pacemaker function was not impaired during scanning with gradient-echo sequences. Next to pacemaker dysfunction, electrode heating has to be considered a possible adverse effect when exposing patients with pacemakers to MRI.

Animals↗
PubMed1997

Visualization of the coronary arteries in three-dimensional reconstructions using respiratory gated magnetic resonance imaging.

OBJECTIVE: To assess the applicability of respiratory-gated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries. METHODS: Twenty subjects (three healthy volunteers and 17 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-triggered gradient-echo sequences to acquire a volume data set consisting of 24-48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.17 mm in-plane resolution). Navigator-echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions. RESULTS: In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 17 cases, the left circumflex artery (LCXA) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 17 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 +/- 7 mm for the LMA, 65 +/- 13 mm for the LADA, 45 +/- 16 mm for the LCXA, and 37 +/- 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast:noise ratio, motion artifacts, and incomplete coverage by the imaging volume. CONCLUSIONS: Navigator-echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.

Case-Control Studies↗
PubMed1996

Evaluation of the non-invasive localization accuracy of cardiac arrhythmias attainable by multichannel magnetocardiography (MCG).

The accuracy of multichannel magnetocardiography (MCG) for the non-invasive localization of cardiac arrhythmias was investigated. A non-magnetic catheter was used in phantom studies and for cardiac pacing of 6 patients. In a clinical setting, 32 patients with WPW-syndrome, 37 patients with premature ventricular complexes and 12 patients with ventricular tachycardia were studied and the MCG results compared to reference methods, including invasive electrophysiological mapping. Phantom and pacing studies demonstrated the spatial localization accuracy to be better than 15 mm for a dipole-to-dewar distance below 15 cm. In all patients with structural cardiac disease, the ectopic focus was localized at the margin of the damaged area, serving as a proof of MCG localization. Invasive mapping confirmed the MCG result whenever performed (42 patients). In 11 patients (9 WPW, 2 VT) the MCG localization result was verified by successful HF catheter ablation as a gold standard. MCG permits the non-invasive localization of cardiac arrhythmias with high spatial accuracy. MCG guided HF catheter ablation constitutes a new concept of non-invasive localization and minimally invasive causal therapy.

Cardiac Pacing, Artificial↗
PubMed1996

Coronary angiography by electron beam tomography.

Electron Beam Tomography (EBT), a non-invasive imaging method with very high spatial and temporal resolution, is well suited for cardiac imaging. We established a protocol for the visualization of the coronary arteries by EBT and have so far evaluated the method in 88 patients. EBT imaging was performed using an Evolution scanner with a matrix of 512 x 512, a field of view of 15 cm and a slice thickness of 3 mm. After venous injection of contrast agent, 40 axial cross-sections of the heart were obtained triggered to the ECG at 80% of the R-R interval in inspiratory breathhold. With a lower threshold of 80 HU, 3D reconstructions of the heart and coronary arteries were rendered using shaded-surface display and maximum-intensity projection techniques. In all patients, the coronary arteries and, if present, aorto-coronary bypass grafts, were evaluated as to their visibility and presence or absence of haemodynamically relevant stenoses. All results were compared to the X-ray angiograms obtained by selective catheterization in a blinded manner. In 90% of cases, image quality was sufficient for evaluation. In 10% of the investigations, the EBT images could not be evaluated, mainly due to respiration artifacts. While the left anterior descending coronary artery was represented in very good image quality, the right coronary artery and left circumflex coronary artery showed decreased image quality due to motion artifacts and close correlation to venous structures such as the coronary sinus and atrial appendages. In a subgroup of 30 patients in which EBT results were compared to quantitative coronary angiography, the correlation of the vessel diameter in EBT and quantitative angiography was 0.82. Twelve out of 14 high-grade stenoses and 5/5 occlusions of the left anterior descending coronary artery as well as 3/4 highgrade stenoses and 1/2 occlusions of the right coronary artery and 2/4 high-grade stenoses of the left circumflex coronary artery were correctly identified. Nine patients were reinvestigated by EBT after successful angioplasty of high-grade coronary artery stenoses. The increase in vessel diameter could be documented in all cases. Twelve patients had a total of 28 aorto-coronary bypass grafts. Except for one mammarian artery graft which could not be evaluated due to small vessel lumen and clip artifacts, graft patency (21 cases) or occlusion (6 cases) was correctly diagnosed by EBT. EBT is a non-invasive method which permits the visualization of the coronary arteries. Stenoses of coronary artery bypass grafts and of the left anterior descending coronary artery can be reliably diagnosed, while reduced image quality, mainly due to faster vessel motion, impairs the results obtained for the right and left circumflex coronary artery.

Adult↗
PubMed1996

[Post-traumatic aneurysma spurium of the right atrium].

In a 61 year old male with heart failure and pulmonary congestion the x-ray shows a right paracardial tumor. The patient suffered from a blunt chest trauma 6 years ago. Since that accident he complains about exercise related dyspnea and cardiac arrhythmia with atrial fibrillation. On echocardiography we found a echolucent cystic tumor with a solid center structure surrounded by a thin membrane. Doppler echocardiography revealed a heart cycle dependent flow at its margin. During dextrocardiography rapid opacification only of the peripheral structures of the tumor could be observed. These findings are consistent with a traumatic rupture of the right atrium, and the diagnosis of a posttraumatic aneurysma spurium of the right atrium was established. Surgery confirmed this diagnosis and the aneurysm was extirpated.

Aneurysm, False↗