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R Brennecke

Publications and source records attributed to R Brennecke.

At least 37 records · Page 2Linked to original sources
PubMed1997

[Effect of qualitative stenosis characteristics on the quality of measurements of various QCA systems].

Reproducibility and accuracy of in vitro measurements are very high using recently developed QCA systems. We analyzed the impact of lesion characteristics ad the image quality on the quality of measurements under clinical conditions. For the study we selected 57 coronary artery lesions which had a clinically relevant distribution for stenosis severity, lesion characteristics, and image quality. Every effort was made to eliminate procedural sources of error. Three investigators measured each lesion five times with each of three QCA systems (AWOS, Cardio and CMS). Only the measurements of the minimal stenosis diameter were analyzed. The precision of all the measurements was high with the AWOS (0.04 mm), the Cardio (0.05 mm), and the CMS systems (0.06 mm). Variability of measurements increased for the following criteria: Ambrose-III morphology (CMS 0.082 mm), surface irregularities (Cardio 0.069 mm, CMS 0.073 mm), TIMI I (Cardio 0.084 mm, CMS 0.0121 mm), and moderate image quality (CMS 0.07 mm). There were no differences in the precision of the measurements in the other groups of lesion characteristics. There were no relevant differences in any of the measurements between the systems (AWOS-Cardio -0.07 mm, AWOS-CMS-0.11 mm, Cardio-CMS-0.04 mm). Smaller diameters were measured with the AWOS system than with the CMS and the Cardio systems when the lesion was calcified (AWOS-Cardio-0.109 mm, AWOS-CMS-0.161 mm). This was only a trend, however, and did not reach statistical significance, which was also true for the other differences found between the systems according to various lesion characteristics. In summary, we found that the measurement quality of the QCA systems used in this study is not altered by the underlying lesion characteristics or the image quality.

Coronary Angiography↗
PubMed1997

Angiocardiographic digital still images compressed via irreversible methods: concepts and experiments.

We defined, implemented and tested two new methods for irreversible compression of angiocardiographic still images: brightness error limitation (BEL) and pseudo-gradient adaptive brightness and contrast error limitation (PABCEL). The scan path used to compress the digital images is based on the Peano-Hilbert plane-filling curve. The compression methods limit, for each pixel, the brightness errors introduced when approximating the original image (i.e. the difference between the values of corresponding pixels as grey levels). Additional limitations are imposed to the contrast error observed when considering along the scan path consecutive pixels of both the original and the reconstructed image. After previous testing on angiocardiographic images selected as clinically significant from 35 mm films, we enlarged our experiment to a set of 38 coronary angiograms digitally acquired. BEL and PABCEL methods were experimented according to several values of the implied thresholds. Up to a compression ratio of 9:1 for the BEL method and 10:1 for the PABCEL method, no deterioration of the reconstructed images were detected by human observers. After a visual evaluation, we performed a quantitative evaluation. The visualization of pseudo-colour difference images showed the capability of BEL and PABCEL for preserving the most significant clinical details of the original images. For comparison, we applied the JPEG (joint photographic experts group) image-compression standard to the same set of images. In this case, pseudo-colour difference images showed a homogeneous distribution of errors on the image surface. Quantitative compression results obtained by testing the different methods are comparable, but, unlike JPEG, BEL and PABCEL methods allow the user to keep under his direct control the maximum error allowed at each single pixel of the original image. These different behaviors are confirmed by the values obtained for the considered numerical quality quantifiers.

Algorithms↗
PubMed1997

Comparison of QCA systems.

AIMS: Excellent agreement between different 'second generation' systems for quantitative coronary arteriography (QCA) has been found in in vitro measurements. To verify the quality and stability of QCA when used in clinical practice, three QCA systems (AWOS, Cardio, and CMS) were used in a representative set of coronary artery lesions. METHODS AND RESULTS: This set consisted of angiographic stenosis images of 57 patients which varied in stenosis severity and morphology. The process of image acquisition, calibration, and measurement was strictly standardized to eliminate procedural sources of error. Three observers performed QCA five times in each lesion with each QCA system. Interobserver variability was low (Dnorm 0.01-0.05 mm, Dmin 0.01-0.02 mm, %stenosis 0.3-0.7%). Values of system precision were excellent (Dnorm 0.11-0.13 mm, Dmin 0.04-0.06 mm, %stenosis 2.1-2.6%). Comparison of measurements between three QCA systems revealed good agreement (range of mean differences for Dnorm 0.03-0.12 mm, Dmin 0.04-0.11 mm, and %stenosis 0.5-3.6%) and high correlation (corr 0.902-0.977). There was a tendency to measure smaller values for Dmin and consequently to identify more severe stenoses with the AWOS system than with the Cardio and CMS systems. All QCA results were compared to measurements done with the Brown Dodge method to reveal failure of the QCA measurements. These results showed excellent agreement without any systematic deviation (mean differences for Dnorm 0.01-0.08 mm, Dmin 0.02-0.06 mm, and %stenosis 1.3-1.8%). None of the differences were statistically significant. CONCLUSION: We therefore conclude that using the defined version of the AWOS, Cardio, and CMS systems, there is no difference in precision or accuracy when used for QCA of coronary artery lesions.

Algorithms↗
PubMed1996

Comparison of myocardial perfusion reserve before and after coronary balloon predilatation and after stent implantation in patients with postangioplasty restenosis.

BACKGROUND: Stents provide a scaffold for coronary arteries after angioplasty and inhibit elastic recoil. METHODS AND RESULTS: In 25 patients with postangioplasty restenosis of the left anterior descending artery, ECG-gated digital subtraction coronary angiograms were recorded at baseline and during hyperemia (12 mg papaverine IC) before and after balloon predilatation (PTCA), after implantation of a Palmaz-Schatz stent, and after 6 months. Densitometric evaluation revealed different time and density parameters to calculate two definitions of myocardial perfusion reserve (MPR1 and MPR2) and maximum flow ratio (MaxFR). Poststenotic MPR1 increased from 1.57 +/- 0.14 to 2.59 +/- 0.86 after PTCA and to 3.10 +/- 0.41 after stenting, with 2.90 +/- 0.65 at follow-up (ANOVA, P < .05), while reference MPR1 remained unchanged at 3.10 +/- 0.40. Poststenotic MPR2 increased from 1.36 +/- 0.28 to 2.50 +/- 1.20 and to 3.40 +/- 0.58, respectively, with 3.20 +/- 0.92 at follow-up (ANOVA, P < .05), while reference MPR2 remained unchanged at 3.40 +/- 0.60. MaxFR was 2.13 +/- 0.53 after PTCA, elasticity 2.83 +/- 0.35 after stenting, and 2.73 +/- 0.58 at follow-up (ANOVA, P < .05). A good correlation was found between minimal stenotic luminal diameter and MPR1 or MPR2 (r = .87 and r = .94) and between luminal gain and MaxFR (r = .75). A negative correlation was measured between recoil and MPR1, MPR2, and MaxFR (r = -.80, r = -.86, and r = -.83). At follow-up, a steeper correlation was found between MPR and minimal stenosis diameter (MPR1: slope, 0.52 versus 0.91; MPR2: slope, 1.48 versus 1.95) and between MaxFR and net lumen gain (slope, 0.78 versus 1.27). CONCLUSIONS: Coronary stent implantation in patients with postangioplasty restenosis normalized poststenotic myocardial perfusion immediately as a result of a larger postprocedural lumen and a more pronounced inhibition of elastic recoil. After 6 months this benefit was sustained despite progressive lumen loss.

Absorptiometry, Photon↗
PubMed1996

[Long term course over 10 years after balloon dilatation in stable and unstable angina pectoris].

OBJECTIVE: To assess the cardiac status of patients ten years after percutaneous transluminal coronary artery angioplasty (PTCA). PATIENTS AND METHODS: Data of 534 patients (436 men, 98 women; mean age 53.2 +/- 8 years) in whom a PTCA had been performed between 1983 and 1986 were analysed, based on a questionnaire answered 121 +/- 11 months after the initial procedure. At the time of PTCA 184 patients (35%) had unstable angina, 350 (65%) stable angina. RESULTS: 116 patients (63%) with unstable angina and 164 (47%) with stable angina had at least one cardiac event after the initial PTCA (repeat PTCA, bypass operation, myocardial infarction, death). None of these events occurred in 68 patients (37%) with unstable or in 186 (53%) with stable angina (P < 0.001). After 10 years 196 of the 302 surviving patients with stable angina (65%) and 104 of the 153 surviving patients with unstable angina (68%) were symptom-free. CONCLUSIONS: Ten-year follow-up after PTCA has shown that cardiac events are significantly more frequent in patients who had had unstable angina than in those with stable angina. This difference already develops in the first year post-PTCA, with no increase later. Symptoms are lastingly improved after 10 years in both groups of patients.

Angina Pectoris↗
PubMed1996

Importance of calibration for diameter and area determination by intravascular ultrasound.

BACKGROUND: Intravascular ultrasound (IVUS) permits quantitative assessment of the lumen diameter and area of coronary arteries. The experimental study was performed to evaluate the accuracy of diameter and area measurements. METHODS AND RESULTS: Lumen quantitation (lumen diameter D and cross-sectional area A) in lucite tubes (lumen diameter 2.5 to 5.7 mm, Plexiglas) was performed using a mechanical IVUS system (HP console, 3.5 F catheter, Boston Scientific, 30 MHz). The influence of fluid type (blood, water and saline solution), fluid temperature (20 degrees C/37 degrees C), catheter to catheter variation, gain setting and ultrasound frequency (12, 20 and 30 MHz) was determined. In blood at 20 degrees C there was a constant deviation of the measured diameter from the true luminal diameter of -0.29 +/- -0.04 mm (p < 0.06). In water and saline solution at 20 degrees C the mean deviation from true diameter was -0.21 +/- -0.06 mm (p < 0.06). At 37 degrees C, the deviation in blood was greater than at 20 degrees (-0.34 +/- -0.02 mm) which is > 10% in a 3 mm tube (p < 0.06). Three of the ten catheters tested in water at 20 degrees C underestimated true diameter by more than -0.3 mm. The deviation from true diameter (5 mm tube) with varying gain settings was -0.14 mm to -0.23 mm compared to -0.19 mm at standard settings (p > 0.288). At 12 MHz diameter measured was over-estimated. The error in absolute area estimation increased with increasing diameter tested in blood at 37 degrees C (-1.21 to -2.72 mm2), whereas the relative error ([Measured Area-True Area]/True Area x 100 [%]) was more striking at smaller diameters (up to -25% in the 2.5 mm tube). CONCLUSION: Luminal diameters and areas are underestimated by this particular IVUS system. When IVUS imaging and measurements are made during coronary interventions this error should be taken into account with regard to appropriate sizing of the device and the assessment of the postprocedure result. Because systematic errors might also occur in other IVUS system (not tested in this study), it is advisable to ensure that each system is validated prior to clinical use, especially when exact measurements are required.

Calibration↗
PubMed1996

Intravascular ultrasound detected classification of coronary lesions as a predictor of dissections after balloon angioplasty.

Dissection after balloon angioplasty of coronary arteries may give rise to an unfavourable early outcome. Compared with coronary angiography, intravascular ultrasound (IVUS) allows more detailed characterisation of dissections. We investigated the incidence and type of dissections after balloon angioplasty in calcified coronary lesions. IVUS was performed in 43 patients with 48 lesions before and after percutaneous balloon angioplasty. Significant calcification was defined as an arc of more than 90 degrees with typical acoustic shadowing. Dissections were classified as type A when the media was not involved by the dissection and as type B when media involvement had occurred. In the group with significant calcification dissection was observed in 79% of the cases vs 38% in the control group (p < 0.03). Type B dissection was present in 71% of the dissections in the calcified lesions vs. 15% in the control group (p < 0.02). The balloon diameter and the ratio of balloon area to vessel area was not different in both groups but the required pressure for the first complete balloon inflation was significantly greater in the group with calcified lesions (9.46 +/- 3.6 atm vs. 6.65 +/- 2.6 atm; p < 0.001). Thus balloon angioplasty in calcified coronary lesions is more likely to lead to dissection with frequency involve the media.

Adult↗
PubMed1996

[Normalization of myocardial perfusion reserve after coronary stent implantation in comparison with balloon angioplasty alone].

Stents scaffold coronary arteries after angioplastic treatment and inhibit elastic recoil resulting in a larger and more circular focal lumen. In 25 patients with significant stenoses of the left anterior descending coronary artery, presenting no collaterals or myocardial infarction, EKG-gated digital subtraction angiograms were recorded at baseline and during hyperemia induced by intracoronary injection of 12 mg papaverine before and after balloon angioplasty, and after adjunct implantation of a single Palmaz-Schatz stent. Densitometric evaluation revealed the time parameters contrast medium appearance time (MCAT) rise time (RT) and mean transit time (MTT) and maximum intensity (Imax). Myocardial perfusion reserve (MPR1) was calculated as the ratio of baseline MCAT and hyperemic MCAT multiplied by the ratio of hyperemic Imax and baseline Imax while MPR2 was calculated as the ratio of baseline RT and hyperemic RT. Maximum flow ratio (MaxFR) was calculated as the ratio of preprocedural hyperemic MTT and postprocedural hyperemic MTT. Post-stenotic MPR1 increased from 1.36 +/- 0.28 to 2.50 +/- 1.20 and to 3.40 +/- 0.58 (ANOVA p < 0.05), while reference MPR1 remained unchanged with 3.40 +/- 0.60. Post-stenotic MPR2 increased from 1.57 +/- 0.14 to 2.59 +/- 0.86 after balloon angioplasty and to 3.10 +/- 0.41 after stenting (ANOVA p < 0.05), while reference MPR2 remained unchanged with 3.10 +/- 0.40. MaxFR was 2.13 +/- 0.53 after balloon angioplasty and 2.83 +/- 0.35 after stenting (p < 0.05). A good correlation was found between minimal stenosis diameter and MPR1 or MPR2 (MPR1: r = 0.94; MPR2: r = 0.87) and between luminal gain and MaxFR (r = 0.75). A negative correlation was measured between recoil, defined as the difference between inflated balloon diameter and resulting minimal stenosis diameter, and MPR1 and MPR2 and MaxFR (MPR1: r = -0.86; MPR2 r = -0.80; MaxFR r = -0.83). In conclusion, adjunct coronary stent implantation normalized post-stenotic myocardial perfusion immediately in contrast to balloon angioplasty alone resulting from a larger postprocedural lumen and a more pronounced inhibition of elastic recoil.

Adult↗
PubMed1996

[Development of standards for quality management in interventional cardiology].

Standardization is one of the fundamental methods for quality management. Standards describe first requirements for adequate delivery of diagnostic and therapeutic services (e.g. in the format of guidelines and protocols), second they define core data sets for documentation of real clinical outcome and of process and structure quality or third they define normal values (standards in the strict sense) or thresholds for critical parameters. This standardization is increasingly performed by the professional societies in international collaboration. We report on the parallel development of methodology. Presently standards for documentation and guidelines are being developed for the areas of cardiac interventional and surgical therapy. Three main methods are described. First, the common approach to guideline definition becomes more formalized as exemplified by the consensus approaches of the RAND group and of physicians in The Netherlands. Second, the definition of core data sets for quality assurance is increasingly based on the statistical evaluation of large interventional databases with the goal of developing predictive models of outcome. Since some of these methods are not yet fully reliable, it is still necessary to combine the results of predictive modelling with consensus on clinical practice. Figure 1 describes one of these approaches to data standards definition. These methods are currently developed within the new Cardiovascular Data Standards Initiative of the American College of Cardiology (ACC) that is open for international collaboration. Figure 2 describes a parallel approach for standardization of digital image communication in angiocardiography. As shown in Figure 3, these data set standards and imaging standards will be applied not only in quality assurance, but also in shared care. Third, the PRESTIGE project of the European Commission is developing computerized tools that support terminology support, guideline authoring, guideline dissemination and protocol-directed care. We show that the elements described can be put to use within the unifying framework depicted in Figure 4. This guideline approach that is fully integrated into daily care delivery provides the physician with instant feedback from the guideline and, in addition, with periodic quality reports based on a comparison of the local clinical reality with the recommendations from the guideline. In our extended concept, these deviations are in addition symmetrically used to trigger, where necessary, the process of evaluation of the guideline. The often poor acceptance of guidelines should be improved both by integrating them into daily practice and by providing a feedback to the guideline authoring committee. We conclude that standardization activities are now entering into a new era due to increased involvement of physicians, international collaboration, integrated approaches to quality management, and improved computerized tools.

Angioplasty, Balloon, Coronary↗
PubMed1995

Improving the applicability of myocardial densitometry and parametric imaging by extended automated densogram analysis.

In clinical applications the analysis of X-ray contrast densograms acquired in regions of interest (ROI's) over the myocardium is disturbed by many complex factors. For this reason we acquire redundant densogram information for quality control before extracting densitometric parameters. In our approach, initially some stable measures of quality for densograms are used to lower the influence of poor quality densograms by a quality weighted averaging. For example a shape quality measure, Q1, is calculated using regions of optimal and minimal acceptable quality defined with respect to a prototype densogram. Not a few myocardial ROI's yield densograms that differ from single-source densograms (SSD's) due to e.g. superposition of different perfusion beds or the position of the ROI relative to the coronary sinus or stenoses. This might result in a densogram shape with oscillating or plateau behavior. For densograms of a such general shape many parameters defined in the usual way do not depend smoothly on the densogram values. The conventional definitions of some parameters (appearance time, rise time) are therefore extended for application to multi-maxima densograms as well as to SSD's. These new methods are evaluated using digitized clinical angiocardiograms and are applied to parametric imaging (pixeldensograms) in a slightly modified way. Taking into account the densogram quality, its shape and its origin results in a considerable improvement both for densitometry and parametric imaging of myocardial perfusion.

Absorptiometry, Photon↗
PubMed1995

Requirements for quality assessment in coronary angiograph and angioplasty.

The application of formal methods of quality assessment in medicine is a relatively new activity. Interventional cardiology is expected to be one of the fields of clinical medicine adopting formal schemes of quality assessment at a relatively early phase because of its invasive nature, the associated risks, the rapid growth of this treatment and the correspondingly increasing total cost. We therefore aim to compile the requirements for the development of quality assessment schemes in angioplasty and coronary angiography. The rather disparate nature of methodologies applied in previous and present quality initiatives is reviewed, grouping the numerous methods of organizing quality initiatives found in the literature into a few generic schemes. This new classification of methods is provided as a prerequisite for the discussion of general problems inherent in current quality initiatives in the medical field and for the selection of approaches to quality development best suited for the environment of the catheterization laboratory. Here we identify the concrete steps of goal definition, quality indicator selection, definition of standards and thresholds for these indicators and the selection of a quality management scheme for monitoring the aspects of quality previously defined. Because of the limitations of each of the original methodologies of quality assessment, we propose a synthesis of the most important approaches as the basis for new quality initiatives in interventional cardiology.

Angioplasty, Balloon, Coronary↗
PubMed1995

[Teaching/learning model for the social medicine course in human medicine at the Berlin Free University].

Considering the discussions on the reform in medical education and the Free University of Berlin's plans for a reformed curriculum for medical studies, a new model in teaching and learning for the course "social medicine" was developed and tested. The model deals with students' interests in topics of social medicine and allows inductive access to matters of social medicine by means of exemplary learning. Teacher's task is to be moderator and organizer of learning processes. Experiences show that this procedure leads to improved interest in and more engagement towards the subject "social medicine" within the reach of the course.

Berlin↗