Sources of error in quantitative coronary angiography

Many studies have reported the accuracy of quantitative coronary angiography (QCA) based on experiments using moderated-size phantoms imaged under unrealistic radiographic conditions. However, these observations may not be generalizable to the setting of clinical angiography. To determine QCA accuracy in a realistic radiographic setting and evaluate the impact of the x-ray system line spread function, plexiglass phantoms were imaged inside and out of a human thorax. A realistic radiographic background was associated with a 38% increase in variability of results (p < 0.05). Low concentrations of contrast and large image intensifier input screens were associated with significantly larger errors and variability in results (p < 0.05). There was a systematic overestimation of diameter in the smallest phantom. A mathematical model of the x-ray line spread function was developed that explains the observed overestimation of the smallest phantom and provide a rational approach for correction of the line spread function for QCA. Many factors encountered in clinical coronary angiography such as nonuniform radiographic background, low concentrations of contrast, and small vessel diameters have a significant adverse impact on the accuracy and/or variability of gradient-based edge detection QCA systems. © 1993 Wiley-Liss, Inc.     

Radiological quality of coronary guiding catheters: A quantitative analysis

Quantitative coronary angiography (QCA) is a validated and widely accepted method to investigate changes in arterial dimension over time. Calibration of measurements is enabled by the use of the coronary catheter as a scaling device. The dimensions and laminar composition of coronary catheters, however, have changed significantly over recent years and the suitability of the current generation of coronary catheters for calibration purposes has not been validated. We therefore recorded 57 coronary guiding catheters on cinefilm, and compared their automated quantitative measurements (Cardiovascular Angiography Analysis System, CAAS) with their true values (precision micrometer). We found an overall underestimation of quantitatively derived dimensions, ranging from ?8.9 to +4% for water-filled catheters and from ?15.5 to ?3.9% for contrast-filled catheters. In conclusion, while the current generation of coronary guiding catheters shows a wide variety in radiological quality, it can be clearly detected by the CAAS system, and is suitable for calibration of QCA measurements (with the exception of the DVI atherectomy catheter), provided that calibration is done on contrast-empty catheters. © Wiley-Liss, Inc.     

Accuracy and precision of quantitative digital coronary arteriography: Observer-, short-, and medium-term variabilities

Coronary arteriograms are increasingly acquired and stored in digital format, which allows instantaneous review of the pictorial data during the cardiac catheterization procedure. To support the angiographer in choosing the optimal sizes of the recanalization devices and studying the efficacy of the recanalization procedures, we have developed a new analytical software package (Automated Coronary Analysis = ACA) on the Philips DCI (-SX) digital cardiac imaging system. The ACA-package allows the objective and reproducible assessment of the morphologic and functional severity of coronary obstructions. Required user interaction is limited to the definition of the start and end points of the coronary segment to be analyzed. Automated contour detection is based on the use of first and second derivative functions along scanlines perpendicular to the automatically computed vessel pathline in the first iteration and perpendicular to the initial contours in the second iteration. These derivative functions have been modified based on the line spread function of the X-ray imaging chain, which is of particular importance for the accurate measurement of small vessel sizes. Phantom studies have indeed demonstrated that vessel sizes down to 0·66 mm can be measured accurately and reproducibly. Inter- and intraobserver variability studies have demonstrated a variability in the obstruction diameter of 0·11 mm and 0·10 mm, respectively, and in the percent diameter stenosis of 5·64% and 3·18%, respectively. These variability studies have been extended to short-term studies with repeated acquisition in the same angiographic views after 5 min and to medium-term studies with repeated acquisition in the initial angiographic views at the end of the catheterization procedures. With these standardized repeated acquisition and analysis procedures, the variabilities in the obstruction diameters increased to 0·19 and 0·18 mm, respectively, and remained below 6% in the percent diameter stenosis (5·61 % and 5·28%, respectively). With an analysis time of ～15 sec on the DCI-SX, an efficient tool is now available in the catheterization laboratory for the objective and reproducible assessment of vessel dimensions and changes therein as a result of recanalization procedures.     

The influence of image enhancement and reconstruction on quantitative coronary arteriography

In the coming years, cinefilm will gradually be replaced by some digital medium for the archiving of angiographic images. However, not only the question which digital archiving medium will be used in the future is important, but also wich images are to be stored. Options are to either archive the raw, unprocessed images, or the enhanced images as they are displayed on the viewing monitor in the catheterization laboratory. In the first case, an off-line workstation will need additional hardware to display the images with the same image quality as they were acquired; in the second case, the question remains whether quantitative analysis programs still provide reliable results.Goal of this study was to investigate the possible effects of image enhancement and reconstruction on the results from quantitative coronary arteriographic (QCA) measurements with the Philips ACA-package (Automated Coronary Analysis). Image enhancement was achieved by an unsharp masking approach; the reconstruction of the original image from the enhanced image was attempted by an iterative deconvolution approach.The evaluation study consisted of two parts; a technical evaluation on eleven phantom tubes with known dimensions, and a clinical evaluation study on 48 coronary lesions. The results of the technical evaluation demonstrate that the measurement errors increase for the smaller vessel sizes (<1.2 mm) when QCA is applied to reconstructed images. The systematic difference on the smallest phantom tube (0.687 mm) on unprocessed images was limited to 0.050 mm, while it increased to 0.089 mm for the reconstructed images. Moreover, the random differences for the smaller vessel sizes increased for all processed images: for 0.159 mm for the unprocessed image to 0.189 mm for the enhanced and 0.204 mm for the reconstructed image (p<0.01). For the larger vessels, in general, no significant differences could be observed between the results of the unprocessed and processed images.The results of the clinical evaluation study demonstrate that especially the obstruction diameter is overestimated when QCA is applied to reconstructed images (0.113 mm). Although the measurements on the enhanced images did not show a significant overestimation of the obstruction diameter, the intra-observer random difference was much higher (0.199 mm for the enhanced images versus 0.140 mm for the unprocessed images, p<0.01). In more general terms, applying QCA on enhanced images increases the random difference values, while reconstructing the original image from the enhanced images increases the systematic errors in the measured diameters.This study has clearly demonstrated that especially the smaller diameter values (<1.2 mm) are influenced by image enhancement. Therefore, to obtain quantitative results with the desired small values for systematic and random differences, requires that the raw, unprocessed image data be archived.This work was supported in part by a grant from Philips Medical Systems, Best, The Netherlands     

Advantages and limitations of two software calipers in quantitative coronary arteriography

Summary Software calipers allowing the measurement of the distances between pairs of manually defined picture elements in digitized images may be useful tools for a rapid assessment of the morphology of coronary vessels, e.g. for choosing the appropriate balloon or stent sizes before or during cardiac intervention procedures. In this paper we have studied extensively the advantages and limitations of two manual software calipers — one developed for a PC-based cinefilm analysis workstation, the other for the Philips DCI system.Based on analyses of a perspex vessel phantom with 17 sectors of known size filled with different concentrations (50 and 100%) of the contrast agent and acquired at two kV-levels (68 and 92 kV), it was found that the cinefilm approach is characterized by a very small overall (averaged over te data from three observers) systematic overestimation of 0.03 mm, and the DCI system by a systematic underestimation of 0.07 mm; the worst case accuracy value for an individual observer on frames with 100% contrast dye concentration was 0.20 mm for cinefilm, and –0.34 mm for the DCI, respectively. The overall variabilities in the measurements (precision) were almost identical for the two approaches (overall 0.07 and 0.08 mm for the cinefilm and digital approaches, respectively, and worst case for individual observers on the 100% contrast frames, 0.16 and 0.13 mm, respectively. Inverting the images (bright or dark contrast containing structures) of the phantom at 100% contrast concentration and acquired at 62 kV had no significant effect on the results obtained with the cinefilm analysis system (overall accuracy –0.12 mm for both situations), whereas it had on the results from the DCI system (overall accuracies –0.29 (dark vessels on bright background) and –0.08 mm (bright vessels on dark background), respectively). Enhancing the digital images on the DCI with unsharp masking techniques did not significantly influence the measurement accuracy and precision. Finally, it was found that woven dacron, polyurethane and polyvinylchloride catheters filled with 100% contrast dye can be measured with an overall accuracy of better than 0.13 mm on the DCI system. On the PC-based system the woven dacron and polyvinylchloride catheters would result in an overall accuracy better than 0.17 mm, and the polyurethane catheter better than 0.30 mm. The evaluation study has made clear that the nylon catheter should not be applied in QCA-studies. Thus based on the data presented and extrapolating these to the routine clinical situations, it can be concluded that the software caliper technique may be a useful tool for the rapid measurement of the size of a contrast filled structure in coronary angiograms, either from digitized cinefilm or from the digital images acquired with the Philips DCI system. However, it is to be expected that the measurements will be less accurate and precise when applied to coronary arteriograms due to additional variabilities caused by the non-uniform and rough size of coronary arterial segments. The accuracy and precision of the measurements can be improved significantly by using more sophisticated techniques with automated edge detection.     

In vivo validation of an experimental adaptive quantitative coronary angiography algorithm to circumvent overestimation of small luminal diameters

The reliability of quantitative coronary angiography (QCA) measurements is of fundamental importance for the study and practice of interventional cardiology. In vivo validation results have consistently reported a tendency for QCA systems to overestimate small luminal diameters. Such a systematic error may result in the underestimation of luminal gain during intracoronary procedures and in the underestimation of progression of coronary artery disease during longitudinal studies. We report the in vivo validation results of an experimental adaptive edge-detection algorithm that was developed to reduce overestimation of small luminal diameters by incorporating a dynamic function of variable kernel size of the derivative operator and variable weighting of the first and second derivatives of the brightness profile. The results of the experimental algorithm were compared to those of the conventional parent edge detection algorithm with fixed parameters. Dynamic adjustment of the edge-detection algorithm parameters was found to improve measurements of small (lt;0.8-mm) luminal diameters as evidenced by an intercept of +.07 mm for the algorithm with variable weighting compared to +0.21 mm for the parent algorithm with fixed weighting. A slope of <1 was found for both the parent and experimental algorithms with subsequent underestimation of large luminal diameters. Systematic errors in a QCA system can be identified and corrected by the execution of objective in vivo validation studies and the consequent refinement of edge-detection algorithms. The overestimation of small luminal diameters may be overcome by the incorporation of a dynamic edge-detection algorithm. Further refinements in edge-detection algorithms will be required to address the issue of underestimation of large luminal diameters before the absolute values derived from QCA measurements can be considered accurate over the full range of clinically encountered luminal diameters. © 1995 Wiley-Liss, Inc.     

Effect of data compression on quantitative coronary measurements

Digital coronary and left ventricular angiography demand high transfer rates and very large data storage if all the clinical data are to be archived. If appropriate compression schemes were available without compromising the quality and resolution of the image data, such demands could be lessened. In this study we compared the influence of different compression factors of the Adaptive Real Time Image Compression (ARTIC) scheme used on the Philips DCI-SX systems on coronary measurements assessed with the Automated Coronary Analysis (ACA) package. Loss-free acquired images of size 512² × 8 bits, which had been stored digitally on tape, were reloaded into the DCI with compression factors of 2, 3, and 4; only the factor 2 is loss free. To evaluate the effect of the different data compressions on the accuracy of the measurements, the diameters of a vessel phantom (tube sizes ranging from 0.687 to 5.062 mm) were determined. To evaluate the reproducibility of the results, the intraobserver variability was determined for the different compression factors from 40 coronary obstructions. The differences in the reference diameter measurements of the vessel phantom were -0.03 ± 0.06 mm, 0.01 ± 0.07 mm, and 0.04 ± 0.08 mm for the compression factors 2 (loss free), 3, and 4, respectively. The results were not statistically significantly different. The intraobserver variabilities in the obstruction diameter measurements of the coronary obstructions were -0.04 ± 0.13 mm, 0.00 ± 0.14 mm, and 0.02 ± 0.13 mm for the compression factors 2, 3 and 4, respectively. The intraobserver variabilities in the reference diameter measurements were -0.02 ± 0.12 mm, 0.01 ± 0.09 mm, and 0.03 ± 0.09 mm for the compression factors 2,3, and 4, respectively. The intraobserver variabilities of the percent diameter stenosis were 0.96 ± 4.19%, -0.01 ± 4.88%, and -0.04 ± 4.68% for the compression factors 2,3, and 4, respectively. None of these differences were statistically significant. Both from a qualitative and quantitative point of view, data compression factors 3 and 4 are acceptable in digital coronary arteriography.     

Effect of lossy data compression on quantitative coronary measurements

With the accepted use of (lossy) data compression at low compression factors (2, 3 and 4 on the Philips DCI), the question was posed whether higher lossy compression ratios can also be used without statistically affecting the results of quantitative coronary arteriography. In this study the influence of two data compression schemes (LOT and JPEG) at three different compression factors (5, 8 and 12) on coronary measurements was assessed with the Automated Coronary Analysis (ACA) package. A series of 30 original acquired digital images were compressed and decompressed at the different factors, and together with the original non-compressed images processed using the ACA package. In these images a total of 37 obstructed coronary segments were analyzed twice to assess the intra-observer variabilities in the obstruction and reference diameters and in the percent diameter stenosis. The results of the first and second measurements in each image were averaged, and from the differences in corresponding images with different compression ratios, the inter-compression variability was obtained. The results show that the intra-observer systematic errors in the absolute diameters are all small (< 0.07 mm), and statistically not significantly different. The intra-observer random errors for the compressed/decompressed series, however, were all larger (up to 0.21 mm) than for the original series(< 0.13 mm). Statistically significant differences in the intra-observer random errors were found for the JPEG compression scheme at a compression ratio of 5 and for the LOT scheme at a compression ratio of 12. The inter-compression systematic errors in the absolute diameter measurements were also small (< 0.07 mm) and not significant, while the random errors were found to be high in the range between 0.23 mm and 0.31 mm. Given the higher intra-observer variabilities for the compressed/decompressed image series as compared to original images, and the fact that all inter- compression variabilities were found to be so high, we must conclude that the higher compression ratios affect the results of QCA in a negative sense. In conclusion, the use of lossy data compression with JPEG or LOT compression schemes at ratios 5, 8 and 12 must be discouraged for QCA.     

Accuracy and precision of quantitative arteriography in the evaluation of coronary artery disease after coronary bypass surgery A validation study

Computer-assisted quantitative coronary arteriography (QCA) has gained widespread acceptance in assessing changes in coronary dimensions over time, but little is known about the utility of QCA in patients having undergone coronary bypass surgery. As a validation study, we analyzed the accuracy and precision of QCA in a subset of the baseline angiograms of a clinical trial in 395 post-bypass men with low HDL cholesterol concentrations who have been randomized to receive double-blind gemfibrozil or placebo for 2 1/2 years. Based on repeat measurements of the same cineframe, the average diameter of a segment (ADS) had a mean coefficient of variation (CV) of 3.1 %. The mean CVs of the minimum luminal diameter (MLD), percent diameter stenosis (PDS) and stenotic flow reserve of an obstruction were 8.6, 10.2 and 9.8%, respectively, but the area of the atherosclerotic plaque had an unacceptably high CV, 24.0%. When the measurements from two contrast injections into a native coronary artery during the same angiographic session were compared, precision (standard deviation of the differences) was 0.198 mm for ADS, 0.192 mm for MLD, and 7.37% for PDS. Variability was not substantially reduced when measurements from 3 or 5 consecutive cineframes were averaged. Comparable repeatability was found when venous bypass grafts were imaged twice, whether the grafts themselves or the grafted native vessels were analyzed. We conclude that QCA has an acceptable accuracy and precision in analyzing coronary dimensions in bypass-grafted patients. A change of 0.40 mm in ADS and MLD, and 20% in PDS represent true progression or regression of coronary atherosclerosis with more than 95% confidence.Abbreviations CAD coronary artery disease - CMS Cardiovascular Measurement System - MLD minimum luminal diameter (of an obstruction) - ADS average diameter of a segment - PDS percent diameter stenosis (of an obstruction) - QCA quantitative coronary arteriography - SFR stenotic flow reserve (of an obstruction)     

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 (D_norm 0.01–0.05 mm, D_min 0.01–0.02 mm, %stenosis 0.3–0.7%). Values of system precision were excellent (D_norm 0.11–0.13 mm, D_min 0.04–0.06 mm, %stenosis 2.1–2.6%). Comparison of measurements between the three QCA systems revealed good agreement (range of mean differences for D_norm 0.03–0.12 mm, D_min 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 D_min 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 systematic failure of the QCA measurements. These results showed excellent agreement without any systematic deviation (mean differences for D_norm 0.01–0.08 mm, D_min 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.     

Reproducibility of quantitative coronary analysis

Because of limited storage capacity for digital images, angiographic laboratories without cinefilm are dependent on locally performed quantitative coronary angiography (QCA) in clinical studies. In the present study the intra-and interobserver variability, as well as variability between different laboratories and variability due to frame selection was analyzed. A total of 20 coronary lesions were studied in two different digital laboratories 12±8 days apart. Images were analyzed on-line and after being transferred to a Cardiac Work Station (CWS). There was no significant difference between the measurement situations. For minimal luminal diameter (MLD) precision (SD of signed errors) ranged from 0.12 mm to 0.20 mm, for reference diameter (RD) from 0.15 mm to 0.28 mm, and for percent diameter stenosis (DS) from 4.2% to 5.8%. Overall relative precision was obtained by normalizing the QCA parameters, and was 11.9% for MLD, 7.0% for RD and 8.5% for DS (p<0.001, RD and DS compared to MLD). The overall variability in the interobserver and in the interlaboratory comparisons was 11.2% and 10.4%, respectively (n.s.) (n.s.). Thus the variability of QCA performed in cinefilmless, digital laboratories is small, and within a range making it an useful tool for clinical practice and group comparisons in clinical studies. However, the error range of QCA measurements must be taken into consideration when judging results from individual patients.     

On-site digital quantitative coronary angiography: comparison with visual readings in interventional procedures

In order to review the morphological criterion for an interventional procedure, diameter stenosis (%DS) of 226 coronary lesions in 200 patients undergoing elective coronary angiography with an option for prima vista angioplasty (pPTCA), was assessed on-site by both visual eye balling (EB) and independent digital quantitative coronary angiography (DQCA) by means of an angiographic workstation. Compared to DQCA, EB overestimated the %DS between 50 and 80% and accounted for the majority of discrepancies with overestimation up to 45%. Concordant estimates of %DS by both methods were observed in only 10 of the total of 226 stenotic segments; in 20 of 226 cases, EB underestimated %DS up to 20%. EB revealed a %DS 60% in 166 stenoses (73.4%), an estimate that led to subsequent pPTCA. However, only 119 (52.6%) of these lesions had a %DS 60% as assessed objectively by DQCA. With regard to the criterion for PTCA 47 of 166 performed pPTCA (28.3%) would not meet the indication criteria based on objective DQCA information. EB and DQCA (± 5%DS) had concordant results and criteria for pPTCA only in 103 of 166 coronary lesions (62.1%). These results lead to the conclusion that, on-site and on-line DQCA by an independent cardiologist eliminates both under- and overestimation of stenoses as seen with EB. DQCA supports immediate decision-making and appears necessary for reliable evaluation of coronary morphology in an interventional catheterization laboratory setting and may eventually ensure intraprocedural quality control.     

Inaccuracy of quantitative coronary arteriography when analyzed from S-VHS videotape

In the transition period between 35-mm cinefilm as the medium for coronary arteriographic data and digital media such as CD-R, S-VHS videotape has been used both as an exchange and store medium, and for quantitative coronary arteriographic (QCA) studies. To determine the extent to which S-VHS video tape affects QCA measurements, an X-ray phantom study was completed. A plexiglass phantom with 12 straight circular tubes (0.51–5.00 mm in diameter) filled with contrast medium was recorded under clinical conditions using both the 5“ and 7” modes of the image intensifier with the phantom tubes positioned horizontally as well as vertically in the field of view. The digitally acquired images were recorded on S-VHS tape without any image enhancement (raw data) and with default image enhancement. Video frames were then selected on a professional VCR such that individual tubes were positioned in the center of the field of view and digitized (512² × 8 bits) with a high-quality frame grabber onto a QCA workstation. The contours along the individual tubes were defined using previously validated automated contour detection techniques. For each tube, an average diameter (mm) and a standard deviation (mm) were calculated. Calibration was based on a cm-grid acquired at the same geometry as the phantom. Due to the poor signal-to-noise ratio and the limited bandwidth of the S-VHS video tape, the following objective observations were made: 1) large overestimations (up to 0.87 mm) occur for tube sizes below 1 mm for vertically positioned tubes; 2) random errors in measurements are much larger for vertically positioned tubes (0.36 mm, 7′ II) than for horizontally positioned tubes (0.17 mm, 7′ II); and 3) little differences in results between enhanced and nonenhanced images were found due to these deteriorating factors. In conclusion, S-VHS video tape is unacceptable for QCA and should be excluded from quantitative angiographic clinical trials. © 1996 Wiley-Liss, Inc.     

In vivo comparison of different quantitative edge detection systems used for measuring coronary arterial diameters

Three different systems for quantitative coronary analysis [Cardiovascular Measurement System (CMS®); Polytron 1000® Angiographic Workstation (AWOS®)] were compared in 109 patients before and after coronary angioplasty and at follow-up coronary angiography. Correlation coefficients were low and 95% limits of agreement were wide. In general, CMS® exhibited a tendency to yield lower values for very small diameters and higher values for larger vessels. The acute gain in minimal luminal diameter was considerably smaller when assessed by AWOS® as compared to Polytron® (0.52 vs. 0.71 mm, P < .0001) and to CMS® (0.52 vs. 0.75 mm, P < .0001). Long-term gain was much larger when assessed by Polytron® as compared to AWOS® (18.8 vs. 11.5%, P < .001) and it was almost double for CMS® as compared to AWOS® (20.7 vs. 11.5%, P < .0001). In conclusion, in the individual patient very different results can be obtained when different QCA systems are used, and systematic differences between the systems are encountered.     

Comparison of digital and cine coronary arteriography

Summary Digital coronary arteriography has advanced from a curiosity to a powerful clinical tool. This development has been motivated by the new imaging demands of interventional cardiology, by the need for quantifying atherosclerotic disease, and by advances in computer and video technology. Digital imaging has now essentially replaced cinefilm for clinical decision making in some catheterization laboratories, although uncertainty remains regarding the diagnostic comparability of the two modalities. Therefore, we compared simultaneously acquired digital and cine arteriograms from 18 patients with multivessel coronary artery disease. Digital utilized pulse-progressive technique, a 512 × 512 pixel × 8 bit image matrix, and no post processing. Four angiographers interpreted the arteriograms, identifying 131 stenotic lesions for measurement with manual calipers. Measurements of percent diameter stenosis by digital and cine correlated closely (r=0.88), but digital estimated stenoses to be significantly more severe than cine (p<0.0001). This difference was most significant in small (< 2 mm diameter) arteries, in branch arteries, and with mild stenoses. The differences between digital and cine were not statistically significant for stenoses > 50% diameter narrowing. Interobserver variability was similar for digital and cine imaging. Thus, unprocessed digital and film-based coronary arteriography yield similar assessments of atherosclerotic stenoses, but the techniques may not be diagnostically interchangeable. This paper discusses the technical advances which have occurred in digital coronary arteriography, the comparability of digital and cine imaging, and the factors which may be responsible for observed differences between the two modalities.     

Measuring progression and regression of coronary atherosclerosis in clinical trials: problems and progress

Interventions that may influence the evolution of coronary atherosclerosis can be evaluated more rapidly and efficiently in clinical trials with angiographic endpoints as opposed to using coronary events as endpoints. Quantitative coronary arteriography provides precise and reproducible measurements of coronary artery dimensions for this purpose. The variability of 2 quantitative systems was assessed in 54 lesions under 4 different conditions:-same film, same frame; -same film, same view; different frame; -same view from different films obtained within one month; and -same view from different films obtained one to 6 months apart. With the Cardiovascular Angiographic Analysis System (CAAS), variability of repeat measurement of minimum diameter, expressed as 1 standard deviation of the mean, increased from 0.088 mm (same frame) to 0.197 mm (films 1 to 6 months apart) as conditions decreased from optimal to those encountered in clinical studies. With the Cardiovascular Measurement System (CMS), 1 standard deviation for repeat measurements of minimum diameter increased from 0.087 mm (same frame) to 0.240 mm (films one to 6 months apart). The differences between the two systems for measurements of minimum diameter were not statistically significant and CMS tracked the arterial edge more meticulously than did CAAS. A change in minimum diameter 0.4 mm for CAAS or 0.48 mm for CMS is more than 2 standard deviations of the mid-term variability and therefore represents a true change, either progression or regression, with greater than 95% probability.Quantitative coronary arteriography is an essential tool in clinical trials to assess the effect of an intervention upon the evolution of coronary atherosclerosis. Some of the problems in data analysis related to this methodology are discussed.     

A new approach for the automated definition of path lines in digitized coronary angiograms

Summary For the quantitative analysis of a coronary segment from a coronary (cine)angiogram, an initial path line is required which functions as a model for the subsequent automated contour detection. For on-line applications, a new method for the automated definition of arterial path lines has been developed. Required user-interaction consists of the manual definition of a beginning and an endpoint of the arterial segment to be analyzed. The method is based on a combination of a beam tracer and a box technique. A validation study was performed on 47 non obstructed arteries of various lengths and diameters, and on 56 arterial segments with obstructions (up to 86 percent diameter stenosis).In 89% of the cases an acceptable path line was found after the first iteration; the success score increased to 99%, if a simple manual correction was allowed (2 iterations). The method is extremely fast: the overall average search time for the first iteration was 266 ms, for the second iteration 211 ms. Therefore, it may be concluded that this new technique for the automated definition of arterial path lines is extremely suitable for on-line applications.     

Quantitative and qualitative coronary angiographic analysis: Review of methods,utility, and limitations

Attempted coronary angioplasty of a right coronary artery sub-total occlusion was unsuccessful due to failure to cross the lesion with the dilatation catheter. Both fixed-wire and over-the-wire systems were tried. Coronary rotational ablation was successful in reducing the stenosis and allowing successful angioplasty. © 1992 Wiley-Liss, Inc.     

Comparison of vessel diameters in electron beam tomography and quantitative coronary angiography

Electron beam tomography (EBT) has been shown to permit non-invasive imaging of the coronary arteries after intravenous injection of contrast agent and 3-dimensional reconstruction. We compared the vessel diameters in EBT reconstructions to quantitative coronary angiography (QCA). 10 patients were investigated by EBT and QCA. 3-dimensional EBT reconstructions (shaded surface display) were performed after acquisition of 40 axial cross-sections of the heart with 3 mm slice thickness (1 mm overlap) which were obtained triggered to the ECG in breathhold following intravenous injection of 120–160 ml of contrast agent. A fixed lower reconstruction threshold of 80 HU was used to selectively visualize the contrast-enhanced coronary artery lumen. At 60 sites in the coronary artery system, the vessel diameters measured in the EBT reconstructions were compared to the diameters found in quantitative analysis of the patients' coronary angiograms. The correlation coefficient of the vessel diameters in EBT and QCA was 0.83. Mean vessel diameters were not significantly different in EBT and QCA (3.06±0.93 vs. 2.97±0.94 mm). However, very small vessel diameters tended to be underestimated in the EBT reconstructions, which was due to the partial volume effect. If only vessel diameters measured in the left main or left anterior descending coronary artery were compared to QCA, the correlation increased to 0.87, since these vessel segments are less prone to artifacts in the EBT investigation. Vessel diameters in EBT and QCA correlate reasonably well. Due to partial volume effects, the diameter of very small vessels and stenotic segments tends to be underestimated by EBT.