High precision quantitative angiography

Three-dimensional blood vessel quantification via centerline deformation

It is clinically important to quantify the geometric parameters of an abnormal vessel, as this information can aid radiologists in choosing appropriate treatments or apparatuses. Centerline and cross-sectional diameters are commonly used to characterize the morphology of vessel in various clinical applications. Due to the existence of stenosis or aneurysm, the associated vessel centerline is unable to truly portray the original, healthy vessel shape and may result in inaccurate quantitative measurement. To remedy such a problem, a novel method using an active tube model is proposed. In the method, a smoothened centerline is determined as the axis of a deformable tube model that is registered onto the vessel lumen. Three types of regions, normal, stenotic, and aneurysmal regions, are defined to classify the vessel segment under-analyzed by use of the algorithm of a cross-sectional-based distance field. The registration process used on the tube model is governed by different region-adaptive energy functionals associated with the classified vessel regions. The proposed algorithm is validated on the 3-D computer-generated phantoms and 3-D rotational digital subtraction angiography (DSA) datasets. Experimental results show that the deformed centerline provides better vessel quantification results compared with the original centerline. It is also shown that the registered model is useful for measuring the volume of aneurysmal regions.

Automatic generation of time resolved motion vector fields of coronary arteries and 4D surface extraction using rotational x-ray angiography

Rotational coronary angiography provides a multitude of x-ray projections of the contrast agent enhanced coronary arteries along a given trajectory with parallel ECG recording. These data can be used to derive motion information of the coronary arteries including vessel displacement and pulsation. In this paper, a fully automated algorithm to generate 4D motion vector fields for coronary arteries from multi-phase 3D centerline data is presented. The algorithm computes similarity measures of centerline segments at different cardiac phases and defines corresponding centerline segments as those with highest similarity. In order to achieve an excellent matching accuracy, an increasing number of bifurcations is included as reference points in an iterative manner. Based on the motion data, time-dependent vessel surface extraction is performed on the projections without the need of prior reconstruction. The algorithm accuracy is evaluated quantitatively on phantom data. The magnitude of longitudinal errors (parallel to the centerline) reaches approx. 0.50 mm and is thus more than twice as large as the transversal 3D extraction errors of the underlying multi-phase 3D centerline data. It is shown that the algorithm can extract asymmetric stenoses accurately. The feasibility on clinical data is demonstrated on five different cases. The ability of the algorithm to extract time-dependent surface data, e.g. for quantification of pulsating stenosis is demonstrated.

Evaluation of an improved technique for automated center lumen line definition in cardiovascular image data

The aim of the study was to evaluate a new method for automated definition of a center lumen line in vessels in cardiovascular image data. This method, called VAMPIRE, is based on improved detection of vessel-like structures. A multiobserver evaluation study was conducted involving 40 tracings in clinical CTA data of carotid arteries to compare VAMPIRE with an established technique. This comparison showed that VAMPIRE yields considerably more successful tracings and improved handling of stenosis, calcifications, multiple vessels, and nearby bone structures. We conclude that VAMPIRE is highly suitable for automated definition of center lumen lines in vessels in cardiovascular image data.

Angiographic Assessment of Initial Balloon Angioplasty Results

PURPOSE

To determine the influence of three factors involved in the angiographic assessment of balloon angioplasty-interobserver variability, operator bias, and the definition used to determine success-on the primary (technical) results of angioplasty in the peripheral arteries.

MATERIALS AND METHODS

Percent stenosis in 107 lesions in lower-extremity arteries was graded by three independent, experienced vascular radiologists ("observers") before and after balloon angioplasty and their estimates were compared with the initial interpretations reported by the physician performing the procedure ("operator") and an automated quantitative computer analysis. Observer variability was measured with use of intraclass correlation coefficients and SD. Differences among the operator, observers, and the computer were analyzed with use of the Wilcoxon signed-rank test and analysis of variance. For each evaluator, the results in this series of lesions were interpreted with three different definitions of success.

RESULTS

Estimation of residual stenosis varied by an average range of 22.76% with an average SD of 8.99. The intraclass correlation coefficients averaged 0.59 for residual stenosis after angioplasty for the three observers but decreased to 0.36 when the operator was included as the fourth evaluator. There was good to very good agreement among the three independent observers and the computer, but poor correlation with the operator (P </= .001). The primary success rates for this series of lesions varied from a low of 47% to high of 99%, depending solely on which definition of success was used. Significant differences among the operator, the three observers, and the computer were not present when the definition of success was based on less than 50% residual stenosis.

CONCLUSIONS

Observer variability and bias in the subjective evaluation of peripheral angioplasty can have a significant influence on the reported initial success rates. This effect can be largely eliminated with the use of residual stenosis of less than 50% to define success. Otherwise, meaningful evaluation of angioplasty results will require independent panels of evaluators or computerized measurements.

Evaluation of center-line extraction algorithms in quantitative coronary angiography

Objective testing of centerline extraction accuracy in quantitative coronary angiography (QCA) algorithms is a very difficult task. Standard tools for this task are not yet available. We present a simulation tool that generates synthetic angiographic images of a single coronary artery with predetermined centerline and diameter function. This simulation tool was used creating a library of images for the objective comparison and evaluation of QCA algorithms. This technique also provides the means for understanding the relationship between the algorithms' performance and limitations and the vessel's geometrical parameters. In this paper, two algorithms are evaluated and the results are presented.

Comparison of Doppler US and CT angiography for evaluation of renal artery stenosis

RATIONALE AND OBJECTIVES

The authors compared Doppler ultrasound (US) with computed tomographic (CT) angiography in the evaluation of stenosis of the main renal artery.

MATERIALS AND METHODS

Fifty-six patients who had undergone conventional angiography of the renal arteries participated in a prospective comparison of Doppler US (45 patients) and CT angiography (52 patients). US evaluation included both the main renal artery and segmental renal arteries.

RESULTS

There were 27 main renal arteries with at least 50% stenosis in 20 patients. In 36 patients, there was no significant stenosis. All cases of main renal artery stenosis detected with Doppler US of the segmental arteries were also identified with Doppler US of the main renal artery. The by-artery sensitivity (63%) of US of the main renal artery was greater than that (33%) of US of the segmental arteries. CT angiography was more sensitive (96%) than Doppler US (63%) in the detection of stenosis, but the specificity of CT (88%) was similar to that of US (89%). The difference in the area under the receiver operating characteristic curve (AUC) between CT (AUC = 0.94) and US (AUC = 0.82) was statistically significant (P = .038).

CONCLUSION

Doppler US of the main renal artery is more sensitive than Doppler US of segmental arteries in the detection of stenosis. CT angiography is more accurate than Doppler US in the evaluation of renal artery stenosis.

The accuracy and reproducibility of a global method to correct for geometric image distortion in the x-ray imaging chain

A method to correct for geometric image distortion in the x-ray imaging chain, so-called dewarping, has been developed. A global two-dimensional polynomial model of which the degree is optimized is used. The performance of the method has been tested in a number of experiments using images of a plate with a 1 cm spaced wire grid put against the input screen of the x-ray image intensifier (14/17/27 cm). Both offline cine film and online video images were analyzed. The accuracy of the dewarp method was derived from the acquired images and from computer-simulated distorted images. The robustness and reproducibility of the dewarp method was evaluated by means of imaging the grid in various random orientations. Three parameters describing the behavior of the algorithm were considered. One is the reproducibility of the location of a dewarped position. The second parameter is the reproducibility of the distance between two adjacent dewarped positions as a measure of the reproducibility of the size of an object under investigation. The third parameter is the reproducibility of the pixel size in the plane of the calibration plate. The major results are: the reproducibility of the location of a dewarped position was 0.01-0.04 mm for cine film and 0.04-0.07 mm for video images. The coefficient of variation of the distance between two dewarped positions was 0.04%-0.11% for cine film and 0.15%-0.18% for video images. The dewarp algorithm turned out to be fast and accurate and the distortion was removed over the whole image field down to a low random residual level. It was found that a random orientation of the grid did not affect the assessment of the distortion nor its correction. The dewarp method proved to be intrinsically robust and highly reliable. Time instability of the imaging chain was the main source of variability in the dewarp results.

Laser balloon angioplasty combined with local intracoronary heparin therapy: immediate and short-term follow-up results

Laser balloon angioplasty (LBA) has been shown to acutely increase angiographic luminal dimensions after conventional balloon angioplasty (PTCA) without a favorable impact on chronic restenosis. Experimentally, laser and thermal energy enhance binding of heparin to the injured arterial wall and to the thrombus. In view of the anticoagulant, antiproliferative, and antifibrotic activities of the drug, a pilot study was performed to evaluate the potential safety and efficacy of LBA combined with local heparin therapy. Ten patients scheduled for elective PTCA were entered in the study. In each patient, a single lesion was treated with a laser balloon and coated with a heparin film (3000 I.U. at a concentration > 100,000 I.U./gm) immediately after optimal PTCA. The mean minimum luminal diameter and mean percent stenosis of the 10 treated lesions after PTCA were 1.62 +/- 0.39 mm and 37% +/- 9%, respectively. After LBA and local heparin therapy, the mean minimal lumen diameter increased to 2.01 +/- 0.34 mm (p < 0.01) and the mean percent stenosis decreased to 20% +/- 10% (p < 0.01). Systemic heparin was discontinued immediately after the procedure in all patients. Acute or inhospital complications, either major or minor, occurred in none (0%) of the 10 patients (95% confidence interval 0% to 31%); all were discharged home on the day after the procedure. All patients remained well and free of cardiac symptoms for at least 2 months after the procedure. However, restenosis developed in six (60%) of the 10 patients (95% confidence interval 26% to 88%) 2 to 6 months after the procedure. The results suggest that LBA and local heparin therapy, with discontinuation of systemic heparin immediately after angioplasty, is a safe treatment modality that yields favorable acute angiographic results.

Controlled trial of fish oil for regression of human coronary atherosclerosis. HARP Research Group

OBJECTIVES

This randomized clinical trial tested whether fish oil supplements can improve human coronary atherosclerosis.

BACKGROUND

Epidemiologic studies of populations whose intake of oily fish is high, as well as laboratory studies of the effects of the polyunsaturated fatty acids in fish oil, support the hypothesis that fish oil is antiatherogenic.

METHODS

Patients with angiographically documented coronary heart disease and normal plasma lipid levels were randomized to receive either fish oil capsules (n = 31), containing 6 g of n-3 fatty acids, or olive oil capsules (n = 28) for an average duration of 28 months. Coronary atherosclerosis on angiography was quantified by computer-assisted image analysis.

RESULTS

Mean (+/- SD) baseline characteristics were age 62 +/- 7 years, plasma total cholesterol concentration 187 +/- 31 mg/dl (4.83 +/- 0.80 mmol/liter) and triglyceride levels 132 +/- 70 mg/dl (1.51 +/- 0.80 mmol/liter). Fish oil lowered triglyceride levels by 30% (p = 0.007) but had no significant effects on other plasma lipoprotein levels. At the end of the trial, eicosapentaenoic acid in adipose tissue samples was 0.91% in the fish oil group compared with 0.20% in the control group (p < 0.0001). At baseline, the minimal lumen diameter of coronary artery lesions (n = 305) was 1.64 +/- 0.76 mm, and percent narrowing was 48 +/- 14%. Mean minimal diameter of atherosclerotic coronary arteries decreased by 0.104 and 0.138 mm in the fish oil and control groups, respectively (p = 0.6 between groups), and percent stenosis increased by 2.4% and 2.6%, respectively (p = 0.8). Confidence intervals exclude improvement by fish oil treatment of > 0.17 mm, or > 2.6%.

CONCLUSIONS

Fish oil treatment for 2 years does not promote major favorable changes in the diameter of atherosclerotic coronary arteries.

Directional low-pass filtering for improved accuracy and reproducibility of stenosis quantification in coronary arteriograms

Considers the quantification of percent diameter stenosis in digital coronary arteriograms of low spatial resolution. To improve accuracy and reproducibility an edge-preserving smoothing method, called the directional low-pass filter (DLF), was developed to suppress quantum noise by averaging image intensity in a direction parallel to the vessel border. Accuracy of stenosis quantification was assessed by using stenosis phantoms. The standard error of the estimate (SEE) was 0.76 pixel-length (p) without spatial filtering and further reduced to 0.50 p by DLF; the average deviation as a measure of the regularity of border definition was also reduced by DLF from 1.00 to 0.68 p (n=50, P<0.001). It was shown that the DLF outperformed the conventional moving average filter and median filter. Reproducibility in terms of intraframe variability was assessed by using coronary arteriograms obtained from 10 patients. Intraframe variability of the percent stenosis measurements was reduced from 3.5% to 2.9% by DLF (n=10, P<0.005). An analysis of variance showed, however, that the interframe variability cannot be reduced by any of the spatial filters under investigation. The result of this study has provided a guideline for angiographically based quantification of percent stenosis under limited imaging resolution and suggests a new method for improving accuracy and reproducibility by directional low-pass filtering.

Effect on coronary atherosclerosis of decrease in plasma cholesterol concentrations in normocholesterolaemic patients. Harvard Atherosclerosis Reversibility Project (HARP) Group

Lipid-lowering therapy ameliorates coronary atherosclerosis in patients with raised concentrations of low-density-lipoprotein (LDL) cholesterol. We have investigated whether a similar benefit can be obtained in normocholesterolaemic patients. We studied 79 normocholesterolaemic patients with coronary heart disease (70 male, 9 female), mean age 58 years, all non-smokers, with mean total cholesterol concentration 5.5 mmol/L. All patients received diet therapy and were randomly assigned placebo (39) or active treatment (40) with pravastatin, nicotinic acid, cholestyramine, and gemfibrozil stepwise as needed to reach the specified goal (total cholesterol < or = 4.1 mmol/L, ratio of LDL/high-density-lipoprotein [HDL] cholesterol < or = 2.0). Coronary angiograms at baseline and after 2.5 years of treatment were analysed by computer-assisted quantitative techniques. There was no significant difference in coronary atherosclerosis during follow-up between the active treatment and placebo groups; the mean minimum diameter narrowed significantly but to the same extent in both groups (change baseline to 2.5 years 0.14 [SD 0.42] and 0.15 [0.42] mm, respectively, both p < 0.001). Similarly, the change in percentage stenosis did not differ between the groups (2.1 [10.6] vs 2.4 [10.3]%). By multiple regression analysis, the adjusted difference between the groups was a 0.04 mm (95% CI -0.04 to 0.12 mm) increase in minimum diameter and a 0% (-1.7 to 1.7) change in percentage stenosis. The groups differed significantly in plasma lipids (% change in active minus % change in placebo group: -28% total cholesterol, -41% LDL-cholesterol, 13% HDL-cholesterol, -26% triglycerides, -31% apolipoprotein B, all p < 0.001). Thus, intensive pharmacological treatment of normocholesterolaemic patients has significant effects on plasma lipid concentrations but no angiographically measurable benefit on the coronary arteries.

Lumen centerline detection in complex coronary angiograms

We have developed a method for lumen centerline detection in individual coronary segments that is based on simultaneous detection of the approximate positions of the left and right coronary borders. This approach emulates that of a clinician who visually identifies the lumen centerline as the midline between the simultaneously-determined left and right borders of the vessel segment of interest. Our lumen centerline detection algorithm and two conventional centerline detection methods were compared to carefully-defined observer-identified centerlines in 89 complex coronary images. Computer-detected and observer-defined centerlines were objectively compared using five indices of centerline position and orientation. The quality of centerlines obtained with the new simultaneous border identification approach and the two conventional centerline detection methods was also subjectively assessed by an experienced cardiologist who was unaware of the analysis method. Our centerline detection method yielded accurate centerlines in the 89 complex images. Moreover, our method outperformed the two conventional methods as judged by all five objective parameters (p < 0.001 for each parameter) and by the subjective assessment of centerline quality (p < 0.001). Automated detection of lumen centerlines based on simultaneous detection of both coronary borders provides improved accuracy in complex coronary arteriograms.

Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model

Experimentally, heparin inhibits mechanisms that promote fibrosis, neointimal cellular proliferation, and thrombin bound to fibrin at the surface of intraluminal thrombus, but only in relatively high concentrations. A preliminary hypothesis was tested and confirmed in vitro that initial binding of 3H-heparin to mechanically injured porcine aorta is concentration-dependent over a 1,000-50,000 units/ml range (r = 0.9). The hypothesis was then tested in vitro that thermal exposure during contact of heparin to arterial tissue and to clot would enhance binding of the drug. 3H-heparin binding to clot, whole blood particulates, and washed erythrocytes was markedly enhanced by exposure to temperatures > 70 degrees C. Thermal exposure (80 degrees C x 40 s) also enhanced tissue persistence of the drug within porcine aorta subjected to a shear rate of 1,100(-1) in an annular Baumgartner chamber perfused with normal saline at 37 degrees C for 48 h. Heparin in vitro anticoagulant activity persisted after thermal exposure and binding to tissues. A new method was developed for local application of a heparin film that provides a maximum concentration with a tolerable systemic dose during an angioplasty procedure. In an in vivo rabbit model of mural fibrosis after iliac artery angioplasty, the 1-month mean angiographic luminal diameter loss (23% compared to the acute postangioplasty result by computer image analysis) in response to conventional balloon angioplasty (BA) and laser balloon angioplasty (LBA) was the same (P > 0.05). Local application of a heparin film (3,000 units at a concentration > 100,000 units/g), however, reduced the mean % loss in diameter 1 month after LBA (12%), but not after BA (29%), compared to arteries subjected to angioplasty without local heparin (P < .05). The results are consistent with the hypothesis that thermal energy enhances heparin binding to tissues and that local application of a heparin film favorably modulates arterial luminal responses to LBA, but not to BA, in this animal model.

The detection and quantification of retinopathy using digital angiograms

An algorithm is presented for the analysis and quantification of the vascular structures of the human retina. Information about retinal blood vessel morphology is used in grading the severity and progression of a number of diseases. These disease processes are typically followed over relatively long time courses, and subjective analysis of the sequential images dictates the appropriate therapy for these patients. In this research, retinal fluorescein angiograms are acquired digitally in a 1024x1024 16-b image format and are processed using an automated vessel tracking program to identify and quantitate stenotic and/or tortuous vessel segments. The algorithm relies on a matched filtering approach coupled with a priori knowledge about retinal vessel properties to automatically detect the vessel boundaries, track the midline of the vessel, and extract useful parameters of clinical interest. By modeling the vessel profile using Gaussian functions, improved estimates of vessel diameters are obtained over previous algorithms. An adaptive densitometric tracking technique based on local neighborhood information is also used to improve computational performance in regions where the vessel is relatively straight.

Relation of vessel wall shear stress to atherosclerosis progression in human coronary arteries

The purpose of this study was to determine the relation between vessel wall shear stress and the rate of atherosclerosis progression. Quantitative angiography was used to calculate the change in coronary arterial diameter over 3.0 years in patients enrolled in the Harvard Atherosclerosis Reversibility Project pilot study (n = 20 arterial segments). Vessel wall shear stress was calculated by means of a validated finite-difference model of the Navier-Stokes' equation that assumes a coronary flow rate of 8 ml/sec. The correlation between vessel wall shear stress and the change in arterial diameter at multiple points (mean, 70) along the length of the artery was then calculated for each of the 20 segments with a focal stenosis. In 15 of the 20 arterial segments there was a significant correlation (p < 0.05) between low shear stress and an increased rate of atherosclerosis progression. A Fisher's z transformation was then used to combine the correlation coefficients from all 20 segments. Low shear stress was significantly correlated (z = 0.37 +/- 0.00074, p < 0.0001) with an increased rate of atherosclerosis progression. This serial quantitative evaluation of human coronary arteries is consistent with previous data that have suggested that low shear stress promotes atherosclerosis progression. Variations in local vessel wall shear stress may explain the previously reported near-independent rate of atherosclerosis progression in multiple lesions within the same patient despite exposure to the same circulating lipoprotein values and systemic hemodynamics.

Simultaneous detection of both coronary borders

A method for simultaneous detection of both coronary borders that is based on three-dimensional graph searching principles is presented. The simultaneous method and the authors' previously reported conventional method were applied to 29 coronary images, of which 19 were selected because conventional methods might be expected to have difficulty. Coronary borders identified by the two methods were visually compared. In the 19 difficult images, simultaneous border detection yielded superior results in 7 images and equivalent results in 12 images. Superior or equivalent results were obtained in the remaining 10 typical images. In a set of 43 uncomplicated images, minimal lumen diameters derived using simultaneous border detection correlated well with diameters derived using conventional border detection (r=0.97), diameters obtained from observer-defined borders (r=0.91), and diameters obtained using the Brown-Dodge quantitative coronary arteriography method (r=0.85). Thus simultaneous detection of left and right coronary borders provides improved accuracy in the detection of vessel borders in difficult coronary angiograms.

Rapid three-dimensional surface reconstruction of magnetic resonance images of large arteries and veins: a preliminary evaluation of clinical utility

We have implemented a computerized system for relatively rapid (< 1 h) three-dimensional (3D) surface rendering of flow-sensitive (gradient refocused) magnetic resonance images. The method has been applied in 8 patients with six different clinical problems and was found to enhance understanding of normal and abnormal aortic, caval, and portosystemic venous anatomy. 3D images are useful for communicating complex anatomic information and may help with difficult diagnoses. Advantages and limitations of the present system are discussed.

Correction of aberration in image-intensifier systems

A mathematical model describing spatial distortions caused by an image intensifier has been developed. These distortions originate from projecting a flat plane onto a curved input phosphor surface. Considering the source of these distortions and their magnification along the radial distance, it is possible to describe them in terms of the geometrical relations between a point on a physical object and its projection onto an input phosphor screen's spherical surface. On the basis of these relations, the correction of pixel coordinates and pixel values has been performed. Parameters included in the derived formula consider the radius of curvature of the input screen, the view angle, the distance from the focal spot to the object, and the distance from the focal spot to the input phosphor screen. These parameters make the correction formula system independent and permit its application to any image projected under different view angle and/or acquired with different image-intensifier system. The correction leads to a nearly distortion-free image.

Quantitative angiographic and statistical methods to assess serial changes in coronary luminal diameter and implications for atherosclerosis regression trials

The purpose of this study was (1) to determine a threshold for categorizing individual coronary lesions as either significantly progressing or regressing, (2) to determine whether multiple lesions within individual patients progress at independent rates, and (3) to calculate sample sizes for atherosclerosis regression trials. Seventeen patients with 46 significant lesions (2.7 lesions/patient) underwent repeat coronary arteriography 3.0 years apart. With use of the standard error of the mean change in diameter from initial to repeat catheterization across 5 pairs of consecutive end-diastolic frames, individual lesions were categorized as either significantly (p less than 0.01) progressing or regressing if there was a 0.27 mm change in minimum diameter or a 7.8 percent point change in percent stenosis. The mean diameter change of a sample of lesions can also be analyzed as a continuous variable using either the lesions or the patient as the primary unit of analysis. A lesion-specific analysis can be accomplished using a multiple regression model that accounts for the intraclass correlation (rho) in the degree of change among multiple lesions within individual patients. The intraclass correlations in percent stenosis (rho = 0.01) and minimum diameter (rho = -0.24) were low, indicating that disease progression in different lesions within individual patients is nearly independent. With use of this model, 50 patients per treatment group would permit the detection of a 5.5% difference between treatment group means in the change in minimum diameter and a 2.7% percentage point (not percent) difference in the change in percent stenosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Segmentation of brain CT images using the concept of region growing

A method is described for extracting and isolating cerebrospinal fluid and tissue areas of brain images obtained with computed tomography. The classification of the pixels into components is based on region growing and nearest neighbor principles. To aid the performance of this method, the algorithm utilizes a priori information on the anatomic composition of the brain, and reduces the 'cupping effect' in the CT image that is attributed to beam hardening artifacts. In order to avoid subjectivity, the performance of the algorithm was tested by superimposing five computer-simulated circular lesions on different areas of the original CT scans, 8 mm thick. These images were taken at different levels in the brain, thereby accommodating different anatomy as well as the apical artifact of CT scanning. In this exploratory investigation, the false negative error of segmentation for lesions having diameter of 20 pixels was found in the order of 25% at an estimated partial volume (PV) effect of 50% that decrease further to about 5% for a PV of 80%. At that point the false positive error becomes the dominant error in the analysis.

Differential impairment of vasodilator responsiveness of peripheral resistance and conduit vessels in humans with atherosclerosis

The purpose of this study was to assess the effect of atherosclerosis on the regulation of limb blood flow. To examine this issue, the reactivity of resistance and conduit vessels was evaluated in 11 patients with peripheral atherosclerotic disease and six control subjects. Responsiveness of resistance vessels was measured by venous occlusion plethysmography. Responsiveness of conduit vessels was determined by quantitative angiography to measure the diameter of the superficial femoral artery. To distinguish endothelium-dependent vasodilation from that caused by direct smooth muscle relaxation, each participant received intra-arterial infusions of methacholine and nitroprusside, respectively. Flow-mediated dilation of the superficial femoral artery was determined during reactive hyperemia. Vasoconstrictor function was determined by the infusion of phenylephrine. Methacholine reduced calf vascular resistance in the control subjects but not in the patients with atherosclerosis (-64 +/- 11% versus 6 +/- 18%, p less than 0.01). Nitroprusside decreased calf vascular resistance comparably in each group (-51 +/- 5% versus -42 +/- 4%, p = NS). The vasoconstrictor effect of phenylephrine was similar in each group (105 +/- 30% versus 108 +/- 22%, p = NS). In the superficial femoral artery, the vasodilator responses to both methacholine (20 +/- 4% versus 1 +/- 4%, p less than 0.05) and nitroprusside (19 +/- 4% versus 5 +/- 4%, p less than 0.05) were blunted in the atherosclerotic patients as was the vasoconstrictive response to phenylephrine (-15 +/- 1% versus -1 +/- 5%, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Percutaneous coronary laser balloon angioplasty: initial results of a multicenter experience

A multicenter clinical trial was initiated to test the potential safety and short-term efficacy of a percutaneous coronary application of laser balloon angioplasty, which has been shown experimentally to alleviate the common causes (dissection, recoil, thrombus) of suboptimal luminal results of conventional balloon angioplasty. Fifty-five patients, the majority (62%) of whom had relatively high risk lesions, were treated in 10 centers with a laser balloon that was identical in size (3 x 20 mm) to a balloon used for conventional balloon angioplasty performed on the same lesion immediately before laser balloon angioplasty. One or more neodymium:yttrium aluminum garnet (Nd:YAG) (1,060 nm) laser doses of 250 to 450 J were each delivered over a 20 s duration per exposure. Immediately and 1 day after laser balloon angioplasty no significant adverse effects on the arterial lumen were noted in any patient. By computerized image analysis of cineangiograms initial conventional balloon angioplasty failed to achieve a minimal luminal diameter greater than 1.5 mm in 14 patients (25%), including 3 patients with acute closure. However, after subsequent laser balloon angioplasty, minimal luminal diameter exceeded this value in all patients including this subgroup. Overall, minimal luminal diameter increased from 1.74 +/- 0.46 mm after conventional balloon angioplasty to 2.32 +/- 0.31 mm after laser balloon angioplasty (p less than 0.001) with no change found on 1 day and 1 month follow-up angiograms. Thus, laser balloon angioplasty is a safe, effective procedure for improving luminal dimensions after conventional balloon angioplasty.

Segmentation of coronary arteriograms by iterative ternary classification

A segmentation algorithm for extracting arterial structures in coronary angiograms is presented. The algorithm mimics the process of interactive interpretation in human vision by iteratively implementing a ternary classification and learning process. Two gray-scale thresholds are computed to define three pixel classes: artery, background, and undecided. Then, two new thresholds for undecided pixels are computed using statistics conditioned upon the current classification. The threshold adaptation is governed by a learning algorithm based on the line and consistency measurements around each pixel. The process converges and results in a binary image. The performance of this algorithm on human coronary arteriograms was compared qualitatively to that of a relaxation algorithm and of a scattering based algorithm. Quantitative comparison was also made possible with computer generated images, which were obtained with the help of a model of the imaging chain and a process of interactive visualization of the modeled data. The iterative ternary classifier showed the best performance over a broad range of image quality. The study also demonstrated the use of visualization and user interaction in model building and algorithm development.

Application of multiresolution spatial filters to long-axis tracking

A method was developed for automatically tracking the long axis of thin objects which have nonuniform width and arbitrary orientation in a two-dimensional image space. This method is used to determine the length of isolated contractile smooth muscle cells, but has applications in other medical areas such as angiographic imaging. Pattern recognition techniques that determine object size and orientation are used to identify the long axis of an imaged object from its responses to difference of Gaussian and orientation filters. This method needs no a priori knowledge of object location, adapts to varying image magnification, requires little human interaction, and yields reproducible results.

Automated analysis of coronary arterial morphology in cineangiograms: geometric and physiologic validation in humans

A method of coronary border identification is discussed that is based on graph searching principles and is applicable to the broad spectrum of angiographic image quality observed clinically. Cine frames from clinical coronary angiograms were optically magnified, digitized, and graded for image quality. Minimal lumen diameters, referenced to catheter size, were derived from automatically identified coronary borders and compared to those defined using quantitative coronary arteriography and to observer-traced borders. computer-derived minimal lumen diameters were also compared to intracoronary measurements of coronary vasodilator reserve, a measure of the functional significance of a coronary obstruction. To test the robustness of the present border detection method, computer-derived coronary borders were compared to independent standards separately for good and poor angiographic images. The accuracy of computer-identified borders was similar in the two cases.

Automated identification of vessel contours in coronary arteriograms by an adaptive tracking algorithm

A tracking algorithm for identification of vessel contours in digital coronary arteriograms was developed and validated. Given an initial start-of-search point, the tracking process was fully automated by utilizing the spatial continuity of the vessel's centerline, orientation, diameter, and density. The incremental sections along a major vessel were sequentially identified, based on the assumptions of geometric similarity and continuation between adjacent incremental sections. The algorithm consisted of an extrapolation-update process which was guided by a matched filter. The filter parameters were adapted to the measured lumen width. The tracking process was robust and extremely efficient as indicated by test results on synthetic images, digital subtraction angiograms, and cineangiograms. The algorithm provided accurate measurement of lumen width and percent stenosis that was relatively invariant to the vessel's orientation, dynamic range, background variation, and degree of blurring.