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Background— Previous studies suggest that management of ambulatory hemodynamics may improve outcomes in chronic heart failure. We conducted a prospective, observational, first-in-human study of a physician-directed patient self-management system targeting left atrial pressure. Methods and Results— Forty patients with reduced or preserved left ventricular ejection fraction and a history of New York Heart Association class III or IV heart failure and acute decompensation were implanted with an investigational left atrial pressure monitor, and readings were acquired twice daily. For the first 3 months, patients and clinicians were blinded as to these readings, and treatment continued per usual clinical assessment. Thereafter, left atrial pressure and individualized therapy instructions guided by these pressures were disclosed to the patient. Event-free survival was determined over a median follow-up of 25 months (range 3 to 38 months). Survival without decompensation was 61% at 3 years, and events tended to be less frequent after the first 3 months (hazard ratio 0.16 [95% confidence interval 0.04 to 0.68], P =0.012). Mean daily left atrial pressure fell from 17.6 mm Hg (95% confidence interval 15.8 to 19.4 mm Hg) in the first 3 months to 14.8 mm Hg (95% confidence interval 13.0 to 16.6 mm Hg; P =0.003) during pressure-guided therapy. The frequency of elevated readings (>25 mm Hg) was reduced by 67% ( P P P P P P =0.15). Conclusions— Physician-directed patient self-management of left atrial pressure has the potential to improve hemodynamics, symptoms, and outcomes in advanced heart failure. Clinical Trial Registration Information— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00547729.

Background: Optimization of coronary images for percutaneous coronary intervention (PCI) remains difficult due to cardiac motion throughout the respiratory and cardiac cycles. We tested a novel system to stabilize angiographic images at the region of interest in order to assist during PCI. Methods: Patients undergoing PCI to the right coronary artery (RCA) (group 1, n = 22) or complex PCI (group 2, n = 16) were prospectively enrolled and the angiographic image sequences of patients who died suddenly of confirmed or presumed stent thrombosis following PCI (group 3, n = 16) were retrospectively reviewed. All image sequences were analyzed off-line by three cardiologists before and after image stabilization for accuracy of stent placement, presence of residual edge dissection, and adequacy of procedural outcome. Results: Image stabilization was successful in 100% of cases in a mean time of 95 ± 71 seconds and was considered to be helpful in 13.6% of group 1, in 18.3% of group 2, and in 10% of group 3 cases. There was good correlation between observers with a kappa statistic of 0.85 to 1.0 for all observations. However, there was no difference in the reviewers' opinions of stent placement, presence of edge dissection, or adequacy of procedural result when comparing the standard angiographic views and the stabilized images. In particular, no previously unrecognized edge dissections were apparent in group 3 with stabilized display. Conclusion: Image stabilization centered on the region of interest was considered helpful in a small subset of patients, particularly the complex PCI patients. However, no differences in objective parameters could be demonstrated.

Background Implantable cardiac pressure monitors require assurance of calibration. This study evaluated if airway pressure responses during Valsalva maneuver (VM) can be used for calibrating intracardiac pressure transducers. Methods and Results Thirty-eight heart failure patients performed VMs while cardiac and airway pressures were recorded. Patients were designated as Lower (L) if baseline PCW was

Catheter-based intracoronary radiation therapy demonstrated reduction of the recurrence rate of in-stent restenosis by 35%–50% when compared to conventional therapy. The objectives of this study were to determine the safety and feasibility of a new balloon-shaped source design and a higher applied dose to reduce the restenosis rates. Thirty-two patients with in-stent restenosis who met study eligibility criteria were successfully treated with standard PCI techniques. Following a successful intervention, a P-32 β-balloon source was positioned to cover the angioplasty site and a dose of a 20 Gy at 1 mm from the surface of the source was administered. The primary endpoint was a composite of major adverse cardiac events (any death, MI, emergent CABG, or repeat target vessel revascularization) during 6 months of follow-up. At 6 months, only one patient underwent repeat PTCA to the target vessel (3%). There were no instances of death, emergency surgery, late thrombosis, total occlusions, or MI. Binary restenosis measured by QCA at the stented segment was 0% and for the whole analysis vessel was 7.5%. Beta-radiation delivered with a balloon P-32 source design for patients with in-stent restenosis results in lower than expected rate of angiographic and clinical restenosis and the absence of late complications. Cathet Cardiovasc Intervent 2002;57:286–294. © 2002 Wiley-Liss, Inc.

Clinical trials suggest an increased frequency of restenosis after coronary intervention in left anterior descending (LAD) compared to the left circumflex or right coronary arteries. Experimental studies correlate stent-induced arterial injury and the extent of neointima formation. This study investigates whether the coronary artery affects the relationship between arterial injury and neointima hyperplasia in the porcine stent model.Non-lipemic farm pigs underwent stent placement in the LAD (n = 26) and the right coronary artery (RCA; n = 30). Quantitative coronary angiography (QCA) was performed before and after stent placement, and at follow-up; quantitative histomorphometry and injury score were analyzed at 30-day follow-up.Initial procedure balloon/artery ratios (LAD 1.17 +/- 0.11 vs RCA 1.17 +/- 0.09, P = NS), and minimal stent lumen diameters (MLD; LAD 2.91 +/- 0.31 vs RCA: 2.93 +/- 0.28 mm, P = NS) were similar suggesting no difference in deployment technique. At follow-up there was more restenosis in the LAD (diameter stenosis: 55.0 +/- 26.4% vs 37.3 +/- 18.1%, and MLD: 1.24 +/- 0.78 mm vs. 1.71 +/- 0.57 mm, P0.05 for both comparisons). No differences were seen for injury score (1.09 +/- 0.51 vs 1.01 +/- 0.57; LAD vs RCA) or stent area (6.13 +/- 0.99 vs 6.55 +/- 1.42 mm2). Histomorphometry demonstrated smaller lumen area (2.15 +/- 0.94 vs 2.96 +/- 1.29 mm2) and thicker neointima (0.63 +/- 0.25 vs 0.51 +/- 0.17 mm; all P0.05) in the LAD. Multiple linear regression analysis identified the LAD as an independent predictive factor for increased neointima formation.These observations establish an animal model that is consistent with clinical experience showing that restenosis after stenting is more common in the LAD. The findings may be useful for understanding and developing systemic and local antirestenotic strategies.

Multiframe quantitative coronary angiography is typically performed by averaging measurements of artery diameter over multiple frames. This approach reduces errors attributable to random noise but may not reduce systematic errors caused by background structures, nonlinear system response, and motion blur. We attempt to reduce these sources of error by decomposing the image sequence into moving layers, one of which includes the artery. We embed simulated arteries into clinical angiographic sequences so that the true vessel dimensions are known accurately. The measurement tasks are minimum diameter, geometric percent stenosis, and densitometric percent stenosis. We compare measurements for single and multiple raw images, single images with fixed mask subtraction, single and multiple images with layered background subtraction, and time-averaged layer images. We find that both multiframe averaging and layer decomposition significantly improve geometric and densitometric accuracy compared with single-frame measurements. The best results were obtained by averaging measurements from multiple frames of layered background-subtracted images.

We are reporting the first case of an accidental radioactive 188Re leakage of a liquid-filled balloon system. Different analytical methods estimated that approximately 4 mCi 188Re were released. The radiation burden was reduced considerably by the combined therapy with perchlorate and forced volume diuresis. Estimated exposures to all organs were very low with 1.8 rad. A total body nuclear scintigraphy demonstrated uniform 188Re distribution, without specific organ concentration.

Background. The major limitation of coronary stenting is restenosis due to exaggerated neointimal thickening. We evaluated a positron-emitting V48 nitinol stent in a porcine coronary model of restenosis. Methods and Results. Pigs (n = 16) received a control nonradioactive and a V48 stent (1.5 or 10.6 μCi) randomized to the left anterior descending artery (LAD) and right coronary artery (RCA). Histology, morphometric variables, and strut injury scores were evaluated after 32 days. Peristrut fibrinoid deposits were greater in the high-dose group (p < 0.0001). Control stent area stenosis (AS) and mean neointimal thickness (NIT) correlated with injury (r = 0.81 and 0.79, respectively). Higher-dose stents reduced AS by 20% (0.57 ± 0.13 vs. 0.71 ± 0.16; p = 0.029) and mean NIT by 35% (0.44 ± 0.16 vs. 0.71 ± 0.24mm; p = 0.001) compared with controls. Lower-dose 1.5-μCi stents did not differ from controls. NIT over individual struts was reduced in the high-dose group compared with controls by 0.18 mm for grade 1 injury, 0.31 mm for grade 2, and 0.38 mm for grade 3 (p < 0.02 for all comparisons). Conclusions. 1.5-μCi V48 nitinol stents did not influence vessel histology or restenotic parameters in pig coronary arteries. In contrast, 10.6-μCi stents created a distinctive histological picture consisting of increased fibrinoid deposits on the neointimal-facing side of the struts without cellular organization. Higher dose radioactive stents significantly reduced AS and mean NIT. The reduction in neointimal thickening was greatest when the depth of strut penetration into the vascular wall was most severe.

Recent preclinical and clinical studies indicate that irradiation using ionizing radiation in the dose range of 15 to 30 Gy may reduce the occurrence of restenosis in patients who have undergone an angioplasty. Several delivery systems of intravascular brachytherapy have been developed to deliver radiation doses in this range with minimal normal tissue toxicity. In late 1995 the American Association of Physicists in Medicine (AAPM) formed a task group to investigate these issues and to report the current state of the art of intravascular brachytherapy physics. The report of this task group is presented here.

A novel method is presented for correcting errors in measurements of biplane projection imaging geometry without prior identification of corresponding points in the two images. For imaged objects that project onto both images, a constraint equation is obtained that relates weighted integrals along corresponding epipolar lines. The integrals are computed to first order in the angular beamwidth, which is assumed to be small. Starting from measured or estimated values, geometrical parameters are computed iteratively in order to maximize the correlation between epipolar line integrals in the two images. Improvement in the computation of corresponding epipolar lines is demonstrated on images of a wire phantom. The root mean square distance of the epipolar lines from the corresponding reference points is improved from 15 pixel widths to less than 4 pixel widths (1.3 mm). Convergence is demonstrated on phantom images for individual parameter variations up to 70% in relative magnification, a relative shift of the imaging planes by 50 pixels, or a relative rotation of at least 35 degrees around either of two axes. Applicability to clinical images is demonstrated by using a biplane angiogram of a pig to align corresponding points determined from images of a Perspex cube acquired with the same geometry.

The study describes the effect of acute changes in aortic blood pressure and heart rate in the intact normal canine coronary circulation on digital angiographic measurements of the mean transit time of the microcirculation compartment and on direct flow meter measurement of resting and maximal hyperemic coronary blood flow. The mean transit time of the radiographic contrast material through the normal coronary circulation was calculated in 20 dogs by the impulse response analysis from serial digital coronary angiograms under systematically changed blood pressure and heart rate conditions. The mean aortic blood pressure (MAP) was controlled by the inflation of a balloon in the descending aorta (70-150 mmHg). The heart rate was altered by atrial pacing (90, 120, and 150/min). The mean transit times (T mu) of contrast material across the myocardial microcirculation which had been recently shown to correlate with coronary flow reserve (CFR) in stenosed arteries in the canine model were calculated under resting and hyperemic flow conditions from 428 selective coronary angiograms after a hand-injected contrast bolus, T mu was found to be heart rate independent. T mu-1 was linearly correlated with MAP (r = 0.7). There was no difference in T mu under resting and hyperemic flow conditions at comparable MAP. The corresponding distribution volume (V mu) of the microcirculation was calculated as the product of the mean transit time T mu and the measured coronary blood flow. Under resting flow conditions, V mu decreased with rising MAP. Furthermore, V mu increased with rising heart rate, V mu was constant during blood pressure or heart rate changes under hyperemic flow conditions. The data suggest that CFR whether by direct measurements of flow or by radiographic assessment of contrast material kinetics should be standardized with respect to hemodynamic conditions of heart rate and MAP.

BACKGROUND We have developed a digital display method that stabilizes the motion of a stenosis in sequential frames of a coronary angiogram, allowing it to be scrutinized at high display frame rates. The purpose of this study was to determine whether this technique improves visual detection of low-contrast luminal morphological features. METHODS AND RESULTS An observer detection study was conducted using computer-simulated arterial segments containing known target features, inserted into clinical digital coronary angiograms. Four observers performed a forced-choice detection of a simulated filling defect in each of 320 angiograms using the conventional and stenosis-stabilized dynamic displays (at 7.5, 15, and 32 frames per second) and a single-frame static display (total of 8960 detections). In a second simulated clinical task, three observers detected a bridging stenotic lumen in 600 angiograms using the two displays (3600 detections). In a third experiment, two angiographers rated the likelihood of intraluminal thrombus in 89 right coronary digital angiograms by consensus reading with both dynamic displays. Detectability of the simulated filling defect was similar for both dynamic display methods at 7.5 frames per second (averaging twice that for static images). As display rate was increased to 32 frames per second, detectability for the conventional display declined, whereas the stabilized display detectability increased for all observers (P < .05). On average, stabilization allowed detection of filling defects equivalent to a 71% increase in feature contrast. Response time for the conventional display averaged 12.9 +/- 4.7 seconds. For the stenosis-stabilized display, response time fell with increased frame rate (P < .05) to 4.9 +/- 1.2 seconds at 32 Hz, similar to the time for static images (4.6 +/- 0.8 seconds). The detectability of the bridging stenotic lumen was increased by 62% with the stabilization compared with conventional dynamic display (P < .00001). Consensus reading of coronary angiograms showed differences between the two dynamic display methods (kappa = 0.11) that may be explained by an improvement in observer uncertainty. A rating of definite for thrombus present or absent was more frequent with the stabilized display (39% versus 15%, P < .0001). CONCLUSIONS These data suggest that stabilized display of coronary angiograms significantly increases detectability, reduces the time required for detection, and improves observer uncertainty for the presence of small luminal morphological features. The method of angiographic display may thus have an impact on clinical coronary angiographic interpretation.

Angiography frequently demonstrates a collateral circulation in severe coronary artery disease. An easily applicable method to quantify collateral flow might be a useful adjunct for the assessment of the hemodynamic effects of coronary artery disease. The purpose of this study was to validate a visual scaling of the extent of angiographic collateral filling by comparison with flowmeter- and microsphere-derived measurements of collateral flow. In 12 open-chest dogs, collaterals from the circumflex artery were angiographically visualized (n = 80) by creating acute critical left anterior descending artery occlusion. The extent of collateral filling was graded in four levels from 0 = no visible filling to 3 = complete epicardial filling. Collateral filling correlated with the change in flow of the collateral supplying circumflex artery (delta Q; r = 0.84) which was + 5.3 +/- 4.6% with grade 1, + 9.1 +/- 3.5% with grade 2 and + 14.6 +/- 4.7% with grade 3 (p0.01). In parallel, coronary flow reserve decreased from 4.1 +/- 0.8 with grade 0 to 2.9 +/- 0.2 with grade 3 (p0.01). Colored microspheres were injected subselectively into the circumflex artery of 9 dogs (45 injections). The ratio of microspheres counted in the collateralized myocardium of the left anterior descending artery to the total number injected increased from 0.6 +/- 0.9% for grade 0 to 17.1 +/- 2.8% with grade 3 (p0.01). Absolute collateral flow derived from the microsphere counts averaged 5.5 +/- 0.9 ml/min with grade 3 and closely correlated with collateral filling grade (r = 0.88). Semiquantitative grading of angiographic collateral filling in response to acute coronary occlusion in a canine model correlates with an increase in collateral source artery flow, absolute collateral flow and a decrease in source artery flow reserve. These data suggest that this scale might be a simple but useful adjunct tool to assess the hemodynamic significance of a collateral circulation.

As an important clinical task, evaluating the placement of multiple coronary stents requires fine judgments of distance between stents. However, making these judgments is limited by low system resolution, noise, low contrast of the deployed stent, and stent motion during the cardiac cycle. We use task performance as a figure of merit for optimizing image display parameters. In previous work, we described our simulation procedure in detail, and also reported results of human observers for a visual task involving discrimination of 4 gap sizes under various frame rates and number of frames. Here, we report the results of three spatial model observers (i.e. NPW, NPWE, and PWMF) and two temporal sensitivity functions (i.e. transient and sustained) for the same task. Under signal known exactly conditions, we find that model observers can be used to predict human observers in terms of discrimination accuracy by adding internal noise.

We compared the ability of three model observers (nonprewhitening matched filter with an eye filter, Hotelling and channelized Hotelling) in predicting the effect of JPEG and wavelet-Crewcode image compression on human visual detection of a simulated lesion in single frame digital x-ray coronary angiograms. All three model observers predicted the JPEG superiority present in human performance, although the nonprewhitening matched filter with an eye filter (NPWE) and the channelized Hotelling models were better predictors than the Hotelling model. The commonly used root mean square error and related peak signal to noise ratio metrics incorrectly predicted a JPEG inferiority. A particular image discrimination/perceptual difference model correctly predicted a JPEG advantage at low compression ratios but incorrectly predicted a JPEG inferiority at high compression ratios. In the second part of the paper, the NPWE model was used to perform automated simulated annealing optimization of the quantization matrix of the JPEG algorithm at 25:1 compression ratio. A subsequent psychophysical study resulted in improved human detection performance for images compressed with the NPWE optimized quantization matrix over the JPEG default quantization matrix. Together, our results show how model observers can be successfully used to perform automated evaluation and optimization of diagnostic performance in clinically relevant visual tasks using real anatomic backgrounds.

We evaluate the effect on human visual detection of a display method that stabilizes the motion of the feature of interest in sequential JPEG compressed x-ray coronary angiogram images. At all levels of image compression the feature stabilized display significantly improved performance with respect to the standard display where the artery is moving. In addition, for both the moving artery and stabilized display, human performance with images compressed at 15:1 was not significantly different from performance with the uncompressed images.

The placement of multiple coronary stents requires fine judgments of distance between a deployed stent and stent/guidewire assembly. The goal of this deployment is to achieve continuous and gapless coverage between them. However, making these judgments is difficult because of limited system resolution, noise, relatively low contrast of the deployed stent, and stent motion during the cardiac cycle. In this work, we extend our previous work by investigating wider range of conditions associated with this task. The present studies consider number of frames and frame rate separately, and include stabilization of the stents as a way to quantify the performance effects of stent motion. We find that (1) stabilization reduces the uncertainty when detecting the gap size; (2) observer performance increases with the number of frames; (3) the effect of display frame rate is highly dependent on the motion of the target.

Evaluating the placement of multiple coronary stents requires fine judgments of distance between two or more deployed stents in order to determine if there is continuous coverage without a gap or overlap between the two. These judgments are made difficult by limited system resolution, noise, relatively low contrast of the deployed stent, and stent motion during the cardiac cycle. In this work, we assess the effect of frame rate and number of frames used in a sequence on the detection accuracy of gaps between the stents. Both of these factors can be used to reduce patient dose. We use real X-ray coronary angiograms as backgrounds along with stents imaged separately with Lucite for similar beam attenuation. Stents and simulated guidewires are embedded in the angiograms by adding optical densities after scatter subtraction. Realistic motion is rendered by manually synchronizing the stent densities to vascular features in each image. We find no significant difference the different frame rates or sequence lengths, indicating potential savings in dose.

Background— We describe the first human experience with a permanently implantable, direct left atrial pressure (LAP) monitoring system in ambulatory patients with chronic heart failure. Methods and Results— Eight patients with established heart failure and at least 1 heart failure hospitalization or unplanned visit for parenteral therapy in the last year underwent device implantation under fluoroscopic guidance. All subjects received aspirin 150 mg and clopidogrel 75 mg daily. Subjects measured LAP twice daily and attended a clinic regularly for data upload and device calibration. Right heart catheterization was performed at the time of device implantation and at 12 weeks. The device was implanted in all subjects with no procedural complications. At the 12-week follow-up, 87% of device LAP measurements were within ±5 mm Hg of simultaneous pulmonary capillary wedge pressure readings over a wide range of pressures (1.6 to 71 mm Hg). Net drift corrected by calibration was −0.2±1.9 mm Hg/mo. During short-term follow-up, there were no device-related complications or systemic emboli. There were no deaths, no unplanned heart failure clinic visits, and no admissions for heart failure. Conclusions— Ambulatory monitoring of direct LAP with a new implantable device was well tolerated, feasible, and accurate at a short-term follow-up. Further follow-up and investigation are warranted to evaluate the clinical utility of LAP monitoring in patients with heart failure.

An 81-year-old man with severe left ventricular dysfunction (left ventricular ejection fraction 24%), prior coronary artery bypass grafting, symptomatic heart failure (New York Heart Association class III), and an investigational percutaneously implanted permanent left atrial pressure (LAP) monitoring system (HeartPOD Savacor, Inc, Los Angeles, Calif) in situ (Figure 1) was admitted with an acute coronary syndrome. High-fidelity resting LAP waveforms were acquired at least twice daily by the …

In a previous meta-analysis of intracoronary brachytherapy (ICBT) studies, we identified the target tissue at 0.6 to 0.7 mm tissue depth and we developed two models, describing the relationship between dose and ICBT effectiveness. The purpose of the present study was to validate the identified target tissue depth and the developed dose models, using the results of 1) two prospective animal studies with ICBT, 2) a retrospective analysis of animal studies with external beam irradiation and 3) results of recent clinical ICBT trials. ICBT effectiveness in the porcine restenosis studies was quantified as inhibition of neointima proliferation. The results of these studies were correlated with the developed dose-effectiveness model. Finally, the agreement of the restenosis rates of the recent clinical trials with the developed dose-restenosis model was tested. The porcine restenosis studies demonstrated a dose-related inhibition of neointima proliferation. The radiation effectiveness of both prospective studies and the effectiveness of the studies with external beam irradiation demonstrated the best agreement with the developed dose model at a tissue depth of 0.6 mm. Furthermore, the restenosis rates of the recent clinical ICBT studies were in concordance with the developed dose-restenosis model. In conclusion, the current study validated the localization of the target tissue for ICBT at a tissue depth of 0.6 to 0.7 mm as well as the relationship between dose and ICBT effectiveness at this depth. The data provide a rationale for setting a common dose prescription point at 0.6 to 0.7 mm tissue depth.

Fluoroscopic images are degraded by scattering of x-rays from within the patient and by veiling glare in the image intensifier. Both of these degradations are well described by a response function applied to primary intensity. We can automatically estimate the parameters of the response function with the aid of a reference object placed in the imaging field. Subtraction of the true reference signal yields artifacts unless proper scatter-glare correction is performed. We adjust the scatter-glare parameters in order to minimize these artifacts. We demonstrate this technique using an anthropomorphic phantom plus additional scattering material. Root mean square error in densitometric measurements of an x-ray phantom is reduced by 54 percent compared with no correction and by 36 percent compared with subtraction of uniform scatter measured under a beam stop.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Layer decomposition is a promising technique for background removal and noise reduction in coronary angiograms. Our layer decomposition algorithm decomposes a projection image sequence into multiple 2D layers undergoing translation, rotation, and scaling. We apply this layer decomposition algorithm to simulated angiograms containing stenotic vessels with and without thrombus. We constructed 85 pairs of simulated angiographic sequences by embedding each of 5 simulated vessels (with and without thrombus) in 17 clinical angiograms. We computed the response of a matched eye filter applied to (1) one raw image of each sequence at the time of minimal motion (RAW), (2) a layered digital subtraction angiography (LDSA) image of the same frame, and (3) the time-averaged vessel layer image (LAYER). We find that on average the LAYER and LDSA images have higher signal-to-noise ration and larger area under the receiver- operator characteristic curves (AUC) than the raw images.

The objective of this randomized pilot trial with 21 patients was to evaluate the effectiveness of a rhenium-188 liquid-filled balloon system to prevent recurrent restenosis after percutaneous transluminal coronary angioplasty for in-stent restenosis. A significant benefit from brachytherapy was seen at 6-month repeat angiography, as well as during the clinical follow-up of 12 months.

Clinical validation of quantitative coronary angiography (QCA) algorithms is difficult due to the lack of a simple alternative method for accurately measuring in vivo vessel dimensions. We address this problem by embedding simulated coronary artery segments with known geometry in clinical angiograms. Our vessel model accounts for the profile of the vessel, x-ray attenuation in the original background, and noise in the imaging system. We have compared diameter measurements of our computer simulated arteries with measurements of an x-ray Telescopic-Shaped Phantom (XTSP) with the same diameters. The results show that for both uniform and anthropomorphic backgrounds there is good agreement in the measured diameters of XTSP compared to the simulated arteries (Pearson's correlation coefficient 0.99). In addition, the difference in accuracy and precision of the true diameter measures compared to the XTSP and simulated artery diameters was small (mean absolute error across all diameters was < or = 0.11 mm +/- 0.09 mm).

Low-contrast features such as thrombus, dissection, and even stents can be difficult to detect in coronary x-ray images or angiograms. For these reasons we propose to improve the clinical visualization of low-contrast structures using layer decomposition. Our method for layer decomposition models the cone-beam projections through the chest as a set of superposed layers moving with translation, rotation, and scaling. We solve for the layer motions using phase correlation methods. We solve for the layer densities by averaging along moving trajectories and subtracting new layer densities from previous layer estimates. We apply layer decomposition to clinical coronary angiograms with and without contrast material. The reconstructed vessel layer represents a motion-compensated temporal average of structures co-moving with the vessel. Subtraction of background layers from the original image sequence yields a tracked background-subtracted sequence which has no vessel-motion artifacts and almost no increase in noise, unlike standard background substraction techniques. Layer decomposition improves vessel definition and visibility of low-contrast objects in cine x-ray image sequences.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fluoroscopic images are degraded by scattering of x rays from within the patient and by veiling glare in the image intensifier. Both of these degradations are well described by a response function applied to either the scatter-free or primary intensity. The response function is variable, with dependence on such factors as patient thickness and imaging geometry. We describe an automated regularization technique for obtaining response function parameters with a minimal loss of signal. This method requires a high-transmission structured reference object to be interposed between the x-ray source and the subject. We estimate the parameters by minimizing residual correlations between the reference object and the computed subject density after a scatter-glare correction. We use simulated images to evaluate our method for both ideal and clinically realistic conditions. We find that the residual root-mean-square (rms) error ideally decreases with an increasing number of independent pixels (N) as (1/N) 1/2 . In simulated 256×256 angiograms mean normalized rms errors were reduced from 40% to 11% in noise-free images, and from 41% to 17% in noisy images, with a similar improvement in densitometric vessel cross-section measurements. These results demonstrate the validity of the method for simulated images and characterize its expected performance on clinical images.

Eigler et al (1994) proposed an optimized display for coronary angiograms where each image of the sequence is digitally shifted so that the feature of interest within an artery remains fixed at the center of the screen and the background moves (stabilized display). We measure the effect of JPEG and CREW (a wavelet-based software) image compression on the detectability of a simulated morphological feature (filling defect) for the stabilized display and compare it to the conventional moving artery display. Our results show that 15:1 compressed JPEG for the stabilized display and the moving artery display does not significantly degrade human performance but a 19:1 CREW did. The stabilized display significantly improved performance with respect to the conventional moving artery display for the uncompressed and the 15:1 JPEG but not for the 19:1 CREW.

We applied three different model observers (non-prewhitening matched filter with an eye filter, Hotelling and channelized Hotelling) to predict the effect of JPEG image compression on human visual detection of a simulated lesion (clinically known as thrombus) in single frame digital x-ray coronary angiograms. Since the model observers' absolute performance is better than human, model performance was degraded to match human performance by injecting internal noise proportional to the external noise. All three model-observers predicted reasonably well the degradation in human performance as a function of JPEG image compression, although the NPWEW and the channelized Hotelling models (with internal noise proportional to the external noise) were better predictors than the Hotelling model.

Quantitative coronary angiography (QCA) diameter measurements are important in determining the extent of coronary artery disease progression and course of treatment in a patient. Traditional QCA techniques filter the X-ray angiographic image in order to enhance the edge profiles. We investigated a new method of obtaining an edge enhancement filter based on the power spectrum of an ensemble of view specific background images for X-ray angiographic images. The band-pass filter is obtained from the power spectra of a particular view imaged with (1) background only and (2) contrast filled arteries plus background. We tested our band-pass filter by measuring the diameters of a coronary artery phantom. The angiograms were filtered with a Sobel kernel to highlight the edges. The same angiograms were band-pass filtered and then Sobel filtered to see if our band-pass filter had any effect on the accuracy of the artery diameter measurement. The mean absolute percent error of the diameter measures decreased with the use of the band-pass filter 14.2% plus or minus 16.5% (n equals 57). Two- way analysis of variance was not statistically significant between the diameter measures (0.5 - 5.0 mm) of the Sobel only filtered image compared to the band-pass edge enhancement plus Sobel filtering.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a method for decomposition of angiographic image sequences into moving layers undergoing translation, rotation, and scaling. We first describe a regularization method for scatter-glare correction which can be used to obtain good estimates of projected x-ray attenuation coefficient. We then compute a set of weighted correlation functions to determine the motion of each layer, and compute the layer densities in the spatial domain by averaging along moving trajectories. We demonstrate the utility of our method by successfully decomposing simulated angiograms into moving layers. We also demonstrate visually acceptable layer decomposition of actual angiograms.

Fluoroscopic images are degraded by scattering of x-rays from within the patient and by veiling glare in the image intensifier. Both of these degradations are well described by a response function applied to the primary intensity. If the response function is known, than an estimate of the primary component of the image can be computed by applying the inverse operation. However, the response function is actually variable, with dependence on such factors as patient thickness and imaging geometry. We describe a technique for estimating a parameterized response function so that a good estimate of the subject density profile can be recovered even if the response function parameters are not known in advance. Our method uses a partially absorbing filter with spatially varying density as a reference object which enables us to compute good estimates of the parameterized response function. We use simulated images to evaluate our method for a wide range of conditions. Our simulation results show that this technique can greatly reduce densitometric errors in fluoroscopic images.

Developing metrics of medical image quality requires an understanding of how anatomic backgrounds reduce human visual detection performance. Visual psychophysics has shown that there are two distinct ways in which a complex background can degrade performance: (1) the presence of a deterministic high-contrast background, (2) variability in the background from location to location. The authors investigated how these two sources of performance degradation reduce human visual performance locating a lesion in anatomic backgrounds.Human performance localizing a disk-shaped lesion in one of four locations (four alternative forced choice) was measured for three background conditions. In the first condition the background was a uniform gray. In the second condition (the repeated background condition) an anatomic background was sampled on each trial and used as a background for the four possible lesion locations. In the third condition (the different background condition) four different anatomic backgrounds were sampled on each trial and used for the four possible lesion locations. Test images consisted of computer simulated lesions mathematically projected on digital x-ray coronary angiograms.For five levels of lesion contrast, visual detection performance for two observers decreased significantly from the uniform background condition to the repeated background condition, and decreased even further for the different background condition.Study results show that both the presence of a deterministic high-contrast background and the background variations contribute to performance degradation of human visual detection of signals in anatomic backgrounds.

Many Receiver Operating Characteristic (ROC) studies rely on establishing "truth" (the gold standard) about lesion absence/presence on the agreement of a panel of experts (consensus expert committees). In addition, in the consensus committee methodology, images where the members of the committee did not reach any agreement aboutthe lesion absence/presence are discarded from the ROC study. But how reliable are "gold standards" established bythese expert committees? And does discarding images where no agreement was reached bias the spectrum ofdifficulty ofthe test image set for the ROC study? Computer simulated lesions (filling defects) of different strengths(signal contrasts) were embedded in real x-ray coronaiy angiogram backgrounds in order to measure the agreementamong the decisions of members of the committee as a function of signal strength, to establish the accuracy of thedecisions ofthe consensus expert conunittee and to compare it to individual more inexperienced readers.Keywords: ROC studies, gold standards, consensus expert committee, assessment of medical image quality

Model observers have been compared to human performance detecting low contrast signals in a variety of computer generated backgrounds including white noise, correlated noise, lumpy backgrounds, and two component noise. The purpose of the present paper is to extend this work by comparing a number of previously proposed model observers (non-prewhitening matched filter, non-prewhitening matched fitler model with an eye filter, Hotelling observer and channelized-Gabor Hotelling observer model) to human visual detection performance in real anatomic backgrounds (x-ray coronary angiograms). Human and model observer performance are compared as a function of increasing added white noise. Our results show that three of the four models (the non-prewhitening matched filter, the Hotelling and channelized-Gabor Hotelling) are good predictors of human performance.

The goal of this work is to demonstrate the feasibility of 3D imaging of coronary stents using fluoroscopy. This technique could potentially provide an inexpensive and non- invasive alternative to stent inspection by intravascular ultrasound. The major difficulty to e overcome is real or apparent motion of the stent between successive views. We solve this problem by tracking a feature point ont he stent prior to performing the 3D reconstruction. We shifted the images to eliminate this apparent motion, then reconstructed the 3D stent image using iterative backprojection. The stent cross-sectional images are successfully reconstructed with spatial resolution of approximately 0.4 mm. This successful reconstruction of a coronary stent in vitro demonstrates the feasibility of 3D imaging of coronary stents using fluoroscopy.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Experiments on visual detection in computer simulated noise (e.g. white noise) show that random variations from location to location in the image (due to noise) degrade human performance. Psychophysical experiments of visual detection of signals superimposed on a known deterministic background ('mask') show that human performance can be degraded by the presence of a high contrast deterministic background through divisive inhibition. The purpose of this paper is to perform a psychophysical experiment to determine the relative importance of these two sources of performance degradation (random background variations and contrast masking effects) in human visual detection in natural medical image backgrounds. The results show that both contrast masking and random background variations degrade human performance for detecting signals in natural medical image backgrounds. These results suggest that current observer models which do not include a source of degradation due to the deterministic presence of the background might need to model such effects in order to reliably predict human visual detection in natural medical image backgrounds.

We propose a novel technique for estimation of image noise amplitude without a priori signal information. Knowledge of the normalized noise distribution is used to construct an approximate Wiener filter parametrized by the estimated noise amplitude. For a given noise amplitude, the resulting signal estimate is subtracted from the image to produce a sample noise estimate. The estimated noise amplitude is varied in order to maximize the probability that the noise estimate is a sample of the known noise distribution with the estimated variance. Probability is measured by the (chi) 2 distribution. The technique is tested for several images by adding stationary zero-mean Gaussian noise with varying amplitude. The variation of estimated versus added noise variance is very nearly linear with unit slope for all of the images tested. The estimated noise variance for images with no added noise is generally small compared to the signal power unless the signal power spectrum is nearly white.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We investigate human visual detection and contrast discrimination of a moving Gabor signal in spatiotemporal white noise. We measure performance as a function of signal contrast for detection and contrast discrimination in a 4 alternative forced choice task. Observers were instructed and trained to maintain their gaze on a fixation point at all times during the experiment. The effect of signal contrast on human detection and contrast discrimination performance (d') for a moving signal in spatiotemporal noise is similar to that found for the case of a stationary signal in spatial noise. It can be described by a linear function with a positive x-intercept for detection and a 0 intercept for contrast discrimination. The difference in x-intercepts for the detection and contrast discrimination tasks are consistent with signal uncertainty. The improvement in performance with increasing number of frames is different for the detection and contrast discrimination tasks. Results show performance improvement with number of frames that saturates much later (750 - 800 msec) than would be expected from the early temporal filters (100 - 150 msec). Observers are more efficient detecting a stationary signal than a moving signal (when no eye tracking is allowed) in spatiotemporal noise. In an additional experiment where the signal interframe displacement was increased, observer performance (d') decreased with increasing interframe signal displacements dropping 50% for an interframe displacement of 70 min. of arc showing that human performance for detection of a moving signal is affected by the specific characteristics of the signal motion.

This paper investigates signal detectability in a fixed structured background as a function of signal contrast, additive white noise and feature motion. We use a 4 AFC (alternative forced choice) detection task where the signal appeared at the center of one of four identical, clearly visible, simulated cylindrical artery segments. All four segments moved identically relative to the background in 32-frame image sequences displayed at 15 frames per second. The background in one condition was uniform and in a second condition was structured noise consisting of a single frame randomly selected from a group of clinical x-ray coronary angiograms. We studied two display formats, the 'moving artery' display in which the background was stationary and the cylinders moved back and forth, simulating the motion of the coronary arteries, and the 'stabilized artery' in which each frame of the sequence was translated to keep the cylinders stationary, while the background moved back and forth. The signal to be detected was a disk superimposed at the center of one of the simulated cylinders. Signal energy and the variance of additive Gaussian spatiotemporal white noise were manipulated. For each level of additive white noise the threshold signal energy for detection (at the 82% correct performance level) was determined. There was no time limit to reach decision. For all conditions the threshold signal energy increased linearly with added white noise variance, with a positive y-intercept. The presence of the structured background increased both the y-intercept and the slope of this relationship between threshold energy and added white noise variance. Thus, the presence of the structured background had a multiplicative effect, as well as an additive effect, on the degradation of performance due to added white noise. The multiplicative effect might be modeled by an increase in induced internal noise (noise proportional to the external noise) with the presence of the structured background. Such an effect, if it occurs in the setting of clinical coronary angiography, would cause changes in radiation exposure (and thus quantum noise) to affect visual perception more than expected from experiments with white noise alone. One possible mechanism for this effect may be that the added random noise interferes with the observer's use of spatiotemporal correlations to 'subtract' or 'read around' the structured noise.

X-ray fluoroscopic images are degraded by x-ray scattering within the subject and veiling glare in the image intensifer. Densitometric accuracy is further degraded by beam hardening. Scattering, veiling glare, or both are modeled as a blurred representation of the primary image plus an offset. If the image can be represented by convolution of the primary with a known response function, then an estimate of the primary component of the image can be computed by deconvolution. We describe a technique for estimating a parameterized response function so that a good estimate of the subject density profile can be recovered even if the response function parameters are not known in advance. This is important for x-ray imaging (particularly fluoroscopy) since the acquisition parameters are variable. A reference object designed to be uncorrelated with the subject is imaged in superposition with the subject. The unknown parameters are then adjusted to minimize a cost function subject to the constraint that the correlation between the known reference density and the estimated subject density be zero. The method can be extended to include a correction for beam hardening.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.