Noncontrast Myocardial Characterization in Acute Myocardial Infarction Using Electron Density Imaging.

PURPOSE: Spectral computed tomography (CT) enables improved tissue characterization, although virtually all research has focused on contrast-enhanced examinations. We hypothesized that changes in myocardial tissue related to acute myocardial infarction (AMI) might potentially be identified without the need for contrast administration using electron density (ED) imaging. PATIENTS AND METHODS: This retrospective observational study involved a small series (n = 15) of patients admitted to our institution with a first AMI without signs of hemodynamic instability and identification of a culprit vessel with invasive coronary angiography during the same admission, who also underwent a noncontrast, low-dose chest CT using a dual-layer spectral CT scanner. Images were assessed in search of dark areas with low density on ED imaging, and the mean percentage ED relative to water (%EDW) was calculated. RESULTS: Using a qualitative approach, ED assessment enabled the identification of 11/15 (73%) affected coronary territories, with a sensitivity of 73% (95% CI: 45; 92%) and a specificity of 87% (95% CI: 69; 96%). AMI segments showed significantly lower ED values than the remote myocardium (103.8 ± 0.8 vs 104.3 ± 0.6 %EDW, P < 0.0001), and a threshold below 103.9 %EDW had a sensitivity of 66% and specificity of 79% for the identification of AMI. In a control group of patients without a history of cardiovascular disease, none had areas with focal reduction of ED following the shape of the myocardial wall. CONCLUSIONS: In our preliminary series, ED imaging showed the potential to enable the identification of myocardial tissue changes related to AMI without iodinated contrast requirement.

Diagnostic accuracy of virtual non-contrast CT for aortic valve stenosis severity evaluation.

BACKGROUND: Computed tomography aortic valve calcium (AVC) score has accepted value for diagnosing and predicting outcomes in aortic stenosis (AS). Multi-energy CT (MECT) allows virtual non-contrast (VNC) reconstructions from contrast scans. We aim to compare the VNC-AVC score to the true non-contrast (TNC)-AVC score for assessing AS severity. METHODS: We prospectively included patients undergoing a MECT for transcatheter aortic valve replacement (TAVR) planning. TNC-AVC was acquired before contrast, and VNC-AVC was derived from a retrospectively gated contrast-enhanced scan. The Agatston scoring method was used for quantification, and linear regression analysis to derive adjusted-VNC values. RESULTS: Among 109 patients (55% female) included, 43% had concordant severe and 14% concordant moderate AS. TNC scan median dose-length product was 116 â€‹mGy∗cm. The median TNC-AVC was 2,107 AU (1,093-3,372), while VNC-AVC was 1,835 AU (1293-2,972) after applying the coefficient (1.46) and constant (743) terms. A strong correlation was demonstrated between methods (r â€‹= â€‹0.93; p â€‹< â€‹0.001). Using accepted thresholds (>1,300 AU for women and >2,000 AU for men), 65% (n â€‹= â€‹71) of patients had severe AS by TNC-AVC and 67% (n â€‹= â€‹73) by adjusted-VNC-AVC. After estimating thresholds for adjusted-VNC (>1,564 AU for women and >2,375 AU for men), 56% (n â€‹= â€‹61) had severe AS, demonstrating substantial agreement with TNC-AVC (κ â€‹= â€‹0.77). CONCLUSIONS: MECT-derived VNC-AVC showed a strong correlation with TNC-AVC. After adjustment, VNC-AVC demonstrated substantial agreement with TNC-AVC, potentially eliminating the requirement for an additional scan and enabling reductions in both radiation exposure and acquisition time.

Evaluation of image quality and radiation dose at prospective ECG-triggered axial 256-slice multi-detector CT in infants with congenital heart disease.

BACKGROUND: There are a limited number of reports on the technical and clinical feasibility of prospective electrocardiogram (ECG)-gated multi-detector computed tomography (MDCT) in infants with congenital heart disease (CHD). OBJECTIVE: To evaluate image quality and radiation dose at weight-based low-dose prospectively gated 256-slice MDCT angiography in infants with CHD. MATERIALS AND METHODS: From November 2009 to February 2010, 64 consecutive infants with CHD referred for pre-operative or post-operative CT were included. All were scanned on a 256-slice MDCT system utilizing a low-dose protocol (80 kVp and 60-120 mAs depending on weight: 60 mAs for ≤ 3 kg, 80 mAs for 3.1-6 kg, 100 mAs for 6.1-10 kg, 120 mAs for 10.1-15 kg). RESULTS: No serious adverse events were recorded. A total of 174 cardiac deformities, confirmed by surgery or heart catheterization, were studied. The sensitivity of MDCT for cardiac deformities was 97.1%; specificity, 99.4%; accuracy, 95.9%. The mean heart rate during scan was 136.7 ± 14.9/min (range, 91-160) with a corresponding heart rate variability of 2.8 ± 2.2/min (range, 0-8). Mean scan length was 115.3 ± 11.7 mm (range, 93.6-143.3). Mean volume CT dose index, mean dose-length product and effective dose were 2.1 ± 0.4 mGy (range, 1.5-2.8), 24.7 ± 5.9 mGy·cm (range, 14.7-35.8) and 1.6 ± 0.3 mSv (range, 1.1-2.5), respectively. Diagnostic-quality images were achieved in all cases. Satisfactory diagnostic quality for visualization of all/proximal/distal coronary artery segments was achieved in 88.4/98.8/80.0% of the scans. CONCLUSION: Low-dose prospectively gated axial 256-slice CT angiography is a valuable tool in the routine clinical evaluation of infants with CHD, providing a comprehensive three-dimensional evaluation of the cardiac anatomy, including the coronary arteries.

Antihypertensive therapy and regression of coronary artery disease: insights from the Comparison of Amlodipine versus Enalapril to Limit Occurrences of Thrombosis (CAMELOT) and Norvasc for Regression of Manifest Atherosclerotic Lesions by Intravascular Sonographic Evaluation (NORMALISE) trials.

BACKGROUND: In patients with coronary artery disease (CAD), therapies designed to prevent clinical events are not always associated with significant reduction in coronary obstruction, as measured by quantitative coronary angiography. We set out to explore the relationship between quantitative coronary angiography parameters, baseline characteristics, and clinical events in a large trial of CAD regression with antihypertensive agents. METHODS AND RESULTS: Patients randomized to amlodipine, enalapril, or placebo in the CAMELOT trial were followed for 24 months for major ischemic events. Among 431 patients participating in the angiographic and intravascular ultrasound substudy NORMALISE, 298 (99 amlodipine, 96 enalapril, and 103 placebo) had complete angiographic and intravascular ultrasound data. The patients did not differ significantly with respect to baseline characteristics (except for diabetes) or extent of CAD. After 24 months, the change in minimal lumen diameter (MLD) was -0.02 +/- 0.13 for amlodipine, -0.03 +/- 0.12 for enalapril, and -0.03 +/- 0.17 mm for placebo (P = .40). Major ischemic events occurred in 20.2%, 24%, and 25.2%, respectively (P = .68). There was no significant correlation between change in MLD and age, sex, statin therapy, or systolic blood pressure at baseline. The change in MLD did not differ in patients with and without cardiovascular events, regardless of treatment assignment (P = .54). Only the extent of CAD was independently predictive of ischemic events. CONCLUSION: As compared to placebo, amlodipine treatment resulted in fewer ischemic events after 24 months of therapy, but the clinical benefit was not associated with a commensurate improvement in arterial lumen dimensions.

Improved sensitivity of computed tomography towards iodine and gold nanoparticle contrast agents via iterative reconstruction methods.

Computed tomography is a widely used medical imaging technique that has high spatial and temporal resolution. Its weakness is its low sensitivity towards contrast media. Iterative reconstruction techniques (ITER) have recently become available, which provide reduced image noise compared with traditional filtered back-projection methods (FBP), which may allow the sensitivity of CT to be improved, however this effect has not been studied in detail. We scanned phantoms containing either an iodine contrast agent or gold nanoparticles. We used a range of tube voltages and currents. We performed reconstruction with FBP, ITER and a novel, iterative, modal-based reconstruction (IMR) algorithm. We found that noise decreased in an algorithm dependent manner (FBP > ITER > IMR) for every scan and that no differences were observed in attenuation rates of the agents. The contrast to noise ratio (CNR) of iodine was highest at 80 kV, whilst the CNR for gold was highest at 140 kV. The CNR of IMR images was almost tenfold higher than that of FBP images. Similar trends were found in dual energy images formed using these algorithms. In conclusion, IMR-based reconstruction techniques will allow contrast agents to be detected with greater sensitivity, and may allow lower contrast agent doses to be used.

Eptifibatide and low-dose tissue plasminogen activator in acute myocardial infarction: the integrilin and low-dose thrombolysis in acute myocardial infarction (INTRO AMI) trial.

OBJECTIVES: This study was designed to test the hypothesis that eptifibatide and reduced-dose tissue plasminogen activator (t-PA) will enhance infarct artery patency at 60 min in patients with acute myocardial infarction (AMI). BACKGROUND: Combination fibrin and platelet lysis improves epicardial and myocardial reperfusion in AMI. METHODS: Patients were enrolled in a dose finding (Phase A, n = 344) followed by a dose confirmation (Phase B, n = 305) protocol. All patients received aspirin and weight-adjusted heparin and underwent angiography at 60 and 90 min. In Phase A, eptifibatide in a single or double bolus (30 min apart) of 180, 180/90 or 180/180 microg/kg followed by an infusion of 1.33 or 2.0 microg/kg per min was sequentially added to 25 or 50 mg of t-PA. In Phase B, patients were randomized to: 1) double-bolus eptifibatide 180/90 (30 min apart) and 1.33 microg/kg per min infusion with 50 mg t-PA (Group I); 2) 180/90 (10 min apart) and 2.0 g/kg per min with 50 mg t-PA (Group II); or 3) full-dose, weight-adjusted t-PA (Group III). RESULTS: In Phase A, the best rate of Thrombolysis In Myocardial Infarction (TIMI) flow grade 3 was achieved using 180/90/1.33 microg/kg per min eptifibatide with 50 mg t-PA: 65% and 78% at 60 and 90 min, respectively. In Phase B, the incidence of TIMI flow grade 3 at 60 min was 42%, 56% and 40%, for Groups I through III, respectively (p = 0.04, Group II vs. Group III). The median corrected TIMI frame count was 38, 33 and 50, respectively (p = 0.02). TIMI major bleeding was reported in 8%, 11% and 6%, respectively; intracranial hemorrhage occurred in 1%, 3% and 2% of patients (p > 0.5 for both). The incidences of death (4%, 5% and 7%), reinfarction or revascularization at 30 days were similar among the three treatment groups. CONCLUSIONS: In comparison with standard t-PA regimen, double-bolus eptifibatide (10 min apart) with a 48-h infusion and half-dose t-PA (Group II) is associated with improved quality and speed of reperfusion. The safety profile of this therapy is similar to that of other combination regimens.

Relation of myocardial perfusion to mortality after primary percutaneous coronary intervention.

In patients who undergo primary percutaneous coronary intervention (PCI), poor post-PCI myocardial blush is associated with increased mortality, even when epicardial perfusion is adequate. This observation has important implications for the methods of evaluating primary PCI results and the strategies used to improve myocardial reperfusion.

Individualized reduction of radiation dose with a chest circumference-adapted technique and iterative reconstructions in 256-slice retrospective and prospective ECG-triggered computed tomography coronary angiography.

PURPOSE: To assess the impact of chest circumference (CC)-adjusted tube current and iterative reconstructions (iDose) on individualized radiation dose reduction and image quality (IQ) in ECG-triggered computed tomography coronary angiography (CTCA). MATERIALS AND METHODS: A total of 102 patients underwent retrospectively ECG-triggered CTCA utilizing CC-adapted tube current [mAs=1000×(0.051×CC-23.765)/900] and filtered back projection (FBP) reconstruction (group A). On the basis of the CC-adjusted tube current technique, 54 patients (group B) underwent retrospective ECG-triggered CTCA with a 20% mAs reduction compared with group A and 90 patients (group C) underwent prospective ECG-triggered CTCA with an 80% mAs reduction compared with group A; both groups B and C were reconstructed with FBP and iDose. Subjective IQ was assessed, and image noise, signal-to-noise, and contrast-to-noise ratios (SNR and CNR) were quantified. RESULTS: Patients in group A had the highest radiation dose, followed by group B and group C. iDose provided decreased image noise and increased SNR and CNR, as did subjective IQ. The image noise was higher and SNR and CNR in group B were obviously lower than those in group A with FBP, but in group B, iDose4 increased the mean objective IQ. There was no difference between group B with iDose and group A with FBP, as was the case with subjective IQ. CONCLUSION: The combination of a CC-adapted technique, prospective triggering, and partial iterative reconstruction techniques reduces the radiation dose significantly, without significant degradation of IQ.

Low-dose, wide-detector array thoracic aortic CT angiography using an iterative reconstruction technique results in improved image quality with lower noise and fewer artifacts.

BACKGROUND: Iterative reconstruction techniques (IRTs) may improve image quality for low-dose imaging compared with filtered back projection (FBP) reconstruction. OBJECTIVES: We compared the results of an IRT for low-dose thoracic aortic computed tomography (CT) imaging with those from FBP reconstruction. METHODS: Data from 50 patients who underwent 256-slice CT for evaluation of the thoracic aorta were reconstructed with FBP and an IRT (iDose(4)) at 3 noise-reduction strengths (levels 2, 4, and 6). A blinded reader graded image quality (scale, 1-5; 5 = high diagnostic confidence) and the extent of shoulder artifact (scale, 1-5; 5 = no artifact) on all reconstructions. A second reader evaluated a subset of 20 cases to determine interreader and intrareader reproducibility. The mean and SD of attenuation were measured at 5 locations along the thoracic aorta and both subclavian arteries. RESULTS: Image noise (SD of attenuation) improved with IRT relative to FBP (aorta: FBP, 31.4 ± 8.6 HU; IRT level 2, 25.1 ± 6.9 HU; level 4, 21.7 ± 6.2 HU; level 6, 17.2 ± 5.4 HU; P < 0.0001; subclavian arteries: FBP, 92.7 ± 34.6 HU; IRT level 2, 50.1 ± 17.1 HU; level 4, 48.9 ± 18.6 HU; level 6, 45.2 ± 19.2 HU; P < 0.0001), whereas mean attenuation was unchanged. Increasing image quality was observed in the aorta and through the shoulders as the contribution from IRT to the final images increased (P < 0.0001). Significant differences were noted between readers in image quality assessment of the aorta but not through the shoulders. CONCLUSION: IRT is associated with reduced noise and shoulder artifact and allows for low-dose aortic CT imaging.

Individualized radiation dose control in 256-slice CT coronary angiography (CTCA) in retrospective ECG-triggered helical scans: using a measure of body size to adjust tube current selection.

PURPOSE: To reduce radiation dose for retrospective ECG-triggered helical 256-slice CTCA by determining an optimal body size index to prospectively adjust tube current. METHODS: 102 consecutive patients with suspected CAD underwent retrospective ECG-triggered CTCA using 256-slice CT scanner. Six body size indexes including BMI, nipple level (NL) bust, thoracic anteroposterior diameter at NL, chest circumference (CC) at NL, left main and right coronary artery (RCA) origin level were measured and their correlation with noise was evaluated using linear regression. An equation was developed to use this index to adjust tube current. Additional 102 consecutive patients were scanned with the index-based mAs adjustment. A t-test for independent samples was used to compare radiation dose levels with and without the index-based mAs selection method. RESULTS: Linear regression indicated that CC RCA had the best correlation with noise (R2=0.603). Effective radiation dose was reduced from 16.6±0.9 to 9.8±2.7 mSv (p<0.01), i.e. 40.9% lower dose with the CC RCA-adapted tube current method. The image quality scores indicated no significant difference with and without the size-based mAs selection method. CONCLUSION: An accessible measure of body size, such as CC RCA, can be used to adapt tube current for individualized radiation dose control.

Segmentation of the heart and great vessels in CT images using a model-based adaptation framework.

Recently, model-based methods for the automatic segmentation of the heart chambers have been proposed. An important application of these methods is the characterization of the heart function. Heart models are, however, increasingly used for interventional guidance making it necessary to also extract the attached great vessels. It is, for instance, important to extract the left atrium and the proximal part of the pulmonary veins to support guidance of ablation procedures for atrial fibrillation treatment. For cardiac resynchronization therapy, a heart model including the coronary sinus is needed. We present a heart model comprising the four heart chambers and the attached great vessels. By assigning individual linear transformations to the heart chambers and to short tubular segments building the great vessels, variable sizes of the heart chambers and bending of the vessels can be described in a consistent way. A configurable algorithmic framework that we call adaptation engine matches the heart model automatically to cardiac CT angiography images in a multi-stage process. First, the heart is detected using a Generalized Hough Transformation. Subsequently, the heart chambers are adapted. This stage uses parametric as well as deformable mesh adaptation techniques. In the final stage, segments of the large vascular structures are successively activated and adapted. To optimize the computational performance, the adaptation engine can vary the mesh resolution and freeze already adapted mesh parts. The data used for validation were independent from the data used for model-building. Ground truth segmentations were generated for 37 CT data sets reconstructed at several cardiac phases from 17 patients. Segmentation errors were assessed for anatomical sub-structures resulting in a mean surface-to-surface error ranging 0.50-0.82mm for the heart chambers and 0.60-1.32mm for the parts of the great vessels visible in the images.

Guidance of percutaneous coronary interventions by multidetector row computed tomography coronary angiography.

Guidance of percutaneous coronary interventions (PCI) by intravascular ultrasound (IVUS) provides more precise information in terms of quantitative measurement and qualitative assessment of coronary artery disease (CAD) than does conventional angiography. Several studies have tested the efficacy of IVUS to guide stent implantation. However, the conflicting results have left behind a continued debate as to whether IVUS-guided PCI has an impact on clinical outcome and angiographic restenosis. IVUS and computed tomography coronary angiography (CTCA) share the ability to evaluate the lumen along with the vessel wall, enabling characterisation of proximal and distal reference segments. Nevertheless, IVUS imaging is expensive and usually precluded in severe stenoses. In the present article, we discuss the potential application of CTCA for the guidance of PCI, particularly of complex lesions such as chronic total occlusions (CTO) and bifurcations.

Accuracy of low-dose prospectively gated axial coronary CT angiography for the assessment of coronary artery stenosis in patients with stable heart rate.

BACKGROUND: Desirable methods for cardiac CT angiography would both reduce radiation exposure from cardiac CT angiography and preserve accuracy. OBJECTIVES: We assessed image quality, radiation dose, and diagnostic accuracy of a low-dose, prospectively gated axial cardiac CT angiography protocol for the evaluation of patients with suspected coronary artery disease (CAD). METHODS: Fifty consecutive patients referred for diagnostic invasive coronary angiography (ICA) and with a stable heart rate < 60 beats/min after beta-blocker administration were prospectively enrolled in a single center study. Subjects underwent CT angiography with a 64-row multidetector CT scanner with a prospectively gated axial imaging protocol. If the examination was determined to be nondiagnostic, then a retrospectively gated helical scan was performed. Two reviewers independently assessed image quality and the presence of significant coronary artery stenosis (>50%). RESULTS: Prospectively gated CT angiography was successfully performed in 46 of 50 patients. Of 794 coronary segments, 777 were determined to be of diagnostic image quality. The overall patient-based sensitivity (95% CI), specificity, positive predictive value, negative predictive value, and accuracy for the diagnosis of significant coronary stenosis were 100% (87%-100%), 75% (53%-90%), 81% (64%-93%), 100% (81%-100%), and 88% (81%-95%), respectively. The mean effective radiation dose for CT angiography and ICA were 3.4 +/- 0.4 mSv and 6.9 +/- 0.8 mSv, respectively. CONCLUSIONS: Cardiac CT angiography performed in a prospectively gated axial mode with 64-row multidetector CT provides an accurate, low-dose alternative for the detection of CAD.

The relation between extent of coronary artery disease measured by quantitative coronary angiography and changes in lipid profile: insights from trials of atherosclerosis regression.

BACKGROUND: While favorable changes in atherogenic lipids are indisputably associated with improved clinical outcomes, a similar correlation with quantitative coronary angiography (QCA) parameters is more difficult to document. OBJECTIVE: To assess the relation between changes in lipid profile and parameters of coronary artery disease (CAD) extent measured by QCA. METHODS: We evaluated 1,315 patients enrolled in trials of atherosclerosis regression and correlated their lipid profile with annualized changes in CAD score (average minimal lumen diameter for all segments evaluated), cumulative stenosis score (sum of stenoses for all segments evaluated) and average plaque area for all segments evaluated. RESULTS: During the study, average low-density lipoprotein (LDL) decreased by 28% (p < 0.001), and average high-density lipoprotein (HDL) increased by 8% (p < 0.001). There was no statistical correlation between annualized changes in CAD score and change in LDL (p = 0.31) or % change in LDL (p = 0.53). There was also no statistically significant correlation between change in cumulative stenosis score and change in LDL (p = 0.20) or % change in LDL (p = 0.10). Neither of these parameters of CAD extent correlated with the summation of % changes in LDL and HDL (p = 0.80 and p = 0.34, respectively). Patients with CAD regression (i.e., greater average MLD at follow up, n = 756) had similar LDL, HDL and C-reactive protein levels while on therapy as patients with CAD progression (n = 555). CONCLUSIONS: Detailed analysis of CAD extent by QCA did not reveal a significant association with changes in lipid profile. These findings challenge the use of QCA as a surrogate endpoint for the effect of antiatherosclerotic therapy.

Influence of coronary artery stenosis severity and coronary collateralization on extent of chronic myocardial scar: insights from quantitative coronary angiography and delayed-enhancement MRI.

OBJECTIVES: In patients with chronic ischemic heart disease, the relationship between coronary artery lesion severity and myocardial scarring is unknown.The purpose of this study was to examine the relationship between proximal coronary artery stenosis severity, the amount of coronary collateralization, and myocardial scar extent in the distal distribution of the affected coronary artery based on both quantitative coronary angiography (QCA) and delayed-enhancement magnetic resonance imaging (DE-MRI). METHODS: Thirty-four patients (26 males, 8 females; age range: 35-86 years) with a coronary artery containing a single, proximal stenosis >/=30% by quantitative coronary angiography (QCA) underwent DE-MRI. The relationship between stenosis severity, collateralization, and myocardial scar morphology (area, transmurality and patchiness) was examined using linear mixed-model ANCOVA. RESULTS: There was a statistically significant correlation between stenosis severity and scar extent (r=0.53, p<0.01). Patients with hemodynamically significant stenoses (>/=70%) exhibited significantly greater collateralization (p<0.05) and scar extent (p<0.01) than patients with <70% stenosis. However, scarring was often found in patients with stenoses <70%. Also, greater stenosis severity (93+/-14%) and mean scar extent (41+/-35%) were found in patients with collaterals than in patients without collaterals (diameter stenosis 48+/-10%, p<0.01) (scar extent 19+/-29%, p=0.01). CONCLUSIONS: Using QCA and DE-MRI, we demonstrate a significant relationship between coronary artery stenosis severity and myocardial scar extent, in the absence of a documented history of acute infarction. The relationship likely reflects increasing ischemia leading to scar formation in the range of angiographically significant stenosis. However, in the absence of collateralization, scar was observed without significant stenosis, especially in females.

Variable sac behavior after endovascular repair of abdominal aortic aneurysm: analysis of core laboratory data.

OBJECTIVES: The behavior of the aneurysm sac after endovascular grafting has been the subject of significant speculation. The importance of sac behavior is manifested by the correlation between aneurysm size or size change and risk for rupture, and potentially further extrapolated to define the need for secondary intervention. This study was undertaken to define graft-specific differences and the effect of endoleak on sac remodeling. METHODS: Core laboratory data were obtained for three US Phase II clinical trials. Patients were included if they met anatomic inclusion criteria and underwent placement of the latest version of a bifurcated endovascular prosthesis. Unsupported Dacron (Ancure), supported Dacron (Zenith), and expanded polytetrafluoroethylene (Excluder) grafts were evaluated. Digitized images were electronically assessed for aneurysm size (area, maximum, minimum diameter) with National Institutes of Health Image software. Two blinded reviewers analyzed each radiographic study to ensure accurate image selection and establish the presence or absence of endoleak. A third reviewer adjudicated discrepancies. chi(2) analysis and mixed nonlinear modeling were used to analyze the results. RESULTS: Of 1506 patients evaluated, 723 (227 Ancure, 343 Excluder, 153 Zenith) met inclusion criteria for the study. Mean follow-up was 23.2 months (Ancure, 31.3 months; Excluder, 19.6 months; Zenith, 19.3 months). The incidence of any endoleak was 39.1% (Ancure, 58.1%; Excluder, 34.7%; Zenith, 20.9%; P <.001). Type of prosthesis, presence or absence of endoleak, and baseline size were determinants of rate of aneurysm shrinkage. Reduction in sac size was greatest with the Zenith graft, followed by the Ancure and Excluder grafts. Presence of endoleak had a moderating effect on rate of sac shrinkage with the Zenith and Ancure grafts; however, sac size increased in the presence of endoleak with the Excluder graft. Finally, baseline size was positively correlated with rate of aneurysm shrinkage. CONCLUSIONS: The behavior of the aneurysm sac depends on the type of prosthesis, presence or absence of endoleak, and baseline size of the sac. Differential sac behavior must be considered when determining the need for secondary interventions, timing follow-up studies, and assessing success or failure of endovascular repair.