Intravascular Ultrasound Frames Research Articles

Five multiresolution-based calcium volume measurement techniques from coronary IVUS videos: A comparative approach

Background and objectiveFast intravascular ultrasound (IVUS) video processing is required for calcium volume computation during the planning phase of percutaneous coronary interventional (PCI) procedures. Nonlinear multiresolution techniques are generally applied to improve the processing time by down-sampling the video frames. MethodsThis paper presents four different segmentation methods for calcium volume measurement, namely Threshold-based, Fuzzy c-Means (FCM), K-means, and Hidden Markov Random Field (HMRF) embedded with five different kinds of multiresolution techniques (bilinear, bicubic, wavelet, Lanczos, and Gaussian pyramid). This leads to 20 different kinds of combinations. IVUS image data sets consisting of 38,760 IVUS frames taken from 19 patients were collected using 40 MHz IVUS catheter (Atlantis® SR Pro, Boston Scientific®, pullback speed of 0.5 mm/sec.). The performance of these 20 systems is compared with and without multiresolution using the following metrics: (a) computational time; (b) calcium volume; (c) image quality degradation ratio; and (d) quality assessment ratio. ResultsAmong the four segmentation methods embedded with five kinds of multiresolution techniques, FCM segmentation combined with wavelet-based multiresolution gave the best performance. FCM and wavelet experienced the highest percentage mean improvement in computational time of 77.15% and 74.07%, respectively. Wavelet interpolation experiences the highest mean precision-of-merit (PoM) of 94.06 ± 3.64% and 81.34 ± 16.29% as compared to other multiresolution techniques for volume level and frame level respectively. Wavelet multiresolution technique also experiences the highest Jaccard Index and Dice Similarity of 0.7 and 0.8, respectively. Multiresolution is a nonlinear operation which introduces bias and thus degrades the image. The proposed system also provides a bias correction approach to enrich the system, giving a better mean calcium volume similarity for all the multiresolution-based segmentation methods. After including the bias correction, bicubic interpolation gives the largest increase in mean calcium volume similarity of 4.13% compared to the rest of the multiresolution techniques. The system is automated and can be adapted in clinical settings. ConclusionsWe demonstrated the time improvement in calcium volume computation without compromising the quality of IVUS image. Among the 20 different combinations of multiresolution with calcium volume segmentation methods, the FCM embedded with wavelet-based multiresolution gave the best performance.

Reliable and Accurate Calcium Volume Measurement in Coronary Artery Using Intravascular Ultrasound Videos.

Quantitative assessment of calcified atherosclerotic volume within the coronary artery wall is vital for cardiac interventional procedures. The goal of this study is to automatically measure the calcium volume, given the borders of coronary vessel wall for all the frames of the intravascular ultrasound (IVUS) video. Three soft computing fuzzy classification techniques were adapted namely Fuzzy c-Means (FCM), K-means, and Hidden Markov Random Field (HMRF) for automated segmentation of calcium regions and volume computation. These methods were benchmarked against previously developed threshold-based method. IVUS image data sets (around 30,600 IVUS frames) from 15 patients were collected using 40 MHz IVUS catheter (Atlantis® SR Pro, Boston Scientific®, pullback speed of 0.5 mm/s). Calcium mean volume for FCM, K-means, HMRF and threshold-based method were 37.84 ± 17.38 mm(3), 27.79 ± 10.94 mm(3), 46.44 ± 19.13 mm(3) and 35.92 ± 16.44 mm(3) respectively. Cross-correlation, Jaccard Index and Dice Similarity were highest between FCM and threshold-based method: 0.99, 0.92 ± 0.02 and 0.95 + 0.02 respectively. Student's t-test, z-test and Wilcoxon-test are also performed to demonstrate consistency, reliability and accuracy of the results. Given the vessel wall region, the system reliably and automatically measures the calcium volume in IVUS videos. Further, we validated our system against a trained expert using scoring: K-means showed the best performance with an accuracy of 92.80%. Out procedure and protocol is along the line with method previously published clinically.

Genetic fuzzy rule based classification systems for coronary plaque characterization based on intravascular ultrasound images

Vascular tissue characterization is of great importance concerning the possibility of an Acute Cardiac Syndrome (ACS). Gray-scale intravascular ultrasound (IVUS) is a powerful tomographic modality providing a thorough visualization of coronary arteries. Among the existing methods, virtual histology (VH) is the most popular and clinically available technique for plaque component analysis. IVUS-VH though suffers from a poor longitudinal resolution due to the electrocardiogram (ECG)-gated frame acquisition. In order to surmount this demerit, a new image-based methodology for plaque assessment is suggested in this paper that differentiates tissue components into four classes: calcium, necrotic core, fibrous and fibro-lipid. The available IVUS frames characterized by VH are used for plaque labeling. In addition, a rich set of five textural feature families are extracted from IVUS images and computed at different scales. To increase the discrimination capabilities between the classes, all features are combined into an integrated feature vector. The classification of plaque types is accomplished using a genetic fuzzy rule-based classification system (GFRBCS) that is able to handle effectively highly-dimensional feature spaces. The incorporated feature selection mechanism along with the rule extraction algorithm allows the creation of compact fuzzy rule bases with enhanced classification accuracy. The high interpretability properties of our classifier assist physicians to gain a deeper insight regarding the impact of features involved in the evaluation of atherosclerotic plaques. An extensive experimental analysis is carried out, where various tests are performed in order to highlight the advantages of the proposed scheme against existing methods of the literature, including other GRBCSs and the support vector machine (SVM) classifier. In particular, the attained results show that the applied classifier exhibits better generalization capabilities than the competing methods, i.e., higher accuracy in characterizing unseen IVUS images.

Long-term effects of maximally intensive statin therapy on changes in coronary atheroma composition: insights from SATURN

To evaluate the effect of long-term maximally intensive statin therapy on indices of coronary atheroma composition in a randomized trial, and how these changes relate to modifications of serum lipoproteins and systemic inflammation. The Study of coronary Atheroma by inTravascular Ultrasound: the effect of Rosuvastatin vs. atorvastatiN (SATURN) employed serial intravascular ultrasound (IVUS) measures of coronary atheroma in patients treated with rosuvastatin 40 mg or atorvastatin 80 mg daily for 24 months. Seventy-one patients underwent serial assessment of indices of plaque composition by spectral analysis of the radiofrequency IVUS signal. Changes in low-density lipoprotein cholesterol [LDL-C; -52 (-72, -33) mg/dL, P < 0.001], C-reactive protein [CRP -0.2 (-1, 0.1) mg/L, P = 0.01], and high-density lipoprotein cholesterol [HDL-C; +2.8 (-0.3, 7.8) mg/dL, P < 0.001] were associated with regression of percent atheroma volume (PAV: -1.6 ± 3.6%, P < 0.001). A reduction in estimated fibro-fatty tissue volume accompanied atheroma regression (P < 0.001), while dense calcium tissue volume increased (P = 0.002). There were no changes in fibrous or necrotic core tissue volumes. Volumetric changes in necrotic core tissue correlated with on-treatment HDL-C (r = -0.27, P = 0.03) and CRP (r = 0.25, P = 0.03) levels. A per-lesion analysis showed a reduction in the number of pathological intimal thickening lesions (defined by ≥3 consecutive IVUS frames containing PAV of ≥40%, predominantly fibro-fatty plaque, with <10% confluent necrotic core and <10% confluent dense calcium) at follow-up (67 vs. 38, P = 0.001). Fibroatheromas and fibrotic lesions remained static in number. Changes in indices of atheroma composition accompany regression of coronary atheroma with maximally intensive statin therapy, and associate with anti-inflammatory effects of statins. NCT000620542.

Reconstruction of coronary vessels from intravascular ultrasound image sequences based on compensation of the in-plane motion

A three-dimensional vessel model is reconstructed by fusing the cross-sectional information of vascular lumen detected from intravascular ultrasound (IVUS) frames with the spatial geometry of the ultrasonic catheter recovered from a pair of nearly orthogonal X-ray angiograms. This model is closer to the actual morphology than those reconstructed from angiograms or IVUS images alone because of the complementarity between angiography and IVUS in imaging coronary vessels. This study proposes a method to reconstruct the coronary vessels from an electrocardiogram (ECG)-gated IVUS image sequence and simultaneously acquired angiograms. The spatial orientation of each cross-section of the vascular lumen detected from IVUS frames was determined through quantitatively compensating the in-plane rigid motion caused by cardiac cycles. Independent validation of the determination of the IVUS spatial orientation with synthetic data was performed. A limited validity study including the back-projection validation and morphology measures with in vivo image data (five datasets) was performed to evaluate quantitatively the reconstruction accuracy.

TCT-305 Correlation Between Predicted to Observed Coronary Drug-Eluting Stent (DES) Expansion as Determined by Intravascular Ultrasound (IVUS): Variance Between Stent Platforms and Impact of Lesion Characteristics

Manufacturer-predicted stent expansion is based on in-vitro testing. Actual expansion is related to stent architecture, lesion characteristics, etc. We evaluated the relationships between these variables on coronary DES expansion via IVUS. 1,652 IVUS frames were acquired and blindly analyzed in 56

A Novel Semiautomated Atherosclerotic Plaque Characterization Method Using Grayscale Intravascular Ultrasound Images: Comparison With Virtual Histology

Intravascular ultrasound (IVUS) virtual histology (VH-IVUS) is a new technique, which provides automated plaque characterization in IVUS frames, using the ultrasound backscattered RF-signals. However, its computation can only be performed once per cardiac cycle (ECG-gated technique), which significantly decreases the number of characterized IVUS frames. Also atherosclerotic plaques in images that have been acquired by machines, which are not equipped with the VH software, cannot be characterized. To address these limitations, we have developed a plaque characterization technique that can be applied in grayscale IVUS images. Our semiautomated method is based on a three-step approach. In the first step, the plaque area [region of interest (ROI)] is detected semiautomatically. In the second step, a set of features is extracted for each pixel of the ROI and in the third step, a random forest classifier is used to classify these pixels into four classes: dense calcium, necrotic core, fibrotic tissue, and fibro-fatty tissue. In order to train and validate our method, we used 300 IVUS frames acquired from virtual histology examinations from ten patients. The overall accuracy of the proposed method was 85.65% suggesting that our approach is reliable and may be further investigated in the clinical and research arena.

Virtual Histology Intravascular Ultrasound Analysis of Non-Culprit Attenuated Plaques Detected by Grayscale Intravascular Ultrasound in Patients With Acute Coronary Syndromes

Noncalcific attenuated plaques identified by grayscale intravascular ultrasound (IVUS) are often seen in patients with acute coronary syndromes and have been associated with no reflow and creatine kinase-MB elevation after percutaneous coronary intervention. Histopathology has shown cholesterol clefts, microcalcification, or organized thrombus. One hundred twenty-four vessels in 64 patients with acute coronary syndromes from the PROSPECT trial were identified for inclusion in the present analysis. After excluding 4 vessels with severe calcification, 9 vessels with <40% plaque burden, and 3 vessels with too few (<3) virtual histology (VH)-IVUS frames for analysis, complete grayscale IVUS and VH-IVUS was available for 108 vessels in 64 patients that contained 39 VH-IVUS thin-capped fibroatheromas (VH-TCFA), 40 thick-capped fibroatheromas (VH-ThFA), and 33 pathologic intimal thickening but no fibrotic or fibrocalcific plaques. Overall, there were 47 grayscale IVUS attenuated plaques in 43 vessels. Compared to the minimum luminal sites of the remaining 65 vessels (controls), attenuated plaques contained larger necrotic core areas (1.5 +/- 0.9 vs 0.9 +/- 0.8 mm(2) in controls, p = 0.001). Fibroatheromas (VH-TCFA or VH-ThFA) were more common at the sites of attenuated plaques than at control sites (VH-TCFA 42.5% vs 29.2%, VH-ThFA 53.2% vs 23.1%, pathologic intimal thickening 4.3% vs 47.7%, p <0.0001). In conclusion, grayscale IVUS attenuated plaques are associated with a large amount of VH-IVUS necrotic core and are markers of the presence of fibroatheromas (VH-TCFA or VH-ThFA). This may explain the biologic instability of these lesions.

3D elastic registration of vessel structures from IVUS data on biplane angiography 1

Planar angiograms and intravascular ultrasound (IVUS) imaging provide important insight for the evaluation of atherosclerotic diseases and blood flow abnormalities. The construction of realistic three-dimensional models is essential to efficiently follow the progression of arterial plaque. This requires an explicit localization of IVUS frames from angiograms. Because of the difficulties encountered when trying to track the position of an IVUS transducer, we propose an elastic registration approach that relies on a virtual catheter path. Deformable surface models of the lumen and external wall are constructed from segmented IVUS contours. A crude registration is obtained using a three-dimensional vessel centerline, reconstructed from two calibrated angiograms. Robust optimization of the virtual catheter path, position, absolute orientation, and regulation of the external wall shape is performed until near-perfect alignment of the back-projected silhouettes on image edges is reached. Visual assessment of the reconstructed vessels showed a good superposition of virtual models on the angiograms. We measured a 0.4-mm residual error value. A preliminary study of convergence properties on 15 datasets showed that initial absolute orientation may affect the solution. However, for follow-ups, coherent solutions were found among datasets. The advantages of the virtual catheter path approach are demonstrated. Future work will look at ways to single out the true solution with a better use of the available information in both modalities and additional validation studies on improved datasets.

Basic ultrasonic characteristics of atherosclerosis measured by intravascular ultrasound and acoustic microscopy

Basic ultrasonic properties of atherosclerotic specimens excised by directional coronary atherectomy (DCA) were measured by in vivo intravascular ultrasound (IVUS) tissue velocity imaging and in vitro acoustic microscopy. Two-dimensional tissue velocity and strain were calculated by the template-matching method of two consecutive IVUS frames. A specially developed acoustic microscope system with 200 MHz frequencies showed the basic ultrasonic parameters of tissue components in atherosclerosis and the presence of macrophages. The integration of both methodologies helped to understand ultrasonic tissue characterization of vulnerable plaque in coronary arteries and the pathophysiology of atherosclerosis.

A 3D computer graphics approach to brachytherapy planning.

Intravascular brachytherapy (IVB) can significantly reduce the risk of restenosis after interventional treatment of stenotic arteries, if planned and applied correctly. In order to facilitate computer-based IVB planning, a three-dimensional reconstruction of the stenotic artery based on intravascular ultrasound (IVUS) sequences is desirable. For this purpose, the frames of the IVUS sequence are properly aligned in space, possible gaps inbetween the IVUS frames are filled by interpolation with radial basis functions known from scattered data interpolation. The alignment procedure uses additional information which is obtained from biplane X-ray angiography performed simultaneously during the capturing of the IVUS sequence. After IVUS images and biplane angiography data are acquired from the patient, the vessel-wall borders and the IVUS catheter are detected by an active contour algorithm. Next, the twist (relative orientation) between adjacent IVUS frames is determined by a sequential triangulation method. The absolute orientation of each frame is established by a stochastic analysis based on anatomical landmarks. Finally, the reconstructed 3D vessel model is visualized by methods of combined volume and polygon rendering. The reconstruction is then used for the computation of the radiation-distribution within the tissue, emitted from a beta-radiation source. All these steps are performed during the percutaneous intervention.

Registration of Biplane Angiography and Intravascular Ultrasound for 3D Vessel Reconstruction

If planned and applied correctly, intra-vascular brachytherapy (IVB) can significantly reduce the risk of restenosis after interventional treatment of stenotic arteries. In order to facilitate computer-based IVB planning, a three-dimensional reconstruction of the stenotic artery based on intravascular ultrasound (IVUS) sequences is desirable. To attain a 3D reconstruction, the frames of the IVUS sequence are properly aligned in space and completed with additional intermediate frames generated by interpolation. The alignment procedure uses additional information that is obtained from biplane X-ray angiography performed simultaneously during the capturing of the IVUS sequence. After IVUS images and biplane angiography data are acquired from the patient, the vessel-wall borders and the IVUS catheter are detected by an active contour algorithm. Next, the twist between adjacent IVUS frames is determined by a sequential triangulation method combined with stochastic analysis. The above procedure results in a 3D volume-model of the vessel, which also contains information from the IVUS modality. This data is sufficient for computer-based intravascular brachytherapy planning. The proposed methodology can be used to improve the current state-of-the-art IVB treatment planning by enabling computerized dosage computations on a highly accurate 3D model.

Three-dimensional coronary artery reconstruction using fusion of intravascular ultrasound and biplane angiography

We have developed an efficient method for 3D reconstruction of coronary arteries. Our approach is based on the fusion of intravascular ultrasound (IVUS) and biplane angiography. The method includes an efficient algorithm for the automatic identification of the regions of interest in IVUS images and a novel methodology for the extraction of the catheter path from biplane angiographies. The estimation of IVUS frames relative twist and the computation of first IVUS frame absolute orientation is also investigated. To assess the performance of the method, a validation procedure is introduced. Several metrics are obtained to verify the reliability of our method in the description of coronary artery morphology.

Geometrically correct 3-D reconstruction of intravascular ultrasound images by fusion with biplane angiography--methods and validation.

In the rapidly evolving field of intravascular ultrasound (IVUS), the assessment of vessel morphology still lacks a geometrically correct three-dimensional (3-D) reconstruction. The IVUS frames are usually stacked up to form a straight vessel, neglecting curvature and the axial twisting of the catheter during the pullback. Our method combines the information about vessel cross-sections obtained from IVUS with the information about the vessel geometry derived from biplane angiography. First, the catheter path is reconstructed from its biplane projections, resulting in a spatial model. The locations of the IVUS frames are determined and their orientations relative to each other are calculated using a discrete approximation of the Frenet-Serret formulas known from differential geometry. The absolute orientation of the frame set is established, utilizing the imaging catheter itself as an artificial landmark. The IVUS images are segmented, using our previously developed algorithm. The fusion approach has been extensively validated in computer simulations, phantoms, and cadaveric pig hearts.

Fusion of angiography and intravascular ultrasound in vivo: establishing the absolute 3-D frame orientation.

Data fusion of biplane angiography and intravascular ultrasound (IVUS) facilitates geometrically correct reconstruction of coronary vessels. The locations of IVUS frames along the catheter pullback trajectory can be identified, however the IVUS image orientations remain ambiguous. An automated approach to determination of correct IVUS image orientation in three-dimensional space is reported. Analytical calculation of the catheter twist is followed by statistical optimization determining the absolute IVUS image orientation. The fusion method was applied to data acquired in patients undergoing routine coronary intervention, demonstrating the feasibility and good performance of our approach.

Towards a geometrically correct 3-D reconstruction of tortuous coronary arteries based on biplane angiography and intravascular ultrasound.

At present, 3-D reconstructions of coronary vessels are generated from intravascular ultrasound (IVUS) by stacking up ECG-gated segmented IVUS frames of a pullback sequence. This simplified approach always results in straight vessel reconstructions and, therefore, gives an incorrect representation of tortuous coronary arteries. A more realistic reconstruction of tortuous vessels may be obtained by data fusion with biplane angiography. The 3-D course of the vessel is first derived from the angiograms and then combined with the segmented IVUS images. In this paper, we focus on two problems associated with the data fusion method: The definition of the pullback path and the estimation of the IVUS catheter twist during pullback. A robust algorithm for calculation of tortuosity-induced catheter twist is reported that is based on sequential triangulation of the 3-D pullback path. The method is analyzed with computer simulations and validated in helical vessel phantoms. A largely automated data fusion approach is proposed and applied to tortuous coronary arteries in cadaveric pig hearts.