Intravascular Ultrasound System Research Articles

A 1.11 mm2 IVUS SoC with ±50°-Range Plane Wave Transmit Beamforming at 40 MHz.

Intravascular ultrasound (IVUS) imaging catheters are significant tools for cardiovascular interventions, and their use can be expanded by realizing IVUS imaging guidewires and microcatheters. The miniaturization of these devices creates challenges in SNR due to the need for higher frequencies to provide adequate resolution. An integrated IVUS system with transmit beamforming can mitigate these limitations. This work presents the first practical highly integrated system-on-a-chip (SoC) with plane wave transmit beamforming at 40 MHz for IVUS on guidewire or microcatheters. The front-end circuitry has a 20-channel ultrasound transmitter (Tx) and receiver (Rx) array interfaced with a capacitive micromachined ultrasound transducer (CMUT) array. During each firing, all 20 Tx are excited with the same analog delay with respect to each other, which can be continuously adjusted between ~0 and 10 ns in two directions, generating a steerable plane wave in a range of ±/-50° for a phased array at 40 MHz. The unit delays are generated via a voltage-controlled delay line (VCDL), which only needs two external controls, one tuning the unit delay and the other determining the steering direction. The SoC is fabricated using a 180-nm high-voltage (HV) CMOS process and features a slender active area of 0.3 mm × 3.7 mm. The proposed SoC consumes 31.3 mW during the receiving mode. The beamformer's functionality and the SoC's overall performance were validated through acoustic characterization and imaging experiments.

Observation of plaque behavior and tissue characterization of coronary plaque using speckle tracking intravascular ultrasound (ST-IVUS) and iMap imaging system.

Tissue characterization plays an important role in the development of acute coronary syndromes. iMap is an intravascular ultrasound (IVUS) tissue characterization system that provides useful information by reconstructing color-coded maps. Mechanical properties due to dynamic mechanical stress during a cardiac cycle may also trigger vulnerable plaque. Speckle tracking IVUS (ST-IVUS) has been introduced to observe plaque behavior in relation to mechanical properties. We report the case of an 84-year-old woman with stable coronary artery disease who underwent percutaneous coronary intervention, at which time IVUS demonstrated mainly three low echoic areas like lipid pools with thick fibrous caps. Pathological evaluation with iMap revealed that one low echoic area was occupied with necrotic tissue and that the other two areas occupied fibrotic. Although those tissue characterizations were different, they showed similar stretching behavior at systole by ST-IVUS which depicted plaque behavior from IVUS images using a color mapping. The mechanical properties of individual coronary plaques may differ depending on the tissue disposition. It is necessary to consider mechanical properties using ST-IVUS as well as to evaluate tissue characterization in plaque risk stratification.

What Is Hidden Behind Yellow Pixels: from Pathology to Intravascular Imaging of Atherosclerotic Plaque.

Intravascular imaging systems can identify lipid-rich and vulnerable plaques and help in treatment guidance. The comparability of different intracoronary imaging methods remains unclear. In this paper, we review atherosclerotic plaque pathology, plaque-stabilising effects of different lipid-lowering therapies and usage of intravascular imaging modalities. We present the results of our study in which we evaluated the correlation of the intravascular ultrasound iMAP system (iMAP-IVUS) and near-infrared spectroscopy (NIRS) in the diagnosis of vulnerable coronary plaques. Lipids have an essential contribution to plaque evolution and vulnerability. Increase in plaque vulnerability alone even without increase in plaque burden defines progression of atherosclerosis. Lipidic tissue has a significant diagnostic value in patient risk stratification and can serve as a treatment target. Different vulnerable plaque parameters can be visualised with iMAP-IVUS and NIRS. Intravascular imaging systems can differ with regard to their sensitivity, specificity and limitations. Lipid-lowering therapy is crucial in plaque stabilisation.

Three-Dimensional Intravascular Ultrasound Imaging Using a Miniature Helical Ultrasonic Motor.

Existing 3-D intravascular ultrasound (IVUS) systems that combine two electromagnetic (EM) motors to drive catheters are bulky and require considerable efforts to eliminate EM interference (EMI). Here, we propose a new scanning method to realize 3-D IVUS imaging using a helical ultrasonic motor to overcome the aforementioned issues. The ultrasonic motor with compact dimensions (7-mm outer diameter and 30-mm longitudinal length), lightweight (20.5 g), and free of EMI exhibits a great application potential in mobile imaging devices. In particular, it can simultaneously perform rotary and linear motions, facilitating precise 3-D scanning of an imaging catheter. Experimental results show that the signal-to-noise ratio (SNR) of raw images obtained using the ultrasonic motor is 5.3 dB better than that of an EM motor. Moreover, the proposed imaging device exhibits the maximum rotary speed of 12.3 r/s and the positioning accuracy of 2.6 [Formula: see text] at a driving voltage of 240 Vp-p. The 3-D wire phantom imaging and 3-D tube phantom imaging are performed to evaluate the performance of the imaging device. Finally, the in vitro imaging of a porcine coronary artery demonstrates that the layered architecture of the vessel can be precisely identified while significantly increasing the SNR of the raw images.

First in‐human evaluation of a novel intravascular ultrasound and optical coherence tomography system for intracoronary imaging

AbstractAimsWe evaluated the first in‐human performance of a novel hybrid imaging catheter that permits simultaneous and co‐registered acquisition of intravascular ultrasound (IVUS) and optical coherence tomography (OCT) images.Methods and ResultsA total of 17 patients undergoing planned percutaneous coronary intervention (PCI) were imaged between August 2018 and August 2019. Eleven patients with both pre‐ and post‐PCI IVUS and OCT images were included in the offline image analysis. IVUS and OCT images were analyzed separately then together with co‐registered images for pre‐stent findings, and only separately for post‐stent findings. A total of 926 frames were analyzed (218 pre‐PCI, 708 post‐PCI). There was substantial agreement to detect calcific plaque between co‐registered IVUS‐OCT and standalone IVUS (Kappa 0.72 [0.65–0.79]) and standalone OCT (Kappa 0.75 [0.68–0.81]) while standalone imaging modalities showed lower agreement to detect lipidic and fibrotic plaques compared with co‐registered IVUS‐OCT. There were more frames with stent underexpansion on IVUS than OCT [72 (28.7%) vs. 58 (23.1%), respectively, p = 0.039]. Detection rates of incomplete stent apposition (present on 20 OCT frames vs. 2 IVUS frames, p < 0.001) and tissue protrusion (40 vs. 27 frames, p < 0.001) were higher on OCT than IVUS. One stent edge dissection was detected in the image analysis and was seen on OCT but not IVUS. All 177 frames with image artifacts contained at least one co‐registered imaging modality with interpretable diagnostic content. There were no study device‐related adverse events.ConclusionsHybrid image acquisition was safe. The availability of both IVUS and OCT changed image interpretation compared to either modality alone, suggesting a complementary role of these two techniques.

Head-to-head comparison of quantitative measurements between intravascular imaging systems: An in vitro phantom study

IntroductionThe present study aimed to compare the accuracy of quantitative measurements by contemporary intravascular imaging systems including optical frequency domain imaging (OFDI), frequency domain optical coherence tomography (FD-OCT), and 6 intravascular ultrasound (IVUS) systems.MethodsWe imaged five cylindrical phantom models made from an acrylic resin with known lumen diameters (1.51, 2.03, 3.04, 4.04, and 5.04 mm, respectively) using OFDI (FastView and LUNAWAVE, Terumo), FD-OCT (Dragonfly JP and ILUMIEN OPTIS, Abbott Vascular), and 6 mechanically rotating IVUS systems including a system, two 40-MHz, one 45-MHz, two 60-Mhz and one broad-band frequency IVUS systems. The OFDI, FD-OCT, and IVUS images were obtained using automated motorized pullback in a tank filled with 37-degree Celsius saline and, in cases of OFDI and FD-OCT, contrast-saline mixture (1:1 ratio) and contrast under the system setting of the refractive index for the corresponding flush medium.ResultsAll the imaging systems showed good accuracy and excellent precision of lumen measurement with the relative differences between the measured diameter and actual phantom diameter being ranging from −2.9% to 8.0% and minimum standard deviations of the measured diameters (≤0.02 mm).ConclusionThe present study demonstrated that contemporary intravascular imaging systems including OFDI, FD-OCT, and IVUS provided clinically acceptable accuracy and excellent precision of quantitative lumen measurement in phantom models in vitro across a wide range of dimensions. Future research to confirm these findings in vivo are warranted.

Performance of Integrated Near-Infrared Spectroscopy and Intravascular Ultrasound (NIRS-IVUS) System against Quantitative Flow Ratio (QFR)

Quantitative flow ratio (QFR) is a new opportunity to analyze functional stenosis during invasive coronary angiography. Together with a well-known intravascular ultrasound (IVUS) and a new player in the field, near-infrared spectroscopy (NIRS), it is gaining a lot of interest. The aim of the study was to compare QFR results with integrated IVUS-NIRS results acquired simultaneously in the same coronary lesion. We retrospectively enrolled 66 patients in whom 66 coronary lesions were assessed by NIRS-IVUS and QFR. Lesions were divided into two groups based on QFR results as QFR-positive group (QFR ≤ 0.8) or QFR-negative group (QFR > 0.8). Based on ROC curve analysis, the best cut-off values of minimal lumen area (MLA), minimal lumen diameter (MLD) and percent diameter stenosis for predicting QFR ≤ 80 were 2.4 (AUC 0.733, 95%CI 0.61, 0.834), 1.6 (AUC 0.768, 95%CI 0.634, 0.872) and 59.5 (AUC 0.918, 95%CI 0.824, 0.971), respectively. In QFR-positive lesions, the maxLCBI4mm was significantly higher than in QFR-negative lesions (450.12 ± 251.0 vs. 329.47 ± 191.14, p = 0.046). The major finding of the present study is that values of IVUS-MLA, IVUS-MLD and percent diameter stenosis show a good efficiency in predicting QFR ≤ 0.80. Moreover, QFR-positive lesions are characterized by higher maxLCBI4mm as compared to the QFR-negative group.

Online coregistration of intravascular ultrasound and optical coherence tomography.

Intravascular imaging using both intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have become important tools in the interventional cardiologist's armamentarium. However, in some centers, intravascular imaging is not widely employed. This is due to several reasons, including lack of training in the use of intravascular imaging. Coregistration with angiography may be a helpful tool for those that use both IVUS and OCT in the cath lab and may reduce the learning curve associated with its use. For experienced operators, coregistration can shorten procedure time and lessen contrast use, which may be particularly important when performing complex or multivessel PCI. As a research tool, coregistration can allow for accurate comparison of interval intravascular images. In this review, we will discuss how to acquire coregistered images using both IVUS and OCT systems, and the potential advantages of this technology over non-coregistered images, and indeed angiography alone.

Recent Advances in Transducers for Intravascular Ultrasound (IVUS) Imaging.

As a well-known medical imaging methodology, intravascular ultrasound (IVUS) imaging plays a critical role in diagnosis, treatment guidance and post-treatment assessment of coronary artery diseases. By cannulating a miniature ultrasound transducer mounted catheter into an artery, the vessel lumen opening, vessel wall morphology and other associated blood and vessel properties can be precisely assessed in IVUS imaging. Ultrasound transducer, as the key component of an IVUS system, is critical in determining the IVUS imaging performance. In recent years, a wide range of achievements in ultrasound transducers have been reported for IVUS imaging applications. Herein, a comprehensive review is given on recent advances in ultrasound transducers for IVUS imaging. Firstly, a fundamental understanding of IVUS imaging principle, evaluation parameters and IVUS catheter are summarized. Secondly, three different types of ultrasound transducers (piezoelectric ultrasound transducer, piezoelectric micromachined ultrasound transducer and capacitive micromachined ultrasound transducer) for IVUS imaging are presented. Particularly, the recent advances in piezoelectric ultrasound transducer for IVUS imaging are extensively examined according to their different working mechanisms, configurations and materials adopted. Thirdly, IVUS-based multimodality intravascular imaging of atherosclerotic plaque is discussed. Finally, summary and perspectives on the future studies are highlighted for IVUS imaging applications.

A Novel Highly-Efficient Amplification Scheme for Wireless Communications in a CathLab Environment

Wireless communication systems are being considered for medical applications to facilitate the doctors' operation and the quality of the medical procedures. A demonstrative example of this is the catheterization laboratory (CathLab), where it is desirable to replace the existent wired connections by wireless alternatives. However, there are some challenging requirements that need to be fulfilled by the wireless link, especially for intra-vascular ultra-sound (IVUS) systems, since the images acquired by the catheter should be transmitted with very high data rate and low latency, together with the highest possible amplification efficiency, to increase the battery life. The communication requirements can be achieved with latest the Wi-Fi standard IEEE 802.11ax (Wi-Fi 6). However, since Wi-Fi is based on orthogonal frequency division multiplexing (OFDM) waveforms, the transmitted signals present high envelope fluctuations, leading to amplification difficulties due to the nonlinear distortion effects and low energy efficiency. In this paper, we present an innovative amplification scheme named quantized digital amplification (QDA). It is shown that the QDA allows a quasi-linear amplification of IEEE 802.11ax signals while maintaining a very high energy efficiency. To demonstrate this, a QDA prototype and a set of performance results, regarding both the linearity of the transmitted signals and the energy efficiency, are presented.

Automated Quantitative Assessment of Coronary Calcification Using Intravascular Ultrasound

Coronary calcification represents a challenge in the treatment of coronary artery disease by stent placement. It negatively affects stent expansion and has been related to future adverse cardiac events. Intravascular ultrasound (IVUS) is known for its high sensitivity in detecting coronary calcification. At present, automated quantification of calcium as detected by IVUS is not available. For this reason, we developed and validated an optimized framework for accurate automated detection and quantification of calcified plaque in coronary atherosclerosis as seen by IVUS. Calcified lesions were detected by training a supported vector classifier per IVUS A-line on manually annotated IVUS images, followed by post-processing using regional information. We applied our framework to 35 IVUS pullbacks from each of the three commonly used IVUS systems. Cross-validation accuracy for each system was >0.9, and the testing accuracy was 0.87, 0.89 and 0.89 for the three systems. Using the detection result, we propose an IVUS calcium score, based on the fraction of calcium-positive A-lines in a pullback segment, to quantify the extent of calcified plaque. The high accuracy of the proposed classifier suggests that it may provide a robust and accurate tool to assess the presence and amount of coronary calcification and, thus, may play a role in image-guided coronary interventions.

Plaque volume reduction after drug-coated balloon angioplasty for superficial femoral artery lesion.

Paclitaxel has a potentially beneficial effect on atherosclerotic plaque volume reduction; however, data about plaque volume reduction in real-world practice are scarce. We herein report a case whose plaque volume of superficial femoral artery was analyzed using high-definition intravascular ultrasound just after endovascular treatment using drug-coated balloon and at 6months after the procedure. From analysis using a quantitative intravascular ultrasound analysis system, the lumen volume was enlarged (from 2909.2 to 4944.1mm3) as a result of not only vessel volume enlargement (from 7242.0 to 8296.3mm3) but also plaque volume reduction (from 4332.8 to 3352.2mm3).

Tip Detection Method Using the New IVUS Facilitates the 3-Dimensional Wiring Technique for CTO Intervention

ObjectivesThis study assessed the efficacy of the tip detection method during intravascular ultrasound (IVUS)–based 3-dimensional (3D) wiring with a new chronic total occlusion (CTO)–specific IVUS system (AnteOwl IVUS [AO-IVUS]) for CTO percutaneous coronary intervention (PCI). BackgroundThe study developed angiography-based 3D wiring for CTO-PCI. Previously, the authors produced a short-tip CTO-specific IVUS system (Navifocus WR IVUS [Navi-IVUS]), which has been upgraded into the AO-IVUS system by adding a pullback transducer system for IVUS-based 3D wiring. MethodsA CTO lesion 20 mm in length composed of 2.5% agar was experimentally inserted into the coronary artery of a beating heart model. The target (a microcatheter with a 0.6-mm lumen) was placed in the distal part of the CTO lesion. IVUS-guided wiring was performed to insert the guidewire into the target using the Navi-IVUS and then using the AO-IVUS 8 times each. In wiring with AO-IVUS, the IVUS-based 3D wiring using the tip detection method was performed. The crossing time and the number of punctures to the target were calculated. ResultsThe crossing time was significantly shortened and the number of punctures was significantly reduced in AO-IVUS–based wiring compared with Navi-IVUS–based wiring (median crossing time 80.5 s [interquartile range: 44.0 to 112.3 s] vs. 333.0 s [interquartile range: 88.8 to 790.0 s]; p = 0.036; median 1.0 puncture [interquartile range: 1.0 to 2.0 punctures] vs. 24.0 punctures [interquartile range: 5.8 to 52.5 punctures]; p = 0.001). ConclusionsThe tip detection method enables the authors to easily perform the IVUS-based 3D wiring, and the new CTO IVUS system will facilitate this method in clinical practice.

Hemorrhoidal disease: is a Vascular Problem? An Up-to-date Approach Based on Intravascular Ultrasound and Iliac Venous System Stenting.

Hemorrhoidal disease: is a Vascular Problem? An Up-to-date Approach Based on Intravascular Ultrasound and Iliac Venous System Stenting.

Single-Crystal High-Frequency Intravascular Ultrasound Transducer With 40-$\mu$ m Axial Resolution

Intravascular ultrasound (IVUS) is one of the most useful tools available today to assist intravascular stenting procedures. Having higher resolution is very important for helping doctors to evaluate the nature of atherosclerotic plaques. The current commercial IVUS systems have a spatial resolution of 70- [Formula: see text] in the axial direction and 200- [Formula: see text] in the lateral direction, which are insufficient for accurate diagnosis. We report here a three-matching-layer IVUS transducer design using a 0.72Pb(Mg1/3Nb2/3O3 - 0.28PbTiO3 single crystal, which can improve the axial resolution to [Formula: see text] without sacrificing the penetration depth. Wire phantom imaging and in vitro porcine coronary artery imaging show noticeably better axial resolution and similar penetration depth compared with a commercial IVUS transducer.

Modifying whole blood oxygen levels via acoustic droplet vaporization nucleated with an intravascular ultrasound system

Modifying whole blood oxygen levels via acoustic droplet vaporization nucleated with an intravascular ultrasound system

Deconvolution in Intravascular Ultrasound to Improve Lateral Resolution.

Intravascular ultrasound (IVUS) is an important diagnostic method for coronary disease. The lateral and axial resolutions of IVUS systems under study are typically ~120 and ~30 µm, respectively. The lateral resolution has a lower quality than the axial one and is restricted by the aperture size of transducers. In addition, this resolution is difficult to further improve physically. However, IVUS is inherently suitable for lateral deconvolution because of its circular imaging area. In this paper, magnitude-based deconvolution was demonstrated to be feasible in IVUS imaging to improve the lateral resolution. The deconvolution process was first simulated to determine the highest feasible resolution. Next, the method was applied to a real system to validate the feasibility. The lateral resolution was improved significantly, that is, 2°-separated targets could be discerned using a transducer with 4.2° -6 dB lateral resolution.

Intravascular ultrasound-guided drug-eluting stent implantation.

Intravascular ultrasound (IVUS) enhances diagnostic assessment with identification and characterization of plaque morphology. Determination of predominant plaque morphology prior to percutaneous coronary intervention can guide optimal treatment strategy. The transducers used with IVUS catheters include solid-state, phased array systems that have multiple stationary transducers, or rotational, mechanical IVUS systems that have a single transducer that rotates on a driveshaft. Real-time online analysis with IVUS allows determination of lumen and vessel size, guiding appropriate stent selection. Following stent implantation, IVUS can assess for parameters that include stent malapposition, underexpansion, and stent edge complications. Multiple stent sizing and stent optimization strategies have been proposed. Clinical data have supported the use of IVUS for improved periprocedural and long-term outcomes, and recent guidelines have evolved to reflect this benefit. Nonetheless, worldwide utilization of intravascular imaging remains low. IVUS has particular benefit in a number of complex lesion subsets including lesions involving the left main coronary artery, severe calcification or in-stent restenosis. The use of IVUS may allow for the reduction of total contrast volume used during percutaneous coronary interventions. Intravascular imaging plays a critical role in procedural planning and stent optimization in the drug-eluting stent era. Greater utilization of IVUS for the treatment of complex lesions may further improve outcomes with drug-eluting stents.

A new nonparametric statistical approach to detect lumen and Media-Adventitia borders in intravascular ultrasound frames

Intravascular ultrasound (IVUS) imaging is widely known as a powerful interventional imaging modality for diagnosing atherosclerosis, and for treatment planning. In this regard, the detection of lumen and media–adventitia (MA) borders is considered to be a vital process. However, the manual detection of these two borders by the physician is cumbersome due to the large number of frames in a sequence. In addition, no approved universal automatic method has been presented so far due to the great diversity in the appearance of the coronary artery in the images acquired by different IVUS systems. To this end, the present study aimed to provide a new border search theory on the radial profile, based upon the nonparametric statistical approach, and to develop a generic and fully automatic three-step process for extracting the lumen and MA borders in IVUS frames based on the proposed theory. Thereafter, the proposed theory and three-step process were evaluated on synthetic images, as well as on a test set of standard publicly available images, respectively. The results showed that our three-step process could segment the borders with ≥0.82 and with ≥0.75 Jaccard measure (JM) to manual borders in IVUS frames acquired by the 20 MHz and 40 MHz probes, respectively. Based on the results, the lumen and MA borders can be extracted automatically, and the border extraction process can be implemented in parallel for a polar image due to the capability of the present proposed method to estimate the borders for each angle independently.

A molecular intravascular ultrasound contrast agent allows detection of activated platelets on the surface of symptomatic human plaques

Background and aimsActivated platelets are amongst the most attractive imaging targets in atherosclerosis due to their important role in early processes of atherogenesis and thrombus formation. We developed a molecular intravascular ultrasound (IVUS) approach to detect activated platelets ex vivo on the surface of human plaques, using an IVUS system applied in clinical routine. MethodsHuman carotid endarterectomy specimens were obtained directly from the operating room and exposed to artificial arterial flow conditions for incubation with the contrast agent. This consists of microbubbles (MB), which are linked to an antibody against the ligand induced binding site (LIBS) of the activated platelet glycoprotein IIb/IIa, and a sialyl Lewis polymer (SL), which mediates binding to selectins (LIBS-SL-MB). IVUS was performed pre and post incubation with LIBS-SL-MB and after rinsing with PBS. In comparison, IVUS was performed pre and post incubation with MBs linked to an unspecific control antibody and a dysfunctional polymer (control-MB). All imaging results were correlated to histology findings. ResultsIVUS imaging showed a high signal enhancement after administration of LIBS-SL-MB. After rinsing with PBS, the signal enhancement remained stable. Immunofluorescence and immunohistochemistry confirmed significant binding of microbubbles to thrombi on the plaque surface. Moreover, thrombus size and number of bound MBs correlated well. ConclusionsLIBS-SL-MB allows ex vivo IVUS imaging of even small numbers of activated platelets on the surface of human carotid endarterectomy specimens. This diagnostic approach could deliver valuable additional information for risk stratification of atherosclerotic plaques, especially since we apply a clinically well-established IVUS imaging system.