Intravascular Ultrasound Imaging System Research Articles

FPGA Implementation of Digital Coordinate Conversion of Intravascular Ultrasound Imaging System Based on CORDIC Algorithm

In order to facilitate doctors to better obtain cardiovascular images by using intravascular ultrasound imaging system and make a more accurate diagnosis, a digital coordinate conversion method of intravascular ultrasound imaging system based on CORDIC algorithm is proposed, it converts polar coordinates into rectangular coordinates through angular rotation and orientation calculation. The experimental simulation test is carried out on the platform of intravascular ultrasound imaging system by FPGA. Experimental simulation shows that, CORDIC algorithm can effectively output sine and cosine values, compared with the traditional table finding method, this algorithm has faster speed, stronger real-time performance and needs less hardware resources. It is more suitable for intravascular ultrasound imaging system.

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.

Golay-Coded Excitations for Rotational Intravascular Ultrasound Imaging

Intravascular ultrasound (IVUS) imaging employs high imaging frequencies (from 20 to 60 MHz) to visualize microvascular structures by sacrificing the depth of penetration with an increased signal attenuation. To compensate for the reduced echo signal-to-noise ratio, chirp-coded excitations, which require complex system configurations in high-frequency ultrasound imaging, are considered as suitable methods for rotational IVUS. Golay-coded excitations, which only need simple electronics and have no range sidelobe artifacts if the incident locations of the Golay pair are the same, have not been considered for rotational IVUS. In this study, computer simulations and experiments with a custom-made IVUS imaging system running at 30 fps are performed to investigate on the optimal operational conditions of Golay-coded excitations in rotational IVUS imaging. While the code length was not a significant factor affecting the range sidelobe level (RSLL), a change in the imaging frequency from 25 MHz to 66 MHz increased the RSLL from -65 dB to -45 dB with 2048 beamlines. In addition, an increase in the number of beamlines from 64 to 2048 reduced the RSLL from -17 dB to -50 dB in the simulation and from -14 dB dB to -38 dB in the experiment. To further decrease the RSLL, a weighted averaging method that compressed the coded pulse was proposed. The RSLL could be suppressed from -50 dB to -80 dB and from -38 dB to -53 dB in the simulation and experiment, respectively. Golay-coded excitation imaging was also successfully demonstrated on freshly harvested pig coronary arteries.

An FPGA-Based Backend System for Intravascular Photoacoustic and Ultrasound Imaging.

The integration of intravascular ultrasound (IVUS) and intravascular photoacoustic (IVPA) imaging produces an imaging modality with high sensitivity and specificity which is particularly needed in interventional cardiology. Conventional side-looking IVUS imaging with a single-element ultrasound (US) transducer lacks forward-viewing capability, which limits the application of this imaging mode in intravascular intervention guidance, Doppler-based flow measurement, and visualization of nearly, or totally blocked arteries. For both side-looking and forward-looking imaging, the necessity to mechanically scan the US transducer limits the imaging frame rate, and therefore, array-based solutions are desired. In this paper, we present a low-cost, compact, high-speed, and programmable imaging system based on a field-programmable gate array suitable for dual-mode forward-looking IVUS/IVPA imaging. The system has 16 US transmit and receive channels and functions in multiple modes including interleaved photoacoustic (PA) and US imaging, hardware-based high-frame-rate US imaging, software-driven US imaging, and velocity measurement. The system is implemented in the register-transfer level, and the central system controller is implemented as a finite-state machine. The system was tested with a capacitive micromachined ultrasonic transducer array. A 170-frames-per-second (FPS) US imaging frame rate is achieved in the hardware-based high-frame-rate US imaging mode while the interleaved PA and US imaging mode operates at a 60-FPS US and a laser-limited 20-FPS PA imaging frame rate. The performance of the system benefits from the flexibility and efficiency provided by the low-level implementation. The resulting system provides a convenient backend platform for research and clinical IVPA and IVUS imaging.

Implementation of a backend system for real-time intravascular ultrasound imaging

Implementation of a backend system for real-time intravascular ultrasound imaging

PMN-PT Single Crystal Ultrasonic Transducer With Half-Concave Geometric Design for IVUS Imaging.

As the key component of intravascular ultrasound (IVUS) imaging systems, traditional commercial side-looking IVUS transducers are flat and unfocused, which limits their lateral resolution. We propose a PMN-PT single crystal IVUS transducer with a half-concave geometry. This unique configuration makes it possible to conduct geometric focusing at a desired depth. To compare performances, the proposed and the traditional flat transducer with similar dimensions were fabricated. We determined that the half-concave transducer has a slightly higher center frequency (35MHz), significantly broader -6dB bandwidth (54%) but a higher insertion loss (-22.4dB) compared to the flat transducer (32MHz, 28%, and -19.3dB, respectively). A significant enhancement of the lateral resolution was also confirmed. The experimental results are in agreement with the finite element simulation results. This preliminary investigation suggests that the half-concave geometry design is a promising approach in the development of focused IVUS transducers with broad bandwidth and high lateral resolution.

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.

Intravascular Ultrasound Imaging With Virtual Source Synthetic Aperture Focusing and Coherence Factor Weighting.

Intravascular ultrasound (IVUS) has been frequently used for coronary artery imaging clinically. More importantly, IVUS is the fundamental image modality for most advanced multimodality intravascular imaging techniques, since it provides a more comprehensive picture of vessel anatomy on which other imaging data can be superimposed. However, image quality in the deeper region is poor because of the downgraded lateral resolution and contrast-to-noise ratio (CNR). In this paper, we report on the application of an ultrasound beamforming method that combines virtual source synthetic aperture (VSSA) focusing and coherence factor weighting (CFW) to improve the IVUS image quality. The natural focal point of conventional IVUS transducer was treated as a virtual source that emits spherical waves within a certain region. Mono-static synthetic aperture focusing was conducted to achieve higher resolution. Coherence factor was calculated using delayed RF signals and applied to the synthesized beam to increase the CNR and focusing quality. The proposed method was tested through simulations in Field II and imaging experiments in both linear and rotational scans. The lateral resolution for linear scan mode is improved from 165-524 to 126-143 μm ; resolution for rotational scan mode improves by up to 42%. CNR improvement by up to 1.5 was observed on the anechoic cysts of different sizes and at different locations. Herein, it is demonstrated that the beamforming method, which combines VSSA and CFW, can significantly improve the IVUS image quality. This approach can be readily integrated into the current IVUS imaging system for enhanced clinical diagnosis.

Micro ultrasound motor with coiled stator for rotationally driving of ultrasound beam of Intravascular ultrasound imaging system

For the purpose of performing radial scanning by rotating ultrasound beam in intravascular ultrasound imaging system for diagnosing the state of thrombus and stenosis in a blood vessel such as the coronary arteries of the heart, we are developing micro Coiled Stator UltraSound Motor (CS-USM). Three types of coiled stators with materials of titanium, stainless steel or copper were prepared. These coiled stators were 5 wound acoustic waveguide with 0.5 mm width and 0.1 mm thickness. Size of coiled stator is 0.9 mm diameter and 3 mm length. PZT ceramic vibrator or hydrothermal PZT film vibrator was employed. When two vibrators-type inner rotor CS-USM having stainless steel coiled stator were driven by voltage of 30Vpp at 311 kHz, rotational speed was 3500 rpm, torque was 0.34μNm. Maximum rotational speed of one vibrator-type inner rotor CS-USM having hydrothermal PZT film was 1100 rpm. Maximum rotational speed of one vibrator-type inner rotor CS-USM with titanium or stainless steel coiled stator was 2400 rpm. Rotational speed of the one vibrator-type inner rotor CS-USM with copper coiled stator driven by same conditions was 3200rpm. Maximum rotational speed of two vibrator-type outer rotor CS-USM with stainless steel coiled stator and PZT ceramic vibrators was 1400 rpm.

Towards a Reduced-Wire Interface for CMUT-Based Intravascular Ultrasound Imaging Systems.

Having intravascular ultrasound (IVUS) imaging capability on guide wires used in cardiovascular interventions may eliminate the need for separate IVUS catheters and expand the use of IVUS in a larger portion of the vasculature. High frequency capacitive micro machined ultrasonic transducer (CMUT) arrays should be integrated with interface electronics and placed on the guide wire for this purpose. Besides small size, this system-on-a-chip (SoC) front-end should connect to the back-end imaging system with a minimum number of wires to preserve the critical mechanical properties of the guide wire. We present a 40 MHz CMUT array interface SoC, which will eventually use only two wires for power delivery and transmits image data using a combination of analog-to-time conversion (ATC) and an impulse radio ultra-wideband (IR-UWB) wireless link. The proof-of-concept prototype ASIC consumes only 52.8 mW and occupies 4.07 [Formula: see text] in a 0.35- [Formula: see text] standard CMOS process. A rectifier and regulator power the rest of the SoC at 3.3 V from a 10 MHz power carrier that is supplied through a 2.4 m micro-coax cable with an overall efficiency of 49.1%. Echo signals from an 8-element CMUT array are amplified by a transimpedance amplifier (TIA) array and down-converted to baseband by quadrature sampling using a 40 MHz clock, derived from the power carrier. The ATC generates pulse-width-modulated (PWM) samples at 2 × 10 MS/s with 6 bit resolution, while the entire system achieved 5.1 ENOB. Preliminary images from the prototype system are presented, and alternative data transmission and possible future directions towards practical implementation are discussed.

In Vivo Evaluation of the Potential of High-Frequency Ultrasound for Arthroscopic Examination of the Shoulder Joint

Accurate arthroscopic evaluation of cartilage lesions could significantly improve the outcome of repair surgery. In this study, we investigated for the first time the potential of intra-articular ultrasound as an arthroscopic tool for grading cartilage defects in the human shoulder joint in vivo and compared the outcome to results from arthroscopic evaluation and magnetic resonance imaging findings. A total of 26 sites from 9 patients undergoing routine shoulder arthroscopy were quantitatively evaluated with a clinical intravascular (40MHz) ultrasound imaging system, using the regular arthroscopy portals. Reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB), and ultrasound roughness index (URI) were calculated, and high-resolution ultrasound images were obtained per site. Each site was visually graded according to the International Cartilage Repair Society (ICRS) system. "Ultrasound scores" corresponding to the ICRS system were determined from the ultrasound images. Magnetic resonance imaging was conducted and cartilage integrity at each site was classified into 5 grades (0 = normal, 4 = severely abnormal) by a radiologist. R and IRC were lower at sites with damaged cartilage surface (P = 0.033 and P = 0.043, respectively) and correlated with arthroscopic ICRS grades (r s = -0.444, P = 0.023 and r s = -0.426, P = 0.03, respectively). Arthroscopic ICRS grades and ultrasound scores were significantly correlated (rs = 0.472, P = 0.015), but no significant correlation was found between magnetic resonance imaging data and other parameters. The results suggest that ultrasound arthroscopy could facilitate quantitative clinical appraisal of articular cartilage integrity in the shoulder joint and provide information on cartilage lesion depth and severity for quantitative diagnostics in surgery.

CRT-600.00 Tissue Characteristics of Culprit Lesion and Myocardial Tissue-level Perfusion in Non-ST-segment Elevation Acute Coronary Syndromes: Novel Findings from the IMAP-ACS-II Study Using 40-MHz Radiofrequency Intravascular Ultrasound Imaging System

The impact of tissue characteristics of culprit lesion on myocardial tissue-level perfusion in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) has not been elucidated. The IMAP-ACS-II study was a prospective observational study to investigate the relationship between pre-percutaneous

Multi-frequency intravascular ultrasound (IVUS) imaging.

Acute coronary syndrome (ACS) is frequently associated with the sudden rupture of a vulnerable atherosclerotic plaque within the coronary artery. Several unique physiological features, including a thin fibrous cap accompanied by a necrotic lipid core, are the targeted indicators for identifying the vulnerable plaques. Intravascular ultrasound (IVUS), a catheter-based imaging technology, has been routinely performed in clinics for more than 20 years to describe the morphology of the coronary artery and guide percutaneous coronary interventions. However, conventional IVUS cannot facilitate the risk assessment of ACS because of its intrinsic limitations, such as insufficient resolution. Renovation of the IVUS technology is essentially needed to overcome the limitations and enhance the coronary artery characterization. In this paper, a multi-frequency intravascular ultrasound (IVUS) imaging system was developed by incorporating a higher frequency IVUS transducer (80 to 150 MHz) with the conventional IVUS (30-50 MHz) system. The newly developed system maintains the advantage of deeply penetrating imaging with the conventional IVUS, while offering an improved higher resolution image with IVUS at a higher frequency. The prototyped multifrequency catheter has a clinically compatible size of 0.95 mm and a favorable capability of automated image co-registration. In vitro human coronary artery imaging has demonstrated the feasibility and superiority of the multi-frequency IVUS imaging system to deliver a more comprehensive visualization of the coronary artery. This ultrasonic-only intravascular imaging technique, based on a moderate refinement of the conventional IVUS system, is not only cost-effective from the perspective of manufacturing and clinical practice, but also holds the promise of future translation into clinical benefits.

Characterization of in-stent neointimal tissue components following drug-eluting stent implantation according to the phase of restenosis using a 40-MHz intravascular ultrasound imaging system

Background and purposeIt is known that drug-eluting stents (DESs) are associated with in-stent restenosis (ISR). However, the characteristics of neointimal tissue components according to the mechanism and time course of DES ISR have not been fully examined. The aim of this study was to characterize the in-stent neointimal tissue components according to the phase of restenosis using radiofrequency signals from 40-MHz intravascular ultrasound (IVUS), called iMAP-IVUS (Boston Scientific Corp., Fremont, CA, USA). MethodsIVUS examinations were performed in 37 angina patients (37 lesions) who underwent repeated percutaneous coronary intervention (PCI) for the treatment of DES ISR. The patients were divided into two groups according to the phase of restenosis: the early ISR group (E-IRS; ≤1 year) and the late ISR group (L-ISR; >1 year). ResultsThere were 18 patients in the E-ISR group and 19 patients in the L-ISR group. The mean follow-up period between stent implantation and repeated PCI was 8.0±2.2 months in the E-IRS group and 40.4±23.9 months in the L-ISR group. The percentage of lipid components and relative necrotic volume were greater in the L-ISR group than in the E-ISR group (5.77±1.81% vs. 4.51±1.71%, p<0.05 and 12.20±2.97% vs. 8.61±2.33%, p<0.001, respectively). Furthermore, there was a positive correlation between the follow-up duration after DES implantation in the L-ISR group and the presence of a necrotic plaque component (r=0.49, p<0.05). ConclusionsThere were differences in the neointimal plaque characteristics after DES implantation according to the phase of restenosis. This information may lead to a better understanding of the mechanisms of DES ISR.

(Invited) CMUT Based Microscale Integrated Ultrasound Systems for Minimally Invasive Intracardiac and Intravascular Imaging

Although catheter based intravascular ultrasound (IVUS) imaging of arterial cross sections and intracardiac echography (ICE) imaging of the heart in two dimensions have proven to be very useful in many interventional procedures used in the diagnosis and treatment of coronary and structural heart diseases, extension of these techniques to three-dimensional (3-D) volumetric imaging will have a dramatic impact. Truly volumetric images in front of an IVUS catheter will enable accurate evaluation and safer crossing of chronic total occlusions (CTOs) in coronary and peripheral arteries. Three dimensional ICE imaging in the heart can improve the outcome of challenging procedures such as trans-catheter valve replacements by providing the clinicians exceptional capability for real-time spatial mapping. These imaging devices would be enabled by miniature ultrasound systems that can be placed at the tip of mechanically flexible catheters.We have been developing technologies for integration of capacitive micromachined ultrasonic transducer (CMUT) arrays and custom designed CMOS front end electronics on the same silicon chip for ultimately miniaturized ultrasound systems for 3-D IVUS and ICE imaging. To implement these CMUT-on-CMOS systems, we post-process CMOS wafers to fabricate CMUTs using a low temperature process [1]. The CMOS electronics are designed specifically for low noise operation with CMUTs and use smart power management to reduce the power consumption, and time division multiplexing to reduce the cable count in the catheter to about 10 for an imaging array with over 100 elements [2]. With this approach, a 300um thick, 1-2mm diameter donut shaped silicon contains most of the required front end functionality, resulting in very flexible 3-7F catheters for 3-D IVUS and ICE imaging applications.Figure 1 shows a CMUT-on-CMOS chip with 1.4-mm-diameter dual-ring CMUT array on a front-end IC implemented in 0.35-µm CMOS process after silicon donut shaping using deep reactive ion etching (left) and after initial flex tape electrical connections (right). The dual-ring array has 56 transmit elements and 48 receive elements on two separate concentric annular rings. The IC incorporates a 25-V pulser for each transmitter element and a low-noise transimpedance amplifier (TIA) for each receiver, along with digital control. The final shape of the silicon chip is a 1.5-mm-diameter donut with a 430-µm center hole for a guide wire. The overall front-end system requires only 13 external connections and provides 4 parallel RF outputs while consuming an average power of 20-mW. The frequency of operation is around 20-MHz, suitable for forward looking volumetric IVUS imaging of CTOs. This device has been tested on wire phantoms and ex vivo chicken heart samples to demonstrate its capability to collect 3-D ultrasound imaging data at 60 fr/s rate and dynamic range comparable to commercial IVUS systems [3]. In addition to providing details of this type of CMUT-on-CMOS systems, we will discuss the use of this approach for implementing MRI compatible intracardiac imaging catheters as well as integration of an IVUS imaging system on a 0.014” diameter guidewire.J. Zahorian, M. Hoffman, T. Xu, G. Gurun, S. Satir, M. Karaman, and F.L. Degertekin “Monolithic CMUT on CMOS Integration for Intravascular Ultrasound Applications,” IEEE Trans. on UFFC, vol. 58, pp. 2659-2667, 2011.G. Gurun, P. Hasler, and F.L. Degertekin, “Frontend Receiver Electronics for High Frequency Monolithic CMUT-on-CMOS Imaging Arrays,” IEEE Trans. on UFFC, vol. 58, 1658-1668, 2011.G. Gurun, C. Tekes, J. Zahorian, T. Xu, S. Satir, M. Karaman and F.L. Degertekin, “Single-Chip CMUT-on-CMOS front-end System for Real Time Volumetric IVUS and ICE Imaging,” IEEE Trans. on UFFC, to appear in February 2014.

Lipid detection in atherosclerotic human coronaries by spectroscopic intravascular photoacoustic imaging

The presence of lipids in atherosclerotic coronary lesions is an important determinant of their potential to trigger acute coronary events. Spectroscopic intravascular photoacoustic imaging (sIVPA) has the potential to automatically detect lipids in atherosclerotic lesions. For real-time in vivo imaging, limiting the number of excitation wavelengths is crucial. We explored methods for plaque lipid detection using sIVPA, with the aim to minimize the number of laser pulses per image line. A combined intravascular ultrasound (IVUS) and photoacoustic imaging system was used to image a vessel phantom and human coronary arteries ex vivo. We acquired co-registered cross-sectional images at several wavelengths near 1200 nm, a lipid-specific absorption band. Correlating the photoacoustic spectra at 6 or 3 wavelengths from 1185 to 1235 nm with the absorption spectrum of cholesterol and peri-adventitial tissue, we could detect and differentiate the lipids in the atherosclerotic plaque and peri-adventitial lipids, respectively. With two wavelengths, both plaque and peri-adventitial lipids were detected but could not be distinguished.

Association between increased epicardial adipose tissue volume and coronary plaque composition

To assess the relationship between epicardial adipose tissue volume (EATV) and plaque vulnerability in significant coronary stenosis using a 40-MHz intravascular ultrasound (IVUS) imaging system (iMap-IVUS), we analyzed 130 consecutive patients with coronary stenosis who underwent dual-source computed tomography (CT) and cardiac catheterization. Culprit lesions were imaged by iMap-IVUS before stenting. The iMAP-IVUS system classified coronary plaque components as fibrous, lipid, necrotic, or calcified tissue, based on the radiofrequency spectrum. Epicardial adipose tissue was measured as the tissue ranging from −190 to −30 Hounsfield units. EATV, calculated as the sum of the fat areas on short-axis images, was 85.0 ± 34.0 cm3. There was a positive correlation between EATV and the percentage of necrotic plaque tissue (R 2 = 0.34, P < 0.01), while there was a negative correlation between EATV and the percentage of fibrous tissue (R 2 = 0.24, P < 0.01). Multivariate analysis revealed that an increased low-density lipoprotein cholesterol level (β = 0.15, P = 0.03) and EATV (β = 0.14, P = 0.02) were independently associated with the percentage of necrotic plaque tissue. An increase in EATV was associated with the development of coronary atherosclerosis and, potentially, with the most dangerous type of plaque.

A comparison between 40 MHz intravascular ultrasound iMap imaging system and integrated backscatter intravascular ultrasound

BackgroundiMap is a newly developed intravascular ultrasound (IVUS) tissue characterization system based on pattern recognition of the radio frequency (RF) signals. PurposeThe purpose of this study was to compare tissue characterization between iMap and another previously validated tissue characterization system, integrated backscatter (IB)-IVUS in vivo and to clarify similarities and differences between these two methods. MethodsA total of 31 lesions from 16 patients with ischemic heart disease were studied. IVUS imaging was performed using 40MHz IVUS catheter. RF signals from each lesion were then exported to analyze tissue characterization using both iMap and IB-IVUS. By iMap, coronary plaque was classified into four categories, fibrotic, lipidic, necrotic, or calcified. By IB-IVUS, coronary plaque was classified into four categories, fibrosis, lipid pool, dense fibrosis, or calcification. After the images were acquired, IB-IVUS and iMap images were compared at exactly the same cross-sections. Because severe calcification is a perfect reflector, dense calcification lesions (>20%) were excluded. ResultsBoth fibrotic and calcified by iMap correlated well with fibrosis and calcification by IB-IVUS (fibrotic vs. fibrosis: r2=0.522, p<0.001, calcified vs. calcification: r2=0.560, p<0.001). Although lipidic by iMap did not correlate with lipid pool by IB-IVUS, necrotic by iMap correlated well with lipid pool by IB-IVUS (r2=0.480, p<0.001). ConclusionAlthough tissue types classified by iMap correlated well with corresponding tissue type by IB-IVUS, some discrepancy presented between the two systems. These results may call for careful interpretation of the tissue types obtained by the different IVUS tissue characterization systems.

An open system for intravascular ultrasound imaging

Visualization of the blood vessels can provide valuable morphological information for diagnosis and therapy strategies for cardiovascular disease. Intravascular ultrasound (IVUS) is able to delineate internal structures of vessel wall with fine spatial resolution. However, the developed IVUS is insufficient to identify the fibrous cap thickness and tissue composition of atherosclerotic lesions. Novel imaging strategies have been proposed, such as increasing the center frequency of ultrasound or using a modulated excitation technique to improve the accuracy of diagnosis. Dual-mode tomography combining IVUS with optical tomography has also been developed to determine tissue morphology and characteristics. The implementation of these new imaging methods requires an open system that allows users to customize the system for various studies. This paper presents the development of an IVUS system that has open structures to support various imaging strategies. The system design is based on electronic components and printed circuit board, and provides reconfigurable hardware implementation, programmable image processing algorithms, flexible imaging control, and raw RF data acquisition. In addition, the proposed IVUS system utilized a miniaturized ultrasound transducer constructed using PMNPT single crystal for better piezoelectric constant and electromechanical coupling coefficient than traditional lead zirconate titanate (PZT) ceramics. Testing results showed that the IVUS system could offer a minimum detectable signal of 25 μV, allowing a 51 dB dynamic range at 47 dB gain, with a frequency range from 20 to 80 MHz. Finally, phantom imaging, in vitro IVUS vessel imaging, and multimodality imaging with photoacoustics were conducted to demonstrate the performance of the open system.

Long-Term Results of Cell-Free Biodegradable Scaffolds for In Situ Tissue-Engineering Vasculature: In a Canine Inferior Vena Cava Model

We have developed a new biodegradable scaffold that does not require any cell seeding to create an in-situ tissue-engineering vasculature (iTEV). Animal experiments were conducted to test its characteristics and long-term efficacy. An 8-mm tubular biodegradable scaffold, consisting of polyglycolide knitted fibers and an L-lactide and ε-caprolactone copolymer sponge with outer glycolide and ε-caprolactone copolymer monofilament reinforcement, was implanted into the inferior vena cava (IVC) of 13 canines. All the animals remained alive without any major complications until euthanasia. The utility of the iTEV was evaluated from 1 to 24 months postoperatively. The elastic modulus of the iTEV determined by an intravascular ultrasound imaging system was about 90% of the native IVC after 1 month. Angiography of the iTEV after 2 years showed a well-formed vasculature without marked stenosis or thrombosis with a mean pressure gradient of 0.51±0.19 mmHg. The length of the iTEV at 2 years had increased by 0.48±0.15 cm compared with the length of the original scaffold (2–3 cm). Histological examinations revealed a well-formed vessel-like vasculature without calcification. Biochemical analyses showed no significant differences in the hydroxyproline, elastin, and calcium contents compared with the native IVC. We concluded that the findings shown above provide direct evidence that the new scaffold can be useful for cell-free tissue-engineering of vasculature. The long-term results revealed that the iTEV was of good quality and had adapted its shape to the needs of the living body. Therefore, this scaffold would be applicable for pediatric cardiovascular surgery involving biocompatible materials.