Acoustic characterization of a miniature matrix transducer for pediatric 3D transesophageal echocardiography

This paper presents the design, fabrication and characterization of a miniature PZT-on-CMOS matrix transducer for real-time pediatric 3-dimensional (3D) transesophageal echocardiography (TEE). This 3D TEE probe consists of a 32 × 32 array of PZT elements integrated on top of an Application Specific Integrated Circuit (ASIC). We propose a partitioned transmit/receive array architecture wherein the 8 × 8 transmitter elements, located at the centre of the array, are directly wired out and the remaining receive elements are grouped into 96 sub-arrays of 3 × 3 elements. The echoes received by these sub-groups are locally processed by micro-beamformer circuits in the ASIC that allow pre-steering up to ±37°. The PZT-on-CMOS matrix transducer has been characterized acoustically and has a centre frequency of 5.8 MHz, -6 dB bandwidth of 67%, a transmit efficiency of 6 kPa/V at 30 mm, and a receive dynamic range of 85 dB with minimum and maximum detectable pressures of 5 Pa and 84 kPa respectively. The properties are very suitable for a miniature pediatric real-time 3D TEE probe.

Fast Volumetric Imaging Using a Matrix Transesophageal Echocardiography Probe with Partitioned Transmit-Receive Array

We describe a 3-D multiline parallel beamforming scheme for real-time volumetric ultrasound imaging using a prototype matrix transesophageal echocardiography probe with diagonally diced elements and separated transmit and receive arrays. The elements in the smaller rectangular transmit array are directly wired to the ultrasound system. The elements of the larger square receive aperture are grouped in 4 × 4-element sub-arrays by micro-beamforming in an application-specific integrated circuit. We propose a beamforming sequence with 85 transmit-receive events that exhibits good performance for a volume sector of 60° × 60°. The beamforming is validated using Field II simulations, phantom measurements and in vivo imaging. The proposed parallel beamforming achieves volume rates up to 59 Hz and produces good-quality images by angle-weighted combination of overlapping sub-volumes. Point spread function, contrast ratio and contrast-to-noise ratio in the phantom experiment closely match those of the simulation. In vivo 3-D imaging at 22-Hz volume rate in a healthy adult pig clearly visualized the cardiac structures, including valve motion.

Feasibility of Multiplane-Transmit Beamforming for Real-Time Volumetric Cardiac Imaging: A Simulation Study

Today's 3-D cardiac ultrasound imaging systems suffer from relatively low spatial and temporal resolution, limiting their applicability in daily clinical practice. To address this problem, 3-D diverging wave imaging with spatial coherent compounding (DWC) as well as 3-D multiline-transmit (MLT) imaging have recently been proposed. Currently, the former improves the temporal resolution significantly at the expense of image quality and the risk of introducing motion artifacts, whereas the latter only provides a moderate gain in volume rate but mostly preserves quality. In this paper, a new technique for real-time volumetric cardiac imaging is proposed by combining the strengths of both approaches. Hereto, multiple planar (i.e., 2-D) diverging waves are simultaneously transmitted in order to scan the 3-D volume, i.e., multiplane transmit (MPT) beamforming. The performance of a 3MPT imaging system was contrasted to that of a 3-D DWC system and that of a 3-D MLT system by computer simulations during both static and moving conditions of the target structures while operating at similar volume rate. It was demonstrated that for stationary targets, the 3MPT imaging system was competitive with both the 3-D DWC and 3-D MLT systems in terms of spatial resolution and sidelobe levels (i.e., image quality). However, for moving targets, the image quality quickly deteriorated for the 3-D DWC systems while it remained stable for the 3MPT system while operating at twice the volume rate of the 3-D-MLT system. The proposed MPT beamforming approach was thus demonstrated to be feasible and competitive to state-of-the-art methodologies.

4-D ICE: A 2-D Array Transducer With Integrated ASIC in a 10-Fr Catheter for Real-Time 3-D Intracardiac Echocardiography

We developed a 2.5 ×6.6 mm ² 2 -D array transducer with integrated transmit/receive application-specific integrated circuit (ASIC) for real-time 3-D intracardiac echocardiography (4-D ICE) applications. The ASIC and transducer design were optimized so that the high-voltage transmit, low-voltage time-gain control and preamp, subaperture beamformer, and digital control circuits for each transducer element all fit within the 0.019-mm ² area of the element. The transducer assembly was deployed in a 10-Fr (3.3-mm diameter) catheter, integrated with a GE Vivid E9 ultrasound imaging system, and evaluated in three preclinical studies. The 2-D image quality and imaging modes were comparable to commercial 2-D ICE catheters. The 4-D field of view was at least 90 ^° ×60 ^° ×8 cm and could be imaged at 30 vol/s, sufficient to visualize cardiac anatomy and other diagnostic and therapy catheters. 4-D ICE should significantly reduce X-ray fluoroscopy use and dose during electrophysiology ablation procedures. 4-D ICE may be able to replace transesophageal echocardiography (TEE), and the associated risks and costs of general anesthesia, for guidance of some structural heart procedures.

A Prototype PZT Matrix Transducer With Low-Power Integrated Receive ASIC for 3-D Transesophageal Echocardiography

This paper presents the design, fabrication, and experimental evaluation of a prototype lead zirconium titanate (PZT) matrix transducer with an integrated receive ASIC, as a proof of concept for a miniature three-dimensional (3-D) transesophageal echocardiography (TEE) probe. It consists of an array of 9 ×12 piezoelectric elements mounted on the ASIC via an integration scheme that involves direct electrical connections between a bond-pad array on the ASIC and the transducer elements. The ASIC addresses the critical challenge of reducing cable count, and includes front-end amplifiers with adjustable gains and micro-beamformer circuits that locally process and combine echo signals received by the elements of each 3 ×3 subarray. Thus, an order-of-magnitude reduction in the number of receive channels is achieved. Dedicated circuit techniques are employed to meet the strict space and power constraints of TEE probes. The ASIC has been fabricated in a standard 0.18-μm CMOS process and consumes only 0.44 mW/channel. The prototype has been acoustically characterized in a water tank. The ASIC allows the array to be presteered across ±37° while achieving an overall dynamic range of 77 dB. Both the measured characteristics of the individual transducer elements and the performance of the ASIC are in good agreement with expectations, demonstrating the effectiveness of the proposed techniques.

Quantification of Left Ventricular Linear, Areal and Volumetric Dimensions: A Phantom and in Vivo Comparison of 2-D and Real-Time 3-D Echocardiography with Cardiovascular Magnetic Resonance

Two-dimensional echocardiography and real-time 3-D echocardiography have been reported to underestimate human left ventricular volumes significantly compared with cardiovascular magnetic resonance. We investigated the ability of 2-D echocardiography, real-time 3-D echocardiography and cardiovascular magnetic resonance to delineate dimensions of increasing complexity (diameter-area-volume) in a multimodality phantom model and in vivo, with the aim of elucidating the main cause of underestimation. All modalities were able to delineate phantom dimensions with high precision. In vivo, 2-D and real-time 3-D echocardiography underestimated short-axis end-diastolic linear and areal and all left ventricular volumetric dimensions significantly compared with cardiovascular magnetic resonance, but not short-axis end-systolic linear and areal dimensions. Underestimation increased successively from linear to volumetric left ventricular dimensions. When analyzed according to the same principles, 2-D and real-time 3-DE echocardiography provided similar left ventricular volumes. In conclusion, echocardiographic underestimation of left ventricular dimensions is due mainly to inherent technical differences in the ability to differentiate trabeculated from compact myocardium. Identical endocardial border definition criteria are needed to minimize differences between the modalities and to ensure better comparability in clinical practice.

Matrix array transducer for the examination of fetal heart

The X6-1 xmatrix array transducer allows a completely new approach to the diagnostic ultrasound: it permits visualization of fetal heart in real time, without the need for gating, and it is unaffected by motion artefacts. It is obtained in real time, without any spatial reconstruction. The authors compared this technology with the traditional one in two case reports: a diagnostic doubt of small muscular ventricular septal defect was solved using this new technique; a diagnosis of complete atrioventricular septal defect was confirmed. Three-dimensional real-time imaging would seem very precise in the study of fetal heart: the defects were fully visualized from any angulations. This new technology is promising but from the authors' limited experience, there is no evidence to use it in routine practice. It should be very useful to commence a prospective study on fetuses at risk while testing the superiority of this technique.

Spatiotemporal accuracy of real-time 3D echocardiography in the neonatal and pediatric setting--validation studies using small dynamic test objects

The precision of real-time 3D-echocardiography (RT3DE) is not sufficiently validated for small, fast-moving structures such as the neonatal and pediatric heart.

PURPOSE

To assess the spatiotemporal accuracy of RT3DE in small, moving test objects.

MATERIALS AND METHODS

Small, calibrated test objects in the size of neonatal and pediatric heart chambers were made from polyurethane foam or metal wire mesh and moved in a water bath through a calibrated dynamic test system. Using matrix transducers (X7-2, ie33 and X4-1, Sonos 7500, Philips, Andover, USA), 2 D and live 3 D datasets under variation of the motion speed (0.033 - 0.133 m/s corresponding to 50 - 200 heart cycles/minute), the volume rate and transducer position were recorded and analyzed (QLab 7.0, Philips).

RESULTS

3 D datasets of the moving test objects showed relevant spatial distortion, which was obviously related to the sequential scanning technology of the matrix transducer. Different segments of a test object were not recorded simultaneously, but rather row-by-row, so that there was a time delay between the first and the last-recorded voxel of a single 3 D volume (mean±SD: 28.9 ± 7.82 m/s or 80 ± 7 % of the time duration of a 3 D volume). With increasing motion speed of the test object and reduced 3 D volume rate, the distortion artifacts increased significantly.

CONCLUSION

3 D acquisitions using matrix technology demonstrate relevant spatiotemporal inaccuracies. This may lead to misinterpretations during the evaluation of the synchronicity of valvular or ventricular motion and incorrect definition of volume estimations. In particular, at higher heart rates and higher rates of movement, these limitations have to be taken into account in clinical practice.

Accuracy of real-time single- and multi-beat 3-d speckle tracking echocardiography in vitro

With little data published on the accuracy of cardiac 3-D strain measurements, we investigated the agreement between 3-D echocardiography and sonomicrometry in an in vitro model with a polyvinyl alcohol phantom. A cardiac scanner with a 3-D probe was used to acquire recordings at 15 different stroke volumes at a heart rate of 60 beats/min, and eight different stroke volumes at a heart rate of 120 beats/min. Sonomicrometry was used as a reference, monitoring longitudinal, circumferential and radial lengths. Both single- and multi-beat acquisitions were recorded. Strain values were compared with sonomicrometer strain using linear correlation coefficients and Bland-Altman analysis. Multi-beat acquisition showed good agreement, whereas real-time images showed less agreement. The best correlation was obtained for a heart rate 60 of beats/min at a volume rate 36.6 volumes/s.

Extended-field-of-view three-dimensional transesophageal echocardiography using image-based X-ray probe tracking

The use of ultrasound imaging for guidance of cardiac interventional procedures is limited by the small field of view of the ultrasound volume. A larger view can be created by image-based registration of several partially overlapping volumes, but automatic registration is likely to fail unless the registration is initialized close to the volumes' correct alignment. In this article, we use X-ray images to track a transesophageal ultrasound probe and thereby provide initial position information for the registration of the ultrasound volumes. The tracking is possible using multiple X-rays or just a single X-ray for each probe position. We test the method in a phantom experiment and find that with at least 50% overlap, 88% of volume pairs are correctly registered when tracked using three X-rays and 86% when using single X-rays. Excluding failed registrations with errors greater than 10 mm, the average registration accuracy is 2.92 mm between ultrasound volumes and 4.75 mm for locating an ultrasound volume in X-ray space. We conclude that the accuracy and robustness of the registrations are sufficient to provide useful images for interventional guidance.

Mode vibrations of a matrix transducer for three-dimensional second harmonic transesophageal echocardiography

Transesophageal echocardiography (TEE) uses the esophagus as an imaging window to the heart. This enables cardiac imaging without interference from the ribs or lungs and allows for higher frequency ultrasound to be used compared with transthoracic echocardiography (TTE). TEE facilitates the successful imaging of obese or elderly patients, where TTE may be unable to produce images of satisfactory quality. Recently, three-dimensional (3-D) TEE has been introduced, which greatly improves the image quality and diagnostic value of TEE by adding an extra dimension. Further improvement could be achieved by optimizing 3-D TEE for harmonic imaging. This article describes the optimal geometry and element configuration for a matrix probe for 3-D second harmonic TEE. The array concept features separated transmit and receive subarrays. The element geometry was studied using finite element modeling and a transmit subarray prototype was examined both acoustically and with laser interferometry. The transmit subarray is suitable for its role, with a 3 MHz resonance frequency, a 40%-50% -3 dB bandwidth and crosstalk levels <-27 dB. The proposed concept for the receive subarray has a 5.6 MHz center frequency and a 50% -3 dB bandwidth.

Front-end receiver electronics for a matrix transducer for 3-D transesophageal echocardiography

There is a clear clinical need for creating 3-D images of the heart. One promising technique is the use of transesophageal echocardiography (TEE). To enable 3-D TEE, we are developing a miniature ultrasound probe containing a matrix piezoelectric transducer with more than 2000 elements. Because a gastroscopic tube cannot accommodate the cables needed to connect all transducer elements directly to an imaging system, a major challenge is to locally reduce the number of channels, while maintaining a sufficient signal-to-noise ratio. This can be achieved by using front-end receiver electronics bonded to the transducers to provide appropriate signal conditioning in the tip of the probe. This paper presents the design of such electronics, realizing time-gain compensation (TGC) and micro-beamforming using simple, low-power circuits. Prototypes of TGC amplifiers and micro-beamforming cells have been fabricated in 0.35-μm CMOS technology. These prototype chips have been combined on a printed circuit board (PCB) to form an ultrasound-receiver system capable of reading and combining the signals of three transducer elements. Experimental results show that this design is a suitable candidate for 3-D TEE.

Fast GPU based adaptive filtering of 4D echocardiography

Time resolved three-dimensional (3D) echocardiography generates four-dimensional (3D+time) data sets that bring new possibilities in clinical practice. Image quality of four-dimensional (4D) echocardiography is however regarded as poorer compared to conventional echocardiography where time-resolved 2D imaging is used. Advanced image processing filtering methods can be used to achieve image improvements but to the cost of heavy data processing. The recent development of graphics processing unit (GPUs) enables highly parallel general purpose computations, that considerably reduces the computational time of advanced image filtering methods. In this study multidimensional adaptive filtering of 4D echocardiography was performed using GPUs. Filtering was done using multiple kernels implemented in OpenCL (open computing language) working on multiple subsets of the data. Our results show a substantial speed increase of up to 74 times, resulting in a total filtering time less than 30 s on a common desktop. This implies that advanced adaptive image processing can be accomplished in conjunction with a clinical examination. Since the presented GPU processor method scales linearly with the number of processing elements, we expect it to continue scaling with the expected future increases in number of processing elements. This should be contrasted with the increases in data set sizes in the near future following the further improvements in ultrasound probes and measuring devices. It is concluded that GPUs facilitate the use of demanding adaptive image filtering techniques that in turn enhance 4D echocardiographic data sets. The presented general methodology of implementing parallelism using GPUs is also applicable for other medical modalities that generate multidimensional data.

Regional cardiac motion and strain estimation in three-dimensional echocardiography: a validation study in thick-walled univentricular phantoms

Automatic quantification of regional left ventricular deformation in volumetric ultrasound data remains challenging. Many methods have been proposed to extract myocardial motion, including techniques using block matching, phase-based correlation, differential optical flow methods, and image registration. Our lab previously presented an approach based on elastic registration of subsequent volumes using a B-spline representation of the underlying transformation field. Encouraging results were obtained for the assessment of global left ventricular function, but a thorough validation on a regional level was still lacking. For this purpose, univentricular thick-walled cardiac phantoms were deformed in an experimental setup to locally assess strain accuracy against sonomicrometry as a reference method and to assess whether regions containing stiff inclusions could be detected. Our method showed good correlations against sonomicrometry: r(2) was 0.96, 0.92, and 0.84 for the radial (ε(RR)), longitudinal (ε(LL)), and circumferential (ε(CC)) strain, respectively. Absolute strain errors and strain drift were low for ε(LL) (absolute mean error: 2.42%, drift: -1.05%) and ε(CC) (error: 1.79%, drift: -1.33%) and slightly higher for ε(RR) (error: 3.37%, drift: 3.05%). The discriminative power of our methodology was adequate to resolve full transmural inclusions down to 17 mm in diameter, although the inclusion-to-surrounding tissue stiffness ratio was required to be at least 5:2 (absolute difference of 39.42 kPa). When the inclusion-to-surrounding tissue stiffness ratio was lowered to approximately 2:1 (absolute difference of 22.63 kPa), only larger inclusions down to 27 mm in diameter could still be identified. Radial strain was found not to be reliable in identifying dysfunctional regions.

Progress in ring array transducers for real-time 3D ultrasound guidance of cardiac interventional devices

As a treatment for aortic stenosis, several companies have recently introduced prosthetic heart valves designed to be deployed through a catheter using an intravenous or transapical approach. This procedure can either take the place of open heart surgery with some ofthe devices or delay it with others. Real-time 3D ultrasound could enable continuous monitoring of these structures before, during and after deployment. We have developed a 2D ring array integrated with a 30 French catheter that is used for transapical prosthetic heart valve implantation. The transducer array was built using three 46 cm long flex circuits from MicroConnex (Snoqualmie, WA) which terminate in an interconnect that plugs directly into our system cable; thus, no cable soldering is required. This transducer consists of 210 elements at 0.157 mm interelement spacing and operates at 5 MHz. Average measured element bandwidth was 26% and average round-trip 50 ohm insertion loss was -58.1 dB after correcting for diffractive losses. The transducer was wrapped around the 1 cm diameter lumen of a heart-valve deployment catheter. Prosthetic heart valve images were obtained in water-tank studies.

3-D phantom and in vivo cardiac speckle tracking using a matrix array and raw echo data

Cardiac motion has been tracked using various methods, which vary in their invasiveness and dimensionality. One such noninvasive modality for cardiac motion tracking is ultrasound. Three-dimensional ultrasound motion tracking has been demonstrated using detected data at low volume rates. However, the effects of volume rate, kernel size, and data type (raw and detected) have not been sufficiently explored. First comparisons are made within the stated variables for 3-D speckle tracking. Volumetric data were obtained in a raw, baseband format using a matrix array attached to a high parallel receive beam count scanner. The scanner was used to acquire phantom and human in vivo cardiac volumetric data at 1000-Hz volume rates. Motion was tracked using phase-sensitive normalized cross-correlation. Subsample estimation in the lateral and elevational dimensions used the grid-slopes algorithm. The effects of frame rate, kernel size, and data type on 3-D tracking are shown. In general, the results show improvement of motion estimates at volume rates up to 200 Hz, above which they become stable. However, peak and pixel hopping continue to decrease at volume rates higher than 200 Hz. The tracking method and data show, qualitatively, good temporal and spatial stability (for independent kernels) at high volume rates.

Real-time three-dimensional echocardiography using a matrix probe with live xPlane imaging of the interventricular septum

OBJECTIVE

To describe a technique to rapidly visualize the in-plane view of the fetal interventricular septum (IVS) to enable the identification of a ventricular septal defect (VSD).

METHODS

One hundred and fifty-one women were invited to participate after their routine fetal morphology scan, including four suspected to have congenital cardiac defects which were confirmed postnatally. A standard examination protocol using real-time three-dimensional (3D) echocardiography with live xPlane imaging was developed. The ability of this new technology to examine the ventricular septum was investigated.

RESULTS

The in-plane view of the fetal IVS was visualized successfully in 150 (99.3%) cases by real-time 3D echocardiography with live xPlane imaging, including 82 (54.3%) cases with the spine posterior and 68 (45.7%) cases with the spine anterior. The in-plane view of the IVS successfully visualized the VSDs in three fetuses with VSD and displayed the intact IVS in one fetus with transposition of the great arteries without VSD.

CONCLUSION

We describe live xPlane imaging, a simple method for the real-time assessment of the in-plane view of the IVS that has the potential to enhance the diagnostic accuracy of fetal cardiac examination.

Live Three-Dimensional Transthoracic Echocardiographic Delineation of Ventricular Septal Rupture Following Myocardial Infarction

We present an elderly patient with ventricular septal rupture following myocardial infarction in whom live three-dimensional transthoracic echocardiography allowed comprehensive noninvasive assessment of the location, shape, and size of the septal defect, which could be clearly visualized en face from both left and right ventricular aspects.

Live Three-Dimensional Transthoracic Echocardiographic Assessment of Left Ventricular Hydatid Cyst

We report an adult patient in whom live three-dimensional transthoracic echocardiography (3DTTE) complemented two-dimensional transthoracic echocardiography (2DTTE) in making a definitive diagnosis of a hydatid cyst located in the left ventricular cavity. The parent hydatid cyst, as well as the daughter cysts, contained within it could be delineated by both 2DTTE and live 3DTTE. However, the tertiary or granddaughter cysts originating from the daughter cysts as well as great-granddaughter cysts budding from tertiary cysts could be visualized only when the live 3DTTE data sets were cropped and sectioned sequentially using multiple cutting planes. In addition, apparent intrinsic mobility of some of the tertiary cysts implying viability was detected only by 3DTTE.

3D echocardiography: "The most powerful predictor of masked CVD in metabolic syndrome"

AIMS & OBJECTIVE: To evaluate the impact of the Metabolic Syndrome (MetS) on various echo variables by 3D Echocardiography.

MATERIALS AND METHODS

100 patients of MetS from indoor and outdoor patient departments were subjected to Echocardiographic and Carotid Doppler evaluation. They were divided into three groups: Group A, Group B and Group C on the basis of age <40 yrs, 40-60 yrs and >60 yrs respectively. The echo variables included left ventricular myocardial performance index (LVMPI), left ventricular mass index (LVMi), left ventricular diastolic dysfunction (LVDD), systolic function (LVEF), left atrial volume index (LAVi) and composite common carotid intima media thickness (CCIMT).

RESULTS

The mean LVMPI was abnormal in all the groups and showed an increasing trend with prolonged LVMPI (> 0.4) in 74% of the total population. Prolonged LVMPI in Group A, Group B and Group C were 12.1%, 52.7% and 35.1% respectively. There was also a strong correlation between LVMPI & LVDD (p-value < 0.0001). Only 9% had systolic dysfunction (LVEF < 50%), but 68% of patients had abnormal diastolic function, of which 53% had grade I LVDD, 12% had grade II LVDD and 3% had grade III diastolic dysfunction. None of our patients had grade IV diastolic dysfunction. The mean LA Vi was normal in all the groups, but LAVi increased with worsening LVDD. The mean LVMi indexed to Body Surface Area (BSA) was normal in all the groups, but showed a statistically significant increasing trend from Group A to Group C (p-value < 0.05). Statistically significant higher LVMi values were observed for males as compared to females (p-value < 0.0001). On analysis of patients having left ventricular hypertrophy (LVH), 76% had concentric remodeling; only 11 % had concentric hypertrophy, but none had eccentric hypertrophy. Most of our patients in Group B & Group C had higher mean Composite CCIMT (0.73 +/- 0.33 & 0.84 +/- 0.42 respectively) which was statistically very significant (p-value < 0.001)

CONCLUSION

Metabolic Syndrome is associated with masked cardiovascular disease (CVD) as evident by 3D Echo in this series of patients. LVMPI was an early indicator and the most robust marker of early LVDD. Impaired relaxation was highly prevalent; while LAVi was less robust predictor of LVDD in this series of patients. Concentric left ventricular remodeling was the most common pattern of LVH. Most of our series of patients had increased Composite CCIMT. Thus 3D Echocardiography has great potential and is very useful for early detection and timely therapeutic interventions in patients with subclinical CVD in MetS.

Real-time three-dimensional echocardiography: a current view of what echocardiography can provide?

The development of real-time three dimensional echocardiography has allowed for the incorporation of 3-dimensional echocardiographic imaging into everyday cardiovascular clinical practice. In this State of the Art Paper we will provide an overview of three dimensional echocardiography and specific indications in which it has incremental value over traditional 2-dimensional echocardiography.

Practical guide for three-dimensional transthoracic echocardiography using a fully sampled matrix array transducer

Real-time three-dimensional (3D) echocardiography is a major innovation in the history of cardiovascular ultrasound. Advances in computer and transducer technologies, especially the fully-sampled matrix array transducer, have permitted real-time 3D image acquisition and display. Several vendors provide 3D imaging but use different terminology for similar functions, creating confusion for consumers. This article provides a practical guide on how to acquire and analyze 3D images on-cart using currently available ultrasound systems (iE33, Philips Medical System, Andover, MA; Vivid7, GE Healthcare, Wauwatosa, WI) in daily clinical practice.

A dynamical shape prior for LV segmentation from RT3D echocardiography

Real-time three-dimensional (RT3D) echocardiography is the newest generation of three-dimensional (3-D) echocardiography. Segmentation of RT3D echocardiographic images is essential for determining many important diagnostic parameters. In cardiac imaging, since the heart is a moving organ, prior knowledge regarding its shape and motion patterns becomes an important component for the segmentation task. However, most previous cardiac models are either static models (SM), which neglect the temporal coherence of a cardiac sequence or generic dynamical models (GDM), which neglect the inter-subject variability of cardiac motion. In this paper, we present a subject-specific dynamical model (SSDM) which simultaneously handles inter-subject variability and cardiac dynamics (intra-subject variability). It can progressively predict the shape and motion patterns of a new sequence at the current frame based on the shapes observed in the past frames. The incorporation of this SSDM into the segmentation process is formulated in a recursive Bayesian framework. This results in a segmentation of each frame based on the intensity information of the current frame, as well as on the prediction from the previous frames. Quantitative results on 15 RT3D echocardiographic sequences show that automatic segmentation with SSDM is superior to that of either SM or GDM, and is comparable to manual segmentation.

An ultrasonic navigation system for endovascular aortic repair

The objective of our research is to develop an ultrasound, time-of-flight triangulation based system for real-time, intraoperative 3-dimensional tracking of minimally invasive surgical instruments. We have chosen to first apply this technology towards tracking catheters used in endovascular aortic stent-grafting. To demonstrate the feasibility of this concept, we have developed a system involving a custom catheter based transducer and performed an experiment in excised porcine tissue with a model aorta.

In vivo spectral domain optical coherence tomography volumetric imaging and spectral Doppler velocimetry of early stage embryonic chicken heart development

Progress toward understanding embryonic heart development has been hampered by the inability to image embryonic heart structure and simultaneously measure blood flow dynamics in vivo. We have developed a spectral domain optical coherence tomography system for in vivo volumetric imaging of the chicken embryo heart. We have also developed a technique called spectral Doppler velocimetry (SDV) for quantitative measurement of blood flow dynamics. We present in vivo volume images of the embryonic heart from initial tube formation to development of endocardial cushions of the same embryo over several stages of development. SDV measurements reveal the influence of heart tube structure on blood flow dynamics.

Real-time three-dimensional echocardiography of congenital heart disease using a high frequency paediatric matrix transducer

New matrix transducers are now available for three-dimensional echocardiography which have a higher frequency and smaller footprint than previous matrix probes. This has resulted in better image resolution in infants and children. Current applications include assessment of cardiac morphology and function. Intraoperative epicardial techniques may be used in addition to a conventional transthoracic approach.

[Quantitative functional evaluation on right ventricle with auto-segmentation and three-dimensional reconstruction]

The authors first segment the right ventricle regions from the echocardiographics by introducig a seeded region growth algorithm. Then they reconstrunct the three dimensional data field of right ventricle by using rotary scanning interpolation algorithm. And then, the authors propose a layer-by-layer, row-by-row, and voxel-by-voxel approach based on the interpolation results to estimate the volume of right ventricle. Finally, some right ventricle functional parameters such as EDV (End-diastolic volume), ESV (End-systolic volume), and RVEF (Right ventricular ejection fraction) are computed according to the volume results. The volume variation curves of several patients during a cardiac cycle have been successfully plotted out. The obtained results are compared with those from Tomtec medial image workstation. The comparison indicates the proposed approach is practical and meaningful.

[Spatio-temporal image correlation (STIC)--new three (3D) dimensional view of the fetal heart]

We present a new form of data image processing obtained by three-dimensional scanning named Spatio-Temporal Image Correlation (STIC) and discuss its technique and clinical implications in fetal echocardiography.

Vibrating interventional device detection using real-time 3-D color Doppler

Ultrasound image guidance of interventional devices during minimally invasive surgery provides the clinician with improved soft tissue contrast while reducing ionizing radiation exposure. One problem with ultrasound image guidance is poor visualization of the device tip during the clinical procedure. We have described previously guidance of several interventional devices using a real-time 3-D (RT3-D) ultrasound system with 3-D color Doppler combined with the ColorMark technology. We then developed an analytical model for a vibrating needle to maximize the tip vibrations and improve the reliability and sensitivity of our technique. In this paper, we use the analytical model and improved radiofrequency (RF) and color Doppler filters to detect two different vibrating devices in water tank experiments as well as in an in vivo canine experiment. We performed water tank experiments with four different 3- D transducers: a 5 MHz transesophageal (TEE) probe, a 5 MHz transthoracic (TTE) probe, a 5 MHz intracardiac catheter (ICE) transducer, and a 2.5 MHz commercial TTE probe. Each transducer was used to scan an aortic graft suspended in the water tank. An atrial septal puncture needle and an endomyocardial biopsy forceps, each vibrating at 1.3 kHz, were inserted into the vascular graft and were tracked using 3-D color Doppler. Improved RF and wall filters increased the detected color Doppler sensitivity by 14 dB. In three simultaneous planes from the in vivo 3-D scan, we identified both the septal puncture needle and the biopsy forceps within the right atrium using the 2.5 MHz probe. A new display filter was used to suppress the unwanted flash artifact associated with physiological motion.

3D ultrasound-guided motion compensation system for beating heart mitral valve repair

Beating heart intracardiac procedures promise significant benefits for patients, however, the fast motion of the heart poses serious challenges to surgeons. We present a new 3D ultrasound-guided motion (3DUS) compensation system that synchronizes instrument motion with the heart. The system utilizes the fact that the motion of some intracardiac structures, including the mitral valve annulus, is largely constrained to translation along one axis. This allows the development of a real-time 3DUS tissue tracker which we integrate with a 1 degree-of-freedom actuated surgical instrument, real-time 3DUS instrument tracker, and predictive filter to devise a system with synchronization accuracy of 1.8 mm RMSE. User studies involving the deployment of surgical anchors in a simulated mitral annuloplasty procedure demonstrate that the system increases success rates by over 100%. Furthermore, it enables more careful anchor deployment by reducing forces to the tissue by 50% while allowing instruments to remain in contact with the tissue for longer periods.

A systematic approach to the use of the multiplanar display in evaluation of abnormal vascular connections to the fetal heart using 4-dimensional ultrasonography

OBJECTIVE

The multiplanar display is a modality that allows the simultaneous visualization of 3 orthogonal planes from volume data sets obtained with 3- and 4-dimensional ultrasonography. Simultaneous display of standard views used in fetal echocardiography and their orthogonal planes may provide novel ultrasonographic views for examination of the fetal heart and its vascular connections. This study was designed to determine the clinical utility of the multiplanar display in the examination of abnormal vascular connections to the fetal heart.

METHODS

We reviewed 4-dimensional volume data sets, acquired with the spatiotemporal image correlation technique, from patients with abnormal vascular connections to the fetal heart. Multiplanar views of the fetal heart were used to simultaneously display standard planes used in fetal echocardiography and their corresponding orthogonal planes.

RESULTS

This study included 4 volume data sets from fetuses with confirmed abnormal vascular connections to the heart, including: (1) an interrupted inferior vena cava with azygos or hemiazygos vein continuation; (2) a persistent left superior vena cava draining into a dilated coronary sinus; and (3) a dilated superior vena cava associated with a thoracic lymphangioma. Simultaneous visualization of orthogonal planes displaying abnormal vascular connections to the fetal heart facilitated identification of the abnormal vessels and their spatial relationships with other vascular structures.

CONCLUSIONS

Multiplanar imaging can be used to assess abnormal vascular connections to the fetal heart and may provide novel ultrasonographic planes for fetal echocardiography using 3- and 4-dimensional ultrasonography.

Development of an electrophysiology (EP)-enabled intracardiac ultrasound catheter integrated with NavX 3-dimensional electrofield mapping for guiding cardiac EP interventions: experimental studies

OBJECTIVE

We have developed an integrated high-resolution intracardiac echocardiography (ICE) catheter for electrophysiology (EP) testing, which can be coregistered in 3-dimensional space with EP testing and ablation catheters using electrofield sensing.

METHODS

Twelve open-chest pigs (34-55 kg) and 3 closed-chest pigs were studied. After introduction from the jugular or femoral venous locations, the 9F side-looking, highly steerable (0 degrees -180 degrees), 64-element array catheters could be manipulated easily throughout the right side of the heart. Multisite cardiac pacing was performed for assessing left ventricular (LV) synchrony using tissue Doppler methods. Also, in the open-chest pigs, right atrial (RA) and right ventricular (RV) ablations were performed with a separate radio frequency catheter under fluoroscopic guidance and visualized with ICE to characterize the changes. In the 3 closed-chest pigs, electrofield NavX 3-dimensional coregistration (St Jude Medical Corp, Minneapolis, MN) allowed us to test whether this additional feature could shorten the time necessary to perform 4 targeted ablations in each animal while imaging the ablation catheter and the adjacent region by ICE.

RESULTS

Intracardiac anatomy, tricuspid, aortic, pulmonary, and mitral valve function, and pulmonary vein flow were all imaged reproducibly from scanning locations in the RA or RV in all animals, along with assessment of cardiac motion and the effects of multisite pacing. Three-dimensional electrofield displays detailed the spatial relationship between the ICE catheter and ablation catheters such that the time to visualize and ablate 4 sites in each of the 3 closed-chest animals was reduced.

CONCLUSIONS

This new technology is a first step in the integration of ICE with EP procedures.

Three-dimensional reconstruction of coronary arteriole plexus image by contrast echocardiography using a high-frequency transducer

OBJECTIVE

This study was established to examine the efficacy of a high-frequency liner probe for visualizing fine anatomy of coronary microcirculation.

METHODS

The vessel size and its velocity-time integral at the anterior wall in dogs by real-time contrast echocardiography with high-frequency liner probe and pulse Doppler methods, and the coronary flow volume, were measured before and after adenosine triphosphate injection. A 3-dimensional (3D) image was reconstructed by the built-in 3D system using intermittent flash echocardiographic images.

RESULTS

The increments of flow volume calculated from vessel sizes and velocity-time integral were well correlated with those of coronary flow volume. Using intermittent flash echocardiographic images, fine dots and lines of contrast echocardiographic-expected arterioles were evident, and easily and quickly reconstructed as coronary plexus by 3D system.

CONCLUSION

A high-frequency liner probe provides the fine-vessel images to evaluate those morphologic changes; a 3D reconstruction image could provide new information about coronary arterioles.

Visualization, volume and surface area calculation of three dimensional (3D) ultrasound images

OBJECTIVE

To segment a 3D ultrasound image data that comprises extraction of surface of interests, smoothing of segmented image, thereby to estimate the surface area and volume of segmented 3D objects (e.g. fetus).

METHOD

(a) Seeded Region Growing (SRG) together with connectivity and marching cubes algorithms are used to segment the three dimensional (3D) ultrasound image data (I) (b) Using VTK (Visualization Tool Kit) a c++ program was developed which relies on the Maximum Unit Normal Component (MUNC) used for surface area measurement and Divergence Theorem Algorithms (DTA) used for volume estimation. The agreement between the program and the formula was tested on (1) computer generated spheres and cube (2) cylindrical shaped phantoms scanned by ultrasound scanner System Five, GE Vingmed (Horten, Norway) using a 3D annular array of 7.5 MHz. (3) 3D ultrasound fetus using cronbach alpha

RESULTS

The cylindrical shaped phantom (diameter 15.4 mm, length. 21.7 mm) with x and y voxel size 1.24921 mm and 0.613032 mm respectively and z voxel size 1.249221 mm yield a percentage error of 5.3% for the surface area and 2.6% for the volume. The volume and surface area of the fetus with x, y, z voxel size 0.465508mm, 0.529645 mm, 1.014201 mm respectively as estimated with the developed program was 3.758ml for volume and 1.937 mm2 fbr surface area, while the measured volume of fetus with EchoPAC-3D was 3.74 ml.

CONCLUSIONS

It was concluded that. The agreement between the formula and the program for different shaped objects indicate that the methodology can provide measurements of the volume and the surface area of different anatomical structures.

Live 3D Echocardiography with the Pediatric Matrix Probe

Three-dimensional echocardiography (3DE) enables new views of heart valves and the septa to be imaged. While the previous 3DE system was cumbersome, the recent introduction of live 3DE allowed for routine use of the technique in adult patients. Here, we report our initial experiences in adapting live 3DE and the adult matrix probe to the pediatric population. Thirty-four 3DE examinations were performed on children, aged 1 day to 12 years (n = 23; median 4 years) and fetuses 20-33 weeks in gestation (n = 11; median 25 weeks), many of whom had various congenital heart diseases. The pediatric matrix probe (2-7 MHz) was used for 2D, Doppler, and 3DE. New modalities of the Vision 2007 (Philips) were applied: live, full volume, thick slice, 3D color Doppler, the QLAB system for navigation, and cropping. The pediatric matrix probe allows for complete 2D and 3D echocardiography, and new acoustic windows are now available to perform live 3DE. The higher frequency of the probe increases the 3D image resolution obtained in neonates and fetuses. This advancement allows new views of the aorta, pulmonary valve, septa and intra cardiac anatomy to be captured. Real time 3DE is a feasible method in addition to conventional 2D echocardiography for evaluating congenital heart disease.

GPU based real-time instrument tracking with three-dimensional ultrasound

Real-time three-dimensional ultrasound enables new intracardiac surgical procedures, but the distorted appearance of instruments in ultrasound poses a challenge to surgeons. This paper presents a detection technique that identifies the position of the instrument within the ultrasound volume. The algorithm uses a form of the generalized Radon transform to search for long straight objects in the ultrasound image, a feature characteristic of instruments and not found in cardiac tissue. When combined with passive markers placed on the instrument shaft, the full position and orientation of the instrument is found in 3D space. This detection technique is amenable to rapid execution on the current generation of personal computer graphics processor units (GPU). Our GPU implementation detected a surgical instrument in 31 ms, sufficient for real-time tracking at the 25 volumes per second rate of the ultrasound machine. A water tank experiment found instrument orientation errors of 1.1 degrees and tip position errors of less than 1.8mm. Finally, an in vivo study demonstrated successful instrument tracking inside a beating porcine heart.

Three-Dimensional Echocardiographic Technology

This article addresses the current state of the art of technology in three-dimensional echocardiography as it applies to transducer design, beam forming, display, and quantification. Because three-dimensional echocardiography encompasses many technical and clinical areas, this article reviews its strengths and limitations and concludes with an analysis of what to use when.

Three-Dimensional Echocardiography: An Historical Perspective

Three-dimensional echocardiography (3DE) has made a dramatic transition from predominantly a research tool to a technology useful in everyday clinical practice. This article outlines the history of 3DE from its beginnings to the most current technology.

Automated 3D freehand ultrasound calibration with real-time accuracy control

3D ultrasound (US) is an emerging new imaging technology that appeals to more and more applications in intraoperative guidance of computer-assisted surgery. In a freehand US imaging system, US probe calibration is typically required to construct a 3D image of the patient's anatomy from a set of 2D US images. Most of the current calibration techniques concern primarily with the precision and accuracy. However, for computer-assisted surgeries that may require a calibration task inside the operating room (OR), many other important aspects have to be considered besides accuracy. In this paper, we propose a novel system for automated calibration that is optimized for the OR usage with real-time feedback and control of the calibration accuracy. We have also designed a novel N-wire phantom, with greatly reduced complexity to facilitate mass production without compromising the accuracy and robustness.

A streaming-based solution for remote visualization of 3D graphics on mobile devices

Mobile devices such as Personal Digital Assistants, Tablet PCs, and cellular phones have greatly enhanced user capability to connect to remote resources. Although a large set of applications are now available bridging the gap between desktop and mobile devices, visualization of complex 3D models is still a task hard to accomplish without specialized hardware. This paper proposes a system where a cluster of PCs, equipped with accelerated graphics cards managed by the Chromium software, is able to handle remote visualization sessions based on MPEG video streaming involving complex 3D models. The proposed framework allows mobile devices such as smart phones, Personal Digital Assistants (PDAs), and Tablet PCs to visualize objects consisting of millions of textured polygons and voxels at a frame rate of 30 fps or more depending on hardware resources at the server side and on multimedia capabilities at the client side. The server is able to concurrently manage multiple clients computing a video stream for each one; resolution and quality of each stream is tailored according to screen resolution and bandwidth of the client. The paper investigates in depth issues related to latency time, bit rate and quality of the generated stream, screen resolutions, as well as frames per second displayed.

[Localization of accessory atrioventricular pathways in patients with manifest premature ventricular excitation syndrome by three-dimensional vector electrocardiography]

Distribution of excitation via ventricular myocardium in patients with accessory atrioventricular pathways (AAVP) was studied using three-dimensional vector ECG. Analysis of the ECGs obtained during the study formed new views on the excitation process in the myocardium in the presence of AAVP, and made it possible to formulate vector ECG (VECG) criteria of AAVP localization. In 30 cases out of 33 it was possible to correctly localize AAVP. Information obtained as a result of VECG analysis made it possible to localize AAVP preoperatively within the limits of 1/14th atrioventricular sulcus with 97.1% accuracy, which is substantially higher than the accuracy of conventional electrocardiographic algorithms. Thus, the study found that in some cases three-dimensional vector ECG allows for substantial increase in the validity of AAVP localization, while in others it is the only sensitive non-invasive method of topical diagnostics of manifest premature ventricular excitation syndrome. Knowledge of the character of intervector interaction during ventricular electric systole makes it possible to predict the character of changes in the trajectory of QRS vector loop in any AAVP localization, i.e. to model the vector loop.

The impact of aberration on high frame rate cardiac B-mode imaging

In echocardiography, especially in 3D echocardiography, achieving high frame rates is a major challenge. A suggested solution is parallel receive beamforming. Without any compensation, this approach is known to produce block-like artifacts, where each block corresponds to one parallel receive group. In this work, in vitro imaging, in vivo imaging, and simulations were used to investigate the artifacts. In vitro, imaging a tissue phantom, the artifacts were successfully compensated for. However, in vivo, imaging the heart, the compensation techniques no longer sufficed and the artifacts persisted. With in vivo imaging, aberrating tissue layers are present between the heart and the probe. To investigate the effects of aberration on a parallel receive system, an in vitro experiment was performed with and without a silicon phase aberrator in front of the probe. The aberrator caused the artifacts to appear even when compensation techniques were applied. Simulations confirmed the measured results and indicated that distorted beam profiles and decorrelation between parallel receive groups caused the artifacts. To quantify the magnitude of the artifacts, a correlation-based indicator was developed. The indicator separated images with and without artifacts and confirmed that the artifacts appeared from the combination of parallel receive beams and aberration.

Semi-automated 3-dimensional intracardiac echocardiography: Development and initial clinical experience of a new system to guide ablation procedures

BACKGROUND

Pre-interventional three-dimensional (3D) reconstruction of the heart by CT or MRI provides important information on cardiac anatomy for electrophysiological interventions. However, updates of 3D-imaging modalities with high soft-tissue contrast are not available during ablation procedures.

OBJECTIVE

We describe the development and first clinical testing of a close to real-time visualization of cardiac anatomy by intracardiac echocardiography (ICE).

METHODS

An electronic phased-array 5-10 MHz ICE-catheter (AcuNav/Siemens/64 elements) was inserted via a straightened femoral vein sheath (12F) and placed in the right atrium in 5 pigs. A custom-made prototype stepper motor allowed automatic rotation around the longitudinal axis from 90 degrees to 360 degrees in 2-5 degrees steps. For every plane 2D images of a complete cardiac cycle were acquired, triggered by respiration and ECG. The ultrasound images were digitized and 3D-reconstruction was performed by a prototype software. After experimental validation the system was tested in 6 patients during electrophysiological studies.

RESULTS

From a single location in the right atrium, 3D-acquisition and reconstruction of both atria and ventricles with good image quality were achieved within 3-5 minutes. Doppler-mode facilitated identification of the great vessels including the pulmonary veins and their entry into the heart. 3D-visualization of ablation catheters was also possible in all patients and pigs.

CONCLUSION

Semi-automated 3D intracardiac echocardiography from a single site inside the right atrium provides the electrophysiologist with a detailed image of both atria and ventricles with repeated updates of the cardiac anatomy.

Transesophageal Real-Time Three-Dimensional Echocardiography

OBJECTIVES

The purpose of this study was to develop a transesophageal probe that: 1) enables on-line representation of the spatial structures of the heart, and 2) enables navigation of medical instruments.

BACKGROUND

Whereas transthoracic real-time 3-dimensional (3D) echocardiography could recently be implemented, there is still no corresponding transesophageal system. Transesophageal real-time 3D echocardiography would have great potential for numerous clinical applications, such as navigation of catheters.

METHODS

The newly developed real-time 3D system is based on a transesophageal probe in which multiple transducers are arranged in an interlaced pattern on a rotating cylinder. This enables continuous recording of a large echo volume of 70 mm in length and a sector angle of 120 degrees . The presentation of the volume-reconstructed data is made with a time lag of <100 ms. The frame rate is up to 20 Hz. In addition to conventional imaging, the observer can obtain a stereoscopic image of the structures examined with red/blue goggles.

RESULTS

It was shown in vitro on ventricle- and aorta-form agar models and in vivo that the system enables excellent visualization of the 3D structures. Shape, spatial orientation, and the navigation of various catheters (e.g., EPS-catheter, Swan-Ganz-catheter), stents, or atrial septal defect occluders could be recorded on-line and stereoscopically depicted. The size of the echo sector enables a wide field of view without changing the position of the probe.

CONCLUSIONS

Transesophageal real-time 3D echocardiography can be technically realized with the system presented here. The in vitro and in vivo studies show particularly the potential for navigation in the heart and large vessels on the basis of stereoscopic images.