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In cardiac diseases or after myocardial infarction, the fibrous layout in the heart can be modified. To determine the local fiber orientation and to characterize the lesion, an imaging method is required. The fiber orientation can be determined by diffusion MRI, but various factors limit its use in a beating heart. It has been demonstrated that ultrafast ultrasound imaging can measure the local fiber orientation of an in vivo heart based on the ultrasound spatial coherence. This method only returns the fiber orientations in planes parallel to the probe surface. We propose a method called 3D coherence function to improve this initial strategy to extract the full 3D local anisotropy. To validate this approach, 3D ultrasound datasets were acquired on a phantom constituted of several wire layers mimicking different fiber layers. The acquisitions were conducted with different angles between the probe surface and the wire layers. For each dataset, the conventional approach and our 3D coherence function were computed to compare the improvement in the fiber angle evaluation. We have demonstrated that when the out-of-plane angle increases, the 3D coherence function allows a better extraction of the angle.

Blood flow evaluation with ultrasound is an extremely usefull tool in the clinics in many different situations. The evaluation of the real 2D or 3D flow direction and amplitude remains an unsolved issue and a challenge to access to the full and correct flow characteristic. In this paper, an advanced 3D ultrasound system is used to estimate the 3D blood flow in an home made phantom with a laminar flow. After the acquisitions, the 3D processing of the beamformed volumes allow the creation of transverse oscillations and motion estimation in several direction to create a complex vector flow map in 3D. The obtained streamlines are coherent through the cycle and the qualitative evaluation of the flow is possible, even in direction perpendicular to the US beam axis. The proposed setup and method must be evaluated more deeply in more complex geometries, but this work demonstrates the feasibility to use such advanced system in 3D+t flow evaluation.

The arrangement of cardiac fibers determines mechanical and electrical properties of the heart and can be altered due to pathology. Hence, the non-invasive assessment of fiber characteristics is of interest from both a pathophysiologic and a diagnostic point of view. Recently, we proposed and validated, by computer simulations, a theoretical framework to have more insight on 3D ultrasound Backscatter Tensor Imaging. The theory showed that spatial coherence (SC) maps of echo signals, across the probe aperture, not only carry information on fiber direction, but also on fiber size and pitch. The aim of this study was to experimentally validate these findings and conduct preliminary in vivo tests. Experiments were conducted on a purposely designed and built phantom consisting of several sets of parallel nylon wires, having different diameter (S) and pitch (P). Finally, preliminary tests were conducted on the biceps of healthy volunteers. Experiments confirmed the simulation results: averaged over all acquisitions, the main-to-secondary lobe distance linearly correlated with P (R2=94%), while the value of the SC at lag 1 (an estimate of the main lobe width) linearly correlated with S (R2=48.6%). In vivo results demonstrated the feasibility of extracting microstructural information of the tissue by the analysis of SC maps.

In the context of acute myocardial infarction, we propose that Low Energy Ultrasound (LEUS) exposures might attenuate the detrimental effects of ischemia and reperfusion injury. Specifically, our goal is to quantify and monitor the effects of ultrasound using an in vitro cardiac cell model of ischemia-reperfusion. The study was conducted using a mono-layer cell model (H9C2 cardiomyoblasts) exposed to a prolonged hypoxia-reoxygenation (HR) challenge. Two groups were formed: i). HR: cells submitted to hypoxia followed by reoxygenation period, and ii). HR+PostCond-LEUS: LEUS applied repeatedly for 20 min starting at the onset of reoxygenation. Cell death was evaluated by flow cytometry for each group at the end of US exposure. Cell viability was clearly improved in the HR+PostCond-LEUS group, at all time points during reoxygenation. This study suggests a potential protective effect of LEUS on cardiomyoblasts exposed to a prolonged hypoxia-reoxygenation insult. More complex in vitro models exploring potential protective mechanisms (SAFE and RISK signaling pathways and in vivo models will be required for a better comprehension of the underlying mechanisms.

Purpose Treatments using high-intensity focused ultrasound (HIFU) in the abdominal region remain challenging as a result of respiratory organ motion. A novel method is described here to achieve 3D motion-compensated ultrasound (US) MR-guided HIFU therapy using simultaneous ultrasound and MRI. Methods A truly hybrid US-MR-guided HIFU method was used to plan and control the treatment. Two-dimensional ultrasound was used in real time to enable tracking of the motion in the coronal plane, whereas an MR pencil-beam navigator was used to detect anterior–posterior motion. Prospective motion compensation of proton resonance frequency shift (PRFS) thermometry and HIFU electronic beam steering were achieved. Results The 3D prospective motion-corrected PRFS temperature maps showed reduced intrascan ghosting artifacts, a high signal-to-noise ratio, and low geometric distortion. The k-space data yielded a consistent temperature-dependent PRFS effect, matching the gold standard thermometry within approximately 1°C. The maximum in-plane temperature elevation ex vivo was improved by a factor of 2. Baseline thermometry acquired in volunteers indicated reduction of residual motion, together with an accuracy/precision of near-harmonic referenceless PRFS thermometry on the order of 0.5/1.0°C. Conclusions Hybrid US-MR-guided HIFU ablation with 3D motion compensation was demonstrated ex vivo together with a stable referenceless PRFS thermometry baseline in healthy volunteer liver acquisitions. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

International audience; Background, Motivation and ObjectiveAfter a myocardium infarction, cell loss is irremediable leading to a progressive local disorganization and change in the tissue structure altering heart function. An imaging method able to render the local tissue directivity would be a powerful tool to characterize the extent of the lesion. In this field, diffusion MRI is the reference. Because of its long acquisitiontime and the difficulty to tackle organ motion, faster imaging strategies such as ultrasound, are mandatory for such clinical applications. One of them is the spatial coherence of US waves, already developed in focused and plane waves (2D and 3D) but never in diverging waves [Papadacci, UFFC 2014]. The advantage of diverging waves is to create an imagewith a higher field of view, which is more appropriate to in vivo cardiac applications. The purpose of this work is to use 2D spatial coherence to determine the fibers orientation and to compare results in 3D steered plane and diverging waves.Statement of Contribution/MethodsSpatial coherence is representative of the tissue structure. In an anisotropic medium, spatial coherence is high in that preferred local direction and the 2D coherence function exhibits an ellipsoidal shape. The main axis of this ellipse corresponds to the local main direction of the underlying tissue structure. Acquisitions have been conducted on a phantom designed from seven angled wires (ø 0.3 mm) embedded in an agar gel. The dataset was obtained using a 1024 channels ultrasound system based on the synchronization of 4 Verasonics Vantage 256 systems. A 1024 elements of a 32x32 elements 3 MHz array (Vermon) was fully controlled to transmit 2D steered plane and diverging waves on the same location. 25 transmission angles from -5° to 5° in x and y direction were used. The 2D coherence function maps were calculated on the spatial points corresponding to the centre of the seven wires and the main axis of ellipsoidal shapes are extracted to render the wires angle.Results/DiscussionThe curves representing the wires angle obtained in both plane and diverging waves are close to the reference. Using diverging waves, a RMSE of 4.8° is obtained which is better than the RMSE of 11.2° obtained with plane wave transmissions. It demonstrates the interest of 3D diverging waves to increase both the field of view and the coherence calculation accuracy. Such results must now be confirmed on heart sample acquisitions.

International audience; Background, Motivation and ObjectiveIn parallel with the increasing interest for 3D ultrasound imaging, different design techniques have been investigated to find the best configurations of 2D sparse arrays to scan an entire volume of interest [Trucco, IEEE UFFC99], [Diarra, IEEE TBME13]. In particular, we recently addressed the issue of driving a full 2D array of 1024 elements with a reduced number of channels (128, 192 or 256): the optimal arrays (opti128, opti192 and opti256) were obtained using simulated annealing to sculpt the radiated wideband pressure field at multiple depths [Roux, IEEE UFFC17]. The aim of the present work is to experimentally validate these optimal configurations by performing 3D focused imaging on phantoms.Statement of Contribution/MethodsThe 1024 elements of a 3 MHz array made by Vermon were individually driven by four synchronized Verasonics Vantage 256 systems. The systems were programmed to transmit 3-cycle sine bursts at 3 MHz focused at 25 mm and to scan a 3D sector with span ±30° in 31×29 steered beams in azimuth and elevation, respectively. Six arrays were compared: the optimal arrays (opti128, opti192 and opti256), an array whose active elements where randomly selected (rand256) and two references (REF716 and REF1024). The circular dense array REF716 corresponds to the full array REF1024 array without the corner elements. The comparison criteria were the lateral resolution (full width at half maximum - FWHM) and the contrast to noise ratio (CNR), measured on the images obtained by scanning a Gammex (Sono410 SCG) and CIRS (054GS) phantoms respectively.Results/DiscussionThe results are reported in Table 1. The opti256 performs the best among all the compared sparse arrays because it presents the same resolution performance as the REF1024 and an acceptable loss of CNR while using only 25% of the active elements of REF1024. The REF716 array is very competitive with only 70% of the active elements of REF1024.

International audience; Background, Motivation and ObjectiveThe emergence of ultrafast imaging allowed new insights into cardiac deformation/motion analysis that enabled new advancements in clinical diagnosis. Several studies showed that a good compromise between the temporal and the spatial resolution can be obtained by transmitting multiple focused beams (MLT) simultaneously. However, the currentimplementation of MLT in 3D cannot be used in dynamic conditions as it was obtained synthetically, by summing the Single Line Transmit (SLT) events before beamforming [Ortega et al., TUFFC, 2016]. The objective of this study is to evaluate for the first time the performance of MLT in 3D ultrasound under dynamic conditions. Statement of Contribution/MethodsThe 3D images were acquired by using four Verasonics research scanners, each of them controlling 8-by-32 elements of a 32-by-32, 3 MHz, Vermon ultrasound transducer. The scan volume was created by stitching 30 triangular sectors (each of angular width = 40°) along the azimuth angular direction. For each triangular sector, 9 transmission events were used for insonifying a full sector by sending simultaneously three focused beams. Thus, the total number of transmissions was 270 corresponding to 27 (elevational) x 30 (azimuthal) focal beams. The Pulse Repetition Frequency (PRF) was set to 2250. Our in vitro model was a tissue mimicking spinning disc having a diameter of 11 cm whose speed could be controlled by a step motor. The disk was placed at approximately 3 cm away from transducer and the image depth was 6.8 cm. Doppler velocities were estimated from the IQ signals using a 2D auto-correlator and a packet length of 7.Results/DiscussionThis study demonstrates the feasibility of Doppler velocity estimation for 3D MLT images. The estimated values presented in the image were in agreement with the expected velocities since the relative mean error was 3.5%. We obtained a three-fold increase in volume rate compared with focus imaging. Analyzing further different MLT/MLA configurations would allow increasing the frequency of volumes and obtaining the optimal compromise between high volume rate and quality color Doppler.

This work shows the feasibility of performing ultrafast 3D ultrasound imaging by producing diverging waves (DW) with 2D sparse arrays. The 3D volumes were experimentally acquired by individually driving the 1024 elements of a full 32×32 matrix array. The volumes obtained with different sparse configurations were compared to those obtained with two references arrays: the full 32×32 array and a dense array of 716 elements where obtained by de-activating the corner elements of the full array. The comparison criteria were the lateral resolution using the full width at half maximum (FWHM) and the contrast to noise ratio (CNR), measured on the images obtained by scanning a grayscale phantom. The results show that ultrafast 3D ultrasound imaging can be performed with a reduced number of channels using 2D sparse arrays. However, there is still space to find the optimal 2D sparse array configurations to best transmit 3D DWs and potential improvements on image quality may be achieved with dedicated optimization e.g. cost function to homogenize DW wave front.

Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU, or MRgFUS) is a hybrid technology that was developed to provide efficient and tolerable thermal ablation of targeted tumors or other pathologic tissues, while preserving the normal surrounding structures. Fast 3-D ablation strategies are feasible with the newly available phased-array HIFU transducers. However, unlike fixed heating sources for interstitial ablation (radiofrequency electrode, microwave applicator, infra-red laser applicator), HIFU uses propagating waves. Therefore, the main challenge is to avoid thermo-acoustical adverse effects, such as energy deposition at reflecting interfaces and thermal drift of the focal lesion toward the near field. We report here our investigations on some novel experimental solutions to solve, or at least to alleviate, these generally known tolerability problems in HIFU-based therapy. Online multiplanar MR thermometry was the main investigational tool extensively used in this study to identify the problems and to assess the efficacy of the tested solutions. We present an improved method to cancel the beam reflection at the exit window (i.e., tissue-to-air interface) by creating a multilayer protection, to dissipate the residual HIFU beam by bulk scattering. This study evaluates selective de-activation of transducer elements to reduce the collateral heating at bone surfaces in the far field, mainly during automatically controlled volumetric ablation. We also explore, using hybrid US/MR simultaneous imaging, the feasibility of using disruptive boiling at the focus, both as a far-field self-shielding technique and as an enhanced ablation strategy (i.e., boiling core controlled HIFU ablation).

Objectives: The combination of ultrasound (US) and magnetic resonance imaging (MRI) may provide a complementary description of the investigated anatomy, together with improved guidance and assessment of image-guided therapies. The aim of the present study was to integrate a clinical setup for simultaneous US and magnetic resonance (MR) acquisition to obtain synchronized monitoring of liver motion. The feasibility of this hybrid imaging and the precision of image fusion were evaluated. Materials and Methods: Ultrasound imaging was achieved using a clinical US scanner modified to be MR compatible, whereas MRI was achieved on 1.5- and 3-T clinical scanners. Multimodal registration was performed between a high-resolution T1 3-dimensional (3D) gradient echo (volume interpolated gradient echo) during breath-hold and a simultaneously acquired 2D US image, or equivalent, retrospective registration of US imaging probe in the coordinate frame of MRI. A preliminary phantom study was followed by 4 healthy volunteer acquisitions, performing simultaneous 4D MRI and 2D US harmonic imaging (Fo = 2.2 MHz) under free breathing. Results: No characterized radiofrequency mutual interferences were detected under the tested conditions with commonly used MR sequences in clinical routine, during simultaneous US/MRI acquisition. Accurate spatial matching between the 2D US and the corresponding MRI plane was obtained during breath-hold. In situ fused images were delivered. Our 4D MRI sequence permitted the dynamic reconstruction of the intra-abdominal motion and the calculation of high temporal resolution motion field vectors. Conclusions: This study demonstrates that, truly, simultaneous US/MR dynamic acquisition in the abdomen is achievable using clinical instruments. A potential application is the US/MR hybrid guidance of high-intensity focused US therapy in the liver.

The treatment of liver cancer is a major public health issue because the liver is a frequent site for both primary and secondary tumors. Rib heating represents a major obstacle for the application of extracorporeal focused ultrasound to liver ablation. Magnetic resonance (MR)-guided external shielding of acoustic obstacles (eg, the ribs) was investigated here to avoid unwanted prefocal energy deposition in the pathway of the focused ultrasound beam.Ex vivo and in vivo (7 female sheep) experiments were performed in this study. Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) was performed using a randomized 256-element phased-array transducer (f∼1 MHz) and a 3-T whole-body clinical MR scanner. A physical mask was inserted in the prefocal beam pathway, external to the body, to block the energy normally targeted on the ribs. The effectiveness of the reflecting material was investigated by characterizing the efficacy of high-intensity focused ultrasound beam reflection and scattering on its surface using Schlieren interferometry. Before high-intensity focused ultrasound sonication, the alignment of the protectors with the conical projections of the ribs was required and achieved in multiple steps using the embedded graphical tools of the MR scanner. Multiplanar near real-time MR thermometry (proton resonance frequency shift method) enabled the simultaneous visualization of the local temperature increase at the focal point and around the exposed ribs. The beam defocusing due to the shielding was evaluated from the MR acoustic radiation force impulse imaging data.Both MR thermometry (performed with hard absorber positioned behind a full-aperture blocking shield) and Schlieren interferometry indicated a very good energy barrier of the shielding material. The specific temperature contrast between rib surface (spatial average) and focus, calculated at the end point of the MRgHIFU sonication, with protectors vs no protectors, indicated an important reduction of the temperature elevation at the ribs' surface, typically by 3.3 ± 0.4 in vivo. This was translated into an exponential reduction in thermal dose by several orders of magnitude. The external shielding covering the full conical shadow of the ribs was more effective when the protectors could be placed close to the ribs' surface and had a tendency to lose its efficiency when placed further from the ribs. Hepatic parenchyma was safely ablated in vivo using this rib-sparing strategy and single-focus independent sonications.A readily available, MR-compatible, effective, and cost-competitive method for rib protection in transcostal MRgHIFU was validated in this study, using specific reflective strips. The current approach permitted safe intercostal ablation of small volumes (0.7 mL) of liver parenchyma.

Magnetic resonance imaging (MRI) and ultrasonography have been used simultaneously in this ex vivo study for the image-guidance of high intensity focused ultrasound (HIFU) treatment in moving tissue. A ventilator-driven balloon produced periodic and non-rigid (i.e. breathing-like) motion patterns in phantoms. MR-compatible ultrasound (US) imaging enabled near real-time 2D motion tracking based on optical flow detection, while near-harmonic reference-free proton resonance frequency shift (PRFS) MR thermometry (MRT) was used to monitor the thermal buildup on line. Reference-free MRT was applied to gradient-echo echo-planar imaging phase maps acquired at the frame rate of 250 to 300 ms/slice with voxel size 1.25×1.25×5 mm(3). The MR-US simultaneous imaging was completely free of mutual interferences while minor RF interferences from the HIFU device were detected in the far field of the US images. The effective duty-cycle of the HIFU sonication was close to 100 % and no off-interval was required to temporally decouple it from the ultrasonography. The motion compensation of the HIFU sonication was achieved with an 8 Hz frame rate and sub-millimeter spatial accuracy, both for single-focus mode and for an iterated multi-foci line scan. Near harmonic reference-less PRFS MRT delivered motion-robust thermal maps perpendicular or parallel to the HIFU beam (0.7 °C precision, 0.5 °C absolute accuracy). Out-of-plane motion compensation was not addressed in this study.

Real-time image-guided extracorporeal high intensity focused ultrasound (HIFU) has been suggested for minimally invasive treatment of valvular dysfunction in the saphenous vein. Local application of heat on the perimeter of the valve zone was previously reported to induce a partial shrinkage of the collagen, which may correct valvular function. In our study, a novel MR compatible HIFU device has been investigated. This device is based on a non-spherical geometry, with two active elements that create a focusing line which is orthogonal to the beam main axis, aiming to cover the valve longitudinally. The prototype performance was characterized by electro-acoustical measurements of the pressure field and by high-resolution MR thermometry. Pressure and thermal fields were found in good agreement with the theoretical predictions. To investigate the therapeutic potential, fresh samples of excised human veins were filled with an agarose gel, embedded in porcine muscle and exposed to HIFU. The power level applied during a fixed duration of 30 s was varied such that the absolute temperature at focus ranged between 52 degrees C and 83 degrees C. Targeting was achieved under MR guidance using a MR compatible XZ positioning system. A dedicated waterproof miniature loop coil was specifically built to achieve high-resolution MRI image-based targeting (0.25 mm x 0.25 mm x 3 mm voxel) and thermometry (0.4 mm x 0.4 mm x 4 mm voxel). The vein wall was clearly identified on MR images before and after HIFU treatment. The thermal buildup created by the non-spherical transducer could be characterized from MR thermometry data. Shrinkage of the vein wall (above 65 degrees C) was determined by absolute temperature and was not a cumulative thermal dose effect.

Magnetic resonance (MR) imaging and ultrasound (US) imaging are complementary and synergetic noninvasive imaging modalities. US imaging is practically free of geometric distortion and provides high temporal resolution and direct visualization of acoustic obstacles. MR imaging offers excellent tissue contrast and a confirmed method for near-real-time thermometry. Their combination may help increase the intraoperative control and assessment in image-guided therapies. The added value of this dual-modality imaging would consist of a more complete description of the anatomy investigated, more accurate targeting, efficient motion tracking, and reliable immediate assessment of the therapeutic results. This chapter focuses on truly simultaneous US/MR technology integration and early applications. A prototype setup designed to clinical standards is described together with the preliminary evaluation of the hybrid imaging performance in the abdomen. In particular, the precision of image coregistration was assessed in healthy volunteers. Furthermore, a complex study investigated the thermal cavitation effects produced by radio-frequency ablations. Simultaneous US imaging/MR imaging acquisition permitted us to demonstrate that the latter effects induce subsequent magnetic-susceptibility-mediated errors in proton resonance frequency shift thermometry, both in ex vivo models and in patients treated for hepatic malignancies. The foreseen perspectives of the hybrid US imaging/MR imaging technique are included in the final section.

A new high intensity focused ultrasound (HIFU) probe has been designed and tested by using MRI. The probe is intended to be used by physicians to correct valvular dysfunction in the saphenous vein, which is known to be the cause of superficial venous insufficiency (SVI) and varicose veins. Treating SVI with HIFU is possible, since venous tissue undergoes localized partial shrinkage when subjected to HIFU. In vitro experiments have demonstrated that diameter shrinkage should be sufficient to restore valvular function, as is done in the more aggressive approach known as external valvuloplasty. Numerical simulations and optimization have led to a probe design with two HIFU elements that focus sound uniformly over a line of length 7 mm, at a depth of 15 mm from the skin. A prototype of the probe has been constructed, with a holder that provides space for an MRI-imaging antenna. The probe has been tested by measuring pressure and temperature fields. Results are in good agreement with those predicted by an analytical approach and numerical simulations.

Objective. To demonstrate the technical feasibility and the potential interest of using a digital optical camera inside the MR magnet bore for monitoring the breathing cycle and subsequently gating the PRFS MR thermometry, MR-ARFI measurement, and MRgHIFU sonication in the upper abdomen. Materials and Methods. A digital camera was reengineered to remove its magnetic parts and was further equipped with a 7 m long USB cable. The system was electromagnetically shielded and operated inside the bore of a closed 3T clinical scanner. Suitable triggers were generated based on real-time motion analysis of the images produced by the camera (resolution 640×480 pixels, 30 fps). Respiratory-gated MR-ARFI prepared MRgHIFU ablation was performed in the kidney and liver of two sheep in vivo, under general anaesthesia and ventilator-driven forced breathing. Results. The optical device demonstrated very good MR compatibility. The current setup permitted the acquisition of motion artefact-free and high resolution MR 2D ARFI and multiplanar interleaved PRFS thermometry (average SNR 30 in liver and 56 in kidney). Microscopic histology indicated precise focal lesions with sharply delineated margins following the respiratory-gated HIFU sonications. Conclusion. The proof-of-concept for respiratory motion management in MRgHIFU using an in-bore digital camera has been validated in vivo.

The emergence of ultrafast imaging allowed new insights into cardiac deformation/motion analysis that enabled new advancements in clinical diagnosis. Several studies showed that a good compromise between the temporal and the spatial resolution can be obtained by transmitting multiple focused beams (MLT) simultaneously. However, the current implementation of MLT in 3D cannot be used in dynamic conditions as it was obtained synthetically, by summing the Single Line Transmit (SLT) events before beamforming [Ortega et al., TUFFC, 2016]. The objective of this study is to evaluate for the first time the performance of MLT in 3D ultrasound under dynamic conditions.

International audience; Background, Motivation and ObjectiveAchieving a high frame rate in echocardiography is highly important for quantifying the short phases of the cardiac cycle that contain valuable information for medical diagnosis. Additionally, the 3D quantitative assessment of the heart would significantly improve the current measurements used in daily clinical routine. Nevertheless, obtaining ultrafast imagesremains a challenge due to the trade-off between the image quality and a high frame rate, especially when volumetric data is acquired. Among the current ultrafast imaging methods, multi-line-transmit imaging (MLT) provides an increased frame rate but in the same time mostly preserves the image quality. However, the current implementation of this methodin 3D proposed by Ortega et al. [IEEE TUFC 2016] is based on generating the MLT data synthetically by summing up the raw data before beamforming. In this paper we present the first real-time implementation of the MLT in 3D ultrasound.Statement of Contribution/MethodsMulti-line-transmission was performed by dividing the angular aperture into three regions. Then, due to practical limitations, three equally spaced focused beams were transmitted simultaneously in the first YZ plane of the first region. Once the transmission for a full YZ plane was completed, the process was repeated for the first YZ plane of the second region. The same steps were followed till the full volume was insonified. Data acquisition was performed using four Verasonics systems synchronized to drive a 32x32 matrix probe. A transmit frequency of 2.97 MHz was used and the images were acquired using a sampling frequency of 11.9 MHz. The focal point was set to 6.7 cm depth along 27 different angles in elevational direction (YZ) and 30 angles in azimuthal direction (XZ) between -20º and 20º.Results/DiscussionThe contrast and the resolution assessment, performed on a CIRS ultrasound phantom (Figure 1) showed a contrast of 6.36 dB and a mean axial (lateral) resolution of 0.9 mm (1.77 mm) measured for different depths. These values are comparable with those obtained for a 3D focused sequence obtained by using the same emission parameters. The results indicate the potential of MLT 3D for achieving high contrast and resolution while increasing the frame rate. This study thus demonstrates the feasibility of 3D MLT in real-time and extends its possible applications to dynamic cardiac imaging.