New and future developments in ultrasonic imaging.

The fast visualisation of cerebral microcirculation supports diagnosis of acute cerebrovascular diseases. However, the commonly used CT/MRI-based methods are time consuming and, moreover, costly. Therefore we propose an alternative approach to brain perfusion imaging by means of ultrasonography. In spite of the low signal/noise-ratio of transcranial ultrasound and the high impedance of the skull, flow images of cerebral blood flow can be derived by capturing the kinetics of appropriate contrast agents by harmonic ultrasound image sequences. In this paper we propose three different methods for human brain perfusion imaging, each of which yielding flow images indicating the status of the patient's cerebral microcirculation by visualising local flow parameters. Bolus harmonic imaging (BHI) displays the flow kinetics of bolus injections, while replenishment (RHI) and diminution harmonic imaging (DHI) compute flow characteristics from contrast agent continuous infusions. RHI measures the contrast agents kinetics in the influx phase and DHI displays the diminution kinetics of the contrast agent acquired from the decay phase. In clinical studies, BHI- and RHI-parameter images were found to represent comprehensive and reproducible distributions of physiological cerebral blood flow. For DHI it is shown, that bubble destruction and hence perfusion phenomena principally can be displayed. Generally, perfusion harmonic imaging enables reliable and fast bedside imaging of human brain perfusion. Due to its cost efficiency it complements cerebrovascular diagnostics by established CT/MRI-based methods.

New concept in echocardiography: harmonic imaging of tissue without use of contrast agent

901–49 Second Harmonic Imaging of Echocardiographic Contrast Agents: Unique Features and Promising Characteristics

Recently, the technique of harmonic contrast imaging has been developed which exploits the nonlinear properties of ultrasound contrast agents by processing the second harmonic echo signal of the transmitted ultrasound pulse. The contrast agent employed is Levovist (Schering), which was released in Japan in 1999. The advantage of harmonic imaging is its selective imaging of differences between tissue and blood perfusion areas.The purpose of the present study was to investigate a method of detecting human brain perfusion by ultrasound with second harmonic signals and contrast agents in eight patients with brain tumors. We used pulse inversion harmonic imaging, which is the latest technique for visualizing ultrasound contrast agents, thereby allowing us to image brain perfusion, and well enhanced perfusion images were obtained in all cases.We performed analysis resulting in wash-in wash-out curves, and concluded that this method could be used for diagnosis of brain hemodynamics.

X-ray computed tomography (CT) imaging plays an essential role in disease diagnosis due to its noninvasive, painless mode and superior penetration depth. However, the resolution of the soft tissue ...

Ultrasound computed tomography (USCT) holds great promise for improving the detection and management of breast cancer. Because they are based on the acoustic wave equation, waveform inversion-based reconstruction methods can produce images that possess improved spatial resolution properties over those produced by ray-based methods. However, waveform inversion methods are computationally demanding and have not been applied widely in USCT breast imaging. In this work, source encoding concepts are employed to develop an accelerated USCT reconstruction method that circumvents the large computational burden of conventional waveform inversion methods. This method, referred to as the waveform inversion with source encoding (WISE) method, encodes the measurement data using a random encoding vector and determines an estimate of the sound speed distribution by solving a stochastic optimization problem by use of a stochastic gradient descent algorithm. Both computer simulation and experimental phantom studies are conducted to demonstrate the use of the WISE method. The results suggest that the WISE method maintains the high spatial resolution of waveform inversion methods while significantly reducing the computational burden.

Purpose: Existing Dopplerultrasound techniques are capable of detecting blood flow in large vessels with velocities high enough (>3 cm/sec) to enable removal of tissue signals. Microbubbleultrasound contrast agents can be administered intravenously to increase the backscatter from blood. The nonlinear behavior of ultrasound contrast agents enable discrimination from tissue both nearly stationary microbubbles in the microcirculation and higher velocitymicrobubbles in the larger vasculature. The visualization of blood flow in both the macro‐ and micro‐circulation has been used to assess organ function and characterize tumors. Method and Materials:Imaging techniques for ultrasound contrast agents have been developed utilizing both the nonlinear and transient nature of contrast agents. These techniques are based on detecting microbubble nonlinear responses to the acoustic field of diagnosticultrasound. Different multi‐pulse transmit sequences will be described that have been used detect the nonlinear activity of the microbubbles (harmonic imaging, pulse inversion, amplitude modulation, and coded excitation). Only low amplitude acoustic fields may be used for interrogation to avoid bubble destruction and enable continuous contrast agent imaging. The difficulties of detecting nonlinear activity with low excitations are addressed. Dopplerimaging techniques are used in cases where transient properties of contrast agents are to be imaged. With these techniques high acoustic amplitude is used to intentionally destroy the contrast microbubbles and form an image. Once the bubbles in a region are destroyed, the user must wait for the area to be replenished before forming another image or move to a new imaging plane. Results: While destruction techniques have an excellent signal to noise ratio (SNR), clinical use is difficult due to the destruction of contrast agent. Nonlinear imaging techniques are clinically easier to use, but suffer from SNR and are often penetration limited. A number of different ultrasound contrast agents have been approved for clinical use in Europe and Asia and are in the Federal Drug Administration approval process in the US. Most these contrast agents can be imaged in real‐time using the nonlinear imaging techniques. Conclusion:Ultrasound contrast agents can be used to imageblood flow in both the micro‐ and macro‐ circulations. Clinical examples of imagingultrasound contrast agent with both low and high amplitude techniques will be presented for both radiology and cardiology applications.

Ultrasound contrast agents: Basic principles

Ultrasound (US) harmonic imaging has shown advantages in better spatial resolution and contrast compared to classic fundamental imaging, but it suffers from more attenuation due to the increased frequency. To achieve more penetration, high dynamic range (DR) front-end electronics is required to receive the weak harmonic components. Typical US front-ends use a variable gain amplifier (VGA) to compensate part of the required DR, in order to avoid using a highly sensitive analog-to-digital converter (ADC). However, in harmonic imaging, the received signal amplitude is dominated by the fundamental component, thus the VGA is less efficient for these small harmonics. An analog front-end filter can be used before the VGA to mitigate this issue but this has an impact on spatial resolution by changing the dominant frequency component and spatial pulse length of the received signal. In this work, a combined acoustic-and-electronic model is made to understand the impact of the use of an analog front-end filter in US harmonic imaging applications in terms of imaging resolution, contrast, and hardware requirements.

The intensity and duration of contrast effect within the left ventricular cavity after an intravenous bolus of Levovist Injection were observed with both harmonic and fundamental imaging in nine patients with known or suspected coronary artery disease. Contrast intensity was assessed by a qualitative grading system (0, none; 1, weak; 2, moderate; 3, good) and by videodensitometric analysis of pixel intensity. Duration of left ventricular contrast effect was determined by measuring time from the initial visual appearance of contrast agent to its disappearance. The mean increase in pixel intensity within the left ventricular cavity from precontrast to peak contrast was significantly greater for second harmonic than for fundamental imaging (25.5 vs 7.1; P < 0.012). The mean contrast intensity qualitative score with harmonic imaging was higher (2.6 +/- 0.73 vs 1.2 +/- 0.44; P < 0.01) and the duration of contrast effect was longer (242 +/- 131 s vs 53 +/- 33 s; P < 0.004). Second harmonic imaging significantly enhanced contrast intensity and prolonged visible duration of contrast effect after a peripheral venous injection of Levovist.

703-3 Second Harmonic Mode Imaging Improves Contrast Agent [SHU 508-A] Visualization in an In Vitro Model

Development of nanoparticles and quantum dots as alternatives to iodinated contrast agents for mono-modal and bi-modal computed tomography imaging.

Ultrasound computed tomography (USCT) is an emerging imaging modality that holds great promise for breast imaging. Full-waveform inversion (FWI)-based image reconstruction methods incorporate accurate wave physics to produce high spatial resolution quantitative images of speed of sound or other acoustic properties of the breast tissues. However, FWI reconstruction is computationally expensive, which limits its application in a clinical setting. This contribution investigates using the use of a convolutional neural network (CNN) to learn a mapping from USCT data to speed of sound estimates. The CNN was trained using a supervised approach that employed a large set of anatomically and physiologically realistic numerical breast phantoms (NBPs) and simulated USCT measurements. Once trained, this CNN can then be evaluated for real-time FWI image reconstruction from USCT data. The performance of the proposed method was assessed and compared against FWI using a hold-out sample of 41 NBPs and corresponding USCT images. Accuracy was measured using relative mean square error (RMSE) and structural self-similarity index measure (SSIM). This numerical experiment demonstrates that a supervised learning model can achieve accuracy comparable to FWI, while significantly reducing computational time and memory requirements.

Optimization of patent foramen ovale detection by contrast transthoracic echocardiography using second harmonic imaging

Contrast-enhanced sonographic reflux diagnosis, i. e. voiding urosonography (VUS), is gradually becoming an alternative for diagnostic imaging of vesicoureteric reflux (VUR). A limiting factor for the widespread application of VUS is the cost of the US contrast agents. The development of new US contrast agents and the possibility of reducing the administered dose are expected to lower the cost. The aim of this study was an in-vitro comparison of the new US contrast agent (SonoVue) and the routinely used contrast agent Levovist, while taking into consideration the physical-chemical properties relevant for reflux diagnosis. The in-vitro experiment setup simulated the in-vivo VUS. The US modalities fundamental and harmonic imaging (THI/ECI, Sonoline Elegra, Siemens) were utilized, the latter with both low and high mechanical indices (MI). SonoVue was tested in concentrations of 0.25 %, 0.5 % and 1 % and Levovist at 5 % volume. The in-vitro contrast duration served as the parameter for comparison. This was defined as the time from the start of the experiment until the time when more than 50 % of the image area was free of microbubbles. The use of different concentrations of SonoVue did not have any impact on the contrast duration. The contrast duration of SonoVue turned out to be significantly longer when the US modality was switched from low to high MI. In the case of THI with high MI as is routinely with Levovist, the contrast duration of Levovist at a concentration of 5 % was 1.1 min, whereas that of SonoVue at a concentration of 1 % reached 7.3 min. This means that despite SonoVue being administered at a dose five times lower than that of Levovist, the in-vitro contrast duration increased by more than 80 %. Moreover, a freshly prepared suspension of SonoVue did not show change in the contrast duration for nearly 6 hours. In the case of Levovist there was a significant reduction in the contrast duration after only a half hour. The in-vivo use of SonoVue is expected to yield a significant dose reduction so that one vial can be used for more than one examination. A measurable cost reduction can consequently be achieved.