Ditlef Martens

Dynamic three-dimensional freehand echocardiography using raw digital ultrasound data.

In this paper, we present a new method for simple acquisition of dynamic three-dimensional (3-D) ultrasound data. We used a magnetic position sensor device attached to the ultrasound probe for spatial location of the probe, which was slowly tilted in the transthoracic scanning position. The 3-D data were recorded in 10-20 s, and the analysis was performed on an external PC within 2 min after transferring the raw digital ultrasound data directly from the scanner. The spatial and temporal resolutions of the reconstruction were evaluated, and were superior to video-based 3-D systems. Examples of volume reconstructions with better than 7 ms temporal resolution are given. The raw data with Doppler measurements were used to reconstruct both blood and tissue velocity volumes. The velocity estimates were available for optimal visualization and for quantitative analysis. The freehand data reconstruction accuracy was tested by volume estimation of balloon phantoms, giving high correlation with true volumes. Results show in vivo 3-D reconstruction and visualization of mitral and aortic valve morphology and blood flow, and myocardial tissue velocity. We conclude that it was possible to construct multimodality 3-D data in a limited region of the human heart within one respiration cycle, with reconstruction errors smaller than the resolution of the original ultrasound beam, and with a temporal resolution of up to 150 frames per second.

Blood flow imaging - a new real-time, flow imaging technique

This paper presents a new method for the visualization of two-dimensional (2-D) blood flow in ultrasound imaging systems called blood flow imaging (BFI). Conventional methods of color flow imaging (CFI) and power Doppler (PD) techniques are limited as the velocity component transversal to the ultrasound beam cannot be estimated from the received Doppler signal. The BFI relies on the preservation and display of the speckle pattern originating from the blood flow scatterer signal, and it provides qualitative information of the blood flow distribution and movement in any direction of the image. By displaying speckle pattern images acquired with a high frame rate in slow motion, the blood flow movement can be visually tracked from frame to frame. The BFI is easily combined with conventional CFI and PD methods, and the resulting display modes have been shown to have several advantages compared to CFI or PD methods alone. Two different display modes have been implemented: one combining BFI with conventional CFI, and one combining BFI with PD. Initial clinical trials have been performed to assess the clinical usefulness of BFI. The method especially has potential in vascular imaging, but it also shows potential in other clinical applications.

Feasibility of color doppler tissue velocity imaging for assessment of regional timing of left ventricular longitudinal movement.

Objective—The feasibility of color Doppler tissue velocity imaging (c‐TVI) with a high time resolution of 10 ms for simultaneous measurement of the temporal characteristics of regional left ventricular (LV) tissue velocities at different LV sites was examined. Methods and results—In 20 subjects with structurally normal hearts, inter‐ and intraobserver agreement and the beat‐to‐beat variation were tested in c‐TVI profiles from basal and mid‐LV segments of the interventricular septum (IS) and of the lateral free wall (LFW). For peak tissue velocities a mean error of less than 1 cm/s was demonstrated. For systolic regional LV velocity time difference, the mean error was ±5 ms, with the best agreement when sampling from basal LV sites. For diastolic regional LV velocity time differences, the mean error was ±12 ms. The longitudinal LV movement pattern demonstrated a pattern of incremental tissue velocity from basal to mid‐LV, and from IS to LFW sites. Conclusion—The c‐TVI method has acceptable inter‐ and intraobserver agreement and is sufficiently accurate to disclose regional time aspects of LV contraction and relaxation.

Blood motion imaging - a new technique to visualize 2D blood flow

In this study we present new signal processing algorithms for visualization of blood flow in ultrasound imaging systems. Color flow systems produce each image from packets of typically 5-15 pulses transmitted along each scan line in the image. The Doppler shift from moving blood is utilized to remove clutter noise, and for color coding of the blood velocity component along the ultrasound beam. Blood motion causes a corresponding movement in the speckle pattern of the received signal from pulse to pulse. In conventional color flow imaging, substantial temporal and spatial averaging is used in order to get reliable detection of blood vessels, and low variance in the velocity estimate. This averaging process suppresses the spatial speckle pattern in the signal amplitude. In our technique the speckle pattern from the moving blood cells is preserved and enhanced, enabling the user to visually track the blood motion from pulse to pulse. The speckle visualization is combined with conventional color flow color encoding. In addition to preserving the speckle pattern, several image frames per packet of pulse transmissions are computed. The perception of movement is further improved if the scatterers in a large spatial region are imaged almost simultaneously. This is obtained by increasing the time between pulse transmissions in the same beam direction, and using a technique called beam interleaving. After transmitting a pulse in a first direction, there is little available to acquire data in several other beam directions before transmitting the next pulse in the first direction. Visualization of the speckle pattern movement gives the user a correct perception of the blood flow direction and magnitude, and is also useful in separating true blood flow from wall motion artifacts.

Method and system for performing real time navigation of ultrasound volumetric data

An ultrasound system is provided that includes a display processor that accesses data volumes stored in an image buffer successively to control generation of at least one of 2D and 3D renderings based on display parameters. The display processor obtains from the image buffer a first data volume defined based on first scan parameter values, while a probe acquires ultrasound information for a second data volume that is entered into the image buffer. The second data volume is defined based on second scan parameter values. A navigation view presents in real time the renderings generated by the display processor with their corresponding 31) orientation. A navigator is provided that controls the display of the navigation view in real time such that, as the user adjusts a display parameter value to change a view plane, images presented in the navigation view are updated to reflect the view plane.

Real-time blood motion imaging a 2D blood flow visualization technique

This paper describes the performance of a real-time implementation of blood motion imaging (BMI), a new method for 2D blood flow visualization. BMI is a qualitative technique for presenting blood flow in any direction, achieved by preservation, enhancement, and display of the speckle pattern originating from the blood flow signal. When played back at the overall modality frame rate, it is possible to visually track the blood flow speckle pattern from image to image in real-time. Two different implementations of real-time BMI have been made, extending the current color flow imaging (CFI) and power Doppler (PD) modalities by modulating the parametric flow images with the speckle pattern images. Initial investigations regarding the clinical usefulness of BMI has shown that it has potential in several areas of medicine. Still, more work has to be done to map the applications for which BMI can make a significant difference.