Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-07-31
2003-06-03
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S459000
Reexamination Certificate
active
06572547
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semi-invasive ultrasound imaging systems, and more particularly to transesophageal imaging systems and transnasal, transesophageal imaging systems that provide several two-dimensional plane views and projection views for visualizing three-dimensional anatomical structures inside a patient.
BACKGROUND
Non-invasive, semi-invasive and invasive ultrasound imaging has been widely used to view tissue structures within a human body, such as the heart structures, the abdominal organs, the fetus, and the vascular system. The semi-invasive systems include transesophageal imaging systems, and the invasive systems include intravascular imaging systems. Depending on the type and location of the tissue, different systems provide better access to or improved field of view of internal biological tissue.
In general, ultrasound imaging systems include a transducer array connected to a multiple channel transmit and receive beamformer. The transmit beamformer applies electrical pulses to the individual transducers in a predetermined timing sequence to generate transmit beams that propagate in predetermined directions from the array. As the transmit beams pass through the body, portions of the acoustic energy are reflected back to the transducer array from tissue structures having different acoustic characteristics. The receive transducers (which may be the transmit transducers operating in a receive mode) convert the reflected pressure pulses into corresponding electrical RF signals that are provided to the receive beamformer. Due to different distances from a reflecting point to the individual transducers, the reflected sound waves arrive at the individual transducers at different times, and thus the RF signals have different phases.
The receive beamformer has a plurality of processing channels with compensating delay elements connected to a summer. The receive beamformer selects the delay value for each channel to combine echoes reflected from a selected focal point. Consequently, when delayed signals are summed, a strong signal is produced from signals corresponding to this point. However, signals arriving from different points, corresponding to different times, have random phase relationships and thus destructively interfere. The receive beamformer selects such relative delays that control the orientation of the receive beam with respect to the transducer array. Thus, the receive beamformer can dynamically steer the receive beams to have desired orientations and can focus them at desired depths. The ultrasound system thereby acquires acoustic data.
To view tissue structures in real-time, various ultrasound systems have been used to generate two-dimensional or three-dimensional images. A typical ultrasound imaging system acquires a two-dimensional image plane that is perpendicular to the face of the transducer array applied to a patient's body. To create a three-dimensional image, the ultrasound system must acquire acoustic data over a three-dimensional volume by, for example, moving a one-dimensional (or a one-and-half dimensional) transducer array over several locations. Alternatively, a two-dimensional transducer array can acquire scan data over a multiplicity of image planes. In each case, the system stores the image plane data for reconstruction of three-dimensional images. However, to image a moving organ, such as the heart, it is important to acquire the data quickly and to generate the images as fast as possible. This requires a high frame rate (i.e., the number of images generated per unit time) and fast processing of the image data. However, spatial scanning (for example, when moving a one-dimensional array over several locations) is not instantaneous. Thus, the time dimension is intertwined with the three space dimensions when imaging a moving organ.
Several ultrasound systems have been used to generate 3D images by data acquisition, volume reconstruction, and image visualization. A typical ultrasound system acquires data by scanning a patient's target anatomy with a transducer probe and by receiving multiple frames of data. The system derives position and orientation indicators for each frame relative to a prior frame, a reference frame or a reference position. Then, the system uses the frame data and corresponding indicators for each frame as inputs for the volume reconstruction and image visualization processes. The 3D ultrasound system performs volume reconstruction by defining a reference coordinate system within which each image frame in a sequence of the registered image frames. The reference coordinate system is the coordinate system for a 3D volume encompassing all image planes to be used in generating a 3D image. The first image frame is used to define the reference coordinate system (and thus the 3D volume), uses either three spherical axes (r
v
, ⊖
v
and &phgr;
v
axes) or three orthogonal axes (i.e., x
v
, y
v
and z
v
axes). Each image frame is a 2D slice (i.e., a planar image) has two polar axes (i.e., r
i
and ⊖
i
axes) or two orthogonal axes (i.e., x
i
and y
i
), where i is the i-th image frame. Thus, each sample point within an image plane has image plane coordinates in the image plane coordinate system for such image plane. To register the samples in the reference coordinate system, the sample point coordinates in the appropriate image plane coordinate system are transposed to the reference coordinate system. If an image plane sample does not occur at specific integer coordinates of the reference coordinate system, the system performs interpolation to distribute the image plane sample among the nearest reference coordinate system points.
To store sample data or the interpolated values derived from the sample data, the system allocates memory address space, wherein the memory can be mapped to the reference coordinate system. Thus, values for a given row of a given reference volume slice (taken along, for example, the z-axis) can be stored in sequential address locations. Also, values for adjacent rows in such slice can be stored in adjacent first memory address space. The system performs incremental reconstruction by computing a transformation matrix that embodies six offsets. There are three offsets for computing the x, y, and z coordinates in the x-direction (along the row of the image), and three offsets for computing the x, y, and z coordinates in the y-direction (down the column of the image). Then, the system computes the corners of the reconstruction volume and compares them with the coordinates of the bounding volume. Next, the system determines the intersecting portion of the acquired image and the bounding coordinates and converts them back to the image's coordinate system. This may be done using several digital signal processors.
Furthermore, the system can compute an orthogonal projection of the current state of the reconstruction volume. An orthogonal projection uses simpler computation for rendering (no interpolations need to be computed to transform from the reference coordinate system to a displayed image raster coordinate system). The system can use a maximum intensity projection (MIP) rendering scheme in which a ray is cast along the depth of the volume, and the maximum value encountered is the value that is projected for that ray (e.g., the value used to derive a pixel for a given raster point on the 2D image projection). The system incrementally reconstructs and displays a target volume in real time. The operator can view the target volume and scan effectiveness in real time and improve the displayed images by deliberately scanning desired areas repeatedly. The operator also can recommence volume reconstruction at the new viewing angle.
The image visualization process derives 2D image projections of the 3D volume over time to generate a rotating image or an image at a new viewing angle. The system uses a shear warp factorization process to derive the new 2D projection for a given one or more video frames of the image. For each change in viewing angle, the p
Beck Heather
Miller David G.
Peszynski Michael
Koninklijke Philips Electronics , N.V.
Lateef Marvin M.
Patel Maulin
Yorks, Jr. W. Brinton
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