This invention relates to an improved system, method and transducer for acquiring two-dimensional image information and relative positional information regarding the image information to allow subsequent three-dimensional or extended field of view reconstruction.
There is growing interest in three-dimensional ultrasonic images. One approach is to use a two-dimensional transducer array to obtain three-dimensional image information directly. A two-dimensional array can be used to scan electronically in any desired orientation, and thereby to acquire the desired information. This approach brings with it considerable problems related to fabrication difficulties, signal to noise difficulties and processing difficulties.
Another approach is to collect multiple two-dimensional image data frames using a one-dimensional transducer array along with relative positional information among the image data frames so that these frames may be subsequently assembled in a three-dimensional volume to form the desired three-dimensional reconstruction. One approach is to use a motorized array to collect the desired set of image data frames by precisely controlling the movement of the transducer array. One example is the transducer shown in U.S. patent application Ser. No. 08/267,318 (Hossack, et al., assigned to the assignee of the present invention). See also Pini U.S. Pat. No. 5,159,931). A related approach is to use a large rotating transducer as described in McCann et al., xe2x80x9cMultidimensional Ultrasonic Imaging for Cardiologyxe2x80x9d (Proceedings of IEEE, 76, 9, pp. 1063-1072, September 1988). Another approach is to use manual motion detection techniques based on analysis of ultrasonic images. See Sapoznikov et al., xe2x80x9cLeft Ventricular Shape, Wall Thickness and Function Based on Three-Dimensional Reconstruction Echocardiographyxe2x80x9d (xe2x80x9cComputers in Cardiology,xe2x80x9d IEEE Computer Society Press, Cat CH 2476-0, pp. 495-498, 1987); and Taruma et al., xe2x80x9cThree-Dimensional Reconstruction of Echocardiograms Based on Orthogonal Sectionsxe2x80x9d (Pattern Recognition, 18, 2, pp. 115-124, 1985). Manual techniques are slow and cumbersome and, therefore have many drawbacks.
Schwartz U.S. Pat. No. 5,474,073 describes a qualitative three-dimensional method using a hand-held transducer array and an assumed scan motion. Qualitative methods have drawbacks, and the present invention is directed to a quantitative method.
Keller U.S. Pat. No. 5,353,354 discloses a transducer array equipped with accelerometers or magnetic sensors designed to measure the orientation of the transducer, and therefore relative motion between respective image planes. Once the image plane positional information is provided, standard methods are employed for assembling the image plane information into a three-dimensional volume and providing an appropriate display such as a cross section, a surface rendering, a segmentation, or the like. One drawback of the Keller approach is that it relies on assessing the position of the transducer array with respect to a fixed surface exterior to the patient, not with respect to the patient or other target. If the patient moves, the absolute position of all target regions is moved, and the accuracy of the three-dimensional reconstruction is degraded or eliminated entirely. Magnetic sensor systems have additional disadvantages, such as potential vulnerability to local magnetic interference from metal objects and electromagnetic fields generated by electronic devices such as cathode ray tubes. Accelerometer systems can be bulky and susceptible to cumulative error, since they rely on two stages of integration to convert acceleration information to displacement information.
The present invention is directed to a new system and transducer which to a large extent overcome the problems discussed above.
According to a first aspect of this invention, a method is provided for registering image information acquired from a target, comprising the following steps:
(a) acquiring a plurality of sets of image information with at least one ultrasonic transducer array, said at least one array moved between at least some of the sets of image information, said plurality of sets comprising a plurality of image data sets and a plurality of tracking sets;
(b) automatically determining a component of motion based on a comparison of at least a portion of the tracking sets acquired in step (a); and
(c) automatically using the component of motion determined in step (b) to register selected ones of the image data sets acquired in step (a).
According to one aspect of this invention, the image data sets are acquired with different transducer arrays. According to another aspect of this invention, motion estimates are used to create an extended field of view, and in this case no separate array may be required for the tracking sets.
This invention is also directed to an improved transducer suitable for use in the method described below. The transducer of this invention includes a support element and first, second, and third transducer arrays coupled to move with the support element. The first transducer array includes first transducer elements arranged along an azimuthal axis and having first and second ends spaced along the azimuthal axis and a first central image plane. The second transducer array comprises second transducer elements positioned near the first end of the first transducer array and comprising a second central image plane. The third transducer array comprises third transducer elements positioned near the second end of the first transducer array and comprising a third central image plane. The first and second central image planes are non-parallel, as are the first and third central image planes.
This arrangement for an ultrasonic transducer allows both tracking information and image information to be collected concurrently. The tracking information is used to determine estimates of the movement of the transducer and/or the target between respective image data frames. This information can then be used in registering the respective image data frames appropriately in three-dimensions to form the desired three-dimensional representation.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.
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