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    Abdominal applications of Tomographic Ultrasound Imaging.

    Michael Ledwidge, BS, RDMS, RVT, CNMT
    Department of Radiology, Sonography Section
    University of Wisconsin Hospital and Clinics
    Jorge Sarmiento, M.D.
    Clinical Specialist, Ultrasound
    GE Healthcare
    Cindy A. Owen, RDMS, RVT
    Baptist Memorial Hospital

    Introduction

    Tomographic Ultrasound Imaging (TUI) is a new technology that allows for a comprehensive sequential analysis of the desired anatomy. There are reports of TUI's clinical benefits in obstetrical studies, but to our knowledge there are no clinical reports of different applications using TUI in radiology. This paper will explain the concept behind TUI and the clinical benefits in abdominal applications.

    Technology

    TUI is a feature of Volume Ultrasound imaging which displays multiple parallel slices within a volume data set. Since the user adjusts the orientation and spacing of the slices, a specific region of interest can be readily evaluated. Displaying multiple slices at one time allows quicker and easier viewing of volume information, as well as a more intuitive way to view Volume Ultrasound images. Using mechanical volumetric 3D/4D transducers, volume data is acquired by capturing frames that are separated by a regular time interval, as the transducer head sweeps from one end to the other. The 2D slices can then be viewed either as separate images or together when projected on a volumetric cube. The acquired frames in the volume are oblique in shape along the probe sweep curvature. The spatial separation between each frame is at an angle. Frames are processed using normalization vectors, which convert them into a set of frames that are parallel to each other. The angle between two frames will be translated to a distance between each frame.

    The volume angle of the sweep will determine how many frames fit inside a data set. A higher quality is achieved when the frames are spaced closer together. The algorithm will compute the number of slices and the distance between each slice. Using the center slice as an index, the location of each slice in the volume is determined by the following equation:
    Slice(n) = Slice(center) + n*D; where the value of n ranges from -(Number of Slices)/2 to +(Number of Slices)/2

    The user will also specify how many of these slices appear on the screen using the display format. Raw data, which is located at a particular slice index, will be loaded and interpolated by applying gray maps. Each of these slices will then be filtered and processed.

    A single bitmap image will be generated that consists of all of the slices displayed per the chosen format. An orthogonal scout image will indicate where each frame is located in the volume. Once the algorithm determines the number of slices separated by the slice distance, the application then allows for viewing between two particular slices. The user can choose the image displayed by adjusting the slice position control.

    Clinical Benefits

    Ultrasound has traditionally been a modality driven by images taken in non-volumetric 2D planes. As technologies have advanced, it has now become possible to collect volumetric data. With TruScanT architecture, the user can obtain data in a volume and manipulate the raw data after the images have been obtained. Tomographic Ultrasound Imaging (TUI) provides numerous clinical benefits to the user.

    1. Dramatically decreasing the scan time for the sonographer as the entire area of interest is imaged by one volumetric sweep.
    2. Capturing images in planes that were not possible with conventional ultrasound
    3. Displaying individual images at any angle
    4. Providing concentrated evaluation of the scan area by allowing the user to define the distance between the slices
    5. Allowing for a comprehensive review of anatomy with a "virtual rescan" of the volumetric data that can be obtained in any plane
    6. Using the raw data to conduct a side-by-side comparison from prior studies
    7. Systematically displaying images of normal and abnormal anatomy, and allowing the reviewer to have the familiarity of conventional images obtained from volumetric data sets in multiple orthogonal planes

    Conclusion

    TUI ushers in the next generation of ultrasound imaging through volumetric datasets, which when manipulated and displayed in a systematic format, allow for better imaging capabilities. The outcome of using this technology will ultimately reduce scan time and benefit patient care. TUI represents a new, faster, and more flexible approach to clinical ultrasound challenges, increasing diagnostic confidence through access to multiplanar views unobtainable in traditional scanning, as well as an intuitive display of the volume. Corroborated clinical studies will be conducted to confirm our exciting initial findings.

    References

    1. DeVore, Greggory R., and Bardo Polanko. Tomographic Ultrasound Imaging of the Fetal Heart: A new technique for identifying normal and abnormal cardiac anatomy. J Ultrasound Med 2005 Dec; 24(12): 1685-96.
    2. Benacerraf BR, Shipp TD, Bromley B. How sonographic tomography will change the face of obstretic sonography: a pilot study. J Ultrasound Med 2005; 24: 371- 378.
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