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  Three-dimensional ultrasound computed tomography imaging systemUSPTO Application #: 20060106307Title: Three-dimensional ultrasound computed tomography imaging system Abstract: A three-dimensional (3-D) ultrasound computed tomography (UCT) system for providing a 3-D image of a target is presented. The 3-D UCT system includes an imaging chamber having a plurality of piezoelectric elements. The plurality of piezoelectric elements are arranged as a plurality of cylindrical rings. When activated, the plurality of piezoelectric elements generate and receive an ultrasound signal in a cone beam form. The 3-D UCT system also includes a processor coupled to the imaging chamber. The processor receives and processes the ultrasound signal and constructs the 3-D image of the target. A display device is also included with the 3-D UCT system. The display device exhibits the 3-D image of the target for analysis. (end of abstract)
Agent: Wiggin And Dana LLP Attention: Patent Docketing - New Haven, CT, US Inventors: Donald P. Dione, Lawrence H. Staib, Wayne Smith USPTO Applicaton #: 20060106307 - Class: 600437000 (USPTO) Related Patent Categories: Surgery, Diagnostic Testing, Detecting Nuclear, Electromagnetic, Or Ultrasonic Radiation, Ultrasonic The Patent Description & Claims data below is from USPTO Patent Application 20060106307. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This is a continuation of application Ser. No. 10/940,299, filed on Sep. 13, 2004 which is a continuation of application Ser. No. 10/402,588 filed on Mar. 28, 2003 which claims priority from U.S. Provisional Patent Application Ser. No. 60/368,453, filed on Mar. 28, 2002, all entitled "Three-Dimensional Ultrasound Computed Tomography Imaging System," the disclosures of which are incorporated by reference herein in their entireties. BACKGROUND OF THE INVENTION [0002] This invention relates generally to a system and method for generating three-dimensional (3-D) images of objects to permit non-destructive inspection of the object in fields such as, for example, medical diagnostics. [0003] The American Cancer Society estimates that in 2001 approximately 192,200 new cases of invasive breast cancer (Stages I-IV) can be diagnosed among women in the United States. Another 46,400 women can be diagnosed with ductal carcinoma in situ, a non-invasive breast cancer. It is has been estimated that over 40,000 deaths can occur from breast cancer in the United States annually. Early detection of breast cancer is vital since early detection has repeatedly been shown to improve the chance of survival. Currently, mammography is a preferred modality for early detection of breast cancer. However, mammography is problematic due to the use of potentially harmful ionizing radiation. Since asymptomatic women are screened repeatedly and the effects of radiation are cumulative, it is recommended that ionizing radiation be avoided. Other limitations include the following: 1) mammography is a two-dimensional (2D) projection modality and is therefore subject to superposition artifacts (i.e. features lying on or near the same line of projection can easily be obscured or made indistinct.); 2) mammography typically cannot differentiate malignant from benign lesions and therefore a subsequent test such as a biopsy is needed; and 3) mammography has a sensitivity of approximately 90% and therefore does not detect an estimated 8-22% of palpable breast cancers. Another modality, echo ultrasound imaging is commonly used as an adjunct to mammography because of its ability to discriminate a cyst from a solid mass. Studies have shown that echo ultrasound, however, has not proven to be an effective screening modality. Screening is the use of a modality to detect disease in an asymptomatic population. Echo ultrasound has a limited field of view, is not reproducible, and produces results that are a balance between depth of imaging (penetration of ultrasound) and image resolution. [0004] Therefore, there is a need for a new, safe and accurate (sensitive and specific) modality. The system of the present invention is a novel three-dimensional (3-D) approach to ultrasound computed tomography which can provide such a modality. In 1974, Greenleaf et al. first published a technique called "Ultrasound Computed Tomography" (UCT); unlike echo ultrasound that visualizes tissue interfaces, UCT measures the acoustic properties of the tissue (sound velocity and sound attenuation), and allows a quantitative image to be reconstructed. Greenleaf, J. F., S. A. Johnson, S. L. Lee, G. T. Herman, E. H. Wood, Algebraic Reconstruction of Spatial Distributions of Acoustic Absorption Within Tissue from Their Two-Dimensional Acoustic Projections. Acoustical Holography, 1974, 5: p. 591-603. Success with this modality was limited due to the limited availability of computational technology in the 1970s and Greeleaf et al., U.S. Pat. No. 4,105,018 titled Acoustic Examination, Material Characterization And Imaging Of The Internal Structure Of A Body By Measurement Of The Time-Of-Flight Of Acoustic Energy Therethrough specifically limited its technology to 2D ultrasound, at col. 8, line 47 to col. 9, line 1, stating that "[t]he advantage of cylindrical and circular cylindrical symmetry in ultrasound image formation is related to the basic property of all cylindrical surfaces; namely, that there is a translation or cylindrical axis. This means that if a cylindrical wave is generated it remains a cylindrical wave in a medium of constant index of refraction. . . . This is equivalent to saying that in cylindrical symmetry each ray is contained in one and only one plane. . . . Thus when using cylindrical waves the coupling of information between adjacent planes perpendicular to the cylinder axis is minimal or small compared to the coupling occurring with spherical waves. This is a great advantage and saves computer time since several small multi-plane problems are much easier to solve in total than one large multiple plane problem." [0005] Currently, echo ultrasound is routinely used as an adjunct to X-ray mammography to determine the differentiation of simple cysts from solid masses. However, echo ultrasound cannot differentiate malignant and benign masses. Also, false positive X-ray mammograms result in a large numbers of unnecessary biopsies; in the United States approximately 75% of the million biopsies performed each year are benign. Thus, a non-invasive, specific, diagnostic modality such as the system of the present invention is needed. [0006] Another use of the system of the present invention is as a screening modality, (to detect almost any lesion) this is the detection function that X-ray mammography is used. However, X-ray mammography misses 8 to 22% of palpable breast cancers. Standard echo ultrasound has not been proven effective for screening asymptomatic patients largely due to its inability to reliably detect microcalcifications. There is significant evidence in the literature that a UCT imager can be very sensitive for lesion detection. There has been great controversy over the starting age and frequency of X-ray mammographic screenings. This controversy arises mainly because of two limitations of mammography. The first is that mammography does not work well in dense breasts, which most young women have. The current recommendation is that most women start screening at age 40. However, 5% of breast cancers occur in women under 40. American Cancer Society, Surveillance Research, 1999. The second controversy is the potential risk of the cumulative effects of ionizing radiation. This worry has some doctors recommending mammographic screenings every two years. Since the most aggressive tumors need detection the earliest, frequent screenings are desirable. The UCT imager may not be able to detect microcalcifications, but it may still have utility as a screening modality in a select patient population in which mammography is not indicated. [0007] A third potential utility of a 3D imager is for image-guided biopsies and surgical planning. The location, size, and stage of a lesion are parameters that are required for effective treatment planning. Therefore, the inventors feel that the optimal diagnostic strategy for the detection and diagnosis of breast abnormalities is a non-invasive imaging method that is not only highly accurate (both sensitive and specific) but also gives the size and 3D location of any lesion detected. [0008] There are several other non-invasive modalities that may be used for screening and/or diagnosis of breast cancer including ultrasound (echo), Single Photon Emitted Computed Tomography (SPECT), Positron Emitted Tomography (PET) and Magnetic Resonance Imaging (MRI). MRI is very expensive and requires the injection of contrast agents to detect tumors. SPECT and PET are low-resolution modalities and require the injection of ionizing radiation. There are several newer technologies emerging (i.e. acoustical holography, infrared, electrical, optical, and elasticity methods) but none have yet proven to be the definitive methodology. History of UCT [0009] The allure of UCT for breast imaging is that it offers the potential to quantitatively image tissue properties. Most of the experimental work to develop an UCT imager was performed in the late 70's and early 80's. In spite of the limited technology available to these investigators, they showed promising results. For example, Greenleaf et al. achieved a sensitivity of 100% for palpable lesions with UCT for a small sample population. Greenleaf, J. F., R. C. Bahn, Clinical Imaging with Transmissive Ultrasonic Computerized Tomography. IEEE Transactions on Biomedical Engineering, 1981. BME-28(2): p. 177-185. Greenleaf et al. also showed that by combining the speed-of-sound with the patient's age and a measure of image texture that malignant and benign lesions could be differentiated. Greenleaf, J. F., R. C. Bahn, Clinical Imaging with Transmissive Ultrasonic Computerized Tomography. IEEE Transactions on Biomedical Engineering, 1981. BME-28(2): p. 177-185. Scherzinger et al. showed that by employing discriminant analysis, using combinations of speed-of-sound and attenuation in and around the lesion, one can accurately differentiate tissue types. Scherzinger, A. L., R. A. Belgam, P. A. Carson, C. R. Meyer, J. V. Sutherland, F. L. Bookstein, T. M. Silver, Assessment of Ultrasonic Computed Tomography in Symptomatic Breast Patients by Discriminant Analysis. Ultrasound in Med. and Biol., 1989. 15(1): p. 21-28. In a larger study (n=78), Schreiman et al. showed that a computer-aided diagnosis using UCT had a sensitivity of 82.5% for the diagnosis of a malignancy. Schreiman, J. S., J. J. Gisvold, J. F. Greenleaf, R. C. Bahn, Ultrasound Transmission Computed Tomography of the Breast. Radiology, 1984. 150: p. 523-530. [0010] One of the main problems that these early investigators encountered was that they could not acquire enough projections (at least not quickly enough) to reconstruct an image without reconstruction artifacts. In a review article in 1993, Jones states that early investigators were often hindered due to the limited memory and processor speed of their current computers, which affected both image acquisition and reconstruction. Jones, H. W., Recent Activity in Ultrasonic Tomography. Ultrasonics, 1993. 31(5): p. 353-360. In addition, the length of time required to acquire a full study of the breast was too long to avoid patient motion and the resulting artifacts. This long imaging time was a byproduct of having to mechanically move the transducers to each scan position and the large number of projections required to reduce reconstruction artifacts. Greenleaf et al., using a specially designed UCT imager, took about 5 minutes to image 8 slices (4 slices at a time, each slice was 3 mm thick with a 7 mm gap between slices) in a clinical trial. In this clinical UCT prototype imager, 60 projections with 200 samples each were acquired, and the image reconstructed into a 128.times.128 matrix. Azhari et al. claim that the need for a large number of projections (i.e. 201 projections for a 128.times.128 pixel image) to reduce reconstruction artifacts makes standard UCT impractical for clinical use. Azhari, H., S. Stolarski, Hybrid Ultrasonic Computed Tomography. Computers and Biomedical Research, 1997. 30: p. 35-48. As recently as 1991, Jago and Whittingham, using a linear array to improve speed of acquisition, required approximately 2 minutes to acquire data for a 2D slice and an additional 2 hours to reconstruct a 64 by 64 matrix. Jago, J. R., T. A. Whittingham, Experimental Studies in Transmission Ultrasound Computed Tomography. Phys. Med. Biol., 1991. 36(11): p. 1515-1527. Andre et al. note that after the initial experimental research, most of the work on UCT, through the mid 1990's, was in theoretical reconstructions and not in experimental designs. Andre, M. P., H. S. Janee, P. J. Martin, G. P. Otto, B. A. Spivey, D. A. Palmer, High-Speed Data Acquisition in a Diffraction Tomography System Employing Large-Scale Toroidal Arrays. International Journal of Imaging Systems Technology, 1997. 8(1): p. 137-147. They attributed this trend to limited technologies and speculate that improved instrumentation has led to a renewed interest in UCT. [0011] There are several limitations to UCT which arise from the behavior of sound as it transverses an inhomogeneous media. These include reflection, refraction, and diffraction. There are a number of methods in the literature to correct or account for these effects. Meyer et al. proposed a method to correct for multipath errors using a parametric multipath modeling and estimation technique. Meyer, C. R., T. L. Chenevert, P. L. Carson, A Method for Reducing Multipath Artifacts in Ultrasonic Computed Tomography. J. Acoust. Soc. Am., 1982. 72(3): p. 820-823. In a noiseless case, they showed an improvement in attenuation estimates. Pan and Liu proposed methods for correcting refractive errors. Pan, K. M., C. N. Liu, Tomographic Reconstruction of Ultrasonic Attenuation with Correction for Refractive Errors. IBM J. Res. Develop., 1981. 25(1): p. 71-82. They proposed to scan a small area around the straight line-of-sight and then use several different methods (i.e. maximum, sum, or average of the scan area) to measure attenuation. Chenevert et al. explored methods such as cross-correlation and phase-insensitive arrays. Chenevert, T. L., D. I. Bylski, P. L. Carson, P. H. Bland, D. D. Adler, R. M. Schmitt, Ultrasonic Computed Tomography of the Breast. Radiology, 1984. 152: p. 155-159; and Schmitt, R. M., C. R. Meyer, P. Carson, L, T. L. Chenevert, P. H. Bland, Error Reduction in Through Transmission Tomography Using Large Receiving Arrays with Phase-Insensitive Signal Processing. IEEE Transactions on Sonics and Ultrasonics, 1984. SU-31(4): p. 251-258. Cross-correlation minimizes the chance of noise being mistaken as the arrival of the received signal by comparing the signal to a water-path only signal. The use of a phase-insensitive array results in a better attenuation image, by accounting for refraction. Klepper et al. showed that reconstructing an image, where each pixel is the slope of attenuation vs. frequency, minimizes errors due to reflection and refraction. They used a range of frequencies from 3 MHz to 7 MHz and fit a straight line to the data. Klepper, J. R., G. H. Brandenburger, J. W. Mimbs, B. E. Sobel, J. G. Miller, Application of Phase-Insensitive Detection and Frequency-Dependent Measurements to Computed Ultrasonic Attenuation Tomography. IEEE Transactions on Biomedical Engineering, 1981. BME-28(2): p. 186-201. Greenleaf et al. also showed that the intercept of attenuation vs. frequency could be reconstructed. Greenleaf, J. F., R. C. Bahn, Signal Processing Methods for Transmission Ultrasonic Computerized Tomography. Ultrasonics Symposium Proceedings, 1980: p. 966-972. This is an image of reflection by structures larger than the wavelength and is highly correlated with back-scattered information imaged in B-mode scans. [0012] Several investigators explored the use of ray-tracing, ray-linking and iterative reconstructions to generate more accurate images. Improvements in restoring macrostructural geometric proportions have been shown for object inhomogeneities of 5-10% (the breast has inhomogeneities of about 8%). These methods begin with a straight ray assumption to reconstruct an initial speed-of-sound image. Then ray-linking is used to create "new" projections, which are subsequently used to reconstruct a new image. This process is then iterated. Most of the ray-linking methods involve a technique called "shooting", iteratively searching for the initial angle of the ray from the transmitter that "hits" within some window around the receiver. These methods are computationally expensive and may not be possible to implement in a 3D imaging system. [0013] Norton proposed an alternative method, which involves transforming the ray equation into an implicit integral equation satisfying the boundary conditions. These equations are then solved via successive approximations. Norton also proposed an explicit expression for the ray equation that is correct to the first order for refractive-index perturbations. Norton, S. J., Computing Ray Trajectories Between Two Points: A Solution to the Ray-Linking Problem. Optical Society of America, 1987. 4(10): p. 1919-1922. Andersen proposed an alternative technique based on rebinning of the projection data. Andersen, A. H., A Ray Tracing Approach to Restoration and Resolution Enhancement in Experimental Ultrasound Tomography. Ultrasonic Imaging, 1990. 12: p. 268-291; and Andersen, A. H., Ray Linking for Computed Tomography by Rebinning of Projection Data. J. Acoust. Soc. Am., 1987. 81(4): p. 1190-1192. In this technique, a new radial coordinate system is constructed passing through the center of the image. Rays are then projected from lines passing through the origin. A rebinning process is used and a new image reconstructed. This method is computationally less expensive than the brute force method typically used in ray-linking, a 60% timesavings. Andersen, A. H., A Ray Tracing Approach to Restoration and Resolution Enhancement in Experimental Ultrasound Tomography. Ultrasonic Imaging, 1990. 12: p. 268-291. We can extend the method of rebinning (center-out) to 3D in our reconstructions, detailed in the method of the present invention. Diffraction Tomography [0014] An alternative to geometrical acoustics for reconstruction is diffraction tomography, which often uses an approximation (Rytov or Born) to the wave equation to reconstruct images. These approximations are only valid in cases of weak scattering. Several investigators have experimented with diffraction imaging. [0015] In order to obtain a linear approximation to the inhomogeneous wave equation, diffraction tomography is often based on the assumption of weak scatters. This assumption is not valid in the human breast due to highly refractive fat layers under the skin. One potential alternative involves the use of higher order approximations to the wave equation. Another alternative is to use iterative methods to solve the wave equation directly. Both of these alternatives are computationally very expensive. For example, the CPU time on a Cray computer was 2.5 hours to reconstruct a 200.times.200 pixel image from 200 projections. The reconstructed image was very accurate both qualitatively and quantitatively. Manry and Broschat showed that the incorporation of a priori information reduced the computation time by reducing the number of iterations approximately 40%, but the image becomes discritized to 3 grey levels. Manry, C. W. J., S. L. Broschat, Inverse Imaging of the Breast with a Material Classification Technique. J. Acoust. Soc. Am., 1998. 103(3): p. 1538-1546. Lu et al. have recently published a new method that involves the creation of a reconstruction method in a finite form utilizing a formal parameter. Lu, Z.-Q., C.-H. Tan, Z.-Y. Tao, Q. Xue, Acoustical Diffraction Tomography in a Finite Form and Its Computer Simulations. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2001. 48(4): p. 969-975. This method utilizes an approximation that is much less restrictive than those in the Born and Rytov approximations. [0016] Much of the work in the area of diffraction tomography is also limited by the assumption that the object is being isonofied by a plane wave, which is not feasible in an imager. Sponheim, N., I. Johansen, Experimental Results in Ultrasonic Tomography Using a Filtered Backpropagation Algorithm. Ultrasonic Imaging, 1991. 13: p. 56-70. Sponheim and Johansen have suggested utilizing a reference wave as a first order correction. There is some theoretical work in which non-plane waves are used. Devaney and Beylkin developed a method for utilizing fan beam (spherical or cylindrical) isonofication for diffraction tomography and for the use of arbitrary transmitter and receiver configurations. Devaney, A. J., Generalized Projection-Slice Theorem for Fan Beam Diffraction Tomography. Ultrasonic Imaging, 1985. 7: p. 264-275; and Devaney, A. J., G. Beylkin, Diffraction Tomography Using Arbitrary Transmitter and Receiver Surfaces. Ultrasonic Imaging, 1984. 6: p. 181-193. Witten et al. included the effects of the transmitter beam pattern in their theoretical design of a practical 2D diffraction tomographer. Witten, A., J. Tuggle, R. C. Waag, A Practical Approach to Ultrasonic Imaging Using Diffraction Tomography. J. Acoust. Soc. Am, 1988. 83(4): p. 1645-1652. It is also interesting to note that they claim that any practical ultrasound based imager must use fixed transducers to eliminate errors due to vibrations and acquire data quickly enough to avoid artifacts due to patient motion. The inventors' clinical design meets these requirements. [0017] Fast (approximately 3 sec per slice) 2D diffraction tomography systems with high-resolution (<1 mm in plane, but 10 mm thick slices) and the utilization of cylindrical waves have been previously developed. However, the systems result in nonisotropic voxels. Such a system is discussed in Andre, M. P., H. S. Janee, P. J. Martin, G. P. Otto, B. A. Spivey, D. A. Palmer, High-Speed Data Acquisition in a Diffraction Tomography System Employing Large-Scale Toroidal Arrays. International Journal of Imaging Systems Technology, 1997. 8(1): p. 137-147. Others have also experimented with a 2D system resulting in nonisotropic voxels; the system has an in-plane resolution of 0.5 mm; however, the slice thickness is again 10 mm. This system is discussed in Sponheim, N., I. Johansen, Experimental Results in Ultrasonic Tomography Using a Filtered Backpropagation Algorithm. Ultrasonic Imaging, 1991. 13: p. 56-70. Both of these experimental systems utilize first order Born or Rytov approximations. [0018] Pixel/voxel number and size are also variables. Isotropic voxels (meaning same dimension in all three directions) is a feature of the present invention. The aforementioned systems do not have isotropic voxels: Many image modalities have good in-plane resolution but have thick slices. This creates partial volume error which is blurring of true tissue properties due to averaging of large sections of the tissue into one value that is displayed in an image. [0019] Most diffraction tomography methods reconstruct only in 2D and thus the 3D scattering effect of the breast is a limiting factor of diffraction tomography, and has not previously been addressed in a practical imaging system. A 3D reconstruction algorithm for diffraction tomography utilizing a filtered back-projection algorithm on the Radon transform has recently reported in Anastasio, M. A., X. Pan, Computationally Efficient and Statistically Robust Image Reconstruction in Three-Dimensional Diffraction Tomography. J. Opt. Soc. Am. A, 2000. 17(3): p. 391-400. The method provides reconstruction that reduces to a series of 2D reconstructions over the 3D volume. This reconstruction is based on the Born or Rytov approximations. [0020] Most of the work in diffraction tomography has been theoretical with few actual experimental devices being tested, and none in 3D. Diffraction tomography suffers from the weak scattering assumption, which is often employed, and is violated by strongly refracting fat layers. Note that phase aberration of ultrasound is not a function of breast size as explained in Trahey, G. E., P. D. Freiburger, L. F. Nock, D. C. Sullivan, In Vivo Measurements of Ultrasonic Beam Distortion in the Breast. Ultrasonic Imaging, 1991. 13: p. 71-90. This is suggestive that the major contributor to phase aberration is subcutaneous fat and not the internal structure of the breast. There have been similar findings in that examination of the wavefront amplitude profiles shows coherent interference, indicating refraction as the cause, as is explained in Zhu, Q., B. D. Steinberg, Wavefront Amplitude Distribution in the Female Breast. J. Acoustical Society of America, 1994. 96(1): p. 1-9. In addition, diffraction tomography is more computationally expensive than ray-based UCT and may be limited by the discrete implementation of the reconstruction process. Therefore, diffraction-based reconstructions is not preferred for use in the present invention. Rather, in the present invention, use of geometrical acoustics, with ray tracing to correct for the refraction caused by subcutaneous fat is preferred. Continue reading... Full patent description for Three-dimensional ultrasound computed tomography imaging system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Three-dimensional ultrasound computed tomography imaging system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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