Image analysis – Applications – Biomedical applications
Reexamination Certificate
2000-03-08
2002-07-16
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Biomedical applications
Reexamination Certificate
active
06421454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to ultrasonic and radiographic non-invasive methods for examining tissue or other solids. In particular, the invention relates to the coordination or fusion of ultrasonic monograms with x-ray or other radiographic imaging techniques to aid in the detection, location and biopsy of micro-calcifications in a human breast.
2. Description of the Related Art
Various means of non-invasive imaging are useful in medicine and other fields for visually modeling the interior structure of a solid subject body. For example, a very common method of screening women for breast cancer is x-ray mammography. Ultrasonic imaging is another, less common technique for examining breast tissue.
X-ray mammography provides excellent detection of certain types of tissues, but nevertheless has shortcomings. This technique provides detailed image information about well differentiated materials within the body (such as bone or other calcified tissue), but it performs poorly at discriminating between soft tissues with subtle differences in density and structure. Some women have mammographically dense breasts, as compared to more fatty breasts; there is a substantially increased risk of missing breast cancers when diagnosing such women by x-ray. The use of x-rays for examination also necessarily results in the exposure of the patient to ionizing radiation, which has well know associated risks. The technique is also limited in that it projects three-dimensional structure onto a two-dimensional plane, and thus does not capture the elevation or depth (position in the direction of radiation propagation) of features of interest
A newer imaging technique, ultrasonic imaging, is widely used for diagnosis in numerous medical fields. When properly used and adjusted, an ultrasound imaging system can non-invasively provide a cross-sectional view of soft tissue being imaged, such as the tissue of a breast, heart, kidney, liver, lung, eye, abdomen, or pregnant uterus.
A typical ultrasound imaging device operates by directing short ultrasonic pulses, typically having a frequency in the range of 1-30 MHZ, into the tissue being examined. The device then detects responses such as echoes, harmonics, phase or frequency shifts, of the ultrasonic pulses caused by acoustic impedance discontinuities or reflecting surfaces within the tissue.
A typical scanhead for an ultrasonic imaging system has a linear array of ultrasonic transducers which transmit ultrasonic pulses and detect returned responses. The array of transducers provides simultaneous views of the tissue at positions roughly corresponding to the positions of the transducers. The delay time between transmitting a pulse and receiving a response is indicative of the depth of the discontinuity or surface which caused the response. The magnitude of the response is plotted against the position and depth (or time) information to produce a cross-sectional view of the tissue in a plane perpendicular to the face of the scanhead.
Sophisticated ultrasonic imaging systems are available which are capable of volume reconstruction by assembling information from multiple two-dimensional cross-sections to form a three dimensional representation of subject tissue. For example, one such system is described in U.S. Pat. No. 5,787,889 to Edwards et al. (1998). An enhanced ultrasound imaging system employing targeted ultrasound is described in U.S. Pat. No. 5,776,062 to Nields (1998) Such systems are potentially useful in the diagnosis of suspicious lesions in the breast. The system of Nields can also be used to guide the biopsy of a potential lesion or suspicious mass in a breast. Compared to x-ray techniques, such ultrasonic techniques are advantageous in that the patient is not exposed to radiation. Ultrasound is also superior for imaging many types of soft, low-density “hidden masses” which are typically invisible or very obscure in x-ray imagery. On the other hand, the lower resolution of ultrasonic imaging (compared to x-ray) makes it difficult or impossible to identify fine features, such as hard micro-calcifications in breast tissue, which would be visible in an x-ray.
Imaging of small calcifications is particularly useful because such calcifications play an important role in the detection of breast cancer. They are typically categorized as either benign, probably benign, or suggestive of malignancy, based on a number of factors including size, shape, and distribution. Mammographically detected calcifications are frequently the only detectable sign of breast cancer, so their proper investigation is crucial. While some benign calcifications cannot be distinguished from those associated with malignancy, many can be so distinguished by their patterns and distribution. If more of these benign calcifications could be detected and characterized by careful analysis, the number of biopsies for benign conditions could be decreased. Therefore, any imaging technique which can enhance the analysis is extremely useful.
Although the smallest micro-calcifications are virtually impossible to detect by ultrasound, larger micro-calcifications, for example those of around 50 micron or greater size, do measurably affect ultrasound propagation (provided that short wavelengths are used). However, their images are not easily perceived in ultrasonographic imagery, because of a characteristic of ultrasonographic imagery called “speckle” or “speckle noise”. Random or disorganized sound reflection and interference cause ultrasonographic images to display a speckled or grainy texture. A closely analogous phenomenon is commonly observed when coherent light is used to view an irregular surface: the smooth surface appears grainy or speckled.
The speckle phenomenon tends to obscure the reading of ultrasonographs to detect micro-calcifications. The target micro-calcifications commonly occur as discrete, small individual members of a larger “constellation” or cluster (the shape of which depends on the type of calcification and its cause). By an unhappy coincidence, it so happens that the size of the individual micro-calcification members is often similar to the characteristic speckle size in many sonographs. In the case of multiple scattering sites per unit volume, the size of the characteristic speckle is a affected much more by the characteristics of the beamforming apparatus than the structure of the tissue being examined. Although a constellation may be present, its recognition is made difficult by the speckle noise in which the pattern is imbedded.
Another problem with breast imaging is the difficulty of combining multiple image modalities. Given that ultrasound and x-ray techniques have somewhat complementary imaging capabilities, it is often desirable to use both techniques to obtain the most imformation possible. Although a patient (or other subject body) can be subjected to multiple imaging techniques (for example x-ray and ultrasound), the images obtained are not easily registered or correlated with one another. Differences in scale, position, or in the orientation of the plane of projection (of a two-dimensional image) are almost inevitable.
U.S. Pat. No. 5,531,227 to Schneider (1996) discloses a method and apparatus for obtaining an image of an object obtained by one modality such that the image corresponds to a line of view established by another modality. However, the method disclosed requires one or more fiducial markers to inter-reference the images. The preferred method disclosed also involves mounting the patient's head immovably to a holder such as a stereotactic frame, which is inconvenient for the patient and the technicians. The method identifies fiducial markers by digital segmentation, feature extraction, and classification steps, which would most suitably be performed with powerful digital hardware and custom software. The method disclosed will perform best with fiducial markers which are easily automatically recognized, as by some simple geometric property; it is described in connection with using circula
Burke Thomas M.
Carrott David T.
Johns Andrew W.
Koppel, Jacobs Patrick & Heybl
Litton Systems Inc.
Nakhjavan Shervin
LandOfFree
Optical correlator assisted detection of calcifications for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical correlator assisted detection of calcifications for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical correlator assisted detection of calcifications for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2866471