System and Method for Low Dose Tomosynthesis
A breast imaging system leverages the combined strengths of two-dimensional and three-dimensional imaging to provide a breast cancer screening with improved sensitivity, specificity and patient dosing. A tomosynthesis system supports the acquisition of three-dimensional images at a dosage lower than that used to acquire a two-dimensional image. The low-dose three-dimensional image may be used for mass detection, while the two-dimensional image may be used for calcification detection. Obtaining tomosynthesis data at low dose provides a number of advantages in addition to mass detection including the reduction in scan time and wear and tear on the x-ray tube. Such an arrangement provides a breast cancer screening system with high sensitivity and specificity and reduced patient dosing.
This application is a continuation-in-part and claims priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 11/791,601, filed Nov. 23, 2005.
FIELD OF THE INVENTIONThis application relates to medical imaging and more specifically to a system and method of acquiring low-dose three-dimensional images and using the low dose images in combination with a conventional mammogram to enable improved detection of calcifications and masses with minimal patient dosing.
BACKGROUNDIn the U.S. breast cancer mortality is second only to that of lung cancer. Because of its role in early tumor detection, mammography has come are the most commonly used tool for breast cancer screening, diagnosis and evaluation in the United States. A mammogram is an x-ray image of inner breast tissue that is used to visualize normal and abnormal structures within the breasts. Mammograms provide early cancer detection because they can often show a breast lumps and/or calcifications before they are manually palpable.
While screening mammography is recognized as the most effective method for early detection of breast cancer, the modality has limitations. One problem with mammograms lies in their low specificity; that is it is often difficult to determine whether a detected abnormality is associated with a cancerous or benign lesion. The difficulty arises from the fact that a mammogram is two dimensional representations of a three dimensional structure, and overlapping structures in the compressed breast may confound diagnosis.
Efforts to improve the sensitivity and specificity of breast x-rays have included the development of breast tomosynthesis systems. Breast tomosynthesis is a three-dimensional imaging technology that involves acquiring images of a stationary compressed breast at multiple angles during a short scan. The individual images are then reconstructed into a series of thin, high-resolution slices that can be displayed individually or in a dynamic ciné mode.
Reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise in single slice two-dimensional mammography imaging. Digital breast tomosynthesis also offers the possibility of reduced breast compression, improved diagnostic and screening accuracy, fewer recalls, and 3D lesion localization. Examples of breast tomosynthesis systems are described in U.S. Pat. Nos. 7,245,694 and 7,123,684, commonly owned by the Assignee of this application.
One goal of any x-ray imaging system is to obtain the highest quality image while minimizing the patient dose. When selecting a radiation dose to use for imaging, a balance must be attained between image quality and patient safety. As a result an effort has been made to limit the dose of radiation administered during tomosynthesis imaging. For example, the article “Micro-Calcification Detection in Digital Tomosynthesis Mammography”, by Wheeler et al. describes that a total patient dosing across tomosynthesis projection images in a single scan should be comparable to that administered during a two view mammography.
SUMMARY OF THE INVENTIONAccording to one aspect of the invention an improved breast imaging system and method reduces patient dose by leveraging the combined strengths of two-dimensional and three-dimensional imaging. The present invention recognizes that calcification detection should be performed by imaging at a radiation dose sufficient to reduce quantum mottle (essentially image noise caused by photon absorption) to a level which enables viewing of micro-calcifications. However, according to one aspect of the invention it is realized that the resolution needed to view calcifications is not required for viewing masses; rather the problem with accurate mass detection results from structure overlay. Thus three-dimensional imaging at a dose that is considerably less that that used for the 2-D imaging provides sufficient information for improved detection of masses. The combination of the 2D image and low-dose 3D image provides a breast cancer screening system with high sensitivity and specificity.
A tomosynthesis breast imaging system comprising an x-ray source and an x-ray detector, the x-ray source and x-ray detector configurable to acquire a two-dimensional image and a three-dimensional image, wherein the two-dimensional image is acquired at a first dose and the three-dimensional image is acquired at a second dose less than or equal to the first dose.
According to a further aspect of the invention an integrated mammography/tomosynthesis system includes an x-ray source and an x-ray detector, the x-ray source and x-ray detector configurable to acquire at least one of a mammogram and a set of tomosynthesis images, wherein the mammogram is acquired at a first dosage and the set of tomosynthesis images are acquired at a second dosage less than or equal to the first dosage.
According to another aspect of the invention, a method of imaging a breast including the step of acquiring a three-dimensional image of the breast using a lower dosage than used to acquire a two-dimensional image of the breast.
A method of imaging a breast including the steps of acquiring a low-dose three-dimensional image of the breast, acquiring a two-dimensional image of the breast using a dose corresponding to a mammogram imaging dose, using the conventional dose mammogram to locate calcifications in the breast and using the low-dose three-dimensional image to locate masses in the breast.
According to further aspect of the invention, a method of imaging a breast includes the steps of acquiring a two-dimensional image of a breast using a first x-ray dose, acquiring a three-dimensional image of the breast using a second x-ray dose less than the first x-ray dose and using the two-dimensional image and three-dimensional image to identify calcifications and masses in the breast.
In describing examples and preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.
Sensitivity is the ability of the imaging technology to detect a cancerous lesion. Specificity is the ability of the imaging technology to ignore artifacts in images which merely appear similar to lesions. The present invention leverages the combined strengths of two-dimensional and three-dimensional imaging to provide a breast imaging system with improved sensitivity, specificity and the added advantage of reduced patient dosing.
One important characteristic of any digital imaging system is the ability to vary the amount and intensity of radiation used to generate any image. Radiation intensity is related to the atomic number (Z) of the x-ray target, the x-ray current (mA), x-ray voltage and x-ray beam filtration. Radiation intensity is varied to improve image quality, which in turn improves diagnostic sensitivity. When radiation intensity increases, quantum mottle (image noise caused by photon absorption) will decrease and visa versa.
Radiation intensity is directly related to patient dosage. The greater the intensity of radiation, the higher the x-ray dose to the patient. Much effort has been put into the design of mammography systems capable of acquiring a quality image at a lowest possible dosage. In the current full field digital mammography systems, the average mammogram dose is 1.2-1.5 mGy.
Many mammography and tomosynthesis systems allow the operator to control x-ray exposure by manually setting technique factors such as mA and mSec. Some systems include Automatic Exposure Control (AEC) functionality which control a duration of administration of radiation, turning off the x-ray source when the desired dose has been administered. Automatic Exposure Control (AEC) methods may vary the dosing parameters, including exposure time, kV, mA and filter modes for an image to vary the exposure and the radiation intensity. According to one aspect of the invention, AEC functionality of a tomosynthesis system may be used to reduce the dosage applied during a tomosynthesis scan, for example by changing any one of the above dosing parameters.
Alternatively (or in addition) the dosage may be controlled by limiting the angle of the scan and or the number of projection images obtained during a scan. The scan angle and number of projection images may also be controlled via a user interface located on the gantry or at the radiologists workstation.
In one embodiment, the sum of the dose administered during acquisition of all of the projection images (i.e., the tomosynthesis dose) is less than equal to the dose of a conventional mammogram. For example the tomosynthesis dose may be in the range of 0.25 to 1.0 of the dose used to acquire a single view of a conventional mammogram. In an exemplary embodiment it has been determined that sufficient information for calcification and mass detection may be obtained using a conventional mammogram view acquired with a dose of 1.0-1.5 mGy and a three-dimensional image reconstructed from fifteen projection images taken at a total dose of 0.6 mGy. In an alternate embodiment, the total dose of 0.6 mGy may be administered from projection images obtained by performing an angular scan over 7°, and obtaining, for example, 7 projection images. Such an arrangement allows the three-dimensional data to be obtained at a lower dose and faster scan time. An additional advantage of low-dose tomosynthesis acquisition is that it increases the longevity of the x-ray tube.
As illustrated in
In standard mammography mode, typically used for screening mammography, tube arm assembly 106 and compression arm assembly 110 are coupled and locked together by 410 in a relative position such as seen in
In tomosynthesis mode, tube arm assembly 106 and compression arm assembly 110 are decoupled by unit 410 such that compression arm assembly 110 stays in one position, compressing the patient's breast, while tube arm assembly 106 rotates about axis 402, for example between the position illustrated in
In one example, 11 images are taken during an angular sweep of tube arm assembly 106, one every approximately 3.degree. However, a different number of images can be taken, for example up to 21 during a single sweep. For tomosynthesis images, the x-ray tube in x-ray tube assembly 108 continuously rotates and the x-ray tube is pulsed for each image, for example, for x-ray energy pulses each lasting approximately 100 mSec, although pulses of different duration can be selected. Alternatively, the rotational motion can stop for taking each image, or continuous motion without pulsing can be used (and the timing of data measurements relied to define pixel values). As seen in
Image data can be obtained and processed into tomosynthesis images for display and/or storage as described in the material incorporated by reference, for example in co-pending patent application Ser. No. 10/723,486 or in U.S. Provisional Application No. 60/628,516, filed Nov. 15, 2004.
In a combination mode, during a single compression of the patient's breast the system takes a conventional mammogram and tomosynthesis images. In this mode, while the breast remains compressed in compression arm assembly 110, (1) tube arm assembly 106 sweeps and x-ray receptor 502 rocks, each through an appropriate angle, and exposures are taken for tomosynthesis images, and (2) a standard mammogram is taken. The standard mammogram can be taken at a 0.degree. relative angle between tube arm assembly 106 and a normal to the imaging plane of x-ray receptor 502, and can be taken before or after the tomosynthesis images are taken or between the taking of two successive tomosynthesis images. Typically, each tomosynthesis image utilizes substantially lower x-ray dose than the standard mammogram.
For example, as described above, the total dosage of all projection images taken during the tomosynthesis scan can range from 0.25 to 1.0 times that of a single dose of a mammogram. The relationship between the two dosages can be user-selected to control any one of the x-ray tube voltage, current, tomosynthesis scan angle, number of projection images obtained, etc. In alternate embodiments, the dosage may be altered via a simple switch on the gantry, or view a user control at a radiologist workstation. In still alternate embodiments the dosage may vary automatically as the radiologist switches between modes.
Again, these are examples, and different steps or orders of steps can be used instead. For example, a preferred approach may be to take the standard mammogram first, then move arm 106 to one end of its rotational range for tomosynthesis and take the tomosynthesis images. The order in which the two types of images are taken may be optimized such that the overall imaging time is minimized, and an order that achieves such minimization can be the preferred order. The exposure (tube current mA, tube voltage kVp, and exposure length msec) techniques for the standard mammogram and the tomosynthesis exposures can be set manually, or by using automatic methods. If the standard mammogram is taken first, its exposure techniques can be used to set an optimal technique for the subsequent tomosynthesis images, and vice versa. The exposure technique can be modified dynamically, if the software senses that the signal reaching the image receptor is either too low or too high and adjust subsequent exposures as needed.
Although the above has described the use of the present invention with regard to a system which supports acquisition of both tomosynthesis and mammogram images, the present invention is not limited to an integrated multi-mode system but may also be used in any system that is capable of performing tomosynthesis. For example the present invention may be used in a system which includes only tomosynthesis imaging capability. Such systems may use a legacy mammogram for example for calcification detection, or may obtain a single tomosynthesis image at higher dosage to use as their 2D image. In addition, the present invention may be used in any system which incorporates tomosynthesis imaging capability with a different modality, such as molecular breast imaging or ultrasound imaging. In short any breast imaging systems which includes tomosynthesis imaging capabilities falls within the scope of the present invention.
The above specific examples and embodiments are illustrative, and many variations can be introduced on these examples and embodiments without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.
Claims
1. A tomosynthesis breast imaging system comprising:
- an x-ray source; and
- an x-ray detector, the x-ray source and x-ray detector configurable to acquire a two-dimensional image and a three-dimensional image, wherein the two-dimensional image is acquired at a first dose and the three-dimensional image is acquired at a second dose less than or equal to the first dose.
2. The tomosynthesis breast imaging system of claim 1 wherein the second dose is a multiple of 0.25 to 1.0 of the first dose.
3. The tomosynthesis breast imaging system of claim 1 wherein the second dose is a multiple of 0.25 to 0.75 of the first dose.
4. The tomosynthesis breast imaging system of claim 1 wherein the second dose is half of the first dose.
5. The tomosynthesis breast imaging system of claim 1 wherein the first and second dose are controlled by varying at least one of the voltage, current, filter and exposure time of the x-ray source.
6. The tomosynthesis breast imaging system of claim 1 wherein the first and second dose are controlled by varying at least one of a scan angle and a number of projection images of a tomosynthesis exposure.
7. The tomosynthesis breast imaging system of claim 1 wherein the first and second dose are selected according to a mode of operation of the tomosynthesis breast imaging system.
8. The tomosynthesis breast imaging system of claim 1 wherein the system further comprises functionality for imaging the breast using at least one modality selected from molecular breast imaging and ultrasound.
9. An integrated mammography/tomosynthesis breast imaging system comprising:
- an x-ray source; and
- an x-ray detector, the x-ray source and x-ray detector configurable to acquire a mammogram and a plurality of tomosynthesis projection images, wherein the plurality of tomosynthesis projection images are acquired at a tomosynthesis dose that is less than a mammogram dose used to acquire the mammogram.
10. A method of imaging a breast including the step of acquiring a three-dimensional image of the breast using a lower dosage than used to acquire a two-dimensional image of the breast.
11. A method of imaging a breast includes the steps of:
- acquiring a two-dimensional image of a breast using a first x-ray dose, acquiring a three-dimensional image of the breast using a second x-ray dose less than the first x-ray dose and using the two-dimensional image and three-dimensional image to identify calcifications and masses in the breast.
12. A method of imaging a breast in a breast imaging system capable of generating two-dimensional images and three-dimensional images, including the steps of:
- in response to an input selecting acquisition of a three-dimensional image, acquiring the three dimensional image including the step of controlling an x-ray dosage administered during the acquisition of the three-dimensional image so that the x-ray dosage is less than a dosage used to acquire a two-dimensional image.
13. The method of step 12 wherein the step of controlling adjusts at least one of an x-ray voltage, x-ray current and x-ray filter.
14. The method of step 12 wherein the step of controlling adjusts at least one of an angle of a tomosynthesis scan and a number of projection images of the tomosynthesis scan.
Type: Application
Filed: Mar 3, 2009
Publication Date: Oct 18, 2012
Patent Grant number: 8565372
Inventors: Jay Stein (Boston, MA), Andrew Smith (Lexington, MA), Zhenzue Jing (Chadds Ford, PA), Loren Niklason (Hillsborough, NC)
Application Number: 12/397,013
International Classification: A61B 6/04 (20060101); H05G 1/42 (20060101);