# Patent

## Title
Method of characterizing breast tissue using multiple contrast enhanced ultrasound renderings

## Abstract

A method for characterizing tissue of a patient, including receiving acoustic data derived from the interaction between the tissue and the acoustic waves irradiating the tissue; generating a morphology rendering of the tissue from the acoustic data, in which the rendering represents at least one biomechanical property of the tissue; determining a prognostic parameter for a region of interest in the rendering, in which the prognostic parameter incorporates the biomechanical property; and analyzing the prognostic parameter to characterize the region of interest. In some embodiment, the method further includes introducing a contrast agent into the tissue; generating a set of enhanced morphology renderings of the tissue after introducing the contrast agent; determining an enhanced prognostic parameter from the enhanced morphology renderings; and analyzing the enhanced prognostic parameter.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of prior U.S. application Ser. No. 13/027,070, filed on 14 Feb. 2011, which is incorporated in its entirety by this reference. This application also claims the benefit of U.S. Provisional Application No. 61/304,360, filed 12 Feb. 2010, which is incorporated in its entirety by this reference.


TECHNICAL FIELD
This invention relates generally to the medical imaging field, and more specifically to an improved method of characterizing tissue of a patient in the ultrasound imaging field.
BACKGROUND
Early detection of breast cancer and other types of cancer is typically an important factor to successfully treat cancer. However, there are several reasons that, for some cancer patients, the disease is not detected early. One reason is limitations in the performance of screening. For example, women with dense breast tissue have a very high relative risk for developing breast cancer, but mammography (the current standard tool for breast screening) has low sensitivity for detection of cancer in patients with dense breast tissue, which leads to a relatively high false negative rate. In other words, the performance of mammography is typically worse for this high-risk group of women with dense breast tissue. Another reason contributing to later detection of breast cancer is limited participation in breast tissue screening. Lower participation rates in annual mammograms are partly due to limited access to the screening tool (mammograms require specialized medical centers and highly trained staff), fear of radiation, and discomfort. Furthermore, due to the ionizing nature of mammography, the use of mammography is limited in younger women, who would otherwise be at risk of excessive radiation over their lifetime.
Although magnetic resonance imaging (MRI) improves on some of the limitations of mammography by providing relatively comfortable, radiation-free imaging capability, MRI is prohibitively expensive for routine use and also has limited accessibility. Improved detection of cancer would decrease the percentage of breast cancer incidence at later stages. Thus, there is a need in the medical imaging field to create an improved method of characterizing tissue in a patient. This invention provides such an improved method.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic of the method of a first preferred embodiment;
FIGS. 2A and 2B are schematics of an ultrasound scanner used in the method of a preferred embodiment;
FIGS. 3A, 3B, 4, 5A, 5B, and 5C are schematics of variations of the step of generating a morphology rendering in the method of a preferred embodiment;
FIG. 6 is a table summarizing the step of determining a prognostic parameter in the method of a preferred embodiment;
FIGS. 7A and 7B are schematic of a decision tree variation and a predictive model variation, respectively of the step of analyzing the prognostic parameter in the method of a preferred embodiment;
FIGS. 8A and 8B are variations of the method of a second preferred embodiment; and
FIG. 9 is a table summarizing the step of determining an enhanced prognostic parameter in the method of a second preferred embodiment.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of preferred embodiments of the invention is not intended to limit the invention to these preferred embodiments, but rather to enable any person skilled in the art to make and use this invention.
As shown in FIG. 1, the method 100 of characterizing tissue of a patient of a preferred embodiment includes the steps of: receiving acoustic data S110 derived from the interaction between the tissue and the acoustic waves irradiating the tissue; generating a morphology rendering from the acoustic data S120, wherein the rendering represents at least one biomechanical property of the tissue; determining a prognostic parameter for a region of interest in the rendering S160, wherein the prognostic parameter incorporates the biomechanical property; and analyzing the prognostic parameter to characterize the region of interest S180. In a second preferred embodiment, the method further includes the steps of introducing a contrast agent S190. The method enables accurate, inexpensive, comfortable and accessible assessment of a volume of tissue within a patient. The method preferably incorporates ultrasound radiation to obtain acoustic data providing measurements of biomechanical properties of the tissue, such as acoustic reflectivity (based on the reflection of acoustic waves from the tissue), acoustic attenuation (based on amplitude changes of acoustic waves in the tissue), and acoustic speed (based on departure and arrival times of acoustic signals between emitters and receives). In one preferred embodiment, the method is used to detect breast cancer in a human or other animal, but may alternatively be used to detect any suitable kind of cancer. The method may also be used to characterize the tissue to diagnose presence of cancer, assess its type and determine its extent (e.g., to determine whether a malignant mass in the tissue is surgically removable), or to assess risk of cancer development (e.g., measuring breast tissue density). The method may be repeated in different examinations of the patient, such as to allow repeated assessments and tissue characterization of the tissue. For example, repeating the method at various times may facilitate the identification and/or monitoring of a growing lesion (e.g., cancer or fibroadenoma) marked by differences in characterization of the tissue between examinations. The method may, however, be used in any suitable application involving characterization of tissue.
The step of receiving acoustic data S110 functions to irradiate or insonify the tissue in order to obtain acoustic measurement of the tissue. The step of receiving acoustic data S110 preferably includes scanning the tissue S112 with a plurality of transmitters that emit acoustic waves towards the tissue and detecting acoustic waves S114 with a plurality of receivers that detect acoustic waves after the acoustic waves interact with the tissue. The detected acoustic waves preferably include acoustic waves scattered by the tissue, where the scattered acoustic waves includes a mix of reflected and acoustic waves. The steps of scanning the tissue S112 and detecting acoustic waves S114 are preferably performed with an ultrasound tomographic scanner and methods similar to those described in U.S. Pat. Nos. 6,385,474 and 6,728,567, and U.S. Patent Publication Number 2008/0275344, which are incorporated in their entirety by this reference. However, any suitable scanner may be used. As shown in FIG. 2A, the steps of scanning the tissue S112 and detecting acoustic waves S114 are preferably performed during a scan of a patient who lies prone on their stomach on a scanner table having a hole. The table, which may be made of a durable, flexible material such as sailcloth, preferably contours to the patient's body, thereby increasing scanning access to the axilla regions of the breast and increasing patient comfort. The hole in the table allows the breast to protrude through the table and be submerged in an imaging tank filled with water or another suitable fluid to propagate acoustic waves. As shown in FIG. 2B, a ring-shaped transducer is located within the imaging tank and encircles or otherwise surrounds the breast. Multiple emitters that direct safe, non-ionizing ultrasound pulses toward the tissue, and multiple detectors that receive and record data scattering from the tissue, are distributed around the ring transducer. During the scanning step S112, the ring transducer passes along the tissue, such as in an anterior-posterior direction between the chest wall and the nipple region of the breast to acquire an acoustic data set including measurements of acoustic reflection, acoustic attenuation, and acoustic speed, preferably at discrete scanning steps, or coronal “slices”. The acoustic data for each “slice” cross-section of the tissue preferably includes an acoustic reflection data set, an acoustic attenuation data set, and an acoustic speed data set. However, the ring transducer may additionally and/or alternatively include any suitable biomechanical property of the tissue during the scanning step. The scanning and detecting steps are preferably quick, such as with a data acquisition time of less than approximately 1 second per “slice”, which helps to avoid motion artifacts in the subsequent morphology renderings and enables the use of contrast agents. The step of receiving acoustic data S110 may additionally and/or alternatively include retrieving acoustic data from a storage device such as a hard drive or an online server.
The step of generating a morphology rendering of the tissue from the acoustic data S120 functions to translate the acoustic data into a medium useful for analysis. As shown in FIGS. 3A and 3B, generating a morphology rendering S120 preferably includes generating a plurality of renderings. Each rendering preferably represents a respective biomechanical property of the tissue. As shown in FIG. 1, in a preferred embodiment, generating a plurality of renderings S120 includes generating an acoustic reflection rendering S124 that represents acoustic reflection from the tissue, generating an acoustic attenuation rendering S132 that represents acoustic attenuation within the tissue, and generating an acoustic speed rendering S136 that represents acoustic speed within the tissue. However, generating a plurality of renderings may additionally and/or alternatively include generating any rendering that represents any measurable biomechanical property of the tissue.
As shown in FIG. 3A, generating an acoustic reflection rendering S124 includes generating a set of two-dimensional (2D) images representing acoustic reflection S125, where each image represents acoustic reflection of the tissue at a particular cross-section of the tissue taken during a particular discrete scanning step. In other words, the set of 2D acoustic reflection images forms a stack of 2D renderings that collectively represents acoustic reflection from the entire (or partial) volume of scanned tissue. The set of 2D acoustic reflection images (Ir) is derived from changes in acoustic impedance of the tissue and provides echo-texture data and anatomical detail for the tissue. Generating an acoustic reflection rendering S124 may additionally and/or alternatively include generating a three-dimensional (3D) acoustic reflection rendering S126 that is a volumetric representation of the acoustic reflectivity of the volume of tissue. In a first variation, as shown in FIG. 3A, generating a 3D acoustic reflection rendering S126 includes combining the set of 2D acoustic reflection images into a three-dimensional (3D) acoustic reflection rendering. In a second variation, as shown in FIG. 3B, generating a 3D acoustic reflection rendering S126′ includes converting 3D volumetric acoustic data, obtained by scanning the tissue in a 3D manner, directly into a 3D acoustic reflection rendering.
Similar to step S124, generating an acoustic attenuation rendering S132 includes generating a set of 2D images representing acoustic attenuation S133, where each image represents acoustic attenuation within the tissue at a particular cross-section of the tissue taken during a particular discrete scanning step, to form a stack of 2D renderings for acoustic attenuation within the tissue. Generating an acoustic attenuation rendering S132 may additionally and/or alternatively include generating a 3D acoustic attenuation rendering S134 that is a volumetric representation of the acoustic attenuation within the volume of scanned tissue, where variations S134 and S134′ may be similar to either variation of analogous steps S126 and S126′ for acoustic reflection.
Similar to steps S124 and S132, generating an acoustic speed rendering S136 includes generating a set of 2D images representing acoustic speed S137, where each image represents acoustic speed within the tissue, to form a stack of 2D renderings for acoustic speed within the tissue. Generating an acoustic speed rendering S136 may additionally and/or alternatively include generating a 3D acoustic speed rendering S138 that is a volumetric representation of the acoustic speed within the volume of scanned tissue, where variation S138 and S138′ h may be similar to either variation of analogous steps S126 and S126′ for acoustic reflection.
In some embodiments, generating a morphology rendering S120 may further includes combining at least one acoustic reflection rendering, at least one acoustic attenuation rendering, and/or at least one acoustic speed rendering into a set of merged 2D or 3D renderings. In one variation, as shown in FIG. 4, generating a morphology rendering S120 includes generating a set of merged 2D renderings S142 by combining at least a portion of the set of the 2D acoustic reflection renderings, at least a portion of the 2D acoustic attenuation renderings, and/or at least a portion of the 2D acoustic speed renderings. In another variation, generating a morphology rendering S120 includes generating a merged 3D rendering S144. Generating a merged 3D rendering S144 may include combining separate 3D biomechanical property renderings S145 (e.g., combining the 3D acoustic reflection rendering, the 3D acoustic attenuation rendering, and/or the 3D acoustic speed rendering), as shown in FIG. 5A. Generating a merged 3D rendering S144 may alternatively include combining the set of merged 2D renderings into a 3D volumetric rendering S146, as shown in FIG. 5B.
The combined, or merged, renderings are overlaid on one another to allow visualization of multiple biomechanical properties to be viewed simultaneously and facilitate a more comprehensive evaluation of features of the tissue. As shown in FIG. 5C, combining the 2D or 3D renderings into a merged 2D or 3D rendering preferably includes combining the acoustic reflection renderings, a thresholded version of the acoustic attenuation renderings, and a thresholded version of the acoustic speed renderings S148. Variations of the combining step S148 may include combining thresholded (with any suitable threshold values) or non-thresholded versions of any of the renderings. In one embodiment, the renderings are merged by adding: (1) the reflection rendering, (2) a first thresholded version of the acoustic speed rendering (including measurements of the acoustic speed rendering falling between a first speed threshold “a” and a second speed threshold “b”) and (3) the combination of a second thresholded version of the acoustic speed rendering (including measurements of the acoustic speed rendering falling above a third speed threshold “c”) and a thresholded acoustic attenuation image (including measurements of the acoustic attenuation image above an attenuation threshold). In one embodiment, the thresholds “a”, “b”, “c”, and “d” are set by determining which threshold values yield mass margins (such as the outlines of legions or tissue structures) most similar to those seen in MRI or other relevant imaging modalities. This merging may be expressed according to the formula below, where the bracketed mathematical operation denotes the logical “AND” operation:

If=Ir+Is=as=b+[Is>c·Ia>d]

However, any suitable formula or algorithm may be used to merge or fuse the various renderings into a single rendering.

The method may further include iterating at least one of the biomechanical property renderings based on the other biomechanical property renderings. For example, altering a threshold used to highlight a region of interest in the acoustic attenuation and/or acoustic speed renderings may change the acoustic attenuation and/or acoustic speed renderings enough to provide additional insight about the nature of the tissue, to iteratively improve the acoustic reflection rendering. However, the iteration may involve revising any of acoustic reflection, acoustic attenuation, and acoustic speed renderings based on any other of the renderings. Furthermore, the method may include iteratively revising thresholds used when merging renderings (e.g., thresholds “a”, “b”, “c”, and “d”).
The method may further include the step of identifying a region of interest in the tissue from the morphology rendering S150, which functions to establish a portion of the tissue that requires further attention, such as for diagnosis and/or monitoring purposes. The region of interest, such as a lesion, is preferably identified and/or marked by outlining a mass as it appears on a 3D acoustic reflection rendering. For instance, a threshold of margin sharpness of a suspected mass on the reflection rendering, or another suitable threshold, may be used to identify the boundary of the region of interest in the tissue. The outline of the identified region of interest is preferably replicated on the 3D acoustic attenuation and/or acoustic speed renderings. The region of interest may alternatively be identified as a 2D lesion or mass among the 2D acoustic reflection image renderings and may be replicated on the 2D acoustic attenuation and/or acoustic speed renderings. However, the region of interest may alternatively be identified on the acoustic attenuation and/or acoustic speed renderings, or other biomechanical property rendering. The boundary of the region of interest may be iteratively identified, such as by progressively refining the boundary among the various biomechanical property renderings.
The step of determining a prognostic parameter S160 for a region of interest in the rendering functions to quantify the biomechanical characteristics of the region of interest in the tissue to provide a measure with which to characterize (e.g., to predict, monitor, or otherwise describe) the region of interest. Determining a prognostic parameter may include determining one or more quantitative prognostic parameters S162 and/or one or more qualitative prognostic parameter S172. The quantitative prognostic parameters may involve a reflection index corresponding to the acoustic reflectivity, absolute or relative volume average values of attenuation, and/or absolute or relative volume average values of sound speed of the region of interest. The qualitative prognostic parameters may involve the shape or other characteristics of the acoustic reflection, acoustic attenuation, and acoustic speed of the region of interest in the merged and/or unmerged morphology renderings. Although preferably all of these quantitative and qualitative prognostic parameters are determined, only a portion of these parameters may be determined. In this manner, the prognostic parameters extend beyond the existing Breast Imaging Reporting and Data System BIRADS criteria that are commonly used for 2D ultrasound applications in characterizing tissue masses, by incorporating quantitative measurements of sound speed, attenuation, and/or other biomechanical properties and/or qualitative morphological characteristics of the tissue and/or lesion. These extended prognostic parameters can further extend beyond the current BIRADS criteria into the realm of 3-D characterization by using lesion characterization derived from all three spatial dimensions. Furthermore, additional prognostic information can be gained by characterizing the time dependence of these parameters as derived from multiple patient exams performed at different intervals of time.
As shown in FIG. 6, determining one or more quantitative prognostic parameters S162 may include calculating a volume average value S166 of a biomechanical property of the region of interest from one or more of the renderings. In one variation, calculating a volume average value S166 includes calculating an absolute average (e.g., mean) value of the biomechanical property S167, averaged over the volume of the region of interest. For example, the absolute values of average acoustic attenuation and acoustic speed measurements are preferably calculated from the 3D acoustic attenuation rendering and the 3D acoustic speed rendering, respectively, although they may alternatively be calculated from the 2D acoustic attenuation and acoustic speed renderings, respectively. The absolute values of these averages are preferably determined by statistical analysis of the pixels within the region of interest on the 3D or 2D renderings, and volume-averaged across the mass of the region of interest. However, the volume average may be a representative value of the biomechanical property of the region of interest calculated in any suitable manner. For example, the average value of acoustic speed may be calculated as described in U.S. Patent Publication No. 2008/0275344. As another example, the volume average may additionally and/or alternatively include other aspects, such as being weighted by a spatial distribution of the values of the biomechanical property throughout the region of interest.
In another variation, calculating a volume average value S166 includes calculating a relative value of the biomechanical property S168 that takes into account the difference between the absolute value of the biomechanical property in the region of interest and the value of the biomechanical property in background tissue surrounding the region of interest. Accounting for this difference exploits the measured differences in the biomechanical properties of the region of interest compared to the rest of the scanned tissue. In this variation, calculating a volume average value S166 further includes calculating a background value of the biomechanical property in the tissue outside of the region of interest. In one example, calculating a relative value of the biomechanical property S168 includes subtracting the background value of the biomechanical property from the absolute value of the biomechanical property in the region of interest. Alternatively, calculating a relative value S168 may include dividing the absolute value of the biomechanical property in the region of the interest by the background value of the biomechanical property. However, calculating a relative value of the biomechanical property D168 may include any mathematical operation or other comparison that relates the biomechanical property or properties of the region of interest to that of background tissue. Since any systematic errors from the scan are present in both the background measurements and absolute values of the biomechanical properties, calculating a relative value of the biomechanical property of the region of interest cancels out the systematic errors, and the resulting relative values for the region of interest are thereby normalized. The background value of the biomechanical property is a measurement of the biomechanical property in the background tissue surrounding the region of interest. For example, the background measurement may be the average value of the biomechanical property (e.g., acoustic attenuation or acoustic speed) in a volume of the tissue surrounding the region of interest between the boundary of the region of interest and a surrounding tissue boundary. The surrounding tissue boundary may be defined by extending the boundary of the region of interest by a particular margin, such as 2 centimeters, or any suitable distance. However, the surrounding tissue boundary may be defined in any suitable manner, and the background measurement may be a measurement of the biomechanical property in any suitable portion of the tissue besides the region of interest. In particular, the prognostic parameter may include a relative volume average value of acoustic attenuation for the region of interest, and/or a relative volume average value of acoustic speed for the region of interest.
As shown in FIG. 6, determining one or more qualitative prognostic parameters S172 may include characterizing aspects of the acoustic reflection rendering, the acoustic attenuation rendering and/or the acoustic speed rendering. For the acoustic reflection rendering, determining one or more qualitative prognostic parameters S174 includes characterizing the margin sharpness (e.g., sharp or indistinct), the shape (e.g., oval or not oval), or the architecture (e.g., presence or absence of altered anatomy in surrounding tissue) of the region of interest S174. For the acoustic attenuation rendering, determining one of more qualitative prognostic parameters S172 includes characterizing the 2D or 3D shape (e.g., smooth or irregular) of the region of interest S176 in the acoustic attenuation rendering. For the acoustic speed renderings, determining one of more qualitative prognostic parameters S172 includes characterizing the 2D or 3D shape (e.g., smooth or irregular) of the region of interest S178 in the acoustic speed rendering. However, the qualitative prognostic parameters may characterize any suitable aspect of the biomechanical property renderings. Furthermore, the qualitative prognostic parameters may be converted into a quantitative measure, such as “1” for an indistinct margin and “2” for a sharp margin of the region of interest in the acoustic reflection rendering. As another example, a qualitative prognostic parameter may be converted to a quantitative measure such as a value on a scale (e.g., 1 to 5) that classifies the degree to which the qualitative aspect is expressed. For instance, margin sharpness of the region of interest in the acoustic reflection rendering could be classified with a reflection index as “1” if it very sharp, “3” if it is moderately indistinct, or “5” if it is very indistinct.
The step of analyzing the prognostic parameter S180 functions to utilize the prognostic parameter to predict or otherwise characterize the region of interest. The analysis preferably predicts whether the region of interest is a cancerous mass, a benign fibroadenoma, a cyst, another benign finding, an unidentifiable mass (for example, there is no finding), or any suitable characterization or classification. However, the analysis may additionally and/or alternatively monitor trends of one or more prognostic parameters over time, or for any suitable application. The step of analyzing the prognostic parameter S180 preferably involves the analysis of multiple prognostic parameters, which may be quantitative or qualitative. For example, as shown in FIG. 6, the analysis may evaluate prognostic parameters that may individually suggest the presence of cancer. For parameters regarding acoustic reflection, the signature of a cancerous mass is typically marked in the acoustic reflection image by having an indistinct and/or ill-defined spiculated or microlobulated margin, a non-oval shape, and architectural distortion including altered anatomy in surrounding tissue due to mass effect and/or retraction. In contrast, a benign mass is typically marked in the acoustic reflection image by having a sharp margin, an oval shape, and little to no architectural distortion. For parameters regarding acoustic attenuation, the signature of a cancerous mass is typically marked by having relatively high absolute and relative volume averaged values of acoustic attenuation, since acoustic waves typically have higher attenuation within a cancerous mass than within surrounding fatty tissue such as breast tissue. In contrast, a benign mass is typically marked by having relatively low absolute and relative volume averaged values of attenuation. For example, acoustic waves transmitted through a tumor at a frequency of 2 MHz typically experience an attenuation of approximately 0.25 to 0.5 dB/cm relative to fat. For parameters regarding acoustic speed, the signature of a cancerous mass is marked by having relatively high acoustic speed, since acoustic waves typically travel at faster speeds within a cancerous mass than within surrounding fatty tissue such as breast tissue. For example, acoustic waves travel approximately 50-150 meters/second faster in a cancerous mass than in fatty tissue. In contrast, a benign mass is typically marked by having relatively low absolute and relative volume averaged values of acoustic speed.
In a first variation, the step of analyzing the prognostic parameter S180 includes navigating a decision tree S182 that compares the prognostic parameters to various thresholds in a branched manner that arrives at a final characterization of the region of interest based on the comparisons between the prognostic parameters to the thresholds. The decision tree preferably incorporates prognostic parameters for acoustic reflection, acoustic attenuation, and/or acoustic speed, but may additionally and/or alternatively incorporate parameters for any suitable biomechanical properties (such as quantitative classifications of qualitative prognostic parameters). In one specific embodiment, a comparison at the “top” of the decision tree branches into a first branch if the absolute or relative volume average acoustic attenuation value is less than or equal to a first threshold, and into a second branch if the absolute or relative volume average attenuation is greater than the threshold. Each of these first and second branches are further divided into different paths based on how the absolute or relative volume averages for reflection index, acoustic attenuation, and acoustic speed compare to other thresholds. By following the decision tree, the prognostic parameters lead to the determination or prediction that the region of interest is, for example, cancerous or not cancerous. The particular thresholds may be determined empirically, such as by comparing the diagnostic results of a set of thresholds to the diagnostic results of other methods such as MRI and/or incorporating data and ultrasound tomography from known cancer patients. Furthermore, the importance of each prognostic parameter is preferably evaluated using attribute selection algorithms such as chi-square method, gain ratio, and information gain, which are strategies known to one ordinarily skilled in the alt.
In a second variation, as shown in FIG. 7B, the step of analyzing the prognostic parameter S180 includes inputting the prognostic parameter into a predictive model S184. The input may include prognostic parameters for acoustic reflection, acoustic attenuation, and/or acoustic speed, but may additionally and/or alternatively incorporate parameters for any suitable biomechanical properties (such as quantitative classifications of qualitative prognostic parameters). The prediction model may be externally validated by using data from known cancer patients or other patients with known types of lesions. However, the prediction model may be validated by any suitable process. Furthermore, in creation of the prediction model, the prediction model is preferably evaluated to identify covariate patterns that may be disproportionately influential or systematically associated with misclassification. The evaluation preferably incorporates a receiver operating characteristic (ROC) curve as a tool to select one or more possibly optimal predictive models. The ROC curve is preferably constructed using model estimates to determine the weighted combination of acoustic reflectivity, acoustic attenuation, and acoustic speed that predicts cancer with the lowest false positive rate while maintaining sensitivity of at least 90%. The area under the ROC curve represents the overall accuracy of the mode, summarizing: (1) sensitivity, or the proportion of patients in the data set with cancer who are determined by the scanner as having cancer, (2) specificity, the proportion of patients in the data set without cancer who are determined by the scanner as not having cancer, (3) the false positive rate, or the proportion of patients in the data set without cancer who are incorrectly determined by the scanner as having cancer, and (4) the false negative rate, or the proportion of patients in the data set with cancer who are incorrectly determined by the scanner as not having cancer. The sensitivity and specific are preferably conditional estimates that are conditional on the finding of a suspicious region of interest among the empirical data set. However, other aspects of the ROC curve, and/or other methods, may further be used to develop and evaluate the predictive mode.
In a third variation, the step of analyzing the prognostic parameter S180 includes evaluating qualitative prognostic parameters that individually suggest the presence of cancer. For parameters regarding acoustic reflection, the signature of cancerous tissue is typically marked in the acoustic reflection image by having (1) an indistinct and/or ill-defined speculated or microlobulated margin, (2) a non-oval shape, and (3) architectural distortion including altered anatomy in surrounding tissue due to mass effect and/or retraction. In contrast, a benign mass is typically marked in the acoustic reflection image by having (1) a sharp margin, (2) an oval shape, and (3) little to no architectural distortion.
Other variations of analyzing the prognostic parameter S180 may include various suitable combinations of the first, second, and third variations. For instance, two or all three of the variations may be performed, and the outcome of the analysis may be the characterization that the majority of the variations produce.
In a second preferred embodiment, as shown in FIG. 8A, the method 200 further includes introducing a contrast agent to the tissue S190, which functions to increase the number of available prognostic parameters and potentially increase accuracy of characterization. In this embodiment, the method preferably further includes: receiving time-dependent sets of enhanced acoustic data S210 after introducing the contrast agent into the tissue; generating a set of enhanced morphology renderings S220 from the time-dependent sets of enhanced acoustic data; determining an enhanced prognostic parameter S260 based on the set of enhanced renderings; and analyzing the enhanced prognostic parameter S280. These steps and the steps of the first preferred embodiment of the method may be performed in any suitable order. For instance, as shown in FIG. 8B, gathering unenhanced and enhanced acoustic data and generating unenhanced and enhanced renderings may be performed before determining and analyzing prognostic parameters and enhanced prognostic parameters.
Introducing a contrast agent the tissue S190 may include introducing into the tissue Definity, Optison, and/or any contrast agent suitable for medical diagnostics. The contrast agent is preferably introduced after a first acoustic data set (without the contrast agent) is obtained, such that the first acoustic data set forms a baseline from which a baseline morphology rendering may be generated. In other words, some or all of the steps of the method of the first preferred embodiment may be initially performed before introducing the contrast agent. Alternatively, in the second embodiment of the method, the step of receiving an acoustic data set prior to introducing the contrast agent may be omitted, such that no baseline rendering without the effects of the contrast agent is formed. The contrast agent may be introduced intravenously (or in any suitable manner) at the beginning of scanning, as known by one skilled in the art, to allow circulation throughout the volume of tissue. The introduction of a contrast agent preferably further enhances the biomechanical differences between a region of interest and its surrounding tissue as they appear in the renderings based on the enhanced acoustic data. In particular, the contrast agent may be used to increase relative acoustic reflectivity and acoustic attenuation, and decreases relative acoustic speed within a region of interest.
Receiving time-dependent sets of enhanced acoustic data S210 functions to obtain data that provides a “snapshot” at various times during the interaction of acoustic waves and the tissue with the contrast agent. Generating an enhanced morphology rendering S220 from the enhanced acoustic data functions to provide one or more chronological renderings that represent time-dependent biomechanical properties. Obtaining time-dependent sets of enhanced acoustic data S210 and generating an enhanced morphology rendering S220 are preferably similar to obtaining acoustic data S110 and generating a morphology rendering S120 of the first preferred embodiment. The ring transducer, or any other suitable transducer, may make repeated passes along the tissue to obtain data at specified time intervals, allowing the generation of a morphology rendering corresponding to various times after the introduction of the contrast agent. For instance, the series of enhanced renderings may include renderings of one or more biomechanical properties corresponding to t=0 seconds (when the contrast agent is introduced), and approximately every 30 seconds up to, for example, 420 seconds. However, the renderings may correspond any suitable intervals of time and length of time after introduction of the contrast agent, including only one point in time after introduction of the contrast agent (renderings corresponding to a singular scan, rather than repeated scans over intervals of time).
Determining an enhanced prognostic parameter S260 based on the set of enhanced renderings functions to establish a measure of the changes of biomechanical properties as a result of the introduction of a contrast agent. One or more enhanced prognostic parameters, similar to the prognostic parameters of the method of the first embodiment (or prior to introduction of the contrast agent) may include: an acoustic reflection parameter representing the acoustic reflectivity, an acoustic attenuation parameter representing the acoustic attenuation, and/or an acoustic speed parameter representing the acoustic speed in the region of interest after the contrast agent is introduced into the tissue. As shown in FIG. 9, determining one or more enhanced prognostic parameters may additionally and/or alternatively include: determining the kinetics of flow of the contrast agent 5262 across the time-dependent set of enhanced renderings (“wash-in, wash-out” flow as visualized, for example, in the acoustic reflection, acoustic attenuation, and/or acoustic speed renderings), determining the maximum change in value of a biomechanical property S264 in the region of interest (e.g., volume averaged values of acoustic attenuation or acoustic speed) between the baseline rendering and among the set of enhanced renderings, and/or determining the maximum value of a biomechanical property in the region of interest S266 (e.g., volume averaged value of acoustic attenuation or acoustic speed) in the set of enhanced renderings. However, the enhanced prognostic parameter may be any of the quantitative or qualitative prognostic parameters as described in the method of the first embodiment, or any suitable enhanced prognostic parameter.
Analyzing the enhanced prognostic parameter S280 functions to evaluate the one or more enhanced prognostic parameters to further characterize the region of interest, such as for distinguishing malignant tissue from benign tissue or other characterizations. Analyzing the enhanced prognostic parameter S280 is preferably similar to analyzing the prognostic parameter S180 as in the method of the first preferred embodiment. For example, analyzing the enhanced prognostic parameter S280 may include navigating a decision tree with enhanced prognostic parameters, and/or inputting the enhanced prognostic parameter into a predictive model. The decision tree and predictive model using the enhanced prognostic parameters may have thresholds and specific algorithms different from or similar to that of the first embodiment with non-enhanced prognostic parameters. However, analyzing the enhanced prognostic parameter S280 may include any suitable analysis.
As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.

## Claims

1. A method for characterizing a volume of breast tissue of a patient, comprising:
introducing a contrast agent into the volume of breast tissue;
scanning the volume of breast tissue with a ring transducer comprising a plurality of transmitters configured to emit acoustic waves towards a volume of contrast agent-enhanced breast tissue and a plurality of receivers configured to detect a plurality of acoustic waves from the volume of contrast agent-enhanced breast tissue;
at a computer processing system receiving an enhanced acoustic data set derived from the plurality of acoustic waves;
at the computer processing system generating a set of enhanced morphology renderings of the volume of contrast agent-enhanced breast tissue from the enhanced acoustic data set, wherein the set of enhanced morphology renderings includes a first enhanced morphology rendering representing a distribution of acoustic speed, a second enhanced morphology rendering representing distribution of acoustic attenuation, and a third enhanced morphology rendering representing a distribution of acoustic reflection within the volume of contrast agent-enhanced tissue;
at the computer processing system, generating a merged rendering based on the first, the second, and the third enhanced morphology renderings;
at the computer processing system identifying a region of interest within the volume of contrast agent-enhanced breast tissue from the merged rendering;
at the computer processing system, determining a set of prognostic parameters for the region of interest, wherein the set of prognostic parameters for the region of interest comprises a volume average value of acoustic attenuation, a volume average value of acoustic speed, and a reflection index characterizing margin sharpness for the region of interest, wherein the reflection index is derived from changes in acoustic impedance within the region of interest; and
at the computer processing system, characterizing the region of interest as at least one of malignant and benign based on a predictive model and the set of prognostic parameters.

2. The method of claim 1, further comprising generating a time-dependent set of enhanced renderings including the set of enhanced morphology renderings, wherein each rendering of the time-dependent set of enhanced renderings corresponds to a respective time point of a series of time points after introducing the contrast agent into the volume of breast tissue.

3. The method of claim 2, further comprising receiving a first acoustic data set and generating a baseline morphology rendering of the volume of breast tissue based on the first acoustic data set before introducing the contrast agent.

4. The method of claim 3, wherein determining the set of prognostic parameters comprises determining a maximum change in a value of at least one of the set of prognostic parameters between an enhanced rendering of the time-dependent set of enhanced renderings and the baseline morphology rendering.

5. The method of claim 2, wherein determining the set of prognostic parameters comprises characterizing kinetics of contrast agent flow across the time-dependent set of enhanced renderings spanning the series of time points.

6. The method of claim 2, wherein determining the set of prognostic parameters comprises determining a maximum volume average value of a biomechanical property for the region of interest, corresponding to a time point of the series of time points, from the time-dependent set of enhanced renderings.

7. The method of claim 1, wherein determining the set of prognostic parameters for the region of interest comprises determining a relative value of at least one of the reflection index, the volume average value of acoustic attenuation, and the volume average value of acoustic speed, wherein the relative value is defined in comparison to values in tissue surrounding the region of interest.

8. The method of claim 1, wherein characterizing the region of interest based on the predictive model and the set of prognostic parameters comprises characterizing the region of interest as at least one of a cancerous tumor, a fibroadenoma, a cyst, a nonspecific benign mass, and an unidentifiable mass.

9. The method of claim 1, wherein determining the set of prognostic parameters includes classifying a margin of the region of interest according to an integer scale of reflection indices, wherein values below a first threshold on the integer scale indicate a sharp margin and values above a second threshold on the integer scale indicate an indistinct margin of the region of interest, and wherein the method further includes characterizing the region of interest based upon the set of prognostic parameters and an architectural distortion parameter characterizing altered anatomy in tissue surrounding the region of interest.

10. The method of claim 9, wherein characterizing the region of interest includes characterizing the region of interest as a cancerous mass if the reflection index is above a threshold value on the integer scale, the volume average value of acoustic attenuation is higher for the region of interest relative to that for fat tissue, the volume average value of acoustic speed is faster for the region of interest relative to that for fat tissue, and the architectural distortion parameter indicates altered anatomy in tissue surrounding the region of interest.

11. The method of claim 1, wherein characterizing the region of interest includes characterizing the region of interest as a benign mass if the reflection index is below a threshold value on an integer scale, the volume average value of acoustic attenuation is below an attenuation threshold for the region of interest, the volume average value of acoustic speed is below a speed threshold for the region of interest, and the architectural distortion parameter indicates no altered anatomy in tissue surrounding the region of interest.