Ultrasonic diagnostic apparatus, ultrasonic image processing apparatus, and medical image diagnostic apparatus

According to one embodiment, an ultrasonic diagnostic apparatus which comprises an ultrasonic transmission/reception unit configured to transmit ultrasonic waves to a scan area including a predetermined region throughout an analysis period, receive reflected waves from the scan area, and acquire ultrasonic data associated with the scan area for each phase in the analysis period, an analysis unit configured to generate a luminance time curve associated with at least one analysis area included in the scan area by using the ultrasonic data in each phase in the analysis period and analyze a stagnant time of the contrast medium associated with at least one analysis area based on the generated luminance time curve, an image generation unit configured to generate a stagnant time image for each phase in the analysis period, with different hues being assigned to at least one analysis area in accordance with the stagnant times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-131421, filed Jun. 8, 2010; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an ultrasonic diagnostic apparatus, an ultrasonic image processing apparatus, and a medical image diagnostic apparatus.

BACKGROUND

Ultrasonic diagnosis allows to display in real time how the heart beats or the fetus moves, by simply bringing an ultrasonic probe into contact with the body surface. This technique is highly safe, and hence allows repetitive examination. Furthermore, this system is smaller in size than other diagnostic apparatuses such as X-ray, CT, and MRI apparatuses and can be moved to the bedside to be easily and conveniently used for examination. In addition, ultrasonic diagnostic apparatuses vary in type depending on the functions which they have. Some compact apparatuses which have already been developed are small enough to be carried with one hand, and ultrasonic diagnosis is free from the influence of radiation exposure unlike diagnosis using X-rays. Therefore, such ultrasonic diagnostic apparatuses can be used in obstetric treatment, treatment at home, and the like.

Recently, intravenous-type ultrasonic contrast media (to be simply referred to as contrast media hereinafter) have been commercialized, and a “contrast echo method” has been practiced. This technique aims at hemodynamics evaluation upon enhancement of a blood flow signal by injecting an ultrasonic contrast medium through a vein in, for example, cardiac and hepatic examinations. Many contrast media function by using microbubbles as reflection sources. For example, a second-generation ultrasonic contrast medium called Sonazoid® which has recently been released in Japan comprises microbubbles each covered with a phospholipid film and containing a perfluorobutane gas. It has become possible to stably observe how a contrast medium refluxes, using ultrasonic transmission waves with an amplitude small enough not to destroy microbubbles.

Scanning a diagnostic region (e.g., liver cancer) after the administration of a contrast medium allows to observe increases and decreases in signal intensity from the inflow of a contrast medium, which circulates on a blood flow, to the outflow of the contrast medium. Studies have been made to enable benignancy/malignancy differential diagnosis of a tumoral lesion or diagnosis of a “diffuse” disease or the like based on such differences in temporal changes in signal intensity.

In general, such temporal changes in signal intensity need to be recorded or interpreted as a moving image unlike simple morphological information. This generally leads to a long time required for interpretation. Under the circumstance, there has been proposed a technique of mapping the inflow time information of a contrast medium to be generally observed in moving images onto a single still image (see Jpn. Pat. Appln. KOKAI Publication No. 2001-269341, and Jpn. Pat. Appln. KOKAI Publication No. 2004-321688). Such a technique expresses, with different hues, the differences between the peak times of signals based on a contrast medium and allows to recognize at a glance the inflow time at each position within a diagnostic slice.

In tumor blood vessels which run in a complicated manner as compared with normal blood vessels, a phenomenon is observed, in which bubbles have nowhere to go and become stagnant or reflux after stagnation (see R. K. Jain, “Normalization of Tumor Vasculature: An Emerging Concept in Antiangiogenetic Therapy”, Science, Vol. 307, pp. 58-62, January 2005). In practice, when performing contrast medium ultrasonic observation using a tumor mouse, the behavior of bubbles like that described above is observed in tumor blood vessels. If it is possible to evaluate the behavior of bubbles with contrast-enhanced ultrasonic waves which enable biological imaging, there is a possibility that this technique can be applied to the evaluation of abnormality of tumor blood vessels.

It has been confirmed by histopathological observation that an antiangiogenic agent (anticancer agent) which has currently been clinically tested fragments/confines tumor blood vessels by destroying blood vessels that nourish the tumor (see M. Yamazaki, et al., “Sonic hedgehog derived from human pancreatic cancer cells augments angiogenic function of endothelial progenitor cells”, Cancer Science, Vol. 99(6), pp. 1131-1138). If it is possible to visualize and quantify, with contrast-enhanced ultrasonic waves, the manner of how bubbles become stagnant in blood vessels fragmented by the antiangiogenic agent, this technique can be expected to be applied to treatment effect determination.

However, mapping of contrast medium inflow times (arrival times) using a conventional ultrasonic diagnostic apparatus cannot express characteristics after the arrival of the contrast medium. For example, it is not possible to discriminate between, for example, a state in which a contrast medium is continuously flowing into a given area and new microbubbles (to be simply referred to as bubbles hereinafter) are replacing old bubbles and a state in which bubbles that have flowed into the area are stagnant.

Note that, for example, the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-269341 displays contrast medium inflow information (e.g., arrival times) in an ultrasonic scanning slice by color mapping with reference to a given time, and hence allows to observe, in an entire image, how a contrast medium flows into each area. However, this technique does not allow sufficient evaluation of the stagnant state of bubbles after the arrival of the contrast medium at each area. In addition, the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-321688 can present the information of arrival times by performing more precise computation based on a logical model of the reflux of microcirculatory blood flows. However, even this technique cannot sufficiently evaluate the stagnant state of bubbles after the arrival of a contrast medium at each area.

DETAILED DESCRIPTION

In general, according to one embodiment, an ultrasonic diagnostic apparatus which acquires an ultrasonic image by scanning, with ultrasonic waves, a predetermined region of an object to which a contrast medium is administered includes an ultrasonic transmission/reception unit configured to transmit ultrasonic waves to a two-dimensional area or a three-dimensional area, which includes the predetermined region, as a scan area throughout an analysis period, receive reflected waves from the scan area, and acquire ultrasonic data associated with the scan area for each phase in the analysis period, an analysis unit configured to generate a luminance time curve associated with at least one analysis area included in the scan area by using the ultrasonic data in each phase in the analysis period and analyze a stagnant time of the contrast medium associated with at least one analysis area based on the generated luminance time curve, an image generation unit configured to generate a stagnant time image for each phase in the analysis period, with different hues being assigned to at least one analysis area in accordance with the stagnant times, and a display unit configured to display the stagnant time image for each phase.

The first and second embodiments will be described below with reference to the views of the accompanying drawing. Note that the same reference numerals in the following description denote constituent elements having almost the same functions and arrangements, and a repetitive description will be made only when required. For the sake of a concrete description, the following description will exemplify a case in which the contrast medium stagnant information generation function to be described later is implemented in an ultrasonic diagnostic apparatus. However, the contrast medium stagnant information generation function described in each embodiment can be implemented in other medical image diagnostic apparatuses such as an X-ray computed tomography apparatus, a magnetic resonance imaging apparatus, and an X-ray diagnostic apparatus.

FIG. 1is a block diagram showing the arrangement of an ultrasonic diagnostic apparatus10according to the first embodiment. As shown inFIG. 1, the ultrasonic diagnostic apparatus10includes an ultrasonic probe12, an input device13, a monitor14, a transmission/reception unit21, a B-mode processing unit22, a Doppler processing unit23, an image generation unit24, a control processor25, a storage unit26, an interface unit29, and an internal memory30. The transmission/reception unit21and the like incorporated in an apparatus main body11may be implemented by hardware such as an integrated circuit and the like, or may be implemented by software programs as software modules. The function of each constituent element will be described below.

The ultrasonic probe12includes a plurality of piezoelectric transducers which generate ultrasonic waves based on driving signals from the transmission/reception unit21and convert reflected waves from an object into electrical signals, a matching layer provided for the piezoelectric transducers, and a backing member which prevents ultrasonic waves from propagating backward from the piezoelectric transducers. When the ultrasonic probe12transmits ultrasonic waves to an object P, the transmitted ultrasonic waves are sequentially reflected by a discontinuity surface of acoustic impedance of internal body tissue, and are received as an echo signal by the ultrasonic probe12. The amplitude of this echo signal depends on an acoustic impedance difference on the discontinuity surface by which the echo signal is reflected. The echo produced when a transmitted ultrasonic pulse is reflected by the surface of a moving blood flow, cardiac wall, or the like is subjected to a frequency shift depending on the velocity component of the moving body in the ultrasonic transmission direction due to the Doppler effect.

The input device13is connected to the apparatus body11and includes a trackball13a, various types of switches13b, buttons13c, a mouse13d, and a keyboard13ewhich are used to input, to the apparatus main body11, various types of instructions, conditions, an instruction to set a region of interest (ROI), various types of image quality condition setting instructions, and the like from an operator.

The monitor14displays morphological information and blood flow information in the living body as images based on video signals from the image generation unit24.

The transmission/reception unit21includes a trigger generation circuit, delay circuit, and pulser circuit (none of which are shown). The pulser circuit repetitively generates rate pulses for the formation of transmission ultrasonic waves at a predetermined rate frequency fr Hz (period: 1/fr sec). The delay circuit gives each rate pulse a delay time necessary to focus an ultrasonic wave into a beam and determine transmission directivity for each channel. The trigger generation circuit applies a driving pulse to the probe12at the timing based on this rate pulse.

The transmission/reception unit21has a function of instantly changing a transmission frequency, transmission driving voltage, or the like in accordance with an instruction from the control processor25. In particular, the function of changing a transmission driving voltage is implemented by linear amplifier type transmission circuit capable of instantly switching its value or a mechanism of electrically switching a plurality of power supply units.

The transmission/reception unit21includes an amplifier circuit, A/D converter, and adder (none of which are shown). The amplifier circuit amplifies an echo signal received via the probe12for each channel. The A/D converter gives the amplified echo signals delay times necessary to determine reception directivities. The adder then performs addition processing for the signals. With this addition, a reflection component from a direction corresponding to the reception directivity of the echo signal is enhanced to form a composite beam for ultrasonic transmission/reception in accordance with reception directivity and transmission directivity.

The B-mode processing unit22receives an echo signal from the transmission/reception unit21, and performs logarithmic amplification, envelope detection processing, and the like for the signal to generate data whose signal intensity is expressed by a luminance level. After the image generation unit24performs predetermined processing for this data, the monitor14displays the resultant data as a B-mode image whose reflected wave intensity is expressed by a luminance.

The Doppler processing unit23frequency-analyzes velocity information from the echo signal received from the transmission/reception unit21to extract a blood flow, tissue, and contrast medium echo component by the Doppler effect, and obtains blood flow information such as an average velocity, variance, and power at multiple points. The obtained blood flow information is sent to the image generation circuit24, and is displayed in color as an average velocity image, a variance image, a power image, and a combined image of them on the monitor14.

The image generation unit24generates an ultrasonic diagnostic image as a display image by converting the scanning line signal string for ultrasonic scanning into a scanning line signal string in a general video format typified by a TV format. The image generation unit24incorporates a storage memory which stores image data. The operator can read out images recorded during examination after, for example, diagnosis. Note that data before it is input to the image generation unit24is sometimes called “raw data”.

FIG. 2is a block diagram for explaining the arrangement of the image generation unit24. As shown inFIG. 2, the image generation unit24includes a signal processing unit24a, a scan converter24b, and an image processing unit24c. The signal processing unit24aperforms filtering for determining image quality at the scanning line level in ultrasonic scanning. The data processed by the signal processing unit24ais sent to the scan converter24band is simultaneously output to an image memory30ain the internal memory30to be temporarily stored.

The scan converter24bconverts the scanning line signal string for ultrasonic scanning into a scanning line signal string in a general video format typified by a TV format. The data after the conversion is output to the image processing unit24c. The image processing unit24cexecutes image processing such as adjustment of a luminance and contrast and spatial filtering, and the processing of combining the generated image with character information of various types of set parameters, scale marks, and the like, and outputs the resultant data as a video signal to the monitor14. The image processing unit24cfurther executes processing and the like based on the contrast medium stagnant information generation function (to be described later) to generate ultrasonic images, stagnant time images, and the like in accordance with control signals from the control processor25.

The control processor (CPU)25is a control unit which has the function of an information processing apparatus (computer) and controls the operation of the main body of this ultrasonic diagnostic apparatus. The control processor25reads out a control program for executing the contrast medium stagnant information generation function (to be described later) from the storage unit26, expands the program in a software storage unit30b, and executes computation, control, and the like associated with each type of processing. The control processor25further executes quantitative analysis of stagnant times by using generated stagnant time images in the processing based on the contrast medium stagnant information generation function (to be described later).

The storage unit26stores control programs for implementing the contrast medium stagnant information generation function (to be described later), various types of scan sequences, image generation, and display processing, hue correspondence maps which defines the correspondence relationship between durations and hues, diagnosis information (patient ID, findings by doctors, and the like), a diagnosis protocol, transmission/reception conditions, and other data. The storage unit26is also used to store images in the image memory30a, as needed. It is possible to transfer data in the storage unit26to an external peripheral device via the interface unit29.

The interface unit29is an interface associated with the input device13, a network, and a new external storage device (not shown). The interface unit29can transfer data such as ultrasonic images, analysis results, and the like obtained by this apparatus to another apparatus via a network.

The internal memory30includes the image memory30aand the software storage unit30b. The image memory30atemporarily stores the image data received from the signal processing unit24afor each frame or volume. For example, the operator can read out data stored in the image memory30aafter diagnosis, and can reproduce the data as a still image or a moving image by using a plurality of frames. The image memory30aalso stores an output signal (radio frequency (RF) signal) immediately after it is output from the transmission/reception unit21, an image luminance signal immediately after it is transmitted through the transmission/reception unit21, other raw data, image data acquired via the network, and the like, as needed. The software storage unit30btemporarily stores the dedicated program read out from the storage unit26when executing the contrast medium stagnant information generation function (to be described later).

(Contrast Medium Stagnant Information Generation Function)

The contrast medium stagnant information generation function will be described next. This function measures a temporal change in each pixel value in an analysis area set in a scan area (a two-dimensional or three-dimensional area in an object subjected to ultrasonic scanning), analyzes the stagnant time of a contrast medium in the analysis area for each pixel by using the measured temporal change in pixel value, and generates and displays a stagnant time image or the like for the evaluation of the stagnant time of the contrast medium based on the analysis result.

Note that an analysis area set in a scan area is, for example, a two-dimensional or three-dimensional area including a diagnosis target area as an analysis target for the contrast medium stagnant information generation function, and is set by the operator at a predetermined timing. One or a plurality of analysis areas may be set in a scan area. In addition, the entire scan area can be one analysis area. Furthermore, it is possible to arbitrarily set or change the size of each analysis area from the size of an area constituted by a single pixel to the size of an area constituted by a plurality of pixels.

FIG. 3is a flowchart for explaining a procedure for processing (contrast medium stagnant information generation processing) based on this contrast medium stagnant information generation function. The contents of processing to be executed in each step will be described below.

[Reception of Inputs such as Patient Information and Transmission/Reception Conditions: Step S1]

The operator inputs patient information and selects transmission/reception conditions (a field angle, focal position, transmission voltage, and the like for determining the size of a scan area), a scan sequence for ultrasonically scanning a three-dimensional area in an object throughout a predetermined period of time via the input device13(step S1). The internal memory30or the like automatically stores the input and selected various types of information and conditions and the like.

The transmission/reception unit21then ultrasonically scans an area including a predetermined region (e.g., a blood vessel as a diagnosis target) of an object as a scan area throughout an analysis period as an analysis target, and acquires ultrasonic data (ultrasonic data for each frame) corresponding to each phase in the predetermined period (step S2). For a concrete description, this embodiment will exemplify a case in which two-dimensional scanning is executed for a two-dimensional area as a scan area. However, this embodiment is not limited to this case, and may execute three-dimensional scanning (volume scanning) for a three-dimensional area as a scan area.

The acquired ultrasonic data are sequentially sent to the B-mode processing unit22via the transmission/reception unit21. The B-mode processing unit22performs logarithmic amplification, envelope detection processing, and the like for the data to generate image data whose signal intensity is expressed by a luminance. The image generation unit24performs harmonic component extraction processing and the like for the generated image data to generate an ultrasonic image (an ultrasonic image for each frame) corresponding to each phase k (k=1, 2, . . . , n) (step S3). The generated ultrasonic image represents the spatial density (density) of the contrast medium at each phase by using a signal value (luminance value).

[Generation of Stagnant Time Image: Step S4]

The image generation unit24sequentially generates the TICs (Time Intensity Curves) of the respective pixels in the analysis area by using the ultrasonic images corresponding to the respective phases, and generates a stagnant time image by analyzing the stagnant time of the contrast medium for each pixel in the analysis area by using the generated respective TICs (step S4).

FIG. 4is a flowchart showing a procedure for the processing of generating a stagnant time image. The processing of generating a stagnant time image based on this flowchart is executed concurrently for each pixel in an analysis area.FIG. 5is a graph for explaining the concept of the processing of generating a stagnant time image, and shows TICs and hue correspondence maps respectively associated with a given pixel a in an analysis area a and a given pixel b in an analysis area b.

As shown inFIG. 4, first of all, the image generation unit24initializes (resets) a timer to 0 in accordance with a predetermined phase (e.g., the ith phase, where i=1, 2, 3, . . . , n), and starts measuring the duration. The image generation unit24also sets a flag representing the presence/absence of a contrast medium to 0 (corresponding to the signal 0 from the contrast medium: “absence of contrast medium”) (step S41). Such initialization can exclude a portion having a high signal intensity such as a tissue signal before the inflow of a contrast medium.

The image generation unit24then compares the signal intensity with a preset threshold, for the pixel, to determine whether the pixel value exceeds the threshold (i.e., whether a contrast medium exists at a position corresponding to the pixel) (step S42). If the pixel value exceeds the threshold, the image generation unit24starts measuring the duration upon setting the flag representing the presence/absence of a contrast medium to 1 (corresponding to “presence of contrast medium”), and keeps measuring the duration by using the timer (step S43). According to the case inFIG. 5, the image generation unit24determines, for the pixel a, that the contrast medium arrival time corresponds to time t1when the pixel value becomes equal to or more than the threshold. The image generation unit24then changes the flag representing the presence/absence of a contrast medium from 0 to 1, and continues to measure the duration by using the timer. The image generation unit24determines, for the pixel b, that the contrast medium arrival time corresponds to time t2when the pixel value becomes equal to or more than the threshold. The image generation unit24then changes the flag representing the presence/absence of a contrast medium from 0 to 1, and continues to measure the duration by using the timer.

The image generation unit24then determines the hue of the pixel at the ith phase (frame) based on the value of the duration timer and the preset hue correspondence map (in the case ofFIG. 5, hue1is made to correspond to duration≦T, and hue2is made to correspond to duration>T) (step S44). Such hue determination processing is executed concurrently for each pixel in an analysis area. As a result, a stagnant time image associated with the ith phase is generated, with the contrast medium stagnant time at each position in the analysis area being represented by a hue, and a signal intensity from the contrast medium at each position in the analysis area being represented by a luminance (step S45). The monitor14displays the generated stagnant time image associated with the ith phase, together with the hue correspondence map, in, for example, the form shown inFIG. 6.

The control processor25then determines whether to terminate the stagnant time image generation (step S46). If the control processor25determines not to terminate the stagnant time image generation, the process returns to step S42. The image generation unit24then compares the pixel value of the pixel at the (i+1)th phase with the preset threshold to determine whether the pixel value exceeds the threshold (step S42). If the pixel value exceeds the threshold, the image generation unit24determines “presence of contrast medium” and continues to measure the duration while keeping the flag at 1. The image generation unit24executes the processing from step S43to step S45for the pixel at the (i+1)th phase. If the pixel value of the pixel at the (i+1)th phase is smaller than the threshold, the image generation unit24stores the value of the duration timer as the stagnant time of the contrast medium at the pixel in the time interval from the time when the flag is set at 1 upon determination of “presence of contrast medium” to the current time in step S43, and holds the hue assigned to the pixel in the previous phase (step S44). With this operation, the image generation unit24generates a stagnant time image associated with the (i+1)th phase, with the contrast medium stagnant time at each position in the analysis area being represented by a hue, and the signal intensity from the contrast medium at each position in the analysis area being represented by a luminance (step S45). The monitor14then displays the generated stagnant time image associated with the (i+1)th phase, thereby updating the stagnant time image associated with the ith phase.

The control processor25executes analysis on the stagnant time in each of the subsequent phases. When a stagnant time image at the nth phase which is the last phase in the analysis period is generated, the control processor25terminates the stagnant time image generation (step S46).

With the above processing, in the case shown inFIG. 5, hue1is assigned to the pixel a in each phase after time t1. Hue1is assigned to the pixel b in each phase after time t2to time t2+T. Hue2is assigned to the pixel b in each phase from time t2+T to time t4. Therefore, by observing the stagnant time image updated/displayed in chronological order in the form shown inFIG. 6, the observer can visually grasp that the duration of the contrast medium is short and the blood flow is relatively fast at the position corresponding to the pixel a, and that the duration is long and the blood flow is relatively slow at the position corresponding to the pixel b.

If, for example, the TIC of a predetermined pixel c in an analysis area is represented by a curve like that shown inFIG. 7, hue1is assigned to the pixel c in each phase from time t1to time t1+T, and hue2is assigned to the pixel in each phase from time t1+T to time t3. In addition, the stagnant time from time t1to time t2is stored at time t2, and the timer is reset. From time t3, measurement of a stagnant time is started again, and hue1is assigned in each phase from time t3to time t3+T, and hue2is assigned in each phase after time t3+T. Therefore, by observing the analysis area which changes in hue from hue1→hue2→hue1→hue2in the stagnant time image updated/displayed in chronological order in the form shown inFIG. 6, the observer can visually grasp how the stagnant time of the contrast medium changes from moment to moment at the position corresponding to the pixel c (that is, how the contrast medium becomes stagnant and inflows/outflows).

The image generation unit24then calculates the statistical value of the duration of each pixel (e.g., the maximum value, average value, minimum value, median value, or the like of the durations at each pixel in an analysis period) by using all the durations stored for the respective pixels. The image generation unit24generates a stagnant time image associated with the analysis period by determining a hue for each pixel in the analysis area based on the calculated statistical values and the hue correspondence map (step S47). The monitor14then displays the generated stagnant time image associated with the analysis period in a predetermined form.

Note that it is also possible to generate a stagnant time image associated with this analysis period by performing Max-Value Holding for each pixel in the analysis area throughout the analysis period.

[Quantitative Analysis of Stagnant Time/Display of Analysis Result Step S5]

The control processor25then executes quantitative analysis of the stagnant time by using the stagnant time image corresponding to each phase in the analysis period and displays the result (step S5). For example, the control processor25calculates the histogram of durations in the analysis area in a predetermined phase or the histogram of durations throughout a predetermined period of time in the analysis area. The control processor25also executes quantitative analysis to calculate a predetermined quantitative value such as the mode value (peak), center of gravity, or variance of the histogram, or the proportion of an area corresponding to a given duration or more to the region of interest. The monitor14displays the calculated histogram and the calculated quantitative value in, for example, the form shown inFIG. 8.

The above embodiment has exemplified the case in which the TIC of each pixel in an analysis area is generated, and the processing of generating a stagnant time image which is shown inFIG. 4is performed by using the TICs. However, this embodiment is not limited to this. It is possible to divide an analysis area into small areas each constituted by, for example, a plurality of pixels, generate TICs by using the average values or maximum values of pixel values in the respective small areas, and perform the processing of generating a stagnant time image by using the TICs.

A stagnant time as a hue boundary in a hue correspondence map can be arbitrarily changed and set. For example, in the hue correspondence map shown inFIG. 9, time T1is defined as a boundary such that hue1changes to hue2at time T1. In this hue correspondence map, for example, time T1′ shown inFIG. 10may be re-defined by, for example, dragging the boundary line between hue1and hue2such that hue1changes to hue2at time T1′. Re-defining the hue correspondence map in this manner will update (enlarge) an area of the stagnant time image which corresponds to hue2from the area shown inFIG. 9to the area shown inFIG. 10.

The number of hues defined by a hue correspondence map (i.e., the number of hues (different colors) representing stagnant times which are defined by a hue correspondence map) can be arbitrarily changed and set. In addition, stagnant times serving as the boundaries between the respective hues can be arbitrarily changed, as described in the second modification.

The operator may want to observe the behavior of each contrast medium bubble by using the ultrasonic probe12as a high-frequency probe. In this case, it is possible to use the analysis according to this embodiment in a state in which each contrast medium bubble is made to be easily observed by reducing the amount of contrast medium administered as compared with normal operation.

The above embodiment has exemplified the case in which the above contrast medium stagnant information generation processing is executed by using ultrasonic data constituted by pixels. However, this embodiment is not limited to this, and it is possible to execute the above contrast medium stagnant information generation processing by using raw data before it is input to the image generation unit24.

This ultrasonic diagnostic apparatus measures a temporal change in each pixel value in an analysis area set in a scan area, and analyzes the stagnant time of a contrast medium for each pixel in the analysis area by using the measured temporal change in each pixel value. Based on the analysis result, this apparatus then generates a stagnant time image for the evaluation of the stagnant time of the contrast medium, and updates and displays the stagnant time image in chronological order. By observing the hues of a stagnant time image which is updated and displayed, the observer can visually grasp a position where the duration of a contrast medium is short and the blood flow is relatively fast, a position where the duration is long and the blood flow is relatively slow, and a position where the duration of the contrast medium changes from moment to moment and blood becomes stagnant and inflows/outflows. This improve the visual comprehension of the stagnant state of a contrast medium in the contrast echo method, and can be expected to contribute to tumor blood vessel evaluation and the determination of the effect of an antiangiogenic agent.

This ultrasonic diagnostic apparatus calculates the statistical value of the duration of each pixel (e.g., the maximum value, average value, minimum value, median value, or the like of the durations at each pixel in an analysis period) by using all the durations stored for the respective pixels. The ultrasonic diagnostic apparatus generates a stagnant time image associated with the analysis period by determining a hue for each pixel in the analysis area based on the calculated statistical values and the hue correspondence map. In addition, it is possible to execute quantitative analysis of stagnant times by using a stagnant time image corresponding to each phase in an analysis period and display the result. This improve the quantitative comprehension of the stagnant state of a contrast medium in the contrast echo method, and can be expected to contribute to tumor blood vessel evaluation and the determination of the effect of an antiangiogenic agent.

Second Embodiment

FIG. 11shows TICs and hue correspondence maps for pixels a′ and b′. As is obvious from each TIC inFIG. 11, the contrast medium continuously flows without becoming stagnant at the pixel a′, and flows slow and becomes stagnant at the pixel b′. If the presence/absence of a contrast medium is determined in such a state of each area based on only comparison between signal intensities and a threshold as in the first embodiment, it is impossible to discriminate the pixel a′ from the pixel b′. It may therefore be determined that the contrast medium flows slow and is stagnant at both the pixels a′ and b′.

The second embodiment, therefore, focuses attention on a point that the flow rate of a contrast medium corresponds to temporal changes in signal intensity, and is configured to more accurately determine the presence/absence of a contrast medium at each position in consideration of temporal changes in signal intensity as well as the comparison between signal intensities and a threshold.

FIG. 12is a flowchart showing a procedure for the processing of generating a stagnant time image according to this embodiment. This flowchart differs from that shown inFIG. 4in the processing in steps S42ato S44. The contents of the processing in steps S42ato S44will be described below.

An image generation unit24compares the pixel value (signal intensity) of each pixel with a preset threshold to determine whether the pixel value exceeds the threshold (that is, whether a contrast medium exists at a position corresponding to the pixel) (step S42a). If the pixel value exceeds the threshold, the image generation unit24calculates the difference between the signal intensities at the positions in consecutive frames and determines whether the absolute value of the difference is larger than a preset threshold (that is, whether the temporal change in signal intensity is larger than a reference value) (step S42b).

If the difference value is smaller than the threshold, the image generation unit24starts measuring the duration upon setting a flag representing the presence/absence of a contrast medium to 1 (corresponding to “presence of contrast medium”) (or while keeping the flag at 1), and continues to measure the duration with the timer (step S43). If the pixel value is smaller than the threshold or the difference value is larger than the threshold, the image generation unit24stores the time from the instant the flag is set to 1 upon determining “presence of contrast medium” to the current time as the stagnant time of the contrast medium at the pixel, which is the value of the duration timer in step S43, and holds a hue assigned to the pixel in the previous phase (step S44).

This makes it possible to discriminate the blood flow at the pixel a′ inFIG. 11from the blood flow at the pixel b′ and to accurately display the pixel a′ with hue1, at which the blood flow in a normal blood vessel or the like is relatively fast, and the pixel b′ with hue2, at which the contrast medium is stagnant in a tumor blood vessel or the like. Although the absolute value of the difference between signal intensities is used in this case, it is possible to reset the duration when the difference is larger or smaller than a preset threshold. In addition, it is possible to use the difference between frames at arbitrary intervals instead of the difference between consecutive frames.

Note that the present invention is not limited to each embodiment described above, and constituent elements can be modified and embodied in the execution stage within the spirit and scope of the invention. The following are concrete modifications.

(1) Each function associated with each embodiment can also be implemented by installing programs for executing the corresponding processing in a computer such as a workstation and expanding them in a memory. In this case, the programs which can cause the computer to execute the corresponding techniques can be distributed by being stored in recording media such as magnetic disks ((Floppy®) disks, hard disks, and the like), optical disks (CD-ROMs, DVDs, and the like), and semiconductor memories.

(2) In each embodiment, ultrasonic scanning on a two-dimensional area or three-dimensional area throughout an analysis period is the processing based on the premise that a slice position or volume position remains the same between phases. In practice, however, no matter how firmly the operator holds the probe, the hand may move or the probe may be moved by the respiration of a patient. That is, it is difficult to perfectly fix a slice or volume position. To correct the positional shift between consecutive slices or volumes by using, for example, the movement correction technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-330764 is very useful when this proposed technique is used for actual examination.

(3) It is possible to measure and display the arrival time of a contrast medium (the time when the contrast medium has arrived first after the administration of the contrast medium), peak time, Wash-In time, Wash-Out time, and the like concurrently with the contrast medium stagnant information generation processing disclosed in each embodiment. It is possible to acquire these pieces of information by analyzing the TIC of each pixel in an analysis area. In such a case, a hue correspondence map can be defined as a map constituted by, for example, two axes, namely an arrival time axis and a duration axis. For example, in step S4, the image generation unit24executes hue assignment by using a hue correspondence map constituted by two axes, namely an arrival time axis and a duration axis.

(4) The second embodiment performs contrast medium stagnant information generation processing in consideration of temporal changes in signal intensity, in addition to comparison between signal intensities and a threshold. In contrast to this, it is possible to perform contrast medium stagnant information generation processing with reference to only temporal changes in signal intensity.