WO2018101396A1 - Ultrasonic imaging device, ultrasonic imaging method, ultrasonic imaging program, and ultrasonic ct device - Google Patents

Abstract

Provided is an ultrasonic imaging device with which the temperature of a subject containing water and fat can be inexpensively detected. The ultrasonic imaging device pertaining to the invention detects the temperature of a subject that contains water and fat, wherein said ultrasonic imaging device comprises a temperature-dependent-characteristic-acquisition means that acquires a temperature-dependent characteristic of the acoustic velocities at each of a plurality of sites of the subject on the basis of a the water content ratios and the fat content ratios at each of the plurality of sites, a first arrival time acquisition means that acquires a measurement value of a plurality of first arrival times at which ultrasonic waves arrive via a plurality of pathways that pass through the subject, and a temperature determination means that determines the temperatures of the plurality of sites on the basis of the measurement values of the plurality of first arrival times and the temperature-dependent characteristic of the acoustic velocities of the plurality of sites.

Description

Ultrasonic imaging apparatus, ultrasonic imaging method, ultrasonic imaging program, and ultrasonic CT apparatus

The present invention relates to an ultrasonic imaging apparatus, an ultrasonic imaging method, an ultrasonic imaging program, and an ultrasonic CT apparatus, and more particularly to temperature detection of a subject including water and fat.

An apparatus for detecting the temperature of the subject has been realized. The first example is thermography. When the subject is a living body, infrared rays emitted from the subject are detected and converted into temperature.

The second example is an MRI (Magnetic Resonance Imaging) apparatus. The temperature can be calculated using the fact that the relaxation parameters (relaxation times T ₁ and T ₂ ) measured by the MRI apparatus, proton resonance frequency (Proton Resonance Frequency: PRF), and the like have temperature dependence.

However, the conventional temperature detection device has the following problems. The thermography as the first example has a problem that the penetration depth (Penetration Depth) of infrared rays into the living body is relatively short and is limited to the measurement of the temperature distribution near the surface of the living body.

The MRI apparatus as the second example is large and has a problem that the introduction cost and the imaging cost are high. Furthermore, there are factors that can be affected when the temperature of the subject is monitored, such as the need to perform imaging in a strong magnetic field.

As a third example, an X-ray CT (X-ray Computer Tomography) apparatus is also conceivable. In the X-ray CT apparatus, a method of calculating a temperature change using a linear attenuation coefficient is conceivable, but the sensitivity of the linear attenuation coefficient to temperature is low, the temperature resolution is limited, and it has not been put into practical use.

Furthermore, as a fourth example, a CT apparatus using reflected ultrasonic waves is also conceivable. However, generally, the correlation coefficient between the echo luminance of the subject and the temperature is very small, and it is difficult to quantitatively calculate the temperature. There is also an attempt to calculate the temperature by paying attention to the echo shift caused by the sound speed change, but it has not been put into practical use because it is difficult to specify the location where the sound speed has changed from the echo shift of the acquired signal.

The present invention has been made in view of such problems, and realizes an ultrasonic imaging apparatus, an ultrasonic imaging method, an ultrasonic imaging program, which realizes temperature detection of a subject including water and fat at a low cost, It is another object of the present invention to provide an ultrasonic CT apparatus.

(1) In order to solve the above-described problem, an ultrasonic imaging apparatus according to the present invention is an ultrasonic imaging apparatus that detects a temperature of a subject including water and fat, and the subject includes the subject. Based on the water content ratio and the fat content ratio in each of the plurality of parts, the temperature dependent characteristic acquisition means for acquiring the temperature dependent characteristics of the sound speed of each of the plurality of parts, and each of the plurality of paths through the subject The first arrival time acquisition means for acquiring a plurality of first arrival time measurement values through which the ultrasonic wave passes, the plurality of first arrival time measurement values acquired by the first arrival time acquisition means, and the plurality Temperature determining means for determining the temperature of each of the plurality of parts based on the temperature dependent characteristic of the sound velocity of each of the plurality of parts acquired by the part temperature dependent characteristic acquisition means.

(2) The ultrasonic imaging apparatus according to (1), wherein the multiple part temperature-dependent characteristic acquisition unit is a temperature environment different from a temperature environment in which measured values of the plurality of first measurement times are measured. The sound speed of each of the plurality of parts is calculated based on the measurement values of the plurality of second measurement times measured below, and based on the sound speed of each of the plurality of parts, the water content ratio and the fat content are calculated. The content ratio may be calculated, and the dependence of the sound speed on each of the plurality of parts may be calculated.

(3) In the ultrasonic imaging apparatus according to (1) or (2), a factor caused by sound speed in each of a plurality of grids in a calculation region including the plurality of parts of the subject is a delay factor. In this case, the temperature determination means is based on a measured value of the first arrival time in a certain path and a delay factor assumed for each of a plurality of grids on the path passing through the path among the plurality of grids of the calculation area. When the arrival time has an arrival time difference, a temperature correction unit may be provided to correct the temperature of each of the plurality of grids on the path so as to reduce the arrival time difference.

(4) In the ultrasonic imaging apparatus according to (3), the temperature correction unit may correct the temperature of each of the plurality of grids on the path so that the arrival time difference becomes zero. .

(5) In the ultrasonic imaging apparatus according to the above (3) or (4), the temperature correction unit may correct the temperature change amount common to the plurality of grids on the path.

(6) The ultrasonic imaging apparatus according to (3) or (4), wherein the temperature correction unit uses a sign of a temperature change for correcting the temperature of each of the plurality of grids on the path as the assumption. It may be determined based on the sign of the temperature differential value of the delay factor and the sign of the arrival time difference.

(7) The ultrasonic imaging apparatus according to (6), wherein the temperature correction unit calculates an absolute value of the temperature change for correcting the temperature of each of the plurality of grids on the plurality of paths. It is good also as a value common in an upper part.

(8) In the ultrasonic imaging apparatus according to (6) or (7), the temperature correction unit may include a sign for the temperature change for correcting the temperature of each of the plurality of grids on the path. If the sign of the temperature differential value of the assumed delay factor and the sign of the arrival time difference are the same, it may be determined to be positive, and if it is different, negative.

(9) An ultrasonic CT apparatus according to the present invention includes the ultrasonic imaging apparatus according to any one of (1) to (8), an ultrasonic measurement unit that measures the plurality of first arrival times, An ultrasonic CT apparatus may be provided.

(10) The ultrasonic CT apparatus according to (9), wherein the ultrasonic measurement unit includes a temperature adjustment function that changes a temperature of at least a part of a measurement region including a subject. Also good.

(11) The ultrasonic imaging method according to the present invention is an ultrasonic imaging method in which a temperature of a subject including water and fat is detected, and water is contained in each of a plurality of portions of the subject. Based on the ratio and the fat content ratio, the temperature-dependent characteristics acquisition step for acquiring the temperature-dependent characteristics of the sound speeds of each of the plurality of parts, and a plurality of ultrasonic waves that pass through each of the plurality of paths that penetrate the subject. A first arrival time acquisition step of acquiring a measurement value of one arrival time, a plurality of measurement values of the first arrival time acquired by the first arrival time acquisition step, and a plurality of part temperature dependent characteristic acquisition steps And a temperature determining step of determining the temperature of each of the plurality of parts based on the temperature-dependent characteristics of the sound speed of each of the plurality of parts.

(12) The ultrasound imaging program according to the present invention is a computer that detects the temperature of a subject including water and fat, and the water content ratio and the fat content in each of the plurality of parts of the subject. Based on the content ratio, the temperature-dependent characteristic acquisition means for acquiring the temperature-dependent characteristics of the sound speeds of the plurality of parts, and the measurement of the plurality of first arrival times through which the ultrasonic waves pass through each of the plurality of paths passing through the subject First arrival time acquisition means for acquiring values, measured values of the plurality of first arrival times acquired by the first arrival time acquisition means, and each of the plurality of parts acquired by the plurality of part temperature-dependent characteristic acquisition means And an ultrasonic imaging program for functioning as temperature determining means for determining the temperature of each of the plurality of parts based on the temperature-dependent characteristics of the sound speed of

According to the present invention, there are provided an ultrasonic imaging apparatus, an ultrasonic imaging method, an ultrasonic imaging program, and an ultrasonic CT apparatus that can realize temperature detection of a subject including water and fat at a low cost.

1 is a block diagram showing a configuration of an ultrasonic CT apparatus according to a first embodiment of the present invention. It is a figure which shows the structure of the principal part of the ultrasonic measurement part 2 which concerns on the 1st Embodiment of this invention. It is a flowchart of the ultrasonic imaging program which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the calculation area | region which concerns on the 1st Embodiment of this invention. It is a flowchart of the temperature dependence characteristic acquisition step which concerns on the 1st Embodiment of this invention. It is a figure explaining SART method. It is a figure explaining T-SART method. It is a flowchart of the temperature determination step which concerns on the 2nd Embodiment of this invention. It is a figure which shows the direction of the correction vector in SART method and T-SART method in a two-dimensional hyperplane. It is a figure which shows the direction of the correction vector in the correction T-SART method in a two-dimensional hyperplane. It is a figure which shows the example of the measurement result by the ultrasonic CT apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the model of the subject set in the ultrasonic imaging apparatus which concerns on the 2nd and 3rd embodiment of this invention. It is a figure which shows the calculation result of the ultrasonic imaging apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the calculation result of the ultrasonic imaging apparatus which concerns on the 3rd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In order to clarify the description, the drawings may schematically represent dimensions, shapes, and the like as compared with actual embodiments, but are merely examples and do not limit the interpretation of the present invention. In addition, in the present specification and each drawing, elements similar to those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description may be omitted as appropriate.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an ultrasonic CT apparatus 1 according to the first embodiment of the present invention. The ultrasonic CT apparatus 1 according to this embodiment includes an ultrasonic measurement unit 2 and an ultrasonic imaging device 3, and the ultrasonic imaging device 3 includes a control unit 4, an input device 5, and a display device 6. And comprising. The control unit 4 includes a CPU unit 11, a storage unit 12, an information input unit 13, and an information output unit 14. The control unit 4 is realized by a commonly used computer, and further includes a ROM (Read Only Memory) and a RAM (Random Access Memory), which are not shown, and the ROM and RAM constitute an internal memory of the computer. The storage unit 12 is a recording medium, and may be configured by a semiconductor memory, a hard disk, or any other arbitrary recording medium. Here, the storage unit 12 is installed inside the computer, but may be installed outside the computer. Further, the storage unit 12 may be a single unit or a plurality of recording media. The information input unit 13 is an interface or the like connected to the input device 5, and acquires information that the user inputs to the input device 5 from the input device 5. The information output unit 14 is an interface connected to the display device 6 and outputs information to be displayed on the display device 6 to the display device 6. The input device 5 is realized by a keyboard, a mouse, a touch panel, etc., and the display device 6 is realized by a generally used display. The control unit 4 of the ultrasonic imaging apparatus 3 includes means for executing each step of the ultrasonic imaging method described below. The ultrasound imaging program 31 according to the embodiment is a program for causing a computer to function as each means. The details of the CPU unit 11 and the storage unit 12 of the control unit 4 will be described later.

The ultrasonic measurement unit 2 of the ultrasonic CT apparatus 1 according to the embodiment will be described. The main configuration of the ultrasonic measurement unit 2 is disclosed in Non-Patent Document 1, for example. The diagnostic apparatus described in Non-Patent Document 1 is a CT apparatus using transmitted ultrasound. Ultrasonic waves are high frequency sound waves that exceed the human audible range (20 Hz to 20 kHz). The frequency of the ultrasonic wave used here is preferably 1 MHz or more and 20 MHz or less. The diagnostic apparatus has a ring array transducer, and a plurality of transducers for transmission and a plurality of detection elements for reception are arranged in a ring shape in the ring array of the ring array transducer. The ring array is fixed on a rail that moves up and down in the water tank, and the ring array can be controlled up and down by a stepping motor. Thereby, the arrival times at which supersonic speeds pass through a plurality of paths penetrating the subject (here, the breast) are measured. The patient only lies on the bed and inserts the subject's breast into the aquarium, and is not squeezed like mammography.

FIG. 2 is a diagram illustrating a configuration of a main part of the ultrasonic measurement unit 2 according to the embodiment. The ultrasonic measurement unit 2 includes a ring array transducer 21, a switching circuit 22 (1024 to 256 multiplexer), an ultrasonic control system 23, and a measurement control unit 24. The ring array transducer 21 is a ring-type vibrator composed of 1024 elements, and includes four transmission / reception probes 25. Each transmitting / receiving probe 25 has a concave shape that constitutes a quarter of the ring, and includes 256 strip-shaped piezoelectric elements. Each strip-type piezoelectric element is usually used for both transmission and reception. A subject 100 is placed inside the ring. It is manufactured by the same manufacturing process as that of a generally used ultrasonic diagnostic probe (convex probe). That is, in the convex type probe, a process of bending so that the middle of the opening protrudes in the middle of the process, but the ring array transducer 21 according to the embodiment performs a process of bending so that the middle of the opening is recessed. Here, although the resonance frequency is 2 MHz, it is needless to say that the present invention is not limited to this.

The switching circuit 22 collects data by the following operation. Each of the four transmission / reception probes 25 transmits a signal, and at this time, all of the four transmission / reception probes 25 receive the signal and acquire the delay time. That is, first, the transmission transducers (1 to 256) of the first transmission / reception probe 25 sequentially transmit signals, and the reception detection elements (1 to 1024) of the four transmission / reception probes 25 receive the signals. . Similarly, the transmission transducers (257 to 512) of the second transmission / reception probe 25 sequentially transmit signals, and the reception detection elements (1 to 1024) of the four transmission / reception probes 25 receive the signals. Further, the transmission transducers (513 to 768) of the third transmission / reception probe 25 sequentially transmit signals, and the reception detection elements (1 to 1024) of the four transmission / reception probes 25 receive the signals. Finally, the transmission transducers (769 to 1024) of the fourth transmission / reception probe 25 sequentially transmit signals, and the reception detection elements (1 to 1024) of the four transmission / reception probes 25 receive the signals.

When the measurement control unit 24 controls the ultrasonic control system 23, when the data collection for one round of the ring array transducer 21 is completed, a sequence in which the measurement controller 24 pauses for a fixed time on the order of 1/10 seconds is performed, and a total of 3 Data collection.

Furthermore, each transmission / reception probe 25 includes a heating element 26. Here, the heating element 26 becomes an ultrasonic oscillator, for example, when a high-intensity focused ultrasound therapy (HIFU: High Intensity / Focused / Ultrasound) is performed. In the HIFU, ultrasonic waves oscillated from a plurality of paths are converged to irradiate the affected area intensively. Further, the heating element 26 may be a plurality of micro heaters. Each microheater has a diameter of, for example, 1.6 mm. When the subject 100 is heated, the microheater is extended from each transmission / reception probe and connected to a region to be heated in the subject 100 (or medium). With a microheater having such a diameter, it is possible to heat a narrow region targeted for heating to a high temperature while suppressing the influence on other measurement regions. The heating element 26 is connected to the ultrasonic control system 23 and the measurement control unit 24. The ultrasonic control system 23 has a thermostat function, and the measurement control unit 24 controls the ultrasonic control system 23 so that a desired condition is applied to the subject 100 (or medium) according to a desired condition. Heat can be applied. Here, the transmission / reception probe 25 is provided with the heating element 26, but is not limited to the heating element for the purpose of heating, and may be a cooling object for the purpose of cooling. It is desirable that the ultrasonic measurement unit 2 includes a temperature adjustment mechanism that heats or cools at least a part of the measurement region including the subject, that is, changes the temperature according to the purpose.

Hereinafter, the ultrasonic imaging apparatus 3 according to the embodiment will be described. As shown in FIG. 1, an ultrasonic imaging program 31 is stored in the storage unit 12. Furthermore, the storage unit 12 includes an information storage unit 32. In the ultrasonic imaging apparatus 3, an ultrasonic imaging program 31 stored in the storage unit 12 is activated. The ultrasonic imaging apparatus 3 according to the embodiment detects the temperature of the subject 100 including water and fat.

FIG. 3 is a flowchart of the ultrasound imaging program 31 according to this embodiment. The ultrasonic imaging program 31 detects the temperature of the subject 100 based on the measurement data acquired from the ultrasonic measurement unit 2. The CPU unit 11 of the control unit 4 includes a temperature-dependent characteristic acquisition unit 41, a first arrival time acquisition unit 42, and a temperature determination unit 43. The temperature-dependent characteristic acquisition unit 41 includes a second arrival time acquisition unit 45, a reference temperature sound speed determination unit 46, and a temperature-dependent characteristic calculation unit 47.

[Temperature-dependent characteristic acquisition step: S1]
Based on the water content ratio and the fat content ratio in each of the plurality of parts of the subject 100, the temperature-dependent characteristics of the sound speed of each of the plurality of parts are acquired (S1: temperature-dependent characteristic acquisition step). In this step, the water content ratio and the fat content ratio in each of a plurality of parts (pixels) of the subject 100 are acquired, and details thereof will be described later.

The temperature dependent characteristics of the sound speed of fat and water are approximated as first and fifth order temperature functions, respectively. Here, when the sound speed (m / s) is SOS and the fat sound speed is SOS ^f , the fat sound speed SOS ^f is approximated by the following Equation 1.

Here, C ₀ = 1506.9 and C ₁ = −3.3. Further, when the sound speed of water is SOS ^w , the sound speed of water SOS ^w is approximated by Equation 2 shown below.

Here, D ₀ = 1402.39, D ₁ = 5.0371, D ₂ = −5.8085 × 10 ⁻² , D ₃ = 3.3420 × 10 ⁻⁴ , D ₄ = −1.4780 × 10 ^{− 6} , D ₅ = 3.1464 × 10 ⁻⁹ . Further, when the subject 100 is a living body, the subject 100 contains substances other than water and fat. Water and fat are greatly different from each other in the temperature-dependent characteristic of sound speed in the region of 20 ° C. to 80 ° C., and the temperature-dependent characteristic of sound speed varies greatly depending on the mixing ratio. The temperature dependence of the sound speed of other substances (tissues) generally depends on whether the sound speed increases as the temperature rises like water or the sound speed decreases as the temperature rises like fat. It can be broadly divided into any kind of characteristics. Therefore, the subject 100 is classified into a plurality of parts (a plurality of pixels), and the temperature-dependent characteristics of the sound speed of each part are determined based on the water content ratio and the fat content ratio in each part. In this embodiment, each part is approximated to a mixture of water and fat as an effective and simple technique. When the content ratio (weight ratio) of fat and water with respect to the whole mixture is R ^f and R ^w , respectively, the sound velocity SOS ^mix of the mixture (each part) is expressed by the following Equation 3.

Here, since each part is approximated to a mixture of water and fat only, R ^f + R ^w = 1. In addition, as shown in Formula 3, each part is a mixture of only water and fat, and the temperature-dependent characteristics of the sound speed of each part are acquired by the content ratio of water and the content ratio of fat. However, other substances may be further considered, not just water and fat. That is, in addition to the water content ratio and the fat content ratio in each part, the temperature-dependent characteristics of the sound speed of each part may be acquired based on the content ratio of other substances.

[First arrival time acquisition step: S2]
A plurality of measured values of the first arrival time through which the ultrasonic wave passes through each of a plurality of paths penetrating the subject (S2: first arrival time acquisition step). The ultrasonic measurement unit 2 measures a plurality of first arrival times, and acquires a measurement value of the first arrival times from the ultrasonic measurement unit 2. In addition, a plurality of measured values of the first arrival time may be recorded in the information storage unit 32, and the measured values of the first arrival time may be acquired from the information storage unit 32.

FIG. 4 is a schematic diagram showing a calculation area (measurement area) according to the embodiment. A transmitting element and a receiving element are arranged on the circumference, and a subject 100 that is a living body is arranged in the circumference. An area including the subject 100 is a calculation area, and the calculation area is divided into a plurality (N) of grids (pixels). A plurality (M) of paths through which ultrasonic waves emitted from a plurality of transmitting elements on the ring circumference reach each of a plurality of receiving elements on the circumference are determined. The subject 100 is arranged on the calculation area, and a plurality of grids classified on the subject 100 become a plurality of parts of the subject 100, respectively, and the plurality of paths include a plurality of paths that penetrate the subject 100. It is out.

Measurements are performed at unknown temperature conditions. For example, the subject 100 is a breast, the breast contains a tumor, and hyperthermia (thermal therapy) for heating tumor cells to 40 ° C. or higher is performed on the breast. Using the ring array transducer 21 of the ultrasonic measurement unit 2, a plurality (M) of arrival times through which the ultrasonic waves pass through each of the plurality (M) of paths are measured, and the plurality of (M) arrival times are measured. A measured value is obtained. A plurality of arrival times measured in an unknown temperature state are a plurality of first measurement times. FIG. 4 illustrates four paths l, l + 1, n, and n + 1, and the arrival times (s) thereof are shown as P _l , P _{l + 1} , P _n , and P _{n + 1} .

[Temperature determination step: S3]
Based on the measured values of the plurality of first arrival times acquired by the first arrival time acquisition step and the temperature-dependent characteristics of the sound speeds of the plurality of portions acquired by the multiple-part temperature-dependent characteristic acquisition step, Is determined (S3: temperature determination step).

If a j-th (j is an integer from 1 to N) grid segment passing through the i-th (i is an integer from 1 to M) path is defined as a weight function W _{i, j} , Since the weight function W _{i, j} is obtained, it can be handled as a known value. Further, a factor resulting from the sound speed in the j-th grid is defined as a delay factor f _j (hereinafter referred to as slowness (s)). The slowness f _j is a value obtained by dividing the size (length) of one grid by the speed of sound SOS, and is the passing time of one grid of ultrasonic waves. _{W i,} j _{f j} is the product of the weight functions _{W i, j} and slowness _{f j} is the transit time of the j-th grid in the i th path. Therefore, the sum of W _{i, j} f _j is the arrival time P _i (s) that the ultrasonic wave passes through the i-th path. The arrival time P _i is expressed by the following Equation 4.

The weight function W _{i, j} shown in Equation 4 is W _{i, j} = 0 for a grid that is not on the i-th path. On the other hand, the grid weight function W _{i, j} through which the i-th path passes has a positive value. For example, A to J are attached to the grid through which the l-th path shown in FIG. 4 passes, and the weighting functions W _{l and A to J} are values of weights (contributions) according to the length passing through the grid. It becomes. For example, when the length of one side of the grid is 1, the weight function W _{i, j} has a value between 0 and √2.

M simultaneous linear equations can be obtained by Equation 4 relating to a plurality (M) of first arrival times P _i (i is an integer of 1 to M) measured from a plurality (M) of paths. From the relationship between the unknown and the number of equations, if M ≧ N ² , the value of the slowness f _j of each grid (pixel) can be determined as a solution. Techniques (sound speed reconstruction method) for calculating a sequential approximate solution for the slowness f _j are well known. For example, the ART (Algebraic Reconstruction Technique) method, the SIRT (Simultaneous Iterative Reconstruction Technique) method, the SART (Simultaneous Algebraic Reconstruction Technique). ) Method and C-SART (Curved-ray SART) method.

When the value of slowness f _j of each site is determined, based on the temperature dependence of the sound velocity shown in the values and formulas 3 slowness f _j at each site, the temperature of each region of the subject 100 is determined, the subject 100 temperature detections (temperature monitoring) are performed. Furthermore, the temperature detection result of the cross section of the subject 100 can be displayed by imaging the temperature of each part.

The ultrasonic imaging program 31 according to the embodiment has been described above. The main feature of the ultrasound imaging program 31 according to this embodiment is that the temperature-dependent characteristics of the sound speed of each of the plurality of parts of the subject 100 are based on the water content ratio and the fat content ratio of each of the plurality of parts. To decide. In the temperature dependent characteristic acquisition step (step S1), there can be many methods for determining the water content ratio and the fat content ratio of each of the plurality of parts. Hereinafter, the temperature dependent characteristic acquisition step (step S1) according to the embodiment will be described below. ) Will be described in detail.

FIG. 5 is a flowchart of the temperature-dependent characteristic acquisition step (step S1) according to this embodiment.

[Second arrival time acquisition step: sa]
Acquires measurement values of a plurality of second measurement times in which ultrasonic waves pass through each of a plurality of paths penetrating the subject, measured in a temperature environment different from the temperature environment in which the measurement values of the plurality of first measurement times are measured. (Sa: second arrival time acquisition step). The ultrasonic measurement unit 2 measures a plurality of second arrival times, and acquires a measurement value of the second arrival times from the ultrasonic measurement unit 2. Further, a plurality of measured values of the second arrival time may be recorded in the information storage unit 32, and the measured values of the second arrival time may be acquired from the information storage unit 32.

Step sa is the same as step S2 (first arrival time acquisition step) except that the measured temperature environment is different. In step S2, the measurement for the running in an unknown temperature state, in step sa, is performed under a known reference temperature T _s environment. When the subject 100 is a breast, the subject 100 is in a temperature environment where the subject 100 is sufficiently cooled to suppress the temperature distribution. Here, the reference temperature T _{s is set} to 25 ° C. However, when the subject is a part of a human body, the reference temperature T _s is preferably set to 20 ° C. or more and 30 ° C. or less. Further, although the correspondence to the deep part of the body and the body surface temperature are generally different, it is also effective to set the temperature gradient as a function of the distance from the body surface. Under such a temperature environment, the temperature distribution of the subject 100 can be regarded as substantially constant. Under a known reference temperature T _s environment, using a ring array transducer 21 of the ultrasonic measuring unit 2, the arrival time of the plurality the plurality of respective paths ultrasound undergoes the (M present) (M number) is measured, A plurality of (M) arrival time measurement values are acquired. A plurality of arrival times measured under a known reference temperature T _s environment is a plurality of second measuring time.

[Reference temperature sound speed determination step: sb]
Based on the measured values of the plurality of second arrival times acquired by the second arrival time acquisition step, the sound speed of each of the plurality of parts is determined (sb: reference temperature sound speed determination step). In step S3 (temperature determination step), the value of the slowness f _j of each grid (pixel) is determined from the simultaneous linear equations consisting of Equation 4 relating to a plurality of first arrival times, whereas in step sb, The value of the slowness f _j of each grid (pixel) is determined from the simultaneous linear equations consisting of Equation 4 relating to a plurality of second arrival times. A slowness value or a sound speed value at each of a plurality of parts of the subject 100 is determined.

[Temperature dependent characteristic calculation step: sc]
Based on the slowness value or the sound velocity value of each of the plurality of parts of the subject determined in the reference temperature sound speed determination step, the temperature dependence characteristic of the sound speed of each of the plurality of parts of the subject is calculated (sc: temperature dependence characteristic calculation). Step). The sound speed SOS ^w of water and the sound speed SOS ^f of fat at a known reference temperature T _s are substituted into Equation 3, and each part approximates a mixture of water and fat only (R ^f + R ^w = 1). Thereby determining the content ratio R ^w and fat content ratio R ^f of water in each of the plurality of sites. Based on the determined water content ratio R ^w and fat content ratio R ^f , the temperature-dependent characteristics of the sound velocity at each of the plurality of parts of the subject 100 are calculated from Equation 3.

Note that it is considered that a region other than the subject 100 in the calculation region (measurement region) is filled with a known medium such as water. The temperature dependence characteristics of the sound speed in these areas are stored in the information storage section 32, and the temperature dependence characteristics of the sound speed in these areas may be acquired from the information storage section 32. In addition, the temperature dependence characteristics of the sound speed at each of the plurality of parts of the subject 100 may be stored in the information storage unit 32, and the temperature dependence characteristics of the sound speed at each of the plurality of parts may be acquired from the information storage unit 32.

The temperature dependent characteristic acquisition step (step S1) according to the embodiment has been described above. In the temperature-dependent characteristic acquisition step according to the embodiment, the water content ratio ^Rw and the fat content ratio ^{Rf of} each of the plurality of parts of the subject 100 are obtained by measurement using the ultrasonic measurement unit 2 according to the embodiment. It is determined. The measurement of the plurality of second arrival times is performed under a temperature environment (reference temperature T _s ) different from the measurement of the plurality of first arrival times, but otherwise, measurement may be performed under common conditions. Therefore, in addition to determining the temperature-dependent characteristics of the sound speed of each of a plurality of parts (multiple grids) with high accuracy, measurement can be performed using the same apparatus (ultrasonic measurement unit 2), thereby reducing measurement time. There are special effects such as a reduction in the cost of preparing the device.

However, the multiple-part temperature-dependent characteristic acquisition step is not limited to the embodiment. By other measurements, the water content ^Rw and the fat content ^Rf may be determined. For example, the water content ratio R ^w and the fat content ratio R ^f are determined by measurement using an MRI apparatus, and a plurality of test subjects are determined based on the determined water content ratio R ^w and fat content ratio R ^f . You may determine the temperature dependence characteristic of the sound speed of each site | part.

Also, it is generally desirable to measure temperature in real time. This is because when a temperature change is given from the outside as in the example of focused ultrasound therapy, the temperature distribution measurement by the method based on the present invention gives information to be fed back to the external temperature control means, and high precision control is achieved. This is because there is a possibility of contributing and it is necessary to calculate the temperature in real time for feedback. Since the process of step S1 is before the temperature change, even if time is required for the reconstruction time, no particular inconvenience occurs. On the other hand, regarding the processes related to steps S2 to S3, high-speed reconstruction is desired in consideration of real-time feedback. The following method is also useful as a method for realizing this. In other words, this is a technique for reconstructing the difference between the first arrival time distribution and the second arrival time distribution instead of reconstructing the first arrival time distribution. In general, the distribution of fat and water in the living body has a more complex spatial distribution than the temperature distribution. This is because the heat diffuses to the surroundings with a constant thermal conductivity, so it is unlikely to have a discontinuous distribution. For example, in the case of breast cancer imaging, the shape of a mixture of mammary gland and fat is intermittent in each other region This is because they often have complex anatomical structures mixed with each other. The complexity of the sound speed distribution increases the calculation cost because it increases the number of iterations in the ART method, SART method, and C-SART method. On the other hand, when the sound velocity distribution reflecting the temperature distribution is obtained by calculating the difference between the first arrival time distribution and the second arrival time distribution, the temperature distribution is locally applied in a temperature change such as focused ultrasound treatment. Since it stays, the number of iterations can be reduced.

[Second Embodiment]
The ultrasonic CT apparatus 1 according to the second embodiment of the present invention is the ultrasonic CT apparatus according to the first embodiment except that the configuration of the temperature determining means 43 provided in the ultrasonic imaging apparatus 3 is different. 1 has the same configuration. The temperature determination unit 43 according to this embodiment includes a temperature correction unit 48.

The inventors devised a T-SART (Temperature considering SART) method in which the temperature distribution is taken into consideration in the SART method and adopted as the sound velocity reconstruction method according to the embodiment. Hereinafter, the T-SART method will be described, but before that, the SART method will be described. In the SART method, correction using Formula 5 shown below is performed at each calculation step.

Here, the subscripts i, j, and k represent the path number, grid number (pixel number), and number of calculation steps, respectively. In addition, g, a, w, and p represent a brightness function, a weight function, a weight function considering a Hamming window function, and projection data, respectively. Here, since the sound velocity is reconstructed, the luminance value is the passing time of each grid, that is, the slowness f, and the projection data is the arrival time P (first arrival time). Here, the model is corrected by calculating the “slowness difference” in a system without sound speed heterogeneity from the “arrival time difference” with a system without sound speed heterogeneity. Therefore, to be precise, here, arrival time means "difference in arrival time with a system without sound speed heterogeneity" and slowness means "difference in slowness with system without sound speed heterogeneity". ing.

FIG. 6A is a diagram for explaining the SART method. As shown in Equation 5, the SART method can be interpreted as making the following modifications. First, paying attention to a certain route, the difference (arrival time difference) between the actual arrival time (p _i ) and the arrival time (a · g) in the current model is calculated. Then, the difference is multiplied by the weight function (wi _{, j} ) for the path of each grid, and is distributed evenly, and the correction amount (in the parenthesis of the summation symbol Σ in the numerator of the second term on the right side of Equation 5) ) To correct the model. As shown in FIG. 6A, for the assumed luminance value (slowness) distribution, the arrival time difference is zero due to the luminance value change (correction amount) common to each of the plurality of grids on the route (i-th route). Then, the luminance value (slowness) distribution is corrected so that the temperature distributions of a plurality of grids on the path are corrected based on the corrected luminance value (slowness) distribution.

In the SART method, since the slowness on the path is corrected equally along the path, the temperature calculation error increases in a region where the change rate of the temperature-dependent characteristic of the sound speed is small. Therefore, in particular, in a model in which the subject is a mixture of water and fat, the temperature-dependent characteristics of each part are convex upward and can be a function having a maximum value near the target temperature. In some cases, there may be no intersection with such temperature dependent characteristics, so a small sound speed error may cause a large temperature error.

On the other hand, in the T-SART method, since the sound velocity is calculated from the temperature distribution, the initial value T _j ⁽⁰⁾ of the temperature distribution of a plurality of grids is set as the initial condition. The luminance value g _j ^(k) (here, slowness) in each calculation step is the reciprocal of the speed of sound and is therefore expressed as a function of the temperature T _j ^(k) . Since the luminance value g _j ^(k) and the temperature T _j ^(k) have a one-to-one correspondence, the initial value g _{j of the} luminance value distribution can be set by setting the initial value T _j ⁽⁰⁾ of the temperature distribution of a plurality of grids. ^There is no need to set ⁽⁰⁾ . The luminance value g _l ^(k) is expressed by the following formula 6.

Furthermore, Formula 6 is represented by Formula 7 shown below by Formula 1 ^{thru |} or 3 and approximation ( ^Rf + ^Rw = 1) with the mixture of only water and fat.

In the T-SART method, the value of the luminance value g _j (slowness) is changed by correcting the temperature using Equation 7. In the T-SART method, as in the SART method, attention is paid to each path of ultrasonic waves. Then, all temperatures on the i-th path are changed evenly by dt _i .

Here, the variable z _{i, j} is defined as a function that becomes 1 when the j-th grid is on the i-th path and 0 when there is no j-th grid on the i-th path. The corrected temperature distribution in the i-th path is expressed by Equation 8 below.

The luminance value after temperature correction is expressed by the following formula 9.

The luminance value (slowness) when temperature correction is given on the path is calculated by Equation 8 and Equation 9. Therefore, it is important to calculate the correction temperature amount dt _i given to the i-th path shown in Formula 8. In the T-SART method, the temperature of the i-th path is corrected so that the arrival time of the ultrasonic wave passing through the i-th path becomes equal to the actual arrival time. The condition for this is defined by Equation 10 shown below.

FIG. 6B is a diagram for explaining the T-SART method. The temperature distribution is corrected by correcting the temperature distribution so that the arrival time difference becomes zero based on the temperature change (correction amount) common to each of the plurality of grids on the i-th path with respect to the assumed temperature distribution. Based on the distribution, the luminance value (slowness) distribution of a plurality of grids on the path is corrected.

By combining Equations 8 to 10, a relational expression for the projection data p _i and the calculated change temperature dt _i can be obtained. However, in practice, it is difficult to directly solve the change temperature dt _i , and in the present embodiment, it is calculated using the following search method.

First, the correction temperature search width ddt is set, and the luminance value G (T _j ^(k) ) is calculated by substituting dt _i = 0 into Equation 9 in order to determine the search direction. Then, the arrival time difference dP _i (T _j ^(k) ) from the projection data (P _i ) given by the following equation 11 is calculated.

Next, the luminance value G (T _j ^(k) + z _{i, j} · ddt) at dt _i = ddt that is changed by the temperature search width ddt is calculated. Similarly, the arrival time difference dP (T _j ^(k) + z _i is calculated. _{, J} · ddt).

Here, if the absolute value of the arrival time difference is reduced by the correction, that is, | dP (T _j ^(k) ) |> | dP (T _j ^(k) + z _{i, j} · ddt) | If so, the search direction is assumed to be correct. On the other hand, if the absolute value of the arrival time difference is increased, that is, if | dP (T _j ^(k) ) | <| dP (T _j ^(k) + z _{i, j} · ddt) | As -ddt, the search direction is corrected in the opposite direction. If the search direction is determined, the _{dt i, 0, ddt, 2} · ddt, 3 · ddt ... and, while changing only search width temperature, calculates the arrival time. As an end condition of the iterative calculation, here, the arrival time difference dP (T _j ^(k) + z _{i, j} · n · ddt) and dP (T _j ^(k) + z _{i, j} · (n + 1) · ddt) is that the sign of the sign is reversed (n is an integer of 1 or more). The fact that the sign of positive / negative is reversed is considered that there is a correction temperature satisfying Equation 10 between the correction temperature n · ddt and the correction temperature (n + 1) · ddt. For example, a correction temperature having a smaller absolute value of the reached temperature difference between the correction temperature n · ddt and the correction temperature (n + 1) · ddt may be employed.

The iterative calculation termination condition is not limited to the above condition, and a method using a relative residual is also conceivable. Further, the search method of dt _i is not limited to these, and other methods may be used.

The correction values for all routes are calculated by the above method. Similar to the SART method, the T-SART method averages the correction values calculated in all the routes, and corrects the model using the following Equation 12. For the distribution of correction values, a Hamming window function is introduced to correct the data density.

FIG. 7 is a flowchart of the temperature determination step (step S3) according to this embodiment. Step S3 based on the described T-SART method will be described below.

[Initial temperature condition setting step: ta]
An initial temperature condition is set for each of a plurality of grids in a calculation region including a plurality of parts of the subject (ta: initial temperature condition setting step). Here, the initial value T _j ⁽⁰⁾ of the temperature distribution of the plurality of grids is set, but the initial value T _j ⁽⁰⁾ of the temperature distribution may be a predetermined temperature (uniform distribution), for example.

[Temperature correction step: tb]
A measured value of the first arrival time in a certain route (i-th route: i is an integer of 1 to M) and a delay factor assumed for each of a plurality of grids on the route passing through the route among a plurality of grids in the computer area When there is a difference in arrival time between the arrival times based on, the temperatures of the grids on the plurality of paths are corrected so as to reduce the difference in arrival time (tb: temperature correction step). Here, it is desirable to correct the temperature of each of the grids on the plurality of paths so that the arrival time difference becomes zero. Furthermore, it is desirable to correct by a temperature change common to a plurality of grids on the path. The plurality of grids on the route are a plurality of grids that penetrate the route among the plurality of grids in the computer area. In the case of the l-th route shown in FIG. 4, the plurality of grids on the route are A to J. . Step tb is repeated for all (M) routes.

In step tb, the temperature distributions T _j ^(k) of the plurality of on-path grids passing through the i-th path are determined by the temperature change dt _i common to the plurality of on-path grids so that the arrival time difference dP _i becomes zero. It is corrected. The method for determining the temperature change dt _i is as already described. One example is shown. (I) A temperature search width ddt having a predetermined value is set. (Ii) The temperature distribution of the grid on the path is changed to (T _j ^(k) + ddt). (Iii) the temperature distribution ^{_(T j} (k) + ddt) luminance values in ^{_{G (T j (k) +}} ddt) is calculated (see Equation 9). Here, the luminance value g _j ^(k ) in the temperature distribution (T _j ^(k) + ddt) based on the temperature-dependent characteristics of the sound speed of each of the plurality of parts of the subject 100 acquired in the temperature-dependent characteristic acquisition step (step S1). ⁾ Calculate (slowness). (Iv) The arrival time difference dP _i (T _j ^(k) + ddt) is calculated (see Expression 11). (V) The sign of ddt is determined by increasing or decreasing the arrival time difference. As described above, if the absolute value of the arrival time difference decreases, the sign of ddt is maintained, and if it increases, the sign of ddt is inverted (ddt = −ddt) to determine the search direction. (Vi) For the temperature distribution (T _j ^(k) + n · ddt) (n is an integer of 1 or more) according to the determined search direction, the above (ii) to (iv) are represented by the sign of the arrival time difference dP _i Repeat until is reversed. (Vii) The temperature change dt _i for correction in this calculation step (k) is determined.

[Calculation result judgment step: tc]
The result of the k-th (k is an integer equal to or greater than 1) calculation step is determined (tc: calculation result determination step). In the first (k = 1) calculation step, the process automatically proceeds to the second (k = 2) calculation step. For the kth (k ≧ 2), the convergence is determined based on the difference between the kth calculation result and the (k−1) th calculation result. If it is determined that the convergence is sufficient, step S3 is terminated. If it is determined that the convergence is not sufficient, k = k + 1 is set, and the process proceeds to the (k + 1) th calculation step.

Through the above calculation, a luminance value (slowness) distribution that minimizes the arrival time difference dP _i of a plurality (M) of routes is acquired, and a temperature distribution that provides the luminance value distribution is acquired.

In this embodiment, unlike the SART method that directly corrects the luminance value (slowness) distribution of the path grid, the temperature distribution of the path grid is corrected so as to reduce the arrival time difference. By simplifying the calculation, a value common to the grid on the path is used for the temperature change for correction in each path. However, although it is desirable to use a common value for shortening the calculation time, it is needless to say that the method is not limited to this method. As long as the arrival time difference is reduced by correcting the temperature distribution of the on-path grid, the temperature distribution is not limited to being corrected by a common value in the on-path grid.

In addition, the reason why the arrival time difference is reduced by correcting the temperature distribution will be explained below. In the process of obtaining the reference temperature sound speed from the second arrival time acquisition, there is always a certain spatial resolution limit for tomographic image reconstruction. For this reason, in the spatial distribution of the mixing ratio of fat and water, the estimation accuracy of the mixing ratio decreases in a region where the change of the mixing ratio is steep. As the estimation accuracy decreases, the temperature-dependent characteristic of sound speed deviates from the original temperature-dependent characteristic. The result of this deviation induces a temperature estimation error. On the other hand, the boundary of the temperature distribution is always gentle due to the effect of thermal diffusion (if there is a region with significantly lower thermal conductivity compared to the surroundings, the thermal diffusion efficiency decreases only in that region, so the temperature spatial gradient is large. However, it is not necessary to assume that there is a region with extremely low thermal conductivity in the tissue in the living body). For this reason, there is a reason that the temperature distribution assumes spatial continuity rather than the spatial continuity of the mixing ratio of fat and water. Therefore, it is appropriate to reduce the arrival time difference by correcting the temperature distribution.

In the above example, the example of obtaining the fat / water mixing ratio from the reference temperature sound velocity and MRI has been described. Another method is to use two reference temperatures and divide the sound speed into two areas: a region where the sound velocity changes positively during this temperature change and a region where the sound velocity changes negatively. Is possible. In this case, when the resolution is sufficiently high, each pixel is divided into a region having a temperature dependence of sound speed similar to water and a region having a temperature dependence of sound speed similar to fat.

[Third Embodiment]
The ultrasonic CT apparatus 1 according to the third embodiment of the present invention is different from the ultrasonic CT apparatus according to the second embodiment except that the configuration of the temperature determining means 48 provided in the ultrasonic imaging apparatus 3 is different. 1 has the same configuration. In the temperature determination unit 48 according to the second embodiment, there may be a problem in convergence. The temperature determining unit 48 according to the embodiment determines the temperature change for correction in consideration of convergence.

First, let us consider the convergence of the T-SART method. From Equation 8, the corrected luminance value (slowness) is approximated by Equation 13 shown below.

Further, the following Expression 14 is obtained as a conditional expression that satisfies the correction temperature dt _i by Expression 10 and Expression 13.

Here, when formula 14 is arranged using the relationship between z _{i, j} and a _{i, j} , formula 15 shown below is obtained as a conditional expression for the correction temperature.

However, the arrival time difference dP _i satisfies Expression 11. Note that Formula 15 is a conditional expression for calculating the correction temperature in the i-th path (one path) to the last, and dP _i and dt _i are scalar quantities. The left side of Equation 15 means the difference between the arrival time of the ultrasonic wave and the actual arrival time in the current model, and the right side of Equation 15 shows the change in arrival time that changes when the correction temperature dt _i is given. I mean. By correcting the temperature so that they are equal, the arrival time of the ultrasonic wave passing through the i-th path is adjusted to be equal to the actually measured value. As shown in Equation 15, the (positive or negative) sign of the correction temperature dt _i is determined depending on the signs of dP _i and a _i ^T (dG / dt). Therefore, the sign of the differential value dG / dT of the luminance value is important.

Assuming that an ideal luminance value distribution (slowness distribution) is g _j ^ideal , dP _i is approximated by Expression 16 shown below.

As described above, since the luminance value (slowness) and the temperature have a one-to-one correspondence, Expression 17 shown below is derived from Expression 16 when an ^ideal temperature distribution T _j ^ideal set in the system is used.

Further, if the difference between the current model and the ideal temperature distribution is dT _j ^(k) , Expression 17 is replaced with Expression 18 shown below.

Furthermore, Equation 18 is approximated to Equation 19 shown below.

Formula 19 means line integration along the path by multiplying the temperature differential value of the brightness value (slowness) in each grid (pixel) by the difference from the ideal temperature. It is assumed that the i-th path starts from one point on the outer periphery of the ring, passes through the central portion where the subject is arranged, and reaches another point on the opposite side of the one point on the outer periphery of the ring. For example, consider a case where the sign of the temperature differential dG / dT of the brightness value is negative near the outer periphery of the calculation area, and the sign of the temperature differential dG / dT of the brightness value is positive near the center of the calculation area. Then, it is assumed that the arrival time difference dP _{i from the} actually measured value in the i-th route is calculated as a positive value.

In the line integration in the i-th path, the absolute value of dG / dT near the outer periphery is larger than the absolute value of dG / dT near the center, or the region where dG / dT is negative is greater than the region where dG / dT is positive. If it is long, the correction temperature dt _{i (} common to all of the plurality of grids on the i-th path) in the T-SART method can be negative from Equation 11. Even in such a case, the signs of dT _j ^(k) may be all positive in all grids on the i-th path. When the value of dT _j ^{(k) in} the central portion is larger than the value of dT _j ^(k) near the outer periphery, both sides of Equation 19 can be positive. In this case, although the actual correction temperature dT _j ^(k) is a positive value in all the grids on the i-th path, the correction temperature dt _i in the T-SART method is negative, and the correction temperature is It is calculated opposite to the original temperature difference, and the convergence may be deteriorated.

In this embodiment, a T-SART method (hereinafter referred to as a modified T-SART method) in consideration of convergence is adopted. In the T-SART method, regardless of the sign of the temperature differential dG / dT of the luminance value (slowness), the correction temperature is set to the correction temperature dt _i common to all the plurality of grids on the i-th path. On the other hand, in the modified T-SART method, the sign of the correction temperature is determined according to the sign of the sign of the temperature differential dG / dT of the luminance value (slowness) in each of the plurality of grids.

In the T-SART method, the correction temperature is set to a correction temperature dt _i common to all the plurality of grids on the i-th path. However, in general, since the correction temperature may be different depending on the grid (pixel), the correction temperature in the j-th grid is set to dt _{i, j} . In this case, Expression 10 is rewritten to Expression 20 shown below.

If j shown in Equation 20 is limited to the grid on the i-th path, Equation 20 can be rewritten as Equation 21 below.

In order to simplify the calculation, the absolute value of the correction temperature in the i-th path is assumed to be equal, and the following formula 22 is set as a condition.

Here, C _i is a constant for the i-th path. The sign of the correction temperature dt _{i, j} in each grid (pixel) is determined according to the sign of the temperature differentiation of the luminance value (slowness). As shown in Equation 23 below, if the arrival time difference dP _i is positive _, the sign of dt _{i, j} is determined so that (dG / dT) dt _{i, j} becomes positive.

As shown in Equation 24 below, if the arrival time difference dP _i is negative, the sign of dt _{i, j} is determined so that (dG / dT) dt _{i, j} is negative.

For ease of explanation, the modified T-SART method is described below using a two-dimensional hyperplane. Assuming that the number of grids is 2 (j is an integer of 1 or 2), the projection data p _i (arrival time) and the luminance value g _j (slowness) are expressed by the following formula 25 using ω _ij as a weight function. The

FIG. 8 is a diagram showing directions of correction vectors in the SART method and the T-SART method on a two-dimensional hyperplane. In the two-dimensional hyperplane, the two formulas shown in Formula 25 can be represented by a straight line l and a straight line m, respectively. In the ART method and the SART method, the model is corrected so that a perpendicular line is extended to a straight line that means a solution to a certain projection. That is, the correction vector of the luminance value (slowness) has a direction orthogonal to the straight line as shown by a broken line in FIG.

On the other hand, in the T-SART method, the temperature is uniformly corrected in each path, and the two-dimensional hyperplane is expressed by the signs of ΔG1 (dT) and ΔG2 (dT) that are components of the correction vector. Region 1 where the signs of ΔG1 (dT) and ΔG2 (dT) are (positive, positive), region 2 (positive, negative), region 3 (negative, negative), and (negative, positive) region 4 is classified into four areas. Among these, as indicated by the solid line in FIG. 8, when the correction vector is region 1 and region 3, it is considered to have good convergence, but when the correction vector is region 2 and region 4, It is considered that there may be a problem with convergence.

FIG. 9 is a diagram showing the direction of the correction vector in the modified T-SART method on the two-dimensional hyperplane. For reference, the directions of correction vectors in the SART method and the T-SART method are also shown. As described above, the correction vector in the SART method has a direction orthogonal to the straight line 1 as indicated by V1 in the figure. In the T-SART method, the correction temperatures of the grid 1 and the grid 2 are the same (both are set to C ₁ here), and thus have a direction indicated by V 2 in the figure. On the other hand, in the modified T-SART method, the sign of the temperature change to be corrected is changed according to the sign of the temperature derivative of the luminance value (slowness). Therefore, in the case shown in FIG. Are different from each other. Therefore, the correction vector has a direction indicated by V3 in the figure.

Hereinafter, the temperature determination step (step S3) according to the embodiment will be described. Step S3 according to this embodiment is as shown in the flowchart of FIG. 7, but the configuration of the temperature correction step (step tb) is different from that of the second embodiment. In this embodiment, as in the second embodiment, the temperature of each of the grids on the plurality of paths is corrected so as to reduce the arrival time difference and, if desired, the arrival time difference is zero. However, in this embodiment, the sign of the temperature change that corrects the temperature of each of the grids on the plurality of paths is determined based on the sign of the temperature differential value of the assumed delay factor and the sign of the arrival time difference. Yes. It is desirable that the absolute value of the temperature change for correcting the temperature of each of the plurality of path grids is a value common to the plurality of path paths. The sign of the temperature change that corrects the temperature of each grid on the path is determined to be positive if the sign of the temperature differential value of the assumed delay factor and the sign of the arrival time difference are the same, and negative if they are different It is more desirable to do this.

In this embodiment, in the temperature correction step (step tb), the absolute value of the temperature change in the plurality of grids is a common value. Therefore, in step tb, the sign of the temperature change in each grid is determined, and the common value is calculated. As described above, the sign of the temperature change in each grid is determined by Equations 23 and 24. The calculation of the common value is similar to the method for determining the temperature change in the second embodiment.

Hereinafter, an example of the temperature correction step (step tb) according to the embodiment will be described. (I) A temperature search width ddt having a predetermined value is set (similar to the second embodiment). (Ii) The temperature distribution of the grid on the path is changed to (T _j (k) + ddt) (similar to the second embodiment). (Iii) A luminance value G (T _j ^(k) + ddt) in the temperature distribution (T _j ^{( k)} + ddt) is calculated (similar to the second embodiment). (Iv) In each grid on the path, the sign of the temperature change is determined based on the sign of the temperature differential value dG / dT of the luminance value (slowness) and the sign of the arrival time difference dP _i (Equations 23 and 24). reference). (V) The arrival time difference dP _i is calculated based on the sign of the temperature change determined in each grid on the path. (Vi) With respect to the temperature distribution (T _j ^(k) ± n · ddt) (n is an integer of 1 or more, and the sign in each on-path grid is ±), (ii), (iii), and (V) is repeated until the sign of the arrival time difference dP _i is reversed. (Vii) The absolute value C _i of the temperature change for correction in this calculation step (k) is determined.

In this embodiment, the absolute value of the temperature change for correction in each path grid is a common value in a plurality of path grids, but is not limited thereto. Further, the sign of the temperature change for correction in each grid on the path is determined by Expressions 23 and 24. However, the sign of the temperature change in the plurality of grids on the path is all determined by Expressions 23 and 24. It does not have to be. What is necessary is just to determine the code | symbol for the temperature change in a part of several grid on a path | route to the extent sufficient to determine the directionality of convergence. Specifically, the “part” is preferably a grid on a route that is 70% or more of a plurality of grids on a route. In this embodiment, the convergence based on Equations 23 and 24 is applied to the T-SART method. However, the present invention is not limited to this, and other sound speed reproduction using the temperature differential value of the luminance value is possible. You may apply to a construction method.

The ultrasonic imaging apparatus, ultrasonic imaging method, ultrasonic imaging program, and ultrasonic CT apparatus according to the embodiment of the present invention have been described above. Below, the measurement result and calculation result by embodiment of this invention are shown below.

FIG. 10 is a diagram showing an example of a measurement result obtained by the ultrasonic CT apparatus 1 according to the first embodiment of the present invention. FIG. 10 is an image of the sound velocity distribution based on the measurement data of the subject 100. Here, an acrylamide gel is used for the subject 100, and a micro heater is used as the heating element 26, simulating a HIFU that warms a small region to a high temperature by ultrasonic waves. The center portion of the subject 100 is heated intensively and the temperature rises due to internal heat generation. The state of the subject 100 is 2 minutes after the start of heating. . Note that the temperature of the subject 100 and the medium (water) before heating is 20 ° C. The sampling rate is 10 MHz, and the sample interval time is 0.1 μs. As shown in FIG. 10, the sound speed at the center of heating is increased to near 1550 m / s, and the sound speed decreases as the distance from the microheater increases. In the medium (water), the sound speed is 1482 m / s in a constant state. It is near s.

FIG. 11A is a diagram showing a model of the subject 100 set in the ultrasonic imaging apparatus 3 according to the second and third embodiments of the present invention. As shown in FIG. 11A, the subject 100 is a cell. For simplicity, the fat content ratio is constant and the diameter of the subject 100 is set to 20 mm. The medium around the subject 100 is water (the content ratio of fat is 0).

FIG. 11B is a diagram showing a calculation result of the ultrasonic imaging apparatus 3 according to the second embodiment of the present invention. FIG. 11B shows a calculation result obtained by performing iteration (number of calculation steps) 100 times on the temperature distribution of the path i shown in FIG. 11A. A temperature distribution curve which is a calculation result by the T-SART method according to the embodiment is shown together with a temperature distribution of a set model. Note that the subject 100 shown in FIG. 11B has a fat content ratio of 20%. That is, the weight ratio of fat to water is 1: 4. When the subject 100 is such a mixture, both the temperature dependence of the water slowness and the temperature dependence of the subject 100 are dG / dT> 0, and the calculation result shows the model temperature distribution and the practical use. The same level of agreement.

FIG. 11C is a diagram showing a calculation result of the ultrasonic imaging apparatus 3 according to the third embodiment of the present invention. FIG. 11C shows a calculation result obtained by performing iteration (number of calculation steps) 50 times on the temperature distribution of the path i shown in FIG. 11A. A temperature distribution curve which is a calculation result by the modified T-SART method according to the embodiment is shown together with a set model temperature distribution. Note that the subject 100 shown in FIG. 11C has a fat content ratio of 60%. That is, the weight ratio of fat to water is 3: 2. When the subject 100 is such a mixture, the temperature dependence of the slowness of water is dG / dT> 0, whereas the temperature dependence of the slowness of the subject 100 is dG / dT <0. In such a case, the T-SART method may cause a problem in convergence. However, in the modified T-SART method according to the embodiment in consideration of convergence, the calculation results have a practical level of coincidence. In addition, a discontinuous jump (jump) in temperature is observed at the boundary between the subject 100 and the medium (water). The measurement results and calculation results according to the embodiment of the present invention have been described above.

The present invention is not limited to the above embodiment, and can be widely applied to ultrasonic imaging. In the above-described embodiment, two-dimensional imaging is taken as an example, and each grid is a pixel (pixel), but is not limited to this, and may be three-dimensional imaging. In this case, each grid is a voxel.

In addition, the example of ultrasonic therapy was mainly demonstrated about the temperature change detected with the ultrasonic imaging apparatus which concerns on embodiment of this invention. However, examples of temperature detection are not limited to this, and there are, for example, the following two examples. The technique of the present invention can be widely applied including these examples.

It is known that when a cancer is imaged, the presence of a tumor, particularly a tumor formed as a result of metastasis, can be visualized by visualizing the difference in the amount of metabolism between the cancer and other sites. This is generally put to practical use as PET (Positron Emission Tomography) as a method of using glucose labeled with a radioactive isotope of fluorine as a contrast agent. It is already known that there is a difference in the temperature distribution because the site where metabolism is active has a lot of fever. It is also known that when temperature changes are applied, only the sites with different metabolic amounts have different temperature change histories. For example, it is known that when the temperature of a living tissue in a certain region is lowered, the temperature change is delayed only at a site with much metabolism, and when the temperature is stopped lowering, the temperature is quickly recovered from the site with much metabolism. . If this is used, a region with different metabolism can be visualized by introducing a temperature change from outside the body to a region where the presence of a tumor is suspected without using a radioisotope like PET. In order to visualize this metabolic abnormality region, it is possible to perform temperature distribution measurement based on the T-SART method. In this case, unlike the therapy monitoring example, it is difficult to obtain an accurate temperature because the assumption that the initial temperature distribution is constant may not be appropriate. However, since the purpose is to depict a region in which the metabolic rate is relatively different from that of the surrounding normal tissue, it is not always necessary to quantitatively calculate the accurate temperature. The above concept can be realized by incorporating a temperature changing mechanism into the apparatus configuration of FIG.

Temperature measurement is also useful in blood flow imaging. When the temperature of only the observation region is lowered to T _ROI , the blood flow at temperature T ₀ flows from the region where the temperature is not lowered (temperature T ₀ ). As a result, a temperature difference of T _ROI -T ₀ is generated in the observation region, so that if the temperature distribution can be visualized, the state of blood flow can be visualized. This can be treated as a contrast agent using thermal energy. A general medical contrast agent introduces a substance that does not originally exist in the living body, and therefore a chemical substance administered from outside the body for a certain period of time remains in the body even after imaging of the contrast agent is completed. However, when a thermal contrast agent is used, if the temperature difference is not significantly large, the contrast effect disappears with time without affecting the living body, so there is a great merit from the viewpoint of biological safety. .

Furthermore, there is one example below for an example of making a diagnosis from a change in sound velocity distribution in addition to a change in temperature. The technique of the present invention can be widely applied to these examples. As an example of performing a diagnosis of a change in sound velocity distribution other than a temperature change, monitoring of anticancer drug treatment is assumed. Since ultrasonic CT can measure three-dimensional data without exposure, it is also useful in monitoring the effect of an anticancer agent during anticancer agent treatment. When the effect of the anticancer drug is effective, a change in the size of the tumor can be observed. That is, the sound speed distribution changes in the time order of the week or month. In this case, unlike the case of the temperature change, since the time for tracking the change with time is extremely long, registration and position correction for correcting the change of the imaging position and the like are required. Regarding the change in the cancer, in addition to the method of taking the difference between the sound velocity distribution maps before and after the change, extracting the change before reconstruction as in the present invention also increases the sensitivity to the change. It is beneficial to.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2016-234424 filed on December 1, 2016, which is incorporated by reference in its entirety.

1 Ultrasonic CT device, 2 Ultrasonic measurement unit, 3 Ultrasonic imaging device, 4 Control unit, 5 Input device, 6 Display device, 11 CPU unit, 12 Storage unit, 13 Information input unit, 14 Information output unit, 21 Ring array transducer, 22 switching circuit, 23 ultrasonic control system, 24 measurement control unit, 25 transmission / reception probe, 26 heating element, 31 ultrasonic imaging program, 32 information storage unit, 41 temperature-dependent characteristic acquisition means, 42 first arrival Time acquisition means, 43 temperature determination means, 45 second arrival time acquisition means, 46 reference temperature sound speed determination means, 47 temperature dependent characteristic calculation means, 48 temperature correction means.

Claims (12)

1. An ultrasonic imaging apparatus for detecting a temperature of a subject including water and fat,
   A temperature-dependent characteristic acquisition unit that acquires a temperature-dependent characteristic of sound speed of each of the plurality of parts based on a water content ratio and a fat content ratio in each of the plurality of parts of the subject; and
   First arrival time acquisition means for acquiring a plurality of measured values of first arrival times through which ultrasonic waves pass through each of a plurality of paths penetrating the subject;
   Based on the measured values of the plurality of first arrival times acquired by the first arrival time acquisition unit and the temperature-dependent characteristics of the sound speeds of the plurality of regions acquired by the plurality of region temperature dependency characteristic acquisition units. Temperature determining means for determining the temperature of each of the plurality of sites;
   An ultrasonic imaging apparatus comprising:
2. The ultrasonic imaging apparatus according to claim 1,
   The multi-site temperature-dependent characteristic acquisition means is
   Based on the measurement values of the plurality of second measurement times measured in a temperature environment different from the temperature environment in which the measurement values of the plurality of first measurement times are measured, the sound speed of each of the plurality of parts is calculated, Based on the sound speed of each of the plurality of parts, to calculate the content ratio of the water and the content ratio of the fat, to calculate the dependence of the sound speed of each of the plurality of parts,
   An ultrasonic imaging apparatus characterized by that.
3. The ultrasonic imaging apparatus according to claim 1 or 2,
   When a factor caused by sound speed in each of a plurality of grids of a calculation region including the plurality of parts of the subject is a delay factor,
   The temperature determining means includes
   A measured value of the first arrival time in a certain route and an arrival time based on a delay factor assumed for each of a plurality of grids on the route passing through the route among the plurality of grids in the calculation region have a difference in arrival time. In case,
   Temperature correction means for correcting the temperature of each of the plurality of grids on the path so as to reduce the arrival time difference;
   An ultrasonic imaging apparatus comprising:
4. The ultrasonic imaging apparatus according to claim 3,
   The temperature correction means corrects the temperature of each of the grids on the plurality of paths so that the arrival time difference is zero.
   An ultrasonic imaging apparatus characterized by that.
5. The ultrasonic imaging apparatus according to claim 3 or 4,
   The temperature correction means includes
   Correction based on a temperature change common to the plurality of grids on the path,
   An ultrasonic imaging apparatus characterized by that.
6. The ultrasonic imaging apparatus according to claim 3 or 4,
   The temperature correction means includes
   The sign of the temperature change for correcting the temperature of each of the plurality of grids on the plurality of paths is determined based on the sign of the temperature differential value of the assumed delay factor and the sign of the arrival time difference.
   An ultrasonic imaging apparatus characterized by that.
7. The ultrasonic imaging apparatus according to claim 6, wherein
   The temperature correction means includes
   The absolute value of the temperature change for correcting the temperature of each of the plurality of grids on the plurality of paths is a value common to the plurality of parts on the plurality of paths.
   An ultrasonic imaging apparatus characterized by that.
8. The ultrasonic imaging apparatus according to claim 6 or 7,
   The temperature correction means includes
   If the sign of the temperature differential value of the assumed delay factor and the sign of the arrival time difference are the same as the sign of the temperature change for correcting the temperature of each of the grids on the plurality of paths, To decide negative,
   An ultrasonic imaging apparatus characterized by that.
9. The ultrasonic imaging apparatus according to any one of claims 1 to 8,
   An ultrasonic measurement unit for measuring the plurality of first arrival times;
   An ultrasonic CT apparatus comprising:
10. The ultrasonic CT apparatus according to claim 9,
    The ultrasonic measurement unit includes a temperature adjustment function for changing the temperature of at least a part of a measurement region including a subject.
    An ultrasonic CT apparatus characterized by that.
11. An ultrasonic imaging method for detecting temperature of a subject including water and fat,
    Based on the water content ratio and the fat content ratio in each of the plurality of parts of the subject, a temperature-dependent characteristic acquisition step for acquiring the temperature-dependent characteristics of the sound speed of each of the plurality of parts;
    A first arrival time acquisition step of acquiring a plurality of first arrival time measurement values through which ultrasonic waves pass through each of a plurality of paths penetrating the subject;
    Based on the measured values of the plurality of first arrival times acquired by the first arrival time acquisition step and the temperature-dependent characteristics of the sound speeds of the plurality of portions acquired by the plurality of portion temperature-dependent characteristic acquisition steps. Determining a temperature of each of the plurality of portions; a temperature determining step;
    An ultrasonic imaging method comprising:
12. Computer
    In order to detect the temperature of a subject containing water and fat,
    Temperature-dependent characteristic acquisition means for acquiring the temperature-dependent characteristics of the sound speed of each of the plurality of parts based on the water content ratio and the fat content ratio in each of the plurality of parts of the subject;
    First arrival time acquisition means for acquiring a plurality of measured values of first arrival times through which ultrasonic waves pass through each of a plurality of paths penetrating the subject;
    Based on the measured values of the plurality of first arrival times acquired by the first arrival time acquisition unit and the temperature-dependent characteristics of the sound speeds of the plurality of regions acquired by the plurality of region temperature dependency characteristic acquisition units. Temperature determining means for determining the temperature of each of the plurality of parts,
    Ultrasonic imaging program to function as

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