Patent Publication Number: US-11395641-B2

Title: Ultrasonic imaging device and imaging method thereof

Description:
TECHNICAL FIELD 
     The disclosure relates in general to an imaging device and an imaging method thereof, and more particularly to an ultrasonic imaging device and an imaging method thereof. 
     BACKGROUND 
     In the technology of ultrasonic image synthesis, there are two key factors that affect image quality, one is the delay error caused by phase aberration during focus imaging, and the other is the size of ultrasonic aperture. The delay error increases the beam side lobes of the ultrasound imaging, and thereby causes degradation of focusing and quality of the ultrasonic image. The size of the ultrasonic aperture, that is, the number of array elements of the ultrasonic probe, affects the resolution of the ultrasonic image, and the more the number of array elements, the higher the cost and the larger the amount of calculation. 
     However, in medical ultrasound field, in order to provide correct clinical diagnosis and analysis, there must be better image quality, such that the hardware of ultrasonic imaging device cannot be further simplified. If the medical ultrasonic imaging device is simplified into a power-saving and portable ultrasonic imaging device, the number of array elements is reduced, the calculation amount of hardware is reduced, and the image quality of ultrasonic imaging device is affected, thereby improvement of image resolution and simplification of hardware device often require trade-off. 
     SUMMARY 
     The disclosure is directed to an ultrasonic imaging device and an imaging method thereof, which can effectively reduce energy loss and hardware burden during ultrasonic emission by reducing the emitting source of focused ultrasound, thereby achieving the effects of power saving, portable and high resolution image. 
     According to one embodiment, an ultrasonic imaging device is provided, which includes an ultrasonic generating unit and an ultrasonic imaging processing unit. The ultrasonic generating unit includes an ultrasonic probe, a transmitting unit and a receiving unit. The ultrasonic probe is connected to the transmitting unit and the receiving unit, and the ultrasonic probe includes M ultrasonic array elements, and the ultrasonic generating unit repeatedly multiple times and selectively turns on N ultrasonic array elements of the ultrasonic probe as a group of array elements for scanning, each scan is to emit an ultrasonic signal by the group of array elements and receive an echo signal of the ultrasonic signal, where M is greater than N, M and N are positive integers greater than one. The ultrasonic imaging processing unit extracts a central echo signal from the echo signal in each scan to form a channel signal. According to an arrival time of each echo signal, each central echo signal in the channel signal is delayed and summed to generate a modified channel signal, and the modified channel signal is subjected to image synthesis process to obtain an ultrasonic image. 
     According to another embodiment, an ultrasonic imaging method is provided, comprising the following steps. The N ultrasonic array elements of the ultrasonic probe are selectively turned on multiple times as a group of array elements for scanning, and each time an ultrasonic signal is transmitted by the array element and an echo signal of the ultrasonic signal is received. A central echo signal is extracted from the echo signal in each scan to form a channel signal. The arrival time of each central echo signal is calculated to delay and sum each of the central echo signals in the channel signal to generate a modified channel signal. The modified channel signal is subjected to image synthesis process to obtain an ultrasonic image. 
     The above and other aspects of the disclosure will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an ultrasonic imaging device according to an embodiment of the disclosure. 
         FIG. 2  is a schematic flow chart of an ultrasonic imaging method according to an embodiment of the disclosure. 
         FIGS. 3A to 3D  are diagrams respectively showing the operation of the ultrasonic generating unit according to an embodiment of the disclosure. 
         FIG. 4  is a schematic diagram showing the ultrasonic imaging processing unit. 
         FIG. 5  is a schematic diagram showing the delay time of each central echo signal. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed descriptions of the disclosure are disclosed below with a number of embodiments. However, the disclosed embodiments are for explanatory and exemplary purposes only, not for limiting the scope of protection of the disclosure. Similar/identical designations are used to indicate similar/identical elements. Directional terms such as above, under, left, right, front or back are used in the following embodiments to indicate the directions of the accompanying drawings, not for limiting the disclosure. 
     According to an embodiment of the disclosure, an ultrasonic imaging device is provided. As shown in  FIG. 1 , the ultrasonic imaging device  100  includes an ultrasonic generating unit  110  and an ultrasonic imaging processing unit  120 . The ultrasonic generating unit  110  includes, for example, an ultrasonic probe  111 , a transmitting unit  114 , a receiving unit  116 , a processor (not shown) and the like. The ultrasonic probe  111  is, for example, a probe of linear array, a probe of phased array, or other types of probes. The ultrasonic probe  111  includes a plurality of ultrasonic array elements  112 , and each of the ultrasonic array elements  112  is a transducer for converting the pulse voltage signal outputted by the high voltage pulse channel in the transmitting unit  114  into a mechanically oscillated ultrasound and the ultrasound is sent to the inside of the organism. In addition, the processor controls the transmission time of the pulse voltage signal of each channel to generate an ultrasonic signal Tx of different transmission time. 
     In addition, the ultrasonic array element  112  can receive the echo signal Rx of the ultrasound reflected by the scatter inside the organism, and the echo signal Rx is converted into a pulse voltage signal to obtain a channel signal from the receiving unit  116 . When the wavelength of the incident ultrasound is much larger than the diameter of the scatter inside the organism, the scattering phenomenon of the ultrasound occurs, and the reverse scatter signal will appear bright speckles randomly in the ultrasonic image. This is the so-called “speckle noise”. The presence of speckle noise and side lobe blurs the fine-grained image and reduces the contrast and resolution of the ultrasonic image. 
     In order to reduce the calculation amount of hardware, in the present embodiment, the ultrasonic generating unit  110  first adjusts the size of the ultrasonic aperture according to the position of the target object, that is, adjusts the respective number and position of the ultrasonic array elements  112  turning on and off in the ultrasonic probe to reduce the number of ultrasonic sources. After that, the ultrasonic imaging processing unit  120  extracts an echo signal from the echo signals Rx of each group for beamforming, and reconstructs an ultrasound image by using a set of channel signals after beamforming. 
     Since the ultrasonic generating unit  110  of the embodiment does not need to turn on all the array elements  112  of the ultrasonic probe, the ultrasonic emission energy can be reduced, and the effect of power saving can be achieved. In addition, the ultrasonic imaging processing unit  120  of the present embodiment can perform image processing with a lower amount of data (only the central echo signal is extracted at one time), thereby avoiding a complicated operation process, and reducing the calculation amount of the hardware. Therefore, the present embodiment can be applied to portable ultrasound imaging devices. 
     Referring to  FIG. 1 , according to an embodiment of the disclosure, the ultrasonic imaging device  100  includes an ultrasonic generating unit  110  and an ultrasonic imaging processing unit  120 . The ultrasonic generating unit  110  includes an ultrasonic probe  111 , a transmitting unit  114 , and a receiving unit  116 . The ultrasonic probe  111  is connected to the transmitting unit  114  and the receiving unit  116  and includes M ultrasonic array elements  112 . The ultrasonic generating unit  110  repeatedly multiple times and selectively turns on N ultrasonic array elements  112  of the ultrasonic probe  111  as a group of array elements for scanning, each scan is to emit an ultrasonic signal Tx by the array group and receive an echo signal Rx of the ultrasonic signal Tx, where M is greater than N, and M and N are positive integers greater than one. In an embodiment, M is 128 as an example, and N is 3 to 5 for example, but the number of M and N is not limited. 
     That is to say, the ultrasonic generating unit  110  selects one group of 3 to 5 ultrasonic array elements  112  at different positions from 128 array elements at each time, so that an ultrasonic signal Tx can be transmitted from the selected array elements and the echo signal Rx is received to detect the position of the imaging point for scanning. When the number of N increases, the brightness of the echo signal Rx can be relatively high. However, when the number of N is too large, the echo signal Rx is too complicated, difficult to focus and excessive noises are generated, it may cause degradation of image resolution. 
     The ultrasonic imaging processing unit  120  is configured to process the received echo signals Rx of the plurality of ultrasonic signals Tx. Referring to  FIG. 1  and  FIG. 2  together,  FIG. 2  is a schematic flow chart of the ultrasonic imaging method according to an embodiment of the disclosure, which includes the following steps S 11 -S 14 . In step S 11 , the ultrasonic generating unit  110  repeatedly multiple times and selectively turns on the N ultrasonic array elements  112  of the ultrasonic probe  111  as a group of array elements Ai for scanning, and each scan is to emit an ultrasonic signal Tx by the group of array elements and receive the echo signal Rx of the ultrasonic signal Tx. In step S 12 , a central echo signal Rc is extracted from the echo signals Rx in each scan to form a channel signal. In step S 13 , according to the arrival time of each central echo signal Rc, each central echo signal Rc of the channel signal is delayed and summed to generate a modified channel signal. In step S 14 , the modified channel signal is subjected to image synthesis process to obtain an ultrasonic image. 
     Referring to  FIG. 3A , in an embodiment, the ultrasonic probe  111  of the ultrasonic generating unit  110  includes M ultrasonic array elements  112 . During a single scan, the N ultrasonic array elements  112  connected to the transmitting unit  114  are selectively turned on from the M ultrasonic array elements  112 , and the selected N ultrasonic array elements  112  can form a group of array elements Ai, and the remaining unselected M-N ultrasonic array elements  112  are turned off. In the single group of array elements Ai, the transmission time of each of the ultrasonic array elements  112  may be the same or different, and when each of the ultrasonic element elements has the same transmission time, a plane wave may be generated; when each of the ultrasonic array elements  112  has different transmission times, an ultrasound having a focusing effect can be generated, so that the ultrasonic signals Tx having different effects can be generated by the same or different transmission times. In addition, when a group of array elements Ai generates the ultrasonic signal Tx, the echo signal Rx of the ultrasonic signal Tx can be correspondingly received by the same group of array elements Ai (i.e., N ultrasonic array elements  112 ). In another embodiment, when the ultrasonic signal Tx is generated by a group of array elements Ai, the echo signal Rx of the ultrasonic signal Tx is received only by the central portion of the ultrasonic array elements  112  of the same group of array elements Ai (i.e., N ultrasonic array elements  112 ), but the embodiment is not limited thereto. 
     Next, referring to  FIGS. 3A to 3D , taking each group of array elements Ai containing three ultrasonic array elements  112  (i.e., N=3) as an example, when a first scan is performed, the leftmost three ultrasonic array elements  112  from the M ultrasonic array elements  112  are selectively turned on as the first group of array elements A 1 , and the first set of ultrasonic signals Tx are transmitted. When the ultrasonic signals Tx are transmitted to the object B and scattered, echo signals Rx are generated and received by the first group of array elements A 1 . Then, during the second scan, the selected three ultrasonic array elements  112  can be shifted to the right from the first group of array elements A 1  by one ultrasonic array element  112 , that is, during the second scan, the second to fourth ultrasonic array elements  112  on the leftmost side of the M ultrasonic arrays elements  112  are selectively turned on as the second group of array elements A 2 , and when the second group of array elements A 2  generates the second set of ultrasonic signals Tx, the second group of array elements A 2  correspondingly receives the echo signals Rx of the second set of ultrasonic signals Tx; during the i-th scan, the i-th set of ultrasonic signals Tx are generated by the i-th group of array elements Ai, and the echo signals Rx of the i-th set of ultrasonic signals Tx can be correspondingly received by the i-th group of array elements Ai, where i=1−P, P may be a positive integer smaller than M. Therefore, after P times of transmission and reception, a total of P set of the echo signals Rx of the ultrasonic signals Tx can be obtained. 
     In the present embodiment, after each set of ultrasonic signals Tx is transmitted (i.e., each scan), the ultrasonic array elements  112  can be shifted by at least one ultrasonic array element  112  to be the next group of array elements Ai until all M array elements  112  are completely transmitted. It is to be noted that the number of ultrasonic array elements  112  that are shifted to scan per each time can be adjusted as needed, and is not limited to those enumerated. As shown in  FIGS. 3A to 3B , the positions of the two groups of array elements A 1  and A 2  that sequentially emit the ultrasonic signals Tx are, for example, separated by the width of one ultrasonic array element  112 . In another embodiment, the positions of the two groups of array elements A 1  and A 2  that sequentially emit the ultrasonic signals Tx are, for example, separated by the width of two or more ultrasonic array elements  112 . 
     When the i-th group of array elements Ai receives the echo signals Rx of the i-th set of ultrasonic signals Tx, the ultrasonic imaging processing unit  120  extracts a central echo signal Rc from the echo signals Rx of the i-th set of ultrasonic signals Tx. For example, when N is an odd number (such as 3 or 5), the central echo signal Rc is an echo signal Rx received from the ultrasonic array element  112  in the center of the group of array elements Ai, that is, the central echo signal Rc is an echo signal Rx received by the (1+N)/2th ultrasonic array element  112  in the group of array elements Ai. When N is an even number (such as 4), the central echo signal Rc is the average of the echo signals Rx received from the two ultrasonic array elements  112  in the center of the group of array elements Ai, that is, the central echo signal Rc is the average of the echo signals Rx received by 1+(N−1)/2th and 1+(N+1)/2th array elements  112  in the group of array elements Ai. In an embodiment, the ultrasonic generating unit  110  can transmit the transmitting ultrasonic signals Tx and receive the corresponding echo signals Rx by the same group of array elements Ai at a time, and then extract the central echo signal Rc by the ultrasonic imaging processing unit  120 . In another embodiment, in each scan, the ultrasonic generating unit  110  transmits the ultrasonic signals Tx from a group of array elements Ai, but only receives the echo signals Rx by the ultrasonic array elements  112  in the center of the same group of array elements Ai. When N is an odd number, the central echo signal Rc is the echo signal Rx received by the intermediate (i.e., (1+N)/2th) ultrasonic array element  112 ; and when N is an even number, the echo signals Rx received by the intermediate (i.e., 1+(N−1)/2th and 1+(N+1)/2th) ultrasonic array elements  112  are averaged first in the ultrasonic imaging processing unit  120  and thus can be used as the central echo signal Rc. The ultrasonic imaging processing unit  120  can form a channel signal by the central echo signals Rc extracted in each scan, wherein the number of central echo signals Rc in the channel signal can be P. 
     Referring to  FIG. 4 , in an embodiment, the ultrasonic imaging processing unit  120  includes an analog-to-digital converter  122 , a time difference compensation circuit  124 , a summing circuit  126 , and an image synthesizing unit  128 . The ultrasonic imaging processing unit  120  captures the central echo signals Rc of each scan to form a channel signal. Since the channel signal is an analog signal, the ultrasonic imaging processing unit  120  can convert the channel signal into a digital channel signal by the analog-to-digital converter  122 . In addition, there is a problem that the number of samples is insufficient (P&lt;M) when the channel signal is converted into a digital channel signal. Therefore, the number of samples obtained from the ultrasonic array elements  112  can be increased by using an interpolation method to make the number of the digital channel signal reaches M. The time difference compensation circuit  124  is configured to receive the converted digital channel signal, and obtain a compensation value for each central echo signal Rc according to the arrival times τ 1  to τ M  and the time difference of each central echo signal Rc. The summing circuit  126  delays and sums each central echo signal Rc in the channel signal according to the compensation value to obtain a modified channel signal after delay and sum. Then, the image synthesizing unit  128  performs beamforming according to the modified channel signal and performs an image synthesis process to obtain an ultrasonic image. 
     The method of how does the ultrasonic array probe synthesize a specific point in the space, use the distance derived from the transmitted and received signals to calculate difference of the delay time of each array element, sum a total of the delay times, and then obtain the image of the specific point in the space is illustrated in the above. This way of synthesizing images is called delay and sum. As shown in  FIG. 5 , in the case of sector scan mode of ultrasound, images at any point in the space can be represented by polar coordinates (R, θ). It is assumed that Si is the central echo signal Rc received by the i-th group of array elements Ai, and O(t) is the delayed and summed image. 
     
       
         
           
             
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     τ(xi, R, θ) is the time when the central echo signal Rc reaches the group of array elements Ai from the object B after the scattering of the ultrasonic signal Tx by the object B, that is τ 1 -τ M , and xi is the vertical distance from the central ultrasonic array element  112  of the group of array elements Ai to the center line L, R is the distance from the object point B to the ultrasonic array element  112  passing through the center line L, and θ is the angle between the line segment R and the center line L, which is calculated as follows, and c is the speed of light: 
     
       
         
           
             
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     In the present embodiment, since the central echo signal Rc is taken as the channel signal in each scan, the central ultrasonic array element  112  of each group of array elements Ai can be regarded to have the same back and forth paths when the current ultrasonic signal Tx transmits to the object B and returns to the central ultrasonic array element  112  by the central echo signal Rc. The transmission time of the ultrasonic signal Tx is the same as the receiving time of the echo signal Rc, both are τ(xi, R, θ), so that a delay time of the central ultrasonic array element  112  of the i-th group of array elements Ai receiving the central echo signal Rc is two times of τ(xi, R, θ), which is expressed as follows: 
     
       
         
           
             
               
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     According to the above result of calculation, the time difference compensation circuit  124  can obtain the delay time of each central echo signal Rc in the channel signal for the summing circuit  126  to perform delay and sum. 
     In the ultrasonic imaging device and the imaging method thereof disclosed in the above embodiments, an ultrasonic probe is used to transmit an ultrasonic signal in linear scan and receive an echo signal of the ultrasonic signal, and then the central echo signal is extracted from each echo signal as a channel signal. Then, the time domain signal processing method of the improved delay and sum is used to improve the image quality of the ultrasonic imaging. The present disclosure performs ultrasonic imaging in the above embodiment, which can reduce the ultrasonic emission energy, achieve power saving and portability, reduce the calculation amount of hardware, reduce cost and improve safety, and the present disclosure can also use the image weighting technology that can effectively reduce speckle noise and improve lateral resolution. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.