Patent Publication Number: US-10321828-B2

Title: Object information acquiring apparatus and control method for the object information acquiring apparatus

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 14/068,090, filed Oct. 31, 2013. It claims benefit of that application under 35 U.S.C. § 120, and claims benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2012-248341, filed on Nov. 12, 2012. The entire contents of each of the mentioned prior applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an object information acquiring apparatus and a control method thereof. 
     Description of the Related Art 
     There is photo acoustic imaging (PAI) as one of optical imaging techniques using light. In the photo acoustic imaging, pulsed light is applied to an object such as a biological body, and an acoustic wave generated by a segment to be tested (e.g., a light absorber such as a tumor) which absorbs optical energy is received by a receiver. Then, an analytical process is performed for a reception signal output from the receiver, thereby obtaining an optical property distribution of the inside of the object as image data. 
     Japanese Patent Application Laid-open No. 2010-022812 discloses an apparatus for receiving an acoustic wave while holding a breast from both sides with holding members and performing two-dimensional scanning on the holding member with the receiver. 
     The receiver two-dimensionally scans, so that pieces of characteristic information at a plurality of positions inside an object can be obtained. 
     Like the apparatus described in Japanese Patent Application Laid-open No. 2010-022812, in a case of an apparatus in which the receiver performs two-dimensional scanning in a main scanning direction and a sub-scanning direction, and acquires acoustic waves in a desired region, an error may occur before scanning and acoustic wave acquisition for the overall desired region are completed. Possible error includes an error resulting from an apparatus, a human error, and the like. Hereinafter, scanning with the receiver for acquiring an acoustic wave will be described as photographing. 
     In a case where an error occurs, photographing may be able to restart immediately depending on the contents of the error. Even though the photographing can restart immediately, and the condition of the photographing remains almost unchanged, in a case where the receiver is returned to a position where the photographing started, and photographing starts again without determination of the contents of the error, it takes time to acquire acoustic waves in the desired region. 
     Particularly, in a case where the region for acquiring acoustic waves are large, when scanning is performed from an initial position with the receiver again, a photographing time is greatly increased, and a binding time for a subject is increased. However, heretofore, there is no means for controlling the receiver on the basis of information such as the content of an error for re-photographing. 
     SUMMARY OF THE INVENTION 
     The present invention has been conceived in order to solve the aforementioned problem, and an object thereof is to suppress increase in a photographing time by re-photographing in accordance with the content of an error, even in a case where the error occurs when characteristic information of the inside of an object is being acquired by scanning with a receiver. 
     The present invention in its one aspect provides an object information acquiring apparatus comprising a receiver receiving an acoustic wave propagating inside an object and convert the acoustic wave into an electric signal; a scanning unit configured to causing the receiver to scan the object; a control unit configured to controlling operation of the scanning unit; a detection unit configured to detecting a status of the acoustic wave reception; and a processing unit for acquiring characteristic information on the inside of the object on the basis of the electric signal, wherein the control unit decides whether or not the operation of the scanning unit is changed, on the basis of a result of detection by the detection unit. 
     The present invention in its another aspect provides a control method for an object information acquiring apparatus, the method comprising operating a receiver to receive an acoustic wave propagating inside an object and convert the acoustic wave into an electric signal, with a receiver; operating a scanning unit to cause the receiver to scan the object; operating a control unit to control operation of the scanning unit; operating a detection unit to detect a status of the reception of the acoustic wave; and an operating processing unit to acquire characteristic information on inside of the object on the basis of the electric signal, wherein in the step of controlling, decision is made on whether or not the operation of the scanning unit is changed, on the basis of a result of detection by the detection unit. 
     According to the present invention, it is possible to suppress increase in a photographing time by re-photographing in accordance with a content of an error, even in a case where the error occurs when characteristic information of the inside of an object is being acquired by scanning with a receiver. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an object information acquiring apparatus to which the present invention can be applied; 
         FIG. 2  is a conceptual diagram showing movement of a receiver of the present invention; 
         FIG. 3  is a flowchart showing an example of a re-photographing method of the present invention; and 
         FIG. 4  is a conceptual diagram showing a start position of the re-photographing of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, size, quality of materials, and shape of components described below, relative arrangement of these, and the like should be appropriately changed according to a configuration of an apparatus to which the invention is applied, or various conditions, and the scope of this invention is not limited to the description described below. 
     In the present invention, an acoustic wave includes an elastic wave referred to as a sound wave, an ultrasound wave, a photoacoustic wave, or a light-induced ultrasound wave, and a receiver receives an acoustic wave propagated inside an object. That is, an object information acquiring apparatus of the present invention includes an apparatus which utilizes a photoacoustic effect of receiving an acoustic wave generated inside an object by applying light (electromagnetic wave) to the object to acquire characteristic information of the inside of the object. 
     In a case of the apparatus utilizing an photoacoustic effect, the acquired characteristic information of the inside of an object indicates object information reflecting initial sound pressure of an acoustic wave generated by light application, or optical energy absorption density derived from the initial sound pressure, an absorption coefficient, concentration of substances configuring tissues, etc. The concentration of the substances includes an oxygen saturation degree or oxyhemoglobin/deoxyhemoglobin concentration, and the like, for example. The characteristic information may be acquired not as numerical data but as distribution information of each of positions inside the object. That is, distribution information such as an absorption coefficient distribution or an oxygen saturation distribution may be acquired as image data. 
     The object information acquiring apparatus of the present invention may be an apparatus which utilizes an ultrasound wave echo technique of transmitting an ultrasound wave to an object, receiving a reflected wave that is reflected on the inside of the object, and acquiring characteristic information of the inside of the object. In a case of the apparatus which utilizes this ultrasound wave echo technique, the acquired characteristic information is information reflecting difference in acoustic impedance of tissues inside the object. 
     The present invention can be grasped as a control method used when the object information acquiring apparatus receives an acoustic wave. 
     The details will be described in respective embodiments. The present invention is characterized in that in a case where an error occurs when an acoustic wave is being acquired, it is determined whether or not re-photographing is possible in accordance with a content of the error. In a case where the re-photographing is possible, a re-photographing method is decided on the basis of a position of a receiver at the occurrence of the error, the content of the error, and photographed size. Note that the same components are generally denoted by the same reference numerals, and description thereof will be omitted. 
     &lt;First Embodiment&gt; 
     An apparatus of this embodiment causes a receiver for receiving an acoustic wave generated by a photoacoustic effect to perform scanning in a main scanning direction and a sub-scanning direction. The sub-scanning direction intersects with the main scanning direction, and is typically orthogonal to the main scanning direction. In a case where an error occurs when an acoustic wave is being acquired, the apparatus determines whether or not re-photographing is possible, in accordance with a content of the error. In a case where the re-photographing is possible, re-photographing is performed on the basis of a position of the receiver at the occurrence of the error, the content of the error, and photographed size. Hereinafter, a basic configuration and a function of the apparatus will be first described, and thereafter, a method of re-photographing in an error which is a characteristic of the present invention will be described. 
     (Basic Configuration of Apparatus) 
       FIG. 1  is a schematic diagram showing a configuration of an object information acquiring apparatus according to a first embodiment. 
     The object information acquiring apparatus of the this embodiment includes holding members  102  for holding a biological body  101  being an object, an irradiation unit  103  for applying light, a receiver  104  for receiving an acoustic wave to convert the same into a reception signal, and a converter  105  for amplifying the reception signal to convert the amplified reception signal into a digital signal. Furthermore, the object information acquiring apparatus includes a signal processor  106  for performing an integration process of the digitalized reception signal or the like, an image construction unit  107  for generating image data by using an output signal from the signal processor, and an image display unit  108  for displaying an image generated by the image construction unit  107 . Moreover, the object information acquiring apparatus includes a scanning controller  109  for the irradiation unit  103  and the receiver  104 , and a re-photographing determination unit  110  for determining a reason in a case where photographing fails due to an error, and transmitting information necessary for re-photographing to the scanning controller  109 . 
     (Holding Member) 
     As the biological body  101 , for example, a breast may be used. The holding members  102  are configured by a pair of two of a first holding member  102 A and a second holding member  102 B, and holds the biological body  101  from both sides. A relative position between the both holding members is controlled by a holding mechanism (not shown) for changing a holding gap and holding pressure. In the following description, in a case where the holding members  102 A and  102 B do not need to be distinguished, the holding members  102 A and  102 B are collectively represented by the holding members  102 . The object is not limited to a biological body, and various objects including a pseudo biological body such as a phantom can be measured. 
     The biological body  101  is sandwiched between the holding members  102  to be fixed, so that a measurement error resulting from movement of the biological body  101  can be reduced. Additionally, the biological body  101  can be adjusted to a desired thickness according to the degree of penetration depth of light. Since the holding member  102 B is located on an optical path from the irradiation unit  103 , a material having high transmittance with respect to used light, such as polymethylpentene is preferable as the material of the holding member  102 B. Additionally, the holding member  102 A on the receiver  104  side is preferably a member having high acoustic consistency with the receiver  104 . After adjusting the position or the shape of the biological body  101  with manipulation, a user fixes the holding members  102 . 
     (Irradiation Unit) 
     The irradiation unit  103  for applying light to the biological body  101  is configured from a light source for generating light, and an irradiation unit for applying the light to an object from the light source. As the light source, a solid-state laser capable of generating pulsed light (pulse width of 100 nsec or less) having a center wavelength on a near-infrared region of 530 to 1300 nm is preferable. For example, Yttrium-Aluminium-Garnet laser or Titan-Sapphire laser is used. The wavelength of measurement light is selected between 530 nm and 1300 nm in accordance with light absorbing substances (e.g., hemoglobin, glucose, cholesterol, etc.) inside a biological body being an object to be measured. 
     Examples of the irradiation unit include, for example, a mirror for reflecting light, a lens for changing the shape of light by collecting and/or enlarging the light, a prism for dispersing, refracting, and/or reflecting light, and an optical fiber for propagating light, and a diffuser panel. As long as light generated from the light source is applied to a desired region in an object so as to have a desired shape, any irradiation unit may be employed. A position of an emission end of light (i.e., irradiated region) from the irradiation unit is controlled by the scanning controller  109 . 
     (Receiver) 
     The receiver  104  includes an element for receiving an acoustic wave to convert the same into an electric signal (reception signal). Examples of the element of the receiver  104  include a conversion element using a piezoelectric phenomenon, a conversion element using resonance of light, a conversion element using change in electrostatic capacitance, and the like. Any element capable of receiving an acoustic wave to convert the same into an electric signal may be used. The receiver  104  includes a plurality of elements in a one-dimensional manner or two-dimensional manner, so that reduction in a measurement time or improvement of measurement accuracy can be expected. 
     Since the sound pressure of the generated acoustic wave is proportional to the light intensity of light, light is preferably applied to a region on a front surface of the receiver in order to improve the signal-to-noise ratio (SNR) of a reception signal. Therefore, the emission end of light of the irradiation unit  103  and the receiver  104  are preferably arranged at such opposed positions as to sandwich an object therebetween. In order to achieve such arrangement, the scanning controller  109  causes the emission end of light and the receiver  104  to scan in synchronization while maintaining the positional relation between the receiver  104  and the emission end of light. The irradiation unit guides light also to the receiver  104  side, so that light may be applied to the biological body  101  also from the same side as the receiver  104 . 
     (Converter) 
     The converter  105  is configured from a signal amplifier for amplifying an analog signal (analog reception signal) input from the receiver  104 , and an A/D converter for converting an analog signal into a digital signal. The signal amplifier controls increase/reduction in amplification gain, etc. in accordance with time from when light is applied until when an acoustic wave reaches the elements of the receiver, so as to obtain image data with uniform contrast regardless of the depth degree in the inside of the biological body. An analog reception signal converted from a photoacoustic wave, or a digital signal for which A/D conversion is performed is also referred to as a photoacoustic signal. 
     (Signal Processor) 
     The signal processor  106  performs sensitivity variation correction of elements for a digital reception signal output from the converter  105 , a complementary process of an element which is physically or electrically lost, a recording operation to a recording medium (not shown), an integration process for noise reduction, and the like. In the integration process which is performed in order to improve the SNR of the reception signals, an acoustic wave is repeatedly received at the same position with respect to the biological body  101 , and reception signals are averaged, thereby reducing system noise. A processing means in the present invention corresponds to the signal processor. 
     (Image Construction Unit) 
     The image construction unit  107  is a characteristic information acquisition unit for acquiring a distribution (property distribution such as an absorption coefficient distribution and an oxygen saturation distribution) indicating optical characteristic information at each position inside the biological body  101 , as image data, by using a signal output from the signal processor  106 . Additionally, the image construction unit  107  may generate image data more preferable for diagnosis, by applying various correction processes such as adjustment of brightness, distortion correction, and cut-out of an attention region, to the generated image data. 
     (Image Display Unit) 
     The image display unit  108  displays an image of a property distribution on the basis of image data input from the image construction unit  107 . 
     (Scanning Controller) 
     As described above, the scanning controller  109  controls scanning positions of the emission end of light and the receiver  104 . Therefore, a mechanism for operating in accordance with control exists. These two-dimensionally scan the biological body  101  to receive an acoustic wave at each scanning position, so that even a compact receiver can obtain a wide range of characteristic information. A range in which the emission end of light and the receiver  104  perform scanning is decided in accordance with a result of control by a photographed-region designation unit  111  which will be described later. The scanning controller  109  holds a current scanning position of the receiver  104 , a position of the receiver  104  at a photographing start point, a position where the receiver  104  starts scanning at each stripe, and a scanning range of the receiver  104  at photographing. A mechanism where the scanning controller causes the receiver and the emission end to move corresponds to scanning means in the present invention. 
     When an error occurs, the scanning position is changed in accordance with a result of control by the re-photographing determination unit  110  which will be described later. The stripe is a region where acoustic waves can be received by a single scanning or a predetermined number of times of scanning in the main scanning direction. In a case where an object is wider compared to the receiver size, measurement can be performed over the overall region by dividing the object into a plurality of stripes. 
     (Photographed-region Designation Unit) 
     The photographed-region designation unit  111  is input means for designating a photoacoustic acquisition region (acoustic wave acquisition region) by a user. The photoacoustic acquisition region indicates an acquisition range of three-dimensional photoacoustic signal in the object that is held by the holding members  102 . As the photographed-region designation unit  111 , a pointing device such as a mouse and a key board, a pen tablet or the like can be utilized. The photoacoustic acquisition region that is input by the user herein is transmitted to the scanning controller  109 , as described above. Then, the scanning controller  109  controls the scanning positions of the emission end of light and the receiver  104  such that a signal in the photoacoustic acquisition region can be acquired. The photographed-region designation unit corresponds to designation means in the present invention. 
     (Re-photographing Determination Unit) 
     The re-photographing determination unit  110  monitors the overall object information acquiring apparatus. The details thereof will be later described. In a case where an error occurs during photographing by the object information acquiring apparatus, the re-photographing determination unit  110  determines whether or not re-photographing is possible, in accordance with a content of the error. Then, in a case where the re-photographing is possible, the re-photographing determination unit  110  decides a position where the receiver  104  restarts photographing, on the basis of a position of the receiver at occurrence of the error, the content of the error, the size of the photoacoustic acquisition region that is input by a user using the photographed-region designation unit  111 , and transmits the decision to the scanning controller  109 . Additionally, the re-photographing determination unit  110  acquires detailed information on the occurrence of the error from each unit configuring the object information acquiring apparatus, at the time of the occurrence of the error. The re-photographing determination unit corresponds to control means in the present invention. Additionally, it can be conceived that the control means includes a control process performed by the scanning controller. 
     (Scanning Control of Receiver) 
       FIG. 2  shows a state where the receiver  104  performs scanning in a photoacoustic acquisition region  201 . In  FIG. 2 , a scanning range by the receiver  104  on the holding member  102 A, based on a photoacoustic signal acquisition region being a three-dimensional range is denoted by a reference numeral  201 . 
     The receiver  104  performs scanning in a main scanning direction  202  and a sub-scanning direction  203  so as to receive a photoacoustic signal in the photoacoustic acquisition region  201 . First, the receiver  104  moves in a main scanning direction  202 A from an initial position located upper left in the photoacoustic acquisition region  201 , to acquire a photoacoustic signal of an uppermost stripe. When reaching upper right, the receiver  104  moves in a sub-scanning direction  203 A by a predetermined sub-scanning distance. 
     Next, the receiver  104  moves in a main scanning direction  202 B to acquire a photoacoustic signal of a middle stage stripe. When reaching a left end of the middle stage, the receiver  104  moves in the sub-scanning direction  203 B to reach a lowermost stage, and moves in a main scanning direction  202 C. The predetermined sub-scanning distance is equal to the width of the receiver  104  herein, but is not limited to this. For example, an overlapped portion between the stripes in the sub-scanning direction may exist. The receiver  104  scans the same stripe a plurality of times, and thereafter moves to a next stripe, so that the SNR can be improved. 
     (Flow of Re-photographing Method in Error) 
     A flow of processes of re-photographing control performed in a case where an error occurs during scanning shown in  FIG. 2  will be described with reference to  FIG. 3 .  FIG. 3  is a flowchart of re-photographing according to this embodiment, and the re-photographing starts from a situation where an error occurs. 
     An error in this flow occurs because it is detected that the light quantity is at a level not suitable for measurement. Such a phenomenon occurs, for example, when the oscillation of light from the light source of the irradiation unit  103  becomes unstable. The light quantity whose level is not suitable for measurement is, for example, such a small light quantity that an acoustic wave with intensity necessary for accurate characteristic information does not generate, and a predetermined standard is not satisfied. 
     In Step S 301 , the re-photographing determination unit  110  detects that an error occurs during photographing. Then, the re-photographing determination unit  110  collects information from each unit in the object information acquiring apparatus to acquire the detail of the error. The re-photographing determination unit  110  acquires, from the scanning controller  109 , information that the light quantity whose level is not suitable for measurement is detected. This error detection can be achieved, for example, by arranging an optical sensor on the scanning controller  109 , monitoring the light quantity, and transmitting a result of detection. In this case, it can be conceived that combination of the optical sensor, and the re-photographing determination unit for determining an error on the basis of sensor information is detection means in the present invention. Similarly, it can be said that each of various sensors according to the types of errors, and the re-photographing determination unit are the detection means in the present invention. 
     In Step S 302 , the re-photographing determination unit  110  determines whether or not the error is such an error that re-photographing is possible, on the basis of the detail of the error acquired in Step S 301 . 
     Examples of the error where re-photographing is possible are as follows. First, as shown in this flow, an error occurs in a case where the oscillation of light from the light source of the irradiation unit  103  becomes unstable, and it is detected that the level of the light quantity is not suitable for measurement. 
     Another example is abnormality of communication in each unit configuring the object information acquiring apparatus. This error is detectable by a circuit for detecting a status of communication of each unit, etc. 
     Additionally, an error occurs in a case where a door (not shown) installed in a housing of an apparatus is opened in order to perform the aforementioned manipulation of the biological body  101 . This error is detectable by a contact sensor (physical or optical sensor). 
     Furthermore, an error occurs in a case where an accuracy error exists between a position of the emission end of light of the irradiation unit  103 , and a scanning position of the receiver  104 , the receiver  104  and the emission end of light being caused to perform scanning in synchronization by the scanning controller  109 . This error is detectable by, for example, a meter for detecting a position. 
     Results of detection by these sensors each may include not only the fact that an error occurs but also a difference from a predetermined value or continuity of a phenomenon detected as an error. 
     If the error is an error where photographing can immediately start, it is determined that re-photographing is possible (S 302 =Yes). The error in this flow is determined as an error where re-photographing is possible. On the other hand, if re-photographing is impossible, the flow is terminated (S 302 =No). 
     If it is determined that re-photographing is possible, it is decided where the receiver  104  moves, on the basis of the detail of the error, the a current position of the receiver  104 , and the size of a photoacoustic acquisition region designated by a user with the photographed-region designation unit  111 , in Step S 303  to S 305 . 
     Examples of a candidate of a position where the receiver  104  moves includes, as shown in  FIG. 4 , a position  401  of the receiver  104  at a photographing start point, a start point  402  of a stripe for which photographing is currently being performed, and a position  403  just before an error occurs. In the figure, it is assumed that the error occurs at an error occurrence point  404 . 
     In Step S 303 , the re-photographing determination unit  110  determines the detail of the error. That is, it is determined whether or not the error that has occurred is an error that continuously influences acquisition of a photoacoustic signal during scanning of a stripe, among various errors where re-photographing is possible. In a case where the error that has occurred is applicable to this, the necessity arises for the receiver  104  to implement re-photographing by moving to the start point  402  of a stripe, for which photographing is currently undergoing. An example of this error includes, for example, a case where the oscillation of light form the light source continuously becomes unstable during scanning by receiver  104 . As another example, there is a case where an accuracy error between scanning positions of the emission end of light and the receiver  104  in the scanning controller  109  is continuously increased. 
     In a case of such a continuous error, in Step S 305  which will be described later, a destination of the receiver  104  is decided as the start point  402  of a stripe for which photographing is being performed. This positional information is the same as a position of the receiver  104  held by the scanning controller  109 , at a photographing start point of a stripe. The re-photographing determination unit  110  transmits, to the scanning controller  109 , indication information that scanning restarts from the position  402 . 
     The error where the oscillation of the light from the light source becomes unstable and the level that is not suitable for measurement is detected, in this flow is a temporary error and not applicable to a continuous error. 
     In Step S 304 , the re-photographing determination unit  110  acquires, from the scanning controller  109 , the size of the photoacoustic acquisition region designated by a user using the photographed-region designation unit  111 , and compares the acquired size with a predetermined value. Then, in a case where the size of the photoacoustic acquisition region is smaller than the predetermined value, it is determined that the receiver  104  moves to the position  401  of the receiver  104  at a photographing start point. In such a case, a total photographing time is short, and the number of times of main scanning and sub-scanning by the receiver  104  are small, and therefore even though the receiver  104  moves to the position  401  to re-photograph, the total photographing time is not greatly increased. 
     When the receiver  104  moves to the position  403  just before an error occurs, or the start point  402  of a stripe for which photographing is currently being performed, to re-photograph, there is a possibility that a photograph condition slightly changes between before and after the error occurs, by an influence of body motion of the biological body  101 . However, the receiver  104  thus moves to the photographing start point to re-photograph, so that the photograph conditions before and after the error occurs are the same, and continuity of data is maintained. 
     The predetermined value serving as the standard for determination as to whether the size of the photoacoustic acquisition region, which is designated by the user with the photographed-region designation unit  111 , is small may be the number or times of main scanning or the number or times of sub-scanning, or may be the length of a total photographing time. That is, since the number of times of movement of the receiver in the main scanning direction and the sub-scanning direction is small, time loss is small even when photographing is performed again. Similarly, in a case where time required for acquiring acoustic waves until an error occurs is short, time loss is small. Alternatively, a configuration where a user sets the standard may be employed. 
     Since the scanning controller  109  holds the position of the receiver  104  at the photographing start point, information that scanning restarts from this position is transmitted to the scanning controller  109 . In this flow, it is assumed that the size of the photoacoustic acquisition region designated by the user is smaller than the predetermined value. 
     In Step S 305 , the re-photographing determination unit  110  decides a position where the receiver  104  moves, on the basis of the results of determination in Step S 303  and Step S 304 . In this flow, in Step S 303 , it is determined that the error is not such an error that continuously influences acquisition of a photoacoustic signal. In Step S 304 , it is determined that the size of the photoacoustic acquisition region designated by the user is smaller than the predetermined value. On the basis of these determination results, the re-photographing determination unit  110  decides that the receiver  104  returns to the position  401  at the photographing start point. 
     In a case where the determination result in Step S 305  does not satisfy both the condition that the receiver  104  moves to the start point  402  of the stripe, and the condition that the receiver  104  moves to the photographing start position  401 , it is decided that the receiver  104  moves to the position  403  just before an error occurs. When the error occurs, the receiver  104  stops scanning. Therefore, information that irradiation starts again from the current position of the receiver  104  held by the scanning controller  109  is transmitted. However, in a case where the scanning speed of the receiver  104  is considered, it is necessary to consider an acceleration distance until the receiver  104  performs scanning at an equal speed. At this time, the scanning controller  109  calculates a position displaced by the movement amount of the acceleration distance until the receiver  104  scans at an equal speed, from the position of the receiver  104 , and scanning restarts from the position. 
     In any case, a position where irradiation can start again for re-photographing from a place where an error occurs and a photoacoustic signal cannot be acquired is transmitted to the scanning controller  109 , and re-photographing can be performed from the position. 
     In Step S 306 , the re-photographing determination unit  110  transmits information calculated by the scanning controller  109  in Step S 305 . The scanning controller  109  receives the information to calculate a position where the receiver  104  moves, from information regarding the position of the receiver  104  held by the scanning controller  109 , and re-photographing restarts from the position. The positional information held by the scanning controller  109  includes the current scanning position of the receiver  104 , the position of the receiver  104  at the photographing start point, the position where the receiver  104  starts scanning in each stripe, and a scanning range of the receiver  104  during photographing. 
     As described above, according to the present invention, even in a case where an error occurs when characteristic information of the inside of an object is acquired by scanning with the receiver, it is determined whether or not re-photographing is possible in accordance with a content of the error. Then, in a case where re-photographing is possible, re-photographing is performed on the basis of a position of the receiver at the time of error occurrence, the content of the error, or the photographed size, thereby enabling suppression of increase in a photographing time. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.