Abstract:
RF signals in predetermined time regions are extracted respectively from a plurality of RF signals which are produced when an examinee is scanned by an ultrasonic wave, and respective IB values are calculated in the time regions. A variance value of the calculated IB values is calculated, and information based on the calculated variance value is output.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to the field of tissue characterization. More specifically, the invention pertains to the filed of ultrasonic signal processing for tissue characterization using ultrasonic waves.  
       BACKGROUND DISCUSSION  
       [0002]     Heretofore, there have widely been used ultrasonic diagnosing apparatus for diagnosing arteriosclerosis and performing a preoperative diagnosis and a postoperative check for coronary intervention using a dilatation catheter or a high-functionality catheter such as a stent or the like.  
         [0003]     One example of ultrasonic diagnosing apparatus discussed below is intravascular ultrasound (IVUS) diagnosing apparatus. Generally, intravascular ultrasound diagnosing apparatus are constructed to include an ultrasonic probe that makes radial scans in an artery of the patient and receives an echo (reflected wave) reflected from a reflecting object in the artery. The echo signal is amplified and detected to convert the echo intensity into an image signal on a gray scale for thereby displaying a B-mode image.  
         [0004]     B-mode images on the gray scale can display a large lipid in plaque deposited in the blood vessel. However, it is difficult for B-mode images to display a small lipid that may be present in an initial phase of plaque growth.  
         [0005]     Since the rupture of vulnerable plaque in an artery is considered to be responsible for acute coronary syndromes such as an acute myocardial infarction, it is clinically desirable to diagnose plaque with a relatively high degree of accuracy. Specifically, when plaque in a blood vessel ruptures, the lipid contained in the plaque blows out into the blood vessel, leading to acute coronary syndromes. Therefore, an indication of the amount of lipid contained in plaque can serve as an important diagnostic marker.  
         [0006]     Consequently, it is desirable in the art to develop ultrasonic diagnosing apparatus capable of sufficiently displaying tissue characters and allowing the user to easily determine whether or not plaque is relatively lipid-rich.  
         [0007]     Efforts have been made with respect to ultrasonic diagnosing apparatus to increase the frequency of a transmitted ultrasonic signal in order to increase the resolution of the B-mode image or to analyze an RF signal obtained by receiving a reflected echo for tissue characterization. For example, a ROI (Region of Interest) is established in an analytic section, some parameters are calculated from the spectrum of an RF signal in the ROI, and tissue characters are displayed by a multivariable analysis.  
         [0008]     It might be possible to attempt to display a smaller lipid by increasing the frequency for higher resolution. However, with this possibility, the range that can be diagnosed is limited because the depth that the ultrasonic wave can reach is reduced. Ultrasonic probes that are commercially available at present emit ultrasonic waves at a frequency of about 40 MHz and it is not clear at present whether high-frequency ultrasonic probes can generally be used for tissue characterization in blood vessels.  
         [0009]     The process of analyzing an RF signal for tissue characterization is still under development at present and established procedures are not yet available. The process of displaying tissue characters by way of a multivariable analysis requires time-consuming calculations because the number of parameters involved is quite large as is the amount of analyzed data, and so this requires calibration of each ultrasonic probe to be used, a task not easy to perform.  
       SUMMARY  
       [0010]     An apparatus for processing an ultrasonic signal comprises IB value calculating means for calculating IB values by extracting RF signals in predetermined time regions respectively from a plurality of RF signals which are produced when an examinee is scanned by an ultrasonic wave, variance value calculating means for calculating a variance value of the IB values calculated by the IB value calculating means, and output means for outputting information based on the variance value calculated by the variance value calculating means.  
         [0011]     With the above arrangement, the existence of small foreign matter in an examinee can relatively easily determined in diagnosing tissue characters of the examinee with ultrasonic waves.  
         [0012]     According to another aspect, an apparatus for processing an ultrasonic signal comprises IB value calculating means for extracting RF signals in predetermined time regions respectively from a plurality of RF signals produced when an examinee is scanned by an ultrasonic wave and calculating respective IB values in the time regions, linear average calculating means for calculating linear averages of the IB values calculated by the IB value calculating means in IB value groups with respect to mutually related time regions, variance value calculating means for calculating a variance value of the linear averages of the IB values calculated by the linear average calculating means, and output means for outputting information based on the variance value calculated by the variance value calculating means.  
         [0013]     Another aspect pertains to a method of processing an ultrasonic signal comprising extracting RF signals in predetermined time regions respectively from a plurality of RF signals which are produced when an examinee is scanned by an ultrasonic wave, calculating respective IB values in the time regions, calculating a variance value of the calculated IB values, and outputting information based on the calculated variance value.  
         [0014]     In accordance with another aspect, a method of processing an ultrasonic signal comprises scanning an examinee by an ultrasonic wave, extracting RF signals in predetermined time regions respectively from a plurality of RF signals which are produced by the scanning of the examinee by an ultrasonic wave, calculating respective IB values in the time regions, calculating linear averages of the calculated IB values in IB value groups with respect to mutually related time regions, calculating a variance value of an additive averages of the calculated IB values, and outputting information based on the calculated variance value.  
         [0015]     Further aspect involve a control program for enabling a computer to perform the disclosed methods and a recording medium storing a control program for enabling a computer to perform the disclosed methods. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0016]      FIG. 1  is a block diagram of an ultrasonic signal processing system for performing an intravascular ultrasonic diagnosis in which the ultrasonic signal processing system incorporates an ultrasonic signal processing apparatus according to a first embodiment.  
         [0017]     FIGS.  2 ( a ) and  2 ( b ) are somewhat schematic views illustrating the manner in which a catheter operates in an intravascular ultrasonic diagnosis.  
         [0018]     FIGS.  3 ( a )-( c ) are diagrams illustrating a general process for processing an ultrasonic signal during intravascular ultrasonic diagnosis.  
         [0019]      FIG. 4  is a diagram showing a B-mode image.  
         [0020]      FIG. 5  is a block diagram of the ultrasonic signal processing apparatus according to the first embodiment.  
         [0021]      FIG. 6  is a flowchart of a processing sequence of the ultrasonic signal processing apparatus according to the first embodiment for performing an intravascular ultrasonic diagnosis.  
         [0022]      FIG. 7  is a flowchart of a processing sequence of an ultrasonic signal processing apparatus according to a second embodiment for performing an intravascular ultrasonic diagnosis.  
         [0023]     FIGS.  8 ( a ) and  8 ( b ) are cross-sectional views illustrating a process of specifying region of interest (ROI) lines.  
         [0024]     FIGS.  9 ( a ) and  9 ( b ) are cross-sectional views illustrating another process of specifying ROI lines.  
         [0025]     FIGS.  10 ( a ) and  10 ( b ) are cross-sectional views illustrative of a process of placing regions of interest (ROIs) on ROI lines. 
     
    
     DETAILED DESCRIPTION  
       [0000]     Configuration of an Ultrasonic Signal Processing System  
         [0026]      FIG. 1  schematically illustrates an ultrasonic signal processing system  100  for performing an intravascular ultrasonic diagnosis. The ultrasonic signal processing system  100  incorporates an ultrasonic signal processing apparatus  130  according to one disclosed embodiment.  
         [0027]     As shown in  FIG. 1 , the ultrasonic signal processing system  100  for performing intravascular ultrasonic diagnosis comprises a catheter  101  and an ultrasonic signal processing apparatus  130 .  
         [0028]     The catheter  101  has an ultrasonic transducer  105  disposed in its tip end. When the catheter  101  is inserted in a blood vessel, the ultrasonic transducer  105  transmits an ultrasonic wave in the cross-sectional direction of the blood vessel based on a pulse signal sent from an ultrasonic signal transmitter/receiver  110  through signal lines  104 ,  103 , receives a reflected wave (echo) of the transmitted ultrasonic wave, and sends an ultrasonic signal (as an electric signal) representative of the echo through the signal lines  104 ,  103  to the ultrasonic signal transmitter/receiver  110 .  
         [0029]     The ultrasonic signal processing apparatus  130  includes a motor  102 , the ultrasonic signal transmitter/receiver  110 , a signal processing circuit  113 , a monitor  114 , and a motor controller  120 .  
         [0030]     The ultrasonic transducer  105  is rotatably mounted in the catheter  101  for being rotated by a motor  102  that is detachably connected to the catheter  101 . When the ultrasonic transducer  105  is rotated circumferentially in the blood vessel, it can detect an ultrasonic echo signal to be used for tissue characterization of the blood vessel in the circumferential direction at a certain cross section of the blood vessel. The operation of the motor  102  is controlled by the motor controller  120  based on a control signal that is sent from the signal processing circuit  113  through a signal line  121 .  
         [0031]     The ultrasonic signal transmitter/receiver  110  has a transmitting circuit  111  and a receiving circuit  112 . The transmitting circuit  111  supplies a pulse signal to the ultrasonic transducer  105  in the catheter  101  based on a control signal that is sent from the signal processing circuit  113  through a signal line  115 .  
         [0032]     The receiving circuit  112  receives an ultrasonic signal sent from the ultrasonic transducer  105  in the catheter  101 . The ultrasonic signal received by the receiving  112  is sent to the signal processing circuit  113 ,which processes the ultrasonic signal and outputs the processed ultrasonic signal to the monitor  114 .  
         [0033]     The monitor  114  displays images based on various signals output from the signal processing circuit  113 . The signal processing circuit  113  is capable of outputting an RF signal, i.e., a signal produced by converting an ultrasonic signal into a digital signal, and a B-mode signal used to generate a B-mode image, to the monitor  114 . The signal processing circuit  113  is also capable of processing such an RF signal and a B-mode signal for performing an intravascular ultrasonic diagnosis and outputting the processed signals to the monitor  114 .  
         [0000]     Operation of the Catheter In an Intravascular Ultrasonic Diagnosis  
         [0034]     FIGS.  2 ( a ) and  2 ( b ) illustrate the manner in which the catheter  101  operates in an intravascular ultrasonic diagnosis.  FIG. 2 ( a ) is a cross-sectional view of a blood vessel with the catheter  101  inserted therein, and  FIG. 2 ( b ) is a perspective view of the blood vessel with the catheter  101  inserted therein.  
         [0035]     As seen in  FIG. 2 ( a ), the ultrasonic transducer  105  mounted in the tip of the catheter  101  is rotated by the motor (the motor  102  shown in  FIG. 1 ) in the direction indicated by the arrow  202 .  
         [0036]     The ultrasonic transducer  105  transmits and receives an ultrasonic wave at each of the angular positions thereof in the blood vessel. Specifically, the ultrasonic transducer  105  transmits an ultrasonic wave along respective radial lines  1 ,  2 , . . . ,  1024  at different angular positions as illustrated by way of example in  FIG. 2 ( a ). While the ultrasonic transducer  105  is rotating 360 degree in the blood vessel cross section  201 , it intermittently transmits and receives an ultrasonic wave a total of 1024 times. The number of times that the ultrasonic transducer  105  transmits and receives an ultrasonic wave while it is rotating 360 degree is not limited to 1024 as this is merely described by way of example. The number of times the ultrasonic transducer  105  transmits and receives an ultrasonic wave while it is rotating 360 degree may thus be selected as desired.  
         [0037]     The ultrasonic transducer  105  transmits and receives an ultrasonic wave along the radial lines  1 ,  2 , . . . ,  1024  while it is traveling in the direction indicated by the arrow  203  (see  FIG. 2 ( b )) in the blood vessel. The scanning process in which ultrasonic transducer  105  repeatedly transmits and receives an ultrasonic wave in each blood vessel cross section while traveling in the direction indicated by the arrow  203  is referred to as the “radial scanning process.” 
         [0000]     General Ultrasonic Signal Processing  
         [0038]     A general process of processing an ultrasonic signal in the intravascular ultrasonic diagnosis will be described below with reference to FIGS.  3 ( a )-( c ).  FIG. 3 ( a ) shows an RF signal representing a reflected ultrasonic wave that is received by the ultrasonic transducer  105 . In  FIG. 3 ( a ), the horizontal axis represents time and the vertical axis the intensity of the RF signal.  
         [0039]      FIG. 3 ( b ) shows a B-mode signal that is produced when the RF signal is amplified and detected by the signal processing circuit  113  to convert the echo intensity into an image signal on a gray scale. In  FIG. 3 ( b ), the horizontal axis represents time and the vertical axis the gray scale. The B-mode signal shown in  FIG. 3 ( b ) represents a signal along one line in the blood vessel cross section  201 .  
         [0040]      FIG. 3 ( c ) shows a B-mode image that is generated from a circumferential array of B-mode signals along the lines  1  through  1024  in the blood vessel cross section  201 . In  FIG. 3 ( c ) the B-mode image includes a blood vessel  301  and plaque  302  deposited in the blood vessel  301 .  
         [0000]     Arrangement of the Signal Processing Circuit  
         [0041]     An arrangement of the signal processing circuit  113  will be described below with reference to  FIG. 5 .  FIG. 5  shows in block form the arrangement of the signal processing circuit  113  according to this embodiment.  
         [0042]     As shown in  FIG. 5 , the signal processing circuit  113  has a central processing unit (CPU)  501 , a control memory (ROM)  502 , and a memory (RAM)  503 . The signal processing circuit  113  also has an output device  504  connected to the monitor  114  for outputting a signal such as a B-mode image signal to the monitor  114 , an input/output interface (I/F) device  505  for sending signals to and receiving signals from the transmission wave circuit  111  and the motor controller  120 , an input device  506  including a track ball, a mouse, a keyboard, etc. for entering signals, a storage device  507  such as a HDD or the like, and a bus  508 .  
         [0043]     Control programs for performing ultrasonic signal processing functions according to this embodiment and data used by the control program are stored in the storage device  507  (representing functions  507 - 1  through  507 - 8  to be described in more detail later). The control programs and data are loaded through the bus  508  into the memory  503  under the control of the CPU  501 , and executed by the CPU  501 .  
         [0000]     Processing of the Ultrasonic Signal Processing Apparatus for an Intravascular Ultrasound Diagnosing  
         [0044]      FIG. 6  shows a processing sequence of the ultrasonic signal processing apparatus  130  according to this embodiment for performing an intravascular ultrasonic diagnosis. The processing sequence of the ultrasonic signal processing apparatus  130  for performing an intravascular ultrasonic diagnosis will be described below with reference to  FIG. 6 . The processing sequence will be described below while referring to a B-mode image shown in  FIG. 4 . The processing sequence shown in  FIG. 6  is premised on the ultrasonic scanner  507 - 1  having been operated and the radial scanning process having been completed.  
         [0045]     In step S 601  shown in  FIG. 6 , a B-mode image display unit  507 - 2  operates to display a B-mode image  400  (see  FIG. 4 ) on the monitor  114 . In step S 602 , a plaque region setting unit  507 - 3  recognizes a plaque area  401  that is designated by the user based on the displayed B-mode image  400 , and sets the plaque area  401  in an IB (integrated backscatter) value calculator  507 - 5 .  
         [0046]     For allowing the user to make various designations or indications on the B-mode image displayed on the monitor  114 , it is assumed that a UI (User Interface) unit  507 - 7  has operated to allow the user to make such various designations or indications through the input device  506 .  
         [0047]     In step S 603 , the user designates M ROI Lines (lines for specifying a direction in which to array ROIs) from the center of the catheter  101  within the designated plaque area  401 .  
         [0048]     In step S 604 , the user designates N ROIs for each of the designated M ROI Lines. A ROI setting unit  507 - 4  recognizes the designated ROIs and sets the recognized ROIs in the IB value calculator  507 - 5 .  
         [0049]      FIG. 4  shows that 10 ROI Lines (arranged circumferentially) multiplied by 5 layers (arranged radially)=50 ROIs are set in the plaque area  401 . For illustrative purposes, the 10 ROI Lines are referred to as ROI Line  1 , ROI Line  2 , . . . , ROI Line  10 , respectively. Of the ROIs designated on the ROI Lines, a ROI group that is closest to the catheter  101  is referred to as ROI Layer  1 . ROI groups that are positioned progressively farther from the catheter  101  are referred to as ROI Layer  2 , ROI Layer  3 , ROI Layer  4 , ROI Layer  5 .  
         [0050]     Each ROI is defined by a ROI Line and a ROI Layer. For example, a ROI on ROI Line  2  in ROI Layer  1  is defined as ROI [ 2 ] [ 1 ], and a ROI on ROI Line  3  in ROI Layer  1  is defined as ROI [ 3 ] [ 1 ].  
         [0051]     As shown in  FIG. 4 , a ROI has a certain radial width and a certain circumferential width. It is assumed in the present embodiment that all the 50 ROIs have the same size. The radial width corresponds to the time region of the RF signal. An encircled region  402  is illustrative of the size of each ROI. According to the present embodiment, one ROI contains  8  lines, 32 samples.  
         [0052]     If an ultrasonic signal is converted into a digital signal at a frequency of 240 MHz, then the 32 samples correspond to about 0.1 mm as calculated according to 1.530×10 6  (mm/sec)/2 (reciprocated)×32 (samples)/240×10 6  (samples/sec)=0.102 mm. If the ultrasonic transducer  105  intermittently transmits and receives an ultrasonic wave a total of 1024 times per rotation, then the eight lines correspond to 2.8 degree as calculated according to 1024 (lines/rotation)×360 (degree/rotation) =2.8 degree.  
         [0053]     As the frequency of the ultrasonic wave emitted by the ultrasonic transducer is higher, a more detailed analysis, i.e., an analysis at a higher resolution, is possible, and a smaller lipid in the plaque can be detected. Therefore, the ultrasonic wave emitted by the ultrasonic transducer should preferably have a frequency of 50 MHz or higher.  
         [0054]     In step S 605  shown in  FIG. 6 , the IB value calculator  507 - 5  operates to calculate an IB (Integrated Backscatter) value for each ROI. In the present embodiment, the IB value calculator  507 - 5  calculates the IB value (total) of the eight lines in each ROI.  
         [0055]     Specifically, the IB value calculator  507 - 5  calculates an FFT (fast Fourier transform) of an RF signal that is produced by converting an ultrasonic signal into a digital signal, thereby determining a power spectrum P(f) which is a function of the frequency f. If it is assumed that the ultrasonic transducer which is used has a bandwidth [f 1 , f 2 ], then an IB value for each ROI is determined by integrating the power spectrum in the range from f 1  to f 2 , dividing the integral by the number of samples (32 samples in the present embodiment) of the RF signal, and standardizing.  
         [0056]     Specifically, the IB value on a line m in a ROI is calculated according to the following equation:
 
 IB   Line m =∫ f1   f2   P   Line m ( f )/32 (32 is the number of samples)
 
 By determining linear average of the IB values on all the lines in the ROI, the IB value for each ROI is determined. Specifically, the IB value for ROI [M] [N] is calculated as follows:
 
 IB   ROI   [M][N]=ΣIB   Line m /8 (8 is the number of lines)
 
 In step S 606 , a variance value calculator  507 - 6  operates to calculate a variance of the IB values for all the ROIs according to the following equation:  
       σ   =       ∑   M     ⁢       ∑   N     ⁢         (       IB       ROI   ⁡     (   M   )       ⁢     (   N   )         -     average   ⁡     (     IB       ROI   ⁡     (   M   )       ⁢     (   N   )         )         )     2     /     (       10   ×   5     -   1     )               
        (10 is the number of ROI Lines, and 5 is the number of ROI Layers) 
 
 In the above equation,  
         average   ⁡     (     IB       ROI   ⁡     (   M   )       ⁢     (   N   )         )       =       ∑   M     ⁢       ∑   N     ⁢       IB       ROI   ⁡     (   M   )       ⁢     (   N   )         /     (     10   ×   5     )               
    (10 is the number of ROI Lines, and 5 is the number of ROI Layers) 
 
 In step S 609 , a diagnosing unit  507 - 8  operates to compare the calculated variance value with a predetermined threshold value (e.g., 32). If the calculated variance value is greater than the threshold value, the diagnosing unit  507 - 8  judges that the plaque  401  is a lipid rich plaque, and displays “Lipid” or the like in the B-mode image. 
 
 According to the above embodiment, as described above, the variance value of the IB values of the ROIs in the plaque area is calculated and compared with the threshold value to determine whether the plaque to be analyzed is lipid rich or not. It is also possible to determine whether the plaque to be analyzed is stable or unstable. According to the above embodiment, furthermore, the processing sequence has a shorter calculation time for an easier analysis than the conventional process. 
       
 
         [0059]     In the first embodiment described above, after the IB values for the ROIs have been calculated, the variance value of the IB values for all the ROIs is calculated and compared with the threshold value to determine whether or not the plaque to be analyzed is lipid rich. However, the present invention is not limited to this embodiment.  
         [0060]     According to a second embodiment, a linear average of IB values for a group of every M ROIs in the same ROI layer is determined, and a variance value of the average IB value is calculated and compared with a threshold value to determine whether or not the plaque to be analyzed is lipid rich.  
         [0061]      FIG. 7  shows a processing sequence of an ultrasonic signal processing apparatus according to a second embodiment of the present invention. Of the processing sequence shown in  FIG. 7 , steps S 601  through S 605  are identical to those shown in  FIG. 6 , and will not be described in detail again.  
         [0062]     In step S 607 , a linear average of IB values of every M ROIs in the ROI layer N is determined. Specifically, the linear average is calculated according to the equation:  
         IB     ROI   ⁢           ⁢   Layer   ⁢           ⁢   N       =       ∑   M     ⁢       IB       ROI   ⁡     (   M   )       ⁢     (   N   )         /   10           
        (10 is the number of ROI Lines) 
 
 In step S 608 , a variance value of the average IB values of each ROI layer is calculated as follows:  
       σ   =       ∑   N     ⁢         (       IB     ROI   ⁢           ⁢   Layer   ⁢           ⁢   N       -     average   ⁡     (     IB   ROILayerN     )         )     2     /     (     5   -   1     )             
    (5 is the number of ROI Layers) 
 
 In the above equation,  
         average   ⁡     (     IB     ROI   ⁢           ⁢   Layer   ⁢           ⁢   N       )       =       ∑   N     ⁢       IB     ROI   ⁢           ⁢   Layer   ⁢           ⁢   N       /   5           
    (5 is the number of ROI Layers)        
 
         [0066]     In step S 609 , the diagnosing unit  507 - 8  compares the variance value determined in step S 608  with a predetermined threshold value. If the variance value is greater than the threshold value, the diagnosing unit  507 - 8  judges that the plaque  401  is a lipid rich plaque, and displays “Lipid” or the like in the B-mode image.  
         [0067]     In the first and second embodiments, processes for the user to designate or specify a ROI have not been described. However, the ultrasonic signal processing apparatus according to the present invention allows a ROI to be designated or specified by any of various processes. A ROI may be specified by specifying the position of a ROI Line and specifying the position of the ROI on the specified ROI Line. A process of specifying the position of a ROI Line and a process of specifying the position of the ROI on the specified ROI Line is described below.  
         [0000]     Process of Specifying the Position of a ROI Line:  
         [0068]     FIGS.  8 ( a ) and  8 ( b ) show by way of example a process of specifying the position of a ROI Line. According to the illustrated process, the number of ROI Lines to be specified is predetermined, and the user specifies only a range in which ROI Lines are positioned. Specifically, as shown in  FIG. 8 ( a ), when the user specifies a ROI Line  801  and a ROI Line  802 , eight equally spaced radial lines are automatically specified between the ROI Line  801  and the ROI Line  802 , as shown in  FIG. 8 ( b ).  
         [0069]     Since the user specifies only a range in which ROI Lines are positioned, the user can specify ROI Lines quickly without a lot of trouble.  
         [0070]     FIGS.  9 ( a ) and  9 ( b ) show by way of example another process of specifying the position of a ROI Line. According to this other process, the user specifies all ROI Lines that the user wants to be specified. Since the user can specify any desired number of ROI Lines at any desired positions while seeing a B-mode image, it is expected that the user can conduct a diagnosis with increased latitude.  
         [0000]     Process of Specifying the Position of a ROI on a Specified ROI Line:  
         [0071]     A process of specifying the position of a ROI on a specified ROI Line will be described below. It is assumed that the process is performed when ROI Lines have been specified according to the specifying process shown in, for example, FIGS.  8 ( a ) and  8 ( b ). However, the process may also be applicable when ROI Lines have been specified according to the specifying process shown in, for instance, FIGS.  9 ( a ) and  9 ( b ).  
         [0072]     FIGS.  10 ( a ) and  10 ( b ) show by way of example a process of specifying the position of a ROI on a specified ROI Line. According to the process, it is assumed that the number of ROIs to be placed on each ROI Line is predetermined (5 ROIs/ROI Line), and the user specifies a range in which ROIs are positioned on the ROI Lines. Specifically, as shown in  FIG. 10 ( a ), the user places ROI [ 1 ] [ 1 ], ROI [ 1 ] [ 5 ], . . . , ROI [ 10 ] [ 1 ], ROI [ 10 ] [ 5 ]in order to specify a range in which to position ROIs on ROI Lines  1  through  10 . Then, as shown in  FIG. 10 ( b ), three new ROIs (e.g., ROIs [ 1 ] [ 2 ] through [ 1 ] [ 4 ]) are automatically placed at equal intervals between the specified ROIs on each ROI Line (e.g., ROI [ 1 ] [ 1 ] and ROI [ 1 ] [ 5 ] on ROI Line  1 ).  
         [0073]     Since the user can specify any desired range in which to place ROIs on ROI Lines, it is expected that the user can specify the positions of ROIs quickly without a lot of trouble.  
         [0074]     The principles and preferred embodiments have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.