Abstract:
An optical coherent tomographic image forming apparatus includes: a first switch for instructing rotation of the optical deflection unit at a first speed; a second switch for instructing rotation of the optical deflection unit at a second speed which is higher than the first speed; and a driving controller which drives the optical deflection unit rotationally at the first speed in case of detecting instruction operation of the first switch and which changes the rotation speed of the optical deflection unit to the second speed, in case of detecting instruction operation of the second switch, under the condition that the optical deflection unit rotates at the first speed when the second switch is instructionally operated.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application contains subject matter related to Japanese Patent Application JP2011-078550 filed in the Japanese Patent Office on Mar. 31, 2011, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an optical coherence tomographic image forming apparatus and a control method thereof. 
     BACKGROUND DISCUSSION 
     Medical care is performed inside a blood vessel depending on a highly functional catheter such as a balloon catheter, a stent and the like. For this medical care, it has been becoming popular to use an imaging apparatus for diagnosis such as an optical coherence tomography (OCT) apparatus and the like for a diagnosis before operation or a follow-up confirmation after operation. 
     This imaging apparatus for diagnosis includes an optical lens at the distal end and further, includes a catheter installed with an optical fiber attached with an optical mirror. Then, a radial scan is carried out by inserting the catheter thereof inside a blood vessel of a patient, by illuminating light onto the blood vessel wall through the optical mirror while rotating the optical mirror and by light-receiving the reflected light again from a biological tissue through the optical mirror thereof, and a cross-sectional image of the blood vessel is to be constructed based on the obtained reflected light. Also, for an improved type OCT apparatus, there has been developed an optical frequency domain imaging (OFDI) apparatus. 
     The basic principle of the optical coherence tomographic diagnostic apparatus lies in that the light outputted from a light source inside the apparatus is divided into a measurement light and a reference light, and the measurement light is emanated through the optical mirror of the abovementioned optical fiber. Then, a scattering light reflected by the biological tissue is light-received through the same optical fiber, there is obtained an interference light with respect to the reference light which is reflected by going through a known distance, a tomographic image of the biological tissue (blood vessel) in the vicinity of the catheter is to be obtained from the intensity thereof. An example is disclosed in Japanese unexamined patent publication No. 2007-267867. 
     In particular, in case of the optical frequency domain imaging apparatus, it is possible, by sweeping the emanated optical wavelength repeatedly within a predetermined range, to obtain reflection-intensity distribution in the depth direction, in which the measurement light and the reference light are referenced to a same point, from the frequency distribution of the interference light obtained without handling the optical path length of the reference light. 
     SUMMARY 
     In case of the optical frequency domain imaging apparatus, the rotation speed of the mirror inside the catheter is made higher than it was before in order to heighten the resolution of the diagnosis image thereof. However, on the other hand, caused by the fact that the rotation speed is heightened, there arises such a problem as occurrence of its frictional heat. As mentioned above, since the catheter is an object inserted into the inside of a blood vessel, the less the influence of the frictional heat with respect to biological tissue is the better the result is. Also, the risk of breakdown is heightened by rotating the mirror at a high speed. Therefore, when rotating the mirror at a high speed, an upper limit is provided for a period during which the high speed rotation thereof is continued. Also, it is necessary for the timing of rotating the mirror at a high speed to match with the timing of carrying out the scan for obtaining the tomographic image of the targeted blood vessel region. 
     On the other hand, it is also required to judge whether or not the catheter is positioned at the measurement region for obtaining the tomographic image and/or to carry out a confirmation process as to whether or not the mirror rotates normally or the like. In this confirmation process, it is sufficient if a rough tomographic image of the blood vessel can be obtained and it is enough if it can be confirmed, by watching the image thereof, whether or not the mirror rotates normally, so that there is no problem even if the rotation speed of the mirror on an occasion thereof is in a low-speed rotation in which the influence of frictional heat can be ignored. 
     From the consideration mentioned above, the inventor here developed a conclusion about setting the rotation speed of the mirror into two stages. But the inventor here also became aware of the fact that there is a further problem in the case of providing an operation switch for simply instructing the high speed rotation and the low speed rotation respectively as desired. That is a problem in case of having instructed a high speed rotation by an erroneous operation. In a case in which the timing of instructing a scan for actually obtaining a tomographic image is near the continuation time-limit of the high speed rotation while not being aware of the fact that a high speed rotation has been instructed by an erroneous operation, the continuation time-limit is reached before the scan is completed and it happens that the measurement becomes invalid. Also, caused by the fact that a high speed rotation has been employed until the edge of the continuation time-limit, at that time point, the catheter becomes relatively in a high temperature. Therefore, it is desired, for the instruction of the high speed rotation again, to wait until there elapses a certain time period during which the temperature lowers adequately. 
     Consequently, the disclosed here is an optical coherence tomographic diagnostic apparatus configured to avoid an operation error involving the rotation speed of the mirror portion as mentioned above, and which it makes it possible to carry out a scan superior in operability. 
     The optical coherence tomographic image forming apparatus comprising a light source; an optical divider configured to divide a light outputted from the light source into a measurement light and a reference light; an optical probe insertable inside a body lumen and comprising an optical deflection unit provided at a distal end of the optical probe, the optical probe configured to emit the measurement light to the biological tissue and receive a reflected light; a drive unit configured to rotate the optical deflection unit centering around the axis thereof into the optical probe; and a signal processing unit configured to generate a cross-sectional image inside a biological tissue based on the light intensity of a interference light which is obtained from the reflected light and the reference light. The drive unit comprises: a first switch operable to instruct rotation of the optical deflection unit at a first speed; a second switch operable to instruct rotation of the optical deflection unit at a second speed higher than the first speed; and a driving controller configured to drive the optical deflection unit rotationally at the first speed upon detecting operation of the first switch and change the rotation speed of the optical deflection unit to the second speed upon detecting operation of the second switch, under a condition that the optical deflection unit rotates at the first speed when the second switch is operated. 
     According to one aspect, the optical tomographic diagnostic apparatus disclosed here is constructed in a way that makes it difficult for erroneous operation, relating to the rotation speed of the mirror portion inside the probe, to occur. The apparatus is also well suited to performing a scan superior in operability. 
     According to another aspect, an optical coherence tomographic image forming apparatus comprises: a light source which outputs light; an optical divider configured to divide light outputted from the light source into a measurement light and a reference light; an optical probe insertable inside a body lumen having biological tissue, the optical probe possessing a distal and portion at which is provided an optical deflection unit possessing an axis, the optical probe being configured to emit the measurement light toward the biological tissue which is reflected as reflected light and to receive the reflected light; a motor operatively connected to the optical deflection unit to rotate the optical deflection unit about the axis of the optical deflection unit at a first speed and a second speed higher than the first speed; a signal processing unit which receives information about light intensity of an interference light obtained from the reflected light and the reference light and uses said information to generate a cross-sectional image of the biological tissue inside the body lumen; and an operation unit operatively connected to the motor. The operation unit includes a first operating device which, upon operation, instructs the motor to rotate the optical deflection unit at the first speed, and a second operating device which, upon operation, instructs the motor to rotate the optical deflection unit at the second speed. A driving controller is configured to control the motor to rotationally drive the optical deflection unit at the first speed upon detecting operation of the first operating device, and to control the motor to rotationally drive the optical deflection unit at the second speed only when the second operating device is operated at a time when the optical deflection unit is rotating at the first speed. 
     Another aspect of the disclosure here involves a control method for an optical coherent tomographic image forming apparatus which divides light outputted from a light source into a measurement light and a reference light and generates a cross-sectional image of biological tissue in a body lumen based on light intensity of an interference light obtained from a reflected light produced by emitting the measurement light toward the biological tissue and the reference light while rotating an optical deflection unit located at a distal end portion of the optical probe positioned in the body lumen. The method comprises rotating the optical deflection unit at a first rotation speed greater than zero while the optical deflection unit is positioned in the living body lumen and while light is emitted from the optical deflection unit, and increasing the rotation speed of the optical deflection unit to a second rotation speed higher than the first rotation speed upon detecting that an operating device has been operated at a time when the optical deflection unit is rotating at the first rotation speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an outward-appearance constitution of an imaging apparatus for diagnosis relating to an embodiment disclosed by way of example. 
         FIG. 2  is a block diagram showing a functional constitution of an imaging apparatus for diagnosis. 
         FIG. 3  is a block diagram showing a functional constitution of a signal processing unit. 
         FIGS. 4A and 4B  are diagrams explaining rotation scanning and axial-direction movement of an optical probe inside a blood vessel, and for explaining illumination of a measurement light and an intake of a reflected light. 
         FIGS. 5A and 5B  are schematic diagrams for explaining an operation of the optical probe inside the blood vessel. 
         FIG. 6  is a diagram showing an operation unit of a scanner &amp; pull-back unit. 
         FIG. 7  is a flowchart showing a process procedure of a signal processing unit with respect to an operation by the operation unit of the scanner &amp; pull-back unit. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, in accordance with the attached drawings, an embodiment disclosed by way of example will be explained in detail. 
     [Explanation of Apparatus Structure and Operation] 
     First of all, it will be explained with respect to the structure of the overall apparatus and operation in this embodiment. 
       FIG. 1  is a diagram showing a system constitution and an outward-appearance constitution of a wavelength sweep type optical coherence tomographic (OCT) image forming apparatus (hereinafter, referred to as imaging apparatus for diagnosis) equipped with the constitution of the embodiment. As shown in  FIG. 1 , the imaging apparatus for diagnosis  100  is provided with an optical probe unit  101 , a scanner &amp; pull-back unit  102  and an operation control apparatus  103 . 
     Also, since a flush liquid described later is made to flow to a blood vessel region targeted for diagnosis, a guiding catheter  115  housing the optical probe unit  101  is used. An insertion hole, into which the optical probe unit  101  is inserted as shown by the arrow in  FIG. 1 , is provided at a rear end  115   a  of this guiding catheter  115  and an opening portion for exposing the optical probe unit  101  to the outside is provided at a distal end  115   b . Then, this guiding catheter  115  is provided with a port  116  for connecting a medicine introducing portion  118  which accommodates the flush liquid described later. By operating this medicine introducing portion  118 , the flush liquid accommodated in the inside is discharged through the distal end portion  11   b.    
     The scanner &amp; pull-back unit  102  and the operation control apparatus  103  are connected by the signal line &amp; optical fiber  104 . The guiding catheter  115  housing the optical probe unit  101  is directly inserted into a body lumen such as a blood vessel and the like, and the state inside the body lumen is measured by using an imaging core provided at a distal end of the optical probe unit  101 . This optical probe unit  101  is constituted by an optical fiber  236  which passes through the inside thereof and a catheter sheath  403  which covers the outside thereof, and at least the vicinity of the distal end portion thereof is constituted by a transparent member (details thereof will be described later). 
     For the above-mentioned flush liquid, a physiological saline and a contrast agent (and a mixture liquid thereof) are used, and it is stored in the medicine introducing portion  118 . The medicine introducing portion  118  is composed, for example, of a syringe, accommodates the flush liquid, and makes the flush liquid flow from a catheter distal end into a blood vessel by pressing a plunger thereof. By replacing the blood with the flush liquid after pushing and flowing away the blood, it become possible to make the scanning in a state in which the effect of the hematocyte component is less exerted. Such an operation mentioned above is generally referred to as a flush operation, but the detail description thereof will be omitted here. 
     The scanner &amp; pull-back unit  102  regulates a radial operation of an imaging core inside the optical probe unit  101  by rotational motion performed by a built-in motor. Also, this scanner &amp; pull-back unit  102  performs an operation (pull-back process) for pulling back the optical fiber  236 , which is rotating inside the optical probe unit  101 , at a constant speed by driving another built-in motor. By this pull-back process, it is possible to obtain a continuous blood vessel tomographic image which is along the axis of a blood vessel. Also, this scanner &amp; pull-back unit  102  is provided with an operation portion  102   a  which is arranged with various kinds of instruction switches for instructing the setting of the rotation speed, start/stop of the rotation and pullback of the optical fiber  236  inside the optical probe unit  101 . 
     On an occasion when carrying out optical coherence tomographic image formation of biological tissue, the operation control apparatus  103  is provided with a function for inputting various kinds of setting values, a function for outputting measurement light, and a function for processing data obtained by measurement and displaying them as tomographic image. In the operation control apparatus  103 , a reference numeral  111  indicates a main body control unit, which processes data obtained by measurement and outputs a processed result. A reference numeral  111 - 1  indicates a printer &amp; DVD recorder and it happens that the processed result in the main body control unit  111  is printed and is stored as data. A reference numeral  112  indicates an operation panel and a user carries out inputs of various kinds of setting values and instruction through the operation panel  112 . A reference numeral  113  indicates an LCD monitor as a display apparatus and it displays a processed result in the main body control unit  111 . 
       FIG. 2  is a functional constitution diagram of the imaging apparatus for diagnosis  100  shown in  FIG. 1 . In the drawing, a reference numeral  208  indicates a wavelength swept light source and a Swept Laser is used. The wavelength swept light source  208  is one kind of an Extended-cavity Laser which is composed of a light source portion  208   a  having an optical fiber  217  connected with an SOA216 (semiconductor optical amplifier) in a ring shape and a polygon scanning filter  208   b . The light outputted from the SOA216 proceeds through the optical fiber  217  and enters the polygon scanning filter  208   b  and the light whose wavelength is selected here is amplified by the SOA216 and finally, is outputted from a coupler  214 . In the polygon scanning filter  208   b , the wavelength is selected depending on the combination of a diffraction grating  212  for light-splitting the light and a polygon mirror  209 . The light which is light-split by the diffraction grating  212  is focused on the surface of the polygon mirror  209  depending on two lenses  210 ,  211 . Thus, only the light of the wavelength perpendicular to the polygon mirror  209  returns to the same optical path and is outputted from the polygon scanning filter  208   b , so that it is possible to carry out the time sweep of the wavelength by rotating the polygon mirror  209 . For the polygon mirror  209 , for example, a 72-facets mirror is used and the rotation speed thereof is around 50000 rpm. Owing to the unique wavelength sweep system in which the polygon mirror  209  and the diffraction grating  212  are combined, it is possible to employ the wavelength sweep of high speed and high power. 
     The light outputted from the coupler  214  of the wavelength swept light source  208  is made to enter one end of a first single mode fiber  230 . The first single mode fiber  230  is guided to an optical coupler  226  which is optically coupled with a second single mode fiber  231  and here, the light is transmitted by being branched into two paths. 
     On the distal end side ahead of the photo coupler unit  226  of the first single mode fiber  230 , there is provided a scanner &amp; pull-back unit  102 . Inside the scanner &amp; pull-back unit  102 , there is provided an optical rotary joint (optical coupling unit)  203  which connects between a non-rotary portion (fixed portion) and a rotary portion (rotationally drive portion) and which transmits the light. Further, a fourth single mode fiber  235  provided on the distal end side of the optical rotary joint  203  is connected in a freely detachable manner with a fifth single mode fiber  236  through an adapter  202 . Thus, while repeating light transmission and reception, the light from the wavelength swept light source  208  is transmitted into an imaging core  201  which is rotationally driven. 
     The light transmitted to the fifth single mode fiber  236  is illuminated from the distal end side of the imaging core  201  with respect to a biological tissue of a blood vessel while performing radial operation. Then, a portion of the reflected light which is scattered on the surface of or in the inside of the biological tissue is taken-in by the imaging core  201  and returns to the first single mode fiber  230  side by way of the reverse optical path, and a portion thereof moves to the second single mode fiber  237  side by the photo coupler unit  226  which has functions as a light splitting unit and a light coupling unit at the same time. In the photo coupler unit  226 , the reflected light is mixed with a reference light described below and is light-received as an interference light by a photo detector (in the embodiment disclosed by way of example, referred to as a photodiode, hereinafter as a PD)  219 . 
     The rotation unit side of the optical rotary joint  203  is rotationally driven by a radial scanning motor  205  of the rotary drive apparatus  204 . Also, the rotary angle of the radial scanning motor  205  is detected by an encoder unit  206 . Further, the scanner &amp; pull-back unit  102  is provided with a linear drive apparatus  207  and defines the insertion-direction (axial-direction) movement of the optical probe unit  101  based on an instruction from a signal processing unit  223 . The axial-direction movement is realized by a mechanism in which a linear drive motor inside the linear drive apparatus  207  operates based on a control signal from the signal processing unit  223 . 
     Also, there is provided a variable mechanism  225  of the optical path length for fine-adjusting the optical path length of the reference light at a distal end on the distal end side from the photo coupler unit  226  of the second single mode fiber  231 . This variable mechanism  225  of this optical path length is provided with an optical path length adjuster for changing the optical path length which corresponds to the fluctuation of the length thereof such that the fluctuation of the length of the individual optical probe  201  can be absorbed in case of using the optical probe (imaging core)  201  by being exchanged. The second single mode fiber  231  and a collimator lens  234  are provided on a one-axis stage  232  which is freely movable in the optical axis direction thereof as shown by an arrow  233  and form the optical path length adjuster, 
     More specifically, in case of exchanging the optical probe  201 , the one-axis stage  232  functions as an optical path length adjuster having such an amount of variable range of optical path length, which can absorb the fluctuation of the optical path length of the optical probe. Further, the one-axis stage  232  is provided also with a function as an adjuster for adjusting an offset. For example, even in a case in which the distal end of the optical probe  201  is not closely attached to the surface of the biological tissue, minutely changing the optical path length by the one-axis stage makes it possible to set a state of interference from the surface position of the biological tissue. 
     The light reflected through mirrors  227 ,  229  and a lens  228  is inputted to a second single mode fiber  231  as the reference light. The reference light whose optical path length is fine-adjusted by the variable mechanism  225  of the optical path length is mixed with the reflected light from the first single mode fiber  230  side at the photo coupler unit  226  which is provided on the way of the second single mode fiber  231 , and becomes the interference light, and it is light-received by the PD  219 . The light which is light-received by the PD  219  is photoelectrically converted and becomes an electric signal, and it is inputted to an amplifier  220  and amplified, and thereafter, it is supplied to a demodulator  221 . In this demodulator  221 , a demodulation process for extracting only the signal component of the interference light is carried out and the output thereof is inputted to an A/D converter  222 . 
     In the A/D converter  222 , the interference light signal is applied with sampling, for example, by 180 MHz for 2048 points and digital data (interference data) of one line are generated. Note that the reason why the sampling frequency is set to be 180 MHz is on an assumption that about 90% of the period of wavelength sweep (12.5 μsec) is extracted as digital data of 2048 points in case of setting the repetition frequency of wavelength sweep to be 80 kHz and it is not limited by this aspect in particular. 
     The interference light data of one line unit, which are generated in the A/D converter  222  are inputted to the signal processing unit  223 . In this signal processing unit  223 , the interference light data are frequency-decomposed by FFT (Fast Fourier Transform) and data in the depth direction are generated, and by coordinate-converting these data, cross-sectional images at respective positions of the blood vessel are formed and outputted to an LCD monitor  113  by a predetermined frame rate. 
     Note that the signal processing unit  223  is connected with an optical path length adjuster control unit  218 . The signal processing unit  223  carries out control of the position of the one-axis stage  232  by means of the optical path length adjuster control unit  218 . Also, the signal processing unit  223  is connected with a motor control circuit  224  and in synchronization with a video synchronization signal when forming a cross-sectional image, the cross-sectional image is stored in an internal memory. In addition, the video synchronization signal of this motor control circuit  224  is transmitted also to the rotary drive apparatus  204  and in the rotary drive apparatus  204 , a drive signal in synchronization with the video synchronization signal is outputted. Further, it happens that the signal processing unit  223  executes sampling of the interference light by the above-mentioned PD  219  and A/D converter  222 . 
       FIG. 4A  is a diagram for explaining an aspect in which the imaging core  201  of the optical probe unit  101  is inserted into a body lumen (into a blood vessel) and a radial scan is carried out. A catheter sheath  403  installed with the imaging core  201  which is constituted by the optical fiber  236  including an optical mirror  401  and an optical lens  402  at the distal end thereof is inserted into, for example, a blood vessel lumen. The rotary drive apparatus  204  rotates the imaging core  201  in an arrow  405  direction in the inside of the catheter sheath  403  and the linear drive apparatus  207  moves it toward the arrow  406  direction (pull-back process). At that time, as shown in  FIG. 4B , the measurement light from the wavelength swept light source  208  is illuminated to the blood vessel wall by the optical mirror  401  by way of the optical fiber  236 . The reflected light to which the illuminated light is reflected is returned to the apparatus from the optical mirror  401  by way of the optical fiber  236 . More specifically, the optical mirror  401  has a function as an optical deflection unit which deflects the axial direction light of the optical probe unit  101  from the optical fiber  236  toward or in the direction of the body lumen wall. For the optical deflection unit, also a prism or the like can be used. 
       FIGS. 5A and 5   b  are schematic diagrams for explaining the operation of the optical probe unit  101  when imaging an intravascular tomographic image.  FIGS. 5A and 5B  are respectively a perspective view and a cross-sectional view of the blood vessel in a state in which the optical probe unit  101  is inserted thereinto. In  FIG. 5A , a reference numeral  501  indicates a blood vessel cross-section into which the optical probe unit  101  is inserted. As described above, the imaging core  201  of the optical probe unit  101  is attached with the optical lens  402  and the optical mirror  401  at the distal end thereof and rotates in the direction shown by a reference numeral  405  in  FIG. 5B  depending on the radial scanning motor  205 . 
     Depending on the optical lens  402 , transmission &amp; reception of the measurement light are carried out at respective rotary angles. Lines  1 ,  2 , . . . ,  512  show illumination directions of the measurement light at respective rotary angles. In this embodiment disclosed as an example, while the imaging core  201  including the optical mirror  401  and the optical lens  402  rotates as much as the angle of 360 degree at the position of a predetermined blood vessel cross-section  501 , the transmission of measurement light &amp; the reception of reflected light intermittently are carried out 512 times. Note that the number of times of the transmission &amp; reception of the measurement light during a period of rotating 360 degrees is not limited by this aspect in particular and it is assumed that the number of times is settable arbitrarily. In this manner, the scan in which the transmission &amp; reception of the signal is repeated while rotating the imaging core  201  is generally referred to as a “radial scan (rotation scan)”. Also, the transmission of the measurement light &amp; the reception of the reflected light by such an imaging core  201  is carried out while the imaging core  201  proceeds in the inside of the blood vessel toward the arrow  406  direction (see  FIG. 4A ). 
     Note that for the rotation speed of the imaging core  201  in the embodiment disclosed by way of example, there are provided two kinds of speeds of 1800 rpm and 9600 rpm. The 1800 rpm is a speed for mainly confirming whether or not the distal end portion of the imaging core  201  has been positioned at the aimed region and confirming whether or not the imaging core  201  is rotating correctly, and by this number of rotation, the pulling-back (pull-back) of the imaging core is not carried out toward the arrow  406  direction in  FIG. 4A . Hereinafter, this rotation process by 1800 rpm is referred to as a process of a radial scan mode. 
     On the other hand, the 9600 rpm is a speed for obtaining a high-resolution blood vessel tomographic image and also, is a mode for obtaining an image in a predetermined range along the blood vessel axis. Accordingly, in this mode, the process of pull-back toward the arrow  406  direction in  FIG. 4A  is carried out while rotating the imaging core  201  by 9600 rpm. The flush operation explained previously (operation of injecting flush liquid) is carried out in this case. Hereinafter, this mode is referred to as a pull-back scan mode. The arrow  406  in  FIG. 4A  is the direction toward which the imaging core  201  is pulled back and it is opposite to the direction toward which the blood flows. When the flush operation is carried out, the medicine is outpoured toward the inside of the blood vessel from the distal end portion  115   b  of the guiding catheter  115  by passing through the empty space between the guiding catheter  115  and the catheter sheath  403 , and at the portion thereof, the blood is drifted away and replaced by the medicine in which a flow without having an influence of the hematocyte component is produced. Then, during the pull-back operation, the distal end portion of the imaging core  201  moves in the area replaced by the medicine toward the arrow  406  direction and it become possible to scan for a highly accurate image. During the pull-back, the guiding catheter  115  is arranged at a position so as not to cover the distal end portion of the imaging core  201 . 
       FIG. 3  shows a constitution of a signal processing unit  223  in the embodiment disclosed by way of example. This signal processing unit  223  carries out a generation process of the tomographic image based on an electric signal (signal from A/D converter  222 ) obtained from the interference light in the radial scan mode and the pull-back scan mode which are mentioned above in accordance with an instruction by an operator depending on the operation panel  112  and the operation unit  102   a . This generation process will be explained next. 
     The signal processing unit  223  stores data of the interference light for one line by the wavelength sweep from the A/D converter  222  sequentially into a line memory unit  301 . Then, depending on an encoder signal of the motor, which is outputted from a motor control circuit  224 , signals are selected and grouped such that the number of lines per one rotation of the motor becomes 512 lines. More specifically, the interference light data per one line are outputted to the line data generation unit  302  by every  512  data per one rotation of the motor. 
     The line data generation unit  302  generates the line data by carrying out an FFT (Fast Fourier Transform) process and concurrently, a line addition-averaging process, a filtering process, a logarithmic conversion and the like are carried out, and the obtained line data are outputted to a post-processing unit  303  at a subsequent stage. The line data is defined as data array which makes a line from center of the cross-sectional image to edge of the cross-sectional image. The line date is produced from coherence light intensity of the emission direction of the transmitting. 
     In the post-processing unit  303 , a contrast adjustment, a brightness adjustment, a gamma correction, a frame correlation, a sharpness process and the like are applied for the line data received from the line data generation unit  302 , and the processed result thereof is outputted to an image construction unit  304 . The image construction unit  304  converts the line data train of polar-coordinate to a video signal and displays it on the LCD monitor  113  as blood vessel cross-sectional images. Note that as one example, there is shown, here, an example of constructing an image by 512 lines, but it is not to be limited by this number of lines. It happens that a control unit  305  controls a series of operations of the respective units mentioned above, but the contents of calculation until the blood vessel tomographic image is obtained and portions relating to the display process thereof do not directly concern the embodiment, so that further detailed explanations will be omitted. 
     [Explanation of User Interface] 
     Next, it will be explained with respect to user interface for an operator in the embodiment disclosed by way of example. First, before moving to an explanation of the user interface, set forth will be an explanation of premise or peripherally related portions. 
     As explained previously, for the scan mode in this example of an embodiment, there are the radial scan mode (process for making the optical mirror  401  rotate by 1800 rpm) and the pull-back scan mode (pull-back process of the optical fiber  236  in which the optical mirror  401  is rotated by 9600 rpm and the optical mirror  401  is made to move by a constant speed toward the arrow  406  direction in  FIG. 4 ). 
     Problems are not caused by rotation at 1800 rpm, but when the optical fiber  236  (optical mirror  401 ) is rotated in the catheter sheath by a high speed such as 9600 rpm, frictional heat is generated there and it happens that the temperature of the catheter sheath will heighten or increase. Therefore, it is not desirable for the biological tissue on the outside of the catheter sheath to continue the rotation (high speed rotation) for a long period. In addition, there also occurs a possibility which leads to breakages of the optical fiber  236  and the optical mirror  401 . Consequently, it was required to set the duration time of the rotation speed referred to as 9600 rpm to be within 42 seconds maximally and more specifically, to provide a limiter for the duration time of the high speed rotation of the pull-back scan mode. 
     However, in a case in which it happens that the operator instructs the high speed rotation by 9600 rpm caused by an erroneous operation and it happens that the pull-back scan is instructed without being aware of a fact that the high speed rotation thereof continues nearly for 42 seconds, it happens that the duration time terminates on the way of the scan and the rotation stops, so that complete measurement data cannot be obtained. Therefore, it is necessary to prevent such an erroneous operation as much as possible. Note that the above-mentioned 42 seconds as the maximum duration time is merely presented as one example and it is a value which is suitably changeable. 
     Also, as explained previously, the pull-back scan mode is a mode in which the tomographic image of a predetermined distance of the blood vessel is scanned while carrying out the pull-back of the optical fiber, so that it is necessary to provide time for achieving the movement over the predetermined distance until the scan is completed. Therefore, the timing for starting the pull-back process has to be set within a time period which is obtained by subtracting as much as an amount of time necessary for the pull-back process thereof from the maximum duration time (42 seconds) by 9600 rpm. Although depending on the length of the scan, in this embodiment disclosed by way of example, it is assumed that the rotation is to be stopped if the start instruction of the pull-back process is not carried out within 30 seconds after the rotation speed becomes 9600 rpm. 
     In light of the foregoing, according to  FIG. 6  showing one example of the operation unit  102   a  in the scanner &amp; pull-back unit  102  and  FIG. 7  showing a process procedure, there will be explained processes (process contents of the signal processing unit  223 ) relating to the user interface in an embodiment. 
     As shown in  FIG. 6 , in the operation unit  102   a  provided at the scanner &amp; pull-back unit  102 , there are provided a switch  610  for stopping the rotation of the optical fiber  236 , a switch  620  for instructing a shifting to the radial scan mode (1800 rpm), a switch  630  for instructing an entering to the pull-back scan mode and a shifting to a state in which the pull-back is possible (9600 rpm), and a switch  640  for carrying out a start instruction of the pull-back. The switches (inclusive of buttons which are also acceptable) are examples of operating devices for initiating the respective noted operations. Also, those switches are installed with LEDs  611 ,  621 ,  631 ,  641  as lighting display devices for notifying the states of the switches respectively. The relationships between driving states of the LEDs and functional states of the switches are as follows. 
     LED turned off: Indicating a state in which the function of the switch thereof is not expressed 
     LED turned on: Indicating a state in which the function of the switch thereof is expressed 
     LED blinking: Indicating a transitional state until the function of the switch thereof is expressed 
     Since it is enough if only the state can be distinguished, it is possible to employ another driving method than the driving method for the LEDs, which was mentioned above. Depending on the case, it is possible to prepare LEDs having a number of light-emitting colors and to change the light-emitting colors in response to the state. 
     Also, the operation unit  102   a  is provided with a display unit  650  for countdown-displaying the remaining number of seconds during which the pull-back switch  640  can be pushed down when the rotation becomes 9600 rpm. 
     Hereinafter, there will be explained processes of the signal processing unit  223  in an embodiment disclosed by way of example in accordance with a flowchart in  FIG. 7 . 
     First, the signal processing unit  223  carries out, in step S 1 , an initial process of each constituent element used for an optical coherence tomographic image formation process. Within this process, there are included a turn-on process of the LED  621  for notifying the fact that the radial scan switch  620  functions, and turn-off processes of the LEDs  611 ,  631 ,  641  for notifying the fact that other switches do not function. It becomes a situation in which the operator carries out, in this state, an operation for guiding the optical probe unit  101  to the inside of the blood vessel in the diagnosis region of a patient. 
     The operator pushes down the radial scan switch  620  in order to confirm the position of the optical probe  201 , to fine-adjust the position and to confirm whether or not the optical mirror portion  401  rotates normally. When the signal processing unit  223  detects the push-down of this radial scan switch  620  (“Yes” in step S 2 ), the driving of the radial scanning motor  205  is carried out for making the optical fiber  236  rotate by 1800 rpm. At that time, the LED of the radial switch  620  is put into a blinking state. Note that even if a switch other than the radial scan switch  620  within the switch group shown in  FIG. 6  is pushed down, that is ignored. The configuration in which the push-down of a switch lying in a turned-off state is ignored will be similar also in the explanation hereinafter. 
     Then, in step S 3 , when it is judged that the speed has reached 1800 rpm, there is carried out a process for obtaining the tomographic image at the rotation speed thereof and there is carried out a process for displaying the image thereof on the LCD monitor  113  (step S 4 ). As a result thereof, it is possible for the operator to confirm and fine-adjust the position of the optical mirror portion  401  and confirm whether or not the optical mirror portion  401  rotates normally. In this situation, in order to obtain a more accurate image, it sometimes happens that the operator carries out a flush operation using a small amount of medicine (operation of making the medicine at the medicine introducing portion  120  flow out from the distal end portion  115   b  of the guiding catheter  115 ). Also, in the course of carrying out the process of this step S 4 , the LEDs  611 ,  631  are turned on, thus providing notification that the push-downs of the stop switch  610  and the pull-back ready switch  630  are to be regarded as effective, and the system then waits for the detection of the push-down of any one of the switches (steps S 5 , S 6 ). 
     Here, when the push-down of the stop switch  610  is detected, the signal processing unit  223  stops the rotation of the optical fiber  236  in step S 7  and the process is returned to step S 1 . 
     On the other hand, when the push-down of the pull-back ready switch  630  is detected, the signal processing unit  223  carries out the driving of the radial scanning motor  205  in order to rotate the optical fiber  236  by 9600 rpm and concurrently, blinks the LED  631  (step S 6 ). Then, in step S 8 , the system waits until the rotation speed reaches 9600 rpm. 
     When the speed reaches 9600 rpm, it becomes a state in which the pullback is possible, there is started the countdown of the residual time (30 seconds in the embodiment) until it is no longer possible to carry out the pullback, and there is started displaying of the residual time thereof on the display unit  650  (step S 9 ). During this countdown, the switches which the operator can operate are the stop switch  610  and the pull-back switch  640 , so that the respective LEDs  611 ,  641  are turned on and the LEDs  621 ,  631  of the other switches are turned off. 
     The signal processing unit  223  judges whether or not the remaining number of seconds by the countdown is zero second in step S 10  and whether or not any one of the stop switch  610  and the pull-back switch  640  has been pushed down in steps S 11 , S 12 , and looping takes place in S 10  to S 12  until any one is judged. Note that if the speed is allowed to return to 1800 rpm, it is allowed during this looping to turn on the LED  621 , to carry out a process of judging whether or not the radial scan switch  620  has been pushed down and to return the process to step S 3  when the push-down thereof is detected. 
     Now, in the looping mentioned above, in a case in which the remaining number of seconds by the countdown has become zero second or the push-down of the stop switch  611  has been detected, the process proceeds to step S 7 , stops the rotation of the optical fiber  236  and returns to step S 1 . At that time, the LED  641  is turned off. 
     On the other hand, when the push-down of the pull-back switch  640  is detected (at that time, operator is carrying out flush operation for introducing medicine into a blood vessel from medicine introducing portion  118 ), the process proceeds to step S 13 . Here, the signal processing unit  223  starts driving of the linear drive apparatus  207  and carries out the process of pulling the optical fiber  236  (rotating at 9600 rpm) by a predetermined speed as much as a distance which is set beforehand. During that period, as explained previously, there is carried out the sampling of the electric signal of the interference light by the A/D converter  222  and there is carried out the process for obtaining the three-dimensional tomographic images of the blood vessel. During this pull-back process, the LED  641  of the pull-back switch  640  is blinking and the LEDs of the other switches are turned off. In this manner, when the pull-back of the optical fiber  236  for the necessary distance is finished, the process proceeds to step S 14 , the process of the pull-back is terminated and the rotation of the optical fiber  236  is stopped. At that time, all of the LEDs are turned off. Thereafter, the process proceeds to step S 15  and information such as the obtained interference light data and the like is stored in a memory unit of a hard disk or the like which is not shown, and this process is finished. 
     As explained above, according to this embodiment, it is not possible to shift to such a high-speed rotation as 9600 rpm without undergoing such a low-speed rotation as 1800 rpm for carrying out the confirmation operation, so that in a non-rotation state, even if the pull-back ready switch is pushed down by an erroneous operation, it is possible to treat the operation thereof as invalid and it become possible to improve safety and operability. Also, there can be obtained a situation in which whether or not each switch is effective can be confirmed by the driving state of the LED provided at each switch and it becomes more possible to prevent erroneous operations. Note that to provide the stage of such a low-speed rotation as 1800 rpm is useful for carrying out various kinds of the confirmation operations for which high-speed rotation is not required, and it becomes effective in case of avoiding heat generation and breakdown. 
     Note that in the embodiment, an example was explained in which each switch is arranged at the scanner &amp; pull-back unit  102 . Instead of or in addition to this aspect, it is also allowed for a similar switch to be provided at the operation panel  112  or to be displayed on the LCD monitor  113 . 
     Also, in the embodiment disclosed by way of example embodiment, examples of 1800 rpm and 9600 rpm were explained for the rotation speeds of the optical fiber  236 , but the present invention is not to be limited by these rotation numbers. It is needless to say that the length of time for counting down also varies depending on the apparatus constitution and/or the setting, so that the present invention is not to be limited by the embodiments mentioned above. 
     The detailed description above describes features and aspects of an embodiment of an optical coherence tomographic image forming apparatus and associated control method disclosed by way of example. The invention is not limited, however, to the precise embodiment and variations described. Various changes, modifications and equivalents could be effected by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims.