the present invention has been made based upon the following basic idea : in an x - ray imaging apparatus including a sold - state imaging element or the like , electron charges produced only at a timing when x - ray pulses are projected to a biological body under medical examination , are picked up from the imaging element as imaging signals , whereas other electron charges generated at a timing when descending lags ( trailing edges ) of the x - ray pulses appear , are not picked up therefrom as imaging signals . as a result , adverse influences caused by the last - mentioned electron charges of the imaging element are not given to the quality of x - ray images , for instance , no blurring phenomenon and also no dark current . referring now to fig3 an overall arrangement of an x - ray imaging apparatus 100 according to a first preferred embodiment of the present invention will be described . the first x - ray imaging apparatus 100 is mainly constructed of an x - ray tube 1 for emitting pulsatory x - ray beams 12 which will then penetrate through a biological body 2 under medical examination and reach an image intensifier 3 ; a charge - coupled device imager 40 for converting an optical image signal of the biological body 3 obtained from the image intensifier 3 into a corresponding electronic image signal ; and a cathode - ray tube 5 functioning as a tv monitor which , receives a tv signal from ccd imager 40 ( although not shown in detail , a television signal processor is employed to process the electronic image signal derived from the ccd imager 40 , thereby producing the tv signal ). the first x - ray imaging apparatus 100 further comprises ; a system controller 50 constituting a major feature of this preferred embodiment , and for controlling an overall system of this x - ray imaging apparatus 100 ( will be discussed later ); an a high voltage generator 8 for applying a high voltage to the x - ray tube 1 so as to emit the pulsatory x - ray beams 12 therefrom : and a ccd drive signal generator 30 for generating a ccd drive signal so as to drive the ccd imager 40 . as will be described later more in detail , under control of the system controller 50 , the ccd drive signal generator 30 produces the ccd drive signal thereby to perform such a timing control for the ccd imager 40 . that is , only electron charges occurring in the ccd imager 40 at a timing when the pulsatory x - ray beams 12 are projected via the biological body 2 to the image intensifier 3 , are read out from the ccd imager 40 as the image signals of the biological body 2 , and also other electron charges produced in the ccd imager 40 at least during occurrence of the pulsatory x - ray lags &# 34 ; l &# 34 ; ( see fig2 ). furthermore , in general , the ccd imager 40 has a so - called &# 34 ; electronic shutter &# 34 ; function . that is , the above - described electron charges occurring within the ccd imager 40 due to the pulsatory x - ray lags &# 34 ; l &# 34 ; ( trailing edges ) can be swept out from the ccd imager 40 by utilizing such an electron shutter function . accordingly , the electron charges occurring within the ccd imager 40 in response to the trailing edges of the pulsatory x - ray beams 12 are not outputted from the ccd imager 40 as the image signal , so that no blurring phenomenon happens to occur in the resultant x - ray images displayed on the tv monitor 5 . fig4 shows a cross - sectional view of the ccd imager 40 . in the major structure of this ccd imager 40 shown in fig4 n - - substrate 13 ( referred to as an &# 34 ; n - - sub &# 34 ;) is provided . on this substrate 13 , a p - region 14 , another p - region 15 and a further p + - region 16 functioning as a channel stopper are formed . furthermore , an n + - region 17 an n - - region 18 are formed on the above - described p - regions . also , a silicon oxide ( sio 2 ) film 19 , an insulating film 20 and a light shield made of aluminum 21 are provided on or above the n - regions , as illustrated in fig4 . symbol &# 34 ; pd &# 34 ; indicates a photodiode part of this ccd imager 40 and symbol &# 34 ; v - ccd &# 34 ; denotes a vertical ccd part thereof . this ccd imager 40 has a vertical overflow drain ( vcd ) structure . accordingly , overcharges occurring in the photodiode part &# 34 ; pd &# 34 ; are not flown into the v - ccd part , but flown into the substrate 13 along a z direction ( see fig4 and 7e ), by controlling the substrate voltage &# 34 ; v sub &# 34 ; . also charges occurring in a very deep portion of the substrate 13 are similarly flown along the z ( substrate ) direction and then disappear . as previously explained , in accordance with the present invention , various types of charge - coupled device elements may be utilized as the ccd imager 40 of the first x - ray imaging apparatus 100 . it should be noted that these charge - coupled device elements are known in the art . for instance , there are known as an it ( interline transfer ) type ccd , a ft ( frame transfer ) type ccd , and a fit ( frame interline transfer ) type ccd . fig5 a pictorically explains a basic operation of an it type ccd imager 42 . as shown in fig5 a , vertical transfer ccd lines 22b are provided adjacent and parallel to light receiving element lines 22a . this it type ccd imager 42 is so constructed that electron charges stored in the light receiving element lines 22a are transferred to a horizontal scanning ccd line 22c every 1 line . fig5 b pictorically explains a basic operation of a ft type ccd imager 44 . as represented in fig5 b , a light receiving ccd block 24a is provided adjacent to a vertical scanning ccd block 24b . this ft ( frame transfer ) type ccd imager 44 is so arranged that electron charges stored in the light receiving ccd block 24a are transferred to the vertical scanning ccd block 24b during the vertical blanking ( flyback or retrace ) period , and subsequently image signals are transferred from the vertical scanning ccd block 24b to a horizontal scanning ccd line 24c . as is known in the art , a fit ( frame interline transfer ) type ccd element is so constructed of combining both functions of the above - described it type ccd element and ft type ccd element . an overall operation of the first x - ray imaging apparatus 100 will now be described with reference to not only fig3 but also fig6 and 7 . fig6 a to 6c are timing charts for the major pulse signals of the first x - ray imaging apparatus 100 , and fig7 a to te pictorically explain the charge transfer operations of the ccd imager 40 . as shown in the timing chart of fig6 a , it is assumed that when the pulsatory x - ray beams are generated at a period of 1 / 30 seconds ( i . e ., 1 frame period ), an x - ray pulse having a normal pulse width defined from a time instant &# 34 ; t 1 &# 34 ; to a time instant &# 34 ; t 2 &# 34 ;, appears and subsequently an x - ray lag ( trailing edge ) &# 34 ; l &# 34 ; appears during a time period defined from a time instant &# 34 ; t 3 &# 34 ; to a time instant &# 34 ; t 4 &# 34 ;. in this first example , both the it type ccd imager 42 ( see fig5 a ) and the ft type ccd imager 44 ( see fig5 b ) are employed as the ccd imager 40 and the non - interlace scanning operation is carried out . it should be also noted that every pulsatory x - ray beams 12 own such a trailing edge ( lag ) &# 34 ; l &# 34 ;. under control of the system controller 50 , when the pulsatory x - ray beams 12 are generated from the x - ray tube 1 , the image intensifier tube 3 produces optical x - ray images of the biological body 2 and transfers the optical x - ray images to the ccd imager 40 . more specifically , as shown in fig7 a and 7b , when the x - ray pulse having the normal width is projected to the biological body 2 from a time period defined from the time instants &# 34 ; t 1 &# 34 ; to &# 34 ; t 2 &# 34 ;, electron charges are gradually stored into the photodiode part &# 34 ; pd &# 34 ; of this ccd imager 40 . at the next time instant &# 34 ; t 3 &# 34 ; when the pulsatory x - ray beam projection is accomplished , a field shift pulse ( will be referred to as &# 34 ; fs &# 34 ;) shown in fig6 b is produced from the ccd drive unit 30 under control of the system controller 50 and supplied therefrom to the ccd imager 40 . as a result , as represented in fig7 c , the electron charges so far stored in the photodiode part &# 34 ; pd &# 34 ; are transferred to the vertical ccd part &# 34 ; v - ccd &# 34 ;, so that these charges are read out as the effective x - ray image signals from the ccd imager 40 . subsequently , as previously explained , when the pulsatory x - ray lag , or trailing edge &# 34 ; l &# 34 ; appears from &# 34 ; t 3 &# 34 ; to &# 34 ; t 4 &# 34 ;, electron charges are newly , gradually stored in the photodiode part &# 34 ; pd &# 34 ; of the ccd imager 40 . furthermore , during this x - ray trailing edge period , electron charges are furthermore stored due to the dark currents of this ccd imager 40 ( see fig7 d ). these ( unnecessary ) electron charges stored during the x - ray trailing edge period may cause adverse influences to the x - ray image quality , e . g ., blurring phenomenon . next , at a time instant &# 34 ; t 5 &# 34 ;, namely just before the subsequent x - ray pulse is produced , the electronic shutter pulse shown in fig6 c is produced in the ccd drive unit 30 under control of the system controller 50 and applied therefrom the ccd imager 40 . thus , as represented in fig7 e , the above - described unnecessary electron charges stored in the photodiode part pd are not transferred to the v - ccd part , but are flown into the substrate 13 along the z direction ( see fig4 ). in other words , these unwanted electron charges are not read out as the x - ray image signals from the ccd imager 40 , but are swept out from this ccd imager 40 . a time period defined from the first time instant &# 34 ; t 1 &# 34 ; to the fifth time instant &# 34 ; t 5 &# 34 ; corresponds to 1 frame period of this ccd imager 40 . subsequently , the above - explained pulse x - ray projection and the x - ray image signal acquisition are repeated in the similar manner in the first x - ray imaging apparatus 100 . as previously described in detail , since the unnecessary electron charges produced during occurrence of the x - ray lags or trailing edges &# 34 ; l &# 34 ; are not read out as the x - ray image signals , no adverse influences caused by these trailing edges &# 34 ; l &# 34 ; can be avoided while acquiring the x - ray image signals of the biological body 2 under medical examination . a more detailed explanation will be made of the system controller 50 employed in the first x - ray imaging apparatus 100 shown in fig3 . this system controller 50 constitutes a major circuit element of the first x - ray imaging apparatus 100 . fig8 shows this system controller 50 and the relevant circuit . the system controller 50 sends various control signals to a camera control unit ( referred to as a &# 34 ; ccu &# 34 ; corresponding to the ccd drive unit of fig3 ) 40 , so that various ccd drive signals such as the field shift pulse &# 34 ; fs &# 34 ; and electronic shutter pulse &# 34 ; s &# 34 ; are supplied from this ccd 30 to the ccd imager 40 . on the other hand , the system controller 50 transfers another control signal to the high voltage generator 8 , whereby the pulsatory x - ray beams 12 are generated from the x - ray tube 1 . the system controller 50 is constructed of a clock generator 52 , a counter 54 , a rom ( read - only memory ) 56 and a buffer 58 , as shown in fig9 . the clock generator 52 generates clock pulses . these clock pulses are supplied to the counter 54 . when the counter 54 counts up a preselected number , since the outputs of this counter 54 are inputted to address terminals &# 34 ; ad &# 34 ; of the rom 56 , the output &# 34 ; o &# 34 ; of this rom 56 is supplied to the buffer 58 , whereby the above - described electronic shutter pulses &# 34 ; s &# 34 ; and field shift pulse &# 34 ; fs &# 34 ; and the like are derived from the buffer 58 . on the other hand , when the output &# 34 ; o &# 34 ; is produced from rdm 56 , this output &# 34 ; o &# 34 ; is also furnished to a reset terminal &# 34 ; rs &# 34 ; of the counter 54 so as to reset the counted value of the counter 54 . subsequently , a series of the above - described operation is repeated so that the above - defined system controlling operation is achieved . as previously stated , any types of ccd elements may be employed as the ccd imager 40 of the first x - ray imager 100 . for instance , referring now to a timing chart of fig1 a - 10d , the interlace scanning operation of the first x - ray imaging apparatus 100 will be described with employment of the it type ccd imager 42 ( see fig5 a ) and fit type ccd imager 44 ( see fig5 b ). in this second example , since the pulsatory x - ray beams 12 are produced at a period of 1 / 60 seconds , an odd field shift pulse ( fig1 b ) is generated at a timing &# 34 ; t 3 &# 34 ; when , for instance , the generation of the first x - ray pulse is completed , whereas an even field shift pulse ( fig1 c ) is generated at another timing &# 34 ; t 6 &# 34 ; when the generation of the second x - ray pulse is accomplished . such an operation is repeated . also , the electronic shutter pulses are produced at each of timings &# 34 ; t 1 &# 34 ;, &# 34 ; t 5 &# 34 ;,-- just before the respective x - ray pulses are generated . under the above - explained ccd imager controlling method , i . e ., the interlace scanning method , although 1 frame image is obtained by acquiring two temporally different x - ray pulses , the resultant image quality is substantially similar to that of the first example as shown in fig6 . as a third example , the fit type ccd imager 44 ( see fig5 b ) is employed as the ccd imager 40 and the first x - ray imaging apparatus 100 is operated in the interlace scanning mode , a timing chart of which is shown in fig1 a - 11d . in this third example , for instance , an odd field shift pulse shown in fig1 b is produced at a timing &# 34 ; t3 &# 34 ; when the generation of the first x - ray pulse shown in fig1 a is accomplished , and also an even field shift pulse indicated in fig1 c is produced at a timing &# 34 ; t 3a &# 34 ; shown in fig1 c . at this timing &# 34 ; t 3a &# 34 ; as shown by an arrow of fig1 , the odd field signal has been transferred from the light receiving section 25 to the storage section 26 in a frame transfer mode . furthermore , electronic shutter pulses shown in fig1 c are generated at a timing &# 34 ; t 5 &# 34 ; just before each of the x - ray pulses is generated . under this interlace scanning control operation , since both of the field signals may be synchronized with the x - ray pulses at the substantially same time phases (&# 34 ; t 3 &# 34 ; and &# 34 ; t 3a &# 34 ;), the resultant image quality may be further improved , as compared with that of the second example . either electronic shutter pulses as shown in fig1 c , or reverse - transfer pulses are produced at a timing &# 34 ; t 5 &# 34 ; just before the respective x - ray pulses shown in fig1 a are generated . in accordance with the fourth embodiment , the unnecessary image signals or electron charges caused by the x - ray trailing edges appearing in the photodiode part pd ( see fig4 ) of the ccd imager 44 can be swept out therefrom by utilizing the electronic shutter operation . otherwise , if the ccd imager is not equipped with such an electron shutter function , these unnecessary electron charges can be swept out therefrom by transferring these unnecessary electron charges from the light receiving section 25 to the drain section 27 , as illustrated by an arrow of fig1 . it should be noted that the typical response time of the conventional i . i . blanking unit is 2 to 3 milliseconds , whereas the typical response time of the ccd imager is shorter than 100 microseconds . in a fourth example , the ft type ccd imager 44 as shown in fig5 b is employed as the ccd imager 40 and the first x - ray imaging apparatus 100 is operated in the non - interlace scanning mode . as represented in a timing chart of fig1 , at a timing &# 34 ; t 3 &# 34 ; when each of the desirable x - ray pulses is ended ( see fig1 a ), a frame transfer pulse as shown in fig1 b is produced from the ccd drive unit 30 , instead of the above - described field shift pulse as shown in , for instance , fig6 b . fig1 is a schematic block diagram for showing an entire arrangement of an x - ray imaging apparatus 200 according to a second preferred embodiment of the present invention . the second x - ray imaging apparatus is so called as &# 34 ; a pulsatory x - ray biplane system &# 34 ;. in the pulsatory x - ray biplane system 200 , one x - ray tube 1f is provided at a frontal side of this system 200 , another x - ray tube 1l is provided at a lateral side of this system 200 , one image intensifier tube 3f and another image intensifier tube 3l are positioned opposite to the x - ray tubes 1f and 1l , respectively , via the biological body 2 under medical examination . furthermore , one ccd imager 40f is employed to receive an optical x - ray image from the image intensifier tube 3f , so that an x - ray image signal at the frontal side is supplied to one tv monitor 5f . the other ccd imager 40l is similarly employed to receive another optical x - ray image from the image intensifier tube 3l , so that an x - ray image signal at the lateral side is supplied to the other tv monitor 5l . both of the x - ray tube 1f at the frontal side and the x - ray tube 1l at the lateral side are energized by a high voltage generator 208 under control of a system controller 250 . similarly , both of the ccd imager 40f at the frontal side and the ccd imager 40l at the lateral side are energized by a ccd drive unit 230 under control of the system controller 250 . referring now to a timing chart shown in fig1 , an operation of the second x - ray imaging apparatus ( pulsatory x - ray biplane system ) 200 will be described . as is known in this medical field , these are adverse influences caused by the scattering x - rays in response to the pulsatory x - ray beam ( 12f , 12l ) projections at both the frontal and lateral sides ( see fig1 a and 16b ). for instance , as represented in fig1 c , undesirable signals &# 34 ; s l &# 34 ; caused by the scattering x - rays in response to projections of the lateral x - ray beam 12l , appear in the output of the frontal i . i . tube 3f , although no frontal x - ray beam 12f is generated from the frontal x - ray tube 1f . to avoid such adverse influences &# 34 ; s l &# 34 ;, the i . i . blanking pulses as shown in fig1 d were required in the conventional pulsatory x - ray biplane system ( not shown in detail ). however , according to the present invention , only frontal field shift pulses ( shown in fig1 e ) and electronic shutter pulses ( shown in fig1 f ) are produced , whereby such as an adverse influences of the scattering x - rays caused by these unnecessary signals &# 34 ; s l &# 34 ; can be completely prevented . that is to say , as shown in fig1 e , the frontal field shift pulses are produced from the ccd drive unit 230 under control of the system controller 250 at a timing &# 34 ; t 3 &# 34 ; when generation of the respective frontal pulsatory x - ray beams 12f with the normal pulse widths is completed . furthermore , the frontal electronic shutter pulses are produced as shown in fig1 f at a timing &# 34 ; t 5 &# 34 ; just before the respective frontal x - ray beams 12f . as a consequence , the adverse influences caused by receiving the lateral pulsatory x - ray beams 12l can be prevented with respect to the frontal x - ray image production . it should be understood that although not shown in this timing chart of fig1 , adverse influences caused by receiving the frontal pulsatory x - ray beams 12f can be avoided in a similar manner with respect to the lateral x - ray image production . fig1 shows a first internal circuit of the system controller 250 employed in the second x - ray imaging system 200 , whereas fig1 represents a second internal circuit of the system controller 250 employed therein . the first internal circuit is arranged by a clock generator 252 , two counters 254a , 254b and two roms 256a , 256b . the memory content of the first rom 256a is not equal to that of the second rom 256b . to the contrary , the second internal circuit employs two roms 258a and 258b , the memory contents of which are equal to each other , and also a delay circuit 255 . the output from the first rom 258a is supplied as a reset pulse directly to the reset terminal of the first counter 254a , and also via the delay circuit 255 to the reset terminal of the second counter 254b . from both of the first and second internal circuits , the first x - ray control signal &# 34 ; x 1 &# 34 ; and the second x - ray control signal &# 34 ; x 2 &# 34 ; are produced with a predetermined delay time , as shown in fig1 . as previously described in detail , in accordance with the present invention , since only the electronic charges produced by the desirable pulsatory x - ray beams can be derived as the effective x - ray image signals from the solid - state image sensor , the adverse influences caused by the pulsatory x - ray trailing edges or lags can be avoided without employing the conventional i . i . blanking unit , but by utilizing the electronic shutter function of the solid - state image sensor . furthermore , according to the present invention , since the conventional i . i . blanking unit having the above - explained slow response time is no longer required , no restriction is made in the operation speed of the x - ray imaging apparatus . in other words , quick movements of a biological body under medical examination can be sufficiently imaged by the x - ray imaging apparatus , according to the present invention , with keeping the better image quality . in addition , another adverse influence caused by the dark current of the ccd imager can be avoided by way of the electronic shutter function thereof in accordance with the x - ray imaging apparatus .