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WO1984000679A1 - Retroprojecteur microprogramme pour systemes tomographiques commandes par ordinateur - Google Patents

Retroprojecteur microprogramme pour systemes tomographiques commandes par ordinateur Download PDF

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Publication number
WO1984000679A1
WO1984000679A1 PCT/HU1983/000044 HU8300044W WO8400679A1 WO 1984000679 A1 WO1984000679 A1 WO 1984000679A1 HU 8300044 W HU8300044 W HU 8300044W WO 8400679 A1 WO8400679 A1 WO 8400679A1
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WIPO (PCT)
Prior art keywords
address
output
backprojection
register
read
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Ceased
Application number
PCT/HU1983/000044
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English (en)
Inventor
Jozsef Fehervary
Laszlo Mezoe
Peter Fueloep
Sandor Oery
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Medicor Muvek
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Medicor Muvek
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Publication of WO1984000679A1 publication Critical patent/WO1984000679A1/fr
Anticipated expiration legal-status Critical
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    • G06T12/20—
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2211/00—Image generation
    • G06T2211/40—Computed tomography
    • G06T2211/421—Filtered back projection [FBP]

Definitions

  • the invention relates to a firmware back projector intended primarily to perform the back projecting phase of the filtered backprojection applied in CT systems, which can be interfaced to the DMA channel of a mini-computer, which is capable of performing the partial or full backprojection of the slice scanned from any given profiles arranged in any sequence.
  • the image reconstruction can be performed in the following forms:
  • the theory of the first two methods is well-known, however, practically they can't be realized (computer problems: insufficient speed of algorithm, divergence, enormous central memory required, etc.).
  • the third method is based upon the Fourier-transformation, basicly the CT producers utilize this solution for image-reconstruction.
  • a well-known procedure is the so-called filtered backprojection.
  • Bp/r, ⁇ / is the density distribution of the backprojected image
  • P(r, cos/ ⁇ - ⁇ /, ⁇ ) are the projections to be backprojected
  • r and ⁇ are polar coordinates
  • ⁇ is the angle under the projections are measured during the scan.
  • a logical compromise among these contradictory measures is to perform the backprojection with finite linear interpolation and selecting the next neighbour among the interpolated values.
  • the backprojection can be performed by ⁇ .) analogic way ⁇ .) software ⁇ . ) hardware.
  • the first method has never been used in commercial CT equipment.
  • the backprojection should be a real-time processing (the pure software solution is too slow, taking into consideration the state-of-the-art scanners)
  • the software backprojection is theoretically obvious.
  • a CT scanner is built around a computer and the slowness of the data acquisition system of the first generation CT scanners promoted the software backprojection.
  • the post-reconstruction time of some minutes is hardly acceptable (the data acquisition takes less than 1 minute).
  • Illustrating the above mentioned with an excellent commercially available CT system (GE CT/T 7800) data acquition : 6-12 seconds post-reconstruction: 90-120 seconds.
  • GE CT/T 7800 data acquition : 6-12 seconds post-reconstruction: 90-120 seconds.
  • Even the development resulted the greater size of the image to be backprojected, nevertheless the operation to be accomplished is proportional to n (where nxn is the image-size).
  • the Densitome CT scanner (CGR, France) had an image size of 128 x 128, the image reconstruction time on a relatively fast POP 11/55 was about 4,5 minutes.
  • the present equipments have a size of 256 x 256, even some high spatial resolution equipments have a size of 512 x 512.
  • the latter image-size requires 64 times as much reconstruction time as the 128 x 128 required.
  • the image reconstruction is accomplished by software (due to the sequential nature of it) it results really 64 times slower reconstruction. Further analyzing the timing: the back- projection of a single profile to a single pixel requires at least the following operations:
  • the best choice is the hardware solution,however, the disadvantages are completed by the rigorous operating requirements (service, air-conditioning, size, etc.).
  • the backprojection to be accomplished in the CT systems seems to be the territory where the optimal solution can be approached by selecting the proper hardware-software ratio, i.e. by applying a firmware solution.
  • the task is to eliminate the disadvantages of the well-known backprojectors by designing a firmware equipment which is capable of economically performing the backprojection by digital precis on, by the speed of the hardware and by the flexibility of the software.
  • the substance of the invention is that it contains SINTAB memory containing a software generated table required by the backproj.ecting procedure, supported by input, output registers and control logic; read-address logic generating the addresses of the pixels on the profiles based upon the data contained in SINTAB memory, driving the address multiplexers of the convolution output memories; two convolution output memories connected to the latter through address multiplexes which have direct connection with the write-address locjic, supported by data multiplexer, containing the convolved or convolved and interpolated data to be back projected, capable to perform pipe-line operation with an external convolver through alternate buffers as well as parallel read/write logic; operating mode selector flip-flop connected to the output register of the SINTAB memory;
  • a favourable realization of the invention has a read-address logic containing: two intermediate registers (SIN and COS registers, respectively) containing the line and column address offset values required for the sequential backprojection, connected to the output register of the SINTAB memory;
  • the A input of the just mentioned multiplexer is connected to the output of the column address adder
  • FIG 1 is the overview of major components associated with the backprojector according to the invention.
  • Figure 2 is the outline of the address generation and Figure 3a, 3b contain the theory of the pixel-size correction.
  • the input of the SINTAB memory 2 is connected to the input register 1 as long as it's output joins the output register 3.
  • Each of the three networks are con-trolled by a control logic 4.
  • the input register 1 contains the data to be written in
  • the output register 3 stores temporarily the data read out
  • the control logic 4 generates the necessary address and control signals determined by the algorithm of the backprojection.
  • the output register 3 joins on one hand to the input of a read-address logic 5, on the other hand it is connected to the input of an operating mode selector flip-flop 21.
  • the output of the component 21 is connected to one of the inputs of an address comparator 22 whose output is determined by the fact the pixel just under backprojection in on the profile or it is out of the range of the profile.
  • the output of the read-address logic 5 is fed-back to the other input of the address comparator 22.
  • the same signal is connected to the B and A inputs of the address multiplexers 14, 15, driving the address lines of the convolution output memories 16, 17, respectively.
  • the multiplexers 14, 15 are driven through their A and B inputs by a write-address logic 25.
  • the output of these multiplexers joins the convolution output meinorie ⁇ 16 and 17, respectively.
  • the memories contain the convolved profiles, the profiles are written by a computer through the inputs "DATA IN".
  • the data outputs of the convolution output memories 16, 17 are connected to the inputs of the data multiplexer 18.
  • This multiplexer forwards the data just read out of one of the convolution output memories to the input of the data register 19.
  • the enable input of the data register 19 joins one of the outputs of the address comparator 22.
  • the other inverted output of the address comparator is connected to the enable input of the zero register 20. Both the outputs of zero register 20 and data register 19 are bussed to one of the inputs of the adder 24.
  • the other input of this adder joins the data out lines of the image memory 23 forming the same time the output of the backprojector unit (OUT), as long as the output of the adder is connected to the data in lines of the image memory.
  • the image memory 23 stores during the backprojection the partially backprojected image as well as at the end of the back projection the image reconstructed is forwarded through it's "OUT" output to the computer or display generator not delineated here.
  • the logic contains an intermediate SIN register 6 and an intermediate COS register 7 for storage of the data read out of the SINTAB memory 2 through the output register 3, both the 6 and 7 components are connected to the input of the read- address logic 5.
  • the output of the intermediate SIN register joins the input of the line address adder 9 as well as the output of the intermediate COS register joins the column address adder 11.
  • the B input of the lins address multiplexer 8 is connected to the output of the line address adder 9, as long as it's A input is connected to the input of the read-address logic 5.
  • the output of the line address multiplexer 8 joins the input of the current line address register 10, the output of the component 10 is connected on one hand to the B input of the address multiplexer 12 on the other hand it is fed back to the input of the line address adder 9.
  • the A input of the address multiplexer 12 is connected to the output of the column address adder 11 as well as it's output is connected to the input of the current operating point register 13.
  • the output of the component 13 forms the common output of the whole read-address logic 5 and it is fed back to one of the inputs of the column address adder 11.
  • the survey of the operation postulates that one of the convolution output memories 16 or 17 already contains the convolved or convolved and interpolated data of a given profile (Table II).
  • a further condition of operation is that the SINTAB memory already contains the data necessary to the backprojection according to Table III.
  • the image memory 23 Before initiating the backprojection, the image memory 23 contains any given background offset value (mostly zero). During the backprojection it stores the partially backprojected image according to Table IV
  • the value located at the ⁇ address of the SINTAB memory is read out and it's operating mode bit is clocked through the output register 3 into the operating mode selector flip-flop 21.
  • the address comparator 22 decides if there is anything to be backprojected or rather the projection of the pixel is not within the range of the given profile. Certainly the range is different if a profile contains 256 or 512 samples. Having clocked the value into the operating mode selector flip-flop, the backprojection of the first profile is similar to any n-th profile.
  • the SINUS value corresponding to the profile is read out and stored in the intermediate SIN register 6.
  • the corresponding COSINUS value is read out and stored in the intermediate COS register 7.
  • the base address (16 LS and 8 MS bits) is clocked into the current line address register 10. This address is the coordinate of the reference pixel (1 line 1 pixel) on the profile under backprojection. Now until the completion of the backprojection of the profile the B input is selected at the line address multiplexer 8. The base address is to be written from the current line address register through the B input of the address multiplexer 12 into the current operating point register 13, too.
  • Such the projection address of the first pixel is stored in point register 13 , now until the completion of the backprojection ⁇ f the profile the component 10 stores the projection address of the first pixel of the line just under backprojection as well as point register 13 stores the projection address of the pixel just under backprojection.
  • the mathemat hical background of the address generation in the coordinate system is surveyed on the basis of Table V and Fig. 2, The angles ⁇ 1 , ⁇ 2 , ⁇ 3 and ⁇ 4 referenced there are the angles under the projections are measured in the different quarters of the coordinate system.
  • the read-modify-write cycle begins at the image memory 23. Since the output of the current operating point register 13 is connected to the address comparator 22 too, the latter is capable to decide if the address is within the range or not. After a 200ns period the data read out of the convolution output memory 16 or 17 (depending on the profile) can be clocked into the data register 19. Now the state of the comparator determines if the data just read out of the convolution output memory or ⁇ is to be added to the data read out of the image memory.
  • the adder 24 performs the addition of the two operands and the sum is written back into the image memory as the completion of it's read-modify-write cycle.
  • a decoder is enabled to sense if a whole line of the image is already processed. If not, so the input of the current operating point register 13 is to be connected with the output of the column address adder 11 by selecting the A input of the address multiplexer 12. The coordinate of the next pixel on the profile (+COS step) is generated by this time at the output of the column address adder 11.
  • the cycle-time of the backprojection (pixel by pixel) within a line of the image is 800ns. If a whole line of the image is already processed, the current line address register 10 is to be clocked.
  • the input of component 10 is connected with the output of the line address adder 9 by selecting the B input of the line address multiplexer 8, The coordinate of the first pixel of the next line on the profile (+SIN step) is generated by this time at the output of the line address adder 9. This value is clocked into 10, If the whole image is not yet processed, the B input of the address multiplexer 12 is selected and the content of the current line address register 10 is written into the current operating point register 13. If the whole image is already processed a shut-down sequence is initiated. At this moment the state of the convolution output memories 16, 17 can be checked if the backprojection of a new profile is to be initiated.
  • the backprojector is restarted. If no new profile is available, the backprojector is waiting in IDLE state or lets the computer to read back the content of the image memory.
  • the backprojector according to the invention performs the pixel-size correction on the basis of the following equations.
  • the distance of data acquisition during a translation by the central beam 26 and a fan beam 27 are (Fig. 3a);
  • ⁇ is the angle between the given fan and central beams (determined by the collimator geometry); n is the number of samples/profile; a is the pixel size determined by the central beam and a' is the pixel size determined by the given fan beam.
  • the backprojector is capable to process the data convolved by the computer.
  • the interpolator unit is located on the data board alongside with the convolution output memories.
  • the interpolator computes the linear interpolation of the data convolved and writes them into the convolution output memories in accordance with Table II.
  • the backprojector is capable to receive the input convolved data from a pipe-line convolver. If so, the input is the preprocessed data for the convolver and the output is the whole reconstructed image from the backprojector.
  • - can be configured as a stand-alone unit or capable to operate parallel to a pipe-line convolver.
  • the convolution output memories can be read in 200 ⁇ s and selecting a read- -modify-write cycle time of 800ns (theoretically it could be slightly faster) at the image memory it is feasable to backproject the profile simultaneously into four image memories (storing different portions of the image to be reconstructed).
  • the equipment maintains the flexibility of a software solution (applying a software generated SINTAB memory content according to the operating mode selected).
  • the equipment substitutes an expensive device, the array-processor.
  • the maintenance is economical (only the special purpose hardware and not a universal hardware is required, the configuration of the central computer can be poorer, some add-on hardware for the corrections can be saved).

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  • Image Processing (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Medical Treatment And Welfare Office Work (AREA)

Abstract

Rétroprojecteur microprogrammé pour systèmes tomographiques commandés par ordinateur contenant un tableau produit par logiciel nécessaire au procédé de rétroprojection, supporté par des registres d'entrée, de sortie et une logique de commande; une logique d'adresse de lecture produisant les adresses des pixels (éléments d'images) sur les profils d'après les données contenues dans la mémoire SINTAB, attaquant les multiplexeurs d'adresses des mémoires de sortie de circonvolution; deux mémoires de sortie de circonvolution connectées à ces dernières par l'intermédiaire des multiplexeurs d'adresses qui ont une connexion directe avec la logique d'adresse d'écriture, supportée par le multiplexeur de données, contenant les données circonvolutées et interpolées à rétroprojeter, capable qu'un fonctionnement en pipeline avec un circonvoluteur extérieur par l'intermédiaire de tampons alternés ainsi qu'une logique parallèle lecture/écriture; une bascule d'un sélecteur du mode de fonctionnement collectée au registre de sortie de la mémoire SINTAB; un comparateur d'adresses validant ou invalidant la correction de densité du pixel (éléments d'images) en cours de rétroprojection, connectée à la sortie de ce dernier ainsi qu'à la logique d'adresse de lecture; un registre de zéro, contenant la valeur zéro à ajouter en cas d'invalidation de la correction de densité; un registre de données connecté à la sortie du multiplexeur de données dont la sortie est validée ou invalidée en fonction de l'état de la sortie du comparateur d'adresses; une mémoire d'image contenant les valeurs de densité des pixels; un additionneur capable d'ajouter la valeur qui vient d'être lue de la mémoire d'image et sa valeur correspondante sur le profil rétroprojeté.
PCT/HU1983/000044 1982-08-19 1983-08-19 Retroprojecteur microprogramme pour systemes tomographiques commandes par ordinateur Ceased WO1984000679A1 (fr)

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HU822702A HU188196B (en) 1982-08-19 1982-08-19 Firmware back-projector for ct systems

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JP (1) JPS59501804A (fr)
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WO (1) WO1984000679A1 (fr)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2654065A1 (de) * 1975-11-28 1977-06-08 Picker Corp Tomographiesystem mit einem extrem schnellen prozessor
US4066903A (en) * 1974-07-20 1978-01-03 Emi Limited Radiology
US4081681A (en) * 1976-01-15 1978-03-28 Emi Limited Treatment of absorption errors in computerized tomography
DE2656634A1 (de) * 1976-12-14 1978-06-15 Siemens Ag Anordnung zum herstellen eines koerperschnittbildes und verfahren zum betrieb der anordnung
US4295195A (en) * 1978-10-24 1981-10-13 E M I Limited Radiography
EP0052342A2 (fr) * 1980-11-17 1982-05-26 Kabushiki Kaisha Toshiba Dispositif de traitement de données pour système de tomographie par calculateur

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4066903A (en) * 1974-07-20 1978-01-03 Emi Limited Radiology
DE2654065A1 (de) * 1975-11-28 1977-06-08 Picker Corp Tomographiesystem mit einem extrem schnellen prozessor
US4081681A (en) * 1976-01-15 1978-03-28 Emi Limited Treatment of absorption errors in computerized tomography
DE2656634A1 (de) * 1976-12-14 1978-06-15 Siemens Ag Anordnung zum herstellen eines koerperschnittbildes und verfahren zum betrieb der anordnung
US4295195A (en) * 1978-10-24 1981-10-13 E M I Limited Radiography
EP0052342A2 (fr) * 1980-11-17 1982-05-26 Kabushiki Kaisha Toshiba Dispositif de traitement de données pour système de tomographie par calculateur

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EP0116590A1 (fr) 1984-08-29
JPS59501804A (ja) 1984-10-25
HU188196B (en) 1986-03-28

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