CN1164313A - Normalization of tomographic image data - Google Patents

Abstract

A monitoring detector assembly is positioned outside the scanning plane of a CT scanner to insure detection of unattenuated x-rays from the x-ray source of the scanner. The monitoring detector assembly preferably provides a sequence of monitor detection measurements simultaneous with the sequential acquisition of the image data from the image detectors during each projection of the scan by a filtered CT scanner. The image data are monitored using the closest in time monitor detection measurement.

Description

The normalization of x-ray tomography image data

The application has U.S. Patent Application Serial Number NO. co-pending relevant together, this U.S. Patent application is applied for simultaneously with the name of John Dobbs and Ruvin Deych, and transferring present assignee (agent's recording mechanism ANA-56), exercise question is " X line focus motion compensating device " (X-RAY FOCAL SPOT M0VEMENT COMPENSATION APPARATUS).

Usually, the present invention relates to improve the quality of x-ray tomography scanned picture, relate to the pictorial data normalization of roentgen radiation x amount reading that use obtains especially in CT (area of computer aided tomography) describes will from this scanning, obtaining.

Third generation CT scanner comprises X line source and the X line detector system on the radially opposite side that is separately fixed at annular disk.The latter is rotatably mounted in the portal support, should rotate around rotating shaft continuously by dish in scanning like this, meanwhile, passes object arrival detector system in the opening that is positioned at this dish from the X line of X line source.

Detector system generally includes a detector array of lining up a single assembling by circular arc, and this circular arc has a center of curvature, locates to send radiation from the X line source at this point (being referred to as focus).X line source and detector array are all fixed, so that the X thread path between this source and each detector all is positioned at the same plane vertical with the rotating shaft of this dish (after this being called " slice plane " or " plane of scanning motion ").Because ray path is risen in basically a point source and extended to detector with different angles, so ray path forms fan-shapedly, and often uses " fan " light beam one to speak to describe at any one time all ray paths.Measure the X line that constantly detects in scan period one and be considered to a branch of " ray " by single detector.By all material part decay, therefore produce as a single intensity value conduct thus is the function of material density on this path also to this ray on its path.Projection or video, just the X line strength is measured usually and is carried out on the everywhere of a plurality of angle positions on the dish.For example, scanner can carry out 2880 projections in continuing about 2 seconds single sweep, and each projection obtains 384 data readings with a data-acquisition system (DAS).

The image of rebuilding according to the data of obtaining at all projected angles in scanning will be to pass the section of scanned object along the plane of scanning motion.Density image for object cross section or " slice plane " in " reconstruction " " visual field " in the plane of scanning motion of determining, usually rebuild this image with cell array, wherein each pixel in the array is that all pass the value of the decay of the light of its relevant position in the plane of scanning motion in scanning in representative.When light source and detector when object rotates, ray from different directions or projected angle see through object, pass the pixel location of various combination.Generate the density distribution of object in these slice plane according to these measured value mathematics ground, and each pixel brightness value is set represents this distribution.The result is exactly the cell array with different value, and it has represented the density image of this slice plane.

In order to produce high-quality image, CT scanner designer makes great efforts to make the error source minimum.So, adopt certain methods usually or come correction error by the correction design or by calibration.For example, in zero X line level, it is important making the signal bias minimum and making it stable, and any like this measured value all will comprise the known constant skew that can make correction.In addition, under full scale chi (full scale), provide the X line and measure, do not have " air " of absorbing material data in the X thread path, make thus because drift in the gain and full scale are measured uncertain caused error minimum down so that be created in.Therefore, two reference points have been arranged, correction data between these 2.Representing between 2 of zero-sum full scale, the curve that concerns between an expression X line level and the data value is being arranged.Because the signal of telecommunication changes with nonlinear way with signal intensity, what cause concerning between X line level and data value is non-linear.So, in order to calibrate this system, the material (for example, water, polyethylene, placements such as polyvinyl chloride) of the known absorbing value of predetermined thickness on the path of fan light beam, and is produced data.These data will be represented the point on this curve.Use these known materials to make and to determine concrete correct dose level and the detector efficiency that scans.Use known technology can easily determine to generate and store look-up table like this by optimal multinomial.

Under the condition of guaranteeing high-quality x-ray tomography image, data represented all detectors also are important to the same detection of any specified rate photon.If representative receives a large amount of photons from a detector during measuring data are different from the data that receive from every other passage to identical measurement, the result illusion occurs in the image of rebuilding.Therefore, adopt certain methods to calibrate the skew and the gain of each data channel in the past, the error that these two factors are caused is reduced to minimum.

Other error is caused by the X line source.Provide constant X line flux output although the X spool is set, the internal radiation of official hour time limit can change between each detector in the number of photons on the detector.As above-mentioned, known each photon all can produce noise.Therefore, the number of photons that detects is few more, and signal to noise ratio (S/N) is poor more.

In addition, the X line source can fluctuate in scan period, particularly worked as it and had arrived life span, when producing the cymomotive force of X line; And under at least a situation, even the photon that the X line source comes to offer for each video determined number is set, signal also can degenerate.Be called " filtering " (filtered) in the CT scanner of CT scanner at some, the measurement that specific video carries out is all accurately carried out at one time by the detector in the array owing to not all, therefore the problem that signal to noise ratio changes in sweep time is even more serious problem.And each detector and filter coupled, each detector is read with a predetermined sequence for each projection like this.For example, licensed to the U.S. Patent No. 4,769,827 (calling " patents of Uno etc. " in the following text) of Uno etc. on September 6th, 4,547,893 and 1988 referring to the U.S. Patent No. that licensed to Bernard M.Gordon on October 15th, 1985.

For example shown in the patent of Uno etc., it can relatively be with it normalized reference signal to be provided at the data-signal that obtains in the video that known opposite end at arc image detector array is installed a pair of reference detector respectively.In each projection, all use these reference detectors to detect X line level one time, the x-ray measurement value that the measured value that is provided carries out near the detector by these array central authorities very much is because the patentee thinks that these values are than more important by the resultant measured value of the detector at detector array two ends.Suppose always can not decay by the X line that reference detector is surveyed.Unfortunately, use this structure, the patient or the patient support table of correct location just can hinder one or two reference detector in the one or many projection of scanning, cause these projections are detected the misdata of relevant X line level by reference detector.In addition, time period of occupying of the measurement of being undertaken by each reference detector in projection equals the All Time (T of projection _o) and less than reading the time spent (T of reference channel institute _Rs).Similarly the time period is used to measure and read all passages, and each cycle of 502 roads (500 data passages and 2 reference channels) all interlocks arranged 502 intervals of single projection.Therefore, same reference signal is used for all 500 data passages, then surveys and time of reading each data-signal has nothing in common with each other between the road of 500 data passages and road.The result, resulting in time will be at a distance of its precision of farthest data-signal (suppose these signals survey) than low with the signal accuracy that obtains by the approaching detector (middle detector supposes it is detector 250 and 251) of reference detector 1 and 502 measurements of carrying out in time by outer detector near reference detector 1 and 502 with reference signal.

General objects of the present invention provides a kind of X line chart image data normalization device of third generation CT scanner, and it can reduce and overcome the problem of prior art effectively.

The present invention's purpose more specifically provides the normalization of the viewdata signal relevant with each projection of the CT scan of filtering, to reduce the time dependent effect of signal on the viewdata signal.

Another specific purposes of the present invention are roentgen radiation x magnitudes of CT scanner in the monitoring scanning, so that the variation of X line strength is proofreaied and correct.

Even an other purpose of the present invention be under observation patient or the patient support table for the incorrect location of image detector array, the normalization of the viewdata signal relevant with each projection of the CT scan of filtering also can be provided.

The more accurate filtering CT scan of the data data that provide than the described system of patent by Uno etc. just are provided another purpose more of the present invention.

Another purpose more of the present invention just provides improved filtering CT scanner, does not require that wherein significant calculating obtains the fluctuation effect of X line flux on the data in just reducing to scan.

The present invention also has an other purpose, just provides improved CT scanner, wherein can fill the rapid fluctuations of X line flux perhaps, prolongs the life-span of X line source.

Other purposes of the present invention propose subsequent section ground and partly explanation.Therefore the present invention comprises the device that has its structure, combination of elements and configuration of components, and relates in several steps and these steps one or more for the relation of other steps and the method for order.They are all incited somebody to action in below the detailed disclosed application range and are illustrated that by example they all will be illustrated in claims.

A kind of improved CT scanner comprises the X line source, is used for producing X ray in x-ray tomography scanning; X line sniffer is used for surveying the X ray that is sent by the X line source in x-ray tomography scanning; With the x-ray tomography scanning means, be used in x-ray tomography scanning, rotating the X line source at least around scanning object.This scanner comprises an improved system and uses the improving one's methods of output flow of monitoring scanner X line source.

According to one aspect of the present invention, rotation monitoring detector assembly is with in each video of one scan, along with light source and pictorial data detector assembly between the path that separates of light path, be preferably in the scanning plane outside, intercepting by the X line of the X line source emission part that do not decay, so that read monitor signal in scanning field of view no any object.

According to another aspect of the present invention, in the filtering CT scanner, in measuring, the alphabetic data of each video of this scanning carries out the monitoring reading more than once by predefined procedure.Each DATA REASONING value of each video preferably is normalized to the function that is worth immediate monitoring accuracy of reading in time with DATA REASONING, so that reduce in the signal of image detector reading over time.

In a preferred embodiment, the monitoring detector assembly comprises a plurality of detectors, wherein represents each monitoring reading from the signal sum of detector, so that increase the resolution of monitoring probe assembly.

By detailed description with reference to the accompanying drawings, invention will be more fully understood, wherein:

Fig. 1 is the simplification end-view that comprises according to the third generation filtering CT scanner of monitoring detector assembly provided by the invention;

Fig. 2 is that the simplification of filtering CT scanner shown in Figure 1 is radially schemed;

Fig. 3 is the block diagram of support circuit of the arc image detector array of pictorial data detector and Fig. 1 and Fig. 2;

Fig. 4 is the simplification isometric chart of monitoring detector assembly;

Fig. 5 is the block diagram of support circuit of the monitoring detector assembly of monitoring detector and the scanner that is used for Fig. 1 and Fig. 2 designed according to this invention.

Fig. 6 be according to of the present invention in a projection reading time line (time-line) the figure example of the monitoring detector assembly reading of the image detector reading of a sequence and a sequence, and a plurality of arrow represents which monitoring assembly reading optimum is used for each image detector reading of normalization;

Fig. 7 is the signal to noise ratio figure as the probe access function, and wherein each image detector all is subjected to use " sliding window " method by normalized full scale chi fan beam intensity;

Fig. 8 is the signal to noise ratio schematic diagram as the probe access function, wherein each image detector all is subjected to full scale chi fan beam intensity, and in each projection video, to use nearest four monitoring readings to be example, according to the preferred embodiments of the present invention with final data normalization;

Fig. 9 is the signal to noise ratio schematic diagram as the probe access function; Wherein each image detector all is subjected to full scale fan beam intensity, and to use nearest eight to monitor readings and be example in each projection video, according to the preferred embodiments of the present invention with final data normalization;

Figure 10 is the signal to noise ratio schematic diagram as the probe access function, wherein each image detector all is subjected to full scale chi fan beam intensity, and in each projection video, to use nearest 16 monitoring readings to be example, according to the preferred embodiments of the present invention with final data normalization; And

Figure 11 and Figure 12 are the signal to noise ratio schematic diagrames as the probe access function, and wherein each image detector all is subjected to full scale chi fan beam intensity, and uses interpolation technique with final data normalization.

For understanding the present invention more completely, describe with reference to accompanying drawing.Fig. 1 and Fig. 2 representative embody third generation filtering CT scanner 20 of the present invention through revising.The described system of Fig. 1 and 2 is included in the dish 22 that installation is rotated on the fixing portal support 24.Dish 22 supports the arc pictorial data probe array assembly 28 that X line source 26 and comprises a plurality of detectors 50.Light source 26 rotates around rotating shaft 30 (direction of extension is vertical with drawing shown in Figure 1) with detector assembly 28, and the object 32 around the central opening that passes dish rotates in CT scan thus.Object 32 can be patient's a part, such as head or trunk.Radiation takes place through slit 44 (shown in Figure 2) in light source 28, and thus in interior definite continuous fan-shaped x-beam 34 (see figure 1)s of scanning plane (vertical with rotating shaft 30, as to see 42 among Fig. 2), this light beam passes the detector detection of object 32 backs by assembly 28.One anti-scatter array 36 between the detector of object 32 and assembly 28 to prevent that significantly scattered beam is detected device and detects.The detector number is 384 and covers 48 ° arc in a preferred embodiment, and this number and angle can change certainly.Dish 22 preferably by light material for example aluminium make, and make it fast and smoothly around axle 30 rotations.Dish 22 is open closed-in constructions, and object 32 can be put into the location through the opening of dish like this.For example can be at pallet or table 38 upper support objects 32, in fact they should be transparent to the X line certainly.When dish 22 rotations, periodically changing in the assembly 28 surveyed device 50 samplings with predefined procedure, come to be provided at the discrete measured value of X line that scanning plane passes object 32 from a plurality of projected angles.Then, utilize appropriate signals treatment facility (will be illustrated) these measured values to be carried out electronics and handle, produce final pictorial information thus by known mathematical method below in conjunction with Fig. 3.This pictorial information is placed in the memory then, analyzes in computer or suitably demonstration.Final image will be the part of the whole that " visual field " (shown in circle among Fig. 1 40) lining of scanner comprises in the plane of scanning motion (42 shown in Fig. 2).Say in a way, system described in the application co-pending of this system and sequence number No.08/190945 is identical, this application co-pending proposes on February 3rd, 1994 with the name of John Dobbs and David Banks, and name is called " the cordwood system type detector configuration of x-ray tomography scanning system (MODULAR DETECTORARRANGEMENT FOR X-RAY TOMOGRAPHIC SYSTEM) " and transfers this assignee together.

In a preferred embodiment, assembly 28 comprises 384 data detectors, in each projection (comprising 2880 such videos) of scanning, order reads these data detectors in the time of 576 microseconds, thereby each detector is read in the interval of 1.5 microseconds.With this service speed, it is very important that the requirement in the calculating becomes.

As shown in Figure 3, each data detector 50 of probe array assembly 28 constitutes an overall part with 48 data-acquisition systems of representing (DAS).DAS48 also comprises preamplifier, low pass filter and the integrator 52 that is used for to the output amplification of each detector of each projection, filtering, integration.The output of each preamplifier, low pass filter and integrator 52 is connected with the multiplexer 54 of DAS48, being used for sequentially output with preamplifier, low pass filter and integrator 52 offers in the input of modulus (A/D) transducer 56 of DAS48, so that be these Analog signals'digital signals of representative with analog signal conversion.The output of the digital signal of A/D converter is applied in the digital signal processor 58 to DAS, it with this storage in memory 60.Processor 58 comprises CPU (CPU), is used for operation with each element of known manner control DAS48, comprises the integration circulation of preamplifier, low pass filter and integrator 52.Memory 60 is enough big, can store at least one group of partial data for a whole scanning.These data can be recovered, and image can be rebuild and be presented on the display 62 with known manner.About this point, memory preferably also links to each other with master computer 64, one group of processor preferably is installed is come image reconstruction, and link to each other so that show the image of rebuilding with display 62.In this case, all detectors all link to each other with a multiplexer.Should be understood that these detectors can be divided into two or more groups, every group of detector all links to each other with A/D converter with its multiplexer, and handles subsequently and store.This has improved the speed of service, but will increase extra hardware costs.

With reference to Fig. 2 and 4, according to one aspect of the present invention, the monitoring detector assembly 70 of monitoring X line source 26 outputs is placed on the outside of the plane of scanning motion 42 in each scanning, therefore the also outside of 40 (see figure 1)s in the visual field, guarantee that thus monitoring detector assembly 70 can both receive unbated basically X line with full intensity in each projection of each scanning regardless of what being put and where be placed in visual field 40.Best, monitoring detector assembly 70 relative X line sources 26 are fixed, and rotate with dish 22 apart from its nearer place than object 32 at distance X line source 26.One hole or slit are determined that element 72 is organized between 70 assemblies in source 26 and monitoring detection and are determined unbated substantially X Line beam 74.When the output of the predetermined detector in the detector 50 that is read probe array assembly 28 for each projection by DAS48 (seeing shown in Figure 3), monitoring detector assembly 70 provides the signal of the X line flux that expression only surveyed by the monitoring detector assembly in the sampling interval of pre-selected.

Usually, foundation and use monitoring detector assembly 70 are found out the primary relationship of x-ray tomography scanning.As shown in Figure 4, when in object 32 is placed on the plane of scanning motion 42 in " visual field " 40, going forward side by side line scanning, produce the X lines along arriving corresponding detector 50 respectively along separate routes from light source 26.These X lines that pass object 32 are partly decayed by object.Determine each detector of corresponding light route of part attenuation measurements obtain along to(for) each projection by the input X line strength (that is the intensity of surveying by corresponding detector 50 wherein) and the ratio of output X line strength (that is the output in source 26).Therefore, for K passage: $\left(1\right)---\frac{I_{\mathrm{ko}}}{I_k}=e^{-\mathrm{l\μdL}}$ In the formula, I _KoIt is the initial or output intensity that is used for the light source 26 in K road; I _kIt is the input intensity by the corresponding detector 50 in K road after the corresponding light path; And e is the constant as the end of natural logrithm; μ is an attenuation coefficient; And L is the thickness of X line along material that corresponding light path is passed.

As above-mentioned, in prior art, I _KoAnd I _kNot simultaneously measured.Measure I when in machine, not having object _Ko(measured value of air) measures I when promptly in machine scanning object being arranged _kThe problem of this method is when carrying out measuring for twice, and light source is not with phase same rate emission X line.For addressing this problem, according to one aspect of the present invention, use monitoring detector assembly 70 in both cases, promptly air is measured and the X line output intensity of measurement light source 26 independently among the scanning of object 32.This can obtain using, and the monitoring reading is normalized, the final relation of the decay of surveying, formula as follows: $\left(2\right)---e^{-\mathrm{l\μdL}}=\frac{I_{\mathrm{ko}}\left(t_o\right)M_j\left(t_j\right)}{M_0\left(t_o\right)I_{\mathrm{kj}}\left(t_j\right)}$

In the formula, M _o(t _o) and I _Ko(t _o) be at moment t _oCarry out the intensity measurements of being undertaken by the monitor assembly 70 and the detector 50 in K road during air is measured;

Mj (tj) and K _Kj(tj) be the intensity measurements of during moment tj carries out the j time projection, being undertaken by the monitor assembly 70 and the detector 50 in K road.

Therefore, according to one aspect of the present invention, intensity measurements I _Ko(to), M _o(to), I _Kj(tj) and M _j(tj) all be on the time period that prolongs, to obtain.The time interval of selecting each ionization meter is as the compromise proposal between data acquisition speed and quantum noise.Because patient often moves, wish to obtain as quickly as possible whole image.Yet, the influence that the signal that the fact that each data in the data set relevant with each intensity measurements all will be subjected to discrete X line quantum being worked with information is associated changes.Therefore, from the viewpoint of noise, preferably spend the time as much as possible to carry out each ionization meter.The speed that is produced the X lines by light source 26 is provided with this actual compromise proposal, and this speed depends on cost, weight and the power of X-ray pipe and be used for high voltage supply source to the X-ray pipe power supply of light source 26.The time of each projection is to survey enough X lines so that there is not the needed time of remarkable noise testing.Therefore, clearly, each the intensity measurements I in the equation (1) of each road and each projection _o(to), M _o(to), I (t) and M (t) are solid cubic content branch (really integrals).For example: $\left(3\right)---I_o\left(t_o\right)={\∫}_{t_o-\mathrm{\Δt}}^{t_o+\mathrm{\Δt}}F(t_o-g)I\left(g\right)d\left(g\right)$

In the formula, F (t _o-g) be that the filtering letter causes;

G is the time that a photon arrives.For M _o(to), I (t) and M (t) also can write out similar expression formula.

By using a kind of analog filter that is used for the known type of CT scanner, can carry out integration to each intensity measurements with electronics method.This filter is the part of each preamplifier, low pass filter and integrator 52 and preamplifier, low pass filter and integrator 80 (below in conjunction with Fig. 3 and 5 explanations), it uses a kind of weighting function, promptly, be the function F (to-g) of the time difference between the photon time of advent (i.e. " g ") and the measurement time t o, make up the electric charge (charge) of a large amount of quantum.Before the time of sampling filter signal, measurement time t o is a known constant.Each preamplifier, low pass filter and integrator 52 and 80 are with charge integration, to provide the signal integration that is equal to equation (3).The time intervals 2 Δ t must long enough can comprise function F (to-g).

I _o(to) and M _o(to) relation between is how much and electrical relation.It depends on the solid angle of two detectors (that is, monitoring detector and be used for a detector of this array in K road), the relative intensity of X line on the electricity gain of these two detectors and this both direction.These three factors, i.e. solid angle, gain and relative intensity are at two measuring intervals of TIME t _oWith time t _kBetween should be made as far as possible and be constant.When obtaining the ratio of equation (2), all factors all can be omitted, and can measure ∫ truly like this _Udl, do not have the variation of machine overrun.

Use this method that certain prerequisite is arranged.The time of supposing to carry out the integration of each intensity measurements I and M is identical.As long as the gain, solid angle and the intensity that produce between any twice Measuring Time do not change, then can allow the Light Difference of measured value.For be sure oing that above-mentioned equation keeps true, not only in the long time period from the video to the video, and in the sub-fraction of the single scanning of electronics reading system, to each video of detector array repeatedly (being 8 times in a preferred embodiment) read X line monitoring detector assembly 70.This point is opposite with prior art, preferably only relates to X line monitoring reading in the circulation of each detector readings once in prior art, and reads at each and not have a plurality of monitoring readings in the circulation.The present invention is used for CT scanner, consequently can allows X line flux to fluctuate faster.The rapid fluctuations of X line strength is the signal that the X-ray tube lifetime stops.Therefore, adopt the present invention, can prolong the life-span of X-ray pipe effectively.

Details are seen shown in Figure 4, preferred monitoring detector assembly 70 comprises the detector array of 16 detectors 76 placed side by side, and carry out following function: (a) collimation of light beam 34 (shown in Figure 1) is fanned in monitoring, it as U.S. Patent Application Serial Number the explanation in the application total co-pending of No., this application exercise question is " an X line focus motion compensating device ", and the name with John Dobbs and Ruvin Deych proposes (agent writes down number ANA-56) simultaneously; (b) the X line strength of monitoring light source 26 is so that carry out normalization according to the present invention is said to data.Detector 76 best (but unnecessary) is identical with the detector 50 of collecting data.Determine that to slit element 72 provides a diamond hole 78, like this when the time with monitoring detector assembly 70 correct collimations, the rhombus light beam irradiates is to detector 76, so that fall to having the flux of maximum on each central detector 8 and 9, do not have X line flux on two end detectors 1 and 16, and the flux of surveying increases progressively to central detector 8 and 9 from detector 2 and 15.As can be seen, on one central detector 8 and 9 identical flux is arranged, detector to 7 with 10 each on flux identical but still less is arranged, detector to 6 with 11 each on flux identical but that also will lack is arranged, have less and identical flux on two detectors 5 and 12, or the like.

With reference to Fig. 3 and 5, each monitoring detector 76 and preamplifier, low pass filter links to each other with integrator 80, for example links to each other with resistance 82 successively, to produce the electric current of summing junction 84.Summing junction provides the low statistical noise that has of the monitoring reading of representing the non-decay of light source 26 X line flux, summation current signal.Need only monitoring assembly and detect whole light beams 74, then the location independent of summing signal and light beam 74.The X line flux of being surveyed by monitoring detector 76 is big more, and the summing signal at node 84 places is big more.Be applied at the summing signal that node 84 provides in the input of A/D converter 86, it offers digital output signal digital signal processor 88 successively again.The Monitoring Data of being handled by processor 88 is stored in the memory 90, and is used for the data normalization that will collect in each projection of one scan according to principle of the present invention.Should be appreciated that and to come the processor 58 of configuration process data-signal and the processor 88 of processing Monitoring Data by a kind of uniprocessor commonly known in the art.Similarly, memory 60 and 90 can be configured to single random-access memory (ram) integrated circuit or such circuit bank.The data of collecting in each X-ray projection can be by normalization when being written into memory.Yet, when this processing is high speed operation, when just in the interval of 1.5 microseconds, reading each data detector 50, preferably after scanning in memory 60 sense datas with data normalization.Content in the memory 60 and 90.Preferably read to handle by array processor and display 62 by master computer 64.

Should know that 76 pairs of damages from incident X-ray flux of monitoring detector are very fragile, cause reducing of sensitivity.This infringement is a kind of process slowly, and the reduction of ultimate sensitivity can use the linear equation of following form to obtain enough compensation:

(4)MON _c＝K*D*MON，

In the formula, MON _CIt is the monitoring reading of proofreading and correct;

MON is uncorrected monitoring reading;

D dynamically changes with continuous renewal and CT scanner characteristic that slowly change, such as current indication mean value, the cathode voltage of X-ray pipe and the mean value of offset correction monitor reading as the power supply source of the X-ray pipe of electric current and voltage measuring value got at a similar time frame; And

K is an experience constant.

According to another aspect of the present invention, air during each projection is measured (perhaps more generally, the material of known decay is placed in the visual field, so that the decay of scheduled volume is provided) in the process, just, in each complete sequence reading of curved detector assembly 28, obtain a plurality of monitoring readings and store, and the data normalization with they will be received by detector 50 in this order reading provides the monitoring reading than more each video of described methods such as Uno.More specifically, in a preferred embodiment with one of 2880 ray casts corresponding each the order reading used 576 microseconds from each detector 50 reading of data to memory 60, among this 576 microsecond, Monitoring Data is read in the memory 90 with pre-determined number.

According to another aspect of the present invention, by in each projection, obtaining the monitoring reading of predetermined quantity with predefined procedure, and preferably use in time and more approaching Monitoring Data reading of the time of obtaining each detector readings, just, relatively each data readings and the monitoring reading that produces recently or will produce (this even represent the shortest time period) the soonest, and each pictorial data reading quilt obtains the normalization of pictorial data thus effectively divided by last immediate monitoring reading of time.For determining in time the monitoring reading of the most approaching generation, the look-up table that provides in the master computer 64 can be provided, it connects immediate monitor assembly reading on each image detector reading and time.

With reference to Fig. 6, an example of " nearest on the time " (closest in time) notion is described.In this explanation, in projection, obtain 8 monitoring readings, they are equi-spaced apart in time.Timeline with 100 expressions is represented 384 image detector readings of a sequence (wherein only illustrating preceding 175), and second timeline 102 is represented 8 monitorings of sequence reading (wherein only illustrating preceding 4).Among in 384 data readings, got 8 the monitoring readings, first monitoring reading A in time with very first time line 100 on the one 48 image detector reading of expression the most approaching.Equally, the second monitoring reading B in time with the 2 48 reading, promptly 49 to 96 readings are the most approaching, also are like this for other monitoring readings.Therefore, when obtaining the reading of the 24th data detector 50, in 1.5 microseconds interval, obtain the first monitoring reading, and when obtaining the reading of the 360th data detector 50, among 1.5 microseconds interval, get monitoring reading (not shown) to the end.When obtaining the 72nd, the 120th, the 168th, the 216th, the 264th and the 312nd data detector readings respectively, obtain the 2nd to the 7th monitoring reading among at interval in 1.5 microseconds.

Ideally, suppose that the X line level in source 26 keeps few, the S/N ratio of each signal of being surveyed by each detector 50 should keep few.Yet as top discussion, unless adopt some method for normalizing, S/N is than descending in time.

Fig. 7 represents by a kind of method for normalizing that we consider how all data readings to be obtained a kind of geostationary S/N ratio.We claim that the method is " sliding window " method.This method requires in each video each detector readings to be obtained simultaneously the monitoring reading of the not pad value of X-ray bundle.Therefore, when in each video, obtaining 384 detector readings, require to have 384 monitoring readings.For with each image detector reading normalization, the monitoring reading addition together with the reading subsequently of the previous reading of a predetermined quantity and a predetermined quantity provides the normalization factor to current image detector reading.Therefore, for example use 8 monitoring reading sums with the sliding window method, among the 9th detector readings of whole 384 reading sequences of detector array, 4 monitoring readings (when producing the 5th to the 8th detector readings of this sequence) and 4 monitoring readings subsequently (in the 10th to 13 the detector readings generation in sequence) addition the preceding, so that a normalization factor to be provided, the 9th reading divided by this factor with the 9th reading normalization.With similar approach, in the middle of the 10th detector readings of the whole reading sequence that reads detector array, the preceding 4 monitoring readings (when the 6th in this sequence when the 9th detector readings produces) and 4 monitoring readings following (when the 11st in this sequence during) addition together to the 14th detector readings generation, so that a normalization factor to be provided, the 10th reading divided by this factor with the 10th reading normalization.In order to carry out normalization, thus the method to each image detector reading (for example 384 detector readings) of the whole sequence of a video use 8 monitoring readings " sliding window " and.So, must calculate 384 sliding window sums to each projection.In the method, can obtain acceptable constant relatively S/N ratio within quantum noise limit.Figure shown in Figure 7 obtains by using " emulation " monitor to calculate.Yet the method also requires a large amount of calculating and extra hardware, and this will increase the cost of scanner and the speed of serious restriction deal with data significantly.Therefore, this method provides good result, but when the speed of obtaining data was very important, a large amount of processing times and additional hardware were unacceptable.

Fig. 8-the 10th is as the S/N (signal and noise) of probe access (1-384) the function figure than (increasing progressively with 1000), wherein each data detector 50 and monitoring detector 76 all are subjected to full scale fan beam intensity, and the object that does not promptly have to absorb the X line is placed in the visual field 40.What Fig. 8 illustrated is 4 nearest technology, only gets 4 uniformly-spaced monitoring readings of (on the time) among 384 data readings.What Fig. 9 and 10 illustrated is 8 nearest and ten six nearest technology, gets equally spaced 8 and 16 monitoring readings on the time in 384 data readings respectively.Very clear, when reading the monitoring reading, the S/N data of Fig. 8 show as at four peak values of easily distinguishing shown in A, B, C and the D.Clearly, more approach adjacent peak-to-peak one at interval the time when the interval of data readings, because normalization becomes not too reliable, S/N reduces.

The S/N data of Fig. 9 show as 8 more undistinguishable peak A-H.8 corresponding 8 monitoring readings in peak.For example, the image detector reading of representing by peak B be in time with 8 monitoring assembly readings in second immediate image detector reading.Notice in time the image detector reading of being separated by farthest to be got with the detector monitors reading, its S/N is than minimum.

Therefore, after the normalization of monitoring reading, the image detector reading of generation is near more apart from the monitoring reading in time, and the S/N of image detector reading is than just high more.And what can know is, for making the S/N maximum of all image detector readings in the video, must reduce from each image detector reading to a monitoring assembly reading in time apart from sum, just each projection is needed more monitoring reading.For reaching this point, the monitoring reading is equi-spaced apart mutually in time, and the image detector reading of equal amount must connect with each monitoring assembly reading, as shown in Figure 6.

With reference to Figure 10, represented wherein in each X line projection, obtaining 16 monitor assembly readings as the ratio of the S/N in Fig. 8 and 9 figure.Although carried out more calculating, nearest method has still been lacked intensity in a large amount of calculating than the sliding window method on the time.Notice the similitude of data of Fig. 7 of the data of Figure 10 and sliding window method, like this for particular instance, nearest 16 technology obviously are best.Therefore, use the calculating than prior art much less, the S/N that the invention provides broadly similar compares figure.

We also compare " closest approach " method and interpolation method.Figure 11 and 12 expressions as the S/N ratio figure that occurs in Fig. 8 and 9 wherein get 4 and 8 monitoring assembly readings respectively in each projection.Use the monitoring reading of these quantity, and, the value of each data readings is inserted, thus with data normalization according to obtaining and two times of corresponding each data readings of monitoring reading recently in time.For example, be used for 8 monitoring readings that the equal intervals place of 384 readings obtains, from reading 24, the normalization factor of using at data readings 24 places is to monitor reading 24.Yet the normalization factor of using at data readings 25 places is 1 times that 47 of 24 places monitoring reading is extraordinarily gone up 72 places monitoring reading, and is final and divided by the quantity of data readings between two monitoring readings (promptly 48).Similarly, the normalization factor of using at data readings 26 places is the twice that 46 of data readings 24 places monitoring reading is extraordinarily gone up the monitoring reading at data readings 72 places, and is simultaneously final and divided by 48, or the like.Interpolation method obtains similar results obviously has more calculating than closest approach technology, and this can be by relatively finding out Figure 10 with Figure 11 and 12.

Therefore, provided the X line chart image data normalization in the filtering CT scanner of the above-mentioned type above, it reduces or has overcome the problem of prior art effectively.The viewdata signal that links with each video of filtering CT scan is by normalization, the noise effect that changes to have reduced on the viewdata signal in time.The roentgen radiation x level of monitoring CT scanner needn't propose a large amount of calculation requirements to system thus and just can carry out at least some corrections to the variation of signal to noise ratio, thereby be better than above-mentioned sliding window method in scanning.The viewdata signal that is associated with each projection of filtering CT scan and the location independent ground that is in the patient of observation or patient support table in the visual field are by normalization.Therefore, native system has been made improvement on the described system of patent of Uno etc.And, by according to normalization data of the present invention, make data readings irrelevant with the fluctuation of X line flux basically, the life-span of X-ray pipe is prolonged.

Should be pointed out that according to the present invention can use provides the every video that can accept the S/N ratio any amount of monitoring reading in each video, its acceptability is partly by using the content decision.Particularly, 4,8,16 monitorings of every video reading has been described, but also can have used any amount of monitoring reading of every video, all 6,7 or 12.The factor that should consider comprises available computational resource in the number of desired image quality, each projected data reading and the CT scanner.

Although the preferred embodiment that has illustrated belongs to third generation CT scanner, the present invention can be used for the X line profile scanning PS of other types, comprise the 4th generation CT scanner.

The spirit and scope that do not depart from the present invention as claimed in claim, those skilled in the art will carry out other modifications and enforcement.So top illustrative purposes is not to be limited in outside the following claim indication basis is bright.

Claims (21)

1, a kind of x-ray tomography scanning means comprises: (a) X line source is used for producing the X line in x-ray tomography scanning; (b) X line sniffer, comprise a plurality of pictorial data detectors, be used for during the successive projection of described x-ray tomography scanning surveying by described X line source emission and the X ray that receives by described data detector, and be used for producing a plurality of image detector signals of the X line flux that representative surveyed by described pictorial data detector during each described projection along predetermined opticpath; (c) x-ray tomography scanning means is used for rotating the X line source in x-ray tomography scan period at least around scanned object; And (d) be used for reading with predetermined order the device of described pictorial data detector for each described projection; Described device also comprises:

The monitoring detector device, be used for surveying the X line that produces and receive by described monitoring detector device by described light source, and be used to provide sequence monitoring measuring-signal, as the function of the X line flux of during each described projection, surveying by described monitoring detector device at the predetermined space place; And

Be used for each normalization of a plurality of image detector signals that will during each projection, obtain, as in time with immediate interval of the time of reading each described image detector signal among the device of function of the monitoring measuring-signal that produces.

2, according to the device of claim 1, wherein said monitoring detector device provides the equidistantly monitoring measuring-signal at interval of a sequence in each projection.

3, according to the device of claim 1, wherein said monitoring detector device provides sequence four measuring signal at least in each projection.

4, according to the device of claim 1, wherein said monitoring detector device provides a sequence at least eight measuring-signals in each projection.

5, according to the device of claim 1, wherein said monitoring detector device provides a sequence at least ten six measuring-signals in each projection.

6, according to the device of claim 1, wherein the monitoring detector device positions with respect to described X line source, so that survey the unbated basically X line that is produced by described X line source.

7, according to the device of claim 1, the described opticpath of the described projection of wherein said scanning is determined the one scan face, and the monitoring detector device is positioned outside the described scanning plane with respect to described X line source.

8, according to the device of claim 1, wherein being used for the device of normalization image detector signal comprises definite device, is used for determining which monitoring measuring-signal is the most approaching with each image detector signal of these a plurality of image detector signals in time in this sequence monitoring measuring-signal.

9, according to the device of claim 1, also comprise the device that is positioned between described X line source and the described monitoring detector assembly, be used for determining a hole so that determine X line monitoring light beam.

10, according to the device of claim 9, wherein this hole is a rhombus.

11, according to the device of claim 1, wherein this monitoring detector assembly comprises a plurality of detectors, and each detector provides a monitoring detector signal, and each monitoring measuring-signal is represented monitoring detector signal sum.

12, a kind of normalized method of X line chart image data that will in CT scan, obtain by a system, this system has the X line source that is used for producing X line flux; A plurality of detectors are used for surveying X line flux from this X line source at the X line source around rotating shaft when rotation of passing a plurality of projections; And reading device, be used in each projection, reading these image detectors once, so that provide a plurality of image detector signals for each projection according to predefined procedure; The method comprises the following steps:

The X line flux level that monitoring is produced by described X line source in each projection is so that produce the monitoring measuring-signal of a preliminary election sequence of relevant each described projection; And

Each of a plurality of image detector signals that normalization is obtained in each projection, as in time with immediate interval of the time of reading each described image detector signal among the function of the monitoring measuring-signal that produces.

13, according to the method for claim 12, the step of wherein monitoring X line flux level comprises the wherein step of decay part basically of monitoring.

14, according to the method for claim 12, wherein normalization step comprises determining step, determine which monitoring measuring-signal in this sequence monitoring measuring-signal in time with this sequence image detector signal in each image detector signal the most approaching; And only use this monitoring measuring-signal in immediate in time this sequence monitoring measuring-signal with an image detector signal normalization.

15, according to the method for claim 12, each of a plurality of image detector signals of in each projection, obtaining of normalization wherein, as in time with immediate interval of the time of reading each described image detector signal among the step of function of the monitoring measuring-signal that produces comprise following step:

The X line flux level that monitoring is produced by described X line source in each projection is so that produce four monitorings of sequence measuring-signal of relevant each described projection.

16, according to the method for claim 12, each of a plurality of image detector signals of in each projection, obtaining of normalization wherein, as in time with immediate interval of the time of reading each described image detector signal among the step of function of the monitoring measuring-signal that produces comprise following step:

The X line flux level that monitoring is produced by described X line source in each projection is so that produce eight monitorings of sequence measuring-signal of relevant each described projection.

17, according to the method for claim 12, each of a plurality of image detector signals of obtaining in each projection of normalization wherein comprises following step as the step of the function of the monitoring measuring-signal that produces among the immediate interval of the time of reading each described image detector signal in time:

The X line flux level that monitoring is produced by described X line source in each projection is so that produce 16 monitorings of sequence measuring-signal of relevant each described projection.

18, according to the method for claim 12, wherein projection all results from the one scan face, and the X line flux level that monitoring is produced by described X line source in each projection is so that produce the step of the step of monitoring measuring-signal of a preliminary election sequence of relevant each described projection below comprising:

Monitoring does not hinder obtaining of pictorial data by the X line flux level that described X line source produces so that guarantee monitoring function outside described scanning plane.

19, a kind of x-ray tomography scanning means comprises: (a) X line source is used for producing the X line in x-ray tomography scanning; (b) X line sniffer, comprise a plurality of pictorial data detectors, be used among the successive projection of the x-ray tomography scanning in the one scan face surveying the X line that receives by described X line source emission and by described data detector determining a visual field along predetermined opticpath, and a plurality of image detector signals that are used for producing the X line flux that representative surveyed by described pictorial data detector in each described projection; (c) x-ray tomography scanning means is used for rotating the X line source at least around scanned object among x-ray tomography scanning; And (d) be used for to read the device of described pictorial data detector for a predefined procedure of each described projection; Described device also comprises:

Place the monitoring detector device outside the described visual field, be used for surveying the X line that produces by described X line source, and be used to provide the function of monitoring measuring-signal as the X line flux of surveying by described monitoring detector device.

20, according to the device of claim 19, wherein the monitoring detector device is positioned outside the described scanning plane.

21, the method for the data in to the scanning process that is positioned over the object among the visual field, obtained of a kind of normalization by CT scanner, its CT scanner comprises an X line source; One detector array is used for surveying the X line by the emission of X line source; Whirligig is used for rotating the X line source at least around rotating shaft, determines the opticpath that is used for scanning projection between described X line source and described detector like this, and therefore determines the visual field within the scanning plane of scanner; And monitoring detector assembly 74, being fixed outside the visual field, to survey the X line of launching by the X line source along at least one opticpath, described method comprises the following steps:

Be placed on the Materials Measurement that has predetermined X line absorption amount among the visual field by described X line emission and by the X line flux that each the described detector and the described monitoring detector assembly of described array are surveyed, determine initial probe device measured value thus;

Obtain data among scanning, this scanning comprises with being placed on object among the visual field measures step by X line flux described X line source emission and that surveyed by each described detector of described detector set, determines X line flux projection measurement value thus;

Among the time interval identical, repeatedly measure with carrying out each described projection measurement by the emission of described X line source and by the X line flux that described monitoring detector assembly is surveyed, determine monitoring detector assembly measured value thus; And

According to described initial probe device measured value, X line flux projection measurement value and the described data of described monitoring detector assembly measured value normalization.

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