CN103393434B - Method for obtaining system response model of positron emission tomography and method for image reconstruction - Google Patents
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Abstract
The invention discloses a method for obtaining a system response model of positron emission tomography, and a method and device for image reconstruction. The method for the image reconstruction of the positron emission tomography includes the steps of obtaining DOI response information of a gamma photon incident to a crystal strip array; generating a DOI response model according to the DOI response information according with a back-to-back gamma photon incidence crystal strip time tick decision; generating the system response model according to the DOI response model; carrying out the image reconstruction according to the system response model.
Description
Technical field
This patent relates to nuclear medicine detection imaging field, particularly relates to the PET system responses model of the various geometry of a kind of accurate acquisition and the method for image reconstruction.
Background technology
Positron emission computerized tomography (positron emission tomography, PET, hereinafter referred to as PET) is important Laminographic device at the field of nuclear medicine, has now been widely used in diagnosis and the research of medical domain.PET effectively can detect the spatial and temporal distributions that marked radioactive trace medicine injected in organism.Because the metabolism of the tissue (as tumor) of some exception of organism is more vigorous relative to normal cell, also compared with normal cell is many in the distribution of these tissues for tracer, so the distribution that PET detects these tracers provides the image (relevant information as tumor) carrying living body functional information, for the diagnosis of infantile tumour and research provide strong reference.
PET can be various different geometry (as flat board, annular etc.), and this is all arranged by the difference of detector module each in PET and formed, but its detection principle is all identical.Before scanning, to the tracer of organism injection containing positron-emitting radionuclides, in tracer, each positron can occur to fall into oblivion the back-to-back γ photon of a generation two i.e. γ photon pair with the negatron of in organism, these two γ photons are through bio-tissue, beat on a pair detector of positron scanning instrument, and carry out a series of electronics response, import signal into computer, record.γ photons pair all like this, all goes on record, and then through image reconstruction, can obtain the image of reflection radioactive tracer distribution.Main element detector in PET is by scintillation crystal, and photomultiplier tube and front-end electronics part form.When γ photon enters scintillation crystal, high-energy photon signal is converted into lower energy photon by scintillation crystal, and lower energy photon is converted into electronics by photomultiplier tube and amplifies, and is exported by front-end electronics.The signal of telecommunication simultaneously exported by two crystal bar ends so is just recorded about above-mentioned γ photon is to the information of a namely annihilation events.Usually describe above-mentioned response condition with some simple models, the response of PET system can be analyzed easily.Conventional model has line model, surface model and body Model, and wherein, line model is the most frequently used.Because two γ photons of annihilation events are back-to-back, can be approximated to be straight line, the back-to-back γ photon that annihilation events produces incides on two crystal bars, the line connecting two crystal bars is called as line of response (line ofresponse, LOR, hereinafter referred to as LOR line), as shown in Figure 1.In Fig. 1, LOR1 and LOR2 is two different LOR lines, and LOR1 is that detector crystal bar a and b meets and detect the LOR line that obtains, and LOR2 to be detector crystal bar c and d meet the LOR line detecting and obtain.
The signal that direct detector is recorded can be organized with different Organization of Data forms.As List mode(list mode) and Sinogram(sinogram).List mode data composition signal packet falls into oblivion the crystal bar numbering of γ photon incidence containing two, energy information and temporal information.Sinogram contains only positional information and the energy information that two are fallen into oblivion γ photon detection, but its recording mode is then utilize LOR line to determine the trend of its back-to-back annihilation photon, its transverse axis is image space LOR line and trunnion axis angle theta, the longitudinal axis is the distance r of image space initial point to LOR line, each LOR line position can be determined by (r, θ).In PET imaging, the image reconstruction of one of key technology utilizes exactly and above-mentionedly meets signal (as Sinogram or List mode) and use corresponding algorithm for reconstructing, reconstructs tracer distributed image in vivo.In process of reconstruction, modeling must be carried out according to PET system geometrical property and detection feature to PET system responses.The levels of precision of this system responses model, has very large relation to the quality rebuilding image.
When setting up system responses model, relate to projector space and image space.Projector space i.e. our space at signal place of detecting, it can be regarded as the once projection that image space does detector.During for system responses Modling model, set up corresponding coordinate system for projector space and image space simultaneously, set up the system responses model based on these coordinate systems.
In detection process, the factor affecting picture quality quality mainly contains: penetration when γ photon and crystal bar interact between crystal bar and scattering process.When γ photon incides on certain crystal bar of detector with certain angle, itself and crystal bar material occurs to interact time, entrance crystal bar can be penetrated on adjacent crystal bar, the crystal bar (the adjacent crystal bar comprising entrance crystal bar He penetrate) by penetrating is made all to produce response, this effect is called penetration, also effect of depth (depthof interaction, DOI, hereinafter referred to as DOI effect) is.As shown in Figure 2 A, suppose that on LOR1, annihilation events occurs certain point, it should be real line of response, is penetrated into b1 respectively when inciding at a certain angle on a1 and a2 a pair crystal bar along the γ photon of LOR1 direction incidence, b2 the absorption that decays, make b1, b2 crystal bar, to also creating signal, can be thought on LOR1 line when rebuilding image like this and LOR2 line all there occurs annihilation events, causing the fuzzy of image effect, resolution reduces, as shown in Figure 2 B.The in like manner scattering process of γ photon between crystal also can cause the resolution of image to decline, as shown in Figure 3A, γ photon there occurs scattering process to b1 crystal bar at upper end detector a1 crystal bar, penetration is then there occurs to b2 crystal bar in lower end, make b1, b2 crystal bar, to also responding, causes the fuzzy of image, resolution reduces, as shown in Figure 3 B.
In order to solve this image blurring effect, can improve DOI problem on hardware, crystal bar is designed to bilayer or multilamellar, but this method cost is very high.If can in the system responses model of PET accurate analog D OI effect, being used in image reconstruction process, going back the distribution of original image more really, is then a kind of effective method.This method cost is low, easily revises, high to the utilization rate of hardware.How can set up system responses model comparatively accurately, to reconstruct high-precision image, the PET research field now becomes the problem of focus.At present, the method obtaining system responses model is divided into three kinds substantially: Analytic Calculation Method, Monte Carlo simulation approach, experiment measuring method.
But current system responses model acquisition methods, mainly exists following several defect: the first, calculating strength is large, length consuming time, and memory space is large, wastes time and energy; The second, low precision, thus high-quality image cannot be obtained; 3rd, poor universality, a lot of method all only can be applicable to a kind of detector of geometry, and when ought not change crystal bar specification, when changing detector shape, then needs to re-start calculating.
Summary of the invention
In view of above-mentioned, the object of the present invention is to provide a kind of picture quality high, highly versatile and the method for the acquisition PET system responses model of can save time cost and carrying cost and image reconstruction and device.
One aspect of the present invention discloses a kind of method obtaining the system responses model of positron emission computerized tomography, and the method comprises:
Obtain the effect of depth response message that γ photon incides crystal strip array;
The effect of depth response model of the line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message; And,
According to described effect of depth response model generation system response model.
Another aspect of the present invention discloses a kind of image rebuilding method of positron emission computerized tomography, and the method comprises:
Obtain the effect of depth response message that γ photon incides crystal strip array;
The effect of depth response model of the line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message;
According to described effect of depth response model generation system response model; And,
Image reconstruction is carried out according to described system responses model.
Another aspect of the invention discloses and a kind ofly obtains the system responses model of positron emission computerized tomography and the device of image reconstruction, and this device comprises:
Acquisition module, incides the effect of depth response message of crystal strip array for obtaining γ photon;
Meet module, the effect of depth response model of the line of response determined during for meeting according to the effect of depth response message obtained and generating back-to-back γ photon entrance crystal bar pair;
Computing module, for calculating generation system response model according to described effect of depth response model; And,
Rebuild module, for carrying out image reconstruction according to described system responses model.
Acquisition PET system responses model provided by the invention and image rebuilding method and device, the DOI response message of crystal strip array is incided by obtaining γ photon, meet and generate the DOI response model of back-to-back γ photon entrance crystal bar to the LOR determined, and apply it in process of reconstruction, it is image blurring that solution DOI effect causes, while obtaining high quality graphic, possesses good transplantability, and can save time cost and carrying cost, as long as the specification of the crystal bar that PET is used is identical, no matter how the geometry of PET changes, the DOI response message produced γ photon entrance crystal bar is not needed to repeat simulation, and it is easy to meet process approach, can generation system response model in process of reconstruction in real time, well time cost and carrying cost are saved.
Accompanying drawing explanation
Describe its example embodiment in detail by referring to accompanying drawing, above-mentioned and further feature of the present disclosure and advantage will become more obvious.
Fig. 1 is the schematic diagram of LOR;
Fig. 2 A is that γ photon is at inter-crystal penetration effect schematic diagram;
Imaging effect figure when Fig. 2 B is γ photon generation inter-crystal penetration effect;
Fig. 3 A is γ photon scattering process schematic diagram between crystal;
Imaging effect figure when Fig. 3 B is scattering process between γ photon generation crystal;
Fig. 4 is a kind of overview flow chart obtaining the method for PET system responses and image reconstruction disclosed by the invention;
Schematic diagram when Fig. 5 A is γ photon vertical incidence crystal bar;
Fig. 5 B is the DOI effect schematic diagram of γ photon when penetrating two crystal;
Fig. 5 C is the DOI effect schematic diagram of γ photon when penetrating three crystal;
Fig. 6 is for the multiple γ photon of simulation is with DOI effect schematic diagram during identical incident angles;
Schematic diagram when angle of incidence is acute angle when Fig. 7 A is the incidence of γ photon;
Schematic diagram when angle of incidence is obtuse angle when Fig. 7 B is the incidence of γ photon;
Fig. 8 is that γ photon is to schematic diagram during entrance crystal bar pair;
Fig. 9 is the fuzzy response schematic diagram that DOI effect produces;
Figure 10 is the schematic diagram of the edge truncation effect of two flat panel detector;
Figure 11 A is the real structure figure of annular detector;
Figure 11 B is the schematic diagram of the edge truncation effect of annular detector;
Figure 12 is the flow chart of iterative reconstruction algorithm in the embodiment of the present invention;
Figure 13 is the disclosed schematic diagram obtaining PET system responses model and equipment for reconstructing image of one embodiment of the invention.
Detailed description of the invention
More fully example embodiment is described referring now to accompanying drawing.But example embodiment can be implemented in a variety of forms, and should not be understood to be limited to embodiment set forth herein; On the contrary, these embodiments are provided to make the present invention comprehensively with complete, and the design of example embodiment will be conveyed to those skilled in the art all sidedly.In the drawings, in order to clear, exaggerate the thickness of region and layer.Reference numeral identical in the drawings represents same or similar structure, thus will omit their detailed description.
Described feature, structure or characteristic can be combined in one or more embodiment in any suitable manner.In the following description, provide many details thus provide fully understanding embodiments of the present invention.But, one of skill in the art will appreciate that and can put into practice technical scheme of the present invention and not have in described specific detail one or more, or other method, constituent element, material etc. can be adopted.In other cases, known features, material or operation is not shown specifically or describes to avoid fuzzy each aspect of the present invention.
The invention discloses a kind of method obtaining PET system responses and image reconstruction, its overall procedure as shown in Figure 4, comprises following steps:
Step S401: obtain the DOI response message that γ photon incides crystal strip array;
Step S402: the DOI response model of the LOR determined when meeting generate back-to-back γ photon entrance crystal bar pair according to this DOI response message;
Step S403: meet the DOI response model generation system response model of generation according to this;
Step S404: carry out image reconstruction according to this system responses model.
Acquisition PET system responses model provided by the invention and image rebuilding method and device, the DOI response message of crystal strip array is incided by obtaining γ photon, meet and generate the DOI response model of back-to-back γ photon entrance crystal bar to the LOR determined, and apply it in process of reconstruction, solve the problem of image blurring that DOI effect causes, while obtaining high quality graphic, possesses good transplantability, and can save time cost and carrying cost, as long as the specification of the crystal bar that PET is used is identical, no matter how the geometry of PET changes, the DOI response message produced γ photon entrance crystal bar is not needed to repeat simulation, and it is easy to meet process approach, can generation system response model in process of reconstruction in real time, well time cost and carrying cost are saved.
The concrete grammar that in above-mentioned overall procedure, each step adopts will be set forth further in the following embodiment of the present invention.
obtain the DOI response message that γ photon incides crystal strip array
In one embodiment of the invention, by inciding crystal strip array based on the GATE software simulation γ photon covering snap gauge plan with different angles, thus the DOI response message of this process generation is obtained.
DOI effect Producing reason is the penetration owing to producing when γ photon incides on crystal bar with certain on-right angle angle.When γ photon impinges perpendicularly on crystal bar, as shown in Figure 5A, γ photon can not be penetrated on other crystal bars; But when γ photon incides on crystal bar with certain angle of inclination, as the schematic diagram of Fig. 5 B and Fig. 5 C, γ photon is penetrated on adjacent crystal bar along its propagation lines direction, produce blurring effect.When the inclination angle of γ photon incidence is different, the situation penetrating crystal bar is different, and the response caused is also different, and as shown in Figure 5 B, γ photon, through two crystal bars, as shown in Figure 5 C, then passes three crystal bars.γ photon is when interacting with crystal bar, because attenuation quotient is identical, so its penetration range in the crystal bar of same material is identical, incide angle in crystal strip array plane and position like this and just determine its penetrativity in crystal bar, and when the crystal bar length of side is enough in short-term (as 3.5mm), incoming position just can be ignored, incident angle just determines this penetrativity completely, if our desired DOI response message is DOI, then DOI ~ θ (θ is the angle of incidence of γ photon) i.e. DOI (θ).According to analysis result, as long as the size of crystal bar is certain, material is certain, no matter the geometry of detector, be all just identical with the angular relationship situation of crystal strip array when γ photon is incident, the difform detector that this pass ties up to same size crystal bar can utilize.
Particularly, can this process of GATE software simulation be passed through, simulate γ photon when inciding on crystal strip array with different angles, the response condition on adjacent even all crystals bar.This response condition comprises the positional information of these crystal bars and corresponding response message.As shown in Figure 6, the same time, N number of γ photon is had with certain angle θ
1incide the crystal bar being numbered 1, but only have n
1individual decay is absorbed on No. 1 crystal bar, n
2individual decay is absorbed on No. 2 crystal bars, n
3on No. 3 crystal bars that individual decay is absorbed in, wherein n
1, n
2, n
3all be less than N, if most γ photon all responds in these crystal bars, i.e. n
1+ n
2+ n
3>q*N, (q is a larger percentage ratio window values that can set here, as 99.5%, works as n
1+ n
2+ n
3just can think during >q*N that Main Function is all 1, on 2, No. 3 crystal bars), then 1,2, the position of No. 3 crystal bars and the percent information of response are exactly the DOI response message of the crystal strip array that we obtain, as shown in table 1.
Table 1DOI response message example
In addition, the DOI in above-mentioned DOI response message responds ratio directly can also use n
1, n
2, n
3replace the percent value in above-mentioned table.
As mentioned above, no matter crystal bar in detector where, γ photon is all identical with the situation of the incident angle of crystal bar, therefore can simulate the DOI response message of the incident crystal bar of γ photon under different incidence angles degree, then reuse at other crystal bars.Incident angle θ span is from (0 °, 180 °) (representing the opener of 0 °-180 ° here).Particularly, start angle can get an arbitrary low-angle close to 0 degree, and cut-off angles can get arbitrary angle close to 180 degree
Degree, to ensure that analog data can be used by the PET of more Multiple Shape.Here angle of incidence is taken into ray and incidence point with the angle at the crystal bar edge on the right side, and angle of incidence is as shown in Figure 7 A acute angle, and the incident angle shown in Fig. 7 B is obtuse angle.In addition, the defining method of above-mentioned angle of incidence can also for determine by other relative coordinate systems, such as, can be taken into firing angle be line of incidence and incidence point with the angle at the crystal bar edge on a left side, or be taken into the angle that firing angle is the normal of crystal bar plane in line of incidence and plane of incidence.The step-length of angle can get value as much as possible between start angle and cut-off angles, as 100 or 200 even more, the number of the present invention to got angle does not limit, and also for ease of and ensures that this time simulation can be used by the PET of more Multiple Shape.Thus, step-length can be obtained:
For the crystal strip array of simulation, also can carrying out organising data according to the form of table 2, reusing to facilitate the result to simulating.
Table 2 γ photon incides the DOI response message of crystal strip array
In table 2, a represents that entrance crystal bar is numbered, and a-x represents the xth crystal bar that the entrance crystal bar a left side is adjacent, and in like manner a+x represents an xth crystal bar adjacent on the right of entrance crystal bar a.θ y represents different incident angles.P represents the probit of simulation, namely responds percent information, and its subscript represents different crystal numberings and the combination of incident angle.Table 2 only lists each 4 the adjacent crystal bars in entrance crystal bar left and right, if in order to calculate more accurately, can also get more many-valued, thus simulate more crystal bar, the present invention does not limit this.
According to analysis, as long as the size of crystal bar is certain, material is certain, no matter the geometry of detector, all just identical with the angular relationship situation of crystal strip array when γ photon is incident, therefore, when inciding crystal strip array to γ photon and simulating, need not for concrete detector geometry, thus the present invention be made to have stronger versatility.
Adoptable Gate software cover concrete grammar flow process that snap gauge intends as:
Step 1: build detector model: crystal strip array attribute is set, and adds collimator in its front, and its size is set;
Step 2: radioactive source attribute is set: the attribute that radioactive source is set, and place it in crystal strip array one segment distance place;
Step 3: physical process is set: the γ photon that the source of setting sends and the physical process that crystal strip array reacts, real simulation practical situation;
Step 4: setting data exports;
Step 5: the direction constantly changing collimator, reaches the object changing γ photon angle of incidence angle.
According to another embodiment of the invention, the method of DOI response message when above-mentioned acquisition γ photon incides crystal strip array, can also comprise and adopt experimental technique to measure γ photon when inciding crystal strip array with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the DOI response message of crystal strip array.The experimental technique that can adopt and above-mentioned concrete analogy method similar, as: experiment tracer radioactive source used is placed on the detector array one segment distance place be made up of crystal bar, collimator is placed before crystal strip array, the direction of continuous change collimator realizes the different incident angle of γ photon, so just obtains the response condition of the γ photon entrance crystal bar under different incidence angles degree.
According to still a further embodiment, the method of DOI response message when above-mentioned acquisition γ photon incides crystal strip array, can also comprise when inciding crystal strip array with the attenuation quotient analytical Calculation γ photon of γ photon in crystal bar with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the DOI response message of crystal strip array.
the DOI meeting the LOR determined when generating back-to-back γ photon entrance crystal bar pair responds mould
type
As mentioned above, in PET system, an event relates to a pair crystal bar, therefore the DOI response message produced during two crystal bars that back-to-back γ photon is incident is needed to meet into the response model of a response events, the DOI response model of the LOR namely determined during back-to-back γ photon entrance crystal bar pair.
This meets process in the process of establishing of whole system response model, occupies very important status, the arrangement mode of the crystal bar of difformity detector, numbering is all different, but arrangement in any case, as long as crystal bar specification used is identical, in known event, the DOI response message of back-to-back γ photon incident two ends crystal strip array, can meet by identical method.
In one embodiment of the invention, particularly, the γ photon using to obtain incides the DOI response message of crystal strip array, meets the response model of an event.As shown in Figure 8, in order to embody generality, the crystal bar related to by response events is numbered a, b, c, d, e; The crystal bar of the other end is numbered f, g, h, i, j, k.Numbering herein only plays schematic effect, does not limit the present invention with this.Suppose in the DOI response message of the γ photon entrance crystal strip array obtained, it is θ that γ photon incides the corresponding incident angle of crystal strip array
1, θ
2response probability (namely responding ratio) as shown in table 3, wherein, 0 represents not response, and the crystal bar that at this moment entrance crystal bar b and g at two ends only has the left side adjacent as can be seen from Table 3 has response.It should be noted that the crystal in table 3 is numbered relative numbering, embody the relative position information between each crystal bar, but not the concrete numbering in Fig. 8, therefore, when incident angle is θ
1time, the entrance crystal bar b in a representative graph 8 in table 3,
And when incident angle is θ
2time, the entrance crystal bar g in a representative graph 8 in table 3.
It is θ that table 3 γ photon incides crystal strip array at angle of incidence
1and θ
2time DOI response message
Because these responses are all simultaneous, so we utilize random combine, carry out combination of two to there being the crystal bar of response and form response crystal bar to determined LOR, and represent that namely corresponding crystal bar exists the probability of LOR to the annihilation events determined with the product of the response ratio in corresponding DOI response message.We represent the probability of the response that x crystal bar and y crystal bar produce with Event (x, y), then have
Event(x,y)=p
x×p
y(1)
Wherein, p
xand p
yrepresent that the DOI of γ photon incident x crystal bar and γ photon incident y crystal bar responds ratio respectively.
In addition, if the γ photon the obtained response ratio incided in the DOI response message of crystal strip array is relative scale, namely the decay of different crystal bar absorbs the ratio between number, then above-mentioned probability product is the product between relative scale.
Under condition of incidence shown in Fig. 8, response condition has 2 × 3=6 kind, and response events probability then calculates by formula (1).Event response model, namely different crystal bar is to the DOI response model of the LOR determined for shown in table 4, so just obtains the system responses situation of all events shown in Fig. 8.
Table 4 meets the event DOI response model of generation
| Response events | Response probability |
| Event(b,g) | p a1*p a2 |
| Event(b,h) | p a1*p a2-1 |
| Event(b,i) | p a1*p a2-2 |
| Event(c,g) | p a1-1*p a2 |
| Event(c,h) | p a1-1*p a2-1 |
| Event(c,i) | p a1-1*p a2-2 |
Obtain herein meet after the response intensity of DOI response model be that probability represents, belong to relative scale value, be only decided by the angle of γ photon incidence.So in process of reconstruction, it is identical that the different pixels point on same LOR obtains the DOI response probability after meeting.But in fact due to the difference of pixel present position, it is different to the absolute intensity of identical crystal bar to the response produced, namely the N in previous step is not identical, so in another embodiment of the present invention, the probabilistic model of the DOI event obtained can also be carried out intensity weighted process according to the position of different pixels point further, obtain the DOI response model of absolute figure.Weights obtain method as: solid angle size that institute's entrance crystal bar opens pixel can be utilized to represent this weights size.
The response generated in table 4 carrys out organising data based on crystal bar coordinate, and the response of this type of organization can be used in the algorithm for reconstructing based on List mode.If follow-up iterative reconstruction algorithm is based on Sinogram, above-mentioned event response can also be converted into the Organization of Data form of Sinogram, namely based on the system responses type of organization of (r, the θ) of LOR line.It meets method is all identical.As long as the position of two of known incident crystal bars and incident angle, can meet desired system responses.
In an embodiment of the invention, optionally, before meet the DOI response model generation system response model of generation according to this, its symmetry information can also be obtained according to the geometry of pet detector.
Meet method according to above-mentioned, as long as the position of known γ photon entrance crystal strip array and incident angle can draw the response model of the event needed for reconstruction according to the DOI response message after the meeting of above-mentioned acquisition, and then draw system responses model.So carry out in the process of rebuilding at acquisition system responses model, can determine that the positional information of the crystal strip array of γ photon incidence and incident angle information become key point.In general, according to the concrete shape of PET and concrete algorithm for reconstructing (rebin+2D or 3D), the response of all pixels used can all be calculated one time.But in specific geometry, there is special symmetry, utilize these symmetry, just can simplify the number of times of calculating, accelerate arithmetic speed.
Particularly, in static two flat panel detector, there is translational symmetry, axial symmetry and exchange symmetry, therefore only needing the point calculating less position, just can draw the system responses of all location points.And in annular detector, system generally can be designed to the shape of regular polygon.Regular polygon has rotational symmetry and axial symmetry, also can meet the response of less point, just can draw the system responses of all location points.In addition, the detector of other shapes, all can have specific geometrical property to exist, so just can simplified operation.
Therefore, obtain the symmetric information of PET geometry, simplification calculation times can be played, accelerate the effect of arithmetic speed.
generation system response model
In one embodiment of the invention, according to the above-mentioned DOI response model generation system response model meeting generation obtained.
Particularly, calculate crystal bar positional information corresponding to the pixel obtained on all LOR and incident angle information, according to the above-mentioned DOI response model generation system response model meeting generation obtained, the system responses information of all pixels namely used in algorithm for reconstructing.
System responses model can be an array, or matrix, and for an array, if system responses model is array P [m] [n], wherein m is used for uniquely determining a pixel, such as, two dimension or three-dimensional coordinate can be used to determine; N is used for uniquely determining a LOR, such as, can use the numbering of corresponding two crystal bars, or aforesaid (r, θ) type of organization; Vice versa, and namely m is used for uniquely determining that LOR, a n are used for uniquely determining a pixel, and the embodiment of the present invention is not as limit; The element that p [m] [n] is array P [m] [n], that is the above-mentioned probability that there is LOR.
The method of computing system response model is, first determines a calculative pixel, for Fig. 8, falls into oblivion at this pixel, and its back-to-back γ photon is respectively with θ
1and θ
2entrance crystal bar to the LOR determined as shown in Figure 8, works as m
1represent this pixel, n
1, n
2, n
3, n
4, n
5and n
6represent (b, g) respectively, (b, h), (b, i), (c, g), (c, h), the LOR that (c, i) is formed, then
p[m
1][n
1]=p
a1*p
a2
p[m
1][n
2]=p
a1*p
a2-1
p[m
1][n
3]=p
a1*p
a2-2
p[m
1][n
4]=p
a1-1*p
a2
p[m
1][n
5]=p
a1-1*p
a2-1
p[m
1][n
6]=p
a1-1*p
a2-2
Change θ
1and θ
2after, continue to calculate this pixel according to said method; Afterwards, after continuing, according to said method, above-mentioned calculating is carried out to the pixel on all LOR, system responses model can be obtained.
If in the step of the DOI response model of the LOR determined when meeting and generating entrance crystal bar pair, also carried out weighting process to this probability product, p [m] [n] is then the probit after its weighting process herein.
In another embodiment of the present invention, if obtained the symmetry information of pet detector geometry, can also according to this symmetry information of acquisition and the above-mentioned DOI response model generation system response model meeting generation.
Particularly, according to the symmetry information of obtained PET geometry, calculate crystal bar positional information corresponding to the pixel obtained on all LOR and incident angle information, according to the above-mentioned DOI response model generation system response model meeting generation obtained, i.e. the system responses information of all pixels.
This process can produce in real time in process of reconstruction, saves memory space; Also before process of reconstruction, the system responses of generation can be stored with a matrix type, accelerate computational speed.
Here during generation system response model, the many steps of method ask for the process of the incidence angle θ of γ photon than ever, i.e. the angle of LOR line and two ends crystal bar plane, and the dimension of system response matrix is also many compared with analytic method of the prior art.
Condition of incidence as shown in Figure 8, can produce 5 and fuzzy system responses occurs.As shown in Figure 9, be the LOR line of solid line originally, create the LOR line shown in other five dotted lines due to DOI effect, show in the system responses of generation by said method, and then embody in process of reconstruction.
It should be noted that at the edge of two flat panel detector due to truncation effect, DOI effect complete as middle can not be produced.As shown in Figure 10, on the crystal bar of the incident upper end of gamma-rays, because entrance crystal bar left end does not have adjacent crystal bar again, so produce truncation effect.Also there is same problem at the block edge of same polygonal arrangement in ring-shaped P ET, as shown in Figure 11 A, is the real structure of annular detector, is spliced into regular polygon structure by multiple block.Each block crystal inside bar becomes array distribution, as shown in Figure 11 B, blocks with regard to there is the edge the same with dull and stereotyped PET at block marginal existence gap place.For the edge truncation of dull and stereotyped PET, because the γ photon that blocks is beaten in atmosphere when the crystal bar of penetration edges, can not cause blooming, so only need according to the situation determination response condition of actual edge, response ratio be according to the situation determination percentage ratio of reality.As in the case illustrated in figure 10, the response of upper end-face edge just only has entrance crystal bar crystal bar, so response ratio is just set to 100%.And for annular detector block edge and dull and stereotyped PET edge similar, also process equally.
image reconstruction
In one embodiment of the invention, the said system response model of acquisition is applied to iterative reconstruction algorithm, carries out image reconstruction.Conventional alternative manner has MLEM based on probabilistic model and its innovatory algorithm OSEM algorithm.The present embodiment adopts OSEM algorithm to be example, and the process of carrying out image reconstruction according to above-mentioned acquired system responses model is described.In addition, the iterative algorithm carrying out rebuilding according to obtained system responses model can also be replaced with other needs system responses model as the iterative reconstruction approach of input, as MLEM, ART, MLEM, OSEM, OSLS, MAP etc.
Figure 12 is iterative reconstruction algorithm flow chart in the embodiment of the present invention, when calculating projection according to new image F each time, obtained system responses model will be used, draw the projection of image F to system, then the projection recorded with experiment contrasts, and corrects original image F.In each correction iterative process, will obtain comparatively accurate image F, namely reconstruct image, concrete steps are as follows:
Step S1201, sets an initial pictures F;
Step S1202, according to obtained system responses model, computed image F is to the projection D of system;
Step S1203, tests together the projection D ' recorded and compares;
Step S1204, calculates correction coefficient and more new images F;
Step S1205, judges whether to meet rule of stopping, if do not met, then re-executes step S1202, and is input in step S1202 by the image F after upgrading; Otherwise, if met, then perform step S1206;
Step S1206, termination of iterations process.
Can calculate in real time according in the process of iterative reconstruction algorithm for obtained system responses model, also can be precalculated and be stored on corresponding equipment, directly read in when rebuilding and use.
It should be noted that the rule of stopping that rule of stopping wherein can adopt any in prior art and used algorithm to adapt does not repeat at this.
In addition, above-mentioned iterative algorithm step only carries out the process of image reconstruction for illustration of how according to above-mentioned acquired system responses model, the embodiment of the present invention not as limit, the system responses model obtained in the embodiment of the present invention can be applicable to arbitrary need system responses model as input in the iterative algorithm of image reconstruction.Acquisition PET system responses model provided by the invention and image rebuilding method and device, the DOI response message of crystal strip array is incided by obtaining γ photon, meet and generate the DOI response model of back-to-back γ photon entrance crystal bar to the LOR determined, and apply it in process of reconstruction, solve the problem of image blurring that DOI effect causes, while obtaining high quality graphic, possesses good transplantability, and can save time cost and carrying cost, as long as the specification of the crystal bar that PET is used is identical, no matter how the geometry of PET changes, the DOI response message produced γ photon entrance crystal bar is not needed to repeat simulation, and it is easy to meet process approach, can generation system response model in process of reconstruction in real time, well time cost and carrying cost are saved.
Figure 13 is the disclosed schematic diagram obtaining PET system responses model and equipment for reconstructing image of one embodiment of the invention.As shown in figure 13, this device specifically comprises:
Acquisition module 1301, incides the DOI response message of crystal strip array for obtaining γ photon;
Particularly, the method that described acquisition γ photon incides the DOI response message of crystal strip array comprises: when inciding crystal strip array by Monte Carlo simulation γ photon with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the DOI response message of crystal strip array; When adopting experimental technique measurement γ photon to incide crystal strip array with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the DOI response message of crystal strip array; And, when inciding crystal strip array with the attenuation quotient analytical Calculation γ photon of γ photon in crystal bar with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the DOI response message of crystal strip array.
Meet module 1302, the DOI response message for inciding crystal strip array according to the γ photon obtained meets the DOI response model of the LOR determined when generating back-to-back γ photon entrance crystal bar pair;
A pair crystal bar response situation that response events relates to is met, thus obtains the DOI response model of this crystal bar to the LOR determined.Concrete meet method and can meet method for probability.
Computing module 1303, for calculating generation system response model according to the DOI response model meeting generation obtained;
Particularly, calculate crystal bar positional information corresponding to the pixel obtained on all LOR and incident angle information, according to the above-mentioned DOI response model generation system response model meeting generation obtained, the system responses information of all pixels namely used in algorithm for reconstructing.
This process can produce in real time in process of reconstruction, saves memory space; Also before process of reconstruction, the system responses of generation can be stored with a matrix type, accelerate computational speed.
Rebuild module 1304, for carrying out image reconstruction according to the system responses model obtained.
According to the system responses model obtained, carry out image reconstruction process by iterative algorithm.
Acquisition PET system responses model provided by the invention and image rebuilding method and device, the DOI response message of crystal strip array is incided by obtaining γ photon, meet and generate the DOI response model of back-to-back γ photon entrance crystal bar to the LOR determined, and apply it in process of reconstruction, solve the problem of image blurring that DOI effect causes, while obtaining high quality graphic, possesses good transplantability, and can save time cost and carrying cost, as long as the specification of the crystal bar that PET is used is identical, no matter how the geometry of PET changes, the DOI response message produced γ photon entrance crystal bar is not needed to repeat simulation, and it is easy to meet process approach, can generation system response model in process of reconstruction in real time, well time cost and carrying cost are saved.
Below illustrative embodiments of the present invention is illustrate and described particularly.Should be appreciated that, the invention is not restricted to disclosed embodiment, on the contrary, the invention is intended to contain and be included in various amendment in the spirit and scope of claims and equivalent arrangements.
Claims (26)
1. obtain a method for the system responses model of positron emission computerized tomography, comprising:
Obtain the effect of depth response message that γ photon incides crystal strip array;
The effect of depth response model of the line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message; And,
According to described effect of depth response model generation system response model.
2. the method for the system responses model of acquisition positron emission computerized tomography according to claim 1, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When inciding crystal strip array by software simulation γ photon with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
3. the method for the system responses model of acquisition positron emission computerized tomography according to claim 1, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When adopting experimental technique measurement γ photon to incide crystal strip array with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
4. the method for the system responses model of acquisition positron emission computerized tomography according to claim 1, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When inciding crystal strip array with the attenuation quotient analytical Calculation γ photon of γ photon in crystal bar with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
5. the method for the system responses model of the acquisition positron emission computerized tomography according to claim arbitrary in Claims 1-4, wherein, the effect of depth response message that described γ photon incides crystal strip array comprises: crystal bar is numbered, effect of depth ratio and incident angle.
6. the method for the system responses model of acquisition positron emission computerized tomography according to claim 5, wherein, described effect of depth ratio be with an incident angle incide γ photon number on a crystal bar with the ratio of all γ photon numbers of this incident angle incidence, or be the described γ photon number incided with an incident angle on a crystal bar.
7. the method for the system responses model of acquisition positron emission computerized tomography according to claim 5, wherein, the defining method of described incident angle comprises: be taken into ray and incidence point with right or with the angle at the crystal bar edge on a left side, or is taken into the angle of normal of crystal bar plane in ray and plane of incidence.
8. the method for the system responses model of acquisition positron emission computerized tomography according to claim 5, wherein, the method for effect of depth response model of the described line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message comprises:
Carry out combination of two to there being the crystal bar of response and form response crystal bar to the line of response determined; And,
Effect of depth ratio in the respective described effect of depth response message of described crystal bar centering is multiplied, to obtain described effect of depth response model.
9. the method for the system responses model of acquisition positron emission computerized tomography according to claim 5, wherein, the method for effect of depth response model of the described line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message comprises:
Carry out combination of two to there being the crystal bar of response and form response crystal bar to the line of response determined;
Effect of depth ratio in the respective described effect of depth response message of described crystal bar centering is multiplied; And,
The product of positional information to above-mentioned steps according to different pixels point is weighted process further, wherein, utilizes solid angle size that entrance crystal bar opens pixel to determine its weights, to obtain described effect of depth response model.
10. the method for the system responses model of acquisition positron emission computerized tomography according to claim 1, wherein, the Organization of Data form of the effect of depth response model that described crystal bar is right comprises: list mode (List mode) form and sinogram (Sinogram) form.
The method of the system responses model of 11. acquisition positron emission computerized tomographies according to claim 1, wherein, described according to described effect of depth response model generation system response model before, also comprise and obtain its symmetry information according to the geometry of the detector of described positron emission computerized tomography, and described according to described effect of depth response model generation system response model be further also according to obtain described symmetry information and described effect of depth response model generation system response model.
The method of the system responses model of 12. acquisition positron emission computerized tomographies according to claim 1, wherein, the described method according to described effect of depth response model generation system response model comprises: the system responses information calculating the pixel in all line of response, thus generates described system responses model.
The image rebuilding method of 13. 1 kinds of positron emission computerized tomographies, comprising:
Obtain the effect of depth response message that γ photon incides crystal strip array;
The effect of depth response model of the line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message;
According to described effect of depth response model generation system response model; And,
Image reconstruction is carried out according to described system responses model.
The image rebuilding method of 14. acquisition positron emission computerized tomographies according to claim 13, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When inciding crystal strip array by software simulation γ photon with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
The image rebuilding method of 15. acquisition positron emission computerized tomographies according to claim 13, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When adopting experimental technique measurement γ photon to incide crystal strip array with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
The image rebuilding method of 16. acquisition positron emission computerized tomographies according to claim 13, wherein, the method that described acquisition γ photon incides the effect of depth response message of crystal strip array comprises:
When inciding crystal strip array with the attenuation quotient analytical Calculation γ photon of γ photon in crystal bar with different angles, response condition on corresponding one or more crystal bar, thus the γ photon obtaining corresponding one or more crystal bar incides the effect of depth response message of crystal strip array.
17. according to claim 13 to the image rebuilding method of the acquisition positron emission computerized tomography described in arbitrary claim in 16, wherein, the effect of depth response message that described γ photon incides crystal strip array comprises: crystal bar is numbered, effect of depth ratio and incident angle.
The image rebuilding method of 18. acquisition positron emission computerized tomographies according to claim 17, wherein, described effect of depth ratio be with an incident angle incide γ photon number on a crystal bar with the ratio of all γ photon numbers of this incident angle incidence, or be the described γ photon number incided with an incident angle on a crystal bar.
The image rebuilding method of 19. acquisition positron emission computerized tomographies according to claim 17, wherein, the defining method of described incident angle comprises: be taken into ray and incidence point with right or with the angle at the crystal bar edge on a left side, or is taken into the angle of normal of crystal bar plane in ray and plane of incidence.
The image rebuilding method of 20. acquisition positron emission computerized tomographies according to claim 17, wherein, the method for effect of depth response model of the described line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message comprises:
Carry out combination of two to there being the crystal bar of response and form response crystal bar to the line of response determined; And,
Effect of depth ratio in the respective described effect of depth response message of described crystal bar centering is multiplied, to obtain described effect of depth response model.
The image rebuilding method of 21. acquisition positron emission computerized tomographies according to claim 17, wherein, the method for effect of depth response model of the described line of response determined when meeting generate back-to-back γ photon entrance crystal bar pair according to described effect of depth response message comprises:
Carry out combination of two to there being the crystal bar of response and form response crystal bar to the line of response determined;
Effect of depth ratio in the respective described effect of depth response message of described crystal bar centering is multiplied; And,
The product of positional information to above-mentioned steps according to different pixels point is weighted process further, wherein, utilizes solid angle size that entrance crystal bar opens pixel to determine its weights, to obtain described effect of depth effect response model.
The image rebuilding method of 22. acquisition positron emission computerized tomographies according to claim 13, wherein, the Organization of Data form meeting the effect of depth response model of the LOR obtained described in comprises: list mode (List mode) form and sinogram (Sinogram) form.
The image rebuilding method of 23. acquisition positron emission computerized tomographies according to claim 13, wherein, described according to described effect of depth response model generation system response model before, also comprise and obtain its symmetry information according to the geometry of the detector of described positron emission computerized tomography, and described according to described effect of depth response model generation system response model be further also according to obtain described symmetry information and described effect of depth response model generation system response model.
The image rebuilding method of 24. acquisition positron emission computerized tomographies according to claim 13, wherein, the described method according to described effect of depth response model generation system response model comprises: the system responses information calculating the pixel in all line of response, thus generates described system responses model.
The image rebuilding method of 25. acquisition positron emission computerized tomographies according to claim 13, wherein, the method that the system responses model described in described basis carries out image reconstruction comprises:
Set an image F;
The projection D of described image F to system is calculated according to described system responses model;
Test together the projection D ' recorded to compare;
Calculate correction coefficient and upgrade described image F; And,
Judge whether to meet and to stop rule: if do not met, then re-execute and describedly calculate the projection D of described image F to system according to described system responses model, wherein said image F is the image F after upgrading; If met, then termination of iterations process.
26. 1 kinds obtain the system responses model of positron emission computerized tomography and the device of image reconstruction, comprising:
Acquisition module, incides the effect of depth response message of crystal strip array for obtaining γ photon;
Meet module, the effect of depth response model of the line of response determined during for meeting according to the effect of depth response message obtained and generating back-to-back γ photon entrance crystal bar pair;
Computing module, for calculating generation system response model according to described effect of depth response model; And,
Rebuild module, for carrying out image reconstruction according to described system responses model.
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