CN104287765A

CN104287765A - Mode body used for PET imaging system detector normalization correction

Info

Publication number: CN104287765A
Application number: CN201410493268.3A
Authority: CN
Inventors: 李楠
Original assignee: JIANGSU SINOGRAM MEDICAL TECHNOLOGY Co Ltd
Current assignee: JIANGSU SINOGRAM MEDICAL TECHNOLOGY Co Ltd
Priority date: 2014-09-24
Filing date: 2014-09-24
Publication date: 2015-01-21

Abstract

The invention relates to a mode body used for PET imaging system detector normalization correction, and relates to the technical field of medical imaging. The mode body comprises a cylinder, the cylinder and a PET detector are coaxial in the axial direction, spiral grooves are formed in the outer surface of the cylinder in an equal-distance mode, guide pipes which are wound outside the cylinder in an equal-distance mode are arranged in each spiral groove, and opening ends are arranged at the two ends of each guide pipe respectively. According to the mode body, on one hand, an even stick source which is expensive does not need to be customized; on the other hand, the mechanical design requirement is simplified, and the requirement that all detection units are evenly irradiated in normalization correction is easily met.

Description

For the die body of PET imaging system detector normalization

Technical field

The present invention relates to medical imaging technology field, particularly can be used for the die body design of the detector normalization of positron emission computerized tomography system.

Background technology

In the field of nuclear medicine, PET(Positron emission computed tomography) be a kind of inspection imaging technique that can show human organ function and metabolism hurtless measure, this technology can be used for instructing treatment of cancer clinically.Its principle is: the malignant tumor tissue metabolism in patient body is vigorous, and metabolite (as glucose sugar, protein etc.) is assembled more.We can utilize radionuclide (as ¹⁸f, ¹¹c etc.) labelling is carried out to metabolite, then use PET imaging system and accurately show by 3 Dimension Image Technique the activity that the gathering of metabolite and activity reflects vital metabolic.As can be seen here, PET provide a kind of directly timely method tumor is diagnosed and analyzes.

The radionuclide of labelling metabolite produces positron by decay, and itself and periphery electron annihilation produce concurrent event, and launches a pair reverse each other photon.This is captured by a pair probe unit in PET detection system photon simultaneously, and so corresponding nucleic can be positioned in this on the determined straight line of probe unit.PET system obtain initial data be exactly a series of by photon to determined concurrent event.These concurrent events are produced three-dimensional sinograms(sinogram by after multi-angle and positional alignment combination), be then reduced to the distribution of three-dimensional radioelement by algorithm for reconstructing.

In order to increase detection efficient, medical PET is a ring-type detection system comprising up to ten thousand probe units normally.By the impact of geometric position and performance difference, such as crystallo-luminescence efficiency, crystal package, crystal and PMT(photomultiplier tube) be coupled, incident angle that electronic system, photon are right is equal, the detection efficient of probe unit is not the same.Therefore, in actual detection process, the output of probe unit can not accurately reflect input photon beam intensity, and such as detector can export result of detection sinograms heterogeneous, even if all probe units are illuminated uniformly.This will inevitably introduce artifact in process of reconstruction, causes doctor to the erroneous judgement of tumor.In order to accurately carry out modeling to detection system, obtain satisfied picture quality, user must correct the detection efficient of detector in advance, and this is called as normalization.PET system generally needs experience two kinds of normalizations, and one is utilize low scattering source to carry out time-independent part in the revise percentage factor before dispatching from the factory, and two is drift impacts on normalization factor of correction of timing detector performance within the hospital.In the first normalization, common way does uniform rotation with all probe units of uniform irradiation with an excellent source containing homogeneous radiation around the axle of PET detection system.Radius of turn is enough large to ensure that track covers the regulation visual field of pet detector ring.Correction test requires lasting tens hours enough to meet event to obtain usually.Since what all probe units detected meets event is statistically identical, so corresponding counting response just can measuring as probe unit efficiency, can calculate normalization factor based on this.Because radioactive source is excellent source, Data processing scatter correction and correction for attenuation can be ignored.These factors need to calculate in advance, are stored in computer with file mode, when checking patient, normalization factor are directly acted on the normalization that measured value just achieves detector.

In order to ensure the correctness of the normalization before dispatching from the factory, must ensure that in test in PET system, all probe units can be illuminated uniformly for a long time, this brings very large difficulty to the processing and fabricating in excellent source and Machine Design:

1. the radioactivity in solid bar source needs very even, and this makes cost of manufacture very high

2., in order to cover the axial visual field of detector, the length in excellent source needs usually more than 20cm, which in turns increases manufacture difficulty

3., because excellent source of decaying needs to repeat customized, which in turns increases cost

4. solid bar source die-away time long (271 days half-life), preserves and needs to strictly observe Shielding principle, prevent radioactive pollution, which increase the complexity of preservation process

5. in normalization test, the rotating shaft in excellent source requires to overlap with the axle of pet detector, and radius of turn needs enough large to ensure that all probe units detected in the visual field are all illuminated uniformly.In addition, rotary speed requires to keep stable in long-time test.Because excellent source bias is placed, it is positioned coaxial, rotating weight or stability all has very high requirement to Machine Design

If 6. excellent source curtailment is to cover the axial visual field of PET, in normalization test, excellent source also needs to carry out stepping along the axis of detector, which in turns increases the complexity of Machine Design

The content of invention

The present invention proposes a kind of die body that can meet normalization before the dispatching from the factory for PET system of the requirement that in normalization, all probe units are illuminated uniformly.

The present invention includes axis and the coaxial cylinder of pet detector ring, offer helicla flute equidistantly at cylindrical outer surface, arrange the conduit be wrapped in equidistantly outside cylinder in spin slot, the two ends of conduit arrange opening respectively.

One aspect of the present invention does not need to customize expensive even excellent source, simplifies mechanical design requirements on the other hand, easily meets the requirement that in normalization, all probe units are illuminated uniformly.

The concrete steps of normalization test are as follows:

First use activity meter test to transport the activity of the FDG solution come, then mix with water in proportion in a reservoir to obtain required activity.Consider the impact in dead time, solution activity can not be too high, usually can get 1mCi.

Whole cylinder is fixed on support, use laser positioning accurate calibration make cylindrical geometrical axis and pet detector ring coaxial.

Inserted one end of conduit in container, the other end connects air pump, utilizes of short duration switch air pump to suck a bit of FDG solution.

Then solution is made to do at the uniform velocity shuttling movement around cylinder in conduit by the change of air pump pressure.Due to the low reaction cross section property of cylinder and tube material, this a bit of FDG solution can be seen as a point source and move in space in pet detector, complete the uniform speed rotation of cross section and axial at the uniform velocity step motion simultaneously, and meet the requirement of all probe units of uniform irradiation.

The event that meets detected in process of the test is filled in sinogram according to its position and angle information.In order to reduce statistical error, each unit of sinogram requires the detection event at least obtaining more than 250, and corresponding detection time needs four hours usually.

Due to FDG solution half-life very short (110 minutes), after having tested, the solution in conduit and container only needs to place in the shield and within one day, just can make its radioactivity reduces to zero.This brings very large convenience to the FDG solution of process.

Test the sinogram obtained to be processed by down-stream, by calculating time-independent part in positive normalization factor and storing as systematic parameter.This test only needs to carry out once.

In the normalization test of reality, this die body has following advantage: first except moving source, and this die body can also be simulated other forms of radioactive source very easily and not need to change overall structure.Such as resorb another section of FDG solution always repeating down when making it rotate a circle in the catheter at suction one section of FDG solution, ensure that every section of solution tangential position is the same, change these FDG solution by the pressure of air pump like this and can regard as in the excellent source of the homogeneous radiation of a uniform rotation within the vision.If sucked multistage FDG solution in one week at equal intervals, many homogeneous radiation rod sources of uniform rotation can be simulated.Further, if long duct is filled FDG solution, just can generate source, an annular homogeneous radiation face, this can increase the unit interval meet event acquisition number and not needs consider correction for attenuation.This motility brings great convenience for we test different schemes.In addition, die body parameter optimization becomes simple possible.In addition, also provide simpler method to change test parameters by being programmed for air pump, such as can by the pressure of programming simple change air pump to change the translational speed of point source.Therefore different moving parameters or different FDG solution radioactivities can be attempted to find best parameter to take into account detection time and signal statistics performance.Secondly, FDG solution is easy to get, and is of value to PET operating cost and controls.FDG solution radioactivity can very fast decay to zero simultaneously, is easy to process.And relative to solid bar source, the test period of this die body can reduce greatly.Again, radioactive source motion do not rely on machinery, simplify Machine Design.Finally, cylinder and the coaxial placement of PET system, the requirement of the stability that is also content with very little and location.

Accompanying drawing explanation

Fig. 1 is a kind of structural representation of the present invention.

Detailed description of the invention

As shown in Figure 1, the present invention is provided with a cylinder 1, offers helicla flute equidistantly at the outer surface of cylinder 1, arranges the conduit 2 be wrapped in equidistantly outside cylinder 1 in spin slot, and the two ends 21 and 22 of conduit 2 arrange opening respectively.

During use, the two ends of conduit 2 are connected on the air pump of a programmable pressure control.Whole cylinder 1 is fixed on support, use laser positioning accurate calibration make cylindrical geometrical axis and pet detector ring coaxial.

The diameter of cylinder 1 needs enough large with the cross section visual field covering pet detector, and length requirement is greater than the axial visual field of pet detector.

The material of cylinder 1 and conduit 2 should careful selection to ensure that they have low-down reaction cross-section within the scope of the available energy window of concurrent event detection, such as cylinder 1 can make of inner polypropylene foam of filling large quantity of air, and conduit 2 can select the medical fine duct of diameter two millimeters.

Claims

1., for the die body of PET imaging system detector normalization, it is characterized in that comprising axis and the coaxial cylinder of pet detector ring, be wound around conduit equidistantly at cylindrical outer surface.

2. die body according to claim 1, it is characterized in that offering helicla flute equidistantly at cylindrical outer surface, described conduit is wrapped in helicla flute.

3. die body according to claim 1, is characterized in that the two ends of conduit arrange opening respectively.