X-ray application in medical diagnosis is mainly based on X-ray penetration,differential absorption,photosensitivity and fluorescence.Because x-rays through the body,by the absorption of different degree,such as bone absorption of X-ray quantity more than the amount of muscle absorption,then through the body after the X-ray quantity is different,so carry the body ministries density distribution of information,on the screen or film caused by fluorescence function or the strength of the photosensitive action there is a bigger difference,thus or photographic film on the screen(after developing and fixing)will show different density shadow.According to the contrast of dark shade,combined with clinical manifestations,test results and pathological diagnosis,it is possible to judge whether a certain part of the human body is normal.As a result,X-ray diagnosis technology has become the world's first non-plane-invasive internal inspection technology.
X-ray is applied to the treatment,mainly based on the biological effects,the application of different energy X ray lesions of cells tissue to the human body,can cause the illuminate tissue damage,or suppressed,so as to achieve for some diseases,especially the aim of treatment for cancer.
While using X ray,it was found that the cause skin burns,the patient hair loss,visual impairment,radiation damage of problem such as leukemia,to prevent X-ray of the harm to human body,the corresponding protective measures must be taken.These constitute the three major medical aspects of X-ray application-diagnosis,treatment and protection.
A brief history of the development of medical X-ray equipment.
Since 1895,X-ray diagnosis and treatment technology has developed rapidly,and the main progress can be divided into the following stages:
(1)ion X ray tube stage(1895~1912)
This is an early stage of X-ray equipment.When X-ray machine structure is simple,low efficiency of the gas bearing type cold cathode ion X ray tube,using heavy high pressure induction coil,bare type high pressure parts,less precise control unit.X-ray machine installed capacity is small,low efficiency,penetrating power,image resolution is not high,the lack of protective zero according to the records,when shooting a X-ray pelvis,40~60 min of exposure time,after the photo into,client X ray burns skin.
(ii)electronic X-ray tube stage(1913~1928)
With the development of electromagnetism,high vacuum technology and other subjects,American physicist W.D.Coolidge published a report on the success of the tungsten filament X-ray tube.Practical use since 1913,it is the biggest characteristic of*state tungsten filament is heated to incandescence in order to provide the required electronic tube current,so to adjust the filament heating temperature can control tube current,so that can independently adjust the tube voltage and tube current,which are needed to improve the quality of image.
The invention of the filter grid in 1913 partially eliminated the scattering line and improved the quality of the image.In 1914,it was made of cadmium tungstate fluorescent screen and began the application of X-ray fluoroscopy.In 1923,the double focus X ray tube was invented,which solved the need of X-ray photography.The power of the X-ray tube can reach several kilowatts,the length of the rectangular focus is only a few millimeters,and the X-ray image quality is greatly improved.At the same time,the gradual application of contrast agent,the diagnostic range of X-ray is also expanding.It is no longer a simple photograph bone image of simple tools,has become one of the human body as the natural contrast in the tissues and organs(to small X-ray absorption)of the gastrointestinal tract,kidney,bladder,bronchi and vessels,ventricle facilities can also check the important medical diagnosis.At the same time,x-rays are being used in treatment.
The way x-rays are produced.
There are three ways to produce x-rays:Bremsstrahlung,electron capture,and internal conversion,and the mechanism of X-ray generation of X-ray machines belongs to Bremsstrahlung.
Beta decay include three kinds:+beta decay,beta decay and electron capture(EC).The electron capture(EC),the decay can be expressed as the mother nucleus captured one orbit outside the core of electronic within a proton into a neutron,and emitting a neutrino,so son nuclear charge number into Z-1,and the mass number remains the same.In general,K level of electronic was captured by the nucleus of the majority,because K layer closest to the nucleus,the most probability to captured but L layer on the electronic captured probability is also exist.The nucleus after the electron was captured,the son of nuclear K or L layer will appear a hole,when an outer electrons to fill the vacancy,may appear the following one of two things:either to identify X-ray excess energy release,the form of either the excess energy to another level of other electron,the electron gain energy away from the atom,become the auger electron.Accompanied by X ray and auger electron emission is the sign of K capture process.
Nucleus can be achieved through some way(such as beta decay)excited state,in the excited state of nuclei can be fired by gamma ray transition to low excited state or ground state,this phenomenon is called gamma decay or gamma transition.Nuclear energy level transition of photon and the atomic energy level transition photon emitted from no essential difference,the difference is the launch of the photon energy only atomic energy level transition eV~keV orders of magnitude,and the launch of the photon energy is nuclear energy level transition MeV orders of magnitude.Without considering the nuclear recoil,photon energy Eg can be expressed as the following form Eg=Es-Ex.Sometimes the nucleus from the excited state to the low-energy state transition does not emit photons,but directly to the extranuclear electron energy,make the electrons from the atoms,this phenomenon is called internal conversion(IC),from the atomic electronic called internal conversion.In the excited state of nucleus through radioactive gamma photons back to the ground state,or can be generated by internal conversion electron back to the ground state,exactly what kind of process,completely depends on nuclear energy features.The internal conversion electron kinetic energy and shell electron ionization energy should be the sum of the nucleus of the energy difference between the two energy levels.That is equal to the transition between the two nuclei level gamma photons emitted by the energy.On the study of internal conversion is important means to obtain the nuclear level knowledge.Of course by internal conversion can also produce the characteristic X-ray of the atom.
The basic principle of X-ray machine.
X-ray was discovered by the German professor in 1895.This radiation line,which can penetrate the object by the vacuum tube,has stronger energy than visible light in the electromagnetic spectrum,shorter wavelength and higher frequency,and similar radiation lines have cosmic rays,X-ray and so on.
X-Ray must have X-Ray tube,and the basic structure of X-Ray tube must have:
Vacuum glass tube(Evacuated glass envelope)
And,of course,the power supply.
X ray characteristic
The scattering of light can be caused by the scattering of light by the scattering of light by the scattering of light in the wavelength range of the visible light in the electromagnetic spectrum.
When X-ray enters an object,there are three situations:
To be absorbed by an object.
To generate scattering(Scatter)
Four factors affecting image effect:
The relationship between the wavelength of X rays and the contrast of the film.
X-rays penetrate the patient,and the penetration rate is mainly related to the patient's tissue structure and X-ray wavelength.
Short wavelength X-ray(high kV)
High energy,good penetrability,resulting in low contrast in the film.
Long wavelength X-ray(low kV)
Lower energy,more easily absorbed by the body,less penetrability,and High contrast in the film.
X-ray machine is widely used in medical and health,science and education,industrial fields,such as X-ray machine can be used in hospitals to help doctors diagnose disease,used in industrial nondestructive flaw detection,the railway station and airport security checks and so on.