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General introduction- fundamental principles X ray & CT Radiology Dept. 1st Hospi. of Peking University 唐光健 Questions to think of with the lecture What is X ray? What kinds of the features of it are useful or harmful? What are the two steps of X ray imaging? How is the grey scale of bone, muscle and air in the X ray film? What is the main difference between the CT imaging and the image of X ray film? What are same and what are different between the processes of CT imaging and imaging of X ray projection? Is the meaning of a CT axial imaging and a section of a body specimen in same location identical? Black box? Wilhelm C Röntgen Black box? Wilhelm C Röntgen Generation and features of X ray High speeding electrons Anode target sudden slow down e special X ray – sequence spectrum narrow consecutive X ray – sequence spectrum wide e X ray Generation and features of X ray electromagnetic waves -ionizing radiation -wave length of medical use: 0.08 ~ 0.71Å -feature of wave; feature of particle Features-Effects Physical effect Chemical effect Biotic effect Generation and features of X ray electromagnetic waves -ionizing radiation -wave length of medical use: 0.08 ~ 0.71Å -feature of wave; feature of particle Features-Effects Penetrability Physical effect Chemical effect Biotic effect Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction Generation and features of X ray Penetrability Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction Features-Effects Physical effect Chemical effect Biotic effect -be able to penetrate ma. of dif. density while attenuated I0 µ l I I= I0 · e µl Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect Penetrability Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction -making some compounds fluoresce -Fluoroscopy, image intensifier Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect Penetrability Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction -making some compounds fluoresce -Fluoroscopy, image intensifier Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect Penetrability Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction -Subject absorb the energy of X ray ionized ionized voltage -ionizing cell auto-exposure X ray detector Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect Penetrability Fluorescent effect Thermal effect Ionizing effect interference，diffraction, reflection, refraction - penumbra, interferential signal image blued Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect sensitization effect coloration effect fundament of X ray filming Generation and features of X ray Features-Effects Physical effect Chemical effect Biotic effect radiated tissue cells restrained, damaged, necrosing X ray protection X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium I0 µ1 µ2 l1 l2 µ3 µ4 l3 l4 I I = I0 · e- µ l · e- µ l · e- µ l · e- µ l 1 1 2 2 3 3 4 4 X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium getting special distribution of different density overlapping of anterioposterior images X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium film-silver bromide decomposed positive correlation with dosage of X ray negative correlation with degree of attenuation flu. screen detectors X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium grey of spots ∽ thickness & density of the mat. in the path way of X ray beam distribution of the spots ∽ anatomic form in the path way of X ray beam difference between the sports contrastimage natural contrast artificial contrast X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium grey of spots ∽ thickness & density of the mat. in the path way of X ray beam distribution of the spots ∽ anatomic form in the path way of X ray beam difference between the sports contrastimage natural contrast artificial contrast X ray Imaging X ray penetrate the subject（body) while attenuated attenuate signal recorded by the accepting medium grey of spots ∽ thickness & density of the mat. in the path way of X ray beam distribution of the spots ∽ anatomic form in the path way of X ray beam difference between the sports contrastimage natural contrast artificial contrast X ray Imaging X ray equipment X ray source X ray tube High voltage generator X ray imaging devices X ray film / image intensifier / plate detector X ray mechanical device exam table frame…… X ray equipment X ray tube filament cathode anode target tube shell X ray equipment X ray tube filament cathode anode target tube shell Protection from X ray X ray protection Cancel X ray exam unnecessary Reduce radiation dosage Distance from X ray source Protective device Principles of imaging diagnosis familiar with imaging methods and body position familiar with the normal imaging anatomy and variations sequential observation imaging manifestations and relationship with neighboring structures of the lesion clinical and laboratory materials understanding the meaning and limitations of the imaging methods fundamental principles of CT fundamental principles of CT CT-Computerized Tomography real tomography，without any overlapping fundamental principles of CT I0 µµ1 1 l1l1 µ2 µ3µ3 µµ44 l2l2 l3 l3 l1 = l1 = l1 = l1 = 1 - µ 1 l1 - µ 2 l2 I = I0 · e I = I0 · ·e I l4 l4 · e- µ l · e- µ l 3 3 µ µ µ µ ( 1+ 2 + 3 + 4) · 1 e 4 4 fundamental princ. of CT Godfrey Hounsfield First laboratory CT scanner 1968 fundamental princ. of CT First clinical head CT scanner Atkinson Morley‘hosp.， London fundamental principles of CT fundamental principles of CT measurement fundamental principles of CT measurement DAS－data acquisition system -detector -bumper -integrator -amplifier -A/D converter detector fundamental principles of CT Reconstruction fundamental principles of CT Reconstruction backprojective method Iterative method Factorial method Fourier method Filt. backprojective method fundamental principles of CT Reconstruction Filt. function (Kernol) High filt. (bone algorithm) low filt. (soft tissue algorithm) fundamental principles of CT Reconstruction Filt. function (Kernol) High filt. (bone algorithm) low filt. (soft tissue algorithm) fundamental principles of CT Reconstruction CT value relative magnitude to water may be used qualitatively but not quantitively [(μobj.- μwater)/μwater]×1000 fundamental principles of CT image display fundamental principles of CT image display 200/30=7HU 1000/30=33HU muscle 50HUfat fat-50HU=100 -50HU=100 ~13gray ~3 greyscale scale ability of identify grey scale eyes：24~30 CT：2000 fundamental principles of CT image display Voxel and pixel voxel – 3D, pixel – 2D CT value of a voxel represent all messages of the elements in the voxel fundamental principles of CT image display partial volume effect fundamental principles of CT enhancement CT high density contrast agent injected into veinintro-vascular/-tissue （extracellular space) CT scan density contrast hypersensitiveness nephrotoxitity fundamental principles of CT enhancement CT high density contrast agent injected into veinintro-vascular/-tissue （extracellular space) CT scan density contrast hypersensitiveness nephrotoxitity fundamental principles of CT enhancement CT high density contrast agent injected into veinintro-vascular/-tissue （extracellular space) CT scan density contrast hypersensitiveness nephrotoxitity fundamental principles of CT Indications No absolute contraindication, suitable for emergency and serious cases exam Single imaging factor，image interpretation easily， anatomy clear and detailed deformation、infection、trauma、neoplasm… Limitations Low soft tissue resolution ，difficult to detect lesion with small density difference from neighbor structure Low sensitivity for the lesion with slight gross change Contrast agent using Questions to think of with the lecture What is X ray? What kinds of the features of it are useful or harmful? What are the two steps of X ray imaging? How is the grey scale of bone, muscle and air in the X ray film? What is the main difference between the CT imaging and the image of X ray film? What are same and what are different between the processes of CT imaging and imaging of X ray projection? Is the meaning of a CT axial imaging and a section of a body specimen in same location identical?
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