X-Ray Interaction with Matter & IR PDF

Topic # 3 X-ray Interaction with Matter & Image Receptor (IR)  Learning Ministerial Topic 3 Objectives...

Topic # 3 X-ray Interaction with Matter & Image Receptor (IR)  Learning Ministerial Topic 3 Objectives Outcome Competency 1. Describe characteristics of the x-ray radiation beam in diagnostic imaging 2, 7, 8 01PZ:E2 2. Explain Incident or Entrance exposure, transmitted, exit exposure, attenuated 2, 7, 8 01PZ:E2 exposure and remnant radiation 3. Define and describe x-ray radiation attenuation and differential absorption with 2, 7, 8 01PZ:E2 matter 4. Explain the Radiologic image, Latent image & Radiographic image 2, 7, 8 01PZ:E2, 01XR;E4 5. Distinguish between a negative and positive image 2, 7, 8 01PZ:E2 6. Explain the definitions of essential and relevant terminology used in the image 2, 7, 8 01XT;E1, 01XR;E4 formation process 7. Correctly use technical parameters, and necessary accessories to obtain useful 01PZ:E2, 01XR;E4, exposures considering patient’s sex and age, ROI, in area of interest, patient’s 7, 8 01XT;E1, condition and history value, clinical information and pathology 01XT;E1, 01PZ:E2, 8. Explain the effect of contrast media on subject and image contrast when used 7, 8 01XR;E4 9. Explain the basic function of the processing area, filing room, laser printers, and 2 01PZ:E2 film digitizers 2  videos History of x-rays: https://www.youtube.com/watch?v=fHUzVqoDnts Attenuation: https://www.youtube.com/watch?v=d3n-kFMAtns Xray interaction with matter & IR: https://www.youtube.com/watch?v=zJ-zs5lpJY8&t=158s Contrast Media: https://www.youtube.com/watch?v=pV4KsXEOpQE Film Digitizer: https://www.youtube.com/watch?v=m7jPxLFTjOg 3  Key terms 1. Ionizing and non-ionizing radiation 21. Scale of contrast 2. Energy, frequency & wavelength size 22. Image sharpness 3. Attenuation 23. Image brightness 4. Differential absorption 24. Subject contrast 5. Heterogeneous x-ray beam 25. IR contrast 6. Radiologic image 26. Spatial Resolution 7. Latent image 27. Contrast resolution 8. Radiographic image 28. Dynamic range 9. IR Exposure, incident exposure, exit/remnant 29. Exposure latitude exposure 30. Signal to Noise Ratio (SNR) 10. mAs & kVp 31. Quantum Noise 11. Compton and Photoelectric Effect 32. Image contrast 12. Electron binding and kinetic energy 33. Scale of contrast 13. Positive image 34. Image sharpness 14. Negative image 35. Image brightness 15. Positive contrast media 36. Radiopaque and radiolucent 16. Negative contrast media 4  Characteristics of X-ray invisible ionizing radiation with high energy & short frequency o Diagnostic x-rays range between 30 KeV to 150 KeV energy levels o 30 petahertz (1000 terahertz) to 30 exahertz (1 million terahertz) frequencies X-rays are transmitted, absorbed or scatter when interacting with subject short wavelength  size range is 0.1 – 1.0 Armstrong or 0.01 - 0.1 nanometers heterogeneous Latent (invisible) image is formed on x-ray and/or light sensitive receptors images are usually displayed as a negative but can be displayed as a positive Exposure time: from 1/1000 sec. to several secs 5  Characteristics of X-ray Quantity and quality of x-rays is controlled primarily by the milliAmperage (mA), exposure TIME (sec.) & kilovoltage (kVp) Number of X-rays transmitted through patient depends primarily on the technical factors (parameters): o kVp - penetrating power of the x-ray photon determines the x-ray quality of the photon o mAs – beam intensity or quantity (total # of x-ray photons that reach the image receptor IR) Amount of X-ray photons transmitted through the patient also depends on the subject tissue composition and thickness of the object 6  The Radiation Exposure In radiology, exposure is defined as the number of individual X-ray units (photons) that emerge from the X-ray tube and subsequently reach the IR o It is expressed in Roentgen (R) Incident or Entrance exposure x rays that enter the object Attenuated Exposure absorbed & scatter x-rays not reaching IR Transmitted or Exit exposure or remnant radiation primary x-rays & scatter reaching the IR Image Receptor Exposure The X-rays captured by IR 7 8  X-ray Interaction with matter There are four different air filled tissues air filled tissues types of tissue in the human fat fat body varying in atomic soft tissues soft tissues number (Z), thickness and bones bones tissue density (ρ) 9  X-ray Interaction with matter X-RAY ATTENUATION: is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption and/or scattering of the x-ray photons and can be affected by different factors such as beam energy, the atomic number of the human tissue, tissue density and thickness of the body part being exposed 10  X-ray Interaction with matter Effect of Attenuation on the X-ray image The variation in transmission of radiation through the body, causes the recording of different shades of grey on the image. Objects that are x-rayed can be: o Radio-opaque: the object absorbs x-rays o Radiolucent: the object transmits x-rays Whether a photon is absorbed, scattered or transmitted depends on factors such as: o Penetrating power or beam energy (kVp) o Atomic number of the object (Z) o Thickness of the object o Tissue Density of the object (ρ = M/V) 11 What is radiopaque? What is radiolucent? 12 Absorption and Transmission 13 Five probable interaction types with matter 1. Coherent Scattering 2. Pair Production 3. Photodisintegration 4. Compton Scattering 5. Photoelectric Effect 14  Coherent Scattering Also known as classical scattering or Thompson scattering Coherent scattering is an interaction between low-energy x-rays and atoms – X-rays with energies below 10 keV The x-ray loses no energy but changes direction slightly No energy is transferred therefore no ionization Negligible effect on image quality The wavelength of the scattered x-ray is equal to the wavelength of the incident x-ray 15  Pair Production Pair production occurs with x-rays that have energies greater than 1.02 MeV The x-ray photon comes close enough to the nucleus of the atom to be influenced by the strong nuclear field, and as a result two electrons of opposite electrostatic charges are created, each with 0.51MeV of energy It does not occur during x ray imaging therefore no effect on image quality 16  Photodisintegration X-rays with energy above 10 MeV absorbed directly by the nucleus therefore, no interaction with electrons and nuclear field Nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment Photodisintegration does not occur in DI 17  Compton Effect (CE) CE is an ionization process following a partial absorption & scattering of an incident photon by an orbital e- Energy of the x-ray photon must be largely greater than the binding energy of the e- Binding energy of the electron refers to the energy required to eject an electron from its orbit. It originates from: o Potential Energy due to electrostatic force between nucleus & electrons o Kinetic energy prevents the e- from falling into the nucleus The inner orbit has the highest binding energy in an atom 18  Compton Effect (CE) Energy of Incident photon (Ei) is equal to: Es + (Eb + EKE) Ei is the energy of the incident x-ray Es is the energy of the scattered x-ray Eb is the electron binding energy EKE is the kinetic energy of the e- A 30-keV x-ray ionizes an atom of barium by ejecting an O-shell electron with 12 keV of kinetic energy. The binding energy of an O-shell electron of barium is 0.04 keV. What is the energy of the scattered x-ray? 30 keV = Es + 0.04 keV + 12 keV, Therefore: Es = 30keV – (0.04 keV + 12 keV) Es = 17.96 keV 19  Compton Effect (CE) Compton-scattered x-rays can be deflected in any direction, including 180 degrees from the incident x-ray (called backscatter). At a deflection of 0 degrees, no energy is transferred to the Compton electron. As the angle of deflection increases to 180 degrees, more energy is transferred to the Compton electron, but even at 180 degrees of deflection the scattered x-ray photon retains at least approximately two-thirds of its original energy 20  ↑ = increase X-ray X-ray ↓ = decrease Absorption Transmission ↑ Penetrating power or ↑ quality (↑ kVp) ↓ Penetrating power or ↓ quality (↓ kVp) ↑ Atomic number (Z) ↓ Atomic number (Z) ↑ Tissue density (ρ) ↓ Tissue density (ρ) ↑ Thickness of object ↓ Thickness of object  Characteristics of x-rays: o ionizing radiation with o short wavelength, high energy & frequency o polychromatic & heterogeneous o Exposure time: 1/1000 sec. to several secs o Quantity of x-rays is controlled primarily by kilovoltage (kVp) o Quality of x-rays is controlled BY the milliAmperage (mA), exposure TIME (sec.) In radiology, exposure is defined as the # of individual X-ray units (photons) that emerge from the X-ray tube and subsequently reach the IR and It is expressed in Roentgen (R) Explain: Incident or Entrance exposure, Attenuated Exposure, Transmitted or Exit exposure or remnant radiation, IR Exposure Which human tissue is the most difficult to penetrate with x-rays? T or F  X-RAY ATTENUATION is the reduction of the intensity of an x-ray beam as it traverses matter. Whether a photon is absorbed or transmitted (it can be also scattered) , it depends on factors such as…  Radiopaque? Radiolucent? Coherent Scattering: classical scattering or Thompson scattering - X-rays with energies below 10 keV Pair Production: Pair production occurs with x-rays that have energies greater than 1.02 MeV - Useful in positron emission tomography (PET) Photodisintegration: X-rays with energy above 10 MeV - no interaction with e- and nuclear field emits a nucleon or other nuclear fragment Compton Effect scattering is an ionization process following a partial absorption & scattering of an incident photon by an orbital e- For CE to happen the Energy of the x-ray photon must be largely greater than the binding energy of the e- A 60-keV x-ray ionizes an atom of barium by ejecting an O-shell electron with 24 keV of kinetic energy. The binding energy of an O-shell electron of barium is 0.10 keV. What is the energy of the scattered x-ray? Ei = Es + (Ebe + EKE) 35.90 T or F As the angle of deflection of the scatter photon increases, the energy transfer to the Compton electron decreases, however, even at 1800 deflection the scatter x-ray will still carry 1/3 of its original energy 24  Tissue density density is the quantity of matter per unit volume, specified in units of kilograms per cubic meter (kg/m3 or grams/cm3). Sometimes mass density is reported in grams per cubic centimeter (g/cm3). A radiographic image is composed of a 'map' of X-rays that have either passed freely through the body or have been variably attenuated (absorbed or scattered) by anatomical structures. The denser the tissue, the more X-rays are attenuated. For example, X-rays are attenuated more by bone than by lung tissue Tissue density describes how much of a type of tissue there is per "space" 25  Probability of Compton Effect Occurrence Compton Effect is proportional to tissue density (ρ): o Occurs mainly in soft tissues (ρ) o An ↑ in ρ results in an equal ↑ in CE (more matter → more interactions) CE is inversely proportional to the energy of the x-ray beam : o Occurs less with ↑ kVp (80 kvp and higher up to 150 kVp) Greater when energy of x-ray photon is much greater than the binding energy of e- Occurs primarily in outer shells CE can also occur in inner shell if the energy (E) of x-ray photon is very high Not affected by the atomic number (Z) of the tissue since the binding energy of the valence shell (outer shell) is the same in all atoms. (≈ 34eV) CE: ρ/E, and is independent of Z 26  Probability of CE Occurrence Compton scattering in tissue can occur with all x-rays and therefore is of considerable importance in x-ray imaging 27  Effect of scatter on image quality, patient dose and Occupational Exposure Scatter radiation reaching the IR lowers the contrast on the image causing more image graying forward scatter ↑ with a higher energy beam (kVp increase) thus increasing amount of scatter reaching the IR Compton Effect predominates over photoelectric effect at higher Energies ↑ occupational exposure Significant effect on image quality, patient dose and occupational dose 28 Image containing Image containing a lower amount of higher amount of scattered x-ray scattered x-ray photons photons 29  Probability of CE Occurrence CE 1/ E Increasing kVp, increases the E of the x ray beam, decreasing scatter radiation produced. However, a higher percentage of scatter the produced is in the forward direction (smaller deflection) and therefore reaching the IR at 80 kVp, 100 scattered photons are produced, and the number of scattered photons in the forward direction is 50 At 100 kVp, 70 scattered photons are produced, and the number of forward scattered photons is 50 30  Photoelectric Effect (PE) PE is an ionization process of matter following total absorption of an incident photon by an orbital é Energy of x-ray photon is slightly greater than the binding energy of the electron (usually k-shell é) Characteristic radiation follows PE Photoelectron Ek = Energy ofPhotoelectric incidentEffect photon – binding energy of é (Low Energy) A B C Incident K L K L K L Photon What happens to Photoelectron them? Characteristic Radiation 31  Probability of PE Occurrence Photoelectric Effect is α Z3 and inversely proportional to E3: Occurs mainly in bones and positive contrast media o A Small ↑ in Z results in a very large ↑ PE absorption Examples:  How much more likely is it that an x-ray will interact with bone than with muscle? Z of bones (13.8) Vs. Z of Soft Tissue (7.4): (13.8/7.4)3 ≈ 6.5 greater effect of PE on bone than soft tissue  what is the relative probability that x-rays will interact with iodine (Z = 54) rather than with soft tissue? o A small ↓ in E results in a very large ↑ PE absorption o Greater with lower kVp (20 to 70 kVp) Greater when Energy of x-ray photon is slightly greater than binding energy of electron Primarily occurs in inner shells PE α tissue density (ρ): more matter → more interactions 32  Photoelectric Effect (PE) Advantages of PE: It improves IC by producing no scatter o no graying of the image no occupational exposures Disadvantages of PE: ↑ patient dose compared to CE Total absorption: o incident photon o secondary radiation:  photoelectron  characteristic radiation 33  Attenuation by PE versus CE Both PE & CE will ↑ with ↓ E (↓ kVp & ↓ filtration) But the effect is much greater with PE because PE is inversely proportional to E3, while CE is inversely proportional to E 34  Attenuation by PE versus CE In the DI range, the two types of interaction that the x- ray beam will have with matter (patient) and that will have an impact on image quality, patient dose and occupational exposure are: Compton (CE) Absorption may be partial Photoelectric (PE) Absorption is total 35 36  Differential Absorption of the x-ray beam The x-ray image results from the difference between those x- rays absorbed by photoelectric interaction and those x-rays that pass through the body as image-forming x-rays Differential absorption controls the contrast of an x-ray image AS mentioned previously, attenuation is the reduction in x-ray beam intensity as it penetrates through tissue. Differential absorption and attenuation of the x-ray beam depend on the following factors: o x-ray energy o Z of the atoms in tissue o ρ of tissue o Object thickness 37 Contrast media, such as iodine and barium, use the principles of differential absorption to image soft tissue organs 38  T or F - density is the quantity of matter per unit volume, specified in units of kilograms per cubic meter (kg/m3 or grams/cm3). T or F - Compton Effect o is proportional to tissue density o is inversely proportional to energy of the beam o occurs mainly in soft tissue o Not affected by the atomic number (Z) of the tissue  T or F - density is the quantity of matter per unit volume, specified in units of kilograms per cubic meter (kg/m3 or grams/cm3). T or F - Compton Effect o is proportional to tissue density o is inversely proportional to energy of the beam o occurs mainly in soft tissue o Not affected by the atomic number (Z) of the tissue  T or F - X-rays are attenuated more by bone than by lung tissue What is the effect of scatter on image quality, patient dose and Occupational Exposure? Why does the image get grayer (IC decreases) when E of the beam increases (kVp)? High and low contrast imaging. Which image has less shades of gray True or false - Increasing kVp, increases the E of the x ray beam, decreasing scatter radiation produced. However, a higher percentage of scatter the produced is in the forward direction (smaller deflection) and therefore reaching the IR  T or F - PE o is an ionization process of matter following total absorption of an incident photon by an orbital é o happens when energy of x-ray photon is slightly greater than the binding energy of the electron (usually k-shell é) o is followed by Characteristic radiation o primarily occurs in inner shells o is α tissue density (ρ): more matter → more interactions o is α Z3 o is inversely proportional to E3 Advantages and disadvantages of PE occurring Differential absorption? Depends on x-ray energy; Z of the atoms in tissue; ρ of tissue; Object thickness what is the relative probability that x-rays will interact with iodine (Z = 54) rather than with soft tissue? (54/7.4)3 = 387 times greater  kVp & mAs They are technical factors found on the control panel of the x-ray machine and used by the MIT to determine amount of radiation need for a given exposure. What is kVp: What is mAs (mA x time) It controls the penetrating It controls the # of photons power of the x-ray beam produced It affects exposure It affects exposure An increase in kVp of 15% If mAs doubles, the will double the exposure exposure doubles It affects IC, therefore, It is It is used to control the # of used to control IC photons that reach the IR It affects patient dose 43  RADIOLOGICAL IMAGE, LATENT IMAGE & RADIOGRAPHIC IMAGE Radiological Image: (invisible image) The remnant radiation (transmitted) forms an invisible image in the space between the patient and the image receptor known as the radiological image or aerial image 45  RADIOLOGICAL IMAGE, LATENT IMAGE & RADIOGRAPHIC IMAGE Latent Image: (invisible image on image receptor) A latent image is a non-processed invisible image on a recording material resulting from an exposure of a suitable medium to X-rays, and/or light 46  RADIOLOGICAL IMAGE, LATENT IMAGE & RADIOGRAPHIC IMAGE Radiographic Image: (visible or manifest image) An image displayed on a monitor, on a film, and sometimes on paper Radiographic Image = Latent Image + Processing 47 Image Display: Negative image versus positive image 48  Image Display - Negative image & positive image negative image positive image  High density tissues (bones)  High density tissues (bones) are seen as light shades are seen as dark shades  Low density tissues (lungs)  Low density tissues (lungs) are seen as dark shades are seen as light shades  Brightness is α to absorbed  Brightness is α to rays rays in the patient transmitted out of the patient  An increase in exposure is  An increase in exposure is needed to make image darker needed to make image whiter 49 50 51 Terms & Definitions used to describe the technical quality of radiological images 52  Image Contrast (IC) Image Contrast: It is the difference between two shades of gray on the image It depends on: – Subject Contrast (SC): Range of differences in intensity of the x-ray beam after it has been attenuated by the patient – Image Receptor Contrast (IRC): the ability of the image receptor to convert SC into IC IC = SC X IRC 53 54  SCALE OF CONTRAST SHORT SCALE OF CONTRAST LONG SCALE OF CONTRAST An image that demonstrates considerable differences An image that demonstrates slight differences between shades of grey between the shades of gray but has a large total number of shades of gray Short (high contrast) Long (low contrast) 55 Image result for black and white short scale of contrast long scale of contrast 56 57 57 58  Image Sharpness It refers to the sharpness of the borders, or edges of structures seen on an image (width of the boundaries). Unsharp image = blurry image Unsharpness decreases image detail (small structures) 59 Image Sharpness 60 Image Sharpness 61  Spatial Resolution is the measure of how small an object of high contrast is recorded by the IR and shown on the image. It refers to the IR’s ability to record detail. The smaller the object or structure shown the higher the spatial resolution. Contrast Resolution refers to the IR ability to differentiate between two objects or structures that have similar tissue densities on an image 62  Image contrast is proportional to SC & IRC SC is the... x ray variation in intensity once is transmitted through the body IRC is the... ability of the IR to manipulate the image contrast when processing the image Image sharpness Scale of contrast Spatial Resolution Contrast Resolution Positive and negative image Radiological image Latent image Radiographic image mAs kV 63  More Terms & Definitions Exposure Latitude: The degree of over or under exposure that can be tolerated while still producing an image of acceptable quality. Higher EL allows a higher % of error in setting technical factors Dynamic Range The ability of the imaging system to detect very low and very high levels of radiation and reproduce them as shades of grey. Dynamic range affects exposure latitude & contrast resolution Signal to noise ratio (SNR): o method used to describe Noise Noise: It is defined as a random disturbance that reduces clarity on the image. The type of Noise due to lack of exposure is known as Quantum Noise o It is the most common type of image noise, and it is created by an insufficient influx of x ray photons reaching the IR (underexposure) The image appears grainy or mottled 64 Quantum Mottle 65 Quantum Mottle 66  IMAGE BRIGHTNESS IS UNAFFECTED BY EXPOSURE THE EXPOSURE MAY NOT AFFECT THE BRIGHTNESS & CONTRAST ON THE PROCESSED IMAGE. HOWEVER, THE LEVEL OF NOISE LEVEL (SNR) ON THE IMAGE IS DIRECTLY AFFECTED BY EXPOSURE 67  Minimum Diagnostic Value It is the amount of diagnostic (useful) information in the region of interest (ROI) Minimum diagnostic value should be obtained to respect the ALADA & ALARA principles A good diagnostic value image should have: o High IC o High sharpness o High Signal to Noise Ration (SNR) o Adequate SoC in the ROI 68 Effect of Contrast Media on Image Quality 69  Contrast Media (CM) Used to enhance the image contrast on an image makes tissues of similar ρ and Z on an image visible Positive CM agents: Negative CM agents: – Barium Sulfate & Iodine – Air & Carbon dioxide – High Z and ρ – High Z and ρ – relatively nontoxic – relatively nontoxic 70  Contrast Media No CM present Positive CM 71  No CM present Negative CM present 72  Contrast Media Colorectal Ca Positive CM Positive and negative CM combined 73