Direct Radiography (DR) Past Paper PDF

Direct Radiography  Videos DR Reverse Engineering: https://www.youtube.com/watch?v=QSVJtwehwh o&list=PLdb_R3CjOFCjSrq5TRO4SMGOZVEGnft5M DR Explained Digital Radiography System Explained (step-by- step) - YouTube 2 ...

Direct Radiography  Videos DR Reverse Engineering: https://www.youtube.com/watch?v=QSVJtwehwh o&list=PLdb_R3CjOFCjSrq5TRO4SMGOZVEGnft5M DR Explained Digital Radiography System Explained (step-by- step) - YouTube 2  Specific Objectives 1. Explain the principals of DR technology. 2. Name and describe the components in a DR system. 3. List and explain the function of the different types of cassette-less digital systems. 4. List advantages/disadvantages of DR. 5. State the differences between a direct and indirect digital system. 6. State the advantages & disadvantages of a direct and indirect digital system. 7. Compare cassette and cassette-less operation in terms of resolution, efficiency, noise 8. Learn to prevent and minimize DR artefacts (will be seen in image critique) 9. Describe the basic QC procedures applied to DR receptors 10. The GE detector principle of operation 3  Digital Radiography It is based on capturing and storing the image signal using discrete (digital) values as opposed to conventional film radiography, which uses analog (continuous) values Direct Digital Radiography (DR) and Computed Radiography (CR) are two imaging systems in Digital Radiography  The sensitivity and spatial resolution of the digital imaging system is directly proportional to the DQE  Wide Dynamic Range: It can record very low levels of radiation exposure, thus offering a greater dynamic range 6  The Digital Image Histogram It is the representation of the Image Receptor Response Function on a graph using the frequency occurrence vs. digital value intervals The horizontal axis of the histogram represents the of shades of gray values o On a traditional digital system depending on the bit depth, up to 16,000 plus shades of gray can be visible. The vertical axis represents the number of pixels that are assigned within each gray value 7  The Digital Image Histogram Digital systems use model histograms and Look Up Tables (LUT) or algorithm values for each body part projection when constructing the images Why is the histogram important? Based on the info. given on an image histogram, the quality of the image can be determined by changing the # of pixels per shades of gray 9  Factors Affecting the Histogram Analysis Collimation The system excludes any information outside of the collimated area in order to create a more precise histogram and of course a better image Body Part Positioning and Centering It affects the optical densities in the image and the histogram analysis 10  Image processing algorithms Algorithm: o how the computer executes the task according to the instructions it receives o In radiology, proprietary image processing algorithms called “Look Up Tables” (LUT) are used o algorithms are automatically applied in the image processing, thus reducing image post-processing 11 RAW IMAGE: BEFORE ALGORITHMS APPLIED ALGORITHMS APPLIED 12  ACCURATE APPLICATION OF ALGORITHMS DEPENDS ON FIELD RECOGNITION 13  Names of processing algorithms used by different vendors Kodak: EVP & USM (Enhanced Visualization Processing & UnSharp Mask) Konica: Hybrid (Mutil-Resolution Hybrid Processing) Fuji: USM & MFP (Multi-Objective Frequency Processing) Philips: UNIQUE (UNified Image QUality Enhancement) CR AGFA: MUSICA (MUlti-Scale Image Contrast Amplification) 14  processing algorithms used by GE Helix Advanced Image Processing | GE HealthCare (United States)  Exposure Index value (EIV) The EIV measures the amount of raw energy embedded in the IR Useful to measure the correct exposure for optimal image & PD (ALADA) on the GE Units the EIV is known as the exposure deviation indicator o Acceptable range → on the Agfa CR unit the EIV is known as the Log Mean Value (LgM) o Acceptable range → 2.0 to 2.3 on the Philips DR Unit the EIV is known as the Sensitivity Number (S-number) o Acceptable range → 100 to 300 16 Post processing Functions Geometric functions Image enhancement Annotation (text/drawing) Reprocessing of the image Printing of hard copies 17  The image formation elements in Digital Radiography CAPTURE ELEMENT component that captures the x-rays COUPLING ELEMENT component that transfers the x-ray–generated signal to the collection element COLLECTION ELEMENT component that collects the x-ray generated signal 18  DIGITAL RADIOGRAPHY IMAGING SYSTEMS DIRECT RADIOGRAPHY CR (DR) COMPUTED RADIOGRAPHY INDIRECT DIRECT INDIRECT CONVERSION CONVERSION CONVERSION SCINTILLATOR - CCD SCINTILLATORS - Amorpheus STORAGE SELENIUM PHOSPHORS SCINTILLATOR - TFT 19  Direct Radiography (DR) abbreviated as DR, DDR or DX is a type of Digital Radiography in which the digital registration of the image takes place directly at the detector with no intermediate processing step such as a cassette readout in computed radiography (CR)  Advantages of DR compared to CR & Film Better spatial resolution than CR but not as good as film Better contrast resolution than CR & film Higher Detective Quantum Efficiency (DQE), thus better dose efficiency than CR & film It is more efficient in the use of time, space, and personnel than film and CR Image processing is within the system 21  TYPES OF DR IMAGING SYSTEMS Cesium Iodide (CsI)/Amorphous Silicon (a-S) - Indirect Conversion Cesium Iodide (CsI)/Charge Couple Device (CCD) - Indirect Conversion Amorphous Selenium (a-Se) - Direct Conversion DEL = DETECTOR ELEMENT 22  Cesium Iodide (CsI)/Amorphous Silicon (a-S) (Indirect Conversion) It consists of an Active-Matrix Array (AMA) Cesium Iodide inside the IR made of individual Detector Layer Elements (DELs) and a layer of Cesium Iodide (CsI) on top CsI is a scintillator that converts x-rays into light A scintillator is a phosphor compound material that emits light when stimulated by x-rays CsI is the Capture Element in this system 23  The Active-Matrix Array (AMA) DEL The Active-Matrix Array (AMA) consists of a matrix of detector elements called DELS 24  CsI/a-Silicon Imaging System Capture Element: Cesium Iodide (CsI) Cesium Iodide Characteristics: To improve spatial resolution the CsI crystals have needle-like shapes and are packed closely together to reduce spreading of the light emitted high x-ray stopping power due to its relative high D & Z higher DQE than film and CR therefore less radiation dose needed Fast, dense, relatively soft and does not cleave Contact with H2O &  humidity should be avoided CsI fluoresces in the green portion of the spectrum 25  CsI/a-S Imaging System Capture Element: Cesium Iodide (CsI) structured crystals (needle-like shape crystals) perpendicular to the collection element (AMA) 26  CsI/a-S Imaging System Collection Element: Amorpheus Silicone (a-Si) Each DEL in the AMA is made of amorphous silicon, a capacitor and TFT The geometry of each DEL is very Amorphous a-Si Collection Silicone (a-S) important because only the a-Si portion Element: DEL is sensitive to the light emitted by the CsI The remaining surface of the DEL is occupied by a capacitor and TFT 27  CsI/a-S Imaging System COLLECTION ELEMENT: Amorphous Silicone (a-Si) The light emitted by the CsI (capture element) is detected by the a-Silicone in each DEL of the AMA In most systems, 80% or more of the DEL’s surface is made up of a-Silicone Collection a-Si A-Silicone is used because it: Element: a-Si o is a semiconductor material that coverts light into electrons o can be used over large areas o can absorb about 80% of the light emitted o has a high DQE 28  Detector Elements (DEL) The Thin Film Transistor (TFT) Charge sensitive device that collects and discharges Amorphous electrons Silicone (a-Si) Storage Capacitor stores energy in the form of an electrostatic field between its plates 29  The electrical charge is stored in Detector Elements (DEL) the DEL’s capacitor, and released line by line through the TFT to the analog to digital converter (ADC) which converts the electrical signal into a computer signal and sends it to the computer to form the image and display it on the monitor ADC 30  THE FILL FACTOR The percentage of the DEL surface sensitive to light (a-Si) is called the fill factor If the fill factor is 80%; then, 20% of the x-ray beam does not contribute to the formation of the image The Fill Factor affects patient dose. The greater the fill factor the lower the amount of radiation needed The spatial resolution of the system is limited by the DEL size 31 The Coupling Element is not needed in this type of imaging system because the Capture element is in immediate contact with the collection element 32  Cesium Iodide (CsI)/Charge Couple Device (CCD) (Indirect Conversion) What is a CCD? a light sensing element that converts the light signal into an electrical signal (electrons) CCD characteristics: o Highly sensitive to light with a Wide Dynamic Range ▪ It responds to very dim and very bright light intensity o The size of the detector element (DEL) can be made up to 100µm X 100µm in size, making it very adaptable to the digital imaging needs o The result is high x-ray capture efficiency and good spatial resolution (up to 5 lp/mm) 33  Cesium Iodide (CsI)/Charge Couple Device (CCD) Indirect Conversion X-ray photons interact with CsI (scintillation material) and as a result light is emitted (the signal) The signal is coupled, by fiber-optics to the collection element (CCDs) The light emitted by the CsI is carried and transferred to the CCDs that convert the light into an electrical charge This charge is stored in a sequential pattern, released line by line and sent to an analog to digital converter (ADC) 34  Amorphous Selenium (a-Se) Direct Conversion It does not involve the use of a scintillator (No CsI coat) The x-ray signal is converted directly into an electrical signal Spatial Resolution is better than Indirect Conversion Systems 35  Amorphous Selenium (a-Se) Direct Conversion The Amorphous Selenium material acts as the capture and coupling element The energy of the incoming photon excites electrons in the selenium material to a state known as the conduction band Normally, in the absence of an electric field, the excited electrons return to their ground state, the valence band. However, in the presence of an electric field, the electrons in the conduction band move along the electric field lines creating ion pairs. Thus, electrons released due to absorption of X-rays are collected when a potential across the selenium material is applied (electric charge) The DELS (TFT & Capacitor) are the collection element DEL (TFT & Capacitor) is the collection element 37 Amorphous Selenium (a-Se) Direct Conversion DEL (TFT & Capacitor) is the collection element 38 Advantages a simpler TFT without a scintillator It is used in its amorphous form; therefore, they can be made large in area relatively easily and inexpensively. high intrinsic spatial resolution achieved by the active collection of ion pairs under a high voltage with minimal resolution-reducing lateral spread. low dark or leakage current HIGHER Detective Quantum Efficiency AT LOWER KVP RANGE Disadvantages o charge-trapping within the thick a-Se absorber, which reduces absorption efficiency, increases signal retention, and causes a greater amount of lag. o potential destruction of a TFT in a detector element by overcharging caused by high X- ray exposures. o More expensive 39 Which system generates the lowest Spatial resolution due to light spread? 40  THE GE DR DETECTOR Primary Function: – To convert x-ray data into digital image data. – To transfer the digital data to an external workstation for processing and display. AMA size: – 2022 x 2022 DELs (40.4 x 40.4 cm) – 14-bit digital data conversion – Detector construction: – carbon fiber material. – The front face contains a graphite x-ray imaging area. 41  Do not use a defibrillator while patient remains in contact with detector. It can sustain a temporary splash or spray, but it is not designed to be immersed in liquid (not even temporarily). Maximum applied weight: 110kg (242 lb) concentrated; 160kg (352 lb) distributed 1 Handles 2 Battery 3 Indicator Lights 4 Power Button 5 Detector Area 6 Antenna (inside the detector) 42 1 Centerline 2 Do not defibrillate 3 RF transmitter 4 This side toward X-ray source 1 Power Button: Push On and Off 2 Indicator Lights 3 & 4 Detector ID Insert 5 battery 6 Battery latch release Detector docking connector 43 44  BATTERY REMAINING: BETWEEN 1% & 24% WIRELESS IN SLEEP MODE DETECTOR FAULT CONDITION 45 The tether is used when: The detector battery is low The detector is unable to connect to wireless signal; 46  The Portable Grid horizontal Portable Grid – Grid Ratio is 6:1 47  ELECTROMAGNETIC INTERFERENCE It has been found that some common equipment in clinical environments can generate EM fields of over 0.1 milliGauss (mG) The Detector can sustain EM energy up to 1 milliGauss (1μTesla) over a low frequency of up to 250khz Some measurements have shown 4mG field strengths which can cause artifacts on x-ray images. EM fields are reduced by the square of the distance between the EM source and the detector (ISL) Possible sources of EM fields: IV pumps, Monitors, Feeding pumps, Patient monitors, ECG equipment, EMG (electromyography) equipment, Infusion pumps, RF ablators, Powered surgical Heaters, Air conditioners, Refrigerators Recommendations: Keep IV pumps, patient monitoring, feeding pumps 1 meter or more away from any detector surface. Consider turning off equipment that cannot be moved. Change the patient or detector orientation /position to maximize distance from any equipment. 48 Cleaning the Detector, Tether and Grid Do not leave disposable wipes or cleaning cloths on the detector or grid for more than 60 seconds. chemicals and products tested and approved by GE – Bleach - 50 % mix with water (5-8% household Bleach) – Glutaraldehyde