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RAD 122 - PP Unit 1

Unit 1 PowerPoint

What is the main difference in film screen versus digital? The RECEPTOR
System characteristics are related to what part of the digital system? the RECEPTOR
what is equivalent to system processing? WORKFLOW
What is NO FAULT technique? in FilmScreen, tech HAD to know correct technique; In DR, wider dynamic range can be processed to enhance image without using best technique
What are pros and cons of NO FAULT technique? wide dynamic range, fewer repeats tech can get lazy with technique, increase patient dose, tech can edit image before it's saved to patient record (PACS)
What is digital imaging? the acquisition of images to a computer rather than directly to film
What has changed with digital? from analog system - visual cues for under/over exposure acquisition & display are coupled (xray is display) DR system - no visual cues (EI or S#), acquisition and display are not coupled (Detector and monitor) DIFFERENCES - processing & detector type
what are visual cues for digital under/over exposure? How does tech know if picture is over/under exposed no visual cues unless quantum mottle present EI or S#
What are differences in film screen and digital processing? Film screen uses chemicals DR uses CR reader or FPD
What is density? amount of blackening due to energy deposited in film's emulsion (film screen term) various densities are result of beam attenuation from tissues
What is contrast? Difference between adjacent densities (film screen) in DR - difference between exposure brightness levels
What is brightness? amount of luminance coming from display monitor PROPERTY of the MONITOR brightness is based upon a pixel value which is determined by xray attenuation (differential absorption) secondary - pathology, patient factors (thin or dense, etc)
How does a thick patient affect pixel value? increased pixel brightness value; based on absorption and attenuation
What is IMAGE CONTRAST? Difference between any two areas of brightness (adjacent differences in receptor exposure) to differentiate among anatomic structures Difference in pixel values (based on attenuation) relative to signal intensity (x-ray exposure) Orth p254/Papp p46
What is contrast used to describe? the shades of gray in an image - GRAY SCALE Orth p 254
What is contrast resolution? the ability of the imaging system to distinguish between small objects that attenuate x-ray beam in a similar manner Orth p 254
What is window width? the values of interest the tech can use to set contrast; adjustment used to change radiographic contrast
What processing algorithm controls IMAGE CONTRAST? LOOK UP Table - a processing algorithm selected at time of study; PP p3
What influences Image Contrast? kVp collimation grids filtration anatomical part (subject contrast ) pathology
What is dynamic range? refers to the range of exposure intensities an IR can accurately detect/display (capture) GRAY SCALE range of gray levels available to construct the image Orth p 256/273 Papp p 44
What is exposure latitude? range of techniques that produce quality image w/ acceptable appearance (low noise) and does not violate ALARA (patient exposure) range of exposures that produce acceptable radiograph w/ brightness in diagnostic range Orth p152 determined by EI or S #
Which axis represents x-ray exposure or intensity in a digital vs film screen response graph? X axis Orth p 272 fig 20.14
Which axis represents detector response in digital vs film screen? Y axis Orth p 272 fig 20.14
Lower values on graph of dynamic range are referred to as _____ increased brightness levels; decreased density (increased attenuation) PP p13
Why need LUT (look up table)? look up table algorithm allows computer to process image to correct contrast level
Why MUST the tech use the EI or S# to determine exposure levels? Because the monitor will always display the appropriate brightness levels even with under/over exposure; no visual cues
PROS of digital system wide dynamic range and wide exposure latitude allows system to capture more information allowing tech to use lower technique (ALARA) greater contrast resolution - improved workflow efficiency (immediate results, remote access via PACS)
CONS of digital system spatial resolution (Orth p251) dependent upon processing algorithm and display characteristics (monitor); dose creep
What are tech responsibilities in evaluating images? ensure anatomy is visible and EI# or S# within range
What is acquisition? how the image is acquired
what is spatial resolution? high contrast resolution? min separation btwn 2 objects at which each can be distinguished as 2 separate objects in image ability of imaging system to create separate images of closely spaced high contrast black & white objects (do 2 objects appear sharp/clear or blur together)
What is IRD? image reader device used in CR
In FPD, what controls spatial resolution? determined by the size of DEL (detector element) or dexel or
What controls spatial resolution in CR reader? Sampling frequency in CR reader Can be manipulated in CR,
how is spatial resolution affected by display? The spatial resolution is linked to the type of display and the associate hardware (cords, wire, wireless, tethered IR) Display limits spatial resolution - different size pixels
Describe artifacts anything that does not belong in the image - removable objects like jewelry, IV lines, O2 tubes, anatomical structures that are superimposed over area of interest/electronic noise
pixel brightness all pixel brightness levels should have an intermediate level of gray ranging from very light gray to very dark gray. may need to be adjusted to achieve the best level of brightness
Pixel - digital image display Orth p 249 Papp p44/49 picture element - pixel on display monitor one of characteristics of digital image can be evaluated for spatial res smallest component of matrix/picture element is smallest item of info digital image-2D representation of image
pixel size measured from end to end (measured in microns 1000 of mm, .001mm)
pixel pitch measure from center of one pixel to center of adjacent pixel (measured in microns 1000 of mm, .001 mm)
pixel density number of pixels/mm determined by pixel size/pixel pitch INCREASED pixel density INCREASED spatial resolution
what happens if I increase pixel size? DECREASE spatial resolution - larger pixels equals less information
what happens if I decrease pixel size? INCREASE spatial resolution - because smaller pixels equals more information
What happens if I decrease pixel pitch? INCREASE spatial resolution - because we are decreasing distance between centers (decreasing pixel size)
What happens if I increase pixel density? Orth p257 INCREASE spatial resolution
What is pixel pitch/size dependent on? matrix size OR Image receptor size OR Field of view
What is pixel size and pixel pitch determined by? DEL size sampling frequency
Pixel values
quantization Orth p 277 process of assigning discrete numerical values to data points *Assigns values based on bit depth *# of gray shades avail per pixel dynamic range of detector (# of gray shades in pixel)
Describe how pixel value is determined The value assigned to each pixel is relative to signal intensity received by detector (xray photon), GOVERNED by bit depth of system
Describe matrix of digital image The digital image is a matrix of numbers, known as pixels, that corresponds to the intensity of the xray beam that strikes a particular area
What happens with spatial resolution and appearance of digital images when matrix is increased from 32x32 to 1024x1024? Orth p 251 fig 19.5 more information is displayed with improved spatial resolution as you increase quantity of pixels Can see individual pixels in 32x32 image, cannot see individual pixels in 1024x1024
How do you get more detail? increase matrix size (more pixels)
What is field of view? FOV - Display monitor (can only change if you change monitor size) FOV - image including anatomy
What happens to matrix size, pixel size, and spatial resolution if you INCREASE field of view? matrix remains constant pixel size remains constant spatial resolution DECREASES
What happens to matrix size, pixel size, and spatial resolution if you DECREASE field of view? matrix remains constant pixel size remains constant spatial resolution INCREASES
What happens to FOV, pixel size, and spatial resolution if you INCREASE matrix size? FOV remains constant pixel size DECREASES spatial resolution INCREASES
What happens to FOV, pixel size, and spatial resolution if you DECREASE matrix size? FOV remains constant pixel size INCREASES spatial resolution DECREASES
Formula for determining pixel size FOV / Matrix
analog versus digital Selman p297 analog computer processes data on unfolding events, REAL TIME (clock with hands that constantly move versus digital watch which changes at defined intervals)
computer operations Operating system Operating system - master control program manages computer functions such as accepting data and controlling operations
Computer components hardware - all components that can be touched software - "untouchables" that include operating system, programs, contents of storage devices
Computer components Input devices Keyboard - input text & #s, FUNCTION keys mouse - pointing device select icons, manage text & images, place cursor data storage (external) - CD-ROM, USB modem - device carries info to/from computer via phone CPU - microprocessor Memory (RAM)
Computer components Output devices Display monitor - CRT, flat panel uses a video card (VGA, SVGA) Printer - creates hard copy (inkjet or Laser) modem - output device converts digital info to audio signals to transmit over phone (internal or external)
Computer operations Input Input - 2 types - Programs - govern acquisition, manipulation and output of data Data - input for processing by computer (arrange into table, spreadsheet etc)
Computer operations Memory Memory - 3 types ROM (read only unchangeable) RAM (random access - functions when computer is on and vanishes when off Storage memory - including hard drive, floppy, optical disk, USB
Computer operations Processing includes accessing and processing by the CPU of data and program instructions temporarily stored in RAM Rapid access by CPU occurs through BUS
What is machine language? uses binary code because simplicity & economy. It comprises two digits - 0 and 1 (allows for on/off or high/low, etc) BIT - each digit (one and zero) smallest unit of info system can process BYTE - 8 bits GATING - opening and closing of microswitches
ADC and machine language ADC assigns pixel values based on bits (0 and 1) pixel will be converted to single numerical value each number is result of 1s and 0s
Increase CONTRAST RESOLUTION. High grayscale - ability to distinguish many shades of gray; dependent on the pixel bit depth (higher bit depth = increased contrast resolution)
Increase CONTRAST. short and high scale, (less grays, more whites and blacks)
Difference between contrast and contrast resolution. Contrast - quantity of grays (high vs low) Contrast resolution is ability of system to separately display two objects with similar subject contrast
What kind of contrast resolution does a 1bit system have? low contrast resolution High contrast; Think 2 bits - 0 and 1 - black and white
What kind of contrast resolution does an 8 bit system have? 256 shades of gray; high contrast resolution LOW contrast; think more bits means more shades of gray available.
What is grayscale? different number of shades of gray that can be stored/displayed on monitor
What is contrast resolution? ability of imaging system to distinguish between small objects that attenuate the xray beam in a similar manner
What is the difference between scale of contrast and contrast resolution? scale of contrast indicates # of shades of gray; Increased contrast resolution will display decreased contrast, more blacks, whites and grays; the ability of the system to display 2 similar density materials as separate objects
What happens to contrast resolution if we increase the pixel bit depth? Allows us to increase contrast resolution because of more shades of gray are available with increased pixel bit depth
What are the types of digital detectors? DR - digital radiography (anytime you use a computer to process or view images) CR - computed radiography (PSP) plate DR - flat panel display (FPD)
what is a FPD? Orth p 265 / 272 flat panel detector array of detectors (DELs, Dexels), electronic components that carry signal to computer image is processed within detector
What does CR use to capture image? cassette based system PSP - photostimulable phosphor (Barium Fluorohalide with Europium) image is stored on IP plate (white plate inside); take to reader to process image
What are the types of FPD? Direct conversion (capture) - uses a-Se Indirect conversion (capture) - uses a scintillator (light producing phosphor)
Explain the parts of CR - capture element, coupling element, collecting element PP p14 Capture Element - BaF PSP Coupling Element - lens/fiber optic Collecting Element - Photo-detector
Explain the elements of Indirect DR - capture element, coupling element, collecting element PP p14 Capture Element - CeI (Cesium Iodide) SCINTILLATOR Coupling Element - Fiber optics Collecting Element - CCD/CMOS Flaw - CCDs are squares, tiled w/in detector, info poss lost in seams (seams poss visible) fix w/FLAT FIELD CORRECTION
Explain the elements of later Indirect DR - capture element, coupling element, collecting element PP p14 Capture Element - CeI (Cesium Iodide), GdOs; Coupling Element - Contact layer (a-Si); Collecting Element - TFT
Explain the elements of Direct DR - capture element, coupling element, collecting element PP p14 Capture Element - a-Se (amorphous Selenium) Coupling Element - none Collecting Element - TFT
Explain cassette-less DR Outpatient services No cassette, built in to wall bucky FPD/TFT CCD/CMOS PSP plate with charge coupled devices
Explain cassette based DR Includes tether based cassettes More flexibility to create images when patient is limited in movement PSP plate Flat panel detector/TFT PSP plate with a CCD
What is the function of the detector? To absorb/capture the remnant beam
Describe indirect conversion Orth p 266 /273 / 275 Radiation to receptor, scintillator produces light, light converted to digital signal (2 steps)
Describe direct conversion Orth p 273 / 275 remnant beam to receptor, immediately converted to analog signal (1 step) NO SCINTILLATOR
Are CR systems direct or indirect? indirect 2 steps in PSP, then use reader to process into image
How does CR reader work?
describe CCD Orth p 273 small, highly adaptive light sensitive devices must have SCINTILLATOR to function (solid state device looks like a sim card)
describe CMOS complementary metal oxide semiconductor light sensitive device with low efficiency vs CCD must have SCINTILLATOR material to function used primarily in dental imaging with lower techniques - not used in diagnostic radiography
Explain TFTs Thin Film Transistor; photosensitive array, made up of small pixels, converts light into electrical charges; switch activated by electrons, capacitor stores electrons
What is AMA? Active matrix array array of DELs or dexels that contain TFTs (all electrical components) that will take info from plate for processing same as TFT array
Explain the FPD AMA. Active Matrix Array matrix of pixels Each pixel has a light sensitive face painted with A-Si (amorphous Silicon), also has TFT embedded in DEL or dexel.
What is a dexel? Orth p 275 a hardware pixel; detector element; has three components: *Semiconductor detector surface area *capacitor *thin-film transistor
Describe fill factor the percentage of the dexel face that is devoted to semiconductor detection area approx 80%, remaining 20% (TFT and capacitor)
Describe types of PSP plates (indirect DR) Orth p 266 have SCINTILLATORs Turbid phosphors Structured phosphors
Describe turbid phosphors. Orth p 266 scattered and random (like a fruitcake) spreads light results in lower spatial resolution
Describe structured phosphors Orth p 266 columns of phosphors (like straws in a box) less light spread improves spatial resolution Used in indirect capture systems to reduce light spread, transmits more directly to the a-Si (to produce electrons)
What phosphor does CR and indirect capture use? Barium Fluorohalide and Europium, Cesium Iodide; turbid and structured, most indirect capture systems use turbid
explain luminescence Orth p 205 the immediate emission of light in response to excitation, not due to heat the ability of a material to emit light in response to excitation
explain phosphorescence Orth p 205 BAD (phosphors glow after stimulation ends) the continuation of light emission after the stimulation ceases creates screen lag/afterglow
explain fluorescence Orth p 205 the production of light during the stimulation of the phosphor by xrays
How does indirect capture work? (CeI) scintillator creates light; a-Si produces electrons from the light
How does direct capture work? Uses same AMA, different capture material - a-Se converts to electrons electrons drift down to TFT capacitor stores within TFT because there is no scintillator there is no loss of info during translation
What are the layers of the PSP plate? p266 Orth/PP p12 Unit 2 Protective layer PHOSPHOR LAYER/active ANTIHALO LAYER/Conductor REFLECTIVE LAYER/Light Shield support layer base layer/backing
describe phosphor layer of PSP plate layer of photostimulable phosphor that traps electrons during exposure Typically made of barium fluorohalide and EUROPIUM held together by binding material turbid or structured
describe antihalo layer CONDUCTOR LAYER; absorbs stimulating laser light and prevents from reaching reflective layer
describe reflective layer sends light in a forward direction to photodetector when released in reader (light shield)
What process allows Europium to store xray energy? photoelectric interaction
How long can Europium maintain image? loses 25% of info within 1st hour
Describe sampling 2nd step in digitizing an image Focused on CR reader but also occurs in FPD converts latent image into electrical signals that can be digitized and displayed the function of detecting and measuring radiation from IR or array
Describe quantization 3rd and final step in digitizing the analog image assigns a value to each pixel to represent a discrete gray level (a number) must be rounded up or down to whole number
What are the steps to digitize the image? Scanning Sampling Quantization
Describe scanning 1st step in digitizing analog image. Each cell is a pixel, assigned a designator, CR reader scans plate in designated # of lines. In DR, pixels are based on TFTs embedded in IP (collimation effectively selects pixels and acts as a scanner)
what is ADC analog to digital converter detectors produce continuously varying signals make up latent image; convert analog signal to digital w/ADC controls sampling frequency closer the samples are, improves spatial resolution stores pixel bit depth
Sampling frequency relationship Increased sampling frequency increases spatial resolution which will decrease pixel pitch increases spatial resolution which will decrease pixel size increases in spatial resolution REMEMBER all independently related to spatial resolution
What influences subject contrast? - Internal factors (tissue densities within part/pathology) - External factors like radiation quality, scatter, contrast agents
Created by: Larobbins