RAD 100 ch 8 att. 3

• what is the purpose of any medical imaging procedure?

  To provide accurate information about the patient's medical condition or disease
• Diagnostic Yield


  amount of clinically useful information on a diagnostic image
• Different medical imaging modalities that provide different types of information?

  Radiography, Sonography, Nuclear Medicine Technology, Interventional Technology, etc
• Each modality has it's own considerations for ordering procedures

  -physicians expect a certain amount of diagnostic yield when the exams are odered

  -diagnostic yield of information must outweigh the input factors (radiation dose, risk to patient, tolerance, cost, timeliness) of the procedure

  -competent imaging professionals will strive to maximize diagnostic yield using a minimum of input factors
• Diagnostic efficacy


  accuracy of diagnostic information -any extraneous information on the image that does not reflect the patient's true medical condition detracts diagnostic efficacy -want diag. efficacy and diag. yield must be optimized as the standard care
• X-ray machine design- contains:

  x-ray tube and support, collimator assembly, radiographic table, generator and control panel, upright image receptor (IR)
• Tube design


  -tube is inside a lead-lined tube housing

  -tube is made of Pyrex glass with a high vacuum

  -tube produces x-radiation when high energy electricity passes through the tube

  -x-radiation exits the tube through a window in housing and is directed toward the patient
• parts of an x-ray tube

  •housing- sturdy, lead-lined metal

  •glass envelope- made of Pyrex glass and is vacuum sealed

  •cathode- negatively-charged side of tube where electrons are leaving the filament

  •anode- positively-charged side of tube , where electrons hit rotating tungsten anode (target)

  •electron beam- electrons move from filament (cathode) to anode

  •x-ray beam- radiation exits housing through window and is directed to the patient
• Collimator


  •x-ray beam limiting device (BLD)

  •controls sias and shape of x-ray field directed toward patient

  •projects high intensity light and represents where x-ray exposure will go

  •May be manual or automatic (PBL)

  *PBL- positive beam limitation- cutting of x-ray that we don't need- can detect size of IR being used
• Radiographic Table


  -may be a fixed height or variable height

  -tabletop is highly translucent

  -4-way "floating" tabletop

  -some table designs permit a variable speed
• Bucky assembly


  -consists of receptor tray

  -tray holds IR tightly in receptor and is centered to long. axis of table

  -radiographic grid oscillates during exposure to blur out the load grid lines

  -used woth film-screen and computed radiography systems
• Generator control


  -control console is interface between radiographer and sophisticated electronics of x-ray machine

  -console features include: on/off switch, exp. technique selections, exp. button

  -most are microprocessor controlled and use a simple computer interface

  -newer systems may be integrated into digital radiography
• Exposure Factors


  kVp, ma, and time
• kVp


  penetration power of x-ray
• mA


  amount of current
• time


  Amount of time current is released

  - mA x s = mAs (total quantity of x-ray exposure)
• Automatic Exposure Control


  -may be optional -expisure technique selection that may be automatically programmed
• focal spot selection


  small focal spot for very defined objects/small body parts (anything 65 kV and below, use a small focal spot)
• X-ray tube supports


  -Two basic designs:

  •floor- mounted tune stands &

  •ceiling- suspended Otc's- very versatile

  -facilitates easy and efficient positioning of x-ray tube assembly around patient in any orientation

  -capable of various motions depending on need

  -ergonomically friendly

  -aesthetically pleasing and not intimidating to patients
• tube angulation


  tubestand rotation around a vertical axis, permitting cross-table exposures and extended x-ray tube vertical travel to about 10-12 in. above floor
• Tube movement controls


  longitudinal, transverse, vertical
• Major responsibility of radiographer

  proper manipulation of the various components of the radiographic system to provide a high-quality image or radiograph of the anatomic area of interest
• ALARA principle


  As Low As Reasonable Achievable
• Image receptor Classification


  Cassette-based or cassette-less
• Cassette- based systems


  employ a screen film combination or a photostimulable storage phosphor (PSP) screen in a light-tight cassette

  -a.k.a.- "computed radiography"
• Remnant radiation


  all radiation that is detected by the receptor
• the only radiation that is of clinical value to us in medicine is radiation that is absorbed by the detector material
• Latent Image


  invisible image
• PSP Technology


  -uses a reusable imaging plate that is flexible and coated with an alkali earth halide metal. -PSP detectors capture the energy of the remnant beam and store it for a period in electron traps. -The laser light energy in PSP material, typically a Ba fluorohalide, and forces the fluorescent emission of light energy from these atomic stored energy electron traps, which is what makes up the signal from the PSP plate. The light is gathered up by a light guide assembly and directed into a photomultiplier tube device for signal amplification. -After plate is scanned the plate is passed in front of an intense white light source and new plate is reinserted in into a cassette for reuse.
• Digital Radiography Technology


  fall into 2 categories:

  •direct

  •indirect

  -often called flat panel detectors

  -both of these use thin film transistor technology for electronic readout of the signal created from x-ray exposure

  -no reader is required
• Digital Radiography Advantages


  -lower dose

  -quicker image presentation

  -better spatial resolution
• Digital Radiography Disadvantages


  -typically more expensive by comparison

  -sensitove to mechanical abuse such as dropping the DR cassette or fluids getting into the DR circuitry
• tether


  -associated with digital radiography

  -flexible cable that is a rechargeable battery pack
• Direct Digital Radiography


  use a-Se as detector material -energy of x-ray beam is captured and directly converted into an electronic digital signal to be used by the computer
• Indirect Digital Radiography


  use a-Si -light is captured with the help of a scintillator that captures the energy of the x-ray beam -the scintillator then emits light on x-ray stimulation and the light is captured by the a-Si to convert to electrons and then to a digital signal
• Fluoroscopy


  real-time images- study of the dynamic action of the human body -used to create images that are continuous and demonstrate vital processes such as gastrointestinal (GI) movement and structure, blood vessels, genitourinary functionality, and joint mobility, among others
• Trendelenburg tilt


  head is lower than the feet
• HIPAA


  Health Insurance Portability and Accountability Act
• Post-processing


  includes operations such as image reversal image annotation, spatial filtering (edge enhancement), magnification, and windowing of brightness contrast (level and width)
• Tomosynthesis


  radiographic procedure that acquires as many as 60 low-dose projection images during a single x-ray tube-detector sweep of patient and with a single breath-hold