1 Radiographic Science Basic Overview of diagnostic radiography Marc Griffiths Overview - Equipment found in a general X- ray room – Diagnostic X-ray tube – Tube support Mechanism – Diagnostic Table – Upright stands – Cassette scatter control (Bucky) units – Exposure control device (control console) – Radiation Protection aids – Cassettes & film – Patients! Methodology of producing a medical radiograph Patient positioned in relation to exam being undertaken Radiographic equipment (ie X-ray tube) positioned Exposure set on control panel Instructions given to patient Radiographer stands behind lead glass screen Exposure undertaken Cassette processed Radiograph reviewed Producing a radiograph(1) Producing a radiograph (2) Electrons produced from filament (-ive) of X-ray tube Attracted to anode (+ive) via a potential difference (kV) Electrons interact with anode to produce X-ray photons (+ a lot of heat!) Each X-ray photon has a specific “energy” up to the maximum potential difference that was applied to the X-ray tube (i.e. 70 kV) An X-ray “Spectrum” is therefore created Diagnostic X-ray Tube
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Diagnostic X-ray Tube - Bristol UWEtea.uwe.ac.uk/radscience/Diagnostic_rad_equipment/basic...2 Diagnostic X-ray Tubes zAttached to a tube support (luckily) zProduces X-rays (& heat)
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Radiographic ScienceBasic Overview of diagnostic radiography
Marc Griffiths
Overview - Equipment found in a general X-ray room
– Diagnostic X-ray tube– Tube support Mechanism– Diagnostic Table– Upright stands– Cassette scatter control (Bucky) units– Exposure control device (control console)– Radiation Protection aids– Cassettes & film– Patients!
Methodology of producing a medical radiograph
Patient positioned in relation to exam being undertakenRadiographic equipment (ie X-ray tube) positionedExposure set on control panelInstructions given to patientRadiographer stands behind lead glass screenExposure undertakenCassette processed Radiograph reviewed
Producing a radiograph(1)
Producing a radiograph (2)
Electrons produced from filament (-ive) of X-ray tubeAttracted to anode (+ive) via a potential difference (kV)Electrons interact with anode to produce X-ray photons (+ a lot of heat!)Each X-ray photon has a specific “energy” up to the maximum potential difference that was applied to the X-ray tube (i.e. 70 kV)An X-ray “Spectrum” is therefore created
Diagnostic X-ray Tube
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Diagnostic X-ray TubesAttached to a tube support (luckily)Produces X-rays (& heat)Operated at high voltage (40 - 150 kVp)> Insulation requiredOil used to cool X-ray tube during exposuresOil also acts as an insulatorX-ray tube lead linedIncorporate safety interlocksLight Beam Diaphragm Integrated Collimation Equipment Earthed (Shockproof)
Ceiling Mounted X-ray Tube
Types of X-ray tube support
Floor Mounted X-ray Tube
Floor Mounted Equipment
Can you think of the disadvantages of floor mounted X-ray tubes?What are the advantages of floor mounted X-ray tubes?
Table Support (2)Strong enough to support large patientsLow attenuation materials (Carbon Fibre)Rise and fall facilities“Kick” buttonsIntegrated “Bucky” trayInsulatedEasy to clean – Cross infection <Pressure switches
Upright Chest Stands (1)
Chest Stand – Similar materials to table top
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Upright Chest Stands (2)
Integral cassette traySupport mechanism for infirm patientsLocation in X-ray important (?)Patient handlesSafety interlocksUtilised for various examinations
– Chests– Cervical Spine– Weight Bearing Knees
Chest Radiography Technique
180 cms Focus Film Distance10 cms Object Film DistanceThink about why we perform chests PA where possible?
Magnification
MAGNIFICATION in Diagnostic Imaging
Magnification is reduced by:
Close contact between object and and film i.e. short Object Film Distance (OFD)Long Focal Film Distance (FFD)
OBJECT
IMAGEIMAGE
FOD
FFD
Focus
OFD
Clinical Example - Cervical Spine Inappropriate FFD
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100 cms FFD100 cms FFDUgUg
10 cms OFD10 cms OFD
Clinical Example - Cervical Spine Inherent large OFD
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180 cms FFD180 cms FFD
10 cms OFD10 cms OFD
Integral Cassette Tray (1)
Integrated within table top Lock mechanism ensures cassette is secureGrid mechanism incorporated within cassette trayGrid reduces scatter radiation from certain examinations
– Abdomen– Pelvis– Hips
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Integral Cassette Tray (2)
Important that X-ray tube and cassette tray are alignedSet distance between X-ray tube and Cassette trayOscillating movement ensures scatter is absorbed before reaching film
Integral Cassette Tray - Images
Right Hip Replacement
Intravenous Urography (IVU)
Exposure consoles (1)
Circ. 1978 Approx. Modern Day Anatomical Programmed Units
Exposure consoles (2)Modern day control consoles anatomically programmedPre-set exposuresManual exposure values available to radiographer (kV, mA, sec)Modern X-ray tubes incorporate exposure factors
Integrated Diagnostic X-ray units
Integrated Exposure Display
Integrated Exposure Controls **Does not include actual exposure button**
Variable densities exist within subjectsThink back to earlier lecture –
– Production of X-ray radiation can be measured
AED’s monitor the beam of X-rays transmitted from the patientLocated under patient but above cassetteMinimises inaccurate exposures
Automatic Exposure Chamber – Ionisation Chamber
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Automatic Exposure Devices (AED) (2)
Exposure terminates once a sufficient quantity of radiation has been received to produce a radiographic image of required densityPermit accurate exposures Usually three AED’s incorporated in table tops and vertical chest standsMarkings usually on surface of table/chest standIndividual chambers may be selected – depending on the exam being performed