1

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

2

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?

Room 1F01

Table supports (1)

Ultra thin, but strong carbon fibre table topsPressure sensors – cut offswitch

Easy clean table topCross infection <

EM Interlock controls

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

3

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

++

--

100 cms FFD100 cms FFDUgUg

10 cms OFD10 cms OFD

Clinical Example - Cervical Spine Inherent large OFD

++

--

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

4

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**

X-ray Tube encased withinLead lined case

Light Beam Diaphragm- incorporatingCollimator adjusters

Automatic Exposure Devices (AED) (1)

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

5

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

Central Chamber

Table Top

Lateral Chambers

Birds eye view of table top

Radiation Protection – Diagnostic X-ray Rooms

Lead (Pb) glass Pb lined doorsPb ScreensBarium plaster wallsLead coatsInverse square lawDose measurement toolsAccurate collimationX-ray beam “hardening” methodsGonad protection devices

Why Lead & Barium?

High Atomic (Z) numbers

Mobile Diagnostic Equipment

Typical features of X-ray unitStability and flexibility requiredLow/medium power unitsDual power operation (battery or wall power)Remote exposure unit

available

Fluoroscopy X-ray Equipment

Fluoroscopy unitsMobile Fluoroscopy Unit Fluoroscopy Unit Barium Enema Radiograph

X-ray Tube

Intensification Utilised in Radiotherapy

Isocentric positioning used in radiotherapy

6

Digital Radiography

http://www.siemens.com/axiom-portal/usa/aristos_fx_im_qu.htm

Computerised Radiography

Direct “Capture” Radiography

Typical kinetics of CR examination

Radiograph Created ID card passed throughID terminal

Barcode of IP read

IP Cassette inserted intothe image reader (30 sec to read 17 x 14 “ IP)

Image manipulated & sent to printer / archive

Laser “dry-view” imager prints film

Digital Images

Resolution will be affect by:matrix size (64 x 64 - 1032 x 1032)pixel sizepixel depthnoise within imagewindow width and heightmonitor resolution

Further information

http://www.siemensmedical.comhttp://www.medical.philips.comhttp://gemedicalsystemseurope.com/ukenhttp://www.fujifilm.co.uk/xray/index.htmlCarter P., (1994) Chesneys equipment for student radiographers, 4th Edition, London, Blackwell Scientific PublicationsBlackboard - Radiographic Science- Radiographic equipment