Diagnostic Imaging

RPA

radiation protection advisor

RPS

radiation protection supervisor

mSv

milisievert

maximum permissable dose

20msv annually

classified person- 30msv

grids

fits over cassette to absorb scatter radiation

kV

kilovoltage

PPE

Gown, thyroid guard, gloves(0.35mm), glasses(0.75mm)

dosimeter

contains lithium fluoride and is sent to HPA for readings every 1-3months

fluorence

crystals that emit visible light which is utilised in the composition of intensifying screens

types of xray machine

portable, mobile, fixed tube heads

xray tube head

where protons are generated

contains anode and cathode

anode

small metal disc that is afixed to a large copper rotor with an electric motor

xray photon production

mAs applied, filament heated, electrons produced, kV applied, electrons stopped/slowed down

fine focus

small filament produces small effective focal spot

cathode

expels electrons from the circuit and focus them in a beam on a focal spot on the anode

Understanding kV

photons have higher energy/frequency when kV is increased

kV increased to increase the amount of radiation coming out of xray tube

photographic density

measurement of how much a substance, such as film, transmits light or electromagnetic radiation

inverse square law

scattering exposure levels decrease proportionally with the inverse of the distance squared fro. the xray source

mA

milliamp

half press button

cathode mateiral

tungsten filament

kV

fully pressed button

anode material

tungsten and copper stem

S

seconds

half pressed + full pressed button

FFD

film focal distance

parrellel linear grid

has lead strips which are vertical and parralel to one another

cheap

can be used at any FFD

grid cut off

uneven density or loss of density on the xray due to undesirable absorption of the primary beam by the radiographic grid

focused linear grid

lead strips are tilted with an increasing angle from the center of the grid

must be specific FFD

prevents grid cut off

pseudofocused grid

lead strips are parallel by height but decreases toward the edge

correct FFD

reduced grid cut off

crossed grid

two parallel linear grids stacked on top of each other

expensive

grid factor

usually 2.5-3

Contrast study

medium that is in contrast to the tissues being imaged, in order to visualise the tissue

Positive

shows up white on xrays (barium sulphate and iodinated contrast media)

negative

shows up black on xray

double

first use a positive medium then negative

negative contrast media

commonly used agent is air, mainily in bladder

negative pressure complications

bladder rupture, intramural air, fatal air embolism, introgenic bladder

barium sulphate properties

• all poms

• used for GI studies

• not absorbed through GI tract

• insoluble in water

Barium sulphate comes in

• paste

• mixed with food

• liquid

• granules

• powder

• barium impregnated polyethelene spheres (BIPS)

Barium Sulphate contrainidications

• not allowed to enter bloodstream

• leakage in body can cause adhesions

• risk of aspiration pneumonia

• can cause GI irritation

iodinated contrast media properties

• all poms

• higher atomic number than the tissues so is radiopaques

• water soluble

• can be ionic/nonionic

Ionic

• dissociates in solutions

• very high osmotic pressure

• should not be used in myelography

• cheaper than non ionic

Non Ionic

• remains a single molecule

• lower osmotic pressure

• less effect on nervous tissue

• expensive

• can be used for everything

iodinated contrast media contraindications

• only non ionic can be used for myelography

• uncontrolled hyperthyroidism in humans

• renal disease due to fluid being passed through kidneys to be excreted

Negative Contrast media

radiolucent

used for bladder, intestinal tract and joints

Air

shows up black

Positive Contrast Media

radiopaque

used for GI tract

barium sulphate

shows up as white

Ionic Iodinated CM

Radiopaque

used for GI, blood vessels, joints, salivary glands

high osmotic pressure

non ionic iodinated cm

used for myelography

low osmotic pressure

rules for contrast studies

no sedation for GI studies

plain xrays first

starve for 24hours

enema 2-3 hours before

catheterise

retrograde large intestinal study

diluted barium given slowly into ascending colon with enema pump or funnel

purse string suture to tighten the anus and keep tube in place

timings for GI studies

Oesphagus- immediatly after

stomach - immediatly after

small intestine - taken in intervals

Intersuseption

block necking of intestine

Angiography

iodinated contrast media

into peripheral vein

60-90mins before it reaches aortic arch

IV Urography

heavily sedated

bladder must be empty

never use on a patient in renal failure

retrograde urethrography

catheterise the urethra with widest catheter possible

tip of catheter is postioned distal to area of interest

retrograde vaginourethrography

pass foley catheter, prefilled with saline

take xray immediatly after admin

myelography

patient must be under GA

Plain xray taken of the area of suspicion

cisternal puncture is required if lesion is from the neck down

lumbar puncture is required if lesion is from the lumbar down

scintigraphy

radioactive isotopes given to the patient

they are then detected by the gamma camera

HYPERTHROIDISM CATS