width and height determine how much scattered radiation is filtered

Substances admimistered to patient that are either more or less radiopaque than the surrounding tissue

Provide detail of organ size, shape, position, internal detail and sometimes function

Can have adverse affects, e.g if injected into the wrong place in the body, it could cause problems.

Can be used with positive contrast agents to give double contrast study

Theoretical risk of air embolus in blood stream, so CO2 can be used which is safer but it isn't used often

Irritant if enters body cavities - take care if suspected perforation

Imaging of cardiovascular system, urinary tract, joints, salivary glands, tear ducts, fistulas/sinuses, gastrointestinal tract, myelography

Ionic: suitable for IV or direct administration (but NOT myleography) e.g. meglumine diatrozoate

Non-ionic: suitable for myelography and any other use – e.g. iohexol. Recommended for all applications as fewer side effects.

Hyperosmolar (ionic)  unpleasant side effects if conscious (nausea, vomiting, etc.)

Contra-indicated IV in hypovolaemia, hypotension and cardiac or severe renal failure (stabilise first)

Myelography (contrast radiography of spine – subarachnoid space)

Intravenous urography (IVU) or excretion urography (intravenous injection of contrast excreted by kidneys)

[Cardio-]Angiography (contrast radiography of [heart and]blood vessels)

Positive contrast cystography (infusion of positive contrast into bladder)

Double contrast cystography (infusion of positive contrast followed by air into bladder)

Many contrast studies are superseded by other imaging techniques e.g MRI for spinal conditions or ultrasounds for cardiac disease

Alternative imaging techniques are not always available (location or cost)

The usefulness of these techniques is directly related to the skill of either the acquirer, the interpreter or both (e.g. ultrasonography)

Blood flow towards the transducer results in the reflected frequency being higher than the transmitted frequency

Blood flow away from the transducer results in the reflected frequency being lower than the transmitted frequency

This difference is called Doppler shift and its magnitude is related to the velocity of the blood cells by the doppler equation

Colour in the sample volume represents: mean velocity and direction

Displayed with velocity (Y axis) and time (x-axis) of the graph. Flow towards transducer is recorded above baseline, flow away from transducer is displayed below the baseline

Some artefacts are useful to indicate the nature of structures and cannot be avoided:

To resolve or prevent: turn of other electrical equipment, and reduce TGC

Occurs in deep tissue interfaces with marked impedance differences

Caused by total reflection of sound waves at tissue interfaces with impedance differences

Structures displayed more clearly deep to fluid-filled organs, such as bladder

Caused by low attenuation of sound beam through anechoic structures

Numerous parallel lies present of decreasing intensity as go deeper - caused by poor transducer contact (air between probe and skin- use more gel)

'Comet tail' or /Ring down' artefact - caused by reverberation between two highly reflective interfaces e.g between gas bubbles in GIT

To resolve: poor contact- use lots of coupling gel, ensure good contact with patient by clipping hair or use a smaller transducer

Faint reversed image of structure/organ adjacent to the original, usually separated by a curved echogenetic structure

Occurs commonly at the diaphragm and may be mistaken as a rupture

To resolve: alter transducer angle and change the gain and TGC settings