Contrast MediaContrast Media

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Aims of this session Aims of this session

Why contrast agents are used Why contrast agents are used What are the desirable features of a contrast What are the desirable features of a contrast

agent agent Types of contrast agents used in clinical Types of contrast agents used in clinical

settings settings Methods of administrating contrast agents Methods of administrating contrast agents Examples of examinations utilising contrast Examples of examinations utilising contrast

agents agents Problems/issues associated with Problems/issues associated with

administrating contrast agents administrating contrast agents

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ContrastContrast

The difference in optical density The difference in optical density between different parts of an between different parts of an image on a radiograph. It is a image on a radiograph. It is a reflection of the different reflection of the different absorption coefficients and bulk of absorption coefficients and bulk of different regions of the part being different regions of the part being radiographed radiographed

Contrast Media

It is a chemical substance of very high or very low atomic number or weight, there for it increase or decrease the density of the organ under examination.

UNIT VII 5

“Contrast Media"– substance placed

in the body to provide added contrast when subject contrast is low

– increases the radiographic contrast between the area containing the CM & areas not containing CM

Without CM

With CM

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Contrast MediaContrast Media

A substance which when A substance which when introduced into the body will introduced into the body will increase the radiographic contrast increase the radiographic contrast in an area where it was absent or in an area where it was absent or low before. low before.

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Brief HistoryBrief History

1897 - First reported GI contrast study 1897 - First reported GI contrast study performed - Bismuth - TOXIC! performed - Bismuth - TOXIC!

1910 - Barium Sulphate used (safer) 1910 - Barium Sulphate used (safer) 1920’s - Sodium Iodide used to treat syphilis. 1920’s - Sodium Iodide used to treat syphilis. Iodine was found to be radio opaque to x-rays. Iodine was found to be radio opaque to x-rays. Bases of all modern contrast agents. Bases of all modern contrast agents. 1927 - First reported IVU with iodised organic 1927 - First reported IVU with iodised organic

salts (Uroselectan)salts (Uroselectan)

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Requirements of a Contrast Agent Requirements of a Contrast Agent (1)(1)

Easy to administer No toxicity Stable compound. – Will not dissociate into

toxic ions When injected the media concentrates in

area(s) required The agent’s physical features allow the

organ to be properly demonstrated e - even barium coating of the stomach in

the presence of an acid environment.

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Requirements of a contrast agent Requirements of a contrast agent (2)(2)

The agent should have rapid elimination.

The agent should not be carcinogenic.

The agent should have a viscosity appropriate to the patient when introduced.

The agent should cause minimal distress to the patient when introduced.

The agent should be cost-effective.

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Methods of administrationMethods of administration

Orally. Rectally. Intra- venously – (injection / infusion).

Mechanically – Filling of a body cavity or potential space.

Intra-muscularly.

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Examples of areas where Examples of areas where

contrast agents are usedcontrast agents are used

Arteriography Angiography (DSA) – Cardiology Venography (replaced by ultrasound-

Doppler) IVU Fluoroscopy – Alimentary tract,

hyserosalpingography, sialography, Computerised Tomography (CT) Magnetic Resonance Imaging (MRI) Ultrasound – Liver, kidney Myelography (replaced by MRI) Arthrography – Knee joints.

Contrast Media

C.M

NegativeAir & its constitution

Positive

Iodine compound Bso4GIT

Water solublePowderOily

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Types of contrast Types of contrast mediamedia Negative Contrast Agents Negative Contrast Agents

- Air - Air

- CO- CO2 2

- O- O2 2

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How do negative contrast agents How do negative contrast agents perform?perform?

The negative contrast agents reduce the atomic number of the area to be demonstrated.

These types of contrast media will have little attenuation of the x-ray beam.

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Positive Contrast Positive Contrast Agents Agents Barium based Barium based Iodine based agents Iodine based agents

– Water soluble (Niopam) Water soluble (Niopam) – Non soluble (Lipiodol, Non soluble (Lipiodol, Myodol) Myodol)

The positive contrast agents increase the atomic number of the area to be demonstrated in relation to the surrounding tissue.

• Powder contrast in a form of tablets e.g. Biloptin, Cistobil.

• Oily contrast e.g. myodil, dinosil & lipidol.

• Water soluble ( addition of sugar).

. Ionic e.g. urografine, urovideo, uromiro,

conray, hexbric & angoigrafine.

Non ionic e.g. Amipaque, omnipaque, ultravist & isovist.

Note:- all nonionic C.M. are more safety than ionic one.

• Water soluble C.M. found in different concentration per ml so you must check it carefully to calculate the dose.

Contraindications Iodine (DO NOT USE)

hypersensitivity to iodineheart or renal failureliver disease

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Double contrast Double contrast agentsagents

Incorporates the use of both positive Incorporates the use of both positive & negative contrast media. & negative contrast media.

eg during a double contrast Barium eg during a double contrast Barium enema examination. enema examination.

CoCo22 + BaSo + BaSo44 = Double = Double ContrastContrast

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Why use Barium Why use Barium Sulphate?Sulphate?

It has a high atomic It has a high atomic number (Z=56) number (Z=56)

Non-toxic Non-toxic Relatively cheap Relatively cheap InertInert

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Pharmacological Pharmacological agentsagents Buscopan Buscopan Glucagon Glucagon Maxalon Maxalon

Why are they given?Why are they given?

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Pharmacological agentsPharmacological agents

Buscopan (20mg iv) & Glucagon (0.3mg Buscopan (20mg iv) & Glucagon (0.3mg iv) both relax smooth muscle (Glucagon iv) both relax smooth muscle (Glucagon more potent & can be used on patients more potent & can be used on patients with glaucoma & cardiovascular with glaucoma & cardiovascular disease). disease).

Useful in barium enema examinations.Useful in barium enema examinations.

Maxalon (20mg iv/oral) increases gastric Maxalon (20mg iv/oral) increases gastric

peristalsis peristalsis

(useful in (useful in follow through examinations) follow through examinations)

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Iodine based contrast agents Iodine based contrast agents

(1)(1) Approximately 90% of all contrast

media used in x-ray imaging are loosely termed intravascular or general contrast media.

The physical properties of the iodine based contrast media include the ions or particles associated with the chemical breakdown of the contrast media when it enters a solution.

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Iodine based contrast agents Iodine based contrast agents (2)(2)

The chemical composition of ionic & non-ionic contrast media contains iodine.

On its own, iodine is unsuitable as a contrast agent as it toxic!

The answer is to attach iodine to a “carrier” molecule

Achieved by basing the molecule on the benzene ring & replacing the carbon atoms at set points with iodine to produce tri-iodinated benzoic rings

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Ionic Contrast AgentsIonic Contrast Agents

An ionic compound dissociates (dissolves) into charged particles when it enters a solution (ie blood)

Ionic media breakdown into cations (+ive charged particles) & anions (-ive charged particles)

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Ionic Contrast AgentsIonic Contrast Agents

An ionic contrast agent has approximately five times the osmolarity of human plasma (hyperosmolar)

The iodine atoms provide the attenuation properties

The additional chemical groups determine the properties of the contrast agent, ie solubility, toxicity, viscosity, osmolarity.

–

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OsmolarityOsmolarity

The osmolarity of a solution is the The osmolarity of a solution is the measurement of the number of molecules & measurement of the number of molecules & particles in a solution per kilogram of water. particles in a solution per kilogram of water.

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ViscosityViscosity

Viscosity describes the thickness or resistance to flow of a contrast agent

The thickness of the contrast agent is related to the concentration, the size of the molecules in a specific contrast agent & the temperature of the contrast agent.

The viscosity affects the rate that the contrast media can be injected.

Q:Why are power injection (Medrad) devices fitted with warming pads? Q:Why are power injection (Medrad) devices fitted with warming pads?

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Medrad - Power Medrad - Power InjectorInjector

Warming pad Keeps the viscosity LOW.

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Non-Ionic contrast Non-Ionic contrast mediamedia

Often referred to as “low osmolar” Often referred to as “low osmolar” Non-ionic contrast media do not dissolve

into charged particles when it enters a solution

For every three iodine molecules in a non-ionic solution, one neutral molecule is produced

Non-ionic contrast media are referred to as 3:1 compounds

Non-ionic contrast agents are therefore far safer than ionic contrast agents

More expensive (++) Non-ionic contrast agents substitute Non-ionic contrast agents substitute

the sodium & meg side chains with non-the sodium & meg side chains with non-ionising radicals (NIRionising radicals (NIR). ).

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Gastrograffin & GastromiroGastrograffin & Gastromiro

Water soluble iodine based contrast agents Water soluble iodine based contrast agents Designed especially for G.I. use Designed especially for G.I. use Characteristic aniseed taste. Characteristic aniseed taste. Particularly useful in neonates & paediatrics Particularly useful in neonates & paediatrics Isotonic at iodine concentrations Isotonic at iodine concentrations

(Gastromiro). (Gastromiro). – Gastrograffin = (370 mg mlGastrograffin = (370 mg ml-1-1) ) – Gastromiro = (300 mg mlGastromiro = (300 mg ml-1-1) )

Satisfactory for good images of the bowel Satisfactory for good images of the bowel Recommended for use where there is a Recommended for use where there is a

suspected leakage into pleural or peritoneal suspected leakage into pleural or peritoneal cavities. cavities.

Also useful in CT to distinguish bowel from Also useful in CT to distinguish bowel from other structures(15ml in 1 litre) other structures(15ml in 1 litre)

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Recent development of Recent development of contrast agents (1)contrast agents (1)

Current contrast agents reaching the Current contrast agents reaching the critical iso-osmolarity stage within the critical iso-osmolarity stage within the human body human body

Increased hydrophilicity due to an Increased hydrophilicity due to an increased number of hydroxyl groups increased number of hydroxyl groups provides a high affinity for water and provides a high affinity for water and shelters the toxic iodine atoms from the shelters the toxic iodine atoms from the human body. human body.

Particularly useful for paediatrics & Particularly useful for paediatrics & hyper-sensitive patients.hyper-sensitive patients.

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Recent development of contrast Recent development of contrast agents(2)agents(2)

MRI MRI Gadolinium is a rare earth metal Gadolinium is a rare earth metal

“heavy metal” “heavy metal” Gadolinium is chelated to DTPA Gadolinium is chelated to DTPA

(Magnevist) (Magnevist) By binding DTPA to the Gadolinium By binding DTPA to the Gadolinium

sites, only one “free” gadolinium site sites, only one “free” gadolinium site is available to attach to water is available to attach to water molecules molecules

Gadolinium chelates are of small Gadolinium chelates are of small molecular weight molecular weight

Diffuse freely & excreted by kidneys Diffuse freely & excreted by kidneys Typical adult dose = 0.2ml/kg (20ml Typical adult dose = 0.2ml/kg (20ml

max) max)

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MRI – Example imagesMRI – Example images

MRI (Gd-DTPA) – Hepatoblastoma MRI (Gd- DTPA) Metastasis