- Contrast media are substances used in medical imaging to increase radiographic contrast in areas where it was previously low or absent. They improve the visibility of internal structures on scans. - There are two main types - positive contrast agents, which increase contrast, and negative contrast agents, which decrease contrast. Common positive agents are iodine-based and barium-based. Common negative agents are air and carbon dioxide. - Contrast media are administered in different ways depending on the area being examined, such as orally, rectally, intravenously, or intra-arterially. They allow detailed examination of organ systems like the gastrointestinal tract, blood vessels, and soft tissues.

1. Contrast Media

2. Aims of this session
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Why contrast agents are used
What are the desirable features of a contrast agent
Types of contrast agents used in clinical settings
Methods of administrating contrast agents
Examples of examinations utilising contrast agents
Problems/issues associated with administrating
contrast agents
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3. Contrast

The difference in optical density
between different parts of an image
on a radiograph. It is a reflection of
the different absorption coefficients
and bulk of different regions of the
part being radiographed
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4. 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.

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
UNIT VII
Without
CM
With
CM
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6. Contrast Media

A substance which when introduced
into the body will increase the
radiographic contrast in an area
where it was absent or low before.
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7. Brief History
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1897 - First reported GI contrast study performed Bismuth - TOXIC!
1910 - Barium Sulphate used (safer)
1920’s - Sodium Iodide used to treat syphilis.
Iodine was found to be radio opaque to x-rays.
Bases of all modern contrast agents.
1927 - First reported IVU with iodised organic salts
(Uroselectan)
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8. Requirements of a Contrast Agent (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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9. Requirements of a contrast agent (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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10. Methods of administration
 Orally.
 Rectally.
 Intra-
venously – (injection /
infusion).
 Mechanically – Filling of a body
cavity or potential space.
 Intra-muscularly.
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11. Examples of areas where contrast
agents are used
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Arteriography
Angiography (DSA) – Cardiology
Venography (replaced by ultrasoundDoppler)
IVU
Fluoroscopy – Alimentary tract,
hyserosalpingography, sialography,
Computerised Tomography (CT)
Magnetic Resonance Imaging (MRI)
Ultrasound – Liver, kidney
Myelography (replaced by MRI)
Arthrography – Knee joints.
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12. Contrast Media
C.M
Negative
Air & its constitution
Positive
Iodine compound
Oily
Bso4
GIT
Powder
Water soluble

13. Types of contrast media

Negative Contrast Agents
- Air
- CO 2
- O2
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14. How do negative contrast agents
perform?
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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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15. Positive Contrast Agents
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Barium based
Iodine based agents
– Water soluble (Niopam)
– Non soluble (Lipiodol, Myodol)
The positive contrast agents increase the atomic number
of the area to be demonstrated in relation to the
surrounding tissue.
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16. • Powder contrast in a form of tablets e.g.
Biloptin, Cistobil.
• Oily contrast e.g. myodil, dinosil & lipidol.
• Water soluble ( addition of sugar).

18. .
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.

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

20. Contraindications Iodine
(DO NOT USE)
hypersensitivity to iodine
heart or renal failure
liver disease

21. Double contrast agents
Incorporates the use of both positive &
negative contrast media.
eg during a double contrast Barium enema
examination.
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Co 2 + BaSo 4
= Double Contrast
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22. Why use Barium Sulphate?
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It has a high atomic
number (Z=56)
Non-toxic
Relatively cheap
Inert
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23. Pharmacological agents
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Buscopan
Glucagon
Maxalon
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Why are they given?
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24. Pharmacological agents
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Buscopan (20mg iv) & Glucagon (0.3mg iv)
both relax smooth muscle (Glucagon more
potent & can be used on patients with
glaucoma & cardiovascular disease).
Useful in barium enema examinations.
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Maxalon (20mg iv/oral) increases gastric
peristalsis
(useful in follow through examinations)
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25. Iodine based contrast agents
(1)
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Approximately 90% of all contrast media
used in x-ray imaging are loosely termed
intravascular or general contrast media.
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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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26. Iodine based contrast agents
(2)
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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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27. Ionic Contrast Agents
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An ionic compound dissociates
(dissolves) into charged particles
when it enters a solution (ie blood)
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Ionic media breakdown into cations
(+ive charged particles) & anions (-ive
charged particles)
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28. Ionic Contrast Agents
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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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29. Osmolarity

The osmolarity of a solution is the measurement of
the number of molecules & particles in a solution
per kilogram of water.
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30. Viscosity
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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 30
pads?
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31. Medrad - Power Injector
Warming pad
Keeps the viscosity LOW.
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32. Non-Ionic contrast media
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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 nonionic solution, one neutral molecule is
produced
Non-ionic contrast media are referred to as
3:1 compounds
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33. 
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Non-ionic contrast agents are therefore far
safer than ionic contrast agents
More expensive (++)
Non-ionic contrast agents substitute the
sodium & meg side chains with nonionising radicals (NIR ).

34. Gastrograffin & Gastromiro
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Water soluble iodine based contrast agents
Designed especially for G.I. use
Characteristic aniseed taste.
Particularly useful in neonates & paediatrics
Isotonic at iodine concentrations (Gastromiro).
– Gastrograffin = (370 mg ml -1 )
– Gastromiro = (300 mg ml -1 )
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Satisfactory for good images of the bowel
Recommended for use where there is a
suspected leakage into pleural or peritoneal
cavities.
Also useful in CT to distinguish bowel from other
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structures(15ml in 1 litre)

35. Recent development of contrast
agents (1)
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Current contrast agents reaching the critical
iso-osmolarity stage within the human body
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Increased hydrophilicity due to an
increased number of hydroxyl groups
provides a high affinity for water and
shelters the toxic iodine atoms from the
human body.
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Particularly useful for paediatrics & hypersensitive patients.
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36. Recent development of contrast
agents(2)
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MRI
Gadolinium is a rare earth metal “heavy
metal”
 Gadolinium is chelated to DTPA
(Magnevist)
 By binding DTPA to the Gadolinium sites,
only one “free” gadolinium site is
available to attach to water molecules
 Gadolinium chelates are of small
molecular weight
 Diffuse freely & excreted by kidneys
 Typical adult dose = 0.2ml/kg (20ml max)
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37. MRI – Example images
MRI (Gd-DTPA) – Hepatoblastoma
MRI (Gd- DTPA) Metastasis
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