This document discusses contrast agents used in medical imaging. It begins by outlining the aims of discussing contrast agents, including why they are used and desirable features. The main types of contrast agents are then described - positive contrast agents like iodine and barium sulfate which increase attenuation, and negative contrast agents like air which decrease attenuation. Methods of administration and examples of examinations using contrast are provided. Risks associated with contrast agents like reactions and nephrotoxicity are also summarized.

1. CONTRAST AGENTS
Dr Fahad Shafi
PG RADIODIAGNOSIS &IMAGING

2. Aims of this session
• 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

3. Why contrast agents are used
• Different tissues within the body attenuate
the beam of X-rays to different degrees.
• The degree of attenuation of an X-ray beam by
an element is complex, but one of the major
variables isthe number of electrons in the
path of the beam with which it can interact.

4. • The number of electrons in the path of the
beam is dependent upon three factors:
• The thickness of the substance being studied
• Its density
• The number of electrons per atom of the
element (which is equal to its atomic number)

5. Where there is inherent considerable
difference between the densities of
two organs

6. • However, if the two organs have similar
densities and similar average atomic numbers,
then it is not possible to distinguish them on a
radiograph, because no natural contrast exists.
• For example, it is not possible to identify
blood vessels within an organ, or to
demonstrate the internal structure of the
kidney, without artificially altering one of the
factors mentioned earlier

8. Two of the factors important in organ
contrast can be artificially altered,
• the density of an organ, and,
• more usefully, the average atomic number of a
structure.

9. The density of a hollow organ can be reduced by
filling it with gas or air, providing negative contrast
• NEGATIVE CONTRAST

10. The average atomic number is
INCREASED positive contrast

11. What are the desirable features of a
contrast agent
• Easy to administer
• No toxicity/carcinogenecity
• Stable compound
• Concentrates in area of interest
• Proper demonstration of the organ system
• Should have rapid elimination
• Minimal distress to patients (viscosity)
• Cost effective

12. Types of contrast media
CONTRAST
MEDIA
POSITIVE
CONTRAST
IODINE
BASED
BARIUM
SULPHATE
NEGATIVE
CONTRAST

13. NEGATIVE CONTRAST AGENTS
• Air
• CO2
• O2
• E.g.
• PEG
• Air arthrogram
• Double contrast barium examinations

15. POSITIVE CONTRAST AGENTS
• BARIUM SULPHATE
• Radiological contrast media are usually water
soluble solutions, but there is one commonly
used variety that is based on a suspension of
large insoluble particles
• Examinations of the upper and lower
gastrointestinal tracts

16. • Barium sulphate suspensions have better
coating properties than the iodinated contrast
media, and tend to form thin layers spread
over the lining of the gut
WHY BARIUM IN GI SERIES

17. BARIUM STUDIES
• BARIUM SWALLOW
• BARIUM MEAL/FOLLOW THROUGH
• ENTEROLYSIS
• BARIUM ENEMA

18. Barium swallow examination

19. Barium meal and Barium follow
through

20. Enteroclysis
• Enteroclysis has shown to be very accurate in
diagnosing small bowel diseases, with a
sensitivity of 93.1% and specificity of 96.9%.
• It permits detection of lesion which may not
be seen with other imaging techniques.
• no significant difference Enteroclysis and
Computer tomographic enterography.

21. Enteroclysis in double contrast technique showing
stenosis of the small intestine

22. Barium enema

23. ADVERSE EFFECTS
• Constipation and abdominal pain
• Toxicity
• Encephalopathy
• Peritonitis, adhesion,granuloma,ENDOTOXIC
SHOCK
• Aspiration pneumonia
• Allergy

24. IODINE BASED
• Early 1920s to treat syphilis with high doses of
sodium iodide. The urine in the bladder was
observed to become radio-opaque during this
treatment. Sodium iodide was too toxic.
• The first suitable structure was a derivative called
pyridine, to which a single iodine atom could be
bound in order to render it radio-opaque.
• The first radiological contrast medium that could
produce safe and reliable intravenous urograms
in patients was Uroselectan

25. • In the 1950s, contrast media were developed
that were based on the six-carbon benzoic
acid ring rather than the five-carbon pyridine
ring. This structure was able to carry three
atoms of iodine, and therefore was even more
radio-opaque.
• Had a very high osmolality

26. WATER VS OIL BASED
• OIL BASED
• NEVER INJECTED
• ONLY DUCTS
• NOT INGESTED
• WATER BASED
• INJECTED VESSELLS/DUCTS
• INGESTED
• Organ function/flow

27. All contrast media are not the same
• Viscosity
• Osmolality
• Chemotoxicity
• LD50

28. Viscosity
• The practical importance of viscosity of a
contrast medium relates chiefly to the force
that is required to inject
• The viscosity can be reduced by lowering the
concentration of the contrast medium, but
result in unsatisfactory opacification. Since
viscosity is inversely related to temperature,
warming the contrast medium may partly
resolve this problem

29. Osmolality
• In general, the higher the osmotic pressure the
poorer the tolerance. Ionic contrast media
undergo this dissociation, whilst newer, non-ionic
contrast media do not.
• Osmolality is directly responsible for a number of
clinically important effects
• The sensations of heat and discomfort or even
pain
• damage to the blood-brain barrier, renal damage
and disturbance or electrolyte balance in small
children.

30. • Both the viscosity of a contrast medium and
its osmolality are INVERSELY related to
tolerance but directly to degree of
opacification.
• With increasing strength of contrast medium,
the opacifying power of the solution
increases, but so, of course, do the osmolality
and viscosity, while tolerance tends to decline.

31. Ways of reducing osmolality, whilst
maintaining satisfactory radio-opacity
• two contrast medium molecules together,
producing a much larger molecule, which still
ionises, but possesses six atoms of iodine per
molecule
• replace the dissociating cationic portion of the
contrast medium molecule completely with a
non-dissociating organic chain

32. CHEMOTOXICITY/LD50
• mechanism responsible for causing the toxic
effects of contrast media that cannot be
explained by other means (e.g. osmolality,
electrical charge).
• There are a number of properties of contrast
media that relate to this tem (e.g.
hydrophilicity/lipophilicity, protein-binding,
histamine release).

34. Methods of Administration
• Orally
• Rectally
• Intravenous
• Intra cavitatory

35. Examples of examinations utilising
contrast agents
• Angiography
• Intravenous urography (IVU), intravenous
pyelography (IVP)
• Computed tomography (CT)
• Interventional techniques
• GI series
• Other examinations

37. Choice of contrast
• Infants (introduction of hyperosmolar fluid into the bodies
of very young children can cause
• problems of fluid balance)
• The elderly (for the same reason)
• Diabetics
• Patients with cardiac impairment
• Patients with renal impairment
• Asthmatics
• Patients who have previously reacted adversely to a
contrast medium
• Patients with a history of allergy
• Patients who are unduly anxious

38. Safety of contrast media
• Contrast media are among the safest of all of
the pharmaceutical products available to the
doctor today. They are not intended to have
therapeutic activity: indeed, the ideal contrast
medium would have no pharmacological
activity at all.
• rate of adverse reactions to iodinated contrast
media on the market is extremely low, but
such reactions do occur - just as they do with
every pharmaceutical product.

39. two groups
• Those reactions that are clearly dependent on
the dose and concentration of the contrast
medium administered......... heat,
pain,vasodilation, cardiac depression and
hypotension,CIN
• and those that are almost independent of
dose and concentration........ allergy-like or
hypersensitive reactions

40. • Most contrast media reactions are minor and need
no treatment. Moderate reactions are encountered
rarely (about 1%) and severe reactions very rarely
(about 0.1%), but all moderate and severe reactions
require adequate treatment. Deaths following
contrast media administration are extremely rare.
• Reported mortality rates vary between 1 in 10,000
and 1 in 169,000 averaging around 1 in 75,000.
• Katayama et al. (Radiology 1990; 175: 621-628)
found that there is a reduction in adverse reaction
rate of about four times using(LOCM) for intravenous
injection compared to HOCM

41. Contrast Agents used in our deptt
• Angiography IOMERON 400 (IOMEPROL)
• CT IOPAMIRO 370
(IOPAMIDOL)
• ELDERLY/DIABETIC VISIPAQUE 270
/HIGH RISK (IODIXANOL)
• IVU IOPAMIRO 370

42. MRI contrast agent
• Gadolinium (Gd):
Extracellular fluid agents
Blood pool agents
Organ specific agents
• Iron oxide
• Iron Platinum
• Manganese

43. CEUS