Contrast media


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Contrast media

  1. 1. Contrast Media
  2. 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 2
  3. 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 3
  4. 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. 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 5
  6. 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. 6
  7. 7. Brief History       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) 7
  8. 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 .   8
  9. 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. 9
  10. 10. Methods of administration  Orally.  Rectally.  Intra- venously – (injection / infusion).  Mechanically – Filling of a body cavity or potential space.  Intra-muscularly.  10
  11. 11. Examples of areas where contrast agents are used            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. 11
  12. 12. Contrast Media C.M Negative Air & its constitution Positive Iodine compound Oily Bso4 GIT Powder Water soluble
  13. 13. Types of contrast media  Negative Contrast Agents - Air - CO 2 - O2 13
  14. 14. How do negative contrast agents 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. 14
  15. 15. Positive Contrast Agents   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. 15
  16. 16. • Powder contrast in a form of tablets e.g. Biloptin, Cistobil. • Oily contrast e.g. myodil, dinosil & lipidol. • Water soluble ( addition of sugar).
  17. 17. . 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.
  18. 18. • Water soluble C.M. found in different concentration per ml so you must check it carefully to calculate the dose.
  19. 19. Contraindications Iodine (DO NOT USE) hypersensitivity to iodine heart or renal failure liver disease
  20. 20. Double contrast agents Incorporates the use of both positive & negative contrast media. eg during a double contrast Barium enema examination.   Co 2 + BaSo 4 = Double Contrast 21
  21. 21. Why use Barium Sulphate?     It has a high atomic number (Z=56) Non-toxic Relatively cheap Inert 22
  22. 22. Pharmacological agents    Buscopan Glucagon Maxalon   Why are they given? 23
  23. 23. Pharmacological agents  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.  Maxalon (20mg iv/oral) increases gastric peristalsis (useful in follow through examinations) 24
  24. 24. Iodine based contrast agents (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. 25
  25. 25. Iodine based contrast agents (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 26
  26. 26. Ionic 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)  27
  27. 27. Ionic 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. – 28
  28. 28. Osmolarity  The osmolarity of a solution is the measurement of the number of molecules & particles in a solution per kilogram of water. 29
  29. 29. Viscosity    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?  
  30. 30. Medrad - Power Injector Warming pad Keeps the viscosity LOW. 31
  31. 31. Non-Ionic contrast media     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 32
  32. 32.    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 ).
  33. 33. Gastrograffin & Gastromiro       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 )    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 34 structures(15ml in 1 litre)
  34. 34. Recent development of contrast agents (1)  Current contrast agents reaching the critical iso-osmolarity stage within the human body  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.  Particularly useful for paediatrics & hypersensitive patients. 35
  35. 35. Recent development of contrast agents(2)  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)  36
  36. 36. MRI – Example images MRI (Gd-DTPA) – Hepatoblastoma MRI (Gd- DTPA) Metastasis 37