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MRI contrast RADIOLOGY

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MRI contrast RADIOLOGY

  1. 1. h BY Henock.N (r2) MRI CONTRAST AGENT 1 H
  2. 2.  MRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in magnetic resonance imaging (MRI).  The most commonly used compounds for contrast enhancement are gadolinium-based. MRI contrast agents alter the relaxation times of atoms within body tissues where they are present after oral or intravenous administration. 2
  3. 3.  Most clinically used MRI contrast agents work through shortening the T1 relaxation time of protons located nearby.  T1 shortens with an increase in rate of stimulated emission from high energy states (spin anti-aligned with the main field) to low energy states (spin aligned). 3
  4. 4.  To, enhance the inherent contrast between tissue, Mri contrast must alter rate of relaxation of the proton within tissue.  Relaxation must be vary for different tissues in order to produce differential enhancement of signal 4
  5. 5.  MRI contrast agent must exert a large magnetic field density( a property imparted by their unpaired electron) to interact with the magnetic moment of proton in the tissue and shorten their relaxation time  The electron magnetic moment also cause the local change in magnetic field promting more rapid proton dephasing and shortens the relaxation time 5
  6. 6.  Agents with unpaired electron pair spins used asMRI contrast agent. This may be classifiedinto three group  Ferromagnetic  Paramagnetic- example gadolinium… Used as major contrast agent made soluble by chelation …shortens T1 relaxation..bright signal on T1 weighted image i.e Hyperintense  Super-magnetic-ferrite.. Used for reduction of T2 relaxation time.. Decreased signal intensity seems black 6
  7. 7. Chelates  Chelate means “claw”  Chelates surround an ion and make a cage around it  A chelate of gadolinium occupies all available space around the ion except water molecule 7
  8. 8. Gd chelate 8
  9. 9.  MRI contrast agents may be administered by injection into the blood stream or orally, depending on the subject of interest.  Oral administration is well suited to G.I. tract scans, while intravascular administration proves more useful for most other scans. A variety of agents of both types enhance scans routinely. 9
  10. 10.  MRI contrast agents can be classified in many ways, including by their:  chemical composition  administration route  magnetic properties  effect on the images 10
  11. 11.  biodistribution and applications:  Extracellular fluid agents (also known as intravenous contrast agents)  Blood pool agents (also known as intravascular contrast agents)  Organ specific agents (i.e.Gastrointestinal contrast agents and hepatobiliary contrast agents)  Active targeting/cell labeling agents (i.e. tumor-specific agents)  pH-sensitive agents 11
  12. 12. 12
  13. 13. Gadolinium containing MRI contrast agents (often termed simply "gado" or "gad") Used for enhancement of vessels in MR angiography or for brain tumor enhancement 13
  14. 14.  For large vessels such as the aorta and its branches, the gadolinium(III) dose can be as low as 0.1 mmol per kg body mass.  Higher concentrations are often used for finer vasculature. 14
  15. 15.  Types of gadolinium contrast agents  Extracellular fluid agents Ionic (i.e. Magnevist and Dotarem) Neutral (i.e. Omniscan, Prohance, Gadavist, OptiMARK)  Blood pool agents Albumin-binding gadolinium complexes (i.e. Ablavar and Gadocoletic acid)  Polymeric gadolinium complexes (i.e. Gadomelitol and Gadomer 17)  Organ-specific agents (i.e. Primovist and Multihance which are used as hepatobiliary agents) 15
  16. 16.  Gadolinium-containing contrast agents approved for human use Presently, nine different types of gadolinium-containing contrast agents are available in different territories gadoterate (Dotarem) gadodiamide (Omniscan) gadobenate (MultiHance) gadopentetate (Magnevist, Magnegita, Gado-MRT ratiopharm) gadoteridol (ProHance) gadoversetamide (OptiMARK) gadoxetate (Primovist) gadobutrol (Gadovist) 16
  17. 17.  Iron oxide: Superparamagnetic Two types of iron oxide contrast agents exist: superparamagnetic iron oxide (SPIO) and ultra small superparamagnetic iron oxide (USPIO). when injected during imaging reduce the T2/ T2* signals of absorbing tissues. SPIO and USPIO contrast agents have been used successfully in some instances for liver tumor enhancement 17
  18. 18. Liver Contrast Agents Iron Magnetite, super paramagnetic agent Makes liver black on T2WI, mets show up as bright white. 18
  19. 19.  Oral administration of contrast agents  A wide variety of oral contrast agents can enhance images of the gastrointestinal tract.  They include gadolinium and manganese chelates, or iron salts for T1 signal enhancement.  SPIO, barium sulfate, air and clay have been used to lower T2 signal. 19
  20. 20. Other contrast agents For MR colonography& MRCP  Water/saline contrast  Negative oral contrast  Geritol  Blueberry juice, pineapple juice 20
  21. 21. Negative contrast agents  Used to make stomach contents black in MRCP  Geritol, blueberry juice, pineapple juice  Iron in Geritol  Mn in these juices 21
  22. 22. MRCP 22
  23. 23. Side effect of MRI contrast  The most common, so called normal, side effects of MRI contrast agent are mild and temporary in nature. They include  warmth  pain or burning at the injection site,  low blood pressure,  minor skin rash,  mild headaches,  changes in blood clotting,  light headedness and nausea.  Typically these side effects do not require any treatments. 23
  24. 24.  The most common allergic reaction symptoms to MRI contrast agents include  swelling of the face,  rashes,  itching,  sweating,  watery or itchy eyes, and  shortness of breath. 25
  25. 25. NSF  Nephrogenic Systemic Fibrosis  Fatal  2-10 wks  Progressive thickening and hyperpigmentation of skin  Most likely caused by free Gd  Prevent by screening patients for renal disease  Calculate estimated creatinine clearance 27
  26. 26. NSF  Risk factors  CKD  AKI  Dialysis  Indications for creatinine  Age>60 yr  Hx of kidney disease  Single kidney or kidney surgery  HTN or DM 27
  27. 27. CONTRAINDICATION  Patient have history of CKD/renal failure i.e. no normal renal clearance  Allergic history  pregnancy 28
  28. 28. Pregnant and lactating  Assumed to cross the placenta  exreted via urinary tract to amniotic fluid  No subsequent evidence of teratogenesis  Small percent excreted in breast milk  No reported direct toxicity  Discard breast milk 12-24 after GBCAS if possible  In children ,it should be used when necessary
  29. 29. References Safe use of contrast media :what the radiologist needs to know; radiographics 2015  ACR manual on contrast media, 2017Needs to Know1
  30. 30. Thank you!!!Radiologist Needs to Know1

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