THIS PRESENTAION CLEARLYEXPLINS ABOUT CONTRAST MEDIA ,T1 AND T2 AGENTS USED IN MRI IAMGING. IT ALSO SHOWS RELAXIVITY AND ITS FORMULA AND CONTRAST ADMINISTRATION I.E,GADOLINIUM. AND CLASSIFICATION OF MRI CONTRAST AGENTS.

1. T1 AND T2 AGENTS,
RELAXIVITY,
GADOLINIUM ADMINISTRATION
VANI PUSHPA
M Sc final year

2. TABLE OF CONTENT
• CLASSIFICATION
• T1 AGENTS
• T2 AGENTS
• GADOLINIUM
• OTHER CONTRAST AGENTS
• ORAL CONTRAST AGENTS
• RELAXIVITY
• GADOLINIUM ADMINISTRATION / DOSE
• CONCLUSION

4. • Magnetic susceptibilities:
It denotes whether a material is repelled out or
attracted of magnetic field.
• Negative magnetic susceptibilities: Diamagnetic materials
• Positive magnetic susceptibilities: Paramagnetic and ferromagnetic
materials

5. GADOLINIUM
• As paramagnetic substances have positive magnetic susceptibilities,
they provide a suitable choice for an enhancement agent in MRI.
• Gadolinium (Gd), a trivalent lanthanide element (a rare earth metal
ion), is ideal because it has seven unpaired electrons and the ability to
allow rapid exchange of bulk water.
• Unpaired electrons have a magnetic moment ( μ ) that is 500 000
times that of a hydrogen proton. It is this large magnetic moment that
creates fluctuations in the local magnetic fields.

9. T1 agents
• Water within the body (such as free water associated with tumors)
tumbles much faster than the Larmor frequency resulting in
inefficient relaxation (long T1 and T2 relaxation times).
• When molecular tumbling creates fluctuations in a magnetic field
near the Larmor frequency, the T1 relaxation time of nearby water
spins is reduced. This results in an increased signal intensity of water
in T1 weighted images. For this reason, gadolinium is known as a T1
enhancement agent or positive relaxation agents
• Ex- Gadolinium,
Mn-DPDP

10. This image demonstrates axial T1 weighted images of the brain in a patient with
metastatic disease.

11. T2 agents
• Although we consider gadolinium to be a T1 agent, it can also be used
to shorten T2, and particularly T2 * . For this reason gadolinium can
also be used as a T2 enhancement agent .
• They affect T2 relaxation and reduces T2 of the tissue where they
accumulate. This results reduction in signal intensity on T2 W images.
• EX: Iron oxide particles,
gadolinium

12. Paramagnetic Agents
• Gadolinium:
• Usually positive agents but at higher doses cause T2 shortening
resulting in decreased T2 W images.
• This effect is use in perfusion studies.

13. Super paramagnetic agent
• They are negative contrast agent.
• They cause proton dephasing leading to T2 shortening and signal loss.
• Example:Iron Oxide(Fe304)

14. Other contrast agents
• Gadolinium is not the only element that could be considered as a
contrast agent in MRI.
• Other elements such as manganese and iron oxide have been shown
to produce alterations in T1 and T2 relaxation times.
Other T1 agents
• Manganese- used for liver imaging
• Hyperpolarized helium gas by inhalation used for imaging of the
lungs.
• Such agents shorten T1 and therefore appear bright on T1 weighted
images

15. • Manganese is taken up by the Kupffer cells in the liver.
• In this case the normal liver will enhance and lesions remain darker

16. T1 weighted gradient echo image of the lungs after inhalation of hyper - polarized
helium gas. The helium gas provides increased signal enhancement on T1 gradient
echo images and therefore provides ventilation information.

18. Negative contrast
• They decrease signal from bowel lumen, therefore, there is no motion
related images degradation.
• Ex: Barium ,
Blueberry juice are used to reduce signals from bowel.

19. Relaxivity
• When contrast agents are used in MRI, it is not the agent itself but
the effects of the agent that are measured. In MRI, it is the function
of the agent on the related tissues that determines image
enhancement.
• The effect of a substance on relaxation rate is known as its relaxivity.

20. Equation of relaxivity:
• 1/ΔT1 = r1 • [C] and 1/ΔT2 = r2 • [C]
• ΔT1 and ΔT2 are given in seconds and
• [C] is measured in millimoles per liter,
• r1 and r2 have units of L/mmol-s.

21. High relaxivity agents
• Most of the gadolinium agents introduced to the market have
exhibited similar relaxivity properties, determined by the amount of
gadolinium present.
• These high relaxivity agents have been developed to allow for better
visualization of pathology and/or the ability to use lower doses.
• One such agent, Gd - BOPTA (brand name of Multi Hance) When
using high relaxivity agents, the relaxivity is essentially twice that of
the standard relaxivity agents.

22. Gadolinium administration / dose
• The recommended dosage of gadolinium is 0.1 millimoles per kilogram
(mmol/kg) of body weight, (0.2 ml/kg).
• RATE: 10mL /15 sec
• The lethal dose, (LD 50 – the dose required to kill half of the study
population) determined in rat studies is between 6 -20 mmol/kg. This is
never approached in the clinical situation.
• As dose increases (to a point), the ability to visualize structures and lesions
also increases.
• Some facilities opt to inject every patient with a standard dose of, for
example, 10 ml. This is an unacceptable method of contrast enhancement.

23. • It is acceptable for the technologist/radiographer to inject contrast
agents in radiology (X - ray, CT, MRI). However, according to the ACR
MRI Safety:
• The ACR approves of the injection of contrast material and diagnostic
levels of radiopharmaceuticals by certified and/or licensed radiologic
technologists and radiologic nurses under the direction of a
radiologist or his or her physician designee who is personally and
immediately available, if the practice is in compliance with
institutional and state regulations
• To comply with these ACR recommendations, a facility must have a
doctor present during an injection of any contrast agent.

25. CONCLUSION
• Although contrast agents are widely used with safe outcomes and
little or no side effects, adverse reactions may occur.
In summary
• Expect the unexpected and be prepared.