MRI Contrast Agent & Its Principle

1. MRI CONTRAST AGENT
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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.
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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).

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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
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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
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6.  Agents with unpaired electron pair spins used as MRI
contrast agent. This may be classified into three group
 Ferromagnetic
 Paramagnetic- example gadolinium… have magnetic
moment which alinged of magnetic field…as magnetic
gradient off alignment is loss.
Used as major contrast agent made soluble by
chelation …shortens T1 relaxation..bright signal onT1
weighted image i.e Hyperintense
 Super-magnetic-ferrite (compound mixed with
oxide of iron), Used for reduction of T2
relaxation time. Decreased signal intensity seems
black
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7. Chelates
 Chelate means “claw”
 Chelates surround an ion an make a cage around it
 A chelate of gadolinium occupies all available space
around the ion except water molecule
 Water molecules exchange in and out of that one
spot. When in that spot, the spins have an extremely
short T1. This accelerates the overall relaxation rate,
shortening T1.
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8. Gd chelate
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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.
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10.  MRI contrast agents can be classified in many
ways, including by their:
 chemical composition
 administration route
 magnetic properties
 effect on the image
 presence and nature of metal atoms
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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)
 Responsive (also known as smart or bioactivated) agents
 pH-sensitive agents
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12. 12

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
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14.  For large vessels such as the aorta and its branches, the
gadolinium dose can be as low as 0.1 mmol per kg body
mass. Higher concentrations are often used for finer
vasculature.
 Gd chelates do not pass the blood–brain barrier
because they are hydrophilic. Thus, these are useful in
enhancing lesions and tumors where the Gd leaks out.
In the rest of the body, the Gd initially remains in the
circulation but then distributes into the interstitial
space or is eliminated by the kidneys.
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15. Types of gadolinium contrast agents
Gadolinium contrast agents can be categorized into:
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 Gadocoleticacid)
Polymeric gadolinium complexes
(i.e. Gadomelitol and Gadomer 17)
Organ-specific agents
(i.e. Primovist and Multihance which are used as hepatobiliary
agents)
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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-MRTratiopharm)
gadoteridol (ProHance)
gadoversetamide (OptiMARK)
gadoxetate (Primovist)
gadobutrol (Gadovist)
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17. Iron oxide: Superparamagnetic
Two types of iron oxide contrast agents exist:
superparamagnetic iron oxide (SPIO)
and ultra small superparamagnetic iron oxide (USPIO).
These contrast agents consist of suspended colloids of iron oxide
nanoparticles and 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
.
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18. Liver Contrast Agents
Iron Magnetite,
super
paramagnetic
agent
Makes liver
black on T2WI,
mets show up as
bright white.
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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. Natural products with high manganese
concentration such as blueberry and green tea can also be
used for T1 increasing contrast enhancement.
 Perflubron, a type of perfluorocarbon, has been used as a
gastrointestinal MRI contrast agent for pediatric imaging.
 This contrast agent works by reducing the number of
hydrogen ions in a body cavity, thus causing it to appear
dark in the images.
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20. Other contrast agents
For MR colonography & MRCP
 Water/saline contrast
 Negative oral contrast
 Geritol
 Blueberry juice, pineapple juice
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21. Negative contrast agents
 Used to make stomach contents black in MRCP
 Geritol, blueberry juice, pineapple juice
 Iron in Geritol
 Mn in these juices
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22. MRCP
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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.
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24.  Gadolinium containing contrast agents usually have no effect
on blood chemistries and hematologic studies except transient
elevation of serum iron and bilirubin levels.
 These elevations peaked at 4 to 6 hours post injection and
returned to baseline values in 24 to 48 hours. The mechanism
of these elevations is uncertain but may be related to mild
hemolysis.
 Deoxygenated sickle erythrocytes align perpendicular to a
magnetic field in in vitro studies raising the possibility of
occlusive complications in patients with sickle cell anemia.
 No clinical reports of this potential problem have been found
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25.  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.
 Frequently, the reactions are mild and can be controlled with medication,
says Radiology Info. If left untreated, however, allergic reaction can
become serious and even life threatening. The patient is advised to contact
the doctor as soon as the allergic reactions appear.
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26.  NSF (Nephrogenic Systemic Fibrosis) was first
described in the medical literature in 2000. The first
case of NSF was identified in 1997.The cause of NSF
is unknown but it has been reported only in patients
who have severe kidney disease.
 NSF causes fibrosis of the skin and connective tissues
throughout the body. Patients develop skin thickening
that may prevent bending and extending joints,
resulting in decreased mobility of joints. NSF usually
starts in the lower extremities. Fibrosis can also
develop in the diaphragm, muscles in the thigh and
lower abdomen, and lung vessels. Over time, NSF
becomes worse and can cause death.
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27. NSF
 Nephrogenic Systemic Fibrosis
 Most likely caused by free Gd
 Prevent by screening patients for renal disease
 Calculate estimated creatinine clearance
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28. CONTRAINDICATION
 Patient have history of CKD/renal failure i.e.
no normal renal clearance
 Allergic history
 pregnancy
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29.  Nephrogenic Systemic Fibrosis
 The most serious side effect caused by MRI contrasts are attributed to
gadolinium.
 The FDA reports that patients with renal failure and kidney diseases
cannot filter the chemical dye quickly enough and it stays in the body.
 There it causes a serious medical condition called nephrogenic systemic
fibrosis, or NSF, according to a study conducted by Dr. Thomas Grobner
that was published in "Nephrology Dialysis Transplantation" in January,
2006.
 NSF symptoms include hardened skin with red patches and are most
commonly found in the limbs. Other frequent symptoms include muscle
tightening, joint pain, yellow spots on the eyes, and internal organ
dysfunction. This rare illness has no cure, but only affects patients with
existing kidney problems injected with gadolinium. Patients who received
other contrast dyes or those who do not suffer from kidney related
problems did not get NSF. Four of the five approved gadolinium contrast
agents linked to NSF include Omniscan, Multihance, Magnevist and
OptiMARK, says the FDA.
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30. Juices "Contrast agents" – orange juice (OJ), grapefruit juice (GJ), apple juice (AJ), pineapple juice
(PJ), milk (M), prune juice (P), cranberry juice (CJ), blueberry and apple juice (BAJ), barium EZ Cat 2% w/v (B),
dilute barium (50:50 with water) (DB), concentrated gastrografin (GG), ferumoxsil (F), and water (W).

31. NITISH VIRMANI
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