Download Contrast Media Contrast media: definition Important Points

Contrast Media
T. Murakami, DVM
Contrast media: definition
• Any substance used to change the
imaging characteristics of the patient,
thereby providing additional information
including:
– Anatomy/morphology: tissue versus fluid,
location
– Physiology: vasculature, vascular integrity,
qualitative assessment of function
Important Points
• Category: is the agent used for photon-based
imaging, magnetic resonance imaging, or
ultrasound?
• Use: what are the special procedures for which a
contrast agent is used? Procedures will be
discussed in subsequent lectures.
• Routes of administration: or more importantly,
how should a contrast medium NOT be given?
• Indications and Contraindications: what could go
wrong?
1
Imaging Modality
Photon-based imaging: radiography
Imaging Modality
Photon-based imaging: fluoroscopy
Imaging Modality
Photon-based imaging: computed tomography
2
Contrast agents for photonbased imaging
• These contrast media work by changing the
photon-attenuating characteristics of the patient.
– Positive contrast agents: increase the
attenuation of tissue, blood, urine, or outline
spaces such as the gastrointestinal lumen or
subarachnoid space.
– Negative contrast agents: normally decrease
attenuation by occupying a space such as the
bladder, GI tract, or (if you’re unlucky) blood
vessels.
Positive contrast agents
• The two major types of positive contrast
agents are barium sulfate agents and
various iodinated compounds.
– Barium sulfate agents include bariumimpregnated spheres (BIPS)
– The iodinated contrast agents are based on
benzene rings, and there are many different
compounds.
Barium sulfate
• Barium sulfate is a white, crystalline compound.
• Barium has a high atomic number (56).
• Barium sulfate is inert and not absorbed by the
gastrointestinal tract. It may have soothing
qualities.
• This compound causes severe reactions within
the body. Its ONLY indications are for use
outside the body (e.g., GI, marking external
structures).
3
Barium sulfate
• Sterile iodinated contrast media should be
used if gastrointestinal perforation is
suspected.
• If barium sulfate gets within the body (e.g.
peritoneal or pleural surfaces), be
prepared to surgically flush out.
• Rarely, barium sulfate can embolize via
mucosal defects, causing severe
reactions.
Barium sulfate
• Barium sulfate is very effective at outlining
mucosal surfaces.
• Most special procedures using barium
involve the GI tract:
– Esophagram
– Upper GI series
– Colonogram (barium enema)
• Barium sulfate is available in different
concentrations
Barium sulfate
• Commercial preparations contain additives
to improve shelf-life, prevent flocculation,
and prevent settling.
• Different special procedures call for
differing concentrations of barium sulfate.
Barium sulfate is generally sold as a
suspension with concentrations expressed
as weight-to-volume % or weight-to-weight
%.
4
Barium sulfate:% weight-to
volume
• A certain amount of barium is added to
enough water to create a predetermined
volume of suspension. For example, 20
grams of barium sulfate in enough water to
create 100 ml of suspension would yield a
20% weight to volume suspension.
Wallack, ST. The Handbook of Veterinary Contrast
Agents. San Diego, San Diego Veterinary Imaging,
Inc., 2003.
Barium sulfate:% weight-to
weight
• A certain weight of barium sulfate is added
to enough water to obtain a predetermined
weight of suspension. For instance, 20
grams of barium sulfate added to 80
grams of water would create 100 grams of
suspension. Therefore, barium sulfate is
20% of the weight of the total suspension.
Wallack, ST. The Handbook of Veterinary Contrast
Agents. San Diego, San Diego Veterinary Imaging, Inc.,
2003.
Barium sulfate
• Recommended concentrations for GI
studies vary with references (more in
subsequent lectures).
• Charts are available for comparison of %
weight-to-volume and % weight-to-weight.
• Preparations are available in liquid form,
as well as pastes/creams. Pick
appropriate formulation based on
procedure.
5
Barium sulfate: BIPS
• Barium-impregnated polyethylene spheres.
• Spheres available in a variety of sizes.
• Can be given with food, and generally less
messy than barium sulfate suspensions.
• No mucosal information, unpredictable gastric
emptying times, little information about the
nature of an obstruction.
• Could be considered to search for obstruction.
Iodinated contrast agents
• Water-soluble agents based on iodinated
benzene rings.
• Can be classified according to whether the
agent dissociates in solution (ionic versus nonionic) and structure (monomer versus dimer)
• In general, the potential for adverse reactions
increases with the osmolality of the contrast
agent.
Iodinated contrast agents
• Solutions containing ionic agents have
higher osmolality due to an increased
number of particles in solution when
compared with non-ionic agents.
• Solutions containing dimeric agents have
more iodine atoms per molecule, and
therefore have lower osmolalities relative
to their monomeric counterparts.
6
Iodinated contrast agents
• Plasma is approximately 290 mOsm/kg.
• The ionic monomeric agents range from 1970 to
2400 mOsm/kg.
• An ionic dimeric agent can have an osmolality
around 577 mOsm/kg (ioxaglate).
• Non-ionic monomers range from 610 to 915
mOsm/kg.
• Non-ionic dimers can be iso-osmolar with
plasma (290 mOsm/kg).
Iodinated contrast agents
• Unfortunately, the ionic monomeric agents are
usually far cheaper than the non-ionic
monomeric agents.
• Dimeric agents are also expensive. Additionally,
the large molecular size of the contrast agent
leads to increased viscosity of the solution.
www.emedicine.com
www.invitrogen.co.jp
Iodinated contrast agents
• High-osmolar agents
– Monomeric ionic agents, including diatrizoate,
iothalamate, ioxithalamate, and metrizoate.
• Low-osmolar agents
– Non-ionic monomers, including iohexol,
iopamidol, iopentol, ioproimide, and ioversol.
– Ionic dimer (ioxaglate)
• Iso-osmolar agents
– Non-ionic dimers (iodixanol, iotrolan)
7
Iodinated contrast agents
• Remember that different preparations of the
same contrast agent may have different
indications.
– Some concentrations of a particular agent
may not be labeled for intrathecal use.
– Non-sterile preparations may be available for
gastrointestinal use. For example,
Gastrograffin (sodium and meglumine
diatrizoate) for gastrointestinal use.
• Always read the label.
Iodinated contrast agents
• Both the ionic and nonionic contrast agents can
be used for:
– Physiologic organ enhancement.
– Blood flow detection or tracing (angiography
or venography.
– Detection of vascular leakage.
– Urinary tract studies.
– Gastrointestinal studies.
– Morphologic studies.
Iodinated contrast agents
• Ionic contrast agents, because of their
hypertonicity, draw water into whatever
space they occupy. Some effects of this
property include:
– Severe pulmonary edema if aspirated.
– Potential hypovolemic effect as water is pulled
into the GI tract if used for an upper GI series.
8
Iodinated contrast agents
• Some preparations of nonionic agents are
labeled for intrathecal use.
• Nonionic agents can be used for
procedures involving injection into other
“sensitive” areas, e.g. joints.
Negative contrast agents
• Gas added to a space, with or without
positive contrast media, to aid in
visualization of organ (s) of interest.
Negative contrast agents
• More commonly used in studies of the
urinary bladder, stomach and colon
(negative and double-contrast studies).
• Less common studies described in the
literature including
pnuemoperitoneograms.
9
Negative contrast agents
• The complication of greatest concern is
the occurrence of gas embolization.
• Highly soluble gases are less likely to
cause problems.
• Gases which are highly soluble in blood
include CO2 and N20. Room air contains
nitrogen, which is not very soluble.
Oxygen diffuses too rapidly to be useful.
Negative contrast agents
• Infusion of negative contrast agents, as
with positive contrast agents, should be
infused carefully to prevent over-inflation.
• Never attach a gas source directly to the
catheter used for infusion. Always load a
syringe with the gas, then attach the
syringe to the catheter.
Imaging Modality
Magnetic Resonance Imaging
www.canineepilepsy.co.uk
10
MRI contrast agents
• Paramagnetic contrast agents: hyperintense on
T1 sequences.
– Low incidence of adverse reactions.
– Ionic or nonionic agents available.
– Uses include detection of physiologic organ
enhancement, vascular leakage, and disruption of the
blood-brain barrier.
• Supraparamagnetic agents based on iron
oxides, many of which are taken up by the
reticuloendothelial system (liver, spleen, bone
marrow).
Imaging Modality
Ultrasound
http://radiographics.rsna
jnls.org
Sonographic contrast agents
• Composed of gas bubbles (air or perfluor gases)
stabilized by a shell of phospholipids,
surfactants, albumin, or polymers.
– Blood pool agents.
– Generally low risk of adverse reactions.
– Currently investigational in veterinary
medicine.
• Physiologic organ enhancement, blood flow
detection, vessel tracing, and vascular leakage.
11
Complications
• Complications due to inappropriate use or
delivery:
– Barium aspiration
– Barium within the body
– Barium embolization
– Aspiration of an ionic iodinated contrast agent
– Hypovolemia due to hyperosmolar contrast
within the GI tract
Complications
• Complications due to inappropriate use or
delivery (continued):
– Gas embolization due to use of low solubility
gas in negative or double-contrast study
• These complications (and others) are
somewhat predictable and can be
avoided with care.
Adverse reactions
• Adverse reactions, on the other hand, usually
cannot be predicted.
• Occur more commonly with hypertonic contrast
agents. Due to the decreased incidence of
adverse events, nonionic agents should be used
in high-risk patients.
• Worsened if the patient is dehydrated (always
correct dehydration prior to procedure).
• Be prepared to intervene (fluids, drugs).
12
Adverse reactions
• Mild reactions may consist of agitation,
vomiting, urination, defecation, erythema,
urticaria, or coughing.
• More severe reactions include mild
hypotension, arrythmias, tachycardia or
bradycardia.
• Severe reactions include severe
hypotension, cardiac or respiratory arrest,
and vetricular fibrillation.
Adverse reactions
• Reactions may also be specific to a
particular organ system, including:
– Contrast-induced renal failure
– Neurologic effects such as seizures or cortical
blindness
• Have the means to intervene (intravenous
catheter, fluids, drugs for resuscitation).
• Discuss the procedure with the owner.
Recommended reading
• Wallack ST. The Handbook of Veterinary
Contrast Radiography. San Diego, San Diego
Veterinary Imaging, Inc. 2003.
• Walter P, Feeney D, Johnston G, Diagnosis and
Treatment of Adverse Reactions to Radiopaque
Contrast Agents. In: Kirk RW, ed. Current
Veterinary Therapy. Small Animal Practice IX.
Philadelphia: WB Saunders Co., 1986; pp 47-52.
• Thrall DE. Textbook of Veterinary Diagnostic
Radiology, 4th ed. Philadelphia: Saunders,
2002.
13