Arteriography contrast meadia 1
Digital subtraction angiography (DSA)
Arteriography is now generally performed as a digital subtraction technique
and the conventional form of arteriography with the use of a film changer
has become obsolete in most departments.
With DSA, a computer is used to subtract an initial image without contrast
medium taken directly from the image intensifier from the subsequent
angiographic images with contrast medium in the blood vessels. The bone,
soft tissue and gas are removed leaving only the contrast-medium-filled
blood vessels in the final subtracted arterial images.
DSA requires cooperative patients who can keep still and hold their breath,
because any type of movement, such as body movement, cardiac pulsation,
respiration and peristalsis, causes significant image degradation.
Abdominal examinations are performed after an intravenous injection of
(Buscopan) to prevent peristalsis.
With patients who are unable to keep still and hold their breath, it is
sometimes better to obtain these digital images without subtraction.
Intravenous DSA
The high contrast resolution of the imaging system allows non-ionic contrast
medium to be injected intravenously in order to produce arterial images in
patients with no femoral pulses.
A large volume of contrast medium is injected rapidly by a pump injector
through a catheter positioned in the SVC or right atrium. The contrast
medium is diluted as it passes through the lungs and into the left side of the
heart and systemic circulation, but the images can be very good in
cooperative patients with a normal cardiac output.
Dr. Abeer El Sobky
Arteriography contrast meadia 2
Carbon dioxide DSA
The high contrast resolution of the imaging system even allows carbon
dioxide to be used as an alternative arterial contrast medium in patients with
a previous hypersensitivity reaction to non-ionic contrast media and in
patients in renal failure. Carbon dioxide is very soluble and rapidly
dissolves in the blood. It produces an image by displacing the blood in the
artery and therefore needs to be injected by a pump injector, even though it
is very compressible. Its use is contraindicated above the diaphragm in the
coronary and cerebral circulations, but it is safe to use elsewhere in the body
and the images are acceptable.
Dose of contrast medium
As a general principle, the dose of contrast medium injected is related to the
flow rate in the vessel being injected.
Small vessels with low flow rates require small amounts at low pressures,
while large vessels with high flow rates require larger volumes at high
pressures.
Peripheral and smaller arteries: The recommended doses for different
smaller arteries can safely be repeated after a short interval. In each case the
injection is made in about 1-2 s.
Of the high-osmolar contrast media, we regarded Urografin 310 as the best
for cerebral angiography and Triosil 370 as preferable for coronary
angiography, as there is experimental evidence that these agents are less
toxic than other high-osmolar products at these sites.
The quantity used for coronary artery injections varies from 4 to 8 ml,
depending on the state of the patient and the flow rate in the individual
vessel.
Dr. Abeer El Sobky
Arteriography contrast meadia 3
As already explained, the new low-osmolar contrast media are preferable to
the older high-osmolar products, and should be used routinely whenever cost
is not a major inhibiting factor.
Larger arteries
1. Arch aortography For injections into the aortic arch, which has the
highest flow rate in the body, 40 ml of high-concentration contrast medium
is injected by a pressure machine at 20 ml/s.
2. Abdominal aortography:
a) High aortic injection, i.e. above the renal arteries, and provided both
kidneys are functioning normally.
Whether performed by catheter or by lumbar injection, 30 ml of
contrast medium delivered in 1.5-2 s, is regarded as a safe dose
However, if there is severe renal impairment or only one kidney
functioning, caution should be observed, and the dose reduced to a
maximum of 20 ml.
A similar precaution is necessary if there is an aortic thrombosis
present which would result in a higher dose to the kidneys.
b) Low aortic injection, i.e. below the renal arteries, 25 ml injected in 1.5
s is usually adequate.
3.The normal celiac axis and superior mesenteric arteries both have high
flow rates and can tolerate injections of 30 ml of contrast medium at one
injection. Some workers recommend doses as high as 50 ml where it is
desirable to show the portal circulation. Speed of injection, however, is
relatively low at 8 ml/s.
Dr. Abeer El Sobky
Arteriography contrast meadia 4
Contrast medium reactions
Reactions to the intravascular injection of contrast media, whether
intravenous or intra-arterial, are not uncommon (about 12% in one major
intravenous series using high-osmolar contrast media).
Fortunately, the vast majority are trivial or of minor importance.
Reactions can be classified as mild, intermediate or severe. The severe
complications are in some cases potentially fatal, but formed less than 0.26%
of the series just quoted.
1. Mild reactions include sneezing, mild urticaria, nausea and vomiting,
conjunctival injection, mild pallor or sweating, limited urticaria or
itchy skin rash, feelings of heat or cold, tachycardia or bradycardia,
and arm pain following intravenous injections. Recovery is rapid and
requires no treatment except reassurance.
2. Intermediate reactions include widespread urticaria, bronchospasm
and laryngospasm, angioneurotic edema, moderate hypotension,
faintness, headache, severe vomiting, rigors, dyspnea, chest or
abdominal pain. Immediate treatment is required but response is rapid.
3. Severe reactions are rare but can be fatal. They include
cardiopulmonary collapse with severe hypotension, pulmonary edema,
refractory bronchospasm and laryngospasm. Also seen are myocardial
ischemia, tachycardia, bradycardia, other arrhythmias, cardiac arrest,
severe collapse, loss of consciousness and edema of the glottis.
The mortality from hyperosmolar intravenous contrast medium injections is
estimated at I case per 40 000 injections. Arterial injections probably carry a
similar risk.
Dr. Abeer El Sobky
Arteriography contrast meadia 5
The risk from the newer low-osmolar media appears to be significantly
lower for minor and intermediate reactions (about 3% as against 12%); it
also appears to be significantly lower for severe reactions, but is not yet
accurately quantified for fatal reactions, where the evidence remains
inconclusive.
Risk factors
 Major risk factors associated with the use of contrast media include:
1. Allergy, especially asthma
2. Extremes of age (under 1 year and over 60 years)
3. Cardiovascular disease
4. History of previous reactions to contrast medium.
 Minor risk factors include diabetes mellitus, dehydration, impaired
renal function, haemoglobinopathy and dysproteinaemia.
Previous minor reactions to contrast medium are not a contraindication to a
repeat examination, but patients with previous severe reactions should be
examined by other means. Patients with previous intermediate reactions
should be carefully assessed and if essential, only repeated under careful
control.
This implies:
 Pretreatment for 3 days with oral prednisone (50 mg) 8-hourly.
 Ephedrine (25 mg) and diphenhydramine (50 mg) are also given 1 h
before the examination.
 Only a lowosmolar contrast medium should be used.
Pretesting for allergy with small doses of contrast medium was once widely
performed but has now been known as completely unreliable. Fatalities have
Dr. Abeer El Sobky
Arteriography contrast meadia 6
occurred after previous negative test doses, and test doses have themselves
resulted in fatalities.
Treatment
Emergency drugs and equipment should be immediately available wherever
contrast media are used.
Intermediate and severe reactions usually involve hypotension, which is
treated by
 Elevation of the legs and
 May require rapid intravascular fluid.
 Oxygen may also need to be administered.
 It is essential to distinguish a vasovagal reaction (characterized by
hypotension with bradycardia) from an allergic or anaphylactic
reaction (characterized by hypotension with tachycardia). The former
requires atropine, whilst the latter requires epinephrine (adrenaline).
Iodism
 The radiologist should be aware that free iodine present in contrast
media will interfere with the performance of radioactive iodine tests
of thyroid function.
 Salivary gland enlargement ('iodine mumps') may follow several days
after the injection.
 Hyperthyroidism may he induced.
 Minor skin rashes may also be seen several days after contrast
medium administration.
Dr. Abeer El Sobky
Arteriography contrast meadia 7
Nephrotoxicity Intravascular contrast media may have a nephrotoxic effect.
Risk factors include large doses of contrast medium, dehydration, diabetes
mellitus, pre-existing renal insufficiency and multiple myeloma. Caution in
administering contrast media is desirable in diabetic patients with impaired
renal function.
Contrast media:
The earliest vascular contrast media mentioned above were far from ideal.
They included lipiodol injected into veins in small quantity (Sicard &
Forestier 1923), and strontium bromide (Berberich & Hirsch 1923) and
sodium iodide (Brooks 1924), which were the first contrast agents injected
into arteries. Thorium dioxide (Thorotrast) was used by Moniz (1931) and
became the standard medium in the 1930s. Unfortunately it was retained
indefinitely by the reticuloendothelial system, and being radioactive gave
rise to delayed malignancy. Abdominal films taken years after injection
showed a characteristic stippling in the spleen resembling military
calcification.
Organic iodide preparations stemmed from the work of Swick (1929), who
developed uroselectan (lopax) (containing one atom of iodine per molecule)
as a reliable agent for intravenous urography.
Later, organic iodines were developed, first with two and then with three
atoms of iodine per molecule. The standard media widely used in the 1970s
and 1980s were Hypaque, Conray and Triosil.
It was estimated that over 50 million doses of iodinated contrast media per
annum were currently used worldwide in radiological practice, and they
represented a major item in the operating expenses of most radiological
departments.
Dr. Abeer El Sobky
Arteriography contrast meadia 8
The ideal contrast medium should be completely non-toxic and completely
painless to the patient in the high concentrations used for angiography. A
further advance toward this ideal was the introduction in the 1980s of lowosmolality contrast media. These agents are relatively painless, compared
with the high-osmolar materials, and are claimed to produce fewer toxic
side-effects. Both these benefits are related to the low osmolality, which is
closer to that of normal plasma.
At an iodine concentration of 280 mg/ml the osmolality measures about 480
mmol/kg H 2 0. This compares with 1500 mmol/kg HO for the equivalent
Conray (high-osmolar) preparation and 300 mmol/kg H20 for plasma.
Further low-osmolality contrast media introduced in recent years include the
non-ionic monomers Ultravist (iopromide) from Schering; and Tomeron
(iomeprol) from Bracco (Italy). Also recently introduced are Isovist
(iotrolan) by Schering, a dimeric non-ionic low-osmolar contrast medium,
and Visipaque (iodixanol) also isotonic non-ionic dimes from Nycomed.
Osmolality is proportional to the ratio of iodine atoms to the number of
particles in solution. In the older hyperosmolar contrast media, this ratio was
3: 2, whereas the new low-osmolar agents have a ratio of 3: I and do not
ionize in solution. loxaglate, which is a monoacid dimer, does ionize in
solution but has a similar iodine : particle ratio (6: 2 or effectively 3: I) and
therefore enjoys the same benefits of low osmolality. To date the only
drawback to the new media is that they cost a good deal more than old
media, and this remains an important factor inhibiting their more widespread
use.
Some useful facts to remember:
Dr. Abeer El Sobky
Arteriography contrast meadia 9
Osmolality is dependent on the number (not the size) of the particles of
solute in solution.
Radio-opacity is dependent on the iodine concentration of the solution and is
therefore dependent on the number of iodine atoms per molecule and the
concentration of the molecules in the solution.
Iodine: particle ratio —the ratio of the number of iodine atoms per molecule
to the number of osmotically active particles per molecule of solute in
solution is a fundamental criterion. This iodine: particle ratio for current
products varies from 3:2 for conventional high-osmolar ionic monomers
(HOCM) to 6:1 for nonionic dimers.
Low osmolality reduces the pain of intra-arterial injections: contrast medium
solutions with an osmolality of below 500 mosmol kg-1 of water are
virtually painless. Digital subtraction angiography (DSA) enhances
electronically the contrast produced by the contrast medium by a factor of
two or three times, and therefore contrast media with 150–200 mg of iodine
per ml are usually adequate for intra-arterial imaging using DSA, although
twice this concentration is needed when the image is recorded on
conventional film-screen radiography without digitization subtraction
enhancement.
Dr. Abeer El Sobky