Contrast agents

Question 1

65. Positive X-ray contrast agents -

Answer 1

absorb X-ray radiation more than the surrounding area

A positive contrast agent is a substance that increases the absorption, therefore appearing whiter on the image.
They usually have a higher proton number.
We have two main types of positive contrast agents – barium and iodine.

Question 2

66. Negative X-ray contrast media -

Answer 2

absorbs X-rays less than the surrounding area

Negative contrast agents decrease the absorption, therefore, they appear darker on images.
The most common example for negative contrast agent is air.
We can also use CO2, methylcellulose or mannitol. In XR imaging we use negative agents usually for intestinal imaging.

Question 3

67. Positive X-ray contrast agents include -

Answer 3

Barium sulfate

The Barium contrast agent contains an undissolvable compound of barium – barium sulfate. It is used strictly for gastrointestinal imaging, because it can cause very severe inflammation in tissues or in the peritoneal cavity. Thus an absolute contraindication of barium imaging is when there is a GI tract perforation. We can administer it per os or per rectum. A great advantage of barium is its adhesiveness – it adheres to the mucosas, thus it nicely outlines the GI tract. Barium is not used for CT because it is very dense and can make an artefacts on CT, the only exception is barium tracking in CT colography.

Question 4

68. Negative X-ray contrast media include -

Answer 4

Air

The most common example for negative contrast agent is air. We can also use CO2, methylcellulose or mannitol. In XR imaging we use negative agents usually for intestinal imaging.

Question 5

69. Contrast agents in X-ray examination –

Answer 5

are both white and black, depending on the type of substance

Question 6

70. A double contrast image refers to -

Answer 6

an examination where we use both positive and negative contrast agents

Question 7

71. Barium contrast agent -

Answer 7

can cause serious complications when in contact with the peritoneum.

The Barium contrast agent contains an undissolvable compound of barium – barium sulfate. It is used strictly for gastrointestinal imaging, because it can cause very severe inflammation in tissues or in the peritoneal cavity. Thus an absolute contraindication of barium imaging is when there is a GI tract perforation. We can administer it per os or per rectum. A great advantage of barium is its adhesiveness – it adheres to the mucosas, thus it nicely outlines the GI tract. Barium is not used for CT because it is very dense and can make an artefacts on CT, the only exception is barium tracking in CT colography.

Question 8

72. Barium contrast agent is used -

Answer 8

essentially only to view the Gastrointestinal tract

Question 9

73. Iodine contrast agent can be used -

Answer 9

intravenously, into cavities or the Gastrointestinal tract

Iodine contrast agents are the most commonly used positive XR contrasts. They contain iodine salts. They are water soluble and can be administred generally anyway you need – mostly intravenously or into the GI tract or cavities. When it gets into the bloodstream, it is excreted by the kidneys. We have two main types of iodine contrast agents.
Ionic (or high molecular contrast) agents, but we don’t use them anymore (there are cheaper but they have more adverse effects when administered into the bloodstream. We use them for all the other indications.
Non-ionic (or low molecular contrasts) are more expensive, but they have less adverse effects, so they are used for i.v. administration.
**There is another type of iodine contrast agent –called an oil contrast, but it is rarely used these days. We can use it for lymphography or for sialography (imaging of salivary glands ducts and lymph nodes).

Question 10

74. Allergic reaction to iodine contrast agent is -

Answer 10

Relatively common

There are two main adverse effects of iodine contrast agent, that happen usually only after i.v. adminstration, other methods of administration are usually safe.

**Allergic reactions, which do not depend on the dosage of contrast agent.
The allergic reaction after iodine contrast agent can be mild, intermediate or severe. Mild reaction includes rashes, nausea, uticaria. Intermediate reactions include tachycardia with hypotension, laryngospasm and difficulty breathing. Severe reaction is generalised and looks like anaphylactic shock.

**Chemo-toxicity, especially nephrotoxicity. This reaction is dependent on the dosage of the agent. Chemo-toxic reaction includes mainly damage to the kidneys, but there has also been instances documented of neuro and cardiac toxicity. The main principle of renal protection is optimalisation of contrast agent usage – that means use as low amount of contrast agent as possible and also hydrate the patient well both before and after the examination.

A special problem is during paravasal application – when the vein in which the contrast is administered bursts and the contrast agent spreads subcutaneously instead.

Question 11

75. A mild allergic reaction to iodinated contrast agents will manifest as -

Answer 11

Urticaria, redness and nausea

Question 12

76. A moderate allergic reaction to iodinated contrast agents will manifest as -

Answer 12

Tachycardia, hypotension and bronchospasm

Question 13

77. A severe allergic reaction to the iodinated contrast agent will manifest as -

Answer 13

Anaphylactic shock

There are two main adverse effects of iodine contrast agent, that happen usually only after i.v. adminstration, other methods of administration are usually safe.

**Allergic reactions, which do not depend on the dosage of contrast agent.
The allergic reaction after iodine contrast agent can be mild, intermediate or severe. Mild reaction includes rashes, nausea, uticaria. Intermediate reactions include tachycardia with hypotension, laryngospasm and difficulty breathing.
*Severe reaction is generalised and looks like anaphylactic shock.

***Chemo-toxicity, especially nephrotoxicity. This reaction is dependent on the dosage of the agent. Chemo-toxic reaction includes mainly damage to the kidneys, but there has also been instances documented of neuro and cardiac toxicity. The main principle of renal protection is optimalisation of contrast agent usage – that means use as low amount of contrast agent as possible and also hydrate the patient well both before and after the examination.

A special problem is during paravasal application – when the vein in which the contrast is administered bursts and the contrast agent spreads subcutaneously instead.

Question 14

78. Which of the following organs are most affected by intravenous iodine contrast media? -

Answer 14

Kidneys

Question 15

79. The nephrotoxicity of iodinated contrast media can be reduced -

Answer 15

by decreasing the amount of iodine contrast agent to a minimum and by sufficient hydration of the patient

Question 16

80. Nephrotoxicity of iodinated contrast agent -

Answer 16

is dose-dependent

Question 17

81. For CT scanning with iodine contrast agent -

Answer 17

the patient should fast 4 hours before examination

Question 18

82. What substrate is used as a contrast medium for ultrasound examination? –

Answer 18

Microbubbles

Ultrasound contrast agents rely on the different ways in which sound waves are reflected from interfaces between substances. Commercially available contrast media are gas-filled microbubbles that are administered intravenously to the systemic circulation. Microbubbles have a high degree of echogenicity that creating great difference in echogenicity between the gas in the microbubbles and the soft tissue surroundings of the body. Thus, ultrasound imaging using microbubble contrast agents enhances the reflection of the ultrasound waves, to produce a sonogram with increased contrast due to the high echogenicity difference.
We use Contrast-enhanced ultrasound to visualize blood perfusion of organs, measure blood flow rate in the heart and other organs, plus many more things. The most common indication is differential diagnosis of liver lesions.

Question 19

83. What substrate is used as a contrast medium for MRI examination? -

Answer 19

Gadolinium chelates

Contrast agents in MRI change the relaxation times of tissues, thus changing the signal intensity. The agents are substances with paramagnetic or superparamagnetic properties, which shorten T1 and T2 relaxation times. The most common substance is gadolinium – it has 7 unpaired electrons making it very paramagnetic.
Most of the MRI contrast agents are extracellular, which means that they are in bloodstream and in the interstitium. Gadolinium needs to be chelated to different ligands since the atom itself is quite toxic. It is administered intravenously and it is excreted through the kidneys with a 90 minute half-life.
Gadolinium is generally much safer than iodine contrast agents. However it can still cause adverse effects such as; nausea, vomiting, headache and paresthesia. Allergies are rare and anaphylactic reactions even rarer.

Question 20

84. How do MRI contrast agents work? -

Answer 20

Paramagnetic substances extend the T1 and T2 weighted times

Question 21

85. Intravenous gadolinium chelating agents (contrast agents for MRI) are excreted from the body mainly -

Answer 21

via the kidneys into the urine

Question 22

86. The administration of gadolinium in pregnancy -

Answer 22

is contraindicated because gadolinium passes across the placenta and can affect fetus