A contrast is a short form for contrast media, while contrast media are x-ray dyes that used to provide contrast for the imaging of tissues or between blood vessels. A contrast media is known as a substance that injected into the body to make radiographic imaging of internal structures much easier. It is also known as a substance that looks like an iodine or suspension which is microscopically visible particles that are dispersed throughout a denser liquid or gas because they are easily filtered but they are not easy to settle because of the system viscosity. Therefore, it is also known as a substance that solution of iodine that comparatively opaque which is in penetrable by a form of radiant energy to x-rays that is introduced into the body by injected or swallowing. Well, the internal part such as the gastrointestinal tract, blood vessels or kidneys, also is the surrounding tissues in radiographic visualizations are called the contrast agent contrast material. Not only that, contrast media is also known as a substance used in radiography to increase image contrast ,therefore positive contrast medium will absorb x-rays strongly compare to negative contrast medium.
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Why do we need contrast media in Medical Imaging?
Where do we use contrast media?
Contrast media is needed because soft tissue has lower absorption and interaction ratio. The degree of attenuation of an X-ray beam by an element is complex, but one of the major variables is the number of electrons in the path of the beam with which it can interact. However, the absorption of contrast media is depending on the atomic number, atomic density, electron density, part thickness and K-shell binding energy.
There are various examinations that need the help of contrast media inconjuction to get a better image and to make doctor's to diagnose easier. Example of examination that require contrast media are :-
Types and uses of contrast media
Basically, in this examination there are two types of contrast agent that have been used. The types of contrast agent are first the contrast agent that base on barium sulphate and next the contrast agent that based on iodine.
contrast agent that base on barium sulphate
contrast agent that based on iodine
As we know, contrast agent is divided in two types. So let's see the first type that is contrast agent that base on barium sulphate, an insoluble white powder. However, the barium sulphate then will be mix with water and other additional ingredients to make the contrast agent. The barium blocks the passage of x-rays, so barium-filled organs stand out better on x-ray exams. This type of contrast agent is used in the examination of the digestive tract; it is either swallowed or administered as an enema. For the examination of esophagus or the stomach, patient will be asked to drink a mixture of barium sulphate with water and also drink with some flavouring such as vanilla or fruit flavour. The mixture is rather thick and white. After the examination, it will be come out as feces. While for the examination of the rectum or colon, the barium will be administer trough the rectally using the enema tube. Once the procedure is done, you will be able to go to the toilet and empty your bowel. This is one of the good idea as this is to increase the fluid intake after the examination and the contrast that in the body is already been removed.
The second type of the contrast agent is contrast agent that based on iodine. The bound for this contrast agent are organic (non-ionic) compound or ionic compound. However, ionic agents is the one been developed first and still it is widely using, but ionic agent have a poor side effect profile. While the organic compound has a fewer side effects because they do not dissociate into component molecules. Examples of organic iodine molecules are ioversol, iohexol and iodixanol. This contrast agent is selling as colourless water solution and the solution is normally expressed as mg l/ml. They will be used intravenously but for various purposes such as intra-arterially or intra abdominally. The ideal contrast medium must fulfil certain requirements for safety such as easy to get administer, it is concentrated in required area when it is injected, it is in stable compound and also non-toxic.
Iodine and non-iodine
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The biggest group of contrast media that been used in radiology department widely are the water soluble organic molecules of iodine. The organic contains carbon and low oxicity and it is high stability. To determine the contrast agent, we can determine it by looking at the number of iodine molecules. The higher the iodine concentration, the more x-ray photons will be absorbed, so the particular contrast agent will be more radiopaque compare to low iodine concentrated agent. Normally contrast agent containing iodine is used to see the image of gallbladder, spleen, liver, bile ducts, urinary tract and blood vessels. This contrast agent will be injected to the patient, and need to be remind patient that is allergic to iodine is not advisable to get injected with this type of contrast agent. It is risky to get injected with this type of contrast agent if you are allergic with it. There are some side effects after the contrast agent is injected such as metallic taste at the mouth, nausea or itchiness. Don't worry the side effect will last temporarily only. The higher the risk of the iodine concentration, the higher will be the risk of adverse reaction.
These contrast agents also contain ionic monomers, ionic dimmers, non-ionic monomers and also non-ionic dimers. The ionic media will breakdown into cations that positively been charged and also negatively been charged. For every three iodine molecules present in an ionic media, one cation and one anion will be produces as it enters the solution. Ionic contrast media generally referred to 3:2 compound. Determination of iodine concentration is determined by the number of iodine molecules in milligrams present in a millimetre of a solution (mg/ml). This ionic agents is push to the high osmolarity contrast media category.
A non-ionic contrast media wont dissolve into charged particles, when it enters a solution. It is also won't dissolve in charged particles as it enters the solution. For every three iodine molecules in a non-ionic solution, one neutral will be produced. While, for three iodine molecules in a non-ionic solution, one neutral molecule is produced. Non Ionics compound will be 3:1. This non-ionic agent is push to the low osmolarity contrast media category. As contrast media is introduced into the vascular system the water from the body tissue will move into the vascular system as an attempt to equalize the concentrations. Then the contrast media particles will draw plasma water towards them, next the water from body tissues will rapidly move into a vascular system via the capillary membranes to balance and equalize the situation. The process known as osmosis. This osmotic effect can cause the arteries of the kidneys to expand. Therefore when the arteries are expand vasoconstrictors will be released to compensate the artery expansions.
Contrast media can be divided into two categories, there are negative and positive contrast media.
Negative contrast media.
It is radiolucent and have low atomic number. Gases are used in here to produce negative contrast media such as if air , the main matters is inspiration during dust radiography, oxygen, it will be introduced into cavities of the body and carbon dioxide, it will be introduces in a gastrointestinal tract with barium sulphate solution for the demonstration of the mucosal pattern. Not only that, it can be used also for the colon examination.
Positive contrast media
Positive contrast media is radiopaque and has high atomic number, it is less readily penetrate compare to the surrounding fill area that appears denser compare to body tissue.
Precautions during contrast media and the side effects.
If you are a diabetic patient and you are taking metformin, you have to stop taking metformin for atleast two days. As metformin can effect you. Contrast media containing iodine has atomic number of 53. It is a stable compound that safely can be carried out into a human body. The carrier molecules are organic,containing carbon, low oxicity and high stability. The advantage of iodinate contrast media are they will have no irritation,leakage,and it is usefull for pathological reason. While the disadvantages of iodinate contrast media it will form poor mucosal coating, it is also expensive and they will be side effects.
ABCD APPROACH FOR PATIENT EVALUATION AND TREATMENT
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A - Airway or oxygen. The assessment for this approach is the severity and category of reaction. It is access ( venous ) - to secure the intravenous line whether it is peripheral or central.
B - Breathing. Please perform CPR if necessary. You can also use the mouth protector barrier. You have to beware of atypical manifestation such as beta-blockers that can prevent tachycardic response.
C - Circulatory assistant. Please categories the reaction and also the patient status. If necessary, please call the cardiopulmonary arrest response team.
D - drug therapy. Please monitor the amount of drug that you giving. And please reassure the patient.
Adverse side effects of contrast media.
Any water soluble ionic contrast media can cause adverse effect. These effect maybe cause by the high osmolarity and chemotoxic effects. Eventhough both ionic and non-ionic leave side effects, but the ionic of higher osmolarity can cause more side effects. The side effects can be categorized in 3 categories such as :-
The sign will appear itself without any evidence. Example of the mild reaction are nausea, cough, nasal stuffiness,sweats, rash, hives, swelling of the eye and face, chills,flushing,itching, pallor, paleness, altered test, shaking, dizziness, warmth and headache.
This sign and symptom will be more pronounces. The moderate degree clinically evident focal or systemic symtoms such as tachycardia,bradycardia,dspnea,mild hypertension,bronchospasm,hypertension,diffuse erythema and laryngeal edema
This effects is a life treatning sign and symptoms. There are laryngeal edema,unresponsiveness,convulsions,,profound hypotension, cardiopulmonary arrest and unresponsiveness.
The treatment for the situations above requires prompt reorganization.
These are the organs that will be effected when iodine based or Gadolinium Based contrast agents are administered.
The adrenal gland will lead to hypertension
The brain part will lead to headache,dizziness,confusion,seizure,rigors,lost or diminished consciousness and also loss or diminished vision
The gastrointestinal tract will cause nausea, diarrhea and intestinal cramping
The heart will cause hypotension, dysrhythmia, pulseless electrical activity and also acute congestive heart failure.
The kidney will lead to oliguria,hypertension and contrast induced nephropathy
The pancreas will be swell up and lead to pancreatitis
The respiratory system will cause laryngeal edema,bronchospasm and pulmonary edema
The salivary gland will swell up and lead to parotis.
The skin and soft tissue will lead to painess, edema,
flushing,pruritis,nephrogenic and erythema
The thyroid will lead to exacerbation of thyrotoxicosis
The vasculary system will cause hemorrhage and thrombophlebitis.