Usually the contrast media is in liquid form that introduce to patient. When using contrast agent, it give the information about size, shape and the location of the particular organs. Contrast media can administrate to patient in several way. Example through the mouth means drinking the contrast solution. Through the injection from vein, artery or through the anus.
Researches try to produce 'ideal' contrast agent but there are no contrast agent in world that can be consider as 'ideal' contrast agent. The requirement for the ideal contrast for safe and effective application is easy to administer, non toxic, a stable compound, non carcinogenic, cost effective, well tolerated by patient and rapidly eliminated when necessary.
The selection for contrast media for radiographic examination must be very careful. Because the specific contrast agent will give specific impact to patient. This important for radiographer to know type of contrast had been use and the physical and physiological of the relevant contrast.
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In radiology department, many procedure that using contrast agent is inject through the blood vessels and radiographer must know the kind of and the location of blood vessels. Example of this procedure is intravenous urogrphy, and examination of gastrointestinal tract (GIT).
Contrast media is classification according to the osmolality (mosm/kg h2o), iconicity (ionic or non ionic), type of molecule (monomer or dimmer) and viscosity at 37 °C
Osmolality is a concentration of osmotically active solute in body fluids. Viscosity is resistance of fluid to flow. It is a standard used as a force needed to move water 1cm at 20 °C and It express in term of centipoises(CP).it depend on the molecular weight, structure and temperature.
Type of contrast media
Contrast media can be divided into two main categories, which is:
1. Negative contrast media
2. Positive contrast media
Negative contrast media
Negative contrast media is a radiolucent mean can penetrated or passing by x-ray. This kind of contrast media normally have low atomic number and more ready for penetrated by x-ray than surrounding tissues. Negative contrast media appear darker in the image that produces due to the less effectiveness to absorb x-ray. Usually gasses are using to produce negative in image.
Air, oxygen and carbon dioxide can be use as a negative contrast media in diagnostic department and can mix with water suspension barium sulphate to produce double contrast media in examination of gastrointestinal tract. Air is use in chest examination through the inhalation to produce double contrast and appear in area of lung field. Oxygen is applied into body cavity for the examination in the knee to show the knee joint. Carbon dioxide is use with barium sulphate solution in gastrointestinal tract examination to show mucosal pattern. Carbon dioxide also use with iodinated contrast media in diagnostic angiography and vascular interventionism both the artery and venous circulation.
With development of new technology today like Computed Tomography and Magnetic Resonance Imaging the using of air as a negative contrast in encephalography and myelograophy almost no more apply. One of the effectiveness using air as a negative contrast in alimentary canal is no have any adverse effect compared to other due to volume of gas
Positive contrast media
Positive contrast media is a radio opaque (opposite radiolucent) and have high atomic number. So, it made x-ray less penetrate mean less absorb by this kind of contrast. This will result this kind of contrast appear denser than body tissue or appear as a white in image. Barium and iodine based solution is one of the contrast use as a positive contrast agent in radiology.
Normally positive contrast agent is divided into iodine based and non iodine based. Non iodine based is a barium sulphate. Iodine based contrast media can divide into four groups depending on their molecular structure; there are:
1. Ionic monomer (high osmolar)
2. Ionic dimmer (low osmolar)
3. Non ionic monomer (low osmolar)
4. Non ionic dimmer (isotonic)
#ionic contrast mean iodine containing contrast
#Monomer mean single molecule.
#osmolarity is measurement the solute concentration and express min term of osmoles.
#osmolality is measurement of the osmoles in solute in solvent per kg.
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The basic molecule Iodine containing contrast media s benzene ring and the carboxyl acids is added to make it soluble.
Iodine based contrast agent primarily is used to visualize blood vessels and cannot using in urinary system examination. They are using in
a. angiography(arterial investigations)
Non iodine based contrast media
We have much type of contrast media that use much examination in imaging department.
The selection of contrast media is depending on physical and chemical properties of relevant contrast media. For radiographic examination of gastrointestinal tract (GIT), the contrast agent that we using is barium sulphate (BaSo4) is a type of non iodine based contrast media. Barium sulphate has few features make it suitable for imaging of GIT, which is:
1. High atomic number (56)
4. cost effective
5.good coating properties.
Barium sulphate always have good coating properties than iodine based contrast media and easy to form thin layer at the surface of intestine. When there is perforation in GIT, the barium sulphate escape from the GIT and drain into peritoneal cavity will cause inflammatory, peritonitis and hypovolemic shock. Fluid replacement therapy, steroid and antibiotic is needed to treat complication that has mention.
The concentration of barium in the solution normally is express as the percentage weight to volume ratio(W/V).the meaning of 100% w/v solution is the solution contain 1 gram of barium sulphate per 100 ml of water and the density of barium is depend on the weight volume. When preparing the barium solution for radiographic examination, it is important to check the expiry dates and ensure the packing is intact. Patient history also must notice for the any contraindication. The following are contraindication for barium sulphate solution:
a. Suspected perforation
b.suspected partial or complete stenosis
When there has contraindication for GIT examination. Water soluble, iodine based contrast media (gastrografin or gastromiro) can be use either orally, rectally or mechanically (via stoma).
Possible side effect of contrast media
Possible side effect of contrast media can divided into primary effect and secondary effect.
Primary effect is involved the image quality that have produce. For example when compare the ionic monomer contrast media with the ionic dimmer contrast media, ionic dimmer contrast media have large molecular compared to monomer and slowly diffuse across vessel wall from vascular space. The osmotic effect will decreased by using monomer due to the small size molecular.
Secondary effect is reaction of patient toward the contrast media. The reaction of patient toward the kind effect can separated into three type, which is mild, moderate and severe reaction. The adverse effect can occur immediately, delay, after, or during administered of the contrast media. The percentage when using high osmolality contrast media and low osmolality contrast media is 5-10% and 1-3%.
The mild reaction simply needed a careful observation of the patient. The most the sign and the symptom will appear few minute after administrate of contrast media. The sign and the symptom including:
warmth nasal stuffiness
headache swelling eye
This kind of reaction does not required treatment and the sign and the symptom that appears is a self limited, without further proggession.requires observation to confirm resolution or lack of progression.
The sign and the symptoms of moderate reaction are more pronuced.The sign and the symptoms including:
Tachycardias generalized or diffuse erythema
hypertension laryngeal edema
dsypnea mild hypotension
Moderate reaction require treatment, close and careful observation for possible progression to a life threatening.
The severe reaction often is life threatening and the treatment including drug therapy, which is:
Laryngeal edema convulsion
unresponsiveness profound hypotension
cardiopulmonary arrest clinically manifest arrthymias
This requires prompt recognition and aggressive treatment, manifest actions and the treatment frequently require hospitalization. It is important to observe the patient during and after contrast media .the volume of contrast media that administrate to patient is no directly relationship to the effect. Cardiopulmonary resuscitation (CPR) equipment should be available when the contrast media are using. The radiographer must have trained how to apply CPR.
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The ABCD approach system is apply to treat the patient. While ABCD is represent Airway open, Breathing restored, Circulation maintained and Drug and definitive therapy. Emergency carts should behave in imaging department.
Apply the oxygen when hypoxia occurs to the patient. Administrate oxygen by the mask is vital and should do immediately
Assessment, assess the patient blood pressure, pulse to check normal or not. Electrocardiogram monitor may need to for evaluate the cardiac rhythm.
Assistance, call the hospital assistance team when necessary to ensure patient safety.
Breathing, begin the CPR when necessary and use the mouth proactive barrier for safety precaution. Radiographer must have knowledge how to perform CPR. If the radiographer doesn't know how to do CPR, don't waste the time and immediately call cardiopulmonary team.
Bag valve (ambu bag) or mouth mask can be use to administrate oxygen to patient. Radiographer must make sure the equipment is available in where the contrast media is used.
Beware of typically manifestation
Circulatory assistance, to administer isotonic fluid (normal saline), infuse rapidly and may use pressure bag or forceful infusion
categorize the reaction and patient status.
using the drug therapy when need. Make sure using correct amount, dose and route drug.
Do monitoring, assess and reassure the patient
don't delay call for help
don't using incorrect dose and drug.
Equipment for emergency carts
Radiographer is responsible to check out the all the important equipment are available before the administer the contrast media in imaging department. The following should be in the emergency carts:
Oxygen mask or ambu bag
Necessary drug and medication
Blood pressure or pulse monitor
Medication like epinephrine, histamine, and aspirin should behave.
it is difficult to know what kind of contrast media will give allergy action to patient. So, this very important to check the patient history regarding the contrast media. If patient have history of hypotension, congenital heart failure, diabetes mellitus, kidney severe, the contrast media cannot be use to the patient. Non ionic contrast media can be applied after given antihistamine to the patient. Must always observe the patient.
The approach to patient about to undergo a contrast media examination to enhance the image quality has 3 general goals:
1.to assure that the administration of contrast is suitable for the patient and meet the requirement of the indication.
2. To minimize the like hood of contrast reaction to patient
3.to be fully prepare the treatment for the reaction that occur.
Before the administration of contrast media, the preparation must be done is:
1.get appropriate and adequate history of each patient
2.preparing the patient appropriately for the examination
3.having equipment available to treat the reaction
4.ensure the expertise is sufficient to treat even the most severe reaction.
For any examination that involved the contrast media, try to choose the contrast which is non ionic, monomer, low osmolality and low viscosity.
Why low osmolality and viscosity:
a. can minimize risk of damage to the blood-brain barrier
b. less time and cost
c. less radiation exposure
d.smooth blood flow
e. no damage to endothelium and to blood cell
The whole procedure must explain to the patient including the side effect and complication of contrast agent and make sure the patient understanding the procedure and why using contrast media. After that patient are required to sign the consent form before examination.