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Contrast media can be defined as a chemical substance either solution or gases that is used in radiography to enhance the visualization of an internal body structure including the anatomical part of internal organ or soft tissue to that is difficult to visualize and differentiate by non-contrast film. By the usage of contrast, many of body's organ and tissues can be demonstrated. Contrast also enhances the effectiveness of many radiology procedures. Different tissues or organ will penetrate different degree or level of x-ray beam. The reasons on contrast media being used include the thickness of the area that being studied or examined in the body and the density of the structures that want to be examined. Contrast media is used because soft tissues are difficult to demonstrate and differentiate from bony part of the body by making the internal structure of body (organ or soft tissues) opaque on x-ray. So, the film that is produced will clearly be demonstrating the structures. Contrast media can be categorized as a drug because the substance in contrast media can be absorbed by body and may affect a physiological response. Contrast media also called as contrast agents and widely used in radiological examinations such as in MRI (Magnetic Resonance Inve) and in computed tomography (CT).
There are two types of contrast media which are positive agents of contrast media and negative agents of contrast media. Positive agents of contrast media is used to increase density difference by making the structures (part to be examined) can be seen opaque or white area on the film. Positive contrast media can be classified as iodine based and non-iodine based. In medical imaging, iodine based are commonly used in Angiography which is for arterial investigation, Venography which is for venous investigation, Voiding Cystourethrogram(VCUG), Hysterosalphinogiogram(HSG), and Intravenous Urography(IVU). Iodine based has high atomic number that enhance the ability to absorb most of the x-ray and provide good contrast between the interested area and the surrounding tissues. The example of positive contrast agents that hve high atomic number are barium; which have 54 as the number of atom in the barium compound and iodine; which has 53 as the number of atom in the iodine compound. So, for these cases (Angiography, Venography, VCUG, HSG and IVU), contrast media is given intravenously by inserted the contrast agent substance into the blood vessel by injection.
Non-iodine based of positive contrast media such as barium (which usually be used in medical imaging), also same as iodine based of contrast media in terms of contrast quality. Non-iodine based of contrast media can also give a good contrast to the structure that being examined as well as to the film produced. Therefore, in medical imaging, non-iodine based (barium) is most commonly used for gastrointestinal(GI) studies especially for large bowel (large intestine) investigation, esophageal investigation, stomach investigation as well as small bowel (small intestine) investigation. The barium solution will be prepared by diluting the barium substances with the water. This also helps to produce lower density of barium solution. Different types of gastrointestinal examination need different preparation of barium with different properties. For esophageal investigation, the barium preparation that is used is barium swallow(BaS) while for the stomach investigation (to demonstrate the stomach and the deudonem), the barium preparation that is used is barium meal(BaM). In the other hand, barium enema(BaE) is prepared for large intestine (colon) investigation and barium meal follow-through (BaM + FT) is prepared to demonstrate small intestine from the deudonem to the ileo caecal. Barium substances are suitable to be used in gastrointestinal studies because it cannot be absorbed by the body unless the patient have suspected in perforated stomach or intestine or any other part in the gastrointestinal tract (GI Tract). For this cases (GI studies), contrast media is given either orally; which is through mouth or rectally; which is through rectum depends on the radiologist or radiographer.
The other type of contrast media which is negative agent of contrast media is specifically known as gases. The gases that are listed in the negative agents of contrast media are air, oxygen and carbon dioxide. In fact, these negative agents are readily available surround us besides the price is too cheap. Carbon dioxide is the most common used in medical imaging as a contrast media besides the usage of other negative contrast media which is oxygen. The negative contrast agents are used to decrease organ density to produce contrast on the structures (part to be examined) and the film produced. So, the film (radiograph) obtained by using this negative contrast agents (air, oxygen or carbon dioxide) will appear black or darker. Mostly carbon dioxide of negative contrast media is used pairly with the barium in the usage of contrast media examination to get the 'double contrast' effect in the procedure as well as increase the quality of film radiograph. Oxygen is not the best preferable choice in performing the double contrast because oxygen is the main factor to induce a fire risk to the patient.
The most criteria or factors that must be take into consideration for radiologist or radiographer in selection of contrast media substances are the history of allergic of the patient to any contrast media substance, the imaging machine that will be used to perform the radiological examination because the type of contrast agents injection varies with the type of imaging machine, drugs or medicine used and the type of group of the patients. Other than that, non-toxic contrast, easily to be removed or excreted from the body and cheap in price also includes in the consideration's factor to choose an ideal contrast media. The groups of patient include, diabetic patient, asthmatic, infant, elderly patient, patient with renal impairment and patient with cardiac impairment. This is to ensure there is no complication to the patient during or after the procedure is done. The other criteria or factors that are important in selection of contrast media substances are the ability of contrast substances to mix with the body fluid, the viscosity of the substances which can be defined as the resistance of fluid to flow in the body, the iodine based preparations (ionic water soluble, non-ionic water soluble, oily agents or agents excreted in the bile) and the osmolality of the substances which means that concentration of all the particle to dissolve in body fluid, type of compound; which is either monomer or dimer compound and the ionicity of the compound substances; which is either ionic compound or non-ionic compound. Normally, substances or compounds with non-ionic monomer that have the ability to mix with the body fluid, and also have low osmolality and viscosity are the best choice by the radiologist or the radiographer as the substances for contrast media. Low osmolality is important to patient as to minimize or reduce the effect on cardiovascular system, blood-brain barrier and local symptoms such as pain, heat and sensation. Low osmolality contrast media also important and be used in all painful of arteriographic procedure because it can reduce or minimize the movement of patient by minimize the patient's discomfort as well as reduce the possibility to repeat the radiograph. For example; iopamidol (non-ionic monomer) with low osmolality (600-850 mOsm/kg H2O) and viscosity between 9-10Centipoise (Cp) at 37° is more preferable than diatrizoate (ionic monomer) which has high osmolality (>1500 mOsm/kg H2O).Therefore, all the criteria and factors are very important in selection of contrast media especially the substance with low osmolality.
Contrast media also have its own complication or any related complication to the contrast media during of any contrast media examination. Complications may also be occurred when using contrast media; either water-soluble contrast media or water-insoluble contrast media. Every patients with contrast media administered will have any reactions but the reactions are varies according to the patients themselves. These because the adverse reactions are differ by patients accordingly to their own antibody reactions towards the contrast media. The complications or adverse reactions can be classified into mild, moderate and severe adverse reactions.
The mild adverse reactions normally do not require treatment but the patient should be monitored and observed carefully for 20-30 minutes after the contrast media procedure for any progression of more severe reactions that required treatment. This type of reaction is generally caused by increasing osmolality of the contrast media. The symptoms are nausea, vomiting, coughing, urticaria (skin condition problem), sensation of heat or warmth and pain at the injection site.
The second stage of adverse reactions is medium stage or the other name is moderate adverse reactions. It is suggested to be given a treatment but not an intensive treatment. Moreover, the symptoms are not immediately appearing after the contrast media procedure. The symptoms includes; bad vomiting, headache, middle stage of urticaria, dyspnea, mild bronchospasm and abdominal cramps.
The final stage of adverse reactions of contrast media is the severe adverse reactions. The patient with severe symptoms must get the life-threatening treatments and intensive care is necessary for this patient. The symptoms for this severe adverse reaction are moderate or severe bronchospasm, moderate or severe laryngeal edema, anaphylactoid shocks and cardiac arrest. The delayed time to get the immediate treatments or contact the physicians for these severe symptoms can lead to death.
Although contrast media has many beneficial in medical imaging, radiologist, radiographer and the clinical staff must keep concern about the patient before, during and after the contrast media procedures. The volume and the description of contrast media and the drugs administered that are used are recorded and keep as history of patient's treatment. Lastly, ensure there is no side effect on patient's condition and ensure the patient's vision has no blurring before the patient can leave the x-ray department. If there are other serious reactions due to the effects of contrast agent, the patients must immediately require to see their physicians for immediate treatment.