All of the examinations designated as special or advanced procedures require the introduction of some type of material into the area of interest to provide contrast. this is necessary because the differences in density among the various in the body are too small to provide adequate contrast for visualization of anatomic details. to compensate for this, it is necessary to increase or decrease the density of the organ to provide the desired contrast. Approximately 90% of all contrast media used in xray imaging are loosely termed intravascular or general contrast media.The physical properties of the iodine based contrast media include the ions or particles associated with the chemical breakdown of the contrast media when it enters a solution, the number & size of the iodine molecules, & the number & size of the molecules of any chemical additive. The development of contrast agents in 1972,a new agent was introduced for radiculography. This was produced by linking two iothalamtemolecules together to form a dimer (Dimer X). Dimer X excessively toxic to patients & was withdrawn from UK. Manufacturers needed to make a contrast agent, which is as near to the osmolarity of blood plasma(270 mOsmols/kg water) as possible. Create a low osmolar contrast media by linking together two tri-iodinated benzoic acid derivatives & replacing one of the acid carboxyl groups with a non ionizing group. In solution this gives six atoms of iodine and two particles. This type of contrast media can be used in a more dilute form (ie with saline) & therefore reducing the effective osmolarity (approximately 690 mOsmols/kg water). They are two type of contrast media, negative contrast agent and positive contrast agent.Negative contrast agent is
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The absorption of x-ray by a substance is dependent upon several factors, one of which is the atomic weight the substance. Negative contrast agent is radiolucent, low atomic number of material, black on film and their example are air, oxygen and carbon dioxide Those materials that have lower atomic weight will attenuate less radiation. The resultant remnant radiation will produce a greater radiographic density (darker image) on the image receptor. This characteristic is useful when the objective is to demonstrate an anatomic structure against the dark background or to provide a silhouette image of the structure. Example of radiolucent or negative, contrast agent are air ,carbon dioxide and water. Air is introduces by the patient during a radiographic examination example inspiration during chest radiography or can also be introduced by the radiographer as part of the examination in a double contrast barium enema. introduced into cavities of the body for example in the knee when performing an arthrogram to demonstrate the knee joint. Carbon dioxide is introduced into the gastrointestinal tract in conjunction with a barium sulphate solution to demonstrate the mucosal pattern for example double contrast barium meal.carbon dioxide can be used as the negative contrast agent in a double contrast barium enema, rather than air, as it causes less immediate abdominal pain as well as less postprocedural pain and discomfort. However, some studies have shown that carbon dioxide produces inferior distension and additional insufflations are required to maintain adequate quality distension. Carbon dioxide can also be used as an alternative contrast to ionated contrasts for diagnostic angiography and vascular interventions in both the arterial and venous circulation. the gas produce negative contrast due to its low atomic number and low density compared with adjacent tissues. Most of available gases have been used as negative contrast agent with varying result, however the four gases listed here are the most commonly used negative contrast agents. The negative contrast agent can also be used in conjunction with a positive contrast agent. One common procedure that used this combination of contrast agent is the double contrast barium enema. Air and oxygen may be dangerous during certain procedure because they can cause gas emboli, but carbon dioxide and nitrogen do not pose the risk of gas emboli and can be used with relative safety. they are also able to be absorbed rapidly by the body. this factor can be advantageous when rapid absorption is desired, but in cases in which many radiographs are taken, it is definite disadvantages. Because of their high atomic number, positive contrast agent cause an increase in the attenuation of a-ray and are considered to be radiopaque. Positive contrast media is radiopaque, high atomic number of material, white on film and their example are bromine, iodine, and barium. They produce an area of decrease radiographic density on the image receptor. Contrast agents that are radiopaque contain element with high atomic number such as iodine, bromine and barium. When these substances are used to fill organ, they essentially make the organ radiopaque, and the image appears clear or white on the radiograph. They can take the form of tablets, powders, and liquids and can be introduced into the body through a variety of routes. They are relatively in non toxic in most cases, but certain patients may exhibit reactions of varying severity, especially to agents containing iodine. In some cases, small doses of these agents may cause death. the positive contrast agent used during the advanced procedures discussed in this text will be organic iodine compound. An ionic compound dissociates (dissolves) into charged particles when it enters a solution (example: blood). Ionic media breakdown into cations (+ive charged particles) & anions (-ive charged particles). Five times the osmolarity of human plasma (hyperosmolar). Example: Conray 280, 325 & 420 (The number refers to the iodine concentration in mg/ml-1).It is Monomer and dissociates into 2 particles in the blood. Non-ionic contrast media do not dissolve into charged particles when it enters a solution. For every three iodine molecules in a non-ionic solution, one neutral molecule is produced. Often referred to as "low osmolar". It have 3:1 compounds. Far safer than ionic contrast agents. Example: Omnipaque 140,180,240,300,350.Dimer and does not dissociate. Generally isomer, more viscous than ionic and also more hydrophilic. The additional chemical groups determine the properties of the contrast agent. There are solubility, viscosity and osmolarity. Properties of Water-soluble Injectibles are, low toxicity, high opacity, low viscosity, high miscibility. Viscosity describes the thickness or resistance to flow of a contrast agent. The thickness of the contrast agent is related to the concentration, the size of the molecules in a specific contrast agent & the temperature of the contrast agent. The viscosity affects the rate that the contrast media can be injected. High viscosity cause damage to vessel endothelia, blood brain barrier, renal tubule. The osmolarity of a solution is the measurement of the number of molecules & particles in a solution per kilogram of water.If cells in a organ are surrounded by a solution of greater osmolarity than the cellular fluid, water will leave the cells which will ultimately shrink & distort, sometimes being disrupted completely (Dawson 1984). Fluid shifts can have a devastating effect on patients. (The osmolarity value of blood plasma & CSF = 270, where as Ionic CM (monomer) = 1400). Enhance subject contrast or render high subject contrast in a tissue that normally has low subject contrast.Therefore changing the Subject contrast will change the Radiographic contrast and film contrast. Visualize organs, masses, etc. otherwise unable to be differentiated (by imaging) otherwise. Identification of changes in vasculature and vascular integrity. Follow blood, lymph or serosal cavity fluid flow. Contrast media is needed because soft tissue has a low absorption/interaction ratio. Absorption is dependent on atomic number, atomic densit, electron density, part thickness, K-shell binding energy (K-edge),P-E interaction is the process of absorption. Treatment of adverse reactions to contrast medium has already been stated that all patient must be keep under constant observation during and after contrast media administration, and emergency drugs and oxygen should be ready available if required. contrast media should be administered at body temperature and the manufacturer's optimum does should not be exceeded. this minimizes the risk of an adverse reaction. Before initiating any treatment, the severity of the event should be carefully evaluated, this ensure the appropriate treatment can be given. reaction to intravenous administration of contrast media can be classified into three categories adverse Reactions (Mild reaction), Adverse Reactions (Moderate reaction) and Adverse Reactions (Severe reaction).Mild reaction is simply required careful observation of the patient. Most of the symptoms will pass within a few minutes post administration. Sign and symptoms are of mild reaction are, nausea & vomiting, cough, warmth (heat), flushed sensation,headache & dizziness, metallic taste in mouth,diaphoresis (sweats), urticaria (hives), anxiety, Itching, pallor, chills,tremors (shaking), nasal stuffiness, swelling of eyes or face. Treatment for the mild reaction are observation & reassurance only. Usually no medical treatment is required and the reaction does not interfere significantly with the examination procedure doing under taken. Sign and symptom for adverse Reactions (Moderate reaction) are pulse change, hypotension, hypertension, dyspnea, bronchospasm, laryngospasm, erythema, pruritis, abdominal pain. Treatment-Close observation, Treat symptoms. Compression and tight clothing should be release and the patient reassured. the patient will need to be seen by a medic and the adverse reaction required information to be entered in the patient's permanent medical record. Drug therapy mat be required, such as administration of anantihistamine (eg:Piriton 10md)intravenously, or adrenaline(epinephrine)0.5 mL 1:1000 solution subcutaneously, to reduce the symptoms. While Adverse Reactions (Severe reaction) potentially life threatening mild & moderate signs & symptoms plus unresponsiveness, convulsions, clinically manifest arrhythmias, cardiopulmonary arrest, renal failure and death. The above classification mild, moderate and severe do not attempt to distinguish between allergic-like and non-allergic like reaction. Rather, they encompass the spectrum of adverse events that can be seen following the intravascular injection pf contrast media. A requirement of a Contrast Agent is easy to administer, no toxicity, stable compound. Will not dissociate into toxic ions. When injected the media concentrates in area(s) required example in order to produce good contrast. The agent's physical features allow the organ to be properly demonstrated (non-flocculating) example even barium coating of the stomach in the presence of an acid environment. The agent should have rapid elimination. The agent should not be carcinogenic. The agent should have a viscosity appropriate to the patient when introduced. The agent should cause minimal distress to the patient when introduced. The agent should be cost-effective. Examples of areas where contrast agents are used in Arteriography- Mesenteric arteries, Angiography (DSA) - Cardiology, Venography (replaced by ultrasound- Doppler),IVU, Fluoroscopy - Alimentary tract, hyserosalpingography, sialography, dacrocystography, computerised Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound - Liver, kidney, Myelography (replaced by MRI) and Arthrography - Knee joints. The following is the summary of somme general precaution to be taken before and after the administration of contrast media. Before injection,discuss the procedure with the patient, obtain an informed consent from the patient, establish a set of baseline vital signs, know the patient, check the chart for history of allergy or hypersensitivity, check the results of the patient's blood work for example blood urea nitrogen, creatinine, prothombin time , in cases of arterial access, partial thromboplastin time, platelet count, check wheather patient has other medical problems such as hepatic or renal diesease, pregnancy, multiple myeloma, congestive heart failure, graves' disease, homozygosity for sickle cell disease, bronchiole asthma, hyperthyroidism. We must know the procedure of contraindication and limitation to the specific special procedure, know the possible reaction that can occur with the contrast agent used, check emergency equipment and know location and content of crash cart. After injection,know where physician may be reached,evaluated patient's vital function for abnormalities of respiration, pulse, blood pressure, presence of cyanosis. Remain with and monitor the patient for at least 20 minutes after injection. Iodised Oils is infrequently used in radiography. It used where water-soluble agents are contraindicated or where a viscous compound is required. Not easily absorbed & in some circumstances, carry a risk of oil-embolus. It formed from poppy seed oil & examples include Lipiodol & Myodil. Safety advanteages uses of contrast media are Smoother blood flow, no damage to the endothelium and to blood cell. No damage to the blood brain barrier and to renal tubule. Ergonomis advantages use of contrast media are Use of higher concentration, use of smaller diameter catheters, less invasive procedure and easier manual injection.
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example of positive contrast media