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Contrast media is a substance widely used in the medical imaging industry to enhance the internal structure or fluids contrast within patients body shown on image for diagnostic purposes. Contrast media is normally solutions or gasses introduced into body for differentiation and visualization of soft tissue structures. This is because it is more difficult to demonstrate soft tissue structure compared to bony structure in a diagnostic image. There are two main categories of contrast media which are positive contrast media and negative contrast media. Positive contrast media is radiopaque and therefore it appears white on the image. There are two different kinds of positive contrast media which are iodine-based and barium-based. On the other hand, negative contrast media is radiolucent and therefore it appears dark on the image. Swallowed air, carbon dioxide, gas crystals and gas bubbles are some of the examples of negative contrast media. There are several of examinations that involve the use of contrast media such as angiography, intravenous urography (IVU), intravenous pyelography (IVP), computed tomography (CT), myelography and etc. Patients undergoing examinations involving contrast media have to be well prepared for in order to prevent discomfort to patients and enable more accurate diagnostic. Despite the benefits of contrast media usage for diagnostic purposes, it poses threat to its receiver as it may leads allergic reaction which may be fatal.
Positive contrast media is more commonly used in radiographic imaging. It is radiopaque and gives a white appearance on radiographic images. It has a higher atomic number and higher density than soft tissues in body. Due to these characteristics, it is able to attenuate more radiation than soft tissues when exposed to radiation thus giving the white appearance on radiographic images produced. There are two common types of positive contrast media currently used for diagnostic purposes which are iodine-based and barium based. Iodine-based contrast media is most commonly used in radiology as it is water soluble and therefore harmless to the body. It is primarily used to visualize vessels. It is most often given intravenously to the patients. Iodine contrast agents are used in Angiography, Venography, Voiding Cystourethrography, Hysterosalpinogram and Intravenous Urography (IVU). Iodine-based contrast media is usually classified as ionic and non-ionic. Ionic contrast media records a higher osmolarity and it tends to give more side effects. Urografin, Telebrix and Gastrografin is some of the radiocontrast agent used in hospitals. Non-ionic contrast media has a lower osmolarity and thus giving lesser side effects. Omnipaque, Ultravist and Visipaque is widely used as non-ionic radiocontrast agents in hospitals. Barium-based contrast media (Barium Sulfate) is mainly used in radiological procedures to image digestive system (gastrointestinal tract). It is water insoluble and exists in a powder form. It has to be mix with water before administering into the body directly. It can be either administered orally or as enema. It leaves the body in feces form after radiological examinations. Barium-based contrast media is normally used for barium enema, double contrast barium enema, barium swallow, barium meal, double contrast barium meal, barium follow through and computed tomography (CT) pneumocolon.
Negative contrast media is usually used together with positive contrast media to give a more define image. It is more radiolucent compared to body tissue and thus gives a dark appearance in the radiographic images. It has a lower atomic number and lower density than soft tissues in body. Due to these characteristics, it attenuates lesser radiation when exposed to radiation. Thus giving the dark appearance in the radiographic image produced. The commonly used negative contrast medias are air and carbon dioxide, whereas gas crystals and gas bubbles are sometimes used in radiological examinations. Air and carbon dioxide is usually used in double contrast barium enema, giving the gastrointestinal tract (GI tract) a more define image and thus producing a clearer image. Gas bubbles are used in ultrasound procedures.
The selection on the usage of contrast media is based on its ionicity and type. The most commonly used contrast media is usually non-ionic, monomer and has low osmolarity as well as low viscosity. This is because it is the safest sort of contrast media and gives fewer complications to patients. Osmotically active solute dissolves all particles (molecules and ions) in body fluid. Low osmolarity solute minimizes the risk of blood-brain barrier damage. This reduces the likelihood of local heat and/or pain. This is an advantage as there is less patients' movement and fewer resultant artifacts which leads to less repetition, less time and cost as well as less radiation exposure. Viscosity is the resistance of fluid to flow in blood stream. High viscosity contrast media may result in damage vessel endothelia, blood-brain barrier and renal tubules. However, low viscosity contrast media gives both safety advantages to patients and ergonomic advantages to the department. As for safety advantages to patients, it gives a smoother blood flow. It causes no damage to the endothelia, blood cells, blood-brain barrier and renal tubules. On the ergonomic advantages, it uses a higher concentration of contrast media and smaller diameter catheters thus resulting in a less invasive procedure. It is also easier to inject to patients manually.
Patients have to be well prepared prior to the administration of contrast media. This is to prevent patients' discomfort and prevent allergic reactions. We, as radiographers must ensure patients are well prepared before any examinations involving contrast media. Patients are required to fast four to six hours prior to examinations. This is to prevent patients from vomiting upon administration of contrast media should there is any discomfort. Patients' history of allergic reaction towards contrast media has to be given serious attention as this may cause complications and may be fatal. We must also be sure of patients' previous reaction to contrast media as well as drugs to determine the safety of patients during examinations. Patients with asthma and heart conditions have to be informed of the risk prior to the administration of contrast media. Special advise and preparations are to be instructed for patients who are suffering from Multiple Myeloma, myelodysplastic syndromes or severe diabetes. They should be well hydrated and encouraged to drink a lot of fluid especially for Intravenous Urogram (IVU). Diabetic patients who are on Glucophage (Metformin) medication will have to stop the intake of medication 48 hours prior to examinations which requires intravenous or intra-arterial contrast media injection. On the other hand, patients who have allergies or previous reactions will most likely be asked to take Prednisolone 40 mg 12 hours and 40 mg, 2 hours prior to the examination. The need for examinations will have to be weighed against the risk. A non-ionic contrast media is normally used for patients suffering from allergies and severe diabetes.
As soon as patients are well prepared, examinations involving contrast media may start. Patients will have to change into the hospital gown and be well instructed prior to the examinations. We as radiographers have to prepare the contrast media with the right concentration before the examinations. Contrast media is not encouraged to be pre-prepared too early as it may lose its effectiveness. We must also determine the pathway for contrast media administration, either orally, rectally (enema) or intravenously (injecting through the vein). When contrast media is administered into patients' body, it must be ensured to not leak or stain the hospital gown as contrast media is radiopaque and it creates an artifact on the image produced. This will greatly affect the image quality and a repeat on the examination is needed. Patients' reactions toward contrast media upon administration have to be closely monitored as well. This is so that emergency measure can be taken should there is any anaphylactic reaction. As for patients care, we must always assist patients and ensure their comfortability throughout the whole procedure. Any complaints of discomfort by patients shall not be taken lightly.
Once examinations are over, patients shall be advised to keep themselves hydrated by consuming lots of fluid. This is so that their body will not be dehydrated with the presence of contrast media. It also helps them to eliminate the contrast media from their body through urination and defecation should they consume fluid after examination. Besides that, we are also responsible to arrange next appointment for outpatients or assist inpatients back to their respective wards upon the completion of examinations.
Despite its proven safety, there ought to be complications or risks occurred to certain patients during examinations. These risks and complications are categorized into three groups which are mild, moderate and severe. Mild reactions recorded include nausea, vomiting or both, generalized transient of warmth felt throughout the body (akin to flushing), rashes which may be transient or lasting for few days and runny nose. These reactions are mostly normal and do not require any treatment. These reactions subside once the contrast media effect on patients subsides. For moderate reactions, patients may experience difficulty in breathing (similar to asthma) and hypotension (sudden drop in blood pressure). These reactions are usually transient and very most rarely to be life threatening. Severe reactions towards contrast media are very rare especially with modern contrast media containing iodine. However, an unpredictable reaction (anaphylactic shock) may occur upon administration of contrast media. This may be fatal at times if immediate treatment is not given. Patients with a history of contrast media reactions are at an increased risk of anaphylactic shock. These patients are normally pretreated with corticosteroids to decrease the incident of adverse reactions. Anaphylactic reactions recorded such as itching, bronchospasm, facial and laryngeal edema. For more severe anaphylactic reactions such as bronchospasm and facial or neck edema, albuterol inhaler, subcutaneous or IV epinephrine, plus diphenhydramine may be needed. An airway must be established if respiration is compromised.
Contrast media is a very useful substance which helps in diagnostic of patients' condition in imaging industry. It is widely used in X-Rays, Computed Tomography (CT Scan), Magnetic Resonance Imaging (MRI) and ultrasound. It enhances the contrast in the image by giving a better visualization between soft tissues and bony tissues. Positive contrast media is most likely used in examinations. There are two main types of positive contrast media which is iodine based and barium based. Modern contrast media gives very rare occurrence of adverse effects though it gives minor physiological disturbance to the patients. Patients have to be very well prepared prior to the administration of contrast media to prevent any discomfort and adverse effects. An emergency trolley has to be on standby in the procedure room so that doctors can react to the anaphylactic shock patients experienced immediately. Despite the minor risk poses by contrast media, it is still widely used as it gives more medical benefits to the patients.