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X-Ray Imaging: Inconceivable Without Contrast Enhancing Agents
The X-ray technique is a frequently used imaging procedure in medicine today second only to ultrasound. However, while high energy electromagnetic waves with short wavelengths are marvellous at visualizing dense structures such as bones, recognition of the soft tissue organs is much less clear: on an X-ray image they can hardly be distinguished from the surrounding area. It was this problem that has driven research into the development of contrast media.
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Why Are Contrast Media Necessary?
Any structures of a similar density will be indistinguishable on an X-ray. Contrast media are therefore necessary to create an artificial contrast between the organ to be diagnosed and the surrounding tissue. X-ray contrast media are based on a non-toxic solution that contains a significant proportion of elements with a high atomic number - for example iodine. When X-rays hit iodine in a contrast medium, the area appears white on the X-ray film and therefore highlights the detail of the organ it has permeated.
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How Are Contrast Media Used?
There are many radiological examinations in practice today that involve the use of contrast media. A few of the most common are described here.
Angiography
The radiological procedure which investigates the condition of blood vessels is called angiography. A distinction between arteriography and venography is usually made, depending on whether arteries or veins are being examined.
Digital subtraction angiography (DSA)
In digital subtraction angiography, the image is produced by subtracting radiographs without contrast media from radiographs taken after contrast media have been administered. The result of this subtraction process is the visualization of vessels filled with contrast media free from overlying structures. These procedures involve the use of specialized electronic equipment, including computing and radiographic hardware, to produce rapid sequential images.
Intravenous urography (intravenous pyelography, IVU, IVP)
Intravenous urography remains the basic radiological examination of the urinary tract and its main purpose is to assess the shape, structure and the function of kidneys. When injected intravenously, most contrast media are rapidly excreted by the kidney, so a series of radiographs taken after the injection will highlight the urinary tract (kidney, ureter, bladder).
Computed tomography (CT)
Since 1973, computed tomography (CT) has grown to become one of the most important radiological examinations procedures in the industrialized world. CT delineates organs in a new way by producing electronic digitized images of cross-sections of a patient. 60-80% of all CT examinations involve the use of a contrast medium.
In recent years, an advanced CT technique called spiral or helical CT, has become increasingly important. Spiral CT achieves the excellent resolution of normal CT but with shorter examination times. In addition, spiral CT provides a powerful new diagnostic tool by providing spatial 3D resolutions and allowing physicians to reconstruct 3D images of the investigated anatomy.
Interventional techniques
A lot of radiologists are now specializing in therapeutic procedures that have been developed from radiological techniques. These procedures include the widening of narrowed arteries (angioplasty, percutaneous transluminal angioplasty, PTA) as well as the deliberate closure of arteries supplying abnormal areas such as tumors, aneurysms and vascular malformations.
Contrast media are often required to monitor the course and success of these treatment procedures.
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Safety of Contrast Media
Adverse reactions to modern X-ray contrast media are very rare. However, as with every pharmaceutical product, they can occur. Any adverse reactions are usually mild to moderate and of short duration and resolve themselves without medical treatment. Among the most frequently observed reactions to contrast media are nausea, vomiting and allergy-like symptoms. Nevertheless, serious adverse reactions have been observed in some cases. To minimize the risk of adverse reactions, healthcare professionals are careful to ask questions about individual patient's medical history - questions such as:
Are you taking any medication (prescribed or over the counter)?
Have you ever had a reaction to X-ray contrast media or any other substance containing iodine?
Do you have any other allergies such as hay fever, medications etc.?
Do you have any pre-existing condition like diabetes, renal or liver disease etc.?
Are you pregnant?
Are you breast feeding?
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Special Preparation for an X-ray
Before an X-ray examination, it may become necessary to remove the following items:
Dentures
Jewelry
Any material that may interfere with X-ray
Should you have any further questions please do not hesitate to consult your physician.
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