Protection of the Examining Physician

Most factors that serve the radiation protection of the patient also diminish the radiation exposure of the radiologist. These include the adequate experience of the examining physician, short fluoroscopy times, strict collimation of the x-ray beam, dose-minimized x-ray equipment, and a strict adherence to the indication list. One very effective protective measure is to keep the greatest possible distance (dose decreases by the square of the distance) from the primary or secondary sources of radiation (the tube and the patient). Another measure is to protect the physician with lead-lined, sometimes movable, walls, lead aprons, gloves, thyroid protectors, and awkward-looking lead-glass goggles or spectacles (Fig. 5.3).

By the way, British radiologists working between 1920 and 1945 showed the same cancer incidence as their nonradiological clinical colleagues and lived longer than the average general practitioner in the United Kingdom at that time.

X-rays Are Everywhere

A standard chest radiograph imparts a radiation dose of about 0.2 mSv; the CT study of the chest exceeds 20mSv. A mammography takes about 2 mSv. One transatlantic flight from cool New York to old, old Europe for that cultural weekend, or vice versa, amounts to 0.1 mSv of cosmic radiation. The healthy life on an Austrian high mountain pasture increases the natural exposure to up to 10 mSv/year.

I Paul Gets Real Serious

I Paul Gets Real Serious

Fig. 5.3 Paul is well equipped for any radiological intervention, wearing a lead skirt that puts the weight on his iliac crests and not on his spine. The lead waistcoat, the thyroid protector, and the trendy lead goggles complete the outfit. In his hand he holds a quartz fiber dosimeter that is worn underneath the lead waistcoat, just like the film dosimeter, during the examination. Behind him you see a movable lead panel. Paul has thrown the clumsy lead gloves that are used in noninterventional fluoroscopy (such as barium enemas) onto the tabletop.

Fig. 5.3 Paul is well equipped for any radiological intervention, wearing a lead skirt that puts the weight on his iliac crests and not on his spine. The lead waistcoat, the thyroid protector, and the trendy lead goggles complete the outfit. In his hand he holds a quartz fiber dosimeter that is worn underneath the lead waistcoat, just like the film dosimeter, during the examination. Behind him you see a movable lead panel. Paul has thrown the clumsy lead gloves that are used in noninterventional fluoroscopy (such as barium enemas) onto the tabletop.

Risks of Ultrasound

Direct relevant risks of ultrasound techniques are not known. However, the results of an ultrasound examination depend strongly on the quality and experience of the examiner and are often difficult to document. The indirect risk to the patient due to nonultrasound procedures that follow false-positive or incorrect ultrasound findings is thus much higher than any direct hazard. There is, nonetheless, a general agreement that multiple ultrasound examinations of the unborn within the mother's womb without clinical indication ("baby-video") should not be performed because of the susceptibility of the unborn to external perils.

Risks of Magnetic Resonance Tomography

The extremely strong magnetic fields can cause malfunctions of mechanical and electronic equipment. Self trials with the inherited Rolex or the American Express card are not really recommended, but variations of the theme are reported on a regular basis. Metal buckets filled with cleaning water and carried into the MRI examination suite by inexperienced cleaning personnel off hours, which then miraculously plunge into the system gantry, emptying themselves and leaving the MRI machine unusable for weeks—it has all been heard of. Figure 5.4 shows a particularly worrisome approach to a 1.5 tesla MRI machine that led to a total loss of the system, fortunately without any damage to human life or health. There is the story of an MRI engineer in a Great Lake City in the United States who was trying to repair something from inside the gantry of a running 1.5 tesla MRI machine propped up on a trailer truck. A fork lifter passed by the trailer; the unsecured forks were torn off the fork lifter and pierced through the trailer wall into the gantry of the machine, killing the engineer. That serves to make the point: MRI is by no means a harmless or risk-free technology. The following perils need to be considered:

• The induction of electrical currents

• The movement of metallic objects

• The noise that is generated by quickly switching gradients

I Fatal Affinity

I Fatal Affinity

Mri Cable Burns
Fig. 5.4 Where raw forces act without reason . . . What you see in the gantry of this MR machine is a 200 kg (31.5 stones or 441 pounds) surgical table.

Induction of currents: Currents are not only induced in the MR receive coil or antenna. This occurs in all conducting structures. Flowing blood is such a conductor. The resulting current boosts the ECG curve at the time of the peak blood flow: the T-wave is raised. In cables, particularly in cable loops (cardiac pacemakers), currents are generated that can lead to overheating and even burns. Loops such as these can also be caused by faulty patient positioning: if the patient's hands or bare calves touch each other, burns can result.

Ear implants, cardiac pacemakers and defibrillators (including residual wires), neurostimulators, and implanted electronic infusion pumps prohibit any MR study.

Firmly anchored osteosynthetic material can disturb the imaging process and heat up. Metallic implants longer than 20 cm should be approached with special care. If the patient feels unwell during the examination, it should be terminated immediately. Paramagnetic materials, which are attracted little by magnetic fields, and ferromagnetic materials, which can be magnetized, can also severely compromise imaging. Tattoos may also hinder imaging and heat up depending on their ingredients. For the same reason, eye shadows (which often contain metal) and jewelry of all sorts (rings, bracelets, piercings, etc.) must be removed (Fig. 5.5).

Movement of metallic objects: The extraordinary danger due to metallic objects outside the body has already been mentioned. But how about metal within the body? One must ensure prior to the examination (e.g. with an orbital radiograph) that retained shrapnel or other metallic for eign bodies are not located in the vicinity of crucial structures such as the eye. The usual prosthetic cardiac valves do not constitute a contraindication for MR imaging. However, as a general rule, patients with loose vascular coils, stents, or filters should not be examined. At least six weeks should go by after implantation before an MR procedure is considered. MRI-induced movement of aneurysm clips on cerebral vessels are really dangerous. Lethal incidents have been reported. The type of clip—which is hopefully documented in the surgical report—and its MR compatibility should be determined with great care. Lists on the MR compatibility of almost all implanted materials are available on the Internet (see the homepage of the Food and Drug Administration, FDA: http://www.fda.gov; or that of the International Society for Magnetic Resonance in Medicine, http://www.ismrm.org).

What Does the FDA Say?

"For a properly operating system, the hazards associated with direct interactions of these fields (static magnetic, pulsed gradient and radio frequency) and the body are negligible. It is the interaction of these fields with medical devices... that create[s] concerns for safety."

Noise generated in the course of gradient switching: The extremely rapid switching of gradients, particularly in modern fast and complex MR sequences, can lead to noise levels beyond 100 dB. Just to remind you: music during an exuberant disco night reaches 140 dB, a jack-hammer about 120 dB. Ear plugs or special protective headphones are thus mandatory for the patient and any other person in the same room (and for your disco visit, obviously ...).

Fig. 5.5 This patient is well prepared for his examination. He brought a pair of pliers along to take his jewelry off. It took him about half an hour.

Further risks to human life and health due to the commonly used MR techniques are not known. Elective MR studies of women in early pregnancy (up to the third month) are nonetheless discouraged because of residual safety concerns. In vital indications in this patient group, however, MR is always preferred to CT because of the lack of definitely harmful ionizing radiation and because MR often has the same or a better diagnostic yield.

The MR room may only be entered after a thorough briefing by and in the company of the MR personnel. Any cables inside the body prohibit MR studies.

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