General notes

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Chapter 1 General notes

Radiology

The procedures are laid out under a number of sub-headings, which follow a standard sequence. The general order is outlined below, together with certain points that have been omitted from the discussion of each procedure in order to avoid repetition. Minor deviations from this sequence will be found in the text where this is felt to be more appropriate.

Methods

A description of the technique for each procedure.

Indications

Appropriate clinical reasons for using each procedure.

Contraindications

All radiological procedures carry a risk. The risk incurred by undertaking the procedure must be balanced against the benefit to the patient as deduced from the information obtained. Contraindications may be relative (the majority) or absolute. Factors that increase the risk to the patient can be categorized under three headings: due to radiation; due to the contrast medium; due to the technique.

Risk due to radiation

Radiation effects on humans may be:

1. hereditary, i.e. revealed in the offspring of the exposed individual, or
2. somatic injuries, which fall into two groups: stochastic and deterministic. The latter, e.g. skin erythema and cataracts, occur when a critical threshold has been reached and are rarely relevant to diagnostic radiology. Stochastic effects, such as malignancy, are ‘all or none’. The cancer produced by a small dose is the same as the cancer produced by a large dose, but the frequency of its appearance is less with the smaller dose. The current consensus held by national and international radiological protection organizations is that, for comparatively low doses, the risk of both radiation-induced cancer and hereditary disease is assumed to increase linearly with increasing radiation dose, with no threshold (the so-called linear no threshold model).1 It is impossible to totally avoid staff and patient exposure to radiation. The adverse effects of radiation, therefore, cannot be completely eliminated, but must be minimized. There is an excess of cancers following diagnostic levels of irradiation to the fetus2 and the female breast,3 and trends of increased rates of cancer are seen in workers in the nuclear power industry exposed to low doses.4 In the United Kingdom about 0.6% of the overall cumulative risk of cancer by the age of 75 years could be attributable to diagnostic X-rays. This percentage is equivalent to about 700 new cases of cancer per year.5

There are legal regulations which guide the use of diagnostic radiation (see Appendix I). These are the basic principles:

1. Justification that a proposed examination is of net benefit to the patient.
2. ALARP – doses should be kept As Low As Reasonably Practicable; economic and social factors being taken into account.6

Justification is particularly important when considering the irradiation of women of reproductive age, because of the risks to the developing fetus. The mammalian embryo and fetus are highly radiosensitive. The potential effects of in-utero radiation exposure on a developing fetus include prenatal death, intrauterine growth restriction, small head size, mental retardation, organ malformation and childhood cancer. The risk of each effect depends on the gestational age at the time of the exposure and the absorbed radiation dose.2 Most diagnostic radiation procedures will lead to a fetal absorbed dose of less than 1 mGy for imaging beyond the maternal abdomen/pelvis and less than 10 mGy for direct abdominal/pelvic or nuclear medicine imaging.7 There are important exceptions which result in higher doses. Computed tomography (CT) scanning of the maternal pelvis may result in fetal doses below the level thought to induce neurologic detriment to the fetus, but, theoretically, may double the fetal risk for developing a childhood cancer.8

Almost always, if a diagnostic radiology examination is medically indicated, the risk to the mother of not doing the procedure is greater than the risk of potential harm to the fetus.9 However, whenever possible, alternative investigation techniques not involving ionizing radiation should be considered before a decision is taken to use ionizing radiation in a female of reproductive age. It is extremely important to have a robust process in place that prevents inappropriate or unnecessary ionizing radiation exposure to the fetus. Previous guidelines recommended that all non-emergency examinations that would involve irradiation of the lower abdomen or pelvis in women of child-bearing age be restricted to the first 10 days (10-day rule) or 28 days (28-day rule) following the onset of a menstrual period.10 This led to some potential practical difficulties, e.g. for women who denied recent sexual intercourse, for those with an irregular menstrual cycle or for those who had been taking the oral contraceptive pill. There are also concerns:

• about the safety of irradiation of the unfertilized ovum during the first part of the menstrual cycle, which may be as hazardous as irradiation of the conceptus
• that, although it had been thought that a damaging radiation dose to the fetus in the first few weeks of pregnancy would result in miscarriage, evidence exists that some carcinogenic mutations are compatible with continuing development of the fetus10
• that the most sensitive fetal gestational age might be the 4th to 8th week after conception when organogenesis takes place. Therefore, irradiation after conception but before the next expected menstrual cycle may be less damaging to organogenesis.

Joint guidance from the National Radiological Protection Board, the College of Radiographers and the Royal College of Radiologists recommends the following:11

When a female of reproductive age presents for an examination in which the primary beam irradiates the pelvic area, or for a procedure involving radioactive isotopes, she should be asked whether she is or might be pregnant. If the patient cannot exclude the possibility of pregnancy, she should be asked if her menstrual period is overdue. Her answer should be recorded and, depending on the answer, the patient assigned to one of the following four groups:

1. No possibility of pregnancy – proceed with the examination.
2. Patient definitely, or probably, pregnant – review the justification for the proposed examination and decide whether to defer until after delivery, bearing in mind that delaying an essential procedure until later in pregnancy may present a greater risk to the fetus.
3. Low-dose examination, pregnancy cannot be excluded – proceed with the examination provided that the period is not overdue. If the period is overdue, follow the advice in the section above.
4. High-dose examination, pregnancy cannot be excluded – either apply the 10-day rule or re-book patients who attend for such examinations and are identified to be in the second half of their menstrual cycle, of child-bearing age and in whom pregnancy cannot be excluded.

If the examination is necessary, a technique that minimizes the number of views and the absorbed dose per examination should be utilized. However, the quality of the examination should not be reduced to the level where its diagnostic value is impaired. The risk to the patient of an incorrect diagnosis may be greater than the risk of irradiating the fetus. Radiography of areas that are remote from the pelvis and abdomen may be safely performed at any time during pregnancy with good collimation and lead protection.

Risk due to the contrast medium

The risks associated with administration of iodinated contrast media and magnetic resonance imaging (MRI) contrast are discussed in detail in Chapter 2 and guidelines are given for prophylaxis of adverse reactions to intravascular contrast.

Contraindications to other contrast media, e.g. barium, water-soluble contrast media for the gastrointestinal tract and biliary contrast media, are given in the relevant sections.

Risks due to the technique

Skin sepsis can occur at the needle puncture site.

Specific contraindications to individual techniques are discussed with each procedure.

Contrast medium

Volumes given are for a 70 kg man.

Equipment

For many procedures this will also include a trolley with a sterile upper shelf and a non-sterile lower shelf. Emergency drugs and resuscitation equipment should be readily available (see Chapter 17).

See Chapter 9 for introductory notes on angiography catheters.

If only a simple radiography table and overcouch tube are required, then this information has been omitted from the text.

Patient preparation

1. Will admission to hospital be necessary?
2. If the patient is a woman of child-bearing age, the examination should be performed at a time when the risks to a possible fetus are minimal (see above). Any female presenting for radiography or a nuclear medicine examination at a time when her period is known to be overdue should be considered to be pregnant unless there is information indicating the absence of pregnancy. If her cycle is so irregular that it is difficult to know whether a period has been missed and it is not practicable to defer the examination until menstruation occurs, then a pregnancy test or pelvic ultrasound (US) examination may help to determine whether she is pregnant. The ‘10-day rule’ should still apply for hysterosalpingography, so that the risks of mechanical trauma to an early pregnancy are reduced.
3. Except in emergencies, in circumstances when consent cannot be obtained, patient consent to treatment is a legal requirement for medical care.12 Consent should be obtained in a suitable environment and only after appropriate and relevant information has been given to the patient.13 Patient consent may be:

a implied consent – for a very low-risk procedure, the patient’s actions at the time of the examination will indicate whether they are content for the procedure to be performed
b express consent – for a procedure of intermediate risk, such as barium enema, express consent should be given by the patient, either verbally or in writing
c written consent – must be obtained for any procedure that involves significant risk and/or side-effects.

The radiologist must assess a child’s capacity to decide whether to give consent for or refuse an investigation. At age 16 years a young person can be treated as an adult and can be presumed to have the capacity to understand the nature, purpose and possible consequences of the proposed investigation, as well as the consequences of non-investigation. Following case law in the United Kingdom (Gillick v West Norfolk and Wisbech Area Health Authority) and the introduction of The Children Act 1989, in which the capacity of children to consent has been linked with the concept of individual ability to understand the implications of medical treatment, there has come into existence a standard known as ‘Gillick competence’. Under the age of 16 years children may have the capacity to consent depending on their maturity and ability to understand what is involved. When a competent child refuses treatment, a person with parental responsibility or the court may authorize investigations or treatment which is in the child’s best interests. In Scotland the situation is different: parents cannot authorize procedures a competent child has refused. Legal advice may be helpful in dealing with these cases.14

4. If an interventional procedure carries a risk of causing bleeding then the patient’s blood clotting should be measured before proceeding. If a bleeding disorder is discovered, or if the patient is being treated with anticoagulant therapy, the appropriate steps should be taken to normalize clotting before performing the procedure.
5. Cleansing bowel preparation may be used prior to investigation of the gastrointestinal tract or when considerable faecal loading obscures other intra-abdominal organs. For other radiological investigations of abdominal organs, bowel preparation is not always necessary, and when given may result in excessive bowel gas. Bowel gas may be reduced if the patient is kept ambulant prior to the examination and those who routinely take laxatives should continue to do so.
6. Previous films and notes should be obtained.
7. Premedication will be necessary for painful procedures or where the patient is unlikely to cooperate for any other reason. Suggested premedication for adults and children is described in Chapter 18.

Preliminary film

The purpose of these films is:

1. to make any final adjustments in exposure factors, centering, collimation and patient position, for which purpose the film should always be taken using the same equipment as will be used for the remainder of the procedure
2. to exclude prohibitive factors such as residual barium from a previous examination or excessive faecal loading
3. to demonstrate, identify and localize opacities which may be obscured by contrast medium
4. to elicit radiological physical signs.

Every radiographic view taken should have on it the patient’s name, registration number, date and a side marker. The examination can only proceed if satisfactory preliminary films have been obtained.

Technique

1. For aseptic technique the skin is cleaned with chlorhexidine 0.5% in 70% industrial spirit or its equivalent.
2. The local anaesthetic used is lidocaine 1% without adrenaline (epinephrine).
3. Gonad protection is used whenever possible, unless it obscures the region of interest.

Films

When films are taken during the procedure rather than at the end of it, they have, for convenience, been described under ‘Technique’.

Additional techniques or modifications of technique

Aftercare

May be considered as:

1. instructions to the patient
2. instructions to the ward.

Complications

Complications may be considered under the following three headings:

Due to the anaesthetic

1. General anaesthesia
2. Local anaesthesia:

a allergic – unusual
b toxic.

Anaesthetic lozenges contribute to the total dose. Symptoms are of paraesthesia and muscle twitching which may progress to convulsions, cardiac arrhythmias, respiratory depression and death due to cardiac arrest. Treatment is symptomatic and includes adequate oxygenation.

Due to the contrast medium

Intravascular contrast media (see Chapter 2)
Barium (see Chapter 3).

Due to the technique

Specific details are given with the individual procedures and may be conveniently classified as:

1. local
2. distant or generalized.

References

1 Wall B.F., Kendall G.M., Edwards A.A., et al. What are the risks from medical X-rays and other low dose radiation? Br. J. Radiol.. 2006;79(940):285-294.

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