General notes

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Last modified 01/04/2015

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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.

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:

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:

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:

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:

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.

Patient preparation

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:

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