Health Informatics
Preparing a patient for a diagnostic technology – Head CT Scan

Throughout history, man has striven to explain poor-health and illness. It was originally thought that disease stemmed from being possessed by evil spirits and other supernatural causes. However, these concepts were rejected by the Greek physician Hippocrates around 400 BC in favour of disease having a physical, rational and therefore measurable cause, (Porter, 1994). Yet it was not until 1895 that Wilhelm Conrad Röntgen discovered x-rays and began to revolutionise the assessment process using non-invasive techniques. (Nobel Lectures, 2012). Since then, many types of diagnostic imaging techniques have been discovered and developed which play an integral role in modern medicine. These include Ultrasounds, Magnetic Resonance Imaging, (MRI), Electrocardiograms (ECG) and Electroencephalography, (EEG). This essay will discuss; the rationale of referring a patient for Computerised-Tomography, (CT) scans; the support given throughout the process; evaluation of the benefits and risks of the technique and resulting diagnosis.

A 28 year old male was brought into hospital by emergency ambulance after being involved in a motor-cycle accident. He had sustained multiple fractures and a dislocated shoulder. The paramedics reported that he had complained of severe headache and was aggressive and disorientated at the scene. He improved en-route to hospital. However, his mental state deteriorated on arrival and he had no memory of the accident or the events leading up to it. He had two episodes of vomiting and his left pupil was visibly more dilated than the right. The initial physical examination showed trauma and swelling around the left temporal region of his skull; his Glasgow Coma Scale (GCS) was 12/15 on arrival at the accident and emergency department. An extradural haematoma and temporal fracture were suspected and the patient was referred for an urgent, non-contrast Computerised-Tomography, (CT), scan of the head. This type of diagnostic imaging technique was clinically indicated as the patient presented with a suspected skull fracture, a GCS of less than 13 and more than one episode of vomiting, (NICE, 2007). This is supported by the Scottish Intercollegiate Guidelines Network, (SIGN) guideline (2009). The CT scan in this case was used to confirm the presence of an extradural haematoma. This is when blood accumulates between the skull and the thick membrane covering the brain, the Dura mater, usually as a result of a skull fracture shearing or tearing a blood vessel.

In the case of emergency head CT scans, contrast agent is not indicated as it can decrease sensitivity because the blood vessels become brightly highlighted so very small bleeds can be missed. Non-contrast scans are also relatively cheaper and faster to perform. CT scans are able to identify the margins between soft tissue, bone, air, water, fat and blood. Because of this x-rays of the head are often not required.
A second CT scan was performed at a later time on this patient with the use of an iodine-based contrast agent to evaluate the integrity of blood-brain barrier and check for cerebral aneurisms. MRI scans could also be used at this point but were not appropriate for this patient as he had orthopaedic metal-work in his leg from an operation following a previous accident.

Kidwell and Wintermark (2008) stated that a head MRI is just as effective as a CT scan in detecting acute brain haemorrhage. However, in trauma situations, CT scans are preferable as they are up to four times faster. Immediate damage and tiny areas of bleeding can be detected and the patient can be assessed and referred for treatment rapidly. The promptness in which this can be carried out can significantly reduce the risk is of permanent neurological damage. The speediness is also a benefit as CT scans are less sensitive to the patient’s movements and are ideal when treating patients who are confused, disorientated or claustrophobic. In emergency scenarios it is not always possible to ascertain a patient’s medical history. As magnets are not utilised in this type of scan it can be safely performed on subjects with implantable medical devices, orthopaedic plates and screws and suspected imbedded fragments of metal. It can also be utilised when intra-venous infusions and other in-dwelling apparatus are attached to the patient, as with this subject.

Prior to the procedure, little preparation of the patient is required, which is an additional advantage of this type of scan. Objects about the person such as glasses, jewellery and dentures should be removed as, although they do not pose an actual risk during the procedure, they can obscure the final images and impair correct diagnosis. In this case study, facial and ear piercings were removed from the patient.

The slightly radioactive contrast, or dye, is administered before a CT scan alters the way the x-rays interact with internal structures within the body; distinguishing normal from abnormal. Depending on what the scan is looking for, the contrast is either administered directly into the blood stream, intrathecally, taken orally, rectally, or an injection into specific structures such as joints. In this case it was via a peripheral cannula. Contrasts which work on a temporary basis, are water-based and are therefore absorbed by the body or excreted by the kidneys. Ideally the clinician should be aware of past medical history with particular regard to renal impairment, asthma, emphysema, severe heart disease and if they have had a previous reaction to contrast. This cannot always be ascertained in emergency which is an additional reason why contrast CT scans are not the first choice. It is good practice to explain before the procedure the risk of contrast could leak under the skin and cause skin to break down, but is rare. In this situation it was of greater importance to help the patient remain as calm as possible so to not alarm him further so this risk was not communicated at the time. I did however explain in ordinary language that he may experience a common side-effect of a feeling of warmth that can feel like passing urine. I was able to reassure him that this was normal and not to be concerned. Patients can sometimes experience a metallic taste in the mouth, nausea and vomiting. I monitored the patient for these effects after the scan.

There is a popular misconception that some people with shellfish allergies can have severe reactions as the contrast material is often iodine-based. However, a literature review conducted by Schabelman and Witting (2010) found this not to be the case. They concluded iodine is not an allergen and that the risk of reaction has found to be similar to that with subjects who have asthma and/or dietary allergies. This type of information is important to convey to patients to alleviate psychological stress and worry.

Computed tomography uses radiation to obtain images by sending x-rays through the body in cross-sectional slices or ‘tomes’. The machine’s x-ray emitter is positioned opposite a detector which measures the amount of energy absorbed by the various structures within the head, therefore measuring the densities. Blood, for instance, is hyper-dense and appears very bright, whereas fat and water appear quite dark. The data from the scan is mapped and compared by a computer and on a numerical scale to differentiate between the structures. The pixelated data is modified so it can be viewed visually on a screen. This process of modification is known as windowing.

X-rays are usually measured and referred to in terms of millisievert (mSv), a scientific unit of effective dose radiation, (Radiological Society of North America, 2012). They are waves of energy that can infiltrate the body for diagnostic imaging purposes and are also used therapeutically in cancer treatments. They waves are small enough to enter and alter the DNA structure of replicating cells but are unfortunately indiscriminate between malignant and normal tissue. Therefore, there is a relative risk of developing cancers following CT scans and x-rays. However, it is dependent on the patients overall exposure to radiation. The Radiological Society of North America, (2012), has calculated that a non-contrast head CT scan delivers 2 mSv of effective dose radiation, systemically as opposed to the targeted area. This is equivalent to around eight months of background radiation that we are exposed to from natural sources. This risk level is deemed ‘very low’ which equates the approximate additional risk of fatal cancer for an adult from this examination as approximately 1 in 100,000 to 1 in 10,000. The risk level of a contrast CT scan of the head is higher, but is still only 1 in 10,000 to 1 in 1000.

These statistics can be very helpful when explaining the risks of CT scanning to a patient as the scientific units have little real-life application and are therefore sometimes meaningless so could provoke more anxiety. However, in this case-study there was very little time to fully explain the procedure to the patient due to the severity of his injury. Nevertheless, I was able to accompany him with a registered nurse and describe what was going to happen in terms he could understand due to his altered consciousness level and was able to act as his advocate, (Nursing and Midwifery Council, 2010). Valid consent is required from a patient before embarking on physical investigations, starting treatment or providing personal care, (Department of Health, 2009). Consent was inferred from the patient in question as despite his GCS, it was decided that he did have mental capacity to appreciate that the CT scan was imperative to his treatment plan and give informed consent. I repeatedly described the procedure and explained that he would be alone whilst the scan was taking place but that I would not be far away. It was also conveyed that it would be quite noisy but someone would be able to communicate with him if necessary. Extremely anxious patients can be given a sedative to help them relax prior to their scan.

The investigation is performed by laying the subject on a horizontal moveable table that passes through a doughnut shaped machine. The CT scanner then rotates rapidly around the patient taking pictures in cross-sectional slices, or tomograms, at approximately one image per second. The machine is capable of building up a complete representation of the subject as part of it can be tilted whilst capturing the images. The images are then sent digitally to a specialised computer where they are processed. They can be stored and viewed using Picture Archiving and Communications Systems, (PACS). This system provides the framework to store and view diagnostics images electronically without the need for physical prints or films. Health professionals can access these at the touch of a button and compare them to previously stored records. This has radically speeded up the diagnostic process and has made patient information easier to share, (National Health Service 2012). Images can be copied onto a CD but unlikely printed onto films; these are very rare due to the advantages of digital methods.

The CT scans showed a left-sided, biconvex mass which was consistent with the suspected diagnosis of an acute extradural haematoma; there was also a linear fracture of the temporal bone. The contrast CT scan did not indicate additional aneurisms. No treatment would have likely resulted in death or permanent brain damage.

Non-trauma patients with asymptomatic extradural haematomas may not require invasive surgery as the body can absorb the clot itself, (Offner, Pham and Hawkes, 2006). However, this patient had immediate neurosurgery to remove the haematoma by drilling burr-holes into the skull and then carefully removing it using suction. Further head CT scans were needed to evaluate the size of the clot and to ensure it was fully removed. These were conducted whilst the patient was unconscious and were deemed essential to sustain life. Due to the prompt diagnosis and treatment, the patient made an excellent recovery. He initially experienced mild muscle weakness down one side of the body but with minimal physiotherapy he regained full movement. This is an outstanding example of how an older imaging technique has been integrated with modern technology to give optimum patient care.

Word Count: 1998

References

Department of Health (2009) Reference guide to consent for examination or treatment, second edition 2009. London: HMSO

Kidwell, C. and Wintermark, M. (2008) Imaging of intracranial haemorrhage. The Lancet Neurology [online] 7(3): pp. 256-267. Available at: http://dx.doi.org/10.1016/S0140-6736(08)61345-8 [Accessed 24 February 2012]

National Health Service (2012) Connecting for Health. Picture Archiving and Communications System (PACS) [online]. Available at: http://www.connectingforhealth.nhs.uk/systemsandservices/pacs [Accessed 24 February 2012].

National Institute for Health and Clinical Excellence (2007) Head injury. Triage, assessment, investigation and early management of head injury in infants, children and adults [CG56]. London: National Institute for Health and Clinical Excellence.

Nobel Lectures, Physics 1901-1921 (2012) Wilhelm Conrad Röntgen Biography [online] http://www.nobelprize.org/nobel_prizes/physics/laureates/1901/rontgen-bio.html [Accessed 20 February 2012]

Nursing & Midwifery Council (2010) The NMC Code of Professional Conduct: Standards for Conduct, Performance and Ethics. London: Nursing & Midwifery Council.

Offner, P., Pham, B. and Hawkes, A (2006) Nonoperative management of acute epidural hematomas: a "no-brainer". American Journal of Surgery. 192(6): pp.801-5. [Abstract]

Porter, R. (1994) The Biographical Dictionary of Scientists (Second Edition). New York: Oxford University Press.

Provenzale, J. (2007) CT and MR imaging of acute cranial trauma. Emergency Radiology. 14(1): pp. 1-12

Radiological Society of North America, Inc. (RSNA) (2012) Radiation Exposure in X-Ray and CT Examinations [online]. Available at: http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray#part3 [Accessed 28 February 2012]

Schabelman, E. and Witting, M. (2010) The Relationship of Radiocontrast, Iodine, and Seafood Allergies: A Medical Myth Exposed. Journal of Emergency Medicine. [online] 39(5): pp.701-707. Available at: http://dx.doi.org/10.1016/j.jemermed.2009.10.014 [Accessed 28 February 2012]

Scottish Intercollegiate Guidelines Network (SIGN) (2009) Early management of adult patients with a head injury guideline [110]. Edinburgh: SIGN