In a health care environment there are many different imaging modalities available which are used to aid diagnosis, or plan patient management and treatment. Modalities within Radiology include X-Ray, Computed Tomography (CT), Ultrasound, Nuclear Medicine, Fluoroscopy and Magnetic Resonance Imaging (MRI). Each modality plays a specific role in answering a clinical question, and each has their own specific advantages and disadvantages. MRI uses a large, powerful magnet and Radio Frequency (RF) pulses to produce cross sectional images of many anatomical area of the body. In recent years MRI has been increasingly used, and its applications and capabilities have advanced to mean that it is used widely as a diagnostic tool in many clinical situations. In fact the number of MRI examinations carried out in England for the NHS has more than doubled from 2003 to 2009 (DOH, 2010).
Imaging techniques have advanced rapidly in almost all fields of medicine. In many cases such as neurology, these advances have meant an increase in the quality of anatomical depiction but also the ability to provide more functional and physiological information such as diffusion and perfusion techniques (Evans, 2006). MR has many advantages at brain imaging compared to other modalities. MR is good at looking at anatomy and pathology using high resolution, multi-planar imaging. The main advantage is that no radiation is used during MRI and it is also a non-invasive examination. Advances have led to high resolution and excellent soft tissue contrast imaging which is exceptionally good for examining brain anatomy, particularly grey and white matter differentiation, posterior fossa and examining blood, including its flow (Armstrong et al 2004). In fact, a big advantage of MRI compared to CT scanning as stated by Munir (see article 2) is that it 'eliminates exposure to ionising radiation and there is no risk of contrast nephropathy...and MRA is associated with reduced patient morbidity and decreased risk of complications associated with conventional contrast angiography'. Other interesting applications which have made an impact in modern MRI departments include Diffusion Weighted Imaging (DWI) and functional MRI (fMRI). DWI looks at water in different areas of the brain and their local characteristics (Department of Health, 2008). (nicked from head case study - need ref pg updated). This sequence has proved a vital tool particularly in stroke and TIA imaging because areas of ischemia are readily visible (Latchaw, et al., 2009 -Journal -3). fMRI uses are still developing however, its applications are growing because it can map areas of the brain that are activated when patients are asked to complete a given task (Koretsky- Journal 4).
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On the other hand there are also disadvantages of MRI compared to other modalities when imaging the brain. For example in trauma cases, CT scanning is often used because it is readily accessible in most hospitals, scan times are short, and there are no contraindications regarding surgery and equipment (Bruce Journal 1). In addition, imaging of haemorrhage with MRI can be complex to interpret because the age, size and state of haemoglobin must be taken into account (Koretsky -Journal 4). Therefore, CT is often the used as first line imaging in cases of acute haemorrhage (Longmore 2004). Furthermore, MRI is inferior when imaging bony structures because cortical bone contains fewer hydrogen protons and therefore returns little signal (Jackson and Thomas, 2005). Another disadvantage of MRI is that it is often prone to artefacts which can degrade image quality, such as, metal artefact from dental fillings and motion artefact due to long scan times (McRobbie, et al., 2003) - get ref from case study).
Other modalities used for imaging the brain include, Digital subtraction angiography (DSA), ultrasound and nuclear medicine. DSA remains the gold standard form some cerebrovasular diseases, such as arteriovenous malformations, however it is an invasive test and can cause serious complications (Latchaw et al 2009 Journal 3). Ultrasound is widely used for scanning the neonatal brain as it does not use radiation, and is particularly good at diagnosing cerebral haemorrhage, developmental malformations and hydrocephalus (Jackson and Thomas 2005). Ultrasound in neonates is possible due to the acoustic window provided by the fontanelle in the skull, however this closes with age and therefore, the use of ultrasound in children is limited to the first two years (Jackson and Thomas 2005). Nuclear medicine, including SPECT and PET, has a role in diagnosis and staging of patients with dementia and other neurological diseases (2005).
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MRI - mets, tumours
CT - Trauma,
Nucmed - mets - whole spine, look for secondary? Get hot spots on specific areas which can lead to MRI scanning a specific area e.g. T-spine.
X-ray - trauma, fractures, spine abnormalities (could be congenital - developmental)
MRI is the 'gold standard' for spinal cord imaging because it is highly sensitive and specific to pathology (Berquist 1996). This is due to good tissue and spatial resolution.
Berquist, T., 1996. MRI of the Musculoskeletal system. 3rd ed. Pennsylvania: Lippincott-Raven Publishers
MRI used to look for meniscal tears in knees
MRI also has many advantages when it comes to imaging the muscular-skeletal. MRI is used to detect small tears for example meniscal tears within the knee and no contrast is needed for this. The synovial fluid within the joint capsule acts as a natural contrast agent enabling small tears to be visualised cleary.
Alsoa rotator cuff tear in the shoulder show up as a nice bright signal which confirms there is a tear within this area of interest. When scanning the shoulder for re-current dislocation an arthrogram study is useful. This is when…. (quote)
Disadvantage of this is its invasive, time consuming, radiation to patient, consultant availability - operator dependant, patient tolerance for procedure - can be uncomfortable, patient is advised not to do any manual work over the next 24hrs after procedure.
CT/Nucmed used for looking at bone
CT shoulder/knee - assessing tibial platto fractures (knee). Fractures, boney lesions. CT can reconstruct images to see boney detail and see where fragments have gone.
U/S used for looking at lumps and bumps
Ultrasound is suitable for assessing subcutaneous abnormalities as it can produce high quality images with high spatial resolution. The same can be said for MRI imaging although Ultrasound can be the preferred modality due to this. (Bearcroft, 2007)
The main disadvantage of using ultrasound in any examination is that the result is operator dependant. . (Bearcroft, 2007)
X-Ray used for looking at bones for breaks and boney tumours.
Plain X-rays are still used on a daily basis but other modalities seem to be used more to answer more clinical specific questions. They are still used in order to confirm mainly bone abnormalities. . (Bearcroft, 2007)
ABDO/PELVIS- In this case, the main disadvantage of MRI, other than safety issues, is that images of the abdomen and pelvis are often degraded by motion artefact caused by respiration, bowel peristalsis and foetal movement (Campos, et al., 1995).
Magnetic resonance imaging is being used increasingly as a diagnostic tool for pregnant patients to assess a wide range of both maternal and foetal conditions. Initially, the applications of MRI in pregnancy were limited due to concerns about foetal safety and also technical problems experienced such as, image degradation from motion (Shellock, 2001). However, technological advances, such as high field scanners and rapid sequences, have meant that MRI has several useful applications for pregnant patients. The imaging technique of choice is currently sonography, however, in some cases sonography is not sufficient to make a diagnosis and MRI may be considered (Abbott, el al., 2004). MRI is being used increasingly in pregnancy because it does not use ionising radiation and is therefore, a good alternative when ultrasound proves inadequate. MRI is suitable for this imaging because it can provide a systematic cross sectional view of the anatomy (Abbott, el al., 2004). In addition, it can provide excellent tissue differentiation and resolution and can also be used to assess function, for example MR urography to evaluate the renal system.
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TIA/CVA - Mention TIA clinic is a new clinic, link to U/S carotids as most TIA cases originate from the neck, get narrowing of carotid arteries.. MRI will show areas where blood supply will be reduced (head scans)