SPORTS MEDICINE RADIOLOGY

computed tomography (CT), radioisotope bone scanning (also called bone scintigraphy), single photon emission tomography (SPECT) and magnetic resonance imaging (MRI). Some imaging modalities employ x-rays and radiation emitted from radioactive compounds. This radiation is known collectively as ionising radiation and carries with it some degree of cancer risk. As a result, there are well-defined regulations and laws relating to the use of ionising radiation in the UK, chief among which are the the Ionising Radiation Medical Exposure Regulations (IRMER) (6,8). Here we describe which modalities use ionising radiation and which do not.

Imaging modalities using ionising radiation Plain radiography Plain radiographs are the most common method of imaging. It combines good bony detail with a low radiation dose, and should be the first imaging modality used when bone pathology is suspected. It readily identifies fractures and dislocations, provides information on bone healing and reveals calcification in soft tissues and masses in bones. Bypassing this modality can result in clinical errors (1–3).

Computed tomography (CT) Computed tomography also uses x-rays. A rotating x-ray tube images cross-sections of the tissues, each one about 1–3 mm thick. The tube can be manipulated in order to obtain views in multiple planes – called multiplanar reformats (MPR) – or three-dimensional images. CT can provide detailed high-resolution images of the bony anatomy, but it has low resolution for soft tissues. It is sensitive to fractures of bones and dislocations of joints and used extensively in the spine, wrist, ankle and foot as well as in polytrauma patients (2,3). Its main shortcoming is the high radiation doses required (see Table 1), so it should be employed only when necessary.

Radioisotope bone scanning (bone scintigraphy) and SPECT Bone scintigraphy uses a radioactive substance called technetium-99m for imaging. It is bound to methylene diphosphonate (MDP) to form Tc-99m-MDP, which has an affinity for areas of high bone turnover. The compound undergoes radioactive decay and is imaged with a gamma camera – a radiation detection device. Bone scintigraphy is commonly used to assess focal bone lesions. Bone lesions that are undergoing increased bone turnover are represented as areas of increased uptake and are called “hot spots”. Conversely, lesions with a low bone turnover are called “cold spots”. Fractures, stress reactions, arthritis and inflammatory conditions all show up as hot spots (1,3,9). The main limitation of bone scintigraphy is its poor resolution; to overcome this problem a technique has been devised that combines a gamma camera with a CT machine. This is called single photon emission tomography, or SPECT. It is increasingly used to characterise “hot” lesions because the bony detail from SPECT characterises them more accurately (1,9,10).

Imaging modalities not using radiation Ultrasound The use of ultrasound in imaging is very similar to its use in physiotherapy. Frequencies between 5 mHz and 20 mHz are used. For musculoskeletal ultrasound, a high-frequency

www.sportEX.net 9 BOX 2: MODALITIES OF IMAGING

n Radiography n CT n Radioisotope bone scanning n SPECT Without ionising radiation n Ultrasound n MRI

probe with frequencies of 10–17 mHz is used to give fine high-resolution images of superficial structures. The main reason for using ultrasound is to enable focused imaging of musculoskeletal structures. It is ideal for scanning soft tissues including the muscles, ligaments and tendons and it is commonly used to scan most of the major joints such as the shoulder and knee. An added advantage of ultrasound is that it can perform dynamic examinations of the joints and assess vascularity (2,3,11). Guided interventions such as subacromial bursa injections or tendon interventions are performed with a high level of precision because the procedure can be visualised in real time. Delivery of medication is also more focused. There are no known adverse effects of ultrasound scanning in adults. Its main disadvantage is its dependence on an operator (1,9,12).

Magnetic resonance imaging (MRI) Magnetic resonance imaging is an established technique for the investigation of musculoskeletal problems. It provides panoramic and multiplanar images of bony and soft tissue structures; the hydrogen content is detected by magnetic fields and radiowaves. All the major joints of the body can be visualised by MRI, and it generates detailed information on the bone marrow, muscles, tendons and ligaments. It

Figure 1: Typical ultrasound appearance of tendonopathy with increased thickness of the proximal patellar tendon associated with darkening of the tissue that indicates increased fluid content.

Figure 2: Ultrasound image of vascular flow with power Doppler showing marked neovascularity within the abnormal tendon.