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Ultrasound (US) uses high-frequency sound waves to image soft tissues of the body. The frequency of the sound is less than that used in other clinical areas (e.g. physiotherapy), so it is not associated with local heating effects and is completely safe. US is relatively inexpensive, readily available in all imaging practices and in some clinical consulting rooms. Unlike other imaging studies, US is a dynamic study in that patient movement can be assessed at the time of the examination and can be correlated with the clinical presenting symptoms.
Sound waves are reflected back to the transducer on the skin at different velocities determined by the type of soft tissue they encounter. Patients with excessive body fat do not do well with US, as the sound waves are reflected by the subcutaneous fat before reaching the organ of concern. Sound does not pass through bone or dense soft tissue (e.g. scar, calcification), so structures beneath these regions cannot be seen.
US is the investigation of choice when the organ of clinical concern is assessable for sound wave interrogation. The closer and more localized the area of clinical concern is to the US transducer, the better the results. This includes assessment for diagnostic purposes or using US guidance for interventional procedures, such as therapeutic injections or drainages.
US can be used in the clinical consulting room for identification of veins for vascular access. Point of care US (POCUS) is becoming more available to the clinician as machines become smaller and cheaper. This is useful to supplement clinical assessment and diagnosis at the bedside, but is not recommended for primary diagnostic purposes.
If you are referring a patient for an ultrasound examination, it would be valuable to include:
There are no absolute contraindications for an ultrasound examination.
In obese patients, the thick subcutaneous fat layer limits sound wave penetration. Where deep structures require interrogation; for example, the pancreas, then alternative methods of imaging, such as computed tomography, should be considered.
Where there is skin sepsis or lack of access allowing skin/transducer contact, then US may be difficult or inappropriate. Practitioners should contact their local imaging provider to discuss possible alternative imaging tests.
Your patient should not experience any adverse effects from ultrasound examination.
Post-procedural information and care will only be required if interventional procedures have been carried out using US guidance.
For simple soft tissue and joint injections, the patient may experience pain at the injection site or in the joint for approximately 24–48 hours. Should the pain continue, or the patient develops systemic symptoms suggestive of infection, then the procedural radiologist should be contacted to discuss further management. If this occurs outside working hours, the patient should be referred to the local emergency department for assessment.
For other interventional procedures: the US department should contact the referring clinician regarding post-procedural care and follow up.
Ultrasound is generally considered a primary diagnostic modality, because it is cheap, easily accessible and very accurate in many settings. Be aware that patients with specific indications may be better referred to computed tomography and magnetic resonance imaging directly.
If you have any doubt about the appropriateness of a diagnostic test, please contact the local diagnostic imaging department, where the consultant radiologist will generally be happy to discuss the best alternative with you.
Page last modified on 11/9/2018.
RANZCR® is not aware that any person intends to act or rely upon the opinions, advices or information contained in this publication or of the manner in which it might be possible to do so. It issues no invitation to any person to act or rely upon such opinions, advices or information or any of them and it accepts no responsibility for any of them.
RANZCR® intends by this statement to exclude liability for any such opinions, advices or information. The content of this publication is not intended as a substitute for medical advice. It is designed to support, not replace, the relationship that exists between a patient and his/her doctor. Some of the tests and procedures included in this publication may not be available at all radiology providers.
RANZCR® recommends that any specific questions regarding any procedure be discussed with a person's family doctor or medical specialist. Whilst every effort is made to ensure the accuracy of the information contained in this publication, RANZCR®, its Board, officers and employees assume no responsibility for its content, use, or interpretation. Each person should rely on their own inquires before making decisions that touch their own interests.