## 4 Who Should Perform US  
Worldwide, US is performed by general practitioners, medical specialists and subspecialists, radiologists and in some countries also by non-medical sonographers with formal ultrasound training. Below we discuss both physician-performed and sonographer-performed US. US can be performed by physicians, including general practitioners, medical specialists and subspecialists, as an extended physical examination as part of their practice. In this setting, services of a radiologist or sonographer are not routinely required [20; 21; 51; 52]. This form of US is applied in many European countries including Germany, Italy, Romania and others. Many medical specialities include US in their teaching curriculum, and specialists perform specific US exams relevant to their areas of expertise. Thus, echocardiography is performed mainly by cardiologists, hepatic and endoscopic ultrasound by gastroenterologists, obstetrical US by obstetricians, and endobronchial ultrasound by pneumologists. The radiological delivery of service by physicians and sometimes by sonographers is traditionally offered in English-speaking countries around the world, notably the United States, Canada and Australia. In such scenarios US is performed and reported as a radiological procedure similar to CT or MRI. In this radiological setting, the examination can be performed by physicians or sonographers. The latter are highly specialized imaging technologists with rigorous formal training and regulatory certification in ultrasound who typically work within a radiology department under the supervision of one or more radiologists [20; 51]. Despite their extensive training and high procedural skill, sonographers function as \"delegated agents of the physician and do not practice independently\" [53; 54], according to the Society of Diagnostic Medical Sonography. Thus, although scanning is done by sonographers, images are evaluated and results reported by radiologists [21; 55]. Historically, radiologists reviewed static images selected by the sonographer as being representative of the entire exam, but it is becoming increasingly common for sonographers to capture cinematic sweeps in different planes through the organ(s) and lesion(s) of interest so that the interpreting radiologist can benefit from the wealth of information gained from the real-time study [20; 21; 51; 52]. In the UK, by comparison, sonographers are independent reporting practitioners in the National Health Service (NHS) [20; 51; 52]. In the NHS, most (about 80%) US services are performed and reported independently by sonographers. The few remaining US examinations are performed by radiologists (19%) and other medically trained practitioners (<1%) [20; 21; 51; 52]. The role of US in the UK is controversial, since non-medical sonographers intrinsically have less medical education, general knowledge and independence than medical doctors [20; 21; 51; 52]. The non-medical sonographer is unlikely to achieve a truly independent status independent of healthcare costs [20; 51; 52]. In other regions of the world, the sonographer is a non-radiologist physician specialized in ultrasound, as is in parts of China [56]. Ideally, to maximize patient care and safety, US practice should be undertaken by educated, qualified and healthcare system regulated personnel. Professional US care should include point-of-care US and specialized primary, secondary and tertiary care level defined qualifications achieved by specialists and subspecialists including radiology. Statement 3: Ultrasound should be performed by physicians in their respective speciality and/or by highly trained, certified medical sonographers. Statement 4: Ultrasound is traditionally part of radiology in Anglo-American countries. Statement 6: The role of non-medical sonographers is controversial. Research is needed to compare the quality and safety of US performed by non-medical sonographers compared to certified medical sonographers and physician specialists.