Trainee radiologists will have ultrasound involvement as a core requisite in the curriculum and are instructed by the radiology trainers, by definition competent in ultrasound techniques and diagnosis. Any clinician, both radiologist and non-radiologist desiring to use ultrasound in their practice, should have the opportunity to be educated by experts. In other clinical skills, such as endoscopy and surgery, medical specialties have defined which training and tasks should be completed to fulfil different levels of competencies. This could also be applied to ultrasound (as is already applied in some countries, when medical subspecialties use ultrasound) with a basic technical education followed by different levels of skills within different anatomical areas. Education and training should be delivered by experts in the ultrasound field—in radiology, this is normally provided by trained radiologists and sometimes by trained ultrasound technicians or sonographers. Invariably radiology trainees are examined in competency prior to qualification.

The practice and the position of ultrasound in various healthcare systems across the world are variable, with the involvement of the radiology department based on the practice of local physicians, surgeons, and primary care doctors. The remit of training and dissemination of ultrasound knowledge may also be quite variable in radiology departments, essentially dependent on the local hospital requirements and the position of ultrasound services in the national healthcare systems. A snapshot, based on the personal experience of the authors, of the remit of ultrasound sections in hospitals across Europe, China, and the USA gives insight into challenges facing the practice of ultrasound within radiology.

Guidelines for medical ultrasound examinations in Germany are primarily provided in the regulations for residency training and ultrasound agreements for the different specialties. In Germany, organ-related ultrasound examinations are performed by radiologists as well as clinicians from the respective specialties under the guidance of the German Society for Ultrasound in Medicine (Deutsche Gesellschaft für Ultraschall in der Medizin, DEGUM). All radiologists in Germany should receive training in ultrasound, lasting between 3 and 6 months, and require certification confirmation from the department head on completion, in order to practice. Radiologists and other physicians performing ultrasound examinations have to keep pace with ongoing technical developments and ensure dedicated and time-consuming training of junior physicians. Provision of staff-intensive on-call services for ultrasound examinations may pose a challenge, especially for small departments. As ultrasound equipment requires regular maintenance and is costly to replace, some departments work with outdated equipment. Reimbursement for ultrasound examinations performed by medical practitioners has been lowered, and many hospitals have a large number of ultrasound machines without making full use of them, which has led to a waste of resources in hospitals. Nevertheless, many specialties insist on continuing to run their own ultrasound sections in an attempt to defend their ‘turf’, also in order not to lose their authorisation to provide ultrasound residency training. A possible strategic way out of this situation could be interdisciplinary cooperation in an ultrasound centre. Model ultrasound centres exist in Munich, Rostock, Regensburg, and Berlin [24]. As with other cross-sectional imaging modalities, such ultrasound centres operate under the roof of radiology. Ultrasound is part of the radiological specialist training in Germany; in the night services, the trainee radiologists often perform the ultrasound examination and offers a comprehensive 24-h service.

Radiology training course includes attendance in the ultrasound section in the first 3 years of training in radiology, with an expectation of 6–8 months in total. Second- and third-year residents personally carry out US examinations under the supervision of an expert tutor. Ultrasound activity is also carried out during the attendance in the interventional radiology sections. Presently, in Italy, ultrasound is performed exclusively by medical practitioners, without any involvement by non-medically qualified practitioners (sonographers). No uniform regulation or organisation for ultrasound exists in the National Health Care System, which is sub-organised into regions with some local autonomy. Radiologists regularly perform ultrasound as part of their daily work practice, and residents are taught by experts, with the expectation of using these skills in their subsequent practice. In other specialties, non-radiologists perform ultrasound, for instance in the emergency department, and some specialties also perform ultrasound both for outpatient and inpatients, as well as in private practice, still within the National Health Care System. The necessity for standardisation of ultrasound practice obliged two organisations, the Italian Society of Medical and Interventional Radiology (SIRM) and the Italian Society of Ultrasound in Medicine and Biology (SIUMB), to establish a task force group, which produced a document called ‘Sonographic Medical Act’ [25], in which the necessary practice, training, and skills for ultrasound practitioners were defined in detail. The two societies have the aim of regulating sonographic examinations, so that these examinations are performed only to complete a clinical assessment and to answer only specific clinical questions, as defined by the Sonography-Assisted Medical Examination (SAME) [26]. However, further mandatory regional and governmental regulations are needed to establish these regulations. Therefore, with strict regulations in place to ensure medical practitioners perform ultrasound, radiology departments are at the forefront of the practice of the modality, with comprehensive training in position.

In Turkey, radiologists play a pivotal role in the ultrasound service. Obstetrics, gynaecology, and cardiology departments practice ultrasound within their own sphere, documenting structured reports based on the diagnostic findings. However, other medical and surgical specialities completely rely on radiology departments for nearly all ultrasound examinations. Although some ultrasound is performed by non-radiologists, there is no appropriate clinical report or appropriate image recording by these practitioners. In many academic state hospitals and private practice, radiology is still the only specialty to conduct a comprehensive ultrasound examination with a formal standard report, documenting the identified pathology [5, 27]. Ultrasound-practising gastroenterologists, rheumatologists, and emergency physicians are increasingly willing to take the responsibility for documenting findings in a formal written report. However, only a few enthusiastic physicians, who are well trained, are willing to undertake systemic ultrasound examinations. In Turkey, there is no law to restrict the application of ultrasound by any physician in their medical practice; although when challenged, the law authorities have placed restrictions that regulate primary care physicians, barring primary care physician from issuing written reports from an ultrasound examination. The public service reimbursement rules dictate that if an ultrasound is performed and reported by a non-radiologist specialist, reimbursement is less than that which is normally reimbursed to a radiologist. Since reimbursement is only symbolic (2–10 euros), many physicians do not document a report and use ultrasound as a continuum of the physical examination. Ultrasound education is a major part of radiology residency and takes a minimum of 1 year, which constitutes almost one quarter of the overall curriculum. In obstetrics, gynaecology, and cardiology, ultrasound education is also an important part of the training programme. In all other specialties, ultrasound education of residents remains unstructured, essentially due to a lack of sufficient educators and teachers.

The Israelian health care system is based on the National Health Insurance Law of 1995. All citizens are required to join one of four official health insurance organisations. Health care is provided mostly in public hospitals and external clinics, maintained by the national government and the health insurance organisations. Ultrasound units in hospitals and community health providers are part of the radiology department. Examinations are performed by sonographers, normally trained radiographers, and supervised by a radiologist [28]. In the last 10 years, point-of-care ultrasound (POCUS) examinations within the emergency department and clinical and surgical wards are increasingly performed by non-radiologists. Programmes for teaching and training non-radiologists in the performance of POCUS have been implemented, in the last few years, by radiologists specialised in ultrasound. Interventional procedures under ultrasound guidance are performed by radiologists. Advanced ultrasound techniques like contrast enhanced ultrasound, elastography, and 3D ultrasound as well as research are performed in the radiology departments, mainly in university hospitals. An increase in the practice of POCUS by clinicians is predicted with further development of radiology-based ultrasound units in the area of teaching and research and the application of advanced techniques with modern ultrasound equipment, for better ultrasound diagnoses and therapeutic procedures. Radiology residents training in ultrasound spend 6 months in the ultrasound unit, together with chest x-ray interpretation, before starting the on-call work. During the on-call shifts, they perform and supervise the ultrasound examinations, subsequently reviewed by the senior ultrasound radiologist. Ultrasound imaging is part of the written and oral board examinations.

In Denmark, all radiology departments offer ultrasound examinations and interventions, and it is part of the curriculum for the residents in radiology to be able to do ultrasound-guided intervention in the pleura, breast, and abdomen. Denmark has a long tradition for ultrasound and ultrasound-guided intervention. Except for abscesses in the breast, all ultrasound examinations of the breasts are performed by dedicated breast radiologists. Some anatomical areas are never examined within the radiological department, but by other medical specialties, which include training in their curricula. Gynaecologists and obstetricians perform all ultrasound examinations of the female reproductive organs and all foetal scans. Cardiologists perform echocardiography, and vascular surgeons perform ultrasound preoperatively. In recent years, some rheumatologists have included ultrasound in their examinations of joints, and some otorhinolaryngologists perform ultrasound of the neck. Other medical specialties include ultrasound as a point of care examination, for instance intraoperative ultrasound in liver surgery and prostate ultrasound by urologists. Emergency medicine doctors and general practitioners may use POCUS to confirm or rule out specific diagnoses as gallbladder calculi, hydronephrosis, aortic aneurysm, pneumothorax, and free intraabdominal fluid. Also, anaesthesiologists use ultrasound for vascular access and in the ambulances and helicopters transferring patients.

Until 1984, Russia had a small number of modern ultrasound equipment mainly in research and educational medical institutions. Since 1984, modern ultrasound systems have begun to arrive in the country in large (for this period) quantities, estimated at > 400 systems per year. Only doctors were entrusted with conducting ultrasound examinations with these sophisticated and expensive ultrasound systems. By 1987, the need to organise a regular systematic training of doctors performing ultrasound examinations in the country became obvious. Two main factors were taken into account: the vast territory of the country with a large number of regions with an extremely low population density and the lack of ultrasound equipment and doctors capable of using this equipment. The solution was to concentrate the equipment in one place and training doctors, who would be employed full-time to do ultrasound examinations. In 1988, by order of the USSR (Union of Soviet Socialist Republics) Ministry of Health, interdisciplinary departments of diagnostic ultrasound were created, and the specialty of ultrasound diagnostics appeared. The advantages of interdisciplinary ultrasound department are as follows: the possibility of more efficient use of ultrasonic equipment (especially of a high level), reducing the waiting time for the study by the patient, a one-step study of various organs and systems in a patient, high specification of an ultrasound diagnostics doctor whose daily work improves the level of expertise and skill, easy redirection of the patients flow in case of illness of one of the doctors, affordable and quick consultation with colleagues. The ultrasound-based doctors are not radiologists; they are from different specialties (including radiology), but after additional training (from 500 h) and passing state accreditation (‘OSCE’), they are accredited in the specialty of ultrasound.

Diagnostic ultrasound in the UK has over the years devolved from radiologists to sonographers (usually radiographers who have gained postgraduate qualifications); it is estimated that 85% of all ultrasound scans in the UK are performed by sonographers [29]. Their training and skills are comprehensive and, in many areas including some obstetric, gynaecological, and general applications, may exceed those of a radiologist. Frequently, in the UK, hospitals have sonographer-led services including general, contrast enhanced ultrasound and paediatrics, and it is not uncommon for sonographers to provide training to radiologists [30]. Some specialised ultrasound examinations, for example, musculoskeletal, head and neck, breast, and interventional ultrasound, are still predominantly performed by radiologists, although more sonographers are now becoming skilled in these techniques as demand continues to escalate. The USA and Australia have similar skilled sonographers, but generally only those in the UK report their findings independently. There are now a small but increasing number of non-radiology clinicians performing focused ultrasound for a quick diagnosis to inform patient management including obstetricians, anaesthetists, intensivists, general medical and emergency department physicians, and allied health professionals such as physiotherapists. The landscape of ultrasound users in the UK is broadening as a consequence of the modality’s wide appeal and versatility. Radiology training has been part of the core curriculum within radiology and with this ultrasound training, the trainees are expected to deal with all aspects of ultrasound whilst performing their on-call duties.

Ultrasound is the most widely used imaging modality in China. It is estimated that there are around 190,000 ultrasound machines nationwide [31] Moreover, the need for ultrasound examinations is still on the rise, and the number of ultrasound practitioners is inadequate. Unlike the ultrasound section incorporated into the radiology departments in most countries, the ultrasound department is an independent unit in China, very much similar to the situation in Russia. In addition, the majority of hospitals in China have only ultrasound physicians performing both the scanning and diagnosis and reporting of the examination. In order to meet the huge and diverse needs for ultrasound since 2007, West China Hospitals, a group of geographically adjacent hospitals in the Western part of China, has been trying a new working model in China by employing both ultrasound physicians and sonographers. The demand for ultrasound can be stratified into four levels: (i) POCUS, (ii) more basic common ultrasound examinations, (iii) more specialised ultrasound examinations, and (iv) interventional ultrasound. Staff with different experiences and educational backgrounds are appointed to meet the corresponding demands. Ultrasound physicians play a vital role in this working model with multiple responsibilities. Specifically, attending (consultant) and senior doctors are engaged in teaching, supervising common ultrasound examinations, and performing examinations for more complicated cases and ultrasound-guided interventional procedures. Sonographers are mainly involved in POCUS and common ultrasound scanning, examination description, and providing ultrasound examination ‘impression’, which is reported by the ultrasound physician. POCUS is becoming a part of the daily practice of some specialists, in particular emergency physicians, anaesthesiologist, and intensivist. Quality control is a key part of the working model. Besides multi-modular training, a real-time consultation platform integrating ultrasound information system (UIS) and audio–video system has been used to guarantee the quality of ultrasound service, especially those carried out by sonographers and junior ultrasound physicians. Moreover, for quality control, reports are scored weekly, including ultrasound images and text, which will be finalised by using artificial intelligence in the near future.

Ultrasound in the USA has traditionally been performed by the departments of radiology, obstetrics, and gynaecology and vascular surgery. Ultrasound examinations are usually performed by sonographers using structured protocols, with back-scanning and interpretation by physicians. Cine clips are widely used. Radiologists perform more scanning in musculoskeletal, paediatrics, and niche applications and during interventional procedures. Ultrasound is a required subject in radiology residency, but the amount of resident scanning is at the discretion of the programme. This traditional practice is being upended by advances in computing capability that have resulted in smaller and cheaper ultrasound devices. The handheld ultrasound scanner is a disruptive technology. It is poised to become the stethoscope of the twenty-first century, a ubiquitous tool used by all healthcare workers. This has given rise to POCUS in which ultrasound is performed as an adjunct to the clinical examination. POCUS is now practiced by a growing number of physicians and paramedical staff. Ultrasound scanning is now taught as a foundational skill in medical schools. As such, the practice of ultrasound will no longer be confined to trained specialists like radiologists, obstetricians, or sonographers. Most ultrasound scans in the USA now occur outside radiology departments. The future of ultrasound in radiology lies in focusing on quality, comprehensive examinations, and advanced modalities such as Doppler ultrasound, contrast-enhanced ultrasound, artificial intelligence, elastography, and 3D that require high-end equipment. Radiology resident scanning has been cut back, as all new trainees now start with ultrasound experience from medical school. The medical students are taught to scan during their emergency department and obstetrics and gynaecology rotations, like past generations were taught to use the stethoscope. All scanning protocols are based on practice parameters published by the American College of Radiology, American Institute of Ultrasound in Medicine, and Society of Radiologists in Ultrasound (ACR/AIUM/SRU), and these practice parameters act as a national quality standard of training, skills, techniques, and recommended conduct. There are over 30 ultrasound practice parameters (https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards).