**1. Introduction**

Ultrasonography (US) has become an integral part of the clinical rheumatology practice. It provides relevant information in many aspects of patient management, both diagnostic and therapeutic. It is a safe, non-invasive and readily accessible imaging modality, with a lack of contraindications. In this respect, US carries significant advantages over other imaging tests, such as CT or MRI. Musculoskeletal ultrasound provides the physician with a real-time evaluation, allows for a dynamic view of target areas and simultaneous scanning of multiple anatomical structures. It is fairly easy to apply imaging techniques, although it requires a prolonged period of training to achieve expert-level assessments. Musculoskeletal ultrasound (MSUS) allows for a fast examination of small and large joints and can guide further diagnostic tests. One of the most important benefits of MSUS is early diagnosis of articular and periarticular inflammation; this is especially the case in rheumatoid arthritis and psoriatic arthritis where diagnostic delay from symptom onset can lead to significant structural progression and poor outcomes. US evaluation is included in the EULAR (European League Against Rheumatism) recommendations for use of imaging in

disease management for both RA and Spondyloarthritis (SpA) [1, 2]. Also, standardization of US procedure is provided through the EULAR standardized procedures for US imaging [3] and OMERACT (Outcome Measures in Rheumatoid Arthritis Clinical Trials) definitions of US pathology [4]. Apart from inflammatory and degenerative joint disease, US can also aid the rheumatologist in the diagnosis and management of connective tissue diseases such as systemic scleroderma, Sjögren's syndrome or vasculitis [5–7].
