Over the past decade, imaging has been readily adopted to facilitate early diagnosis of the most common immune-mediated form of large vessel vasculitis (LVV), giant cell arteritis (GCA) [1]. In the 2022 ACR/EULAR classification criteria, imaging findings, including a positive halo sign on temporal artery ultrasound, 18F-fluorodeoxyglucose (18F-FDG) uptake in the arterial wall of the aorta on positron emission tomography (PET) and bilateral axillary involvement using ultrasound, angiography (computed tomography [CT], magnetic resonance imaging [MRI], or catheter-based), or PET/CT have been incorporated into the definition of GCA for research purposes [2]. This shift to incorporate imaging alongside temporal artery biopsy (TAB) in the criteria reflects the accumulated evidence supporting the adequacy of an imaging-based GCA diagnosis, compared to traditional TAB, among patients with cranial manifestations such as headache, scalp tenderness, jaw claudication, or acute visual loss. Another key factor driving acceptance of imaging as a diagnostic tool is the increasing recognition of the extra-cranial form of GCA, known as large vessel GCA (LV-GCA), that affects the aorta and its main branches. While the need for histopathological diagnosis will remain in certain situations (for example, an individual with a high pre-test probability of GCA but negative imaging), imaging modalities additionally provide the potential of surveillance for the development of long-term, life-threatening vascular complications and may prove useful in assessing the patient's response to treatment. Following the therapeutic revolution that the landmark GIACTA trial has spurned in GCA, disease activity monitoring while on treatment has become one of profound clinical significance [3]. In the absence of a reliable biomarker due to the effect of interleukin-6 (IL-6) blockade upon conventional systemic inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), imaging offers an appealing means by which to assess disease activity, providing the results can be shown to be reliable, reproducible and clinically relevant. Moreover, any modality utilized in this manner should be widely available and performed by a provider with sufficient expertise (see Table 1).

In the following chapter, the fast-evolving literature in this field will first be reviewed regarding the present-day performance of modalities, including ultrasound, MRI, and PET/CT for the diagnosis of GCA. Emerging data for the utilization of imaging to monitor disease activity will additionally be covered, along with the available evidence regarding monitoring for the development of vascular complications.