**5. US and others imaging techniques**

Other imaging techniques, such as high-resolution magnetic resonance imaging (MRI), magnetic resonance-angiography (MR-A), computer tomography angiography (CT-A), positron emission tomography (PET) provide valuable information regarding the structure of large vessels, highlighting with much greater precision the thoracic aorta, compared with US [45–47].

There are few studies that compared US with other imaging techniques. Some of them indicated that there is a good correlation between US and PET, even though PET might have a little more sensitivity for vertebral arteries examination [45–46]. 18F-fluorodeoxyglucose-positron emission tomography/ computed tomography (FDG-PET/CT) has a higher sensitivity for detection of large arteries and aortic involvement - analysis of the arterial wall [45, 46]. The diagnostic power of highresolution MRI and color-coded duplex US of extra-cranial arteries in detecting GCA are equivalent [47].

The disadvantages of this techniques are: they are more expensive, hardly accessible, some of them are limited by invasiveness, nephrotoxicity (angiography) and exposure to high radiations (CT,PET), this is why they might be unnecessary (excepting those patients with exclusively thoracic aorta involvement) and are not accepted as diagnostic methods in GCA. They should only be used when interventions are required [45–47].

All these imaging techniques should always be performed by well-trained specialists, using suitable equipment and operational protocols [45–47].

Nevertheless, US is particularly useful in examining the orbital vessels [9–16, 28, 31, 32, 41].

The diagnostic work-up of AION benefits from the combined used of fluorescein angiography and noninvasive multimodal imaging, including CDI of the orbital vessels and structural Optical Coherence Tomography (OCT) of the optic nerve head (ONH) and OCT angiography [10, 48]. They provide very detailed information regarding the structural (retinal nerve fiber layer-RNFLthickness/optic disc edema) and vascular impairments (microvascular defects-vessel tortuosity, and vessel density reduction) of the ONH, respectively [10, 48].

## **6. Conclusions**

US should be used as a first-line diagnostic investigation for patients presenting with clinical and biological features suggestive for GCA, taking into consideration that it has a high sensitivity to detect vessel wall thickening (dark hallo sign) in the case of large/medium vessels. In a few cases of our studies, the CCAs and the ICAs were also involved.

In consequence, in our department, CCDS has emerged as a safe and reliable alternative to TAB as a point of care diagnostic tool in the management of temporal arteritis.

The eye involvement in GCA is frequent and consists in A-AIONs or CRAO, with abrupt, painless, and severe loss of vision of the involved eye.

Because findings of TAs US do not correlate with eye complications in GCA, CDI of the orbital vessels is of critical importance, in order to quickly differentiate the mechanism of eye involvement (arteritic, versus non-arteritic). This US tehnique may be helpful to detect the blood flow in the orbital vessels, especially in cases of opacity of the medium, or when the clinical appearance of ophthalmologic complications in temporal arteritis is athypical.

*An Integrated Approach to the Role of Neurosonology in the Diagnosis of Giant Cell Arteritis DOI: http://dx.doi.org/10.5772/intechopen.96379*

The Spectral Doppler Analysis of the orbital vessels in GCA with eye involvement reveals low blood velocities, especially EDV, and high RI in all orbital vessels, in both orbits, for all patients (especially on the affected side).

A huge advantage of CDI of orbital vessels is that it provides immediate information that can be used to inform treatment decisions, including a potential reduction in loss of sight and avoidance of unnecessary long-term steroid treatment by early exclusion of mimics.
