**2. Extracranial duplex sonography in giant cell arteritis (GCA)**

Ultrasonography (US) is a safe, noninvasive, without radiations, widespread accessible, fast, and low-cost bedside screening technique which has the unique capacity of studying real-time hemodynamics. It presents the ability to evaluate the anatomy of vessel's wall, identifying equally parietal abnormalities (wall thickening, hypoechoic plaques, clotting, parietal hematoma, dissections) and the external diameter of the artery; it can rule out both stenosis and occlusion. Therefore, the use of US is widespread in neurological clinical practice, mainly in the evaluation of arterial atherosclerotic process but also for monitoring other diseases such as medium/large-vessel vasculitis [17–19].

Olah noted that for US imaging of extracranial vessels different modes are being used:

	- The strength of the echo is recorded as a bright dot, while the location of different gray dots corresponds to the depth of the target [17].

#### b.*The duplex image*


#### c.*Color Doppler flow imaging*

• Measure mean frequency shift in each sample volume.


### d.*Power Doppler mode*


The advantages of US over other imaging techniques in GCA are represented by its safety, accessibility, tolerability, fast (may take about 15-20 minutes, if it's conducted by an experienced sonographer) and the more important, its high resolution (a high –frequency probe offers both an axial and a lateral resolution of 0.1 mm) [19–27]. The smaller the vessel diameter, the more difficult is to appreciate the vessel wall damages, so that, in this case, the most informative US data are based on Doppler spectral evaluation. This is also valid for the assessment of medium to small vessel inflammation such as intracranial vasculitis. Small vessel vasculitis (the ANCA-associated or the immune complex vasculitis) are not a domain of ultrasound [19].

Furthermore, US has a higher sensitivity than TAB, the last one evaluating only a restricted anatomical region in a systemic disease. Using US, we can reveal pathological characteristics in GCA: non-compressible arteries (compression sign), the wall thickening ("halo" sign), stenosis and vessel occlusion. A normal intima-media complex (IMC) of an artery is represented by US as a homogeneous, hypoechoic or anechoic echo structure delineated by two parallel hyperechoic margins [19–27].

There is imperative to underline the importance of establishing the arteries that should be routinely examined in a patient suspected for GCA and these are: the TAs, and axillary arteries. If US of these arteries does not reveal suggestive lesions, in the presence of a clear patient history and of an obvious clinical examination, other arteries should be examined: other branches of the ECAs (the internal maxillary, the facial, the lingual, the occipital arteries), the vertebral, the subclavian, the common carotid arteries-CCAs, and the internal carotid arteries-ICAs [9, 19, 21].

Regarding the adequate US equipment for the diagnosis of GCA, modern high-resolution linear probes providing Doppler mode should be used, especially for examination of TAs. We should take into consideration that tissue penetration increases with lower frequencies and the resolution of US increases with higher

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

frequencies. Probes that provide frequencies >20 MHz allow the clearly visualization of the normal IMC of TAs probes with frequencies ≥15 MHz are usually used for detection of minor wall thickening [19, 21].
