**Abstract**

Medical image segmentation and classification algorithms are commonly used in clinical applications. Several automatic and semiautomatic segmentation methods were used for extracting veins and arteries on transverse and longitudinal medical images. Recently, the use of medical image processing and analysis tools improved giant cell arteries (GCA) detection and diagnosis using patient specific medical imaging. In this chapter, we proposed several image processing and analysis algorithms for detecting and quantifying the GCA from patient medical images. The chapter introduced the connected threshold and region growing segmentation approaches on two case studies with temporal arteritis using ultrasound (US) and magnetic resonance imaging (MRI) imaging modalities extracted from the Radiopedia Dataset. The GCA detection procedure was developed using the 3D Slicer Medical Imaging Interaction software as a fast prototyping open-source framework. GCA detection passes through two main procedures: The pre-processing phase, in which we improve and enhances the quality of an image after removing the noise, irrelevant and unwanted parts of the scanned image by the use of filtering techniques, and contrast enhancement methods; and the processing phase which includes all the steps of processing, which are used for identification, segmentation, measurement, and quantification of GCA. The semi-automatic interaction is involved in the entire segmentation process for finding the segmentation parameters. The results of the two case studies show that the proposed approach managed to detect and quantify the GCA region of interest. Hence, the proposed algorithm is efficient to perform complete, and accurate extraction of temporal arteries. The proposed semi-automatic segmentation method can be used for studies focusing on three-dimensional visualization and volumetric quantification of Giant Cell Arteritis.

**Keywords:** Giant Cell Arteritis, Enhancement, Detection and Classification, Segmentation

## **1. Introduction**

Giant cell arteritis (GCA), also called temporal arteritis or cranial arteritis is a systemic inflammation of medium to large-sized vessels [1]. The cause of the disease is currently unknown; however, autoimmunity is one hypothesis [2].

GCA most commonly occurs in females (female to male ratio 2-4:1) over the age of 50 years [3]. Temporal artery involvement classically presents with sudden onset of severe headache associated with inflammatory and ischemic symptoms; [1] however, GCA may involve other large-sized arteries, namely the aorta, subclavian, iliac, ophthalmic, occipital, and vertebral arteries, which have different presentation and may be involved independently from the cranial arteries [4].

Left untreated, GCA can lead to permanent visual loss and various systemic complications; therefore, there is a need for effective diagnosis. The American College of Rheumatology proposed criteria for the diagnosis of GCA [5]. The diagnosis mainly relies on clinical presentation, inflammatory markers (typically high erythrocyte sedimentation rate (ESR)), and usually histological confirmation by temporal artery biopsy. Temporal artery biopsy has been the standard test to confirm the diagnosis of GCA, which although highly specific, is considered invasive and lacks sensitivity [2, 6, 7]. Consequently, diagnosis of GCA often relies on the combination of clinical symptoms, serum inflammatory markers, and radiological imaging.

## **2. Diagnosis of GCA by radiological imaging**

The role of radiological imaging is becoming increasingly important in the diagnosis and follow-up of GCA. Generally, the different radiological imaging modalities visualize different aspects of the involved vessel wall thickening and luminal stenosis. The first line imaging modality, especially for cranial GCA is color duplex sonography (CDS) [4, 8, 9]. CDS assesses vascular wall anatomy and luminal lining and diameter. A characteristic finding of GCA on CDS is the (halo) sign, which is homogenous, hypoechogenic circumferential vessel wall thickening. Another finding is the lack of compressibility of the artery manifested by the application of transducer-imposed pressure on the temporal arteries (compression sign) [4, 8]. The (halo) sign has a sensitivity ranging from 55 to 100% and specificity of 78 to 100% in the diagnosis of temporal arteritis [8]. The wide range of sensitivity may be attributed to operator experience and arterial involvement. A systematic review published in 2016 discussed the use of the different imaging modalities in the diagnosis and follow-up of GCA [10]. The review findings suggest that CDS is an easy, cost-effective diagnostic imaging tool for the evaluation of cranial vessels, as well as the carotid, subclavian, axillary, and brachial vessels. The reliability of the unilateral halo sign is debatable; however, the presence of a bilateral (halo) sign discards the need for temporal artery biopsy. Many studies have compared ultrasound (US) imaging versus temporal artery biopsy in the evaluation of GCA [11–15]. In a prospective cohort study published in 2019, Zou *et al.* discussed the results of clinical examination following the US versus biopsy of the temporal artery biopsy directly, considering MRI as a reference diagnostic data. The study included 980 patients with a mean age of 61.12 ± 6.56 years who complained of at least one symptom consistent with GCA but have not been diagnosed or treated with glucocorticoids [11, 14]. US and MRI imaging included bilateral temporal arteries, axillary arteries, and their branches. The study concluded that the clinical examination following US detection of GCA had high accuracy and a lower risk of overdiagnosis and unnecessary glucocorticoid treatment of low to medium risk GCA [2]. Moreover, there was a higher number of false-negative diagnoses reported by temporal artery biopsy. These results are consistent with other studies like the TABUL study [1].

Other important noninvasive imaging modalities are contrast-enhanced computed tomography (CT) scan and CT angiography (CTA). Both scans visualize cranial and extracranial arteries, the aorta for example, and can visualize associated

#### *Medical Image Processing and Analysis Techniques for Detecting Giant Cell Arteritis DOI: http://dx.doi.org/10.5772/intechopen.97161*

complications [16, 17]. On CT, the diseased vessel wall appears edematous with concentric enlargement and usually shows late contrast enhancement. CTA on the other hand is better for visualization of the luminal vascular pathology. Both modalities are excellent for the diagnosis of GCA when the involvement of a largesized vessel other than the temporal artery is suspected. However, there is a scarcity of data on the use of CT/CTA in the diagnosis of GCA. Berthod *et al.* discussed in a case–control study CT imaging of the aorta in suspected GCA, which included 174 participants (64 with GCA, 43 with polymyalgia rheumatica, and 67 controls) [18]. The study results showed that using CT in the evaluation of the aorta is diagnostic of GCA which is morphologically different that atheromatous lesions. The study set an aortic wall thickness of ≥2.2 mm as pathological and indicative of GCA.

Additionally, magnetic resonance imaging (MRI) and MR-angiography (MRA) have a prominent role in the diagnosis of GCA. The t2 weighted MRI images show a hyperintense rim at the edematous segment of the vessel wall. Moreover, t1 weighted images depict mural thickening and contrast enhancement. MRA, as CTA, better visualizes irregular luminal lining and can assess the extent of arterial wall damage and the effectiveness of treatment [8]. The use of MRI in the clinical setting is available; however, its diagnostic accuracy is still indefinite as the available literature has approached this issue differently. A systematic literature review and meta-analysis discussed the diagnostic accuracy of MRI imaging of the temporal and occipital arteries. They reviewed six studies with 509 patients that used either clinical diagnosis or temporal artery biopsy as the reference standard. They found that when the clinical diagnosis was used as the reference standard, MRI had a lower pooled sensitivity and specificity (73%, 88%) than that of the US (77% and 96%, respectively). However, when compared with temporal artery biopsy, MRI had a higher sensitivity (93% vs. 70%) and a similar specificity to sonography (81% vs. 84%). Thus, they advised that both modalities have good diagnostic accuracy of superficial temporal arteries GCA [17].

Furthermore, fluoro-D-glucose integrated with computed tomography (FDG-PET/CT) is also currently used in the diagnosis of large-sized vascular wall inflammation. This modality shows the increased uptake of glucose by the inflammatory cells lining the vessel wall [19].

The choice of image processing technique depends on the available imaging modality and the level of expertise in the clinical setting, taking on consideration the risks of radiation or contrast exposure, in contrast to the benefit of timely and accurate diagnosis of GCA versus the overdiagnosis and overtreatment of GCA based on conventional diagnostic criteria. The European League Against Rheumatism (EULAR) has issued recommendations on the use of different imaging modalities in the evaluation of large vessel vasculitis [20]. However, currently, there is no clearly defined protocol for imaging in suspected GCA; yet, there is increasing attention over the advantages and disadvantages of using each imaging modality in accordance with the clinical presentation.
