## 1 Introduction  
Head and neck cancers represent the sixth most common form of cancer worldwide. More than 90% of head and neck cancers are squamous cell carcinomas of the oral cavity, oropharynx, and larynx mucosal tissues [1]. Radiotherapy (RT) is generally included in the primary oncologic treatment, as it improves clinical and functional outcomes for cancer patients, especially in the case of oropharyngeal cancers (OPC) [2]. In addition to its therapeutic effects, RT can cause injuries to the tissues inside and surrounding the irradiated area, and approximately 90% of patients undergoing radiotherapy for head and neck cancers suffer from clinically relevant xerostomia [3; 4]. Xerostomia is defined as dryness of the oral cavity resulting from insufficient saliva secretion [5; 6]. RT-induced xerostomia is caused by salivary gland dysfunction resulting from X-ray related tissue damage [5; 7; 8]. In regard to the diagnosis of xerostomia, the basic tests include the determination of stimulated and unstimulated salivary flow rate, palatal secretion, and parotid secretion [9; 10; 11]. These measurements constitute the simplest methods of assessing the secretory function of salivary glands. Very low unstimulated and stimulated salivary flow rates are defined as <0.1 mL/min and <0.7 mL/min, respectively [10; 11; 12]. Such values are confirmatory of xerostomia, whether or not they co-exist with specific symptoms for this condition, such as oral soreness, dry lips, halitosis, decreased or altered sense of taste, recurrent mouth infections, tooth decay and gum disease, and difficulty speaking, eating, or swallowing [13; 14; 15]. Because of the high-contrast resolution and the ability to study complex anatomical regions without the use of radiation, magnetic resonance imaging (MRI) is considered the most relevant imaging technique for the identification of head and neck lesions [16; 17; 18; 19]. Diffusion-weighted imaging (DWI) is an established diagnostic tool that evaluates the tissue microanatomy by studying the spontaneous molecular diffusion of protons corresponding to the stochastic Brownian motion of water molecules [16; 20; 21]. The apparent diffusion coefficient (ADC) is calculated from DWI and consists of the quantitative assessment of the impedance of water molecule diffusion within tissues [20]. The ADC is typically reduced in hypercellular tissues and increased in situations where water molecules are free to move [16; 17]. The ADC values are calculated automatically and integrated into a parametric map, upon which regions of interest (ROIs) can be traced at a workstation to determine the ADC values of specific portions of a tissue [16; 17; 18]. Dynamic contrast-enhanced, perfusion-weighted imaging (DCE-PWI) is a functional MRI technique that allows one to infer blood perfusion to specific tissues by measuring the changes in tissues over time after the intravenous administration of a contrast agent [22]. DCE-PWI is crucial in the detection of focal lesions since it mainly assesses the vascular permeability [23]. Changes in hemodynamic parameters can precede abnormalities on conventional MRI and can thus be used to help with the diagnosis [22; 23; 24; 25; 26]. Radiomics has been rapidly developing over the last few years; it is a hybrid analytical process aimed at determining the correlation between the characteristics of tissues and their corresponding digital images [17; 27]. Texture analysis is a form of radiomics, in which macroscopic heterogeneities of tissues can be non-invasively studied to infer information about their microscopic architecture beyond the possibilities of the human eye as if it were a \"virtual biopsy\" [17; 28; 29]. Texture analysis is based on the extraction of parameters representing the distribution frequency, intensity, or direction of gray levels within the ROI in order to evaluate the single pixel, its interactions with adjacent pixels, and the distribution of pixels and voxels in the image [17; 29].