## 1 Introduction  
Ultrasonography is an effective non-invasive imaging technique used in musculoskeletal medicine both for (1) investigating the skeletal muscle structure and calculating quantitative muscle parameters [1; 2; 3; 4] and for (2) qualitative and quantitative assessment of tendon structure (echo-intensity) and size (thickness, length, and cross-sectional area) [5; 6; 7; 8]. Ultrasound imaging presents many advantages, including the fact that it is portable, has low associated costs, is non-invasive, and does not use any ionizing radiation for imaging, but rather innocuous high frequency sound waves. On the other hand, however, it is a very operator-dependent technique and presents a high intra- and inter-reader variability [9].  
Ultrasound imaging of the patellar tendon is commonly employed to study tendon abnormalities that could occur because of repetitive overload, which is a common happening in professional athletes of various disciplines [10; 11; 12; 13]. Patellar tendonopathy (PT) is especially common in athletes that play sports that require jumping, such as basketball and volleyball, giving it its common-term name of \"jumper's knee\" [14; 15]. Recent studies focused on the analysis of changes in elastic properties of the patellar tendon using shear wave imaging [16; 17; 18; 19; 20; 21]. [PERSON] et al. [18] showed that athletes with unilateral PT had a stiffer tendon (i.e., higher shear elastic modulus) on the non-painful side when compared to the painful side (25.8 \(\pm\) 10.6 kPa vs. 43.6 \(\pm\) 17.9 kPa, respectively), whereas healthy controls showed no difference of stiffness between sides (27.5 \(\pm\) 11.3 kPa vs. 27.9 \(\pm\) 8.4 kPa). In their study, they also conducted a morphological analysis and found that the athletes with PT had a larger painful tendon compared with the contralateral non-painful side (thickness: 6.9 \(\pm\) 1.8 mm vs. 4.6 \(\pm\) 0.6 mm, respectively), whereas the controls had no difference between sides (5.6 \(\pm\) 1.2 mm vs. 5.3 \(\pm\) 1.0 mm). Morphological abnormalities in the tendon ultrasound image, such as increased tendon thickness, neovascularization, and presence of hypoechoic areas, have also been found in a large percentage of asymptomatic athletes [9; 11; 13; 22]. Recently, [PERSON] et al. [23] also conducted a study of patellar tendon size and structure in throwers and found that the prevalence of subclinical tendonopathy was high in the non-dominant patellar tendon as a possible result of the repeated non-dominant lower limb overload. To do so, the authors arbitrarily defined subclinical tendonopathy as \"the presence of either light structural changes in association with at least mild neovascularization or moderate/severe structural changes with/without neovascularization\" [23]. In the study, however, the determination of structural changes was done by quantitative assessments of tendon echo intensity and size and by qualitative analysis of the B-mode ultrasound images of both the dominant and non-dominant side, which is a very subjective technique and can depend greatly on the ultrasound scanner settings [24]. On the contrary, texture features that can be calculated on the B-mode ultrasound image are intensity-invariant and have proven to be informative in the characterization of various tissues, such as breast [25], ovarian tumors [26], thyroid lesions [27], liver [28], and recently also in musculoskeletal images [29].  
In this study, we aim to quantitatively analyze the presence of patellar tendon abnormality and subclinical tendonopathy in professional asymptomatic players using a texture-based morphological approach and the same image database as presented in [23]. In particular, the study provides quantitative texture features calculated on the images initially used for the determination of a qualitative structure score [23], and analyzes the capability of this approach to discriminate between the dominant and non-dominant side of the player, and to determine the presence of subclinical tendonopathy as defined previously.