## 2 Materials and Methods  
### Measures  
Pre-assessment, post-assessment, and six-month follow-up measures.  
The following measures were assessed before starting the experimental treatment (ABMT and MET), at the end of the experimental treatment, and after a six-month follow-up period.  
1. Body-related AB was quantified using the patient's visual fixation, defined as the act of sustaining one's gaze on a specific location for a minimum duration of 100 ms [36]. This measure was applied to specific Areas of Interest (AOIs) based on the Physical Appearance State and Trait Anxiety Scale (PASTAS) [37]. The AOIs were categorized as follows: * Weight-related body parts: thighs, buttocks, hips, stomach, legs, and waist. * Non-weight-related body parts: neck, chest, shoulders, arms, and feet.  
The head was excluded from the AOIs, because it was obscured by a head-mounted display (HMD) and hat.  
Visual fixation was determined using two measures [8; 38; 39]:  
* Number of fixations on AOIs: the total number of fixations on each specified AOI group.
* Complete fixation time on AOIs: the cumulative duration of fixations on each specified AOI group, measured in milliseconds.
2. Body dissatisfaction and drive for thinness were assessed using the Spanish versions of the subscales from the Eating Disorder Inventory-3 (EDI-3) [40], as translated and validated by [PERSON] et al. [41].
* Body dissatisfaction (EDI-BD): This subscale is comprised of 10 items, with scores ranging from 0 to 40. Higher scores indicate greater dissatisfaction with one's body.
* Drive for thinness (EDI-DT): This subscale consists of 7 items, with scores ranging from 0 to 28. Higher scores indicate a stronger desire to be thin.  
The Spanish version of this instrument exhibits a [PERSON]'s alpha ranging from 0.74 to 0.96.
3. Anxiety Toward Weight-related Body Parts: Assessed using the Weight Scale of the PASTAS, with a total score range of 0 to 32. Higher scores indicate increased anxiety toward weight-related body parts. The scale demonstrates good internal reliability, with a [PERSON]'s alpha ranging from 0.82 to 0.92. It also shows good test-retest reliability (r = 0.87) and convergent validity indices for the W scale (r = 0.74 with EDI-BD, r = 0.62 with EDI-DT) [40].
4. Body-Checking Behaviors: Measured using the 23-item Body-Checking Questionnaire (BCQ) [42], which includes three subscales and has a total score ranging from 23 to 115. Higher scores indicate more frequent body-checking behaviors. The BCQ is noted for its good test-retest reliability (r = 0.94).
5. Body Apprecation: Employed using the 12-item Spanish version of the Body Apprecation Scale for adolescents (BAS) [43], translated and validated by [PERSON] and [PERSON] [44], with scores ranging from 13 to 65. Higher scores reflect greater body appreciation. The Spanish version demonstrates adequate internal consistency ([PERSON]'s \(\alpha\) = 0.908) and construct validity.  
Ongoing assessments at each session.  
1. BMI: Calculated by dividing the patient's weight (in kilograms) by the square of their height (in meters).
2. Visual analog scales (VAS) ranging from 0 (not at all) to 100 (completely) were used to assess the following measures:Full-body ownership illusion (FBOI): The degree to which the patient felt the virtual body was her own.
* Fear of weight gain (FGW): The extent to which the patient feared gaining weight while embodied in the virtual body.
* Anxiety: The level of anxiety the patient experienced while having the virtual body.  
Other measures.  
At the post-treatment session, the System Usability Scale (SUS) [45], a 10-item questionnaire, was administered to assess the perceived usability of the VR and ET system, with scores ranging from 0 to 100. A score up to 70 indicates good usability.  
The timeline of the assessment for this study is presented in Figure 1.