From the surgery done below, name the gold standard investigation used to diagnose this condition:

The specimen in the image is Appendix and the surgery performed is Appendectomy CECT done to confirm diagnose at a 5-6 ALVARADO Score as it is Equivocal. Gold standard for Dx of Acute Appendicitis-CECT. Features seen in CECT in case of acute appendicitis- Diy fat thickened mesoappendix Appendicular faecolith Arrowhead sign- Thickened caecum funneling contrast into orifice of appendix Gold standard for Dx of Acute Appendicitis in Children-ULTRASOUND