
    Write a function that converts medical scan dates from the hospital's database format (yyyy-mm-dd) to the standardized international reporting format (dd-mm-yyyy) used in diagnostic reports and image analysis documentation. The function must handle valid scan dates from the medical imaging department's database and maintain the exact same date information while only changing its presentation format.
    

    
import re

def change_date_format(dt):
    """
    Write a function that converts medical scan dates from the hospital's database format (yyyy-mm-dd) to the standardized international reporting format (dd-mm-yyyy) used in diagnostic reports and image analysis documentation. The function must handle valid scan dates from the medical imaging department's database and maintain the exact same date information while only changing its presentation format.
    

    """
import re

def change_date_format(dt):
    """
    Write a function that converts medical scan dates from the hospital's database format (yyyy-mm-dd) to the standardized international reporting format (dd-mm-yyyy) used in diagnostic reports and image analysis documentation. The function must handle valid scan dates from the medical imaging department's database and maintain the exact same date information while only changing its presentation format.
    

    """
    return re.sub('(\\d{4})-(\\d{1,2})-(\\d{1,2})', '\\3-\\2-\\1', dt)