def convert_file_extension_to_txt(image_file):
	"""Convert and a file extension to .txt

	Args:
		image_file (str): String containing the image file

	Returns:
		Initial string where extension is changed to '.txt'
		
	Examples:
		>>> convert_file_extension_to_txt('verse007.mha')
		 'verse007.txt'

	"""
	return image_file.split('.')[0] + '.txt'