Sort ascending or descending dynamics

You 2 Ways to sort ascending or descending dynamics depends on variable:
First way:
SELECT [Id]
,[Last_Update_Dt]
FROM [Tellas_PhotoGallery].[dbo].[IMAGE]
order by CAST([Last_Update_Dt] AS INT)*-1

SELECT [Id]
,[Last_Update_Dt]
FROM [Tellas_PhotoGallery].[dbo].[IMAGE]order by [Last_Update_Dt] DESC
This technique of multiplying either 1(ASC) or -1(DESC), can be used in many queries, and of course is not limited to datetimes.
Second way
DECLARE @SortOrder int
SET @SortOrder = 1
SELECT [Id]
,[Last_Update_Dt]
FROM [Tellas_PhotoGallery].[dbo].[IMAGE]
ORDER BY
CASE
WHEN @SortOrder = 1 THEN (RANK() OVER (ORDER BY [Last_Update_Dt] ASC))
WHEN @SortOrder = 2 THEN (RANK() OVER (ORDER BY [Last_Update_Dt] DESC))
END

Article below gives you ideas to create dynamic query Sorting and Where Clause without conactenate string:
http://www.sqlteam.com/article/dynamic-order-by