Como removo caracteres ASCII estendidos de uma string no T-SQL?

CREATE FUNCTION RemoveNonASCII 
(
    @nstring nvarchar(255)
)
RETURNS varchar(255)
AS
BEGIN

    DECLARE @Result varchar(255)
    SET @Result = ''

    DECLARE @nchar nvarchar(1)
    DECLARE @position int

    SET @position = 1
    WHILE @position <= LEN(@nstring)
    BEGIN
        SET @nchar = SUBSTRING(@nstring, @position, 1)
        --Unicode & ASCII are the same from 1 to 255.
        --Only Unicode goes beyond 255
        --0 to 31 are non-printable characters
        IF UNICODE(@nchar) between 32 and 255
            SET @Result = @Result + @nchar
        SET @position = @position + 1
    END

    RETURN @Result

END
GO