How To Comparing NText Fields...?

Hi all

I have a table with one nText Field , some times i need to realize whether two records have the same value in that nText Field or not , so how can i compare

these two records based on their ntext Fields.? in the other words i'm looking for some thing like the follows:

declare  @a nText
declare  @b nText

select @a=MynTextField from MyTable where PK=18
select @b=MynTextField from MyTable where PK=21

if @a=@b
 print 'Records Are the same'
else
 print 'Record are not the same'

 

Thanks in advance.

Regards.