How to repair corrupted registry hive?

I have NT 4.0 SP4 PDC that has crashed. Now the system does not start. I have installed another copy of NT and found uut that my software registry hive on original system is corrupt. (I cannot load it from parallel installation). Other hives and file system are ok. Unfortunatly, there is no backup and no useful repair info available. I see registry hive as some kind of database, that is corrupt. Is there any way to repair corrupted registry hive? Any suggestions? Third party utility maybe?