RE: [Histonet] cryostat question

From:"Mickie Johnson"

Hi Jennell,

I teach technicians to cut Mohs frozen sections every week and on
Reichert-Jung and Leica cryostats,  and can offer some advice re: your
1. Your cryostat is designed to operate in a room temp range of from 68 - 72
degrees F, optimal. So the tissue was possibly not cold enough. Also make
sure the vents on the left and right side of the cryostat are unobstructed
so the compressor coils will work as efficiently as possible. Is the defrost
time set to midnight or there about?
2. Build-ups (pre frozen OCT on a chuck) should be made fresh each morning.
They should be made one at a time so the chuck is not too cold when the OCT
is applied and can run down into the grooves completely.
3. Build-ups over a day old have freeze-dried and so the new OCT applied
does not stick well to the old dried out stuff on the chuck and the OCT on
the chuck has dried and shrunken somewhat and does not hold well to the
4. The knife angle that seems to work best for me is 2.5 degrees rather than
the 5 degrees often set by Leica reps and from the factory. I have
encountered knife angles everywhere from zero to 10 degrees.
5. Everything from the clamping of the knife holder to the microtome base,
angle clamp, knife lateral adjustment clamp and knife clamp should be very
tight with no movement at all. Looseness here and with the chuck can lead to
chatter which will eventually lead to chunking of the block. Cut slower.
6. The screw clamping the chuck into the microtome and the chuck angle clamp
should also be tight.
7. If the OCT shows condensation of moisture inside the bottle, then it was
probably less hydrated and this would affect cutting consistency, but this
would be minor compared to the above. This could be because the room is so

This is what comes to mind but without being there, this does not rule out
something major wrong with the microtome itself. Also, all clamps on the
knife holder should tighten toward the user except for the knife blade clamp
which most people push toward the back from vertical. 

Lymph node usually tends to shatter when cut even at  minus 20 degrees.
Warming the face slightly with the thumb before taking the section may help
this a little. Knife angle is also a problem if too steep.

Hope this helps a little.

Best Regards,


Mickie Johnson, B.S., HTL(ASCP)
Mohs Histology Consulting Services, LLC
  & Mohs Lab Staffing
2507 S. Manito Blvd.
Spokane, WA 99203
Web:  &  

-----Original Message-----
[] On Behalf Of
Sent: Monday, April 09, 2007 4:39 PM
Subject: [Histonet] cryostat question

So today I had a sentinel node from the OR. I had many frozen sections on t
his case but couldn't seem to get a good section. I couldn't even cut a
section without it chunking my block. Here are a couple things I noticed.
frozen section room was extremely hot...I would say about 85 degrees. I had
make all knew chucks b/c the one's in the cryostat's were old. we had 
previously opened bottles of oct. They all had condensation in them. The
chucks that 
I made had been sitting at room temperature. I need some help
the fact that with both cryostat's the 1800 and the 1850 keep biteing into
chuck without advancing it. Please help...thanks Jennell

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