When recutting a block or having one where the embedded tissue is a bit out
whack for decent cutting alignment, then the x/y axis IS adjusted. The
blade angle is generally not adjusted, only the x/y axis is changed. Even
moving a blade sideways to access a sharp, new edge can alter the x/y
orientation slightly. When this happens, reapproaching the blade, x/y
adjustement may be needed to get first sections coming off the block - often
the sections one absolutely must have.
We don't change the blade angle unless someone tweaks the lever (generally
an inexperienced tech or student who has no clue what is going on but they
love flipping levers around). Sometimes a blade angle is readjusted from a
new blade lot even though the manufacturer of the blade is the same. The
blade manufacturing process can introduce minute changes in blades. When
changing from high to low profile blades we readjust blade angle slightly at
times - the low profiles being thinner in metal thickness and narrower width
from top to bottom than the high profile.
Rembedding and refacing a block is not ideal. As Amos points out, the danger
of losing the region of interest in the embedded tissue is just too high
especially on a recut. One can always turn a block in the holder, but that
means some clever, careful x/y axis adjustment - we do this all the time.
I vote for Amos's way as he just described it, and that is how we do it in
our lab. We meaning "I" do it, the x/y axis way. The lever tweakers are
generally gently repirmanded and taught the correct way for where a blade
angle works best for the preferred blade in the lab.
Gayle M. Callis
----- Original Message -----
From: "Amos Brooks"
To: "Rene J Buesa"
Sent: Wednesday, May 14, 2008 4:42 PM
Subject: Re: [Histonet] Standardized Microtomes
I absolutly disagree with that. The exact opposite: *Not* modifying the
angle of your block holder to suit the block, is not good practice. You are
bound to loose tissue when cutting archived blocks, or blocks from other
labs or even slight variations within your own lab. If you don't adapt to
the blockyou are cutting. Without modifying the angle of the holder, one has
2 choices: Just cut thru it (refacing) or re-embedding and thereby needing
to re-trim. Both scenerios will loose tissue.
Often I have cut a freshly embedded block where the cassette didn't sit
perfectly flat on the mold, otherwise the embedding was perfect. (Often due
to poorly dissected tissue with high points). This results in an angle that
is slightly askew. Adjusting the block holder is much faster than
re-embedding the block. If it is done properly you can actually modify the
block angle without ever cutting any tissue even on a previously cut block.
We're going to have to disagree on this,
On Wed, May 14, 2008 at 9:14 AM, Rene J Buesa wrote:
> All in all the practice of "changing the angle to match the block you have
> to recut as needed" is not a good practice.
> During it you could end loosing tissue when trying to "build" a new flat
> surface from a block that was originally cut at a different angle, while
> "sculping" the new surface.
> The best practice is to have all the microtomes cutting at the same angle
> and try to convince those HTs that say that "I have always cut with this
> angle" that they are flat wrong and a general angle can be good for the
> majority of blocks.
> René J.
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