A cryostat is a refrigerated cabinet with a microtome inside it. It freezes a tissue sample and slices it into sections a few microns thick, so the tissue can be stained and read under a microscope within minutes. In a Mohs lab it is the instrument the whole surgical day depends on; in a hospital it produces the frozen sections a surgeon waits on mid-operation.
How a cryostat works
The chamber is held well below freezing, usually around -20 °C, by a refrigeration system similar to a small freezer. Inside it:
- The specimen is frozen onto a metal chuck, often on a fast-freeze shelf or with a cold block, embedded in a compound such as OCT
- The specimen head holds the chuck and can be cooled separately, because different tissues cut best at different temperatures
- The microtome mechanism advances the specimen by a set thickness and moves it past the blade with each turn of the handwheel
- The blade holder and anti-roll plate hold a disposable blade steady and keep each section flat as it comes off
- The section is picked up on a glass slide, fixed and stained
Because the chamber, the specimen head and sometimes the blade are temperature-controlled, a good technician tunes the settings to the tissue. Fatty skin, for example, usually needs to be colder than other tissue to section cleanly.
What goes wrong
Most cryostat problems fall into two groups, and it helps to know which one you are dealing with before you call for service.
Temperature problems
The chamber won't reach set point, ice builds up, the compressor runs constantly or the unit alarms. Common causes are dirty condensers, failing compressors or fans, door seals and blocked vents.
Sectioning problems
Thick-and-thin sections, chatter, Venetian-blind lines, sections that roll or crumble. These are often mechanical: worn springs, a loose blade holder or clamp, a damaged anti-roll plate, or play in the feed mechanism. Blade condition and technique play a part too.
Keeping a cryostat cutting well
- Clean and disinfect the chamber after every surgical day, and remove trimmings
- Defrost on the schedule your model calls for
- Keep the condenser and vents clear of dust
- Book preventive maintenance at least once a year, more often for busy Mohs labs
- Write down symptoms when they start, so the technician knows what to look at
Our cryostat repair and service covers Leica, Thermo/Epredia and Avantik units, with loaners from our Miami shop. Preventive maintenance is available starting from $600 per cryostat, or starting from $50 a month on the Cryostat Care Plan. If your cryostat is already down, read how to minimize Mohs lab downtime.