Microwave Tissue Processing
From Donna Willis, Harris Methodist Hospital, Ft. Worth, Texas
To provide rapid tissue processing that will decrease turn-around-time.
Microwave exposure is used to dehydrate, clear and impregnate tissue
samples. Fixation of tissue samples is achieved prior to processing
in the microwave oven. processing schedules are developed using tissue
thickness as a determining factor. Dehydration is accomplished using
Ethyl Alcohol. Isopropanol is substituted for xylene as a clearing
agent. The isopropanol is "boiled out" of the tissue during
the impregnation process by heating paraffin above the boiling point
- Commercial Microwave operating at approx. 600 watts.
- Paraffin pot. Temperature set at 84°C.
This instrument is used to recycle paraffin.
- Paraffin pot. Temperature set at 60°C.
Follow departmental Microwave Tissue processing Quality Assurance
- Ethyl Alcohol:
Safety Data: Health hazards of Flammable
and Irritant should be considered when using this chemical. NFPA
rating of 2,3,0 should be followed. Target organs are nerves
and liver. Personal Protective Equipment to be used: impervious
lab coat, gloves, eye protection, respiratory protection if exposure
is above threshold limits. First Aid procedures: Swallowing:
If victim is conscious and able to swallow, have victim drink
water or milk to dilute. Never give anything by mouth if victim
is unconscious or having convulsions. CALL A PHYSICIAN OR CONTROL
CENTER IMMEDIATELY. Induce vomiting only if advised by physician
or Poison Control Center. Inhalation: Immediately remove victim
to fresh air. If victim has stopped breathing, give artifical
respiration, preferable mouth-to-mouth. GET MEDICAL ATTENTION
IMMEDIATELY. Contact with eyes or skin: Immediately flush affected
area with plenty of cool water. Eyes should be flushed for at
least 15 minutes. Remove and wash contaminated clothing before
reuse. GET MEDICAL ATTENTION IMMEDIATELY. All splashes to the
eyes must be reported to Employee Health. Disposal: Do not flush
to drain. Distill and reuse or collect and dispose at an approved
hazardous waste site.
- Isopropanol: Purchased from Allegience Scientific Products.
Safety Data: Health hazards of Flammable,
Teratogen, Irritant should be considered when using this chemical.
NFPA rating of 22.214.171.124 should be followed. Target organs are
eyes, nose, throat, skin, CNS, respiratory tract and GI tract.
Personal Protective Equipment to be used: lab coat, gloves, eye
protection. First Aid procedures- Inhalation: Remove from exposure
area to fresh air immediately. If breathing has stopped, give
artificial respiration. If breathing is difficult give oxygen.
Get medical attention immediately. Eye Contact: Flush eyes immediately
with large amounts of water, occasionally lifting upper and lower
lids for at least 15-20 minutes. If irritation persists, seek
medical attention. All splashes to the eyes must be reported
to Employee Health. Skin Contact: Remove contaminated clothing
and shoes immediately. Wash effected area with soap and mild
detergent and large amounts of water. If irritation persists,
seek medical attention. Ingestion: If swallowed, induce vomiting
by giving two glasses of water and sticking fingers down throat.
Keep victims head lower than hips to prevent aspiration into
lungs. Never give anything by mouth to an unconscious person.
Call a physician immediately. Disposal: Do not flush to drain.
Collect and dispose at an approved hazardous waste site.
Safety Data: Health hazards: Under
normal working conditions, the use of this product is deemed
non-hazardous. According to OSHA, paraffin fume may be considered
to be hazardous if the workplace airborne concentration exceeds
2mg/m3. Skin Contact: Exposure to hot product may cause thermal
burns. Eye contact: Exposure to hot products may cause thermal
burns.. Ingestion: If large quantities are consumed, nausea and
vomiting may occur. NFPA rating of 0,1,0 should be considered
when using this product. Personal Protective Equipment: Ventilation;
Provide general ventilation to insure fume concentrations do
no exceed 3mg/m3. Gloves: Use protective gloves when handling
hot material. Eye Protection: Safety glasses should be worn as
good laboratory practices. First Aid: Inhalation: Remove from
exposure area to fresh air immediately. If breathing has stopped,
give artificial respiration. If breathing is difficult, give
oxygen. Get medical attention immediately. Skin Contact: In case
of skin contact with product under normal conditions, wash thoroughly
with mild detergent and large amounts of water. Immediately contact
a physician for treatment to thermal burns. Eye Contact: If hot
product is splashed into eyes, flush immediately with clear water
and contact a physician. Ingestion: If very large amounts are
swallowed seek medical advice. Disposal: Ensure compliance with
local, state and federal regulations.
Microwave Biopsy (1mm thick) procedure (process time 45 minutes
- Tissue samples are placed in plastic prelabeled cassettes and
allowed a fixation time of 30 minutes for fresh tissue. (Most samples
are fixed adequately upon receipt.) Fresh samples should be placed
on a rotomixer agitator to enhance fixation.
- Rinse cassettes with water to eliminate the possibility of a
salt precipitation when the cassettes are placed in the Ethyl Alcohol.
- Place cassettes into the Teflon
processing rack. 20 cassettes will fit in 1 rack leaving the top
level empty to allow for evaporation.
80 cassettes can be processed at a time using 4 racks and 4 plastic
processing containers. (If you are processing less than 8 cassettes
you should place at least 8 empty cassettes in the bottom of
the rack. This will regulate the temperature and ensure proper
- Place processing rack in plastic container and fill
with 100% Ethyl Alcohol to rinse off water. Discard alcohol and
400 mL. of fresh 100% Ethyl Alcohol.
- Place the plastic container in the microwave oven and place
the temperature probe centrally into the container. Make sure the
probe does not touch the cassettes.
- When starting the microwave follow these steps:
- Depress the power switch and observe that after a brief
period, during which the vent system comes up to speed, the
stop switch indicator extinguishes.
- Depress the lamp switch and observe that the chamber light
- The turntable is not used therefore the switch should
not be depressed.
- The airflow bubblier is not used therefore the switch
should not be depressed
- Set the timer select pushbutton to the minutes selection.
- Set the time-at temperature mode using the timer mode
- Set the time pause position (out) of timer/door button.
- Microwave at a temperature of 67°C.
for 5 minutes.
- Take the plastic container and processing rack from the microwave
and remove the rack from the container draining the rack on a paper
towel. Dump the Ethyl Alcohol.
- Place the processing rack back into the plastic container and
fill with Isopropyl Alcohol.
- Place the plastic container in the microwave.
Add the temperature probe centrally into the bath and microwave
at a temperature of
74°C. for 3 minutes.
- Remove the plastic container and rack from
the microwave. Place the processing rack into an empty container
and fill with paraffin
that is at a temperature setting of 60°C. Agitate the rack
so that the excess Isopropanol will mix with the Paraffin. Pour
this paraffin into a paraffin pot that is at a temperature of 84°C.
Refill the container with fresh Paraffin that is 60°C.
- Place the container in the microwave. Add
the temperature probe centrally into the bath and microwave at
a temperature of 65°C.
for 2 minutes.
- Open the microwave door and agitate the
rack several times to ensure temperature consistency. Adjust
the temperature setting
to 80°C. for 5 minutes.
- Remove the container from the microwave
and dump paraffin into the paraffin pot that is set at a temperature
- Remove the processing rack from the plastic container and place
cassettes at embedding center.
- Place processing rack into xylene to remove excess paraffin.
Both plastic containers can be reused for the next run.
- The microwave must be vented just like a chemical fume hood.
Do not vent to regular return air vents.
- Cassettes should be equally distributed in cassette rack.
- When processing less than 8 cassettes use a minimum of 8 empty
cassettes on the bottom of the rack to regulate temperature.
H2800 Microwave processor User's Manual.