Microwave tissue processing explained

Histopathology is a branch of pathology which deals with the study of disease in a tissue section. The tissue undergoes a series of steps before it reaches the pathologist’s desk to be thoroughly examined microscopically to arrive at a particular diagnosis. One of the most crucial steps within this process is tissue processing.

Tissue processing is the procedure by which fixed tissues are made suitable for embedding within a supportive medium such as paraffin, and consists of three consecutive steps: dehydration, clearing, and infiltration. In most clinical and research settings, tissue processing is accomplished by using an automated tissue processor, with or without microwave-assistance. To ensure high-quality results, processing protocols are tailored to tissue size and composition by modifying variables such as reagents used and the timing of the various steps.

Conventional tissue processing is an established 100-year-old technique and remains the gold standard against which all new technologies and methods should be assessed. Conventional tissue processing is as old as 100 years and remains the gold standard against which all new technologies and methods need to be assessed. However, the changing situation caused by modernisation in the field of medical technology has led to the replacement of traditional techniques by newer ones, such as microwave tissue processing.

During the various steps within the tissue processing procedure, heat is required. In conventional tissue processors, this heat is created by means of heating mantles situated around the processing chambers. This results in 12-14 hours of processing time.

With microwave tissue processors, also known as hybrid processors, heat is created by means of heating mantles as well as microwaves. This results in a significant reduction in processing times, with improved homogeneity and efficiency.

A microwave is an electromagnetic non-ionizing wave with a frequency (300 MHz to 300 GHz) and wavelength that can be found about halfway between a radio wave and visible light in the electromagnetic spectrum.

The first Microwave technique was applied in the processing of tissues in 1985 by Kok and Boon from the Netherlands and Anthony Leong from Australia. It was in the 1990’s that the first microwave histoprocessor was released to the world by Milestone technology.

Microwaves can cause the rotation of polar or charged molecules, whilst non-polar molecules will not be affected. When negative charges are brought near an electromagnetic (microwave) field, there is repulsion as they are ‘like’ charges, causing the molecules to rotate due to their asymmetrical orientation. They rotate rapidly through 180° at the rate of 2.45 billion cycles per second. This rotational movement produces heat. As the molecules collide, they absorb the microwaves and convert the energy into kinetic and thermal energy.

Rebuttals to these misconceptions include the following:

• Microwaves enter the processing chamber up to 3.5cm, never touching the tissue directly. The effect of the microwaves occurs merely within the reagent, resulting in a decrease of viscosity, allowing the reagents to penetrate the tissues much faster. There is not nearly enough energy during this process to break molecular bonds, therefore tissue processed in a hybrid tissue processor is suitable for immunohistochemistry and molecular analyses.
• Fatty/bloody/difficult samples have to be processed in accordance with the thickness of the tissue, or one parameter above the specimen’s thickness. Overnight protocols are also available for such difficult samples

What are the differences between Microwave and Conventional histoprocessing?

• Fixation is achieved much faster in microwave histoprocessing.
• Dehydration is achieved in one step in microwave histoprocessing, instead of the 2 to 6 steps used in conventional procedures.
• Isopropanol can be used as intermedium between alcohols and wax in microwave histoprocessing, which means it is a completely XYLENE FREE process. Xylene is non-polar and will therefore not react to the microwaves. Xylene is also classified as a toxic carcinogen.
• The impregnation paraffin can be re-used in microwave histoprocessing. In conventional processing Xylene chemically binds to the paraffin wax, resulting in complete replacement of the wax every 3-5 cycles. In microwave processing, Isopropanol does not bind to the wax, which means it can be removed from the wax at a certain temperature and pressure. The paraffin wax therefore has to be cleaned every 5 cycles but replaced every 30 days.

What are the main advantages of Microwave histoprocessing?

• Improved processing turnaround times resulting in same-day-processing. The below table depicts the fastest processing times for tissue processors currently on the market, for all tissue types:

*All times include fixation and reagent pumping in/out. Protocols can last a few more minutes if loaded at full capacity.
Batch up to 210 biospecimens with 5 Lt. container.
**(i.e. small biopsies like GI/Endoscopic)

• Rapid histopathologic diagnosis
• Improved end-user and environmental safety
• Increased specimen throughput
• Increased productivity
• Increased patient safety

Overall advantages for the histologist:

• Improved workload distribution
• Process tissues as required for a more even workload distribution
• Flexibility
• Process 240-600 cassettes
• Easy sectioning

For the pathologist:

• Microwave-processed slides enable the pathologist to deliver same-day diagnosis of lesions
• Same-day diagnosis will enhance the pathologist’s role in management of the cancer patient

For the lab administrator:

• Improved work environment for laboratory personnel
• Reduced cost for reagents storage and disposal

For the oncologist/clinician:

• Within hours, oncologists and clinicians can advise patients on the base of definitive diagnosis
• Treatment can be initiated immediately

For the hospital administrator:

• Reduced patient anxiety and stress by providing results within hours
• Dramatic improvements in efficiency and laboratory productivity

For the patient:

• Elimination of needless stress while waiting for a diagnosis
• More timely start of needed treatment

References:

Substantiating the microwave technique:

“An initial Experience with rapid Mw processing” E. Parkin et al
“One-day core needle biopsy in a breast clinic: 4 years experience” J.P.Bulte et al
“Microwave histoprocessing versus Conventional histoprocessing” A.M.Mathai et al
“Microwave processing in the Histology Lab” Deborah H. at Johns Hopkins
“Effect of microwave fixation and decalcification…” Marr A. et al, Pfizer

https://www.milestonemedsrl.com/tissue-processing/

Substantiating IHC and Molecular Analyses:

“Mw Heating of long term formalin fixed” Shanshui Wu et al
“Pathos Processing the Liverpool experience” E.Colgan
“Microwave Enhancement of CISH for HER-2 Oncogene” A.S.Y.Leong
“A Comparison of Immunohistochemical Stain Quality in Conventional and Rapid Microwave Processed Tissues” L.E.Lyska et al
“Initial Intermittent Microwave Irradiation…” Y.Kitayama et al
“An improved Processing Method for Breast…. Laibao Sun et al
Breast and Logos processing, in Press, C. Doglioni et al
“Validation of Histology Tissue Processing and Stain Quality of Logos…” R.J.Zarbo et al

https://www.milestonemedsrl.com/tissue-processing/

Substantiating improved turn-around times and same-day-diagnosis:

“CAP today” E.Fody
“Optimization Of Fixation And Processing Of Biopsy Gun Prostate Needle Biopsy Specimens”
“Integration of Microwave technology to reduce fixation and processing…” R.J.Zarbo et al
“Definitive histologic diagnosis on prostate biopsies in 3 hours” L.Nava et al
“The fast track biopsies” T.Ragazzini et al
“Same-Day EM-Diagnosis” J.A.Schroeder et.al

https://www.milestonemedsrl.com/tissue-processing/