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Caution: Federal law restricts this device to sale by or on the order of a physician or a practitioner trained and certified in its use. Assisted Hatchling, Embryo Biopsy and PGD are not recommended for routine use in all IVF patients. Please Note: For animal research and human stem cell applications, the XYClone® should be used.
ZILOS-tk® and Embryo Safety
Isotherm Rings (Patent Issued July 4, 2006) help the user prevent potential harmful effects on blastomeres adjacent to the zona due to heat from the laser drilling.
The Isotherm Rings appear on the screen as a series of six concentric circles of varying colors (left) and indicate the maximum temperature reached at the ring diameter at various laser pulse durations (right). At longer pulse duration, it is apparent that temperatures radiate farther into the center of the embryo, increasing the likelihood of blastomere damage. The orange ring (second from center) is also a useful indicator of the drill hole size at the selected pulse duration.
With this interactive Isotherm Rings feature, a user can now "see" the heating and drill hole size and eliminate the temperature "guesswork."
The heat conduction into the embryo, as shown by the Isotherm Rings, is based on published scientific algorithms that are built into the software. For increased embryo safety, the Isotherm Rings are hardwired and their specifications cannot be altered or deleted by users. With the Isotherm Rings you can be confident that what you see is accurate and determined according to scientific definitions, not by individual preference.
Compare the degree of heat penetration versus the drill hole size (orange ring) in the following animation that shows the degree of heat radiation at varying pulse durations.
Note how the heat penetrates further into the embryo as the pulse length increases. So even if the actual drill hole (orange ring) does not come close to the blastomeres, the blastomeres are exposed to the heat generated by the laser beam at longer pulse lengths. By using the Isotherm Rings feature of the ZILOS-tk, you can "see" the heat conduction prior to treatment and adjust the pulse length and embryo positioning accordingly.
Calculation of the heat diffusion was based on the assumption that the zona pellucida thermal conductivity is close to that of water. Since the zona pellucida is composed of approximately 80% water, this was most likely a very good assumption. In fact, this assumption was even on the conservative side, since the presence of proteins would lessen the conductivity and the resultant rings would even be smaller.
To predict the maximum temperatures reached near the laser beam during the laser pulse, the heat diffusion equation was used. Limits on these temperatures were measured experimentally in water (based on the reasoning above), confirming the calculations. (An explanation of the heat diffusion equation can be found at scienceworld.wolfram.com.)
For detailed information on the ZILOS-tk laser calculations, please see:
Lasers produce light beams of varying intensity, and are categorized in accordance with the emitted power. Class 1 represents the lowest intensity and safest laser, and the power gets progressively higher with increasing potential of harmful effects through Class 2, Class 3A, 3B and Class 4.
Class 1 includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any exposure conditions inherent in the design of the laser product. Many lasers in this class are lasers which are imbedded in an enclosure that prohibits or limits access to the laser radiation. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure. These lasers are exempt from most control measures.
For more information on thermal effects of laser hatching on embryos, download the ZILOS-tk Technical Update entitled: Focus on Heat Diffusion and Embryo Safety During Laser-Assisted Zona Dissection (PDF file, ~ 1.3 MB). (Please note that this document references older versions of lasers.)