Lethal isotherms of cryoablation in a phantom study: effects of heat load, probe size, and number.
OBJECTIVE
To assess the effects on the proportions of lethal ice (ie, colder than -30 degrees C) in phantoms with different heat loads created by varying the size and number of cryoprobes spaced 2 cm apart.


METHODS
Thermocouples at 0.5-, 1.0-, and 1.5-cm intervals from 1.7- or 2.4-mm-diameter cryoprobes were held by jigs accommodating a maximum of four cryoprobes. Agar phantoms (N = 24) used three sets of baseline temperatures: approximately 6 degrees C, 24 degrees C, and 39 degrees C. Temperatures during 15-minute freeze cycles were correlated with actual thermocouple locations seen within the ice by computed tomography (CT). Diameters and surface areas of the -30 degrees C lethal isotherm were assessed over time as percentages of the overall ice ball.


RESULTS
The high-heat load phantom experiments (39 degrees C) showed the greatest impact on lethal zones by percentage for all probe configurations. At 15 minutes, single-, double-, triple-, and quadruple-probe arrangements of 2.4-mm cryoprobes had average lethal ice diameters of 1.2, 3.3, 4.1, and 4.9 cm, respectively, comprising 13%, 46%, 51%, and 56% surface areas of lethal ice, respectively. Surface areas and diameters of lethal ice made by 1.7-mm cryoprobes were 71% and 84% of those made by 2.4-mm cryoprobes, respectively. Lethal ice resides less than 1 cm behind the leading edge for nearly all probe configurations and heat loads.


CONCLUSIONS
Single cryoprobes create very low percentages of lethal ice. Multiple cryoprobes overcome the high heat load of body temperature phantoms and help compensate for the lower freeze capacity of thinner cryoprobes.
Littrup
Peter J
PJ
Department of Radiology, Karmanos Cancer Institute, 721 Harper Professional Building, Detroit, MI 48201, USA. littrupp@karmanos.org
Jallad
Bassel
B
Vorugu
Vinaya
V
Littrup
Gunnar
G
Currier
Brandt
B
George
Mikhail
M
Herring
Donald
D
D040761:Biomimetic Materials; D001831:Body Temperature / Q000502:physiology*; D003198:Computer Simulation; D003452:Cryosurgery / Q000295:instrumentation*; D004735:Energy Transfer / Q000502:physiology; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008954:Models, Biological; D014781:Viscera / Q000502:physiology* / Q000601:surgery*
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