Studying the performance of bifurcate cryoprobes based on shape factor of cryoablative zones

Conventional cryosurgical process employs extremely low temperatures to kill tumor cells within a closely defined region. However, its efficacy can be markedly compromised if the same treatment method is administrated for highly irregularly shaped tumors. Inadequate controls of freezing may induce tumor recurrence or undesirable over-freezing of surrounding healthy tissue. To address the cryosurgical complexity of irregularly shaped tumors, an analytical treatment on irregularly-shaped tumors has been performed and the degree of tumor irregularities is quantified. A novel cryoprobe coined the bifurcate cryoprobe with the capability to generate irregularly shaped cryo-lesions is proposed. The bifurcate cryoprobe, incorporating shape memory alloy functionality, enables the cryoprobe to regulate its physical configuration. To evaluate the probe’s performance, a bioheat transfer model has been developed and validated with in vitro data. We compared the ablative cryo-lesions induced by different bifurcate cryoprobes with those produced by conventional cryoprobes. Key results have indicated that the proposed bifurcate cryoprobes were able to significantly promote targeted tissue destruction while catering to the shape profiles of solid tumors. This study forms an on-going framework to provide clinicians with alternative versatile devices for the treatment of complex tumors.     

Comparison of iceball diameter and temperature distribution achieved with 3-mm accuprobe cryoprobes in porcine and human liver tissue and human colorectal liver metastases in vitro

We aimed to assess the thermal profile and size of iceballs produced by Accuprobe cryoprobes in fresh porcine and human liver and human colorectal cancer liver metastases in vitro to allow better planning of cryosurgical treatment of liver metastases. Iceballs were produced by a 20-min single freeze cycle using 8-mm cryoprobes in pig liver in a waterbath at 37 degrees C (n = 8) and 3-mm cryoprobes in pig liver (n = 8), human liver (n = 3), and human colorectal cancer liver metastases (n = 8). The iceball diameters and the temperatures at different distances from the cryoprobe were measured. Mean iceball diameters produced by 8-mm cryoprobes in pig liver were 56.3 mm and varied from 38.7 to 39.6 mm for 3-mm cryoprobes in the different tissues used. There was no significant difference in iceball size in the different tissues. The diameter of the zone of -40 degrees C or less was approximately 44 mm using 8-mm cryoprobes in porcine liver and between 27 and 31 mm using 3-mm cryoprobes in the different tissues examined. The results may allow better preoperative planning of the cryosurgical treatment of liver metastases with Accuprobe cryoprobes.     

Computerized planning of prostate cryosurgery using variable cryoprobe insertion depth

The current study presents a computerized planning scheme for prostate cryosurgery using a variable insertion depth strategy. This study is a part of an ongoing effort to develop computerized tools for cryosurgery. Based on typical clinical practices, previous automated planning schemes have required that all cryoprobes be aligned at a single insertion depth. The current study investigates the benefit of removing this constraint, in comparison with results based on uniform insertion depth planning as well as the so-called “pullback procedure”. Planning is based on the so-called “bubble-packing method”, and its quality is evaluated with bioheat transfer simulations. This study is based on five 3D prostate models, reconstructed from ultrasound imaging, and cryoprobe active length in the range of 15-35 mm. The variable insertion depth technique is found to consistently provide superior results when compared to the other placement methods. Furthermore, it is shown that both the optimal active length and the optimal number of cryoprobes vary among prostate models, based on the size and shape of the target region. Due to its low computational cost, the new scheme can be used to determine the optimal cryoprobe layout for a given prostate model in real time.     

24-gauge ultrafine cryoprobe with diameter of 550 μm and its cooling performance

This paper describes the development of a novel cryoprobe with the same size as a 24-gauge injection needle and the evaluation of its cooling performance. This ultrafine cryoprobe was designed to reduce the invasiveness and extend application areas of cryosurgery. The ultrafine cryoprobe has a double-tube structure and consists of two stainless steel microtubes. The outer diameter of the cryoprobe is 550 μm, and the inner tube has a 70-μm inner diameter to depressurize the high-pressure refrigerant. By solving the bioheat transfer equation and considering freezing phenomena, the relationship between the size of the frozen region and the heat transfer coefficient of the refrigerant flow in an ultrafine cryoprobe was derived analytically. The results showed that the size of the frozen region is strongly affected by the heat transfer coefficient. A high heat transfer coefficient such as that of phase change heat transfer is required to generate a frozen region of sufficient size. In the experiment, trifluoromethane (HFC-23) was used as the refrigerant, and the cooling effects of the gas and liquid phase states at the inlet were evaluated. When the ultrafine cryoprobe was cooled using a liquid refrigerant, the surface temperature was approximately −50 °C, and the temperature distribution on the surface was uniform for a thermally insulated condition. However, for the case with vaporized refrigerant, the temperature distribution was not uniform. Therefore, it was concluded that the cooling mechanism using liquid refrigerant was suitable for ultrafine cryoprobes. Furthermore, to simulate cryosurgery, a cooling experiment using hydrogel was conducted. The results showed that the surface temperature of the ultrafine cryoprobe reached −35 °C and formed a frozen region with a radius of 4 mm in 4 min. These results indicate that the ultrafine cryoprobe can be applied in actual cryosurgeries for small affected areas.     

Advances in the design of special cryosurgical apparatus in China

Advances in the design of special cryobiomedical apparatus and a review of the trend of developments in the field of cryosurgery in China are discussed. The typical structure of two special cryoprobes for treatment deep in the body and the technology of designing these probes are presented in detail. Some cases which are treated successfully with the above cryoprobes will also be discussed. The experimental aspects of heat transfer in frozen tissue and of the temperature profiles both of a human brain during surgery and of the cryoprobe are described. Other improvements in the field of cryosurgical devices, e.g., four main ways of attaching freezing tips to cryoprobes during surgery and an LN2 transfer tube with high dexterity are also presented. Finally, the development of commercial cryosurgical apparatus in China is also discussed.     

Computerized planning for multiprobe cryosurgery using a force-field analogy

Cryosurgery is the destruction of undesired biological tissues by freezing. For internal organs, multiple cryoprobes are inserted into the tissue with the goal of maximizing cryoinjury within a predefined target region, while minimizing cryoinjury to the surrounding tissues. The objective of this study is to develop a computerized planning tool to determine the best locations to insert the cryoprobes, based on bioheat transfer simulations. This tool is general and suitable for all available cooling techniques and hardware. The planning procedure employs a novel iterative optimization technique based on a force-field analogy. In each iteration, a single transient bioheat transfer simulation of the cryoprocedure is computed. At the end of the simulation, regions of tissue that would have undesired temperatures apply "forces" to the cryoprobes directly moving them to better locations. This method is more efficient than traditional numerical optimization techniques, because it requires significantly fewer bioheat transfer simulations for each iteration of planning. For demonstration purposes, 2D examples on cross sections typical of prostate cryosurgery are given.     

Development and estimation of a novel cryoprobe utilizing the Peltier effect for precise and safe cryosurgery

We have developed a novel cryoprobe for skin cryosurgery utilizing the Peltier effect. The four most important parameters for necrotizing tissue efficiently are the cooling rate, end temperature, hold time and thawing rate. In cryosurgery for small skin diseases such as flecks or early carcinoma, it is also important to control the thickness of the frozen region precisely to prevent necrotizing healthy tissue. To satisfy these exacting conditions, we have developed a novel cryoprobe to which a Peltier module was attached. The cryoprobe makes it possible to control heat transfer to skin surface precisely using a proportional-integral-derivative (PID) controller, and because it uses the Peltier effect, the cryoprobe does not need to move during the operation. We also developed a numerical simulation method that allows us to predict the frozen region and the temperature profile during cryosurgery.We tested the performance of our Peltier cryoprobe by cooling agar, and the results show that the cryoprobe has sufficient cooling performance for cryosurgery, because it can apply a cooling rate of more than 250 °C/min until the temperature reaches −40 °C. We also used a numerical simulation to reconstruct the supercooling phenomenon and examine the immediate progress of the frozen region with ice nucleation. The calculated frozen region was compared with the experimentally measured frozen region observed by an interferometer, and the calculation results showed good agreement. The results of numerical simulation confirmed that the frozen region could be predicted accurately with a margin of error as small as 150 μm during use of the cryoprobe in cryosurgery. The numerical simulation also showed that the cryoprobe can control freezing to a depth as shallow as 300 μm.     

Cryosurgery planning using bubble packing in 3D

As part of an ongoing project to develop automated tools for cryosurgery planning, the current study focuses on the development of a 3D bubble packing method. A proof-of-concept for the new method is demonstrated on five prostate models, reconstructed from ultrasound images. The new method is a modification of an established method in 2D. Ellipsoidal bubbles are packed in the volume of the prostate in the current study; such bubbles can be viewed as a first-order approximation of a frozen region around a single cryoprobe. When all cryoprobes are inserted to the same depth, optimum planning was found to occur at about 60% of the length of the prostate (measured from its apex), which leads to cooling of approximately 75% of the prostate volume below a specific temperature threshold of - 22 degrees C. Bubble packing has the potential to dramatically reduce the run time for automated planning.     

A helium gas probe for use in cryosurgery

The design and testing of a prototype cryosurgical probe utilizing helium gas precooled with liquid nitrogen are described. An 8-mm-diameter probe produced an ice ball with a diameter of 28 mm after 10 min freezing using a helium gas flow rate of 42 liter/min. This indicated a surface heat transfer coefficient of 0.34 W/cm² °K and temperature of ?138 °C at the probe tip. Improved performance figures can be achieved using higher gas pressures and flow rates. A helium gas flow system schematic for use with this new type of cryoprobe is also presented. It is claimed that this system will overcome the problems of developing both multiple-tipped probes and small-diameter needle probes for use in cryoanalgesia.     

A Comparative Laboratory Study of Liquid Nitrogen and Argon Gas Cryosurgery Systems

Cryotherapy can now be applied using a variety of delivery systems and cryogens. We compared the Cryotech LCS 3000 liquid nitrogen system (Spembly, Andover, UK) with the CRYOcare argon gas-based system (Irvine, CA, U.S.A.) using three different 3-mm cryoprobes: anoldliquid nitrogen probe (N-probe), anewN-probe featuring gas bypass and an argon gas probe. Each probe was tested in two models: (i) fresh sheep liver at 20°C—the probe was inserted to a depth of 1.5 cm; the rate of ice ball formation was monitored by recording radial temperatures every 15 s at 5, 10, 15, and 20 mm from the cryoprobe, and the ice-ball diameter was measured every 2.5 min. After 10 min, the probe was warmed and the time taken until it could be extracted from the liver was recorded. (ii) Warm water bath—the probe was immersed in warm water (42°C) for 15 min and the ice-ball diameter was measured at 5-min intervals. Radial temperatures in liver declined more rapidly (P< 0.001) and time to probe extraction was less (P< 0.01) when the argon gas system was used. ThenewN-probe performed better than its older counterpart, but was still slower than the argon gas system. In liver (20°C), ice-ball diameters were similar after 10 min, but in warm water, they were larger when thenewN-probe was used (P< 0.02). It would appear that the argon gas system is initially faster, but it does not achieve as large an ice ball in a warm environment as the liquid nitrogen system.     

Magnetic resonance study of freezing damage development in rat liver tissue.

Cryolesions were produced by contact cryoprobes on male Wistar rat livers. The development of freezing damage was followed in vivo for 24 hr by morphological examinations, proton spin lattice relaxation times T₁, and paramagnetic center concentration measurements. Significant proton T₁ increase, related to an increased tissue water content, as well as a concentration decrease of the paramagnetic centers, was observed for the cryolesion, as compared to the undamaged liver tissue of the same animal. The concentration decrease was observed for the g = 2.00 free radicals and g = 1.94 reduced state iron protein centers, specified by the parameter g indicating the position of their absorption lines in the electron paramagnetic resonance spectrum.It was also found that the rate of damage development following a single freezethaw cycle depends significantly on the cooling capacity of the cryoprobe. The final changes produced by 6- and 4-mm-diameter liquid nitrogen-cooled cryotips are comparable, but the development of damage was different.     

Two-phase computerized planning of cryosurgery using bubble-packing and force-field analogy

BACKGROUND: Cryosurgery is the destruction of undesired tissues by freezing, as in prostate cryosurgery, for example. Minimally invasive cryosurgery is currently performed by means of an array of cryoprobes, each in the shape of a long hypodermic needle. The optimal arrangement of the cryoprobes, which is known to have a dramatic effect on the quality of the cryoprocedure, remains an art held by the cryosurgeon, based on the cryosurgeon's experience and "rules of thumb." An automated computerized technique for cryosurgery planning is the subject matter of the current paper, in an effort to improve the quality of cryosurgery. METHOD OF APPROACH: A two-phase optimization method is proposed for this purpose, based on two previous and independent developments by this research team. Phase I is based on a bubble-packing method, previously used as an efficient method for finite element meshing. Phase II is based on a force-field analogy method, which has proven to be robust at the expense of a typically long runtime. RESULTS: As a proof-of-concept, results are demonstrated on a two-dimensional case of a prostate cross section. The major contribution of this study is to affirm that in many instances cryosurgery planning can be performed without extremely expensive simulations of bioheat transfer, achieved in Phase I. CONCLUSIONS: This new method of planning has proven to reduce planning runtime from hours to minutes, making automated planning practical in a clinical time frame.     

Controlled freezing of nonideal solutions with application to cryosurgical processes.

Success of a cryosurgical procedure, i.e., maximal cell destruction, requires that the cooling rate be controlled during the freezing process. Standard cryosurgical devices are not usually designed to perform the required controlled process. In this study, a new cryosurgical device was developed which facilitates the achievement of a specified cooling rate during freezing by accurately controlling the probe temperature variation with time. The new device has been experimentally tested by applying it to an aqueous solution of mashed potatoes. The temperature field in the freezing medium, whose thermal properties are similar to those of biological tissue, was measured. The cryoprobe temperature was controlled according to a desired time varying profile which was assumed to maximize necrosis. The tracking accuracy and the stability of the closed loop control system were investigated. It was found that for most of the time the tracking accuracy was excellent and the error between the measured probe temperature and the desired set point is within +/- 0.4 degrees C. However, noticeable deviations from the set point occurred due to the supercooling phenomenon or due to the instability of the liquid nitrogen boiling regime in the cryoprobe. The experimental results were compared to those obtained by a finite elements program and very good agreement was obtained. The deviation between the two data sets seems to be mainly due to errors in positioning of the thermocouple junctions in the medium.     

Dielectric changes in hyaluronate solutions at microwave frequencies as a function of concentration,system pH,and temperature

The dielectric response of human umbilical cord hyaluronic acid in various environments has been studied at microwave frquencies using a resonant microwave cavity as a probe. Both the real and imaginary parts of complex dielectric constant and the loss tangent for hyaluronate solutions are obtained by utilizing equations for perturbation of a resonant cavity. Dielectric changes at room temperature have been observed in aqueous solutions of hyaluronic acid as a function of concentration ranging from 0 to 350 mg/ml. The data indicate the existence of ordered phases in hyaluronate solutions at selective concentrations, that is, exhibiting lyotropic-type transitions. Hyaluronate solutions at 1.5 and 3 mg/ml concentrations have been studied at various pH in the range of 6–8 and at constant ionic strength 0.1. A temperature-dependent transition in hyaluronate solution of 120 mg/ml concentration has been observed at physiological temperature. It is shown that this temperature-dependent behavior can be related to the orientational polarizability term in the Debye theory of polar molecules in liquids.     

Analysis of thermal stress in cryosurgery of kidneys

In this study, the thermal stress distribution in cryosurgery of kidney was investigated using a multiphysics finite element model developed in ANSYS (V8.1). The thermal portion of the model was verified using experimental data and the mechanics portion of the model (elastic) was verified using classic analytical solutions. Temperature dependent thermal and mechanical properties were used in the model. Moreover, the model accounts for thermal expansion due to both thermal expansion in single phase and volumetric expansion associated with phase change of tissue water to ice. For a clinical cylindrical cryoprobe inserted into the renal cortex from the top-middle renal capsule, it was found that the thermal stress distributions along the radial position are very different at different depths from the top renal capsule. The thermal stress is much higher at both ends than in the middle of the cryoprobe surface. It was found that there might be more tissue next to the top renal capsule than other region undergoing microcrack formation or plastic deformation. Furthermore, it was found that macrocrack formation is more likely to occur in tissue adjacent to the cryoprobe surface (especially on the sharp point tip) and during the thawing phase of cryosurgery. It was further found that the volumetric expansion associated with phase change induced much higher thermal stress than thermal expansion in a single phase and might therefore be the main cause of the frequently observed crack formation shortly after initiation of thawing in cryosurgery. Because the thermal stress adjacent to the cryoprobe is much higher than the yield stress of frozen renal tissue, a plastic stress model is required for better modeling of the thermal stress distribution in cryosurgery of kidney in future. However the computational effort will then be drastically increased due to the strong nonlinear nature of the plastic model and more experimental studies are indispensable for better understanding of the mechanical behavior of frozen tissue in cryosurgery.     

Improved pain relief after thoracotomy: use of cryoprobe and morphine infusion.

In a randomised controlled trial carried out during the first to days after thoracotomy patients who had had intercostal nerves frozen with a cryoprobe or were given morphine by continuous intravenous infusion had significant less pain at rest than patients given intramuscular morphine. Differences between the groups with respect to pain on movement and during physiotherapy were not significant. Pain was estimated using visual analogue scales, and an arc sine transformation was carried out on values obtained from these scales before comparison using an analysis of variance. The trial did not distinguish between the cryoprobe and infusion treatment. The simplicity of the cryoprobe had much to commend it, but in units without access to this equipment a small infusion pump offers a satisfactory alternative.     

Empirical validation of the S-Score algorithm in the analysis of gene expression data

Background

Current methods of analyzing Affymetrix GeneChip^® microarray data require the estimation of probe set expression summaries, followed by application of statistical tests to determine which genes are differentially expressed. The S-Score algorithm described by Zhang and colleagues is an alternative method that allows tests of hypotheses directly from probe level data. It is based on an error model in which the detected signal is proportional to the probe pair signal for highly expressed genes, but approaches a background level (rather than 0) for genes with low levels of expression. This model is used to calculate relative change in probe pair intensities that converts probe signals into multiple measurements with equalized errors, which are summed over a probe set to form the S-Score. Assuming no expression differences between chips, the S-Score follows a standard normal distribution, allowing direct tests of hypotheses to be made. Using spike-in and dilution datasets, we validated the S-Score method against comparisons of gene expression utilizing the more recently developed methods RMA, dChip, and MAS5.

Results

The S-score showed excellent sensitivity and specificity in detecting low-level gene expression changes. Rank ordering of S-Score values more accurately reflected known fold-change values compared to other algorithms.

Conclusion

The S-score method, utilizing probe level data directly, offers significant advantages over comparisons using only probe set expression summaries.     

Freezing by a flat, circular surface cryoprobe of a tissue phantom with an embedded cylindrical heat source simulating a blood vessel

The effects of a thermally-significant blood vessel, simulated by an embedded acrylic tube, 4.8 mm outer diameter on the freezing field caused by a surface cryoprobe were studied experimentally in a tissue phantom. The flat, 15 mm diameter, circular cryoprobe was operated at a constant cooling rate of -8 degrees C/min by liquid nitrogen down to -60 degrees C. Water flow rates of 30 and 100 ml/min, at a constant temperature of 32.5 degrees C, were maintained in the embedded tube. The latter flow rate is typical to the lower range of blood flows in large arteries in the human body. The phase changing medium (PCM) used was a 30/70% by volume mashed potatoes flakes-water solution. Temperature measurements inside the PCM were performed in one plane perpendicular to the embedded tube, relative to which the cryoprobe was placed at 5 locations in separate experiments. This novel experimental method reduced the perturbation caused by the thermocouple junctions while facilitating rather detailed measurements of the temperature fields developing in the PCM. Results show the development of two hump-like formations on either side of the embedded tube. Freezing was retarded in the region away from the surface cryoprobe and under the tube. This accentuated the dominance of the axial effects, due to the embedded tube, over the radial ones due to the cryoprobe. Results of this study should be considered in designing protocols of cryosurgical procedures performed in the vicinity of thermally-significant blood vessels.     

Viscoelasticity of F-actin measured with magnetic microparticles

Dispersed submicroscopic magnetic particles were used to probe viscoelasticity for cytoplasm and purified components of cytoplasm. An externally applied magnetic field exerted force on particles in cells, in filamentous actin (F-actin) solutions, or in F-actin gels formed by the addition of the actin gelation factor, actin-binding protein (ABP). The particle response to magnetic torque can be related to the viscoelastic properties of the fluids. We compared data obtained on F-actin by the magnetic particle method with data obtained on F-actin by means of a sliding plane viscoelastometer. F-actin solutions had a significant elasticity, which increased by 20-fold when gels were formed by ABP addition. Both methods gave consistent results, but the dispersed magnetic particles indicated quantitatively greater rigidity than the viscoelastometer (two and six times greater for F-actin solutions and for F-actin plus ABP gels, respectively). These differences may be due to the fact that, compared with traditional microrheometers, dispersed particle measurements are less affected by long-range heterogeneity or domain-like structure. The magnetometric method was used to examine the mechanical properties of cytoplasm within intact macrophages; the application of the same magnetometric technique to both cells and well-defined, purified protein systems is a first step toward interpreting the results obtained for living cells in molecular terms. The magnetic particle probe system is an effective nonoptical technique for determining the motile and mechanical properties of cells in vitro and in vivo.     

Numerical simulation of selective freezing of target biological tissues following injection of solutions with specific thermal properties

Recently, we proposed a method for controlling the extent of freezing during cryosurgery by percutaneously injecting some solutions with particular thermal properties into the target tissues. In order to better understand the mechanism of the enhancement of freezing by these injections, a new numerical algorithm was developed to simulate the corresponding heat transfer process that is involved. The three-dimensional phase change processes in biological tissues subjected to cryoprobe freezing, with or without injection, were compared numerically. Two specific cases were investigated to illustrate the selective freezing method: the injection of solutions with high thermal conductivity; the injection of solutions with low latent heat. It was found that the localized injection of such solutions could significantly enhance the freezing effect and decrease the lowest temperature in the target tissues. The result also suggests that the injection of these solutions may be a feasible and flexible way to control the size of the ice ball and its direction of growth during cryosurgery, which will help to optimize the treatment process.