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

Improved Thermal Sensitivity Using Virtual Monochromatic Imaging Derived from Photon Counting Detector CT Data Sets: Ex Vivo Results of CT-Guided Cryoablation in Porcine Liver

PURPOSE

To investigate differences in thermal sensitivity of virtual monoenergetic imaging (VMI) series generated from photon-counting detector (PCD) CT data sets, regarding their use to improve discrimination of the ablation zone during percutaneous cryoablation.

MATERIALS AND METHODS

CT-guided cryoablation was performed using an ex vivo model of porcine liver on a PCD-CT system. The ablation zone was imaged continuously for 8 min by acquiring a CT scan every 5 s. Tissue temperature was measured using fiberoptic temperature probes placed parallel to the cryoprobe. CT-values and noise were measured at the tip of the temperature probes on each scan and on VMI series from 40 to 130 keV. Correlation of CT-values and temperature was assessed using linear regression analyses.

RESULTS

For the whole temperature range of [- 40, + 20] °C, we observed a linear correlation between CT-values and temperature in reference 70 keV images (R2 = 0.60, p < 0.001) with a thermal sensitivity of 1.4HU/°C. For the most dynamic range of [- 15, + 20] °C, the sensitivity increased to 2.4HU/°C (R2 = 0.50, p < 0.001). Using VMI reconstructions, the thermal sensitivity increased from 1.4 HU/°C at 70 keV to 1.5, 1.7 and 2.0HU/°C at 60, 50 and 40 keV, respectively (range [- 40, + 20] °C). For [- 15, + 20]°C, the thermal sensitivity increased from 2.4HU/°C at 70 keV to 2.5, 2.6 and 2.7HU/°C at 60, 50 and 40 keV, respectively. Both CT-values and noise also increased with decreasing VMI keV-levels.

CONCLUSION

During CT-guided cryoablation of porcine liver, low-keV VMI reconstructions derived from PCD-CT data sets exhibit improved thermal sensitivity being highest between + 20 and - 15 °C.

Acute Phase Response and Postprocedural Evaluation of Open and Laparoscopic Cryoablation Procedures in Porcine Pancreases

OBJECTIVES

Cryoablation is a potentially less invasive locoregional ablation modality. Although cryoablation has been used to treat malignancy in various organs, a limited application of this modality in the pancreas has been reported.

METHODS

Acute phase response assessments and postprocedural course evaluations of 2 experimental locoregional ablation methods were conducted. In one method, open and laparoscopic cryoablation of a porcine pancreas using an argon-helium gas-based cryoablation system and monitoring of tissue temperature during the procedure were performed. In the other method, open cryoablation of a porcine pancreas using liquid nitrogen was performed. The animals were evaluated postoperatively.

RESULTS

The size of the cryolesion was larger in the second treatment than in the first. Laparoscopic cryoablation was associated with the formation of an iceball, which possibly affected the surrounding structures. The ablated region was adequately cooled with 10 minutes of freeze/repeat cycles. The area cooled to a temperature of less than -40°C was approximately half the size of the cryolesion in diameter. The swine used for the evaluation of the postprocedural course survived 3 weeks after the procedure with a temporal elevation of the serum lipase level.

CONCLUSIONS

Cryoablation of the pancreas was experimentally practicable without severe complications under direct or laparoscopic vision.

Imaging findings during and after percutaneous cryoablation of hepatic tumors

OBJECTIVE

Imaging plays a key role in the assessment of patients before, during, and after percutaneous cryoablation of hepatic tumors. Intra-procedural and early post-procedure imaging with CT and MRI is vital to the assessment of technical success including adequacy of ablation zone coverage. Recognition of the normal expected post-procedure findings of hepatic cryoablation such as ice ball formation, hydrodissection, and the normal appearance of the ablation zone is crucial to be able to differentiate from complications including vascular, biliary, or non-target organ injury. Delayed imaging is essential for determination of clinical effectiveness and detection of unexpected findings such as residual unablated tumor and local tumor progression. The purpose of this article is to review the spectrum of expected and unexpected imaging findings that may occur during or after percutaneous cryoablation of hepatic tumors.

CONCLUSION

Differentiating expected from unexpected findings during and after hepatic cryoablation helps radiologists identify residual or recurrent tumor and detect procedure-related complications.

Generalized solution and estimation method for cooling performance of downscaled cryoprobe

In cryosurgery, downscaling of cryoprobes is important to minimize surgical invasion. In this study, a set of analytical solutions to the freezing phenomenon around a cryoprobe in a dimensionless form is derived and the general trend is discussed to clarify the relationship between the freezing ability of a biological tissue and the cooling power of a cryoprobe. A one-dimensional axisymmetric model in the steady-state condition is considered. The relationship between the size of the frozen region, fluid temperature in the cryoprobe, and heat transfer coefficient on the wall of the cryoprobe in the dimensional form is derived under the condition mentioned above. The fluid temperature and heat transfer coefficient are eliminated from the solutions by introducing the steady-state cryoprobe surface temperature. This transformation indicates that the steady-state surface temperature directly affects the size of the frozen region and combination of fluid temperature and heat transfer coefficient occurs, which has the same cooling effect. The derived solutions are transformed into a dimensionless form using the characteristic length of bioheat transfer and normalizing the temperature distribution in an unfrozen tissue. The applicability of these analytical solutions is evaluated by comparing them with numerical simulation results from existing studies. The dimensionless solutions describe the general trend of the relationship between the frozen region and the cooling power of a cryoprobe, which is independent of the type of organ, fluid temperature, and heat transfer coefficient. Finally, the concept of freezing limit is established using the derived solutions. The freezing limit describes the minimum requirements to freeze a tissue, and it can be used as guideline to design future downscaled cryoprobes with a suitable cooling mechanism.

Liver Tumor Cryoablation: A Commentary on the Need of Improved Procedural Monitoring

Cryoablation is a method used for in situ destruction of liver tumors not eligible for surgical resection. Local recurrences following such treatment have been reported at rates of 5–44%. Insufficient procedural monitoring of the ablation is one plausible explanation for these recurrences. The cryoablative procedure is usually monitored by ultrasonography, but acoustic shadowing and loss of signals, compromise visualisation of the cryolesion circumference. Other monitoring modalities such as computer tomography and invasive methods like the use of thermocouples and impedance measurements have also been studied, but are not in common clinical use as single monitoring modalities. Thermodynamic conditions assumed adequate for tumor eradication are likely to occur only in parts of the cryolesion. This tumoricidal part of the cryolesion is not adequately depicted using any of these modalities.

Magnetic resonance imaging (MRI) provides a clear delineation of the cryolesion circumference. Noninvasive temperature measurements assisted by MRI indicate which parts of the cryolesion that may be subject to complete necrosis. In this article MRI monitored cryoablation of liver tumors is discussed. Improved peroperative monitoring as offered by MRI may reduce the rates of local recurrences after treatment, but further technological improvements are required.

Modeling Cryotherapy Ice Ball Dimensions and Isotherms in a Novel Gel-based Model to Determine Optimal Cryo-needle Configurations and Settings for Potential Use in Clinical Practice

Objective

To gain a better understanding of ice ball dimensions and temperature isotherms relevant for cell kill when using combinations of cryo-needles we set out to answer 4 questions: (1) what type of cryo-needle? (2) how many needles? (3) best spatial configuration? and (4) correct duty cycle percentage?

Methods

We conducted laboratory experiments to monitor ice ball dimensions and create multi-needle planar isotherm maps for 17G and 10G cryo-needles using a novel multi-needle thermocouple fixture within gel at body temperature. We tested configurations of 1-4 cryo-needles at duty cycles of 20%-100% with 1-2.5 cm spacing.

Results

Analysis of various combinations shows that a central core of ≤−40°C develops at a distance of ~1 cm around the cryo-needles. Temperature increases linearly from this point to the ice ball leading edge (0°C), which is a further ≈1 cm away. Thus, the −40°C isotherm is approximately 1 cm inside the leading edge of the ice ball.

The optimum distance between cryo-needles was 1.5-2 cm, at duty cycle settings of 70%-100%. At distances further apart or with lower duty cycle settings, ice balls either had a central core >−40°C or had an hourglass shape.

Conclusion

In answer to questions 1-3, tumor length, diameter, and shape will ultimately determine the number of needles and their configuration. However, we propose a conservative distance for cryo-needle placement between 1 and 1.5 cm should be adopted for clinical practice. In answer to question 4, using low duty cycle settings runs the risk of incomplete −40°C isotherm coverage of the tumor, and thus in routine practice we suggest that settings of 70%-100% are most appropriate.

Experimental and Numerical Evaluation of Small-Scale Cryosurgery Using Ultrafine Cryoprobe

The objective of this work is to experimentally and numerically evaluate small-scale cryosurgery using an ultrafine cryoprobe. The outer diameter (OD) of the cryoprobe was 550 μm. The cooling performance of the cryoprobe was tested with a freezing experiment using hydrogel at 37 °C. As a result of 1 min of cooling, the surface temperature of the cryoprobe reached −35 °C and the radius of the frozen region was 2 mm. To evaluate the temperature distribution, a numerical simulation was conducted. The temperature distribution in the frozen region and the heat transfer coefficient was discussed.

Experimental Study on Pulmonary Cryoablation in a Porcine Model of Normal Lungs

Objective of this study is to analyze the range of necrosis after using different freezing times and freeze-thaw cycles during percutaneous cryosurgery, in order to create a suggestion for optimizing the technique for lung cryoablation. Six healthy pigs were given a CT scan and histological investigation after percutaneous cryosurgery on both lungs. Three cryoprobes were inserted into both the left and right lungs of each pig, respectively. Cryoablation was performed with two cycles of an active 10-minute freezing using argon in the left lung, each freeze followed by an active 5-minute thaw using helium. In contrast to the left lung cryoablation, the right lungs underwent 3 cycles of freeze/thaw, the first and second cycles consisted of an active 5-minute freezing followed by an active 5-minute thaw, and the third cycle of 10-minute freezing and an active 5-minute thaw. The CT imaging change of an ice ball was continuously observed. The lung tissues were taken 4 hours after cryosurgery on day 3 and on day 7, respectively, for pathological observation. One pig presented acute symptoms including bradycardia and hypothermia 30 minutes after cryosurgery, and died 4 hours after the freezing, and the other 5 pigs experienced a weak condition for 4–6 hours and then exhibited relatively normal behavior and regularly took food. The freezing area (ice ball) on CT imaging during the cryoablation grew gradually in relation to the increase over time, and along with the increase in the number of cycles. The size of the cryolesion on the lung samples became larger than the ice ball during cryosurgery, regardless of whether 2 or 3 freeze-thaw cycles were performed. The area of necrosis histologically gradually increased for the time being. Percutaneous cryosurgery on the lung can achieve complete ablation of targeted tissue. Three freeze-thaw cycles are recommended, and the range of cryoablation may not be mandatory “1 cm safe border” during cryosurgery in order to avoid harming the organ and tissue which is close to the cancer. Correct use of the technique is especially important to treat the lung neoplasms, especially the malignant tumors, which are close to the heart and large vessels.

[Imaging and pathological features of percutaneous cryosurgery on normal lung evaluated in a porcine mode]

背景与目的

肺癌已成为最常见死因的恶性肿瘤之一，对不能手术切除的肺癌，冷冻是一种安全可选择的消融治疗手段，但肺为含气组织，与冷冻肝脏、胰腺等实体器官不同，在理论上冷冻范围很难超过肿瘤边缘。本研究旨在通过正常猪肺模型实验了解不同冷冻-复温循环对肺部组织坏死范围的影响并探讨经皮冷冻肺治疗的技术方案。

方法

采用6只平均体重为23 kg的正常西藏小型猪作为模型，在CT引导下选择猪肺上叶1点和下叶2点作为靶点，使用直径为1.7 mm的冷冻探针分别插入肺叶各靶点做经皮穿刺冷冻。左肺行冷冻10 min、复温5 min共2个周期的冷冻-复温循环；右肺先行冷冻5 min、复温5 min的2个冷冻-复温循环，然后行冷冻10 min、复温5 min的第3个冷冻-复温循环。左右肺的实验条件和实验方法均相同。实验中，观察CT影像下冰球的形态学变化。分别取冷冻后4 h、3 d和7 d的猪肺标本，观察其大体形态及其在光镜下的组织学变化。

结果

猪肺冷冻过程中随着时间的延长和循环次数的增加，冰球逐渐增大；无论2个或3个冷冻-复温循环，所产生的冷冻范围（“假定坏死区”）在大体标本上均超过CT上冷冻过程中显示的冰球大小；冷冻后随着时间延长，组织学坏死区逐步增大，3天及以后，假定坏死区即为组织学坏死区。

结论

经皮冷冻肺可以达到有效破坏靶组织的目的；在技术上，肺冷冻以3个冷冻-复温循环为佳；冷冻范围不强求冷冻“1 cm安全边缘”。上述研究结果对于简化冷冻治疗过程及减少并发症具有临床价值。

Percutaneous cryoablation of renal lesions with radiographic ice ball involvement of the renal sinus: analysis of hemorrhagic and collecting system complications

OBJECTIVE

The purpose of this study was to determine the incidence of collecting system and hemorrhagic complications resulting from CT-guided percutaneous cryoablation of renal tumors in which the radiographic ice ball abuts or involves the renal sinus.

MATERIALS AND METHODS

From November 2005 through July 2009 at our institution, we performed 129 CT-guided percutaneous cryoablation procedures on 107 patients (mean age, 64 years) with renal masses suspicious of being renal cell carcinoma. Radiographic ice balls that abutted or overlapped the renal sinus were classified as central; the other lesions were classified as noncentral. Medical records and follow-up images were retrospectively reviewed for hemorrhage requiring intervention and for evidence of collecting system injury. The mean follow-up period was 9.3 months.

RESULTS

The radiographic ice ball was classified as central in 67 cases. In these central ablations, the mean sinus involvement was 6.2 mm (range, 0-19 mm), 41 ice balls overlapping the renal sinus by 6 mm or more (mean, 9.4 mm). No cases of collecting system injury were identified for any ablation. Overall, there was only one hemorrhagic complication requiring intervention, and it occurred in a noncentral ablation.

CONCLUSION

CT-guided percutaneous cryoablation of renal masses with ice ball overlap of the renal sinus resulted in no cases of collecting system injury or serious hemorrhagic complications in our series.

The experimental study for efficacy and safety of pancreatic cryosurgery

OBJECTIVE

This study was designed to basic information concerning the efficacy and safety of cryosurgery for pancreatic cancer. Fifteen healthy pigs were used to perform biochemical analysis and histological assessment.

METHODS

Following anesthesia and laparotomy, an argon-helium cryoprobe was inserted into the pancreas. The introduction of argon gas induced a rapid decrease in temperature to -160 degrees C (Group I, 5 pigs) or -110 degrees C (Group II, 5 pigs), respectively, resulting in ice-ball formation of 15-20mm diameter after 5 min. Following freezing, helium gas was circulated in the probe tip to increase the temperature to 10-20 degrees C over 3 min to thaw. The freeze/thaw cycle was then repeated. Group III (3 pigs) had a cryoprobe inserted, but without freezing, and Group IV (2 pigs) included untreated or normal control animals. Levels of serum amylase (AMY), IL-6 and C-RP were measured prior to freezing and for 7 days following the procedure. All pigs were euthanized 7 days post-treatment and pancreases were examined histologically.

RESULTS

Neither hyperaemia, edema or hemorrhage were observed in the un-frozen parts of the pancreas. Histological assessment revealed a significant level of necrosis in the central and lateral regions of the tissue frozen within the ice-ball. All cellular ultrastructure was destroyed and only observable as a few of remaining nuclei with broken crests and degranulated mitochondria and rough endoplasmic reticulum. There was a significant increase of serum AMY levels for a brief period in both "deep frozen" and the "shallow frozen" groups. However, the AMY also increased in two pigs in the "normal control" group and one pig from the "inserted cryoprobe without freeze" control group. All experimental pigs appeared healthy until the sacrifice time.

CONCLUSION

Cryosurgery is a safe and effective ablative procedure for pancreatic tissue resulting in minimal complications.

Sequential use of transarterial chemoembolization and percutaneous cryosurgery for hepatocellular carcinoma

AIM: To evaluate the efficacy of sequential use of transarterial chemoembolization (TACE) and percutaneous cryosurgery for unresectable hepatocellular carcinoma (HCC).

METHODS: Four hundred and twenty patients were enrolled in this study. The patients, who were considered to have unresectable tumors due to their location or size or comorbidity, were divided into sequential TACE-cryosurgery (sequential) group (n = 290) and cryosurgery alone (cryo-alone) group (n = 130). Patients in the sequential group tended to have larger tumors and a greater number of tumors than those in the cryo-alone group. Tumors larger than 10 cm in diameter were only seen in the sequential group. TACE was performed with the routine technique and percutaneous cryosurgery was conducted under the guidance of ultrasound 2-4 wk after TACE.

RESULTS: During a mean follow-up period of 42 ± 17 mo (range, 24-70 mo), the local recurrence rate at the ablated area was 17% for all patients, 11% and 23% for patients in sequential group and cryo-alone groups, respectively (P = 0.001). The overall 1-, 2-, 3-, 4- and 5-year survival rate was 72%, 57%, 47%, 39% and 31%, respectively. The 1- and 2-year survival rates (71% and 61%) in sequential group were similar to those (73% and 54%) in cryo-alone group (P = 0.69 and 0.147), while the 4- and 5-year survival rates were 49% and 39% in sequential group, higher than those (29% and 23%) in cryo-alone group (P = 0.001). Eighteen patients with large HCC (> 5 cm in diameter) survived for more than 5 years after sequential TACE while no patient with large HCC (> 5 cm in diameter) survived more than 5 years after cryosurgery. The overall complication rate was 24%, and the complication rates were 21% and 26% for the sequential and cryo-alone groups, respectively (P = 0.06). The incidence of hepatic bleeding was higher in cryo-alone group than in sequential group (P = 0.02). Liver crack only occurred in two patients of the cryo-alone group.

CONCLUSION: Pre-cryosurgical TACE can increase the cryoablation efficacy and decrease its adverse effects, especially bleeding. Sequential TACE and cryosurgery may be the better procedure for unresectable HCC, especially for large HCC.

The Performance of 17-gauge Cryoprobes In Vitro

In cryosurgery it is crucial that the performance of cryoprobes is predictable and constant. In this study we tested the intra- and interneedle variation between 17-gauge cryoprobes in two homogeneous mediums. Also, a multiprobe setup was tested. Cryoprobe performance was defined as the time it takes one cryoprobe to lower the temperature from 0 to −20 °C as measured by four thermosensors each at 3 mm distance from the cryoprobe. In agar eight cryoprobes were tested during six freeze cycles, and in gel four cryoprobes during four freeze cycles; each freeze cycle in a different cup of agar or gel. Using more accurate ‘bare’ thermosensors three cryoprobes were tested in gel during two freeze cycles. A multiprobe configuration with four cryoprobes was tested during two freeze cycles in both agar and gel. Statistical analyses were done using ANOVA for repeated measures.

There was no significant intraneedle variation, whereas both in agar and gel there was a significant interneedle variation (p<0.05). Mean performance in gel was better than in agar (p<0.001). Also, there was a significant variation between the four thermosensors (p< 0.001). Using bare thermosensors mean performance was 2.7 times faster compared to measurements by regular thermosensors (p<0.001). In a multiprobe configuration, overall performance seems less variable and more reproducible compared to a single cryoprobe.

In conclusion, the performance of cryoprobes differs depending on the medium and measuring device used. Cryoprobes deliver reproducible freeze cycles, although there is variation between different cryoprobes. In a multiprobe configuration performance seems less variable.

Differences in ablation size in porcine kidney, liver, and lung after cryoablation using the same ablation protocol

OBJECTIVE

The purpose of our study was to assess the variation in size of acute necrosis and the variation in thermal map measured during cryoablation in multiple organs using the same ablation protocol for each organ.

MATERIAL AND METHODS

Eight female pigs underwent one cryoablation per organ of kidney, lung, and liver performed with open surgery with a 2.4-mm cryoprobe. A 12- and 8-minute double-freeze cycle was used. Intratissue temperatures were monitored using 16-gauge thermometers spaced at 5.0-mm increments from the cryoprobe. The comparison of results among tissues was performed using the multiple analysis of variance. The -20 degrees C thermal diameter was correlated with tissue damage. The kidneys, lungs, and liver were removed and examined histologically for a pathologic complete coagulative necrosis zone.

RESULT

A single 2.4-mm cryoprobe had a mean ice ball diameter in kidney, lung, and liver of 38.5 +/- 4.7, 35.5 +/- 3.6, and 32.5 +/- 2.7 mm, respectively. A mean -20 degrees C thermal diameter was achieved at 24.07 +/- 1.38 mm in kidney, 12.76 +/- 3.0 mm in lung, and 8.8 +/- 3.7 mm in liver by means of regression analysis. The acute pathologic complete coagulative necrosis zone size was 21.0 +/- 1.56 mm (kidney), 11.6 +/- 1.48 mm (lung), and 8.0 +/- 1.20 mm (liver).

CONCLUSION

The inherent characteristics of different organs manifest different ablation zone sizes during cryoablation despite the same ablation protocol being used. This information should be factored into planning for ablation procedures.

An analytical study on the thermal effects of cryosurgery on selective cell destruction

The aim of cryosurgery is to kill cells within a closely defined region maintained at a predetermined low temperature. To effectively kill cells, it is important to be able to predict and control the cooling rate over some critical range of temperatures and freezing states in order to regulate the spatial extent of injury during any freeze-thaw protocol. The objective of manipulating the freezing parameters is to maximize the destruction of cancer cells within a defined spatial domain while minimizing cryoinjury to the surrounding healthy tissue. An analytical model has been developed to study the rate of cell destruction within a liver tumor undergoing a freeze-thaw cryosurgical process. Temperature transients in the tumor undergoing cryosurgery have been quantitatively investigated. The simulation is based on solving the transient bioheat equation using the finite volume scheme for a single or multiple-probe geometry. Simulated results show good agreement with experimental data obtained from in vivo clinical study. The calibrated model has been employed to study the effects of different freezing rates, freeze-thaw cycle(s), and multi-probe freezing on cell damage in a liver tumor. The effectiveness of each treatment protocol is estimated by generating the cell survival-volume signature and comparing the percentage of cell damaged within the ice-ball. Results from the model show that employing freeze-thaw cycles has the potential to enhance cell destruction within the cancerous tissue. Results from this study provide the basis for designing an optimized cryosurgical protocol which incorporates thermal effects and the extent of cell destruction within tumors.

A pig model of hepatic cryotherapy. In vivo temperature distribution during freezing and histopathological changes

We aimed to assess the temperature distribution in the cryolesion during hepatic cryotherapy and the association with postoperative histological changes to optimise the technique and allow better preoperative planning. Hepatic cryolesions were produced in 22 pigs following laparotomy using a CMS-cryosystem and 8mm-AccuProbe-Cryoprobes. The temperature was measured in 1 min intervals at different distances from the probe during freezing. The animals were treated in 5 groups: (i) single freezing of 20 min; (ii) double freezing of 20 min each; (iii) single freezing of 40 min; (iv) single freezing of 20 min (n=4), histology at 1 week p.o., and (v) single freezing of 20 min and Pringle manoeuvre; [(i)-(iii) and (v): histology at 24 h p.o.]. The mean diameter of the -38 degrees C isotherm, i.e., the zone of effective treatment for colorectal metastases was 37 mm for group (i) with a mean iceball diameter of 59 mm and about 46 mm for groups (ii, iii, and v) with mean iceball diameters of 78, 75, and 75 mm, respectively. At 7 days postoperatively secondary necrosis was seen in the largest central part of the lesion, wherever temperatures of -15 degrees C or lower were achieved during cryosurgery. Under the hypothesis that -38 degrees C is the effective temperature for the destruction of colorectal liver metastases, a lesion of 37-mm diameter may be effectively treated with a single 8mm-AccuProbe-Cryoprobe and a 20 min single freeze cycle and a lesion of 46 mm may be effectively treated when a double freeze-thaw cycle of 20 min each, a single freeze cycle of 40 min, or a 20 min single freeze cycle with additional Pringle manoeuvre is used, when it is perfectly placed in the lesion.

An analytic method to predict the thermal map of cryosurgery iceballs in MR images

This paper presents a newly developed method to estimate, in magnetic resonance (MR) images, the temperatures reached within the volume of an iceball produced by a cryogenic probe. Building on the direct measurements of the MR signal intensity and its correlation with independent temperature variations at the phase transition from liquid to solid, the thermal information embedded in the images was accessed. The volume and diameter of the growing iceball were estimated from a time series of MR images. Using regressions over the volume in the time and thermal domains, this method predicted the cryogenic temperatures beyond the range of sensitivity of the MR signal itself. We present a validation of this method in samples of gelatin and ex vivo pig liver. Temperature predictions are shown to agree with independent thermosensor readings over a range extending from 20 degrees C down to -65 degrees C, with an average error of less than 6 degrees C.

Percutaneous cryoablation in treatment of liver cancer: a report of 31 cases

AIM

To describe the indication, efficacy and clinical significance of percutaneous cryoablation in the treatment of liver malignancy.

METHODS

Total 31 patients with histologically or clinically confirmed primary or metastatic malignancies were treated pucutaneously under ultrasound guidance using the cryocare surgical system from July 2001 to January 2002. All patients were followed up to determine the serum tumor marker, and reveal CT scans, MRI images or utra-sound images.

RESULTS

This therapy was performed in 31 patients including 26 cases with Child A liver reserve, 4 cases with Child B and 1 cases with Child C. There were 21 cases of primary liver cancer and 10 metastastic liver cancer. AFP positive small liver cancer became AFP negative in 80% patients. The rate of completely concreted necrosis in small hepatic cancer with negative AFP was 66.7%, shown by CT or MRI. The curative rate for metastasis liver cancer was 50% at CT, MRI or tumor marker level.

CONCLUSION

Percutaneous cryoablation is a kind of new palliative treatment for liver carcinoma. It is minimally invasive, safe and effective especially for patients with unresectable liver cancer.

Surgical emphysema and Collet-Sicard syndrome after cryoblockade of the inferior alveolar nerve

We present a case of Collet-Sicard syndrome (palsy of cranial nerves IX-XII) together with cervicofacial emphysema after cryoblockade to the mandibular division of the trigeminal nerve.

Intralesional cryotherapy for enhancing the involution of hypertrophic scars and keloids

Although therapeutic management of hypertrophic scars and keloids using contact or spray cryosurgery has yielded significant improvement or complete regression of hypertrophic scars and keloids, it requires one to 20 treatment sessions. This study was designed to assess the clinical safety and efficacy of an intralesional needle cryoprobe method in the treatment of hypertrophic scars and keloids. Ten patients, ranging in age from 3 to 54 years, with a total of 12 hypertrophic scars and keloids of more than 6 months duration and of diverse causes, were included in this study. The 18-month trial evaluated volume reduction of the hypertrophic scars and keloids after a single session of intralesional cryotherapy. Objective (hardness and color) and subjective (pain/tenderness and itchiness/discomfort) parameters were examined on a scale of 0 to 3 (low score was better). Pretreatment and posttreatment histomorphometric studies of the collagen fibers included spectral picrosirius red polarization and fast Fourier transformation orientation index. A specially designed cryo-needle was inserted into the long axis of the hypertrophic scars and keloids so as to maximize the volume of the hypertrophic scars and keloids to be frozen. The cryo-needle was connected by an adaptor to a cryogun filled with liquid nitrogen, which was introduced into the cryoprobe, thereby freezing the hypertrophic scars and keloids. After the hypertrophic scars and keloids were completely frozen, the cryoprobe defrosted and was withdrawn. An average of 51.4 percent of scar volume reduction was achieved after one session of intralesional cryosurgery treatment (average preoperative hypertrophic scars and keloids volume, 1.82 +/- 0.33; average posttreatment volume, 0.95 +/- 0.21; p < 0.0022). Significant alleviation of objective and subjective clinical symptoms was documented. Mild pain or discomfort during and after the procedure was easily managed. Only mild local edema and epidermolysis, followed by a short reepithelialization period, were evident. During the 18-month follow-up period, there was no evidence of bleeding, infection, adverse effects, recurrence, or permanent depigmentation. The histomorphometric analysis demonstrated rejuvenation of the treated scars (i.e., parallelization) and a more organized architecture of the collagen fibers compared with the pretreated scars. This study demonstrated the increased efficacy of this method as a result of increased freezing area of deep scar material compared with that obtained with contact/spray probes. As a result, fewer treatment cycles are needed. Because the reepithelialization period is short, treatment intervals, if any, can be shortened to 2 to 3 weeks. This intralesional cryoneedle method is simple to operate and safe to use, it necessitates less postoperative care of the wound, and it can easily be added to any preexisting cryosurgical unit.

Future directions for cryosurgery computer treatment planning

Computer treatment planning for cryosurgery is an area of research and development that will greatly assist the practicing physician and will promote improved quality assurance for clinical procedures. Good planning and precision image-guided treatment delivery are complementary in achieving an optimal treatment outcome. State-of-the-art cryosurgery treatment planning systems are at an early stage of development in comparison with radiation treatment planning systems for external beams. Using 30 years of progress in the area of radiation treatment planning as a guide, this article presents a summary of the avenues for research and development in cryosurgery treatment planning that are likely to accelerate the practical application of precision cryosurgery to a broad spectrum of anatomical sites. Emphasis is placed on prostate cryosurgery, imaging techniques, and recommendations for manufacturers of these systems. Optimization of the clinical procedure in the planning stage using mathematical algorithms to define the positioning and operation of cryoprobes is discussed.

Magnetic resonance imaging-estimated three-dimensional temperature distribution in liver cryolesions: a study of cryolesion characteristics assumed necessary for tumor ablation

The goal of this study was to estimate the three-dimensional (3D) temperature distribution in liver cryolesions and assess the margin of the transition zone between the tumoricidal core of the lesion and the surrounding unfrozen tissue, using criteria proposed in the literature. Local recurrences after liver tumor cryoablation are frequent. Temperatures below -40 degrees C and a 1-cm zone of normal tissue included in the cryolesion are considered necessary for adequate ablation. The 3D temperature distribution in 10 pig cryolesions was estimated by numerical solution of a simplified bioheat equation using magnetic resonance imaging data to establish cryolesion border conditions. Volumes encompassed by the -20, -40, and -60 degrees C isotherms were estimated. The shortest distance from every voxel on the -40 degrees C isotherm to the cryolesion edge was calculated and the mean and the maximal of these distances were defined for each cryolesion. Median cryolesion volumes with temperatures of -20, -40, and -60 degrees C or colder were 53, 26, and 14% of the total cryolesion volume, respectively. The median cryolesion volume was 12.3 cm(3). The median of the mean distances calculated between the -40 degrees C isotherm and the cryolesion edge was 4.1 mm and increased with increasing cryolesion volume. The median of the largest of these distances calculated for each cryolesion was 8.1 mm. Temperatures claimed to be adequate for tumor destruction were obtained only in parts of the cryolesion. The adequacy of a 1-cm zone of normal liver tissue included in the cryolesion to ensure tumor ablation is questioned.