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.     

MMP-9 is differentially expressed in primary human colorectal adenocarcinomas and their metastases

Matrix metalloproteinase-9 (MMP-9) is up-regulated in macrophages in various human cancer types. In human colon cancer, MMP-9 is expressed in a macrophage subpopulation located at the tumor edge, indicating a specific induction of MMP-9 in macrophages in direct association with cancer invasion. To test whether MMP-9 is also induced in tumor edge macrophages in metastases from colorectal adenocarcinomas, we have compared the expression pattern of MMP-9 in primary colorectal adenocarcinomas (n = 15) with that in liver metastases (n = 15) and local lymph node metastases (n = 7) from the same patients by in situ hybridization and immunohistochemistry. In all the colorectal adenocarcinomas, the expression of MMP-9 mRNA and immunoreactivity in macrophages was located at the invasive front. In contrast, only 3 of the 15 liver metastases had MMP-9 mRNA and immunoreactivity at the periphery, and this expression was confined to small foci of macrophages located either among lymphocytes or in a dense desmoplastic stroma. Expression of MMP-9 mRNA and immunoreactivity was in all liver metastases seen in macrophages located in the lumen of malignant glandular structures and in central necrotic tissue. In all the 7 lymph node metastases, MMP-9 mRNA and immunoreactivity was seen in macrophages located in the stromal tissue surrounding the metastases. We conclude that MMP-9 is not up-regulated in tumor edge macrophages in liver metastases like in their primary tumor and local lymph node metastases, suggesting that disseminating colorectal cancer cells can adopt alternative proteolytic mechanisms for invasion depending on the local microenvironment.     

Experimental measurements and theoretical calculations on muscle and liver tissue during cryosurgery. I. Experiments on freezing of rabbit tissue.

Experiments on freezing of muscle and liver tissue of 113 rabbits were performed. The diameter on the frozen surface, and the thickness and the mass of the iceball were measured for the live and dead, body-temperature, animal. Four continuously cooled and six massive probes (2.5–20-mm diameter) were used with liquid nitrogen as the cooling agent. The following conclusions can be drawn: (1) with use of round probe-tips, the iceball has approximately spherical symmetry. However, the depth of the frozen tissue is about 15% smaller than the lateral extension on the visible surface. (2) For continuously cooled probes the diameter of the iceball in the steady state is about five times as large as the probe diameter. The maximal iceball diameter for massive probes is two times larger than the probe diameter. (3) The different blood circulation of liver and muscle tissue has an influence of only 10% on the size of the iceball. For clinical applications this difference is of little importance. (4) For live tissue the iceball is about 15% smaller than for body-temperature dead tissue. Thus, the main heat-transport process in tissue is heat condition.     

Monitoring liver alterations during hepatic tumorigenesis by NMR profiling and pattern recognition

Human hepatocellular carcinoma (HCC) is the most recurrent malignancy of the liver and represents one of the main causes of cancer death worldwide. Furthermore, the liver is the most frequent site of metastatic colonization, and hepatic metastases are far more common than primary cancers in Western countries. A possible way of investigating liver diseases is to study the tissue metabolic profiles. High-resolution nuclear magnetic resonance (NMR) spectroscopy of hepatic tissue extracts was combined with pattern-recognition and visualization techniques to uncover metabolic differences among analyzed tissue types. Extracts were from primary HCC, chronic hepatitis-C-virus related cirrhotic tissues, hepatic metastases from colorectal carcinomas, and non-cirrhotic normal liver tissues adjacent to metastases as controls. We identified all metabolites present in the NMR spectra, and after statistical evaluation of all spectral classes, we were able to define the metabolic changes underlying the different liver conditions and diseases. In particular, the lactate and the glucose tissue signals were found to primarily discriminate the different histological samples. We followed the biochemical changes of human hepatic lesions through primary (HCC) and secondary (metastases from colorectal carcinoma) liver tumors, cirrhotic tissues, and non-cirrhotic histologically-confirmed normal liver tissues adjacent to metastases, achieving a metabolic differentiation of the various pathological states based upon the variation of the intracellular lactate/glucose ratio. It is suggested that such a signal pattern may act as a potential marker for assessing pathological hepatic lesions.     

Cryosurgery of normal and tumor tissue in the dorsal skin flap chamber: Part I--thermal response

Current research in cryosurgery is concerned with finding a thermal history that will definitively destroy tissue. In this study, we measured and predicted the thermal history obtained during freezing and thawing in a cryosurgical model. This thermal history was then compared to the injury observed in the tissue of the same cryosurgical model (reported in companion paper (Hoffmann and Bischof, 2001)). The dorsal skin flap chamber, implanted in the Copenhagen rat, was chosen as the cryosurgical model. Cryosurgery was performed in the chamber on either normal skin or tumor tissue propagatedfrom an AT-1 Dunning rat prostate tumor. The freezing was performed by placing a approximately 1 mm diameter liquid-nitrogen-cooled cryoprobe in the center of the chamber and activating it for approximately 1 minute, followed by a passive thaw. This created a 4.2 mm radius iceball. Thermocouples were placed in the tissue around the probe at three locations (r = 2, 3, and 3.8 mm from the center of the window) in order to monitor the thermal history produced in the tissue. The conduction error introduced by the presence of the thermocouples was investigated using an in vitro simulation of the in vivo case and found to be <10 degrees C for all cases. The corrected temperature measurements were used to investigate the validity of two models of freezing behavior within the iceball. The first model used to approximate the freezing and thawing behavior within the DSFC was a two-dimensional transient axisymmetric numerical solution using an enthalpy method and incorporating heating due to blood flow. The second model was a one-dimensional radial steady state analytical solution without blood flow. The models used constant thermal properties for the unfrozen region, and temperature-dependent thermal properties for the frozen region. The two-dimensional transient model presented here is one of the first attempts to model both the freezing and thawing of cryosurgery. The ability of the model to calculate freezing appeared to be superior to the ability to calculate thawing. After demonstrating that the two-dimensional model sufficiently captured the freezing and thawing parameters recorded by the thermocouples, it was used to estimate the thermal history throughout the iceball. This model was used as a basis to compare thermal history to injury assessment (reported in companion paper (Hoffmann and Bischof, 2001)).     

VIP receptors in pig liver cells: binding characteristics and role in degradation

The physiological role of VIP in the liver is controversial. VIP receptors are present, but their function in the metabolic regulation is uncertain. The interaction of porcine VIP with isolated cells from pig liver was studied with respect to receptor-binding, degradation and glycogenolytic action. In this model, VIP and liver showed homology of animal species. 1. Receptor-binding was heterogenous with Kd values of 10(-9) mol/l and 4 X 10(-8) mol/l, and a total amount of binding sites of 7 X 10(-11) mol per 10(9) cells. The peptide specificity showed that porcine and chicken VIP were equally potent in inhibiting receptor-bound 125I-VIP; secretin was about 30 times less potent; glucagon and somatostatin were ineffective. 2. Receptor-bound 125I-VIP was degraded since about 70% was released as radioactivity not reacting with VIP-antiserum. 3. Glucose-release was not stimulated by VIP (10(-6) mol/l) whereas the rate was increased two-fold by glucagon (10(-6) mol/l). In conclusion, VIP receptors in pig liver cells are different from other tissues regarding peptide specificity. It is suggested that receptor-binding mediates degradation of VIP by pig liver rather than metabolic effects.     

Comparison of dual- and triple-freeze protocols for pulmonary cryoablation in a Tibet pig model

The purpose of this study was to compare a dual-freeze protocol with a triple-freeze protocol for pulmonary cryoablation in a porcine lung model. Five dual- (10-5-10-5) and five triple-freeze (5-5-5-5-10-5) cryoablations were performed on an exposed operation field in normal porcine lung. Changes in the temperature of the cryoprobes and the diameter of the iceballs were measured during the ablation and pathologic changes in the cryozones (zones of tissue destruction) were reviewed 7 days after the procedure. The diameter of the iceball surface differed between the two protocols. Pathologically, the triple-freeze protocol was associated with a longer complete necrosis zone than the dual-freeze protocol, though the two protocols produced cryolesions and cryozones of similar length, and in both cases there were five areas of tissue destruction. With the same duration of freezing (20 min), the triple-freeze protocol may be better for pulmonary cryoablation than the dual-freeze protocol.     

Strain energy density as a rupture criterion for the kidney: impact tests on porcine organs, finite element simulation, and a baseline comparison between human and porcine tissues

High-velocity (up to 25 m/s) impact tests were performed on pig kidneys to characterize failure behavior at deformation rates associated with traumatic injury. Cylindrical tissue samples (n = 45) and whole perfused organs (n = 34) were impacted using both falling weights and a high-velocity pneumatic projectile impactor. Impact energy was incrementally increased until visible rupture occurred. The strain energy density failure threshold fell between 25 and 60 kJ/m3 for excised porcine tissue samples, and between 15 and 30 kJ/m3 for whole, perfused organs. The relationship between localized failure in whole organ impacts and tissue level failure thresholds observed in cylindrical tissue samples was explored using a detailed finite element model of the human kidney. The model showed good correlation between experimentally observed injury patterns and predicted strain energy density distributions within the renal parenchyma. Finally, to facilitate interpretation of the porcine renal impact results with regard to human trauma, quasi-static compression test results of freshly excised human kidney cortex samples (n = 30) were compared against similar tests on pig kidneys. Human tissues failed at Lagrange strain levels similar to porcine tissue (63+/-6.3%), but at 52% lower Lagrange stress (116+/-28 kPa), and 35% lower strain energy density (17.1+/-4.4 kJ/m3). Thus conservative interpretation of porcine test results is recommended.     

EST-based gene discovery in pig: virtual expression patterns and comparative mapping to human

A molecular understanding of porcine reproduction is of biological interest and economic importance. Our Midwest Consortium has produced cDNA libraries containing the majority of genes expressed in major female reproductive tissues, and we have deposited into public databases 21,499 expressed sequence tag (EST) gene sequences from the 3 end of clones from these libraries. These sequences represent 10,574 different genes, based on sequence comparison among these data, and comparison with existing porcine ESTs and genes indicate as many as 4652 of these EST clusters are novel. In silico analysis identified sequences that are expressed in specific pig tissues or organs and confirmed the broad expression in pig for many genes ubiquitously expressed in human tissues. Furthermore, we have developed computer software to identify sequence similarity of these pig genes with their human counterparts, and to extract the mapping information of these human homologues from genome databases. We demonstrate the utility of this software for comparative mapping by localizing 61 genes on the porcine physical map for Chromosomes (Chrs) 5, 10, and 14. The following Accession numbers were assigned to our deposited sequences: BF701840 – BF704551, BF708383, BF708386 – BF713604, BG322266 – BG322271, BI398567 – BI405235, BQ597354 – BQ605166.     

Oncolytic viral therapy for human colorectal cancer and liver metastases using a multi-mutated herpes simplex virus type-1 (G207).

G207 is a multi-mutated, replication-competent type-1 herpes simplex virus designed to target, infect, and lyse neurological tumors. This study examines the feasibility of using G207 in the treatment of human colorectal cancer and defines the biological determinants of its antitumor efficacy. This virus was tested on five human colorectal cancer cell lines in vitro to determine efficacy of infection and tumor cell kill. These results were correlated to measures of tumor cell proliferation. In vivo testing was performed through direct injections of G207 into xenografts of human colorectal cancer tumors grown in flanks of athymic rats. To evaluate an alternate method of administration, hepatic portal vein infusion of G207 was performed in a syngeneic model of liver metastases in Buffalo rats. Among the five cell lines tested, infection rates ranged between 10% and 90%, which correlated directly with S-phase fraction (8.6%-36.6%) and was proportional to response to G207 therapy in vitro (1%-93%). Direct injection of G207 into nude rat flank tumors suppressed tumor growth significantly vs. control (0.58 +/- 0.60 cm(3) vs. 9.16 +/- 3.70 cm(3), P<0. 0001). In vivo tumor suppression correlated with in vitro effect. In the syngeneic liver tumor model, portal infusion resulted in significant reduction in number of liver nodules (13 +/- 10 nodules in G207-treated livers vs. 80 +/- 30 nodules in control livers, P<0.05). G207 infects and kills human colorectal cancer cells efficiently. In vitro cytotoxicity assay and tumor S-phase fraction can be used to predict response to treatment in vivo. This antineoplastic agent can be delivered effectively by both direct tumor injection and regional vascular infusion. G207 should be investigated further as therapy for colorectal cancer and liver metastases.     

A comparison of biomechanical properties between human and porcine cornea

Due to the difficulty in obtaining human corneas, pig corneas are often substituted as models for cornea research. The purpose of this study is to find the similarities and differences in the biomechanical properties between human and porcine corneas. Uniaxial tests were conducted using an Instron apparatus to determine their tensile strength, stress-strain relationship, and stress-relaxation properties. The tensile strength and stress-strain relation were very similar but significant differences between the two tissues were observed in the stress-relaxation relationship. Under the same stretch ratio lambda=1.5, porcine cornea relaxed much more than human cornea. If tensile strength and the stress-strain relation are the only mechanical factors to be investigated, porcine cornea can be used as a substitute model for human cornea research. However, when stress relaxation is a factor, porcine corneas cannot be used as an appropriate model for human corneas in mechanical property studies. It is very difficult to get enough specimens of human cornea, so we did the experiments for stress-strain relationship at a specific value of strain rate (corresponding to the velocity of loading 10mm/min), and for stress relaxation at a specific stretch ratio lambda=1.5.     

Elevated serum endothelin-1 levels in patients with colorectal cancer; relevance for prognosis

BACKGROUND: It has been demonstrated that the Doppler Perfusion Index (DPI) is increased in patients who are at risk of developing liver metastases from colorectal cancer. It has been postulated that a circulating hormonal factor is involved in the relative vasoconstriction throughout the splanchnic bed. Endothelin-1 (ET-1), a potent vasoconstrictor which has been associated with tumor growth and is produced by colorectal tumors, may play an important role in this phenomenon. In this paper the prognostic value of serum ET-1 in colorectal cancer is discussed. METHODS: Preoperative serum levels of ET-1 were assessed in three groups of patients: group A underwent resection of the colorectal tumor and remained free of recurrence (n=20); group B developed metachronous liver metastases at least six months after colorectal resection (n=14); and group C presented with colorectal cancer and synchronous liver metastases (n=22). RESULTS: The mean (SD) serum ET-1 levels in groups A, B and C were 1.59 (0.41) pmol/L, 1.70 (0.32) pmol/L and 1.85 (0.47) pmol/L, respectively. These values were significantly different from those of healthy controls (1.22 (0.31), p<0.05). Kaplan-Meier analyses revealed no prognostic value of preoperative serum ET-1 levels. CONCLUSIONS: These preliminary results demonstrate that serum ET-1 levels are raised in patients with colorectal cancer. Serum ET-1 levels do not seem to be of prognostic value for survival.     

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.     

Cryopreservation of pig and human liver slices

The ability to cryopreserve human liver slices would greatly enhance the opportunities to test potentially hepatotoxic drugs and environmental contaminants as well as the metabolism of these compounds. This study focused on trying to cryopreserve pig and human liver slices. Since the acquisition of human liver tissue is unpredictable and scarce, an animal model was sought to predict problems associated with cryopreservation of human tissue. The pig liver was chosen because of its anatomical and physiological resemblance to human liver. The human liver tissues that did become available were obtained through the Arizona Organ Bank and the National Disease Research Interchange and from surgical liver resections. An in vitro culture system that employed precision-cut liver slices was used in this study. Different types and concentrations of cryoprotectants, cooling rates, and culture media were all tried in an attempt to cryopreserve pig and human liver slices. The viabilities of fresh and cryopreserved liver slices were evaluated using slice K+ retention and protein synthesis. Pig liver slices following cryopreservation retained between 80 and 85% of intracellular K+ content and protein synthesis as compared to controls using 1.4 M Me2SO, a 12 degrees C/min cooling rate, and a rapid rewarming rate of direct submersion of the slice into 37 degrees C fetal calf serum. Human liver slices following cryopreservation retained between 54 and 89% of intracellular K+ content and protein synthesis as compared to controls using the same protocol as for pigs, except that lower cooling rates were giving better results. The large variation seen in cryopreserved human liver slices was due to the length of warm and cold ischemia to which the tissue was exposed before arriving at the laboratory. This study indicated that pig and human liver slices can be cryopreserved and used for future toxicological and metabolic studies.     

Modulation of hypoxia in murine liver metastases of colon carcinoma by nicotinamide and carbogen

There is increasing evidence that modulation of tumor hypoxia may improve therapy outcome. However, most preclinical data are derived from subcutaneous rather than orthotopic tumor models. We investigated the effect of the hypoxia-modulating agents nicotinamide and carbogen on tumor hypoxia, tumor blood perfusion, and proliferative activity in liver metastases of the murine colon carcinoma line C26a. In untreated C26a liver metastases, we observed a considerable amount of hypoxia, similar to the amount in liver metastases of patients with colorectal cancer. Compared to untreated mice, we observed a significantly smaller hypoxic fraction in the liver metastases of mice treated with nicotinamide and carbogen breathing as single treatments or in combination. In the group of mice that underwent carbogen breathing, perfusion was significantly lower than in the untreated group, but the decrease was only marginal. The proliferative activity was similar in all groups. In C26a subcutaneous tumors, a similar effect on hypoxia has been observed that was, however, combined with a decrease in proliferative activity. The different effects of nicotinamide and carbogen on parameters of the tumor microenvironment in liver metastases and subcutaneous tumors suggest that the host tissue influences the mechanism by which nicotinamide and carbogen exert their effects. Since tumor hypoxia may be a clinical problem in colorectal liver metastases, our results open possibilities for further research on the effect of hypoxia modifiers on colorectal liver metastases to improve therapy outcome.     

Increased content of chondroitin sulfate proteoglycan in human colorectal carcinoma metastases compared with the primary tumor as determined by an anti-chondroitin-sulfate monoclonal antibody

To determine if the amount of chondroitin sulfate proteoglycan (CSPG) in human colorectal tumor tissue correlates with the tumor's aggressiveness we immunochemically determined the CSPG levels in colorectal carcinomas at different stages. A total of 50 specimens--4 polyps, 15 stage B tumors, 9 stage C tumors, 12 stage D tumors, 7 liver metastases, and 3 lymph node metastases--were examined. Tumor tissues were extracted with 4 M guanidine hydrochloride containing protease inhibitors. The extracts were serially diluted and blotted onto nitrocellulose membranes. Reactivity of a chondroitin sulfate-specific mouse monoclonal antibody (CS-56) was determined by biotinylated goat antimouse Ig and avidin-biotin-peroxidase complex. After comparing tissues from tumors at different stages (classified by the presence or absence of metastasis), we could not find a positive or negative correlation between the amount of CSPG in primary colorectal carcinoma tissues and the tumor's metastatic potential. However, the metastatic foci in the liver or lymph node contained higher amounts of CSPG than the primary tumors did. Immunohistochemical staining of colon carcinoma tissue with CS-56 revealed that CSPG is predominantly localized in fibrotic portions in the tumor tissues. Two-year follow-up studies indicated that a high level of CSPG in primary tumors was not predictive of recurrence.     

Growth and the initiation of steroidogenesis in porcine follicles are associated with unique patterns of gene expression for individual componentsof the ovarian insulin-like growth factor system

Ovarian follicular growth and steroidogenesis are controlled by the interaction of insulin-like growth factors (IGFs) and gonadotropins. The objective was to determine the temporal and spatial relationships for gonadotropin receptor, steroidogenic enzyme, and IGF system gene expression during the development of preovulatory porcine follicles. Sows (n = 18) were weaned and follicles were monitored by transrectal ultrasonography. Ovaries were collected from sows when the mean diameter of the preovulatory follicular cohort was approximately 2, 4, 6, or 8 mm. mRNA were measured by in situ hybridization for individual follicles within the preovulatory cohort (3 to 5 follicles per sow). Patterns of gene expression detected by in situ hybridization were confirmed by RNase protection analyses of pooled RNA samples. The amount of LH receptor mRNA and steroidogenic enzyme mRNA (17alpha-hydroxylase and aromatase) increased as the mean diameter of the follicular cohort increased from 2 to 6 mm, but then decreased abruptly for 8-mm follicles. Estradiol concentrations in follicular fluid closely followed the expression patterns of steroidogenic enzymes and LH receptor mRNA. FSH receptor mRNA was present in cohorts of 2-mm follicles but declined in 4-mm follicles and was undetectable in 6- and 8-mm follicles. The expression of IGF-I and type I IGF receptor mRNA were similar for follicles of 2, 4, 6, and 8 mm. In contrast, IGF-II mRNA progressively increased in follicles collected from 2-, 4-, and 6-mm cohorts, and then decreased slightly at 8 mm. Type II IGF receptor mRNA was greatest in 8-mm follicles. IGF binding protein-2 (BP-2) mRNA decreased as follicles achieved progressively larger sizes during the preovulatory period (2 to 8 mm), whereas the IGFBP-4 mRNA remained relatively low for follicles in 2- to 6-mm cohorts but then increased markedly in 8-mm follicles. In summary, temporal and spatial patterns of gene expression for gonadotropin receptor, steroidogenic enzyme, and IGF system genes were characterized in preovulatory porcine follicles by using in situ hybridization and RNase protection analyses. The unique patterns of gene expression suggest interdependence among specific genes that may be essential for preovulatory follicular development.     

Imaging of interstitial cryotherapy--an in vitro comparison of ultrasound, computed tomography, and magnetic resonance imaging.

RATIONALE AND OBJECTIVES: To evaluate the imaging capabilities of ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) in monitoring interstitial cryotherapy and to compare them with visual control. METHODS: An experimental MR-compatible, vacuum-insulated and liquid nitrogen-cooled cryoprobe was inserted under in vitro conditions into a porcine liver, which was kept at a temperature of 37 +/- 1 degrees C, in a water bath with continuous stirring. The freezing procedure was controlled macroscopically, by US (Toshiba Sonolayer, 7.5-MHz linear array transducer), by CT (Siemens Somatom Plus, slice thickness 2-8 mm, 165-210 mA at 120 kV), and by MRI (Philips Gyroscan ACS-NT, FFE TR/TE/FA = 15/5.4/25 degrees, T1-SE 550/20, T2-TSE 1800/100) after the iceball reached its maximum size. RESULTS: The maximum iceball diameter around the probe tip was 12.0 mm by visual control, 12.4 mm by US, 12.7 mm by CT, and within 12.8 mm by spin echo sequences and 11 mm by gradient echo sequence. Due to the nearly signal-free appearance of the frozen tissue on MR images, the ice/tissue contrast on T1-weighted and gradient echo images was superior to T2-weighted images and CT images. Sonographically, the ice formation appeared as a hyperechoic sickle with nearly complete acoustic shadowing. CONCLUSION: Due to the better ice/tissue contrast, T1-weighted or gradient echo MR images were superior to CT and US in monitoring interstitial cryotherapy. Gradient echo sequences generally underestimated the ice diameter by 15%.