CT-monitored percutaneous cryoablation in a pig liver model: pilot study

Clinical translation of abdominal histotripsy: a review of preclinical studies in large animal models

Histotripsy is an emerging noninvasive, non-thermal, and non-ionizing focused ultrasound (US) therapy that can be used to destroy targeted tissue. Histotripsy has evolved from early laboratory prototypes to clinical systems which have been comprehensively evaluated in the preclinical environment to ensure safe translation to human use. This review summarizes the observations and results from preclinical histotripsy studies in the liver, kidney, and pancreas. Key findings from these studies include the ability to make a clinically relevant treatment zone in each organ with maintained collagenous architecture, potentially allowing treatments in areas not currently amenable to thermal ablation. Treatments across organ capsules have proven safe, including in anticoagulated models which may expand patients eligible for treatment or eliminate the risk associated with taking patients off anti-coagulation. Treatment zones are well-defined with imaging and rapidly resorb, which may allow improved evaluation of treatment zones for residual or recurrent tumor. Understanding the effects of histotripsy in animal models will help inform physicians adopting histotripsy for human clinical use.

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.

Interventional Treatment Strategies in Intrahepatic Cholangiocarcinoma and Perspectives for Combined Hepatocellular-Cholangiocarcinoma

cHCC-CCA is an uncommon type of liver cancer that exhibits clinical and pathological characteristics of both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), which are the two main forms of primary liver cancer. The similarity to HCC and CCA makes therapeutical strategies challenging. The poor prognosis of CCA in general, as well as for cHCC-CCA, is mainly attributable to the fact that diagnosis is often at an advanced stage of disease. During the last decade, locoregional therapies usually performed by interventional radiologists and its established role in HCC treatment have gained an increasing role in CCA treatment as well. These comprise a wide range of options from tumor ablation procedures such as radiofrequency ablation (RFA), microwave ablation (MWA), computed tomography high-dose rate brachytherapy (CT-HDRBT), and cryoablation to transarterial chemoembolization (TACE), including the option of intra-arterial administration of radioactive spheres (transarterial radioembolization-TARE), and much attention has focused on the potential of individual concepts in recent years. The purpose of this review is to provide an overview of current radiologic interventions for CCA (excluding options for eCCA), to review and appraise the existing literature on the topic, and to provide an outlook on whether such interventions may have a role as treatment for cHCC-CCA in the future.

Recent Perspectives on the Mechanism of Recurrence After Ablation of Hepatocellular Carcinoma: A Mini-Review

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors. Hepatectomy, liver transplantation, and ablation are the three radical treatments for early-stage hepatocellular carcinoma (ESHCC), but not all patients are fit for or can tolerate surgery; moreover, liver donors are limited. Therefore, ablation plays an important role in the treatment of ESHCC. However, some studies have shown that ablation has a higher local recurrence (LR) rate than hepatectomy and liver transplantation. The specific mechanism is unknown. The latest perspectives on the mechanism of recurrence after ablation of HCC were described and summarized. In this review, we discussed the possible mechanisms of recurrence after ablation of HCC, including epithelial–mesenchymal transition (EMT), activating autophagy, changes in non-coding RNA, and changes in the tumor microenvironment. A systematic and comprehensive understanding of the mechanism will contribute to the research and development of related treatment, combined with ablation to improve the therapeutic effect in patients with ESHCC.

Percutaneous Cryoablation of Large Tumors: Safety, Feasibility, and Technical Considerations

INTRODUCTION

Large tumors may prove unsuitable for surgical cure or other local therapies due to their size, involvement of critical structures, prior non-ablative treatment failure, or coexisting disease burden. This study was performed to assess the safety and feasibility of percutaneous cryoablation for treatment of large tumors exceeding 6 cm in size, and to highlight the key technical considerations inherent to such cases.

MATERIALS AND METHODS

This single-institution retrospective study identified 77 patients (42 male, 35 female; median age 55 years) who underwent 96 cryoablation procedures for treatment of 78 tumors (mean diameter 9.8 ± 3.6 cm) from 2008 through 2020. Technical success, procedure-related complications, mortality, oncologic outcomes, and procedural logistics were evaluated. Technical success was defined as ice ball extension at least 5 mm beyond the tumor margins.

RESULTS

Intentional subtotal ablations were performed in 32% of cases due to tumor encroachment on vulnerable structures or as part of staged/combined therapies. Of the 68% of cases that were planned for complete ablation, the technical success rate was 100%. Major complications occurred after 19/96 (20%) procedures, with hemorrhage and acute kidney injury each occurring in 6/96 (6%). Post-procedural myositis occurred in 24/96 (25%) cases and was not considered a major complication in the absence of acute kidney injury. Local recurrence occurred in 2/23 (8.7%) of patients undergoing ablation for cure or local control at a median follow-up duration of 13 months.

CONCLUSION

Percutaneous cryoablation may be used to treat large (> 6 cm) tumors with a high degree of technical success and an acceptable safety profile.

Image-guided tumor ablation in gynecologic oncology: Review of interventional oncology techniques and case examples highlighting a collaborative, multidisciplinary program

As interventional oncology services within radiology mature, image-guided ablation techniques are increasingly applied to recurrent gynecologic malignancies. Ablation may be performed using thermal techniques like cryoablation, microwave ablation, or radiofrequency ablation, as well as non-thermal ones, such as focused ultrasound or irreversible electroporation. Feasibility and approach depend on tumor type, size, number, anatomic location, proximity of critical structures, and goals of therapy. Current indications include local control of limited metastatic disease or palliation of painful bone metastases refractory or unsuitable to conventional therapies. Technical aspects of these procedures, including methods to protect nearby critical structures are presented through illustrative examples. Cases amenable to image-guided ablation include, but are not limited to, hepatic or pulmonary metastases, musculoskeletal metastases, retroperitoneal nodal metastases, pelvic side wall disease, abdominal wall disease, and vaginal or vulvar tumors. Protective maneuvers, such as hydro-displacement of bowel, neuromonitoring, and retrograde pyeloperfusion through ureteral stents, permit safe ablation despite close proximity to vulnerable nerves or organs. Image-guided ablation offers an alternative modality to achieve local tumor control without the risks associated with surgery or systemic treatment in appropriately selected patients. A multidisciplinary approach to use of image-guided ablation includes collaboration between gynecologic oncology, interventional radiology, anesthesia, urology and radiation oncology teams allowing for appropriate patient-centered case selection. Long-term follow up and additional studies are needed to determine the oncologic benefits of such techniques.

Trends in Musculoskeletal Ablation: Emerging Indications and Techniques

Image-guided percutaneous thermal ablation plays an increasingly important role in the multidisciplinary management of musculoskeletal lesions. Established indications for ablation in this setting include the treatment of osteoid osteomas, palliation of painful skeletal metastases, local control of oligometastatic disease, and consolidation of bone tumors at risk for fracture. Emerging indications include the treatment of symptomatic soft tissue masses such as extra-abdominal desmoid tumors and abdominal wall endometriosis. This review will discuss considerations in patient selection and preprocedural workup, ablation technology and techniques, strategies to avoid complications, and expected outcomes of ablation in the musculoskeletal system.

High-Frequency Jet Ventilation in the Prone Position to Facilitate Cryoablation of a Peridiaphragmatic Pulmonary Neoplasm: A Case Report

Percutaneous cryoablation of pulmonary tumors at the posterior lung base is challenging due to diaphragmatic motion and the requirement for prone positioning. High-frequency jet ventilation allows oxygenation and ventilation with minimal diaphragmatic movement. In this case report, we describe the use of high-frequency jet ventilation in the prone position to facilitate the cryoablation of a peridiaphragmatic pulmonary neoplasm.

Clinical utility of virtual noncalcium dual-energy CT in imaging of the pelvis and hip

Dual-energy virtual noncalcium images are increasingly used to identify marrow edema which accompanies bony pelvic injuries and marrow pathology obscured by cancellous bone. We present a clinical perspective of our experience using virtual noncalcium images in the work up of pelvic osseous pathology.

Ablation of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma is the second most common primary liver cancer but represents only a small portion of all primary liver cancers. At the time of diagnosis, patients are often not surgical candidates due to tumor burden of other comorbidities. In addition, there is a very high rate of tumor recurrence after resection. Local regional therapies, specifically ablative therapies of radiofrequency ablation, microwave ablation, cryoablation, and irreversible electroporation, have proven to be beneficial with other hepatic tumors. The purpose of this review is to provide an overview and update of the medical literature demonstrating ablative therapy as a treatment option for intrahepatic cholangiocarcinoma.

Feasibility of CT-CT fusion imaging for evaluation of the cryoablation margins in visible hepatocellular carcinoma on unenhanced CT images: Initial experience

Objective

To demonstrate the feasibility of CT-CT fusion imaging for assessment of the cryoablation margins in visible hepatocellular carcinoma (HCC) on unenhanced CT images.

Methods

This retrospective study analyzed 14 patients with 14 HCC lesions treated with CT-guided cryoablation. Nine lesions in nine patients who developed local tumor progression (LTP) during the follow-up period of at least 8 months were reviewed. The unenhanced CT data were used to retrospectively create fusion images of the intraoperative CT images on a workstation. The minimal ablative margin (MAM) was assessed on the fusion images. The concordance between the site of LTP and the MAM area was also assessed.

Results

Eight of the nine lesions with LTP were in the subcapsular region of the liver. Seven of the nine cases were treated by cryoablation combined with transcatheter arterial chemoembolization. The median time required to fuse the images for the nine lesions was 5:17 min (range, 5:04–7:37 min). The site of LTP relative to the HCC lesion was craniocaudal in nine, dorsoventral in six, and lateral in seven lesions. In all lesions, the site of LTP was congruent with the MAM area.

Conclusions

CT-CT fusion imaging enables a real-time intraoperative treatment evaluation for HCC lesions visible on unenhanced CT images. Fused imaging evaluation has proved to be an accurate and useful tool for assessment of the cryoablation margins.

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.

Veterinary Clinics: Tumor Ablation

Over the past decade, interventional oncology techniques have become integrated into the treatment plans of companion animals with cancer on a regular basis. Although procedures such as stenting are performed commonly, other less frequently utilized techniques for locoregional therapy, such as embolization and ablation, are emerging and demonstrating promise. Tumor ablation techniques are categorized into two subgroups: chemical ablation and energy-based ablation. Increased utilization of ablation will allow for the determination of specific indications and evaluation of outcomes for these techniques.

Assessment of the cryoablation margin using MRI-CT fusion imaging in hepatic malignancies

AIM

To demonstrate the feasibility of magnetic resonance imaging (MRI)-computed tomography (CT) fusion imaging for the assessment of the ablative margin after cryoablation in hepatic malignancies.

MATERIALS AND METHODS

This retrospective study analysed 35 patients with 47 liver tumours treated with CT-guided cryoablation. Fusion images of pre-ablation MRI and intraoperative CT data were created on a workstation. Minimal ablative margin (MAM) assessment was categorised into three groups: (I) MAM <0 mm (tumour protruded through the ablation zone), (II) MAM 0-5 mm, and (III) MAM ≥5 mm. Local tumour progression (LTP) was assessed during follow-up.

RESULTS

MRI-CT fusion imaging was successfully achieved in 46 (97.9%) of 47 lesions. LTP was detected in 67.4% (31/46) of cases. Twenty-four (77.4%) of 31 LTPs occurred in the subcapsular region of the liver. Using fusion images, the MAM was classified as groups I, II, and III in 18, 25, and three tumours, respectively. In group I, LTP was found in 15 (83.3%) of 18 lesions, whereas in group II, LTP was detected in 16 (64%) of 25 lesions. The cumulative LTP rate in group II was significantly lower than that in group I (p=0.012).

CONCLUSION

Pre-ablation MRI and intraoperative CT fusion imaging is feasible and useful for evaluating the MAM of cryoablation in hepatic malignancies.

Current State of Tumor Ablation Therapies

The most common primary liver malignancy, hepatocellular carcinoma (HCC), has a high likelihood of mortality, and much effort into early detection and treatment has occurred. Multiple staging systems have surfaced of which some guide treatment. Curative intent is a goal of early-staged HCC treatment, and this can be achieved with surgical resection, liver transplantation, and minimally invasive percutaneous therapies such as tumor ablation. Many of the newer ablation techniques have evolved from shortcomings of prior methods which have resulted in an expanded number of applications for tumor ablation. Our review focuses on current mainstream image-guided percutaneous ablation modalities which are commonly performed as an alternative to surgery.

Thermal Ablation of Bone Metastases

Image-guided, minimally invasive, percutaneous thermal ablation of bone metastases has unique advantages compared with surgery or radiation therapy. Thermal ablation of osseous metastases may result in significant pain palliation, prevention of skeletal-related events, and durable local tumor control. This article will describe current thermal ablation techniques utilized to treat bone metastases, summarize contemporary evidence supporting such thermal ablation treatments, and outline an approach to percutaneous ablative treatment.

Percutaneous cryoablation for hepatocellular carcinoma

Local ablation therapy is considered as a conventional treatment option for patients with early stage hepatocellular carcinoma (HCC). Although radiofrequency (RF) ablation is widely used for HCC, the use of cryoablation has been increasing as newer and safer cryoablation systems have developed. The thermodynamic mechanism of freezing and thawing used in cryoablation is the Joule-Thomson effect. Cryoablation destroys tissue via direct tissue destruction and vascular-related injury. A few recent comparative studies have shown that percutaneous cryoablation for HCCs is comparable to percutaneous RF ablation in terms of long term therapeutic outcomes and complications. Cryoablation has several advantages over RF ablation such as well visualization of iceball, no causation of severe pain, and lack of severe damage to great vessels and gallbladder. It is important to know the advantages and disadvantages of cryoablation compared with RF ablation for improvement of therapeutic efficacy and safety.

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.

Cryoablation of Hepatocellular Carcinoma with High-Risk for Percutaneous Ablation: Safety and Efficacy

PURPOSE

The aim of this study was to evaluate the safety and effectiveness of cryoablation in the treatment of subcapsular hepatocellular carcinoma (HCC) adjacent to various organs.

MATERIALS AND METHODS

Twenty-eight patients with subcapsular HCC were treated with cryoablation in our institution. The degree of peri-procedural pain was measured using the visual analog scale (VAS). Technical success, local tumor progression, and overall disease progression rates were calculated. Procedure-related complications were identified by reviewing electronic medical records. Biochemical data, including serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin levels before and after the procedure were collected.

RESULTS

Subcapsular HCC tumors were located near the gallbladder, colon, stomach, kidney, diaphragm, or abdominal wall. The technical success rate of cryoablation was 96.4 % (27/28). Local recurrence- and progression-free survival rates were 96 and 84 % at 6 months, and 82 and 43 % at 1 year, respectively. All patients survived during the follow-up period. The VAS pain score ranged from 0 to 3 (mean, 1.57). A major complication occurred in one patient (3.6 %) and minor complications occurred at a rate of 17.9 %. Transient elevations of serum AST, ALT, and bilirubin levels were observed.

CONCLUSION

Cryoablation is a safe and an effective procedure for the treatment of subcapsular HCC adjacent to various major organs.

Percutaneous cryoablation of hepatic tumors: long-term experience of a large U.S. series

PURPOSE

To report our long-term experience with percutaneous cryotherapy for primary and metastatic liver tumors, including historical perspectives on complications over time and local recurrence rates.

MATERIALS AND METHODS

Following IRB approval under HIPAA compliance, 342 CT fluoroscopic-guided, percutaneous cryotherapy procedures were performed for 443 masses in 212 outpatients with hepatocellular carcinoma (HCC; N = 36), or metastatic disease (N = 176), grouped as colorectal carcinoma (CRC) and non-CRC metastases. Tumor and ablation sizes were noted in relation to adjacent vasculature. All complications were graded according to standardized criteria. Patients were followed by CT and/or MRI at 1, 3, 6, 12, 18, 24 months and yearly thereafter. Local recurrences were defined as either "procedural" within the ice ablation zone, or "satellite" within 1 cm of the ablation rim to evaluate recurrence patterns.

RESULTS

Average tumor diameter of 2.8 cm was treated by average cryoprobe number of 4.5, which produced CT-visible ice ablation zone diameters averaging 5.2 cm. Grade >3 complications were primarily hematologic [N = 20/342; (5.8%)], and appeared related to pre-procedural anemia/thrombocytopenia, carcinoid tumor type, and large ablation volumes. No significant central biliary leak, strictures, or bilomas were noted. At a mean follow-up of 1.8 years, local tumor recurrences were 5.5%, 11.1%, and 9.4% for HCC, CRC, and non-CRC metastases, respectively, consisting mainly of satellite foci. No significant difference was noted for local recurrences near major blood vessels or tumors >3 cm diameter.

CONCLUSIONS

Percutaneous hepatic cryotherapy is a well-visualized, safe procedure that produces very low local recurrence rates, even for tumors near vasculature and diameters over 3 cm. Cryoablation deserves to be in the armamentarium of percutaneous hepatic ablation, especially with careful patient selection for tumors <4 cm and patients with platelet counts >100,000. Percutaneous hepatic cryoablation represents a highly flexible technique with particular benefits near central biliary structures and/or adjacent crucial structures.

Unresected Breast Cancer: Evolution of Imaging Findings Following Cryoablation

Cryoablation has been used to treat both benign and malignant breast tumors. In all but one published case, cryoablation in breast cancer has been followed by post-procedural tumor resection. We present a case of an 85-year-old woman with two nonpalpable breast cancers treated with cryoablation with 18 months of mammographic, ultrasound and histologic follow-up.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Percutaneous tumor ablation tools: microwave, radiofrequency, or cryoablation--what should you use and why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Characterization of a CMOS sensing core for ultra-miniature wireless implantable temperature sensors with application to cryomedicine

In effort to improve thermal control in minimally invasive cryosurgery, the concept of a miniature, wireless, implantable sensing unit has been developed recently. The sensing unit integrates a wireless power delivery mechanism, wireless communication means, and a sensing core-the subject matter of the current study. The current study presents a CMOS ultra-miniature PTAT temperature sensing core and focuses on design principles, fabrication of a proof-of-concept, and characterization in a cryogenic environment. For this purpose, a 100 μm × 400 μm sensing core prototype has been fabricated using a 130 nm CMOS process. The senor has shown to operate between -180°C and room temperature, to consume power of less than 1 μW, and to have an uncertainty range of 1.4°C and non-linearity of 1.1%. Results of this study suggest that the sensing core is ready to be integrated in the sensing unit, where system integration is the subject matter of a parallel effort.

Percutaneous Cryoablation for Liver Cancer

Based on the primary tumor site, liver cancer can be divided into two categories: (1) primary liver cancer and (2) metastatic cancer to the liver from a distant primary site. Guided cryoablation via many imaging methods induces iceball formation and tumor necrosisand is an attractive option for treating unresectable hepatocellular carcinoma (HCC) and metastatic liver cancer. There are several advantages to using cryoablation for the treatment of liver cancer: it can be performed percutaneously, intraoperatively, and laparoscopically; iceball formation can be monitored; it has little impact on nearby large blood vessels; and it induces a cryo-immunological response in situ. Clinically, primary research has shown that percutaneous cryoablation of liver cancer is relatively safe and efficient, and it can be combined with other methods, such as radiation therapy, chemotherapy, and immunology, to control disease. Although research is preliminary, cryosurgery is fast becoming an alternative treatment method for HCC or liver tumors. Here, we review the mechanisms of liver tumor cryoablation, cryoablation program selection, clinical efficiency, and complications following treatment.

Computed tomography imaging-guided percutaneous argon-helium cryoablation of muscle-invasive bladder cancer: initial experience in 32 patients

PURPOSE

To evaluate the initial clinical experience of computed tomography (CT) imaging-guided percutaneous cryotherapy of bladder cancer.

PATIENTS AND METHODS

This study was approved by the human subjects committee. Written informed consent was obtained from all patients. Thirty-two patients (22 males and 10 females; mean age, 62.7 years) with muscle-invasive bladder cancer were treated with CT imaging-guided percutaneous cryoablation. By using CT imaging system and local anesthesia in patients, a single or multiple 1.47 mm cryoprobes were used to freeze the target bladder tumor (mean tumor size, 2.8 cm; range, 1.3-4.5 cm) with a dual freeze-thaw cycle. Follow-up was performed to assess the clinical and technical outcome of patients treated with cryoablation for a minimum of 6 months (mean, 33 months; range, 6-48 months). Tumors were considered completely ablated if there was no evidence to suggest tumor enhancement at follow-up CT images.

RESULTS

Bladder cryoablation was clinically and technically successful in all 32 cases, 30 of which required only one treatment session. Bladder integrity was maintained in all patients. Major complications were not observed in any patient.

CONCLUSION

Our initial experience of a minimally invasive method for ablating bladder tumors with CT imaging-guided percutaneous argon-helium cryoablation appears to be favorable, with acceptable operative and short-term clinical outcomes. The technique is safe and effective for the treatment of patients with muscle-invasive bladder cancer; however, long-term follow-up is needed.

Neuroanatomic considerations in percutaneous tumor ablation

Percutaneous ablation is increasingly being used as focal therapy for tumors in the chest, abdomen, and pelvis, including tumors in proximity to neural structures. To ensure that tumor ablation is performed safely, knowledge of the regional neuroanatomy is particularly important because most relevant nerves are not visualized with the conventional imaging techniques used to guide ablation procedures. Familiarity with the expected course of nerves in commonly targeted areas is helpful in preventing inadvertent nerve injury and in accurately informing the patient of potential risks. In the chest and shoulder girdle, the brachial plexus as well as the phrenic, recurrent laryngeal, intercostal-subcostal, long thoracic, dorsal scapular, and suprascapular nerves may be encountered. Vulnerable neural structures in the abdomen and pelvis arise from the lumbar and sacral plexuses and include the femoral, obturator, sciatic, and pudendal nerves. Nerve protection and monitoring techniques should be used, when appropriate, to minimize the risk of neural injury during percutaneous tumor ablation and depend on the vulnerable nerve, the location of the targeted tumor, and the ablation device used for treatment. Nerves may be protected using displacement techniques, including instillation of air or fluid, insertion and insufflation of angioplastic or endoscopic balloons, and mechanical manipulation of the ablation device. Nerves may be monitored with cross-sectional imaging evaluation of the critical nerve or ablation zone, or with functional evaluation using electromyographic equipment or focused clinical examination. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg334125141/-/DC1.

Radiation dose reduction for CT-guided renal tumor cryoablation

OBJECTIVE

The purpose of this article is to retrospectively determine the image quality and degree of radiation dose reduction that is clinically acceptable for CT-guided renal tumor cryoablation.

MATERIALS AND METHODS

A total of 15 patients (17 procedures; mean age, 67 years; range, 38-85 years) undergoing clinically indicated CT-guided renal tumor cryoablation procedures were included in this retrospective study. A previously validated noise-insertion tool was used to simulate reduced-dose scans at 75%, 50%, 25%, and 10% of the original dose at four representative phases of the cryoablation procedure. Images obtained at different dose levels were randomized and reviewed by three radiologists blinded to the level of dose reduction, who scored them independently with a 5-point scale (1-5, with 5 the best). Images with a mean score of 3 or higher were considered diagnostically acceptable. The minimal acceptable dose was that at which 90% of images were considered diagnostically acceptable. Interrater agreement was assessed using the weighted kappa statistic.

RESULTS

The weighted kappa value was 0.68, indicating substantial agreement among the reviewers. The averaged percentage of diagnostically acceptable images for the four series was 100% for a full dose, 98-100% for the 75% dose level, 94-98% for the 50% dose level, and less than 90% for images obtained at the 25% and 10% dose levels, which was considered unacceptable.

CONCLUSION

On the basis of results from 15 patients (17 procedures), images obtained from CT acquisitions at 50% (volume CT dose index, 12.2 mGy) of the original dose level (volume CT dose index, 24.4 mGy) were acceptable for the purpose of CT monitoring of renal cryoablation procedures.

[Computerized liver volume for evaluation and following liver regeneration after partial hepatectomy in swines]

OBJECTIVES

To analyze the hepatic volume by computerized tomography using a semiautomatic computerized program of acquisition and processing digitalized images, to follow the hepatic regeneration in swine after partial hepatectomy.

METHODS

Twelve female young Landrace swine were separated in three groups according to the observation time between hepatectomy and sacrifice: G5 (5 days), G10 (10 days) and G15 (15 days). All animals were submitted to partial hepatectomy of the right lobe and followed until sacrifice, when regenerated liver was ressected. The surgical piece and the regenerated liver were weighted and submitted to tomographic volume evaluation by the software HEPATO, taking place acquisition and analysis of the tomography images in a semiautomatic way. Statistical analysis used the non-parametric Kruskal-Wallis and Wilcoxon tests.

RESULTS

Medium weigh of regenerated liver was G5=434,5 g, G10=449,25g and G15=486,5 g (p=0,592). The regeneration index obtained using liver weight was 83,58% (G5), 94,95% (G10) and 101,63% (G15) (p=0,197). Medium volume of regenerated liver was G5=403,58 cm(2), G10=450,88 cm(2) and G15=458,93 cm(2) (p=0,941). Liver regeneration index obtained using liver volume was 74,25% (G5), 88% (G10) and 100% (G15) (p=0,326). Liver regeneration index was not different when assessed using liver weigh or liver volume.

CONCLUSION

The liver volumetric evaluation by computerized tomography using a computerized semiautomatic program of digitalized images acquisition and processing is a trustworthy method for evaluation and following the liver regeneration in swine after partial hepatectomy.

Lethal isotherms of cryoablation in a phantom study: effects of heat load, probe size, and number

PURPOSE

To assess the effects on the proportions of lethal ice (ie, colder than -30 degrees C) in phantoms with different heat loads created by varying the size and number of cryoprobes spaced 2 cm apart.

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

Single cryoprobes create very low percentages of lethal ice. Multiple cryoprobes overcome the high heat load of body temperature phantoms and help compensate for the lower freeze capacity of thinner cryoprobes.

CT-guided percutaneous cryotherapy of renal masses

PURPOSE

To assess the results of initial and current techniques for percutaneous renal cryotherapy, including long-term imaging outcomes.

MATERIALS AND METHODS

Computed tomography (CT)-guided percutaneous cryotherapy was performed on 49 masses in 48 outpatients and procedure comfort noted for each. These 49 masses included 36 primary renal cell carcinomas (RCCs), 3 oncocytomas, 1 angiomyolipoma, 6 renal inflammatory lesions, 2 benign parenchymal changes, and 1 colon cancer metastasis. All complications were graded according to standardized criteria.

RESULTS

Patients received only local anesthesia and moderate sedation during the procedure and were discharged with minimal discomfort within 4-6 hours. All cryotherapy zones were well defined by CT during ablation as hypodense ice with an average diameter of 5.3 cm, covering an average tumor size of 3.3 cm. Average ablation zone diameters showed significant reduction over time (P < .001), becoming significantly less than the original tumor size by 12 months (P < .05). Major and minor complications were seen in 3 (6%) and 11 (22%) procedures, respectively. At a mean follow-up of 1.6 years (range, 1 week to 3.8 years) for primary RCC patients, four failures (11.1%) by imaging criteria were noted, but one proved to be inflammatory tissue at re-biopsy (estimated neoplastic failure rate = 3/36 = 8.3%).

CONCLUSIONS

Percutaneous renal cryotherapy is a well-tolerated outpatient procedure that allows safe, CT monitoring of ice formation beyond visible tumor margins. With appropriate cryoprobe placements, a low failure rate appears less dependent on tumor size or location. Ablation volume involution was >80% after 6 months.