MR imaging-guided percutaneous cryotherapy of liver tumors: initial experience

Beyond Excision: Cryotherapy as a Non-surgical Treatment for Palatal Solitary Neurofibroma

Palatal solitary neurofibromas (SNFs), not linked to neurofibromatosis type 1, are uncommon. A 45-year-old female with a palatal SNF underwent non-surgical treatment using liquid nitrogen cryotherapy (LNC). The lesion, initially 9 x 8 x 3 mm, was treated with two 1-2 minute freeze-thaw cycles, progressively extended to two 2-2 minute freeze-thaw cycles to address the refractoriness. After four LNC sessions, the lesion resolved without recurrence at five months. This case demonstrates LNC's efficacy as a surgical alternative for palatal SNF, offering a non-invasive option for patients declining surgery. The positive outcome warrants further research into LNC's role in managing similar benign lesions.

Interventional treatments for hepatic hemangioma: A state-of-the-art review

Hepatic hemangiomas (HHs) are the most common benign tumors of the liver. These tumors are mainly asymptomatic and do not require treatment. Nevertheless, there are some special cases that require therapeutic intervention, and surgery and intervention are currently the primary treatment modalities. Despite significant advances in the development of minimally invasive techniques and their popularization, interventional treatment of HH is still the preferred choice. In the present review, we discuss the pathological properties, type of blood supply, and treatment indications for HH and assess the status and progress of the existing interventional treatments.

Image-guided Cryotherapy for Musculoskeletal Tumors

BACKGROUND

This article represents a review of the use of image-guided cryotherapy in the treatment of musculoskeletal tumor lesions. Cryotherapy is able to induce a lethal effect on cancer cells through direct and indirect mechanisms. In this manuscript, we combined our experience with that of other authors who have published on this topic in order to provide indications on when to use cryotherapy in musculoskeletal oncology.

DISCUSSION

Image-Guided percutaneous cryotherapy is a therapeutic method now widely accepted in the treatment of patients with musculoskeletal tumors. It can be used both for palliative treatments of metastatic bone lesions and for the curative treatment of benign bone tumors, such as osteoid osteoma or osteoblastoma. In the treatment of bone metastases, cryotherapy plays a major role in alleviating or resolving disease-related pain, but it has also been demonstrated that it can have a role in local disease control. In recent years, the use of cryotherapy has also expanded for the treatment of both benign and malignant soft tissue tumors.

CONCLUSION

Percutaneous cryotherapy can be considered a safe and effective technique in the treatment of benign and malignant musculoskeletal tumors. Cryotherapy can be considered the first option in benign tumor lesions, such as osteoid osteoma, and a valid alternative to radiofrequency ablation. In the treatment of painful bone metastases, it must be considered secondarily to other standard treatments (radiotherapy, bisphosphonate therapy, and chemotherapy) when they are no longer effective in controlling the disease or when they cannot be repeated (for example, radiotherapy).

Magnetic resonance and ultrasound image-guided navigation system using a needle manipulator

PURPOSE

Image guidance is crucial for percutaneous tumor ablations, enabling accurate needle-like applicator placement into target tumors while avoiding tissues that are sensitive to injury and/or correcting needle deflection. Although ultrasound (US) is widely used for image guidance, magnetic resonance (MR) is preferable due to its superior soft tissue contrast. The objective of this study was to develop and evaluate an MR and US multi-modal image-guided navigation system with a needle manipulator to enable US-guided applicator placement during MR imaging (MRI)-guided percutaneous tumor ablation.

METHODS

The MRI-compatible needle manipulator with US probe was installed adjacent to a 3 Tesla MRI scanner patient table. Coordinate systems for the MR image, patient table, manipulator, and US probe were all registered using an optical tracking sensor. The patient was initially scanned in the MRI scanner bore for planning and then moved outside the bore for treatment. Needle insertion was guided by real-time US imaging fused with the reformatted static MR image to enhance soft tissue contrast. Feasibility, targeting accuracy, and MR compatibility of the system were evaluated using a bovine liver and agar phantoms.

RESULTS

Targeting error for 50 needle insertions was 1.6 ± 0.6 mm (mean ± standard deviation). The experiment confirmed that fused MR and US images provided real-time needle localization against static MR images with soft tissue contrast.

CONCLUSIONS

The proposed MR and US multi-modal image-guided navigation system using a needle manipulator enabled accurate needle insertion by taking advantage of static MR and real-time US images simultaneously. Real-time visualization helped determine needle depth, tissue monitoring surrounding the needle path, target organ shifts, and needle deviation from the path.

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.

Invasive management of symptomatic hepatic hemangioma

Hepatic hemangioma is common among benign liver tumors and usually grows slowly. About 50-70% of hepatic hemangiomas are asymptomatic, and management is not necessary; however, management should be considered in symptomatic patients. The optimal management of symptomatic hepatic hemangioma depends on multiple factors. Invasive management of symptomatic hepatic hemangioma mainly consists of surgery and interventional radiology, including transarterial embolization, ablation, percutaneous sclerotherapy, and percutaneous argon-helium cryotherapy. Although both surgery and interventional radiology are promising in the management of symptomatic hepatic hemangioma, multiple and/or giant hemangiomas represent a clinical dilemma because the complication rate and recurrence rate are relatively high, and symptom relief is not always achieved. However, a review of recent advances in treatment is lacking. We therefore summarized the current invasive management techniques for symptomatic hepatic hemangioma to potentially facilitate clinical decision-making.

Safety and efficiency of low-field magnetic resonance imaging in patients with cardiac rhythm management devices

PURPOSE

Low-field magnetic resonance imaging (MRI), i.e. MRI with a static magnetic field strength <0.5 T, has been reported to be safe in patients with pacemakers, however there are no data about the safety of low-field MRI in patients with implantable cardioverter defibrillators (ICD) and/or cardiac resynchronization therapy (CRT). We aimed to investigate the safety and diagnostic efficiency of routine low-field MRI in patients with different devices for cardiac rhythm management (i.e. pacemakers and ICD, including devices with CRT).

METHOD

MRI scans of 446 regions of interest were evaluated with field strength of 0.2 T in 338 patients (62% male; age at MRI scan 76.1 ± 9.2 years; time since device implantation 4.1 ± 3.2 years) with cardiac rhythm management devices (298 pacemakers, 25 ICD, 8 CRT-ICD, and 7 CRT pacemakers). This analysis included 62 pacemaker-dependent patients (18.3%), 52 patients with 1.5-Tesla-MR conditional pacemakers (15.4%) and 13 patients with abandoned leads (3.9%).

RESULTS

Except for one examination, which was interrupted because of recurrent severe nausea, all MRI scans could be analyzed efficiently. No induction of arrhythmia or inhibition of pacemaker function occurred. Compared to the device interrogation before MRI, there were no significant changes in battery voltage, pacing capture threshold, sensing of intrinsic ECG, lead impedance, as well as shock impedance in ICD devices after completed examination.

CONCLUSIONS

Low-field MRI examinations (0.2 T) were efficient and safe regarding clinical and technical complications in patients with devices for cardiac rhythm management, even in case of pacemaker-dependency or the presence of abandoned leads.

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.

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.

Safety and Efficacy of Percutaneous Cryoablation for Small Hepatocellular Carcinomas Adjacent to the Heart

PURPOSE

This study evaluated the safety and efficacy of percutaneous cryoablation for treatment of the left subdiaphragmatic small hepatocellular carcinomas (HCCs) adjacent to the heart.

MATERIALS AND METHODS

Between September 2013 and March 2018, 189 consecutive patients underwent cryoablation for small HCCs (≤3 cm); 70 patients (mean: 61.3 ± 10.6 years of age; range: 40-82 years) with left hepatic tumors (22 juxtacardiac and 48 nonjuxtacardiac tumors) were retrospectively analyzed. Patients were divided into juxtacardiac and nonjuxtacardiac tumor groups (tumor margins: ≤10 mm and >10 mm, respectively, from the heart border). The rates of technical success, complete ablation, complications, and local tumor recurrence (LTR) were evaluated.

RESULTS

No significant intergroup differences were observed in the mean diameter of the tumor (17.9 ± 5.5 mm vs. 17.5 mm ± 5.2, respectively; P = 0.781) and of the ablation zone (41.3 ± 4.2 mm vs. 43.5 ± 5.8 mm, respectively; P = 0.115). Technical success was achieved in all patients. No procedure-related major complications occurred in either group. The median follow-up period was 15 months (range: 3.1-49.6 months). No statistically significant intergroup differences were observed in the rates of complete ablation (90.9% vs. 93.8%, respectively; P = 0.646) and LTR (20% vs. 15.6%, respectively; P = 0.725).

CONCLUSIONS

Cryoablation is a safe treatment modality for patients with juxtacardiac small HCCs, without an increased risk of cardiac complications compared to treatment of HCCs that are nonjuxtacardiac, and with comparable efficacy.

Focal therapy for localized prostate cancer: is there a "middle ground" between active surveillance and definitive treatment?

In recent years, it has come a long way in the diagnosis, treatment, and follow-up of prostate cancer. Beside this, it was argued that definitive treatments could cause overtreatment, particularly in the very low, low, and favorable risk group. When alternative treatment and follow-up methods are being considered for this group of patients, active surveillance is seen as a good alternative for patients with very low and low-risk groups in this era. However, it has become necessary to find other alternatives for patients in the favorable risk group or patients who cannot adopt active follow-up. In the light of technological developments, the concept of focal therapy was introduced with the intensification of research to treat only the lesioned area instead of treating the entire organ for prostate lesions though there are not many publications about many of them yet. According to the initial results, it was understood that the results could be good if the appropriate focal therapy technique was applied to the appropriate patient. Thus, focal therapies have begun to find their "middle ground" place between definitive therapies and active follow-up.

Motion compensation for MRI-compatible patient-mounted needle guide device: estimation of targeting accuracy in MRI-guided kidney cryoablations

Patient-mounted needle guide devices for percutaneous ablation are vulnerable to patient motion. The objective of this study is to develop and evaluate a software system for an MRI-compatible patient-mounted needle guide device that can adaptively compensate for displacement of the device due to patient motion using a novel image-based automatic device-to-image registration technique. We have developed a software system for an MRI-compatible patient-mounted needle guide device for percutaneous ablation. It features fully-automated image-based device-to-image registration to track the device position, and a device controller to adjust the needle trajectory to compensate for the displacement of the device. We performed: (a) a phantom study using a clinical MR scanner to evaluate registration performance; (b) simulations using intraoperative time-series MR data acquired in 20 clinical cases of MRI-guided renal cryoablations to assess its impact on motion compensation; and (c) a pilot clinical study in three patients to test its feasibility during the clinical procedure. FRE, TRE, and success rate of device-to-image registration were 2.71 ± 2.29 mm, 1.74 ± 1.13 mm, and 98.3% for the phantom images. The simulation study showed that the motion compensation reduced the targeting error for needle placement from 8.2 mm to 5.4 mm (p  <  0.0005) in patients under general anesthesia (GA), and from 14.4 mm to 10.0 mm (p < 1.0 × 10(−5)) in patients under monitored anesthesia care (MAC). The pilot study showed that the software registered the device successfully in a clinical setting. Our simulation study demonstrated that the software system could significantly improve targeting accuracy in patients treated under both MAC and GA. Intraprocedural image-based device-to-image registration was feasible.

How to Perform a Routine Cryoablation Under MRI Guidance

In the last decade, the spectrum of interventional magnetic resonance imaging (MRI)-guided procedures, including percutaneous ablation, has substantially grown, and among the available MRI-compatible ablative techniques, cryoablation is progressively gaining a predominant position.The aim of the present narrative review is to discuss the technical requirements necessary to perform a percutaneous MRI-guided cryoablation in a closed-bore machine; to highlight the relative advantages and drawbacks; and to briefly summarize the results available in the literature.

A Radiologist's View of Tumor Ablation in the Radiology Suite

Image-guided percutaneous, minimally invasive ablation techniques offer a wide variety of new modalities to treat tumors in some of the most medically complicated patients coming to our hospitals. The use of computed tomography, PET, ultrasound imaging, and MRI to guide radiofrequency ablation, microwave ablation, and cryoablation techniques now makes it possible to treat patients on a short stay or outpatient basis with very good immediate outcomes. This rapid expansion of new tumor ablation techniques often presents challenges for the non-operating room anesthesia team. Collaboration and communication between the radiologist and anesthesiologist are key to safety and excellent patient outcomes.

Percutaneous Image-Guided Cryoablation of Hepatic Tumors: Single-Center Experience With Intermediate to Long-Term Outcomes

OBJECTIVE

The purpose of this article is to report our intermediate to long-term outcomes with image-guided percutaneous hepatic tumor cryoablation and to evaluate its technical success, technique efficacy, local tumor progression, and adverse event rate.

MATERIALS AND METHODS

Between 1998 and 2014, 299 hepatic tumors (243 metastases and 56 primary tumors; mean diameter, 2.5 cm; median diameter, 2.2 cm; range, 0.3-7.8 cm) in 186 patients (95 women; mean age, 60.9 years; range, 29-88 years) underwent cryoablation during 236 procedures using CT (n = 126), MRI (n = 100), or PET/CT (n = 10) guidance. Technical success, technique efficacy at 3 months, local tumor progression (mean follow-up, 2.5 years; range, 2 months to 14.6 years), and adverse event rates were calculated.

RESULTS

The technical success rate was 94.6% (279/295). The technique efficacy rate was 89.5% (231/258) and was greater for tumors smaller than 4 cm (93.4%; 213/228) than for larger tumors (60.0%; 18/30) (p < 0.0001). Local tumor progression occurred in 23.3% (60/258) of tumors and was significantly more common after the treatment of tumors 4 cm or larger (63.3%; 19/30) compared with smaller tumors (18.0%; 41/228) (p < 0.0001). Adverse events followed 33.8% (80/236) of procedures and were grade 3-5 in 10.6% (25/236) of cases. Grade 3 or greater adverse events more commonly followed the treatment of larger tumors (19.5%; 8/41) compared with smaller tumors (8.7%; 17/195) (p = 0.04).

CONCLUSION

Image-guided percutaneous cryoablation of hepatic tumors is efficacious; however, tumors smaller than 4 cm are more likely to be treated successfully and without an adverse event.

Cryosurgery for Tumors — A Clinical Overview

Cryosurgery, a method of treating disease by the production of freezing temperatures in the tissue, is a useful technique for the treatment of tumors. When the modern era of cryosurgery began in the mid 1960's, the technique was used only for tumors easily accessible by direct observation or via endoscopy, such as those of the skin, oral cavity, and prostate gland. In general, the technique had limited usefulness in the next two decades. However, with the advent of intraoperative ultrasound as a method of monitoring the process of freezing and with the development of more effective cryosurgical apparatus, the cryosurgical treatment of tumors of the viscera and other deep tissues became practical in the 1990's. This review assesses the present day status of cryosurgery in the management of diverse tumors.

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.

Three-dimensional quantitative assessment of ablation margins based on registration of pre- and post-procedural MRI and distance map

PURPOSE

Contrast-enhanced MR images are widely used to confirm the adequacy of ablation margin after liver ablation for early prediction of local recurrence. However, quantitative assessment of the ablation margin by comparing pre- and post-procedural images remains challenging. We developed and tested a novel method for three-dimensional quantitative assessment of ablation margin based on non-rigid image registration and 3D distance map.

METHODS

Our method was tested with pre- and post-procedural MR images acquired in 21 patients who underwent image-guided percutaneous liver ablation. The two images were co-registered using non-rigid intensity-based registration. After the tumor and ablation volumes were segmented, target volume coverage, percent of tumor coverage, and Dice similarity coefficient were calculated as metrics representing overall adequacy of ablation. In addition, 3D distance map around the tumor was computed and superimposed on the ablation volume to identify the area with insufficient margins. For patients with local recurrences, the follow-up images were registered to the post-procedural image. Three-dimensional minimum distance between the recurrence and the areas with insufficient margins was quantified.

RESULTS

The percent tumor coverage for all nonrecurrent cases was 100 %. Five cases had tumor recurrences, and the 3D distance map revealed insufficient tumor coverage or a 0-mm margin. It also showed that two recurrences were remote to the insufficient margin.

CONCLUSIONS

Non-rigid registration and 3D distance map allow us to quantitatively evaluate the adequacy of the ablation margin after percutaneous liver ablation. The method may be useful to predict local recurrences immediately following ablation procedure.

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.

Real-Time MRI-Guided Cardiac Cryo-Ablation: A Feasibility Study

INTRODUCTION

MRI-based ablation provides an attractive capability of seeing ablation-related tissue changes in real time. Here we describe a real-time MRI-based cardiac cryo-ablation system.

METHODS

Studies were performed in canine model (n = 4) using MR-compatible cryo-ablation devices built for animal use: focal cryo-catheter with 8 mm tip and 28 mm diameter cryo-balloon. The main steps of MRI-guided cardiac cryo-ablation procedure (real-time navigation, confirmation of tip-tissue contact, confirmation of vessel occlusion, real-time monitoring of a freeze zone formation, and intra-procedural assessment of lesions) were validated in a 3 Tesla clinical MRI scanner.

RESULTS

The MRI compatible cryo-devices were advanced to the right atrium (RA) and right ventricle (RV) and their position was confirmed by real-time MRI. Specifically, contact between catheter tip and myocardium and occlusion of superior vena cava (SVC) by the balloon was visually validated. Focal cryo-lesions were created in the RV septum. Circumferential ablation of SVC-RA junction with no gaps was achieved using the cryo-balloon. Real-time visualization of freeze zone formation was achieved in all studies when lesions were successfully created. The ablations and presence of collateral damage were confirmed by T1-weighted and late gadolinium enhancement MRI and gross pathological examination.

CONCLUSION

This study confirms the feasibility of a MRI-based cryo-ablation system in performing cardiac ablation procedures. The system allows real-time catheter navigation, confirmation of catheter tip-tissue contact, validation of vessel occlusion by cryo-balloon, real-time monitoring of a freeze zone formation, and intra-procedural assessment of ablations including collateral damage.

Treatment of osteolytic solitary painful osseous metastases with radiofrequency ablation or cryoablation: A retrospective study by propensity analysis

The present study aimed to measure the improvement in pain relief and quality of life in patients with osteolytic solitary painful bone metastasis treated by cryoablation (CA) or radiofrequency ablation (RFA). Fifty patients with solitary osteolytic painful bone metastases were retrospectively studied and selected by propensity analysis. Twenty-five patients underwent CA and the remaining twenty-five underwent RFA. Pain relief, in terms of complete response (CR), the number of patients requiring analgesia and the changes in self-rated quality of life (QoL) were measured following the two treatments. Thirty-two percent of patients treated by CA experienced a CR at 12 weeks versus 20% of patients treated by RFA. The rate of CR increased significantly with respect to baseline only in the group treated by CA. In both groups there was a significant change in the partial response with respect to baseline (36% in the CA group vs. 44% in the RFA group). The recurrence rate in the CA and RFA groups was 12% and 8%, respectively. The reduction in narcotic medication requirements with respect to baseline was only significant in the group treated by CA. A significant improvement in self-rated QoL was observed in both groups. The present study seems to suggest that CA only significantly improves the rate of CR and decreases the requirement of narcotic medications. Both CA and RFA led to an improvement in the self-rated QoL of patients after the treatments. However, the results of the present study should be considered as preliminary and to serve as a framework around which future trials may be designed.

Cryoablation Versus Radiofrequency Ablation for Hepatic Malignancies: A Systematic Review and Literature-Based Analysis

The aim of this study is to summarize and quantify the current evidence on the therapeutic efficacy of cryoablation compared with radiofrequency ablation (RFA) in patients with hepatic malignancies in a meta-analysis.Data were collected by searching PubMed, Scopus, and Cochrane databases for reports published up to May 26, 2015. Studies that reported data on comparisons of therapeutic efficacy of cryoablation and RFA were included. The random effects model was used to estimate the pooled relative risks of events comparing cryoablation to RFA for therapy of hepatic malignancies.Seven articles met the inclusion criteria and were included in the meta-analysis. The meta-analysis showed that there was no statistically significant difference in mortality of at least 6 months (odds ratio [OR] = 1.00, 95% confidence interval [CI]: 0.68-1.49) and local tumor progression according to both patients (OR = 1.64, 95% CI: 0.57-4.74) and tumors (OR = 1.81, 95% CI: 0.74-4.38) between cryoablation group and RFA group. However, the risk of complications was significantly higher in the cryoablation group than that in the RFA group (OR = 2.93, 95% CI: 1.15-7.46). When considering the specific complications, only thrombocytopenia (OR = 51.13, 95% CI: 2.92-894.21) and renal impairment (OR = 4.19, 95% CI: 1.34-13.11) but not other complications were significantly higher in the cryoablation group.In conclusion, the 2 methods had almost equal mortality and nonsignificant difference in local tumor progression, with higher risk of complications in cryoablation. Further large-scale, well-designed randomized controlled trials are needed to identify the current findings and investigate the long-term effects of cryoablation compared with RFA for therapy of hepatic malignancies.

Potential of minimally invasive procedures in the treatment of uterine fibroids: a focus on magnetic resonance-guided focused ultrasound therapy

Minimally invasive treatment options are an important part of the uterine fibroid-treatment arsenal, especially among younger patients and in those who plan future pregnancies. This article provides an overview of the currently available minimally invasive therapy options, with a special emphasis on a completely noninvasive option: magnetic resonance-guided focused ultrasound (MRgFUS). In this review, we describe the background of MRgFUS, the patient-selection criteria for MRgFUS, and how the procedure is performed. We summarize the published clinical trial results, and review the literature on pregnancy post-MRgFUS and on the cost-effectiveness of MRgFUS.

Minimal invasive treatments for liver malignancies

Minimal invasive therapies have proved useful in the management of primary and secondary hepatic malignancies. The most relevant aspects of all these therapies are their minimal toxicity profiles and highly effective tumor responses without affecting the normal hepatic parenchyma. These unique characteristics coupled with their minimally invasive nature provide an attractive therapeutic option for patients who previously may have had few alternatives. Combination of these therapies might extend indications to bring curative treatment to a wider selected population. The results of various ongoing combination trials of intraarterial therapies with targeted therapies are awaited to further improve survival in this patient group. This review focuses on the application of ablative and intra-arterial therapies in the management of hepatocellular carcinoma and hepatic colorectal metastasis.

CT-guided percutaneous cryoablation of central lung tumors

PURPOSE

Cryoablation has been successfully used to treat lung tumors. However, the safety and effectiveness of treating tumors adjacent to critical structures has not been fully established. We describe our experience with computed tomography (CT)-guided percutaneous cryoablation of central lung tumors and the role of ice ball monitoring.

MATERIALS AND METHODS

Eight patients with 11 malignant central lung tumors (nine metastatic, two primary; mean, 2.6 cm; range, 1.0-4.5 cm) located adjacent to mediastinal or hilar structures were treated using CT-guided cryoablation in 10 procedures. Technical success and effectiveness rates were calculated, complications were tabulated and intraprocedural imaging features of ice balls were described.

RESULTS

All procedures were technically successful; imaging after 24 hours demonstrated no residual tumor. Five tumors recurred, three of which were re-ablated successfully. A hypodense ice ball with well-defined margin was visible during the first (n=6, 55%) or second (n=11, 100%) freeze, encompassing the entire tumor in all patients, and abutting (n=7) or minimally involving (n=4) adjacent mediastinal and hilar structures. Pneumothorax developed following six procedures (60%); percutaneous treatment was applied in three of them. All patients developed pleural effusions, with one patient requiring percutaneous drainage. Transient hemoptysis occurred after six procedures (60%), but all cases improved within a week. No injury occurred to mediastinal or hilar structures.

CONCLUSION

CT-guided percutaneous cryoablation can be used to treat central lung tumors successfully. Although complications were common, they were self-limited, treatable, and not related to tumor location. Ice ball monitoring helped maximize the amount of tumor treated, while avoiding critical mediastinal and hilar structures.

Magnetic Resonance Imaging-Guided Spine Interventions

MR imaging-guided interventions for treatment of low back pain and for diagnosis and treatment of soft tissue and bony spinal lesions have been shown to be feasible, effective, and safe. Advantages of this technique include the absence of ionizing radiation, the high tissue contrast, and multiplanar imaging options. Recent advancements in MR imaging systems allow improved image qualities and real-time guidance. One exciting application is MR imaging-guided cryotherapy of spinal lesions, including treating such lesions as benign osteoid osteomas and malignant metastatic disease in patients who are not good surgical candidates. This particular technique shows promise for local tumor control and pain relief in appropriate patients.

Treatment of Solitary Painful Osseous Metastases with Radiotherapy, Cryoablation or Combined Therapy: Propensity Matching Analysis in 175 Patients

PURPOSE

aim of this study was to identify outcomes in pain relief and quality of life in patients with a solitary painful osseous metastasis treated by radiotherapy, cryoablation or the combination using a propensity score matching study design.

MATERIALS AND METHODS

175 patients with painful bone metastases were included in the study. Twenty-five of them underwent a radiation course (20 Gy in five daily fractions) 15 days after the cryoablation. These subjects were retrospectively matched by propensity analysis with a group of subjects treated by radiotherapy (125 subjects) and with a group treated byCryoablation (25 subjects). The pain relief in terms of complete response, rate of subjects requiring analgesics after treatments and the changes in self-rated quality of life were measured. Informed consent was obtained from the subject and the study was approved by the local Ethical Committee.

RESULTS

An higher proportion of subjects treated by cryoablation (32%) or cryoablation followed by RT (72%;) experienced a complete response compared with patients treated by radiotherapy alone (11.2%). After Bonferroni correction strategy, the addition of radiotherapy to cryoablation significantly improved the rate of complete response compared with cryoablation alone (p = 0.011) and this paralleled with an improved self-rated quality of life. Seventeen subjects (13.6%) of patients in the radiotherapy group, 9 (36%) in the cryoablation group, and 19 (76)% in the cryoablation- radiotherapy group did not require narcotic medications.

CONCLUSIONS

The addition of radiotherapy to cryoablation favorably impacts on perceived pain, with a favorable toxicity profile. However, our data should be interpreted with caution and could serve as a framework around which to design future trials.

Image-guided tumor ablation: standardization of terminology and reporting criteria--a 10-year update

Image-guided tumor ablation has become a well-established hallmark of local cancer therapy. The breadth of options available in this growing field increases the need for standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison among treatments that use different technologies, such as chemical (eg, ethanol or acetic acid) ablation, thermal therapies (eg, radiofrequency, laser, microwave, focused ultrasound, and cryoablation) and newer ablative modalities such as irreversible electroporation. This updated consensus document provides a framework that will facilitate the clearest communication among investigators regarding ablative technologies. An appropriate vehicle is proposed for reporting the various aspects of image-guided ablation therapy including classification of therapies, procedure terms, descriptors of imaging guidance, and terminology for imaging and pathologic findings. Methods are addressed for standardizing reporting of technique, follow-up, complications, and clinical results. As noted in the original document from 2003, adherence to the recommendations will improve the precision of communications in this field, leading to more accurate comparison of technologies and results, and ultimately to improved patient outcomes.

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.

Percutaneous imaging-guided cryoablation of liver tumors: predicting local progression on 24-hour MRI

OBJECTIVE

The purpose of this study was to determine which MRI features observed 24 hours after technically successful percutaneous cryoablation of liver tumors predict subsequent local tumor progression and to describe the evolution of imaging findings after cryoablation.

MATERIALS AND METHODS

Thirty-nine adult patients underwent technically successful imaging-guided percutaneous cryoablation of 54 liver tumors (hepatocellular carcinoma, 8; metastases, 46). MRI features pertaining to the tumor, ablation margin, and surrounding liver 24 hours after treatment were assessed independently by two readers. Fisher exact or Wilcoxon rank sum tests (significant p values < 0.05) were used to compare imaging features in patients with and without subsequent local tumor progression. Imaging features of the ablation margin, treated tumor, and surrounding liver were evaluated on serial MRI in the following year.

RESULTS

A minimum ablation margin of 3 mm or less was observed in 11 (78.6%) of 14 tumors with and 15 of 40 (37.5%) without progression (p = 0.012). A blood vessel bridging the ablation margin was noted in 11 of 14 (78.6%) tumors with and nine of 40 (22.5%) without progression (p < 0.001). The incidence of tumor enhancement 24 hours after cryoablation was similar for tumors with (10/14, 71.4%) or without (25/40, 62.5%) local progression (p = 0.75). MRI enabled assessment of the entire cryoablation margin in 49 of 54 (90.7%) treated tumors.

CONCLUSION

MRI features at 24 hours after liver cryoablation that were predictive of local tumor progression included a minimum ablation margin less than or equal to 3 mm and a blood vessel bridging the ablation margin. Persistent tumor enhancement is common after liver cryoablation and does not predict local tumor progression.

Multimodality imaging to assess immediate response to irreversible electroporation in a rat liver tumor model

PURPOSE

To compare changes on ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) images after irreversible electroporation (IRE) ablation of liver and tumor tissues in a rodent hepatoma model.

MATERIALS AND METHODS

Studies received approval from the institutional animal care and use committee. Forty-eight rats were used, and N1-S1 tumors were implanted in 24. Rats were divided into groups and allocated for studies with each modality. Imaging was performed in normal liver tissues and tumors before and after IRE. MR imaging was performed in one group before and after IRE after hepatic vessel ligation. US images were graded to determine echogenicity changes, CT attenuation was measured (in Hounsfield units), and MR imaging signal-to-noise ratio (SNR) was measured before and after IRE. Student t test was used to compare attenuation and SNR measurements before and after IRE (P < .05 indicated a significant difference).

RESULTS

IRE ablation produced greater alterations to echogenicity in normal tissues than in tumors. Attenuation in ablated liver tissues was reduced compared with that in control tissues (P < .001), while small attenuation differences between ablated (42.11 HU ± 2.11) and control (45.14 HU ± 2.64) tumors trended toward significance (P = .052). SNR in ablated normal tissues was significantly altered after IRE (T1-weighted images: pre-IRE, 145.95 ± 24.32; post-IRE, 97.80 ± 18.03; P = .004; T2-weighted images, pre-IRE, 47.37 ± 18.31; post-IRE, 90.88 ± 37.15; P = .023). In tumors, SNR differences before and after IRE were not significant. No post-IRE signal changes were observed after hepatic vessel ligation.

CONCLUSION

IRE induces rapid changes on gray-scale US, unenhanced CT, and MR images. These changes are readily visible and may assist a performing physician to delineate ablation zones from the unablated surrounding parenchyma.

Percutaneous treatment of hepatocellular carcinoma in patients with cirrhosis: a comparison of the safety of cryoablation and radiofrequency ablation

PURPOSE

To compare the safety of image-guided percutaneous cryoablation and radiofrequency ablation in the treatment of hepatocellular carcinoma in patients with cirrhosis.

MATERIALS AND METHODS

This retrospective HIPAA-compliant study received institutional review board approval. Forty-two adult patients with cirrhosis underwent image-guided percutaneous ablation of hepatocellular carcinoma from 2003 to 2011. Twenty-five patients underwent 33 cryoablation procedures to treat 39 tumors, and 22 underwent 30 radiofrequency ablation procedures to treat 39 tumors. Five patients underwent both cryoablation and radiofrequency ablation procedures. Complication rates and severity per procedure were compared between the ablation groups. Potential confounding patient, procedure, and tumor-related variables were also compared. Statistical analyses included Kruskal-Wallis, Wilcoxon rank sum, and Fisher's exact tests. Two-sided P-values <0.05 were considered significant.

RESULTS

The overall complication rates, 13 (39.4%) of 33 cryoablation procedures versus eight (26.7%) of 30 radiofrequency ablation procedures and severe/fatal complication rates, two (6.1%) of 33 cryoablation procedures versus one (3.3%) of 30 radiofrequency ablation procedures, were not significantly different between the ablation groups (both P=0.26). Severe complications included pneumothoraces requiring chest tube insertion during two cryoablation procedures. One death occurred within 90 days of a radiofrequency ablation procedure; all other complications were managed successfully.

CONCLUSION

No significant difference was seen in the overall safety of image-guided percutaneous cryoablation and radiofrequency ablation in the treatment of hepatocellular carcinoma in patients with cirrhosis.

[Image-guided therapy with closed MRI: an update]

STANDARD RADIOLOGICAL METHODS

Standard imaging modalities for percutaneous minimally invasive therapy are ultrasound, fluoroscopy and computed tomography.

METHODICAL INNOVATIONS

Magnetic resonance imaging is becoming increasingly more popular for minimally invasive procedures. The advantages are high soft-tissue contrast, the possibility of free selection of multiple imaging slices, multiple tools for intrainterventional monitoring and the absence of ionizing radiation for the patient and the interventional radiologist.

ACHIEVEMENTS

Magnetic resonance imaging is a promising imaging modality for minimally invasive procedures. The most common clinical applications are thermoablative procedures for treatment of hepatic, renal and prostatic malignancies.

Methods for characterizing convective cryoprobe heat transfer in ultrasound gel phantoms

While cryosurgery has proven capable in treating of a variety of conditions, it has met with some resistance among physicians, in part due to shortcomings in the ability to predict treatment outcomes. Here we attempt to address several key issues related to predictive modeling by demonstrating methods for accurately characterizing heat transfer from cryoprobes, report temperature dependent thermal properties for ultrasound gel (a convenient tissue phantom) down to cryogenic temperatures, and demonstrate the ability of convective exchange heat transfer boundary conditions to accurately describe freezing in the case of single and multiple interacting cryoprobe(s). Temperature dependent changes in the specific heat and thermal conductivity for ultrasound gel are reported down to -150 °C for the first time here and these data were used to accurately describe freezing in ultrasound gel in subsequent modeling. Freezing around a single and two interacting cryoprobe(s) was characterized in the ultrasound gel phantom by mapping the temperature in and around the "iceball" with carefully placed thermocouple arrays. These experimental data were fit with finite-element modeling in COMSOL Multiphysics, which was used to investigate the sensitivity and effectiveness of convective boundary conditions in describing heat transfer from the cryoprobes. Heat transfer at the probe tip was described in terms of a convective coefficient and the cryogen temperature. While model accuracy depended strongly on spatial (i.e., along the exchange surface) variation in the convective coefficient, it was much less sensitive to spatial and transient variations in the cryogen temperature parameter. The optimized fit, convective exchange conditions for the single-probe case also provided close agreement with the experimental data for the case of two interacting cryoprobes, suggesting that this basic characterization and modeling approach can be extended to accurately describe more complicated, multiprobe freezing geometries. Accurately characterizing cryoprobe behavior in phantoms requires detailed knowledge of the freezing medium's properties throughout the range of expected temperatures and an appropriate description of the heat transfer across the probe's exchange surfaces. Here we demonstrate that convective exchange boundary conditions provide an accurate and versatile description of heat transfer from cryoprobes, offering potential advantages over the traditional constant surface heat flux and constant surface temperature descriptions. In addition, although this study was conducted on Joule-Thomson type cryoprobes, the general methodologies should extend to any probe that is based on convective exchange with a cryogenic fluid.

Percutaneous ultrasonography and computed tomography guided pancreatic cryoablation: feasibility and safety assessment

OBJECTIVE

To assess the safety and feasibility of percutaneous cryoablation on pancreatic cancer via ultrasonography (US) and computed tomography (CT) guidance.

MATERIALS AND METHODS

This retrospective review was approved by the institutional review board and of informed consent. Thirty-two patients (18 men and 14 women; median age 62; age range, 30-77 years) with pancreatic cancer (stage II/III/IV, 3/11/18) treated with percutaneous US and CT guided cryoablations between February 2009 and February 2010 were eligible for this review. Thirteen tumors in pancreatic head and 19 in pancreatic body and/or tail measuring 2-11 cm (mean, 5.2 cm±8 [standard deviation]) were ablated with 49 procedures in total. Feasibility was analyzed by enhanced CT 1-3 months post procedure and safety was assessed by clinical signs, symptoms and laboratory results.

RESULTS

Neither procedural death nor serious complications occurred. Fifteen tumors (46.9%) smaller than 5 cm were successfully ablated by one session of cryoablation. Twenty-seven patients experienced a ≥50% reduction in pain score, 22 experienced a 50% decrease in analgesic consumption and 16 experienced a ≥20 increase in Karnofsky Performance Status (KPS) Score. Partial response (PR) and stable disease (SD) turned up in 9 and 21 patients, respectively, lesions in whom were identified controlled by none enhancement on enhanced CT. Mean and median survival was 15.9 and 12.6 months, respectively. The 6-, 12- and 24-month survival rates were 82.8%, 54.7% and 27.3%, respectively.

CONCLUSION

US and CT guided percutaneous cryoablation is a safe and promising local treatment for pancreatic cancer.

[Update on interstitial brachytherapy]

CLINICAL/METHODICAL ISSUE

Minimally invasive treatment procedures, such as image-guided local tumour ablation have gained increasing relevance in oncologic concepts. Limitations of thermal ablation procedures have led to the development of percutaneous, computed tomography (CT) guided brachytherapy.

STANDARD RADIOLOGICAL METHODS

Thermal ablation procedures, such as radiofrequency ablation (RFA) and laser-induced thermotherapy (LITT) show limitations regarding maximum tumour size (<5 cm), cooling effects of adjacent vessels and surrounding risk structures.

METHODICAL INNOVATIONS

The image-guided interstitial brachytherapy allows the single application of high-dose rate (HDR) irradiation with an extensive protracted cytotoxic effect. Adjacent risk structures play a minor role due to the steep dose gradient outside the clinical target volume.

PERFORMANCE

Studies using CT-guided brachytherapy resulted in a local tumour control rate of approximately 90% after 12 months in the treatment of hepatocellular carcinoma (HCC) and 70-90% in the treatment of colorectal metastases or cholangiocellular carcinoma (CCC). Similar response rates were also seen in the treatment of metastases of renal cell carcinoma (RCC), non-small cell lung cancer (NSCLC) or neuroendocrine tumours. In colorectal liver metastases and HCC the method has proven to have a positive impact on prognosis.

ACHIEVEMENTS

In contrast to thermal ablation the method can be used without restriction with respect to tumour location. Cooling effects do not play a role. It has already been applied in more than 5,000 cases and it is used in clinical routine.

PRACTICAL RECOMMENDATIONS

Image-guided brachytherapy is safe and effective and has found its way into the clinical routine.

The current role of minimally invasive therapies in the management of liver tumors

This is a review of minimally invasive therapy options for liver tumors, such as highly focused ultrasound, microwave ablation, and irreversible electroporation, as well as new aspects of radiofrequency ablation. Radiofrequency ablation is recommended for patients with early-stage HCC with up to 3 lesions with a tumor diameter within 3 cm and for patients with non-resectable liver metastasis. Indications and contraindications to treatment are designated, and different modalities for image-based therapy guidance are compared. Options for therapy monitoring and controlling are reviewed, namely intraprocedural tools, imaging and functional parameters and their evolution during therapy. Prevention and control of local recurrences is discussed. We also present a short review of current clinical results in treating liver metastasis and primary liver tumors.

MRI contrast enhancement of malignant liver tumours following successful cryoablation

OBJECTIVES

To assess the incidence and degree of MRI contrast enhancement in liver tumours following successful percutaneous cryoablation.

METHODS

Thirty-eight patients with liver metastases (n = 29) or hepatocellular carcinoma (n = 9) underwent percutaneous cryoablation of 45 tumours between March 2004 and June 2009, with complete ablation zone coverage of the tumour and no local recurrence on follow-up imaging to date (range 3-60 months, mean 16). Contrast-enhanced MRI was used to assess 45 tumours at 24 h, 32 tumours at 2-4 months, and 21 tumours at 5-7 months. Percentage of tumours with contrast enhancement was assessed using dynamic spoiled gradient echo T1-weighted images.

RESULTS

Twenty-four hours post-cryoablation, 23 out of 45 tumours (51%) enhanced compared with 42 out of 43 (98%) pre-ablation (p < 0.001). Mean percentage tumour enhancement decreased from 157% (range 26-745%) pre-ablation, to 107% (27-260%) at 24 h (p = 0.003), and 43% (24-103%) at 2-4 months (p < 0.001). The incidence and degree of tumour enhancement decreased through 5-7 months.

CONCLUSIONS

Unlike previously reported studies of radiofrequency ablation, successful cryoablation of liver tumours is often associated with persistent tumour contrast enhancement on MRI performed at 24 h and decreasing over 2-7 months.

KEY POINTS

• Liver neoplasms often demonstrate MRI contrast enhancement following successful percutaneous cryoablation. • This differs from radiofrequency ablation techniques where contrast enhancement suggests residual tumour • This difference could potentially lead to important errors in follow up strategies.

Biologic and clinical features of benign solid and cystic lesions of the liver

The widespread use of imaging analyses, either routinely or to evaluate symptomatic patients, has increased the detection of liver lesions (tumors and cysts) in otherwise healthy individuals. Although some of these incidentally discovered masses are malignant, most are benign and must be included in the differential diagnosis. The management of benign hepatic tumors ranges from conservative to aggressive, depending on the nature of the lesions. New imaging modalities, increased experience of radiologists, improved definition of radiologic characteristics, and a better understanding of the clinical features of these lesions have increased the accuracy of diagnoses and reduced the need for invasive diagnostic tests. These advances have led to constant adjustments in management approaches to benign hepatic lesions. We review the biologic and clinical features of some common hepatic lesions, to guide diagnosis and management strategies.

Estimated effective dose of CT-guided percutaneous cryoablation of liver tumors

PURPOSE

To estimate effective dose during CT-guided cryoablation of liver tumors, and to assess which procedural factors contribute most to dose.

MATERIALS AND METHODS

Our institutional review board approved this retrospective, HIPAA-compliant study. A total of 20 CT-guided percutaneous liver tumor cryoablation procedures were performed in 18 patients. Effective dose was determined by multiplying the dose length product for each CT scan obtained during the procedure by a conversion factor (0.015mSv/mGy-cm), and calculating the sum for each phase of the procedure: planning, targeting, monitoring, and post-ablation survey. Effective dose of each phase was compared using a repeated measures analysis. Using Spearman correlation coefficients, effective doses were correlated with procedural factors including number of scans, ratio of targeting distance to tumor size, anesthesia type, number of applicators, performance of ancillary procedures (hydrodissection and biopsy), and use of CT fluoroscopy.

RESULTS

Effective dose per procedure was 72±18mSv. The effective dose of targeting (37.5±12.5mSv) was the largest component compared to the effective dose of the planning phase (4.8±2.2mSv), the monitoring phase (25.5±6.8mSv), and the post-ablation survey (4.1±1.9mSv) phase (p<0.05). Effective dose correlated positively only with the number of scans (p<0.01).

CONCLUSIONS

The effective dose of CT-guided percutaneous cryoablation of liver tumors can be substantial. Reducing the number of scans during the procedure is likely to have the greatest effect on lowering dose.