MR-guided laser thermal ablation of primary and secondary liver tumours

Tissue Ablation: Applications and Perspectives

Tissue ablation techniques have emerged as a critical component of modern medical practice and biomedical research, offering versatile solutions for treating various diseases and disorders. Percutaneous ablation is minimally invasive and offers numerous advantages over traditional surgery, such as shorter recovery times, reduced hospital stays, and decreased healthcare costs. Intra-procedural imaging during ablation also allows precise visualization of the treated tissue while minimizing injury to the surrounding normal tissues, reducing the risk of complications. Here, the mechanisms of tissue ablation and innovative energy delivery systems are explored, highlighting recent advancements that have reshaped the landscape of clinical practice. Current clinical challenges related to tissue ablation are also discussed, underlining unmet clinical needs for more advanced material-based approaches to improve the delivery of energy and pharmacology-based therapeutics.

Interstitial Optical Monitoring of Focal Laser Ablation

Focal laser ablation is a minimally invasive method of treating cancerous lesions in organs such as prostate, liver and brain. Oncologic control is achieved by inducing hyperthermia throughout the target while minimizing damage to surrounding tissue. Consequently, successful clinical outcomes are contingent upon achieving desired ablation volumes. Magnetic resonance thermometry is frequently used to monitor the formation of the induced thermal damage zone and inform the decision to terminate energy delivery. However, due to the associated cost and complexity there is growing interest in the development of alternative approaches. Here we investigate the utility of real-time interstitial interrogation of laser-tissue interaction as an inexpensive alternative monitoring modality that provides direct assessment of tissue coagulation without the need for organ specific calibration. The optical contrast mechanism was determined using a Monte Carlo model. Subsequently, four interstitial probe designs were manufactured and assessed in a tissue mimicking phantom under simultaneous magnetic resonance imaging. Finally, the optimal probe design was evaluated in ex vivo bovine muscle. It was found to be capable of providing sufficient feedback to achieve pre-defined ablation radii in the range 4-7mm with a mean absolute error of 0.3mm. This approach provides an inexpensive monitoring modality that may facilitate widespread adoption of focal laser ablation.

Methods of monitoring thermal ablation of soft tissue tumors - A comprehensive review

Thermal ablation is a form of hyperthermia in which oncologic control can be achieved by briefly inducing elevated temperatures, typically in the range 50-80°C, within a target tissue. Ablation modalities include high intensity focused ultrasound, radiofrequency ablation, microwave ablation, and laser interstitial thermal therapy which are all capable of generating confined zones of tissue destruction, resulting in fewer complications than conventional cancer therapies. Oncologic control is contingent upon achieving predefined coagulation zones; therefore, intraoperative assessment of treatment progress is highly desirable. Consequently, there is a growing interest in the development of ablation monitoring modalities. The first section of this review presents the mechanism of action and common applications of the primary ablation modalities. The following section outlines the state-of-the-art in thermal dosimetry which includes interstitial thermal probes and radiologic imaging. Both the physical mechanism of measurement and clinical or pre-clinical performance are discussed for each ablation modality. Thermal dosimetry must be coupled with a thermal damage model as outlined in Section 4. These models estimate cell death based on temperature-time history and are inherently tissue specific. In the absence of a reliable thermal model, the utility of thermal monitoring is greatly reduced. The final section of this review paper covers technologies that have been developed to directly assess tissue conditions. These approaches include visualization of non-perfused tissue with contrast-enhanced imaging, assessment of tissue mechanical properties using ultrasound and magnetic resonance elastography, and finally interrogation of tissue optical properties with interstitial probes. In summary, monitoring thermal ablation is critical for consistent clinical success and many promising technologies are under development but an optimal solution has yet to achieve widespread adoption.

Monitoring Focal Laser Ablation with Interstitial Fluence Probes: Monte Carlo Simulation and Phantom Validation

Focal laser ablation offers a minimally invasive method of treating solid organ tumors via hyperthermia. Real-time monitoring of the induced tissue damage is critical for clinical success, and is typically accomplished using thermal measurements and Arrhenius models. In this manuscript, the utility of interstitial fluence probes in assessing coagulation directly in real-time was assessed through a Monte Carlo simulation and an experimental study in tissue mimicking prostate phantoms. In the simulation results, fluence increases greater than 100% were observed inside the coagulation zone, as coagulation effectively acts as a 'light trap'. Moreover, the passing of the coagulation boundary at any given point was shown to correspond with an inflection in fluence with a mean absolute difference of 0.1mm and 0.4mm observed for the simulation and phantom respectively. These results suggest that interstitial fluence probes may be capable of providing real-time feedback during focal laser ablation.

Laser Ablation for Cancer: Past, Present and Future

Laser ablation (LA) is gaining acceptance for the treatment of tumors as an alternative to surgical resection. This paper reviews the use of lasers for ablative and surgical applications. Also reviewed are solutions aimed at improving LA outcomes: hyperthermal treatment planning tools and thermometric techniques during LA, used to guide the surgeon in the choice and adjustment of the optimal laser settings, and the potential use of nanoparticles to allow biologic selectivity of ablative treatments. Promising technical solutions and a better knowledge of laser-tissue interaction should allow LA to be used in a safe and effective manner as a cancer treatment.

CT imaging during microwave ablation: analysis of spatial and temporal tissue contraction

PURPOSE

To analyze the spatial distribution and temporal development of liver tissue contraction during high-temperature ablation by using intraprocedural computed tomography (CT) imaging.

METHODS

A total of 46 aluminum fiducial markers were positioned in a 60 × 45 mm grid, in a single plane, around a microwave ablation antenna in each of six ex vivo bovine liver samples. Ablations were performed for 10 min at 100 W. CT data of the liver sample were acquired every 30 s during ablation. Fiducial motion between acquisitions was tracked in postprocessing and used to calculate measures of tissue contraction and contraction rates. The spatial distribution and temporal evolution of contraction were analyzed.

RESULTS

Fiducial displacement indicated that the zone measured postablation was 8.2 ± 1.8 mm (∼20%) smaller in the radial direction and 7.1 ± 1.0 mm (∼10%) shorter in the longitudinal direction than the preablation tissue dimension. Therefore, the total ablation volume was reduced from its preablation value by approximately 45%. Very little longitudinal contraction was noted in the distal portion of the ablation zone. Central tissues contracted more than 60%, which was near an estimated limit of ∼70% based on initial water content. More peripheral tissues contracted only 15% in any direction. Contraction rates peaked during the first 60 s of heating with a roughly exponential decay over time.

CONCLUSIONS

Ablation zones measured posttreatment are significantly smaller than the pretreatment tissue dimensions. Tissue contraction is spatially dependent, with the greatest effect occurring in the central ablation zone. Contraction rate peaks early and decays over time.

Laser ablation for small hepatocellular carcinoma: State of the art and future perspectives

During the last two decades, various local thermal ablative techniques for the treatment of unresectable hepatocellular carcinoma (HCC) have been developed. According to internationally endorsed guidelines, percutaneous thermal ablation is the mainstay of treatment in patients with small HCC who are not candidates for surgical resection or transplantation. Laser ablation (LA) represents one of currently available loco-ablative techniques. In this article, the general principles, technique, image guidance, and patient selection are reported. Primary effectiveness, long-term outcome, and complications are also discussed. A review of published data suggests that LA is equivalent to the more popular and widespread radiofrequency ablation in both local tumor control and long-term outcome in the percutaneous treatment of early HCC. In addition, the LA technique using multiple thin laser fibres allows improved ablative effectiveness in HCCs greater than 3 cm. Reference centres should be equipped with all the available techniques so as to be able to use the best and the most suitable procedure for each type of lesion for each patient.

Thermal ablation of liver metastases from colorectal cancer: radiofrequency, microwave and laser ablation therapies

Surgery is currently considered the treatment of choice for patients with colorectal cancer liver metastases (CRLM) when resectable. The majority of these patients can also benefit from systemic chemotherapy. Recently, local or regional therapies such as thermal ablations have been used with acceptable outcomes. We searched the medical literature to identify studies and reviews relevant to radiofrequency (RF) ablation, microwave (MW) ablation and laser-induced thermotherapy (LITT) in terms of local progression, survival indexes and major complications in patients with CRLM. Reviewed literature showed a local progression rate between 2.8 and 29.7 % of RF-ablated liver lesions at 12-49 months follow-up, 2.7-12.5 % of MW ablated lesions at 5-19 months follow-up and 5.2 % of lesions treated with LITT at 6-month follow-up. Major complications were observed in 4-33 % of patients treated with RF ablation, 0-19 % of patients treated with MW ablation and 0.1-3.5 % of lesions treated with LITT. Although not significantly different, the mean of 1-, 3- and 5-year survival rates for RF-, MW- and laser ablated lesions was (92.6, 44.7, 31.1 %), (79, 38.6, 21 %) and (94.2, 61.5, 29.2 %), respectively. The median survival in these methods was 33.2, 29.5 and 33.7 months, respectively. Thermal ablation may be an appropriate alternative in patients with CRLM who have inoperable liver lesions or have operable lesions as an adjunct to resection. However, further competitive evaluation should clarify the efficacy and priority of these therapies in patients with colorectal cancer liver metastases.

MRI-guided stereotactic aspiration of brain abscesses by use of an optical tracking navigation system

BACKGROUND

Owing to the high risk of abscess drainage by craniotomy, imaging-guided stereotactic aspiration is considered an ideal choice in the management of brain abscesses. Interventional magnetic resonance imaging (MRI) represents a valuable technique for the treatment of brain abscess as a guiding modality.

PURPOSE

To evaluate the safety and efficacy of an interventional MRI system in performing the procedure.

MATERIAL AND METHODS

Thirteen brain abscesses in 11 patients were treated with percutaneous aspiration. All procedures were performed solely under the guidance of a 0.23-T open-configuration MRI scanner with optical tracking. Clinical and imaging follow-up was at 1 week, 1 month, 3 months, and 6 months. The changes of abscess, MRI features, and clinical symptoms were recorded. Procedure efficacy and safety were evaluated by success rate, procedure time, decrease of abscess, recovery rate, and complication. Descriptive statistical analysis was performed.

RESULTS

MRI-guided stereotactic aspirations were performed successfully in 13/13 (100%) abscesses. The mean operating time was 70 min (range, 45-100 min). Follow-up MRI at 1 week after the procedure showed average reduction of abscesses by 60% (2.1/3.5). And the abscesses continued to get smaller by up to 89.7% (3.14/3.5) at 1-month follow-up. All cavities resolved at the end of the 6-month follow-up period. The recovery rate was 100% for fever, headache, vomiting, papilledema, meningismus, altered sensorium, 75% (3/4) for hemiparesis, and 83.3% (5/6) for epilepsy. There were no complications.

CONCLUSION

Punctures of brain abscesses with subsequent aspiration can be performed safely and efficiently by monitoring the procedure using an open interventional MRI system.

[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.

Laser ablation for small hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide and is increasingly detected at small size (<5 cm) owing to surveillance programmes in high-risk patients. For these cases, curative therapies such as resection, liver transplantation, or percutaneous ablation have been proposed. When surgical options are precluded, image-guided tumor ablation is recommended as the most appropriate therapeutic choice in terms of tumor local control, safety, and improvement in survival. Laser ablation (LA) represents one of currently available loco-ablative techniques: light is delivered via flexible quartz fibers of diameter from 300 to 600 μm inserted into tumor lesion through either fine needles (21g Chiba needles) or large-bore catheters. The thermal destruction of tissue is achieved through conversion of absorbed light (usually infrared) into heat. A range of different imaging modalities have been used to guide percutaneous laser ablation, but ultrasound and magnetic resonance imaging are most widely employed, according to local experience and resource availability. Available clinical data suggest that LA is highly effective in terms of tumoricidal capability with an excellent safety profile; the best results in terms of long-term survival are obtained in early HCC so that LA can be proposed not only in unresectable cases but, not differently from radiofrequency ablation, also as the first-line treatment.

Emerging local ablation techniques

Local ablation technologies for hepatic malignancy have developed rapidly in the past decade, with advances in several percutaneous or externally delivered treatment methods including radiofrequency ablation, microwave ablation, laser ablation, and high-intensity focused ultrasound. Research has focused on increasing the size of the ablation zone and minimizing heat-sink effects. More recent developments include improvements in treatment planning and navigation with integration of several imaging modalities, as well as automated delivery of the ablation through robotics. These improvements will allow increased consistency in treatment delivery and will facilitate translation to the community setting. Combination therapies with multimodality guidance are on the cutting edge of image-guided, minimally invasive cancer therapies. Local ablation is being combined with regional therapies, such as arterial chemoembolization and local activation of systemically administered drugs, with promising results. Potential combinations with local ablation also include external radiation therapy and antitumor immune modulation. Image-guided oncology is emerging as an important part of the interventional radiology practice, thanks in part to the innovation and imaging background that lies at the roots of our discipline.

MRI & MRS assessment of the role of the tumour microenvironment in response to therapy

MRI and MRS techniques are being applied to the characterisation of various aspects of the tumour microenvironment and to the assessment of tumour response to therapy. For example, kinetic parameters describing tumour blood vessel flow and permeability can be derived from dynamic contrast-enhanced MRI data and have been correlated with a positive tumour response to antivascular therapies. The ongoing development and validation of noninvasive, high-resolution anatomical/molecular MR techniques will equip us with the means to detect specific tumour biomarkers early on, and then to monitor the efficacy of cancer treatments efficiently and reliably, all within a clinically relevant time frame. Reliable tumour microenvironment imaging biomarkers will provide obvious advantages by enabling tumour-specific treatment tailoring and potentially improving patient outcome. However, for routine clinical application across many disease types, such imaging biomarkers must be quantitative, robust, reproducible, sufficiently sensitive and cost-effective. These characteristics are all difficult to achieve in practice, but image biomarker development and validation have been greatly facilitated by an increasing number of pertinent preclinical in vivo cancer models. Emphasis must now be placed on discovering whether the preclinical results translate into an improvement in patient care and, therefore, overall survival.

Modeling of laser coagulation of tissue with MRI temperature monitoring

Light energy from a laser source that is delivered into body tissue via a fiber-optic probe with minimal invasiveness has been used to ablate solid tumors. This thermal coagulation process can be guided and monitored accurately by continuous magnetic resonance imaging (MRI) since the laser energy delivery system does not interfere with MRI. This report deals with mathematical modeling and analysis of laser coagulation of tissue. This model is intended for "real-time" analysis of magnetic resonance images obtained during the coagulation process to guide clinical treatment. A mathematical model is developed to simulate the thermal response of tissue to a laser light heating source. For fast simulation, an approximate solution of the thermal model is used to predict the dynamics of temperature distribution and tissue damage induced by a laser energy line source. The validity of these simulations is tested by comparison with MRI-based temperature data acquired from in vivo experiments in rabbits. The model-simulated temperature distribution and predicted lesion dynamics correspond closely with MRI-based data. These results demonstrate the potential for using this combination of fast modeling and MRI technologies during laser heating of tissue for online prediction of tumor lesion size during laser heating.

Ablative therapies for colorectal liver metastases

Ablative therapies remain a useful adjunct in the multidisciplinary treatment of patients with colorectal liver metastases not amenable to hepatic resection. This review summarizes the rationale, underlying mechanisms, techniques, complications, and outcomes of current and emerging ablative modalities.

Multimodal management of neuroendocrine liver metastases

BACKGROUND

The incidence of neuroendocrine tumours (NET) has increased over the past three decades. Hepatic metastases which occur in up to 75% of NET patients significantly worsen their prognosis. New imaging techniques with increasing sensitivity enabling tumour detection at an early stage have been developed. The treatment encompasses a panel of surgical and non-surgical modalities.

METHODS

This article reviews the published literature related to management of hepatic neuroendocrine metastases.

RESULTS

Abdominal computer tomography, magnetic resonance tomography and somatostatin receptor scintigraphy are widely accepted imaging modalities. Hepatic resection is the only potentially curative treatment. Liver transplantation is justified in highly selected patients. Liver-directed interventional techniques and locally ablative measures offer effective palliation. Promising novel therapeutic options offering targeted approaches are under evaluation.

CONCLUSIONS

The treatment of neuroendocrine liver metastases still needs to be standardized. Management in centres of expertise should be strongly encouraged in order to enable a multidisciplinary approach and personalized treatment. Development of molecular prognostic factors to select treatment according to patient risk should be attempted.

Minimally invasive image-guided therapy for inoperable hepatocellular carcinoma: What is the evidence today?

Hepatocellular carcinoma (HCC) is a primary malignant tumor of the liver that accounts for an important health problem worldwide. Only 10-15% of HCC patients are suitable candidates for hepatic resection and liver transplantation due to the advanced stage of the disease at time of diagnosis and shortage of donors. Therefore, several minimally invasive image-guided therapies for locoregional treatment have been developed. Tumor ablative techniques are either based on thermal tumor destruction, as in radiofrequency ablation, cryoablation, microwave ablation, laser ablation and high-intensity focused ultrasound, or chemical tumor destruction, as in percutaneous ethanol injection. Image-guided catheter-based techniques rely on intra-arterial delivery of embolic, chemoembolic or radioembolic agents. These minimally invasive image-guided therapies have revolutionized the management of inoperable HCC. This review provides a description of all minimally invasive image-guided therapies currently available, an up-to-date overview of the scientific evidence for their clinical use, and thoughts for future directions.

Construction and evaluation of an anatomically correct multi-image modality compatible phantom for prostate cancer focal ablation

PURPOSE

Focal therapy using lasers is emerging as an alternative strategy for prostate cancer treatment. However, to our knowledge no anatomically correct models are available to test imaging and ablation techniques. Animal models present ethical, anatomical and cost challenges. We designed and validated an inexpensive but anatomically correct prostate phantom incorporating tumor, rectum and urethra that can be used for simulated and experimental magnetic resonance guided focal intervention. Our secondary aim was to asses the phantom using other imaging modalities.

MATERIALS AND METHODS

The phantom, which was constructed of ballistic gel, includes an 80 gm prostate with urethra, tumor, perineum and rectum. Gadolinium was added to make the gel visible to magnetic resonance imaging. To recreate a tumor an irregularly shaped 5 cc volume of coagulable gel was inserted into the prostate phantom. The phantom was evaluated using magnetic resonance, computerized tomography and transrectal ultrasound. Thermal ablation was delivered via interstitial placement of laser fibers. Magnetic resonance thermometry was done to record real-time tissue temperatures during thermal ablation.

RESULTS

With all modalities tested the phantom emulated human prostate anatomy. The coagulable gel tumor allowed us to generate focal thermal lesions. The phantom had magnetic resonance imaging properties comparable to in vivo properties, allowing ablative zones to be accurately assessed and magnetic resonance thermometry to be done.

CONCLUSIONS

The phantom is a useful tool to test different aspects of thermal focal ablation for prostate cancer using multiple imaging modalities, particularly magnetic resonance. It is inexpensive and easily constructed, and may be considered a valuable model to train on and teach focal therapy.

Hepatocellular carcinoma: current trends in worldwide epidemiology, risk factors, diagnosis and therapeutics

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related death worldwide and, owing to changes in the prevalence of the two major risk factors, hepatitis B virus and hepatitis C virus, its overall incidence remains alarmingly high in the developing world and is steadily rising across most of the developed world. Early diagnosis remains the key to effective treatment and there have been recent advances in both the diagnosis and therapy of HCC, which have made important impacts on the disease. This review outlines the epidemiological trends, risk factors, diagnostic developments and novel therapeutics for HCC, both in the developing and developed world.

Laser ablation of hepatocellular carcinoma-A review

A wide range of local thermal ablative therapies have been developed in the treatment of non resectable hepatocellular carcinoma (HCC) in the last decade. Laser ablation (LA) and radiofrequency ablation (RFA) are the two most widely used of these. This article provides an up to date overview of the role of laser ablation in the local treatment of HCC. General principles, technique, image guidance and patient selection are discussed. A review of published data on treatment efficacy, long term outcome and complication rates of laser ablation is included and comparison with RFA made. The role of laser ablation in combination with transcatheter arterial chemoembolization is also discussed.

Volumetric evaluation of liver metastases after thermal ablation: long-term results following MR-guided laser-induced thermotherapy

PURPOSE

To volumetrically analyze liver metastases and posttherapeutic findings of the thermally ablated area after thermal ablation with magnetic resonance (MR)-guided laser-induced thermotherapy in a long-term evaluation using contrast-enhanced MR imaging.

MATERIALS AND METHODS

The study was approved by the institutional review board, and informed consent was obtained from all patients. In 40 patients (27 women, 13 men; age range, 33-94 years; mean age, 62.5 years) in whom colorectal cancer (n = 20) and breast cancer (n = 20) had metastasized to the liver, initial tumor volume and thermal-induced necrosis after MR-guided laser-induced thermotherapy were retrospectively analyzed. All patients presented with oligonodular liver metastases and underwent follow-up with contrast-enhanced MR imaging for at least 3 years. No concomitant oncologic therapies were performed.

RESULTS

Volumetric MR imaging evaluation depicted 40 metastases with an initial tumor volume less than 5 mL (x = 1.75), nine metastases with initial volume of 5-20 mL (x = 12.35), and eight metastases with initial volume more than 20 mL (x = 50.57). The mean volume of the thermally damaged area was 498% of the initial volume for colorectal cancer metastases and 604% of the initial volume for breast cancer metastases. The ischemic and necrotic volume for colorectal cancer metastases had decreased by a mean of 48.6% after 3 months, by 63% after 6 months, by 70.2% after 12 months, and by 92.2% after 36 months. For breast cancer metastases at 36 months, the necrotic volume had decreased by 80.61%; the reduction in the volume of the thermally damaged region was statistically significantly lower than that of colorectal cancer metastases.

CONCLUSION

MR-guided laser-induced thermotherapy induced a high volume of thermal ablation; the greatest reduction in the necrotic volume occurred in the first year, and lower values were seen in the next period. The reduction was statistically significantly higher in colorectal cancer metastases.

Dynamics of MRI-Guided thermal ablation of VX2 tumor in paraspinal muscle of rabbits

This study combines fast magnetic resonance imaging (MRI) and model simulation of tissue thermal ablation for monitoring and predicting the dynamics of lesion size for tumor destruction. In vivo experiments were conducted using radiofrequency (RF) thermal ablation in paraspinal muscle of rabbit with a VX2 tumor. Before ablation, turbo-spin echo (TSE) images visualized the 3-D tumor (necrotic core and tumor periphery) and surrounding normal tissue. MR gradient-recalled echo (GRE) phase and magnitude images were acquired repeatedly in 3.3 s at 30-s intervals during and after thermal ablation to follow tissue temperature distribution dynamics and lesion development in tumor and surrounding normal tissue. Final lesion sizes estimated from GRE magnitude, post-ablation TSE, and stained histologic images were compared. Model simulations of temperature distribution and lesion development dynamics closely corresponded to the experimental data from MR images in tumor and normal tissue. The combined use of MR image monitoring and model simulation has the potential for improving pretreatment planning and real-time prediction of lesion-size dynamics for guidance of thermal ablation of tumors.

Radiation dose limits and liver toxicities resulting from multiple yttrium-90 radioembolization treatments for hepatocellular carcinoma

PURPOSE

To assess the relationship between cumulative hepatic lobar radiation dose and liver toxicities in patients with hepatocellular carcinoma (HCC) treated with multiple sessions of yttrium-90 radioembolization.

MATERIALS AND METHODS

Forty-one patients with HCC (age range, 46-82 years) underwent radioembolization with 90Y. Patients were classified according to the Okuda scoring system. All patients received single liver lobar treatments on two or more occasions according to standard clinical 90Y embolization protocol. Cumulative radiation dose to each liver lobe was measured and patients were followed to assess liver toxicities. Statistical analysis was performed with the Student t test and Kaplan-Meier analysis.

RESULTS

Patients with Okuda stage I disease received more treatments than those with Okuda stage II disease (mean, 2.65 vs 2.24; P<.05). For average cumulative radiation dose, patients with Okuda stage I disease received 247 Gy (range, 88-482 Gy) and those with Okuda stage II disease received 198 Gy (range, 51-361 Gy; P<.05). A total of 13 toxicities occurred in seven patients (16%). Patients with Okuda stage I disease were given a greater cumulative dose than patients with Okuda stage II disease before worsening of liver function: 390 Gy versus 196 Gy (P<.005). For patients with Okuda stage I disease, a higher cumulative radiation dose was associated with occurrence of one or more toxicities: 222 Gy (no toxicities) versus 390 Gy (>or=1 toxicity; P<.005). No correlation between cumulative radiation dose and liver toxicities existed in patients with Okuda stage II disease. The maximum tolerated dose was between 222 and 390 Gy. Median survival times were 660 and 431 days for patients with Okuda stage I and stage II disease, respectively.

CONCLUSIONS

Patients with HCC can tolerate high cumulative radiation doses with 90Y therapy. Compared with patients with Okuda stage II disease, patients with Okuda stage I disease tolerate a higher cumulative radiation dose without liver toxicity, but liver toxicities increase with increasing cumulative radiation doses.

Magnetic resonance imaging and model prediction for thermal ablation of tissue

PURPOSE

To monitor and predict tissue temperature distributions and lesion boundaries during thermal ablation by combining MRI and thermal modeling methods.

MATERIALS AND METHODS

Radiofrequency (RF) ablation was conducted in the paraspinal muscles of rabbits with MRI monitoring. A gradient-recalled echo (GRE) sequence via a 1.5T MRI system provided tissue temperature distribution from the phase images and lesion progression from changes in magnitude images. Post-ablation GRE estimates of lesion size were compared with post-ablation T2-weighted turbo-spin-echo (TSE) images and hematoxylin and eosin (H&E)-stained histological slices. A three-dimensional (3D) thermal model was used to simulate and predict tissue temperature and lesion size dynamics.

RESULTS

The lesion area estimated from repeated GRE images remained constant during the post-heating period when the temperature of the lesion boundary was less than a critical temperature. The final lesion areas estimated from multi-slice (M/S) GRE, TSE, and histological slices were not statistically different. The model-simulated tissue temperature distribution and lesion area closely corresponded to the GRE-based MR measurements throughout the imaging experiment.

CONCLUSION

For normal tissue in vivo, the dynamics of tissue temperature distribution and lesion size during RF thermal ablation can be 1) monitored with GRE phase and magnitude images, and 2) simulated for prediction with a thermal model.

Surgical robotics and image guided therapy in pediatric surgery: emerging and converging minimal access technologies

Minimal access surgery (MAS) is now commonplace in the armamentarium of the pediatric surgeon, and is being applied to a growing list of pediatric surgical diseases. Robot-assisted surgery and image guided therapy (IGT) have evolved as innovative minimal access approaches, and hold the promise of advancing MAS far beyond what is currently possible. The aims of this article are to describe the currently available robotic, and image guided therapy systems, review their present and potential applications, and discuss the future directions of these converging technologies.

Intraoperative magnetic resonance imaging for ablation of hepatic tumors

BACKGROUND

The most significant rise in the use of hepatic ablation has come from image-guided techniques with both computed tomography (CT) and ultrasound (US). The recent development of open-configuration magnetic resonance scanners has opened up an entire new area of image-guided surgical and interventional procedures. Thus the aim of this study was to evaluate the use of intraoperative MRI (iMRI) ablation of hepatic tumors performed by surgeons.

METHOD

Percutaneous iMRI hepatic ablation was performed from January 2003 to February 2005 for control of either primary or secondary hepatic disease.

RESULTS

Eighteen hepatic ablations were performed on 11 patients with a median age of 71 (range: 51-81) years for metastatic colorectal cancer (n = 6), hepatocellular cancer (n = 2), cholangiocarcinoma (n = 2), and metastatic neuroendocrine (n = 1). Median hospital stay was 1 day, with complications occurring in 2 patients. After a median follow up of 18 months, there have been no local ablation recurrences, 5 patients are free of disease, 4 are alive with disease, 1 has died of disease, and 1 has died of other causes.

CONCLUSIONS

Image-guided hepatic ablations represent a useful technique in managing hepatic tumors. Intraoperative MRI represents a new technique with initial success that has been limited to European centers. Further evaluation in U.S. centers has demonstrated iMRI to be useful for certain hepatic tumors that cannot be adequately visualized by US or CT.

An Augmented Reality System for MR Image–guided Needle Biopsy: Initial Results in a Swine Model

PURPOSE

To evaluate an augmented reality (AR) system in combination with a 1.5-T closed-bore magnetic resonance (MR) imager as a navigation tool for needle biopsies.

MATERIALS AND METHODS

The experimental protocol had institutional animal care and use committee approval. Seventy biopsies were performed in phantoms by using 20 tube targets, each with a diameter of 6 mm, and 50 virtual targets. The position of the needle tip in AR and MR space was compared in multiple imaging planes, and virtual and real needle tip localization errors were calculated. Ten AR-guided biopsies were performed in three pigs, and the duration of each procedure was determined. After successful puncture, the distance to the target was measured on MR images. The confidence limits for the achieved in-plane hit rate and for lateral deviation were calculated. A repeated measures analysis of variance was used to determine whether the placement error in a particular dimension (x, y, or z) differed from the others.

RESULTS

For the 50 virtual targets, a mean error of 1.1 mm +/- 0.5 (standard deviation) was calculated. A repeated measures analysis of variance indicated no statistically significant difference (P > .99) in the errors in any particular orientation. For the real targets, all punctures were inside the 6-mm-diameter tube in the transverse plane. The needle depth was within the target plane in 11 biopsy procedures; the mean distance to the center of the target was 2.55 mm (95% confidence interval: 1.77 mm, 3.34 mm). For nine biopsy procedures, the needle tip was outside the target plane, with a mean distance to the edge of the target plane of 1.5 mm (range, 0.07-3.46 mm). In the animal experiments, the puncture was successful in all 10 cases, with a mean target-needle distance of 9.6 mm +/- 4.85. The average procedure time was 18 minutes per puncture.

CONCLUSION

Biopsy procedures performed with a combination of a closed-bore MR system and an AR system are feasible and accurate.

Liver Metastases in Rats: Chemoembolization Combined with Interstitial Laser Ablation for Treatment

PURPOSE

To assess the effect of transcatheter arterial chemoembolization (TACE) combined with laser-induced thermotherapy (LITT) for treatment of liver metastases in an animal model.

MATERIALS AND METHODS

All experiments were approved by the German government and the institutional animal research review board. After subcapsular liver implantation of colorectal cancer cells in 30 WAG rats (on day 0), the animals were randomly assigned to three interventional treatment groups. In the 10 rats in group A, TACE was performed: Fourteen days after cancer cell implantation and within 20 minutes after laparotomy and retrograde placement of a microcatheter into the gastroduodenal artery, these rats were injected with mitomycin (0.1 mg), iodized oil (0.1 mL), and degradable starch microspheres (5.0 mg). In the 10 rats in group B, LITT was performed: Also on day 14, the tumors in these animals were exposed to Nd:YAG laser light of 1064 nm at 2 W for 5 minutes. In the 10 rats in group C, combined treatment was administered: TACE was performed on day 14, and LITT was performed on day 21. Tumor volumes were measured before (on day 13) and after (on day 28) treatment with magnetic resonance (MR) imaging, and the mean tumor growth ratio (day 13 tumor volume divided by day 28 tumor volume) was calculated.

RESULTS

The mean tumor volumes measured before and after the treatments were, respectively, 0.11 and 0.60 cm(3) in group A, 0.11 and 0.68 cm(3) in group B, and 0.11 and 0.35 cm(3) in group C. The mean tumor growth ratio was 5.42 in group A, 6.14 in group B, and 3.15 in group C. According to Bonferroni test results, compared with the rats in groups A and B (controls), the group C rats had significantly inhibited tumor growth (P < .01 for both comparisons).

CONCLUSION

Use of combined TACE-LITT treatment, compared with the use of TACE or LITT alone, significantly inhibits tumor growth.

Magnetic resonance guidance of thermal ablation

The aim of this study is to describe all aspects of the process of using MR imaging to control thermal ablation procedures and the strengths and weaknesses of the individual thermal ablation modalities in relation to their use in the MR environment. Magnetic resonance thermal sequences, MR scanner configurations, and the different thermal ablation modalities are discussed in the context of how they are commonly used in MR scanners to provide optimal image guidance of therapy. The outcomes of completed research on some of the applications of thermal tissue ablation using MR guidance are described to indicate how these processes may impact patient treatment. At the end of this review, the reader should have an understanding of how MR guidance of thermal ablation may be carried out, in what areas it is currently most used, and were it may develop in the near future.

A review of technical advances in interventional magnetic resonance imaging

Initial research in the development of interventional magnetic resonance (MR) imaging in the late 1980s and early to mid-1990s focused on pulse sequences, devices, and clinical applications. This focus was largely a result of the limited number of areas in which the academic research community leading the development could provide innovation on the MR systems of the time. However, during the past decade, computational power, higher bandwidth graphical displays, faster computer networks, improved pulse sequence architectures, and improved technical specifications have accelerated the pace of development on modern MR systems. Today, it is the combination of multiple system factors that are enabling the future of interventional MR. These developments, their impact on the field, and newly emerging applications are described.

MR Imaging-guided percutaneous procedures in children

Magnetic resonance imaging (MRI)-guided therapeutic interventions in children are very rare. In comparison to other imaging techniques, it is very unusual for MRI to be used for diagnostic percutaneous interventions despite its imaging benefits. We provide a brief description of available MRI systems and instruments and use clinical examples to present and discuss typical indications for percutaneous procedures while showing possibilities for percutaneous therapeutic interventions.

The Effect of Catheter-Directed CT Angiography on Yttrium-90 Radioembolization Treatment of Hepatocellular Carcinoma

PURPOSE

Yttrium 90 radioembolization is a transcatheter therapy for unresectable hepatocellular carcinoma (HCC) that delivers internal radiation to tumors. In contrast to the usual method of lobar regional delivery, catheter-directed computed tomographic (CT) angiography was investigated as a potentially useful technique to evaluate the administration of segmental 90Y tumor radiation doses superselectively without significantly altering liver function or Child-Pugh classification.

MATERIALS AND METHODS

Fourteen patients underwent 90Y therapy for unresectable HCC. After standard angiographic placement of a 3-F microcatheter in a segmental hepatic artery supplying the tumor, each patient underwent CT angiography with use of segmental hepatic artery injection of iodinated contrast agent to confirm segmental perfusion and delineate segmental liver volume. 90Y was later injected into the same segmental artery. Target dose was calculated according to infused 90Y activity and targeted hepatic volume with standard lobar volume (before CT angiography) versus segmental liver volume (after CT angiography). The Wilcoxon signed-rank test (alpha = 0.05) was used to compare the estimated 90Y dose before CT angiography with the actual 90Y dose after CT angiography, as well as changes in serum bilirubin level and Child-Pugh classification as a result of treatment.

RESULTS

The mean estimated tumor dose before CT angiography (SD) was 100 Gy +/- 43 (range, 35-169 Gy). The mean actual tumor dose after CT angiography was 348 Gy +/- 204 (range, 105-857 Gy), which was significantly greater (P < .001). The mean bilirubin level before treatment was 1.0 mg/dL +/- 0.97 (range, 0.2-4.0 mg/dL), whereas the mean bilirubin level after treatment was 1.3 mg/dL +/- 0.85 (range, 0.5-3.8 mg/dL). This difference, although statistically significant (P = .03), was not clinically important. Thirteen of 14 patients had no change in Child-Pugh class.

CONCLUSION

CT angiography can be used to delineate the blood supply and volume to a targeted hepatic segment, allowing superselective 90Y radioembolization. This approach significantly increases effective 90Y tumor radiation dose without clinically altering liver function or Child-Pugh class.

Pediatric MR-guided interventions

MRI guided interventions are a relatively new but steadily growing field within surgery in pediatric age. Besides the advantages of MRI, such as multiplanar capability and excellent soft tissue contrast and spatial resolution, particularly relevant for the pediatric population is the lack of ionizing radiation. There is meanwhile a group of well defined diagnostic or therapeutic indications for applying MR imaging during pediatric interventions. Aim of this review is to give an overview about indications of MR-guided procedures in children as well as the advantages and disadvantages of MR-guided interventions. We also briefly discuss interventional MR-systems and MR-compatible devices. It is our opinion that MR-guidance for pediatric interventions is a promising technique at the beginning of its development.

Intraoperative magnetic resonance imaging ablation of hepatic tumors

BACKGROUND

The use of hepatic ablation of tumors for both primary and secondary cancers has continued to increase at a significant rate. The most significant increase in the use of hepatic ablation has come from image-guided techniques with computed axial tomography and ultrasound. Limitations to targeting hepatic lesions by these techniques remain morbid obesity, abnormal hepatic parenchyma, and inability to visualize lesions without the use of intravenous contrast. In contrast, magnetic resonance imaging (MRI) has continued to provide a high contrast of soft tissue-to-lesion conspicuity without the need for intravenous dye. The recent development of open-configuration magnetic resonance scanners--which have allowed improved patient access, near real-time imaging, and more available MRI-compatible equipment--has opened up an entire new area of image-guided surgical and interventional procedures.

METHODS

The principles and indications for all types of image-guided hepatic ablations are described.

RESULTS

The success and limitations of image-guided ablation techniques.

CONCLUSIONS

Image-guided hepatic ablation represents a useful technique in managing hepatic tumors. Intraoperative MRI represents a new technique with initial success that has been limited to European centers. Further evaluation in United States centers has demonstrated intraoperative MRI to be useful for certain hepatic tumors that cannot be adequately visualized by ultrasound or computed axial tomography. A multidisciplinary approach involving a surgical oncologist and interventional radiologist remains integral to the short- and long-term success of image-guided ablation.

Non-surgical treatment of hepatocellular carcinoma

A wide variety of non-surgical therapies can result in clinical responses in patients with hepatocellular carcinoma. Two recent studies have suggested that transarterial chemoembolisation can, in highly selected patients with good liver function, result in an improvement in survival. No other approaches have, to date, demonstrated convincing evidence of survival advantage.

Nuclear magnetic resonance parameters for monitoring coagulation of liver tissue

A new NMR parameter is suggested as a sensitive tool for monitoring thermal coagulation of liver tissue. That parameter is the proton magnetization exchange time (tau(MEX)) between water and the proteins. tau(MEX) was very sensitive to coagulation and insensitive to temperature, therefore representing only damage to the tissue, independent of effects caused by temperature fluctuations. The measurement of tau(MEX) by two different methods revealed the existence of two or more groups of proteins, characterized by their different transverse relaxation time, and tau(MEX).

Interventional and intraoperative MR: review and update of techniques and clinical experience

The concept of interventional magnetic resonance imaging (MRI) is based on the integration of diagnostic and therapeutic procedures, favored by the combination of the excellent morphological and functional imaging characteristics of MRI. The spectrum of MRI-assisted interventions ranges from biopsies and intraoperative guidance to thermal ablation modalities and vascular interventions. The most relevant recently published experimental and clinical results are discussed. In the future, interventional MRI is expected to play an important role in interventional radiology, minimal invasive therapy and guidance of surgical procedures. However, the associated high costs require a careful evaluation of its potentials in order to ensure cost-effective medical care.

Magnetic resonance imaging of the liver with ultrashort TE (UTE) pulse sequences

PURPOSE

To assess the feasibility of imaging the liver in volunteers and patients with ultrashort echo time (UTE) pulse sequences.

MATERIALS AND METHODS

Seven normal controls as well as 12 patients with biopsy-proven generalized liver disease and three patients with focal disease were examined using pulse sequences with initial TEs of 0.08 msec followed by three later echoes, with or without frequency-based fat suppression. T(2)* values were calculated from regions of interest in the liver.

RESULTS

Good image quality was obtained in each subject. There was a highly significant difference in the mean T(2)* values between the normal controls and patients with generalized liver disease (P = 0.001). T(2)* was significantly decreased in hemochromatosis (P = 0.002) and increased in cirrhosis (P = 0.04), compared with controls. T(2)* also correlated with functional status assessed by Child's grade (P = 0.001). A hepatocellular carcinoma showed reduced short T(2) components in the region of thermal ablation and evidence of a subcapsular hematoma which were not apparent with conventional imaging.

CONCLUSIONS

Imaging of the liver with UTE sequences showed good image quality and tolerance of abdominal motion. T(2)* was specifically correlated with the presence of hemochromatosis, cirrhosis, and functional grade. Imaging of short T(2) relaxation components may provide useful information in disease.

Stability of real-time MR temperature mapping in healthy and diseased human liver

PURPOSE

To determine the stability and quality of MR temperature mapping using the proton resonance frequency (PRF) method in the liver of hepatic tumor patients.

MATERIALS AND METHODS

The standard deviation (SD) of a series of temperature maps was determined in 30 patients (21 patients with cirrhotic livers with carcinoma, and nine patients with noncirrhotic livers with metastasis or angioma) and in five volunteers at normal body temperature under free breathing. A respiratory-gated segmented echo-planar imaging (EPI) sequence (three slices in one expiration phase) was performed with sensitivity encoding (SENSE) acceleration on a 1.5 T scanner. Motion-corrupted images were identified by calculation of the cross-correlation coefficient, and discarded.

RESULTS

A T2* range of 10-33 msec was found, with especially low values in advanced cirrhotic livers. The mean temperature SD in patients was 2.3 degrees C (range = 1.5-5.0 degrees C). The stability in healthy livers was slightly better than that in cirrhotic livers, and it was higher in the right liver than in the left liver. The gating failed in 4% of the images when the respiratory cycle was irregular, leading to motion artifacts and errors in the temperature maps.

CONCLUSION

The achieved temperature stability and image quality makes real-time quantitative monitoring of thermal ablation of liver tumors feasible on a clinical scanner.

Robotic Surgery: Urologic Implications

Current medical robots have nothing in common with the anthropomorphic robots in science fiction classics. They are in fact, manipulators, working on a master-slave principle. Robots can be defined as "automatically controlled multitask manipulators, which are freely programmable in three or more spaces." The success of robots in surgery is based on their precision, lack of fatigue, and speed of action. This review describes the theory, advantages, disadvantages, and clinical utilization of mechanical and robotic arm systems to replace the second assistant and provide camera direction and stability during laparoscopic surgery. The Robotrac system (Aesculap, Burlingame, CA), the First Assistant (Leonard Medical Inc, Huntingdon Valley, PA), AESOP (Computer Motion, Goleta, CA), ZEUS (Computer Motion), and the da Vinci (Intuitive Surgical, Mountain View, CA) system are reviewed, as are simple mechanical-assist systems such as Omnitract (Minnesota Scientific, St. Paul, MN), Iron Intern (Automated Medical Products Corp., New York, NY), the Bookwalter retraction system (Codman , Somerville, NJ), the Surgassistant trade mark (Solos Endoscopy, Irvine, CA), the Trocar Sleeve Stabilizer (Richard Wolf Medical Instruments Corp., Rosemont, IL), and the Endoholder (Codman, Somerville, NJ).