P697New indices for a best quantification of left ventricular function in heart valve diseases.

Aims.The Assessment of left ventricular (LV) function remains a clinical challenge especially in patients with preserved LV ejection fraction (EF) and valvular heart diseases (VHD). Mechanical dispersion is supposed to be a strong predictor of events and, to be related to the extent of fibrosis. Regional cardiac work is a new validated and very promising approach to quantify LV-function.We investigated the differences in mechanical dispersions and global LV work (totW) and wasted work fraction (WWF) in normal subjects and in patients with severe primary mitral regurgitation (MR) and severe aortic stenosis (AS). METHODS AND RESULTS: A complete transthoracic echocardiography was performed in 21 normal subject, 97 patients with severe valvulopathy (47 AS, 50 MR) and preserved LV EF. Segmental strain analysis was performed in all patients and the dispersion of regional LV strain curves was computed automatically considering peaks and integrals. The LV-pressure was estimated non-invasively using a standard waveform fitted to valvular events and scaled to systolic blood pressure. Using pressure-strain loops, regional cardiac work indices were computed.LVEF was 66±12 in controls, 65±9 in MR and 65±4% in AS (p=0.125). Global longitudinal strain was -23±2.7 in controls, -24±2.9 in MR and -18±3.2% in AS (p < 0.001). The mechanical dispersion was 38±7.9 in controls, 36±11 in MR, and much higher in the hypertrophied LV of the AS: 60±19ms (p < 0.001). Cardiac work was 2200±260 in controls, 2100±270 in MR, and much lower in AS: 1700±280 mmHg.% (p < 0.001). The wasted work fraction (WWF) was even more describing how different the LV systolic function is in the 3 groups (figure1). CONCLUSION: Longitudinal strain data are robusted and new indices might be calculated based on them. These seem especially promising for a more pathophysiological driven analyzing of LV-functions. Abstract P697 Figure.Abstract P697 Figure.

Dynamic MRI scan plane control for passive tracking of instruments and devices.

This paper describes a novel image-based method for tracking robotic mechanisms and interventional devices during Magnetic Resonance Image (MRI)-guided procedures. It takes advantage of the multi-planar imaging capabilities of MRI to optimally image a set of localizing fiducials for passive motion tracking in the image coordinate frame. The imaging system is servoed to adaptively position the scan plane based on automatic detection and localization of fiducial artifacts directly from the acquired image stream. This closed-loop control system has been implemented using an open-source software framework and currently operates with GE MRI scanners. Accuracy and performance were evaluated in experiments, the results of which are presented here.

Intra-operative visualisation of 3D temperature maps and 3D navigation during tissue cryoablation.

Thermotherapeutic tools are increasingly used for tissue ablation, although the intra-operative monitoring is not adequate for such procedures. This is a main challenge for more extensive use of any ablative technique. The present work focuses on treatment of hepatic tumours by cryo therapy. For any thermotherapeutic tool there are specific thermal conditions that have to be met to ensure treatment adequacy. A software tool was made to calculate and visualise 3D temperature distributions during hepatic cryoablation combined with a 3D intra-operative navigation system. This system aids the user in placing the cryoprobe using an optical tracking system and 3D visualisation of the probe placement in relation to the target anatomy and the planned trajectory. 3D temperature distributions are calculated and visualized intra-operatively. The system is integrated with an interventional Magnetic Resonance 0.5T scanner. The system was tested in an animal experiment, exemplifying the usefulness of the navigation system and its ability to give intuitive feedback to the user on thermodynamic conditions induced in the target region. The system constitutes a novel tool for enhanced intra-operative control during cryoablative procedures, and motivates for studies using this tool to investigate predictors applied as indicators of treatment adequacy and patient outcome.

Integrated neuronavigation system with intraoperative image updating.

OBJECTIVE: Recently, MRI has entered the field of image-guided surgery as a new intraoperative imaging modality. In spite of its obvious benefits, this type of iMRI scanner has some drawbacks that have limited its utilization. The goal of the work presented here was to overcome some of these disadvantages. METHODS: A system that allows intraoperative images to be acquired during surgery and have the ability to conduct surgery outside the constraints of the narrow gap of the open magnet was implemented. Ability to conduct tasks inside the scanner with real-time image guidance was also maintained. The system allowed navigation with neuronavigation tools both inside the gap of an open magnet and outside the magnet, utilizing two different optical camera-sets and a dynamic reference frame. Automatic patient registration was implemented. RESULTS: The average difference between tracking position measured outside and inside the magnet was 0.8 +/- 0.1 mm. CONCLUSION: In the work presented in this note we have introduced a dynamic reference frame to compensate for transport of the patient to a location outside the scanner employing a second camera set. The integrated system showed adequate accuracy.

Impact of intraoperative MRI on the surgical results for high-grade gliomas.

OBJECTIVE: The impact of intraoperative MRI (iMRI) on the surgical procedure, patient outcome and median survival for a series of patients harbouring high-grade gliomas forms the basis of this study. Their outcome has been compared to a matched cohort of patients operated in a conventional manner to determine if the use of intraoperative MRI can be shown to improve the results of surgery and prognosis for this type of patient. MATERIALS AND METHODS: 32 microsurgical open craniotomies, performed in the intraoperative iMRI scanner for grade IV supratentorial gliomas, with follow-up periods of more than 2 months, were analyzed for this study. A group of 32 primary high-grade glioma patients (no recurrent tumors) were matched for age, preoperative clinical grade, gender and histology and operated during a corresponding time interval in a conventional manner acted as controls. RESULTS: All 64 patients were examined and analyzed for the occurrence of postoperative increased neurological morbidity or death. No complications directly related to the intraoperative scanning procedures were observed and no intraoperative death occurred in either group. The average operating time in the intraoperative scanner was 5.1 hours and was significantly longer than in the conventional OR (3.4 hours). The mean overall survival time for the 32 patients in the study group was 14.5 months (95 % confidence interval 12.0 - 16.6) compared to 12.1 months (95 % confidence interval 10.2 - 14.1) for the matched control group. CONCLUSION: Although iMRI is an effective way of imaging residual tumor, this study could not demonstrate an increased efficacy of surgery utilizing this technique for patients harbouring grade IV gliomas compared to more conventional methods. No statistical significance was noted between the two groups (p = 0.14). The complication rate was within the range reported for other series, in both control as well as the study group.

Image-guided stereotaxy in the interventional MRI.

BACKGROUND: Stereotactic procedures employing frame-based systems and utilizing pre-operative MR or CT have several shortcomings such as long procedure time, patient discomfort and transport, poor fail-safe capabilities and targeting inaccuracies due to brain shift. Conducting all procedural steps in an interventional MRI has the potential of alleviating some of these deficiencies. METHODS: A stereotactic system consisting of a skull-mounted mechanical positioning device and customized navigation software has been developed. The accuracy of this system was tested within an interventional MRI employing a skull phantom. RESULTS: The mean distance between the targets hit and the planned target coordinates was 0.70 mm +/- 0.3 mm with a maximum distance of 1.3 mm. INTERPRETATION: The results indicate that the proposed stereotactic system can be used for stereotactic procedures in the interventional MRI.

Magnetic-resonance-guided percutaneous cryoablation of hepatic tumours.

OBJECTIVE: To study the feasibility of percutaneous cryoablation of hepatic tumours monitored by magnetic resonance imaging (MRI). DESIGN: Prospective study SETTING: University hospital, Norway PATIENTS: Six patients with hepatic metastases from colorectal cancer. INTERVENTIONS: Percutaneous cryoprobe positioning under general anaesthesia. Positioning and freezing monitored by near-real-time MRI using an open 0.5 Tesla MRI configuration system. MAIN OUTCOME MEASURES: Safety and feasibility of the procedure. Measurement of volumes of cryolesions. RESULTS: One patient developed a biliary leakage that had to be drained. Four patients developed pleural fluid. Two small tumours were adequately cryoablated. In the remaining 4 patients with large (>4 cm) tumours, an adequate cryolesion could not be formed. Cryolesion volumes larger than 105 cm3 were not produced even using 3-4 probes. MRI visualised the growing cryolesion well, but positioning of the cryoprobes was time-consuming. CONCLUSION: MR guided cryoablation is clinically feasible and gives good visualisation of the procedure. Patients with small tumours (<3 cm) seem to be best suited to this percutaneous approach as cryolesion volumes claimed to be adequate for tumour destruction can be produced. Measurement of tumour volume preoperatively may help to select patients who will respond.

Validation of estimated 3D temperature maps during hepatic cryo surgery.

A simple model for estimating temperature distribution within the frozen region during cryo ablation was tested for accuracy. Freezing experiments were conducted in both ex vivo and in vivo porcine livers. Temperature was measured during freezing using a fiber-optic temperature sensor. Three-dimensional MR images were obtained at the end of each freezing cycle. From the MR image volumes, three-dimensional temperature maps were calculated numerically using a simplified bio-heat model. Estimated temperatures were compared to measured temperatures. The median difference between measured and estimated temperature was 3.03 degrees C. The median distance from a sensor element to the closest point on a isotherm surface with the corresponding estimated temperature was 0.70 mm. The accuracy of this model is acceptable. Temperature maps as outlined here may be used for monitoring of cryotherapy in order to increase clinical effectiveness.

[Cryoablation--a treatment option for inoperable liver tumors?]. / Kryoablasjon--aktuell behandling av inoperable leversvulster?

BACKGROUND: Most patients with primary and secondary liver tumours are inoperable by conventional surgery. This has prompted the development of different techniques of local destruction of liver tumours, i.e. cryosurgical ablation radiofrequency, laser, and microwave ablation. MATERIAL AND METHODS: On the basis of relevant literature and our own experience we describe the principles of local destruction by cryoablation of colorectal metastases. RESULTS: Indications for ablation are mainly colorectal metastases and hepatocellular carcinoma. Mechanisms for tumour destruction include intra- and extracellular ice crystal formation, cellular membrane rupture, cellular dehydration and ischaemic damage. Ablation is regularly monitored by ultrasonography, which is suboptimal because of inadequate visualisation of the iceball. Long-term outcome of local destruction of liver tumours is not documented and randomized trials are not ethically acceptable. This complicates analyses of patient outcomes. INTERPRETATION: Local ablation of liver tumours is experimental therapy and should only be performed as a part of prospective trials.

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

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

[Image guided and robotic treatment--the advance of cybernetics in clinical medicine]. / Bildeveiledet og robotisert behandling--kybernetikkens inntog i klinisk medisin.

The introduction of advanced technology in hospitals has changed the treatment practice towards more image guided and minimal invasive procedures. Modern computer and communication technology opens up for robot aided and pre-programmed intervention. Several robotic systems are in clinical use today both in microsurgery and in major cardiac and orthopedic operations. As this trend develops, professions which are new in this context such as physicists, mathematicians and cybernetic engineers will be increasingly important in the treatment of patients.

Neuronavigation in intraoperative MRI.

OBJECTIVE: We describe the development and implementation of an image-guided surgical system combining the best features of conventional frameless stereotactic systems and the recently developed superconductive vertically configured intraoperative magnetic resonance scanner. The incorporation of intraoperatively updated magnetic resonance imaging (MRI) data sets into the neuronavigation computer overcomes one of the main disadvantages of these systems, i.e., intraoperative brain shift. METHODS: The integrated system consists of a 0.5-T MRI scanner (Signa SP General Electric Medical Systems, Milwaukee, WI), a neuronavigation computer with associated software (OTS Radionics, Burlington, MA), and an emulation program linking the two. The scanner has a 60-cm-wide vertical gap where both imaging and surgery are conducted, in-bore infrared linear cameras and monitors for interactive surgical neuronavigation, and flexible surface coils specially designed for surgery. RESULTS: Phantom studies showed navigational accuracy to be better than that obtained using conventional preoperative images and surface markers for patient registration. Our initial 17 cases using this integrated system comprised 16 craniotomies and one biopsy, and demonstrated decreased operative duration, greater frequency of interactive image guidance utilization, and better assessment of the progress of surgery compared to the cases previously done in the intraoperative MRI. CONCLUSION: This initial study of the addition of frameless stereotactic systems to the basic intraoperative MRI concept has demonstrated its clinical usefulness. The use of the intraoperative MRI greatly reduces the basic weakness of neuronavigation inaccuracy due to target shift. The surgical procedure performed in the imaging volume of the MRI scanner eliminates the problems of patient or scanner transport during the procedure. Immobilization of the patient throughout the procedure eliminated the need for reregistration of the patient, by taking advantage of the fixed camera system in the bore of the MRI system.

Intraoperative image-directed dye marking of tumor margins.

The incorporation of interactive image guidance during intracranial tumor surgery offers the possibilities of reduced operative trauma, shorter operation time, greater precision, and an increased understanding of complex anatomy and pathology. A basic weakness with these systems though is that they cannot account for movement of target points due to brain shift by draining of CSF or removal of pathology during the operative procedure. We have developed a stereotactic (frameless) guided injector probe for marking the tumor boundary with dye injection in conjunction with a neuronavigation system. The device consisted of a rigid blunt hollow probe (2 mm dia.) with 4 small side holes at the tip. The catheter is mounted in a holder equipped with 3 LEDs supplying guidance information for the neuronavigation system. A small manual aliquoting pump delivers a measured amount of dye in each track. Isotonic methylene blue was injected in 6 to 8 tracks around the periphery of the tumor as determined by the contract ring in MR scans. The dye was injected using image-directed guidance before resection of the tumor was started (often with the dura intact). Tumor tissue could then be resected until the dye became visible at the tumor boundary. Identification of the dye in the tissue was enhanced with the use of the operating microscope. The 3-dimensional position of the dye track could be determined at the end of tumor resection and compared with its initial position giving a good estimate of local brain shift. The method has proved especially helpful for the resection of large gliomas allowing for a more radical operative result.