Modelling liver tissue properties using a non-linear visco-elastic model for surgery simulation.

In this work, we introduce an extension of the linear elastic tensor-mass method allowing fast computation of non-linear and visco-elastic mechanical forces and deformations for the simulation of biological soft tissue. We aim at developing a simulation tool for the planning of cryogenic surgical treatment of liver cancer. Percutaneous surgery simulation requires accurate modelling of the mechanical behaviour of soft tissue, and previous experimental characterizations have shown that linear elasticity is only a coarse approximation of the real properties of biological tissues. We first show that our model can simulate different types of non-linear and visco-elastic mechanical behaviours at speeds which are compatible with real-time applications. Then an experimental setup is presented which was used to characterize the mechanical properties of deer liver tissue under perforation by a biopsy needle. Experimental results demonstrate that a linear model is not suitable for simulating this application, while the proposed model succeeds in accurately modelling the axial load measured on the needle.

An analytic method to predict the thermal map of cryosurgery iceballs in MR images.

This paper presents a newly developed method to estimate, in magnetic resonance (MR) images, the temperatures reached within the volume of an iceball produced by a cryogenic probe. Building on the direct measurements of the MR signal intensity and its correlation with independent temperature variations at the phase transition from liquid to solid, the thermal information embedded in the images was accessed. The volume and diameter of the growing iceball were estimated from a time series of MR images. Using regressions over the volume in the time and thermal domains, this method predicted the cryogenic temperatures beyond the range of sensitivity of the MR signal itself. We present a validation of this method in samples of gelatin and ex vivo pig liver. Temperature predictions are shown to agree with independent thermosensor readings over a range extending from 20 degrees C down to -65 degrees C, with an average error of less than 6 degrees C.

Improved image contrast with mangafodipir trisodium (MnDPDP) during MR-guided percutaneous cryosurgery of the liver.

The present study was undertaken to measure the gain observed in the liver-to-tumor contrast of perioperative images when using mangafodipir trisodium, a liver-specific contrast agent, during percutaneous cryosurgery of the liver performed under the guidance of magnetic resonance images. Retrospective quantitative analyses of MR images were performed on eleven patients having a total of 30 liver tumors treated by MR-guided percutaneous cryosurgery. An initial group of four patients were treated with no contrast agent, and was compared with a second group of 7 patients who received an intravenous injection of 5 microM/kg of mangafodipir for their cryosurgery. The percutaneous cryosurgery was monitored under the near-real-time-imaging mode of a 0.5T open-configuration MRI system using a T(1)-weighted Gradient-recalled echo pulse sequence. A significant improvement in the liver-to-tumor contrast-to-noise ratio was observed with mangafodipir (p < 0.05, paired t test) in 0.5T preoperative images. Along with the stability of the mangafodipir contrast enhancement during the entire cryosurgical procedure, the resulting gain in contrast allowed for better visualizing the presence of residual untreated tumor margins at the periphery of the cryosurgery iceball directly from perioperative images acquired with patients under narcosis. Consequently, it not only became easier for the interventionalist to determine the need for an additional cryoprobe to increase the size of the iceball during the procedure, but also to decide on the appropriate end point of the cryosurgery.

Acromiohumeral distance in a seated position in persons with impingement syndrome.

PURPOSE: To compare the acromiohumeral distance (AHD) of both shoulders in subjects with a unilateral shoulder impingement syndrome (SIS) and healthy subjects in a seated position during free shoulder movements of large amplitude. MATERIALS AND METHODS: Using a 0.5-Tesla SIGNA-SP/i trade mark open-configuration magnetic resonance imaging (MRI) system, the AHD was measured at several arm positions, in a standardized seated position. RESULTS: In flexion (rest to 130 degrees ), the mean AHD of SIS varied from 8.3 to 2.8 mm, as compared to from 8.7 to 4.1 mm for asymptomatic contralateral shoulders. In abduction (rest to 110 degrees ), the AHD varied from 8.1 to 3.4 mm and from 8.8 to 4.6 mm for SIS and asymptomatic shoulders, respectively. The smallest AHD (P <.01) was observed at 110 degrees. From 80 degrees of arm elevation, the AHD was significantly smaller in impingement than in asymptomatic shoulders (P <.05). The AHD of asymptomatic shoulders did not differ from that of healthy subjects. In SIS, the AHD at rest was correlated with its reduction at all shoulder positions (r(p) = 0.62-0.88), but was a poor predictor of the smallest AHD observed at 110 degrees (flexion, R(2) = 0.09; abduction, R(2) = 0.08). CONCLUSION: In the critical arm elevation positions for impingement, AHD is discriminative for SIS, compared to asymptomatic shoulders and healthy ones. AHD at rest is a good indicator of the magnitude of its reduction in elevation, but not of the smallest AHD in arm elevation.

Magnetic resonance-guided percutaneous cryosurgery of breast carcinoma: technique and early clinical results.

PURPOSE: This phase I study was designed to demonstrate the feasibility, safety, efficacy and predictability of percutaneous cryosurgery, guided under magnetic resonance (MR) imaging, in the treatment of invasive breast carcinoma. PATIENTS AND METHODS: Under the guidance of near-real-time T1-weighted FSE images of a 0.5-T open-configuration MR system, percutaneous cryosurgery was performed in 25 patients with operable invasive breast carcinoma, 4 weeks prior to their scheduled mastectomy. Predictive assessments by interventional radiologists using 4 breast-imaging techniques (mammography, sonography, scintigraphy and MR) were correlated with postmastectomy results of histopathology and assessed for predictability. Local and systemic morbidity were also evaluated during the month of follow-up preceding mastectomy. RESULTS: Percutaneous cryosurgery resulted in no serious complications, either local or systemic. All tumoural tissues included in the cryogenic "iceball" were destroyed, with no viable histologic residues. Ablation was total in 13 of the 25 tumours treated. Combining periprocedural MR images with postprocedure scintimammographic findings enabled a 96% rate for predicting the cryosurgical results. CONCLUSIONS: MR-guided cryosurgery of breast carcinoma is feasible, safe and efficient, with predictable results. Major drawbacks are that the cryolesion (a palpable iceball) persists for a month or more after the procedure, undermining the reliability of the physical examination; and that breast imaging (mammography, ultrasound and MR) presents the same difficulty of interpretation as the physical exam even 1 month after the procedure. More studies are required to refine this treatment method.