Temporal evaluation of the microwave ablation zone and comparison of CT and gross sizes during the first month post-ablation in swine lung.

PURPOSE: The purpose of this study was to investigate the development and evolution of the microwave ablation (MWA) lesion in the normal lung by using a swine model at various time points and to compare post-procedural computed tomography (CT) and gross pathologic findings during the first month post-ablation. MATERIALS AND METHODS: Twenty-seven percutaneous MWA procedures were performed on swine lungs at 100W for either 2min (low dose, 18 ablations) or 10min (high dose, 9 ablations). Animals were sacrificed at either 2 days (n=5) or 28 days (n=5) after ablation. All animals underwent CT imaging immediate post-treatment and prior to sacrifice, with additional imaging at 7 and 14 days for the 28-day cohort. After euthanasia, lungs and trachea were removed en bloc and underwent gross pathology analysis. RESULTS: In both dose treatment groups, CT measurements of the ablation zone were maximum at Day 7 (low dose: 7.50±3.08 cm3; high dose: 24.87±11.34 cm3) and significantly larger compared to the immediate post-ablation measurements (low dose: 2.54±1.81 cm3; P=0.00011; high dose: 9.14±3.42 cm3; P=0.00374). No significant differences in dimensions were observed between CT and gross pathologic images for both high and low dose ablations in both cohorts. CONCLUSION: The treatment zone following MWA in the lung can vary in the sub-acute setting, achieving largest size at 7 days post-treatment. Furthermore, measurements from CT closely matched with gross pathologic ablation size.

Irreversible electroporation and thermal ablation of tumors in the liver, lung, kidney and bone: What are the differences?

Focal treatment with radiofrequency, microwave and cryoablation has been increasingly used for the treatment of tumors in patients who cannot undergo surgical resection and in select patients with early stage or oligometastatic disease. Each of these ablation modalities has a unique working principle and biophysics underlying the ablative effect, which largely determines the clinical indication for its application. Irreversible electroporation, a relatively new ablation technique with a predominantly nonthermal cell killing mechanism has emerged as an alternative treatment technique for tumors that are contraindicated for thermal ablation because of safety or efficacy considerations. Here, established thermal ablation techniques are compared with irreversible electroporation for treatment of tumors in the lung, liver, kidney and bone, and rationale is provided to guide selection of the most appropriate technique for each clinical setting.

Contrast enhanced ultrasound imaging can predict vascular-targeted photodynamic therapy induced tumor necrosis in small animals.

AIMS: To evaluate the accuracy of contrast-enhanced ultrasound (CEUS) for monitoring tumor necrosis following WST-11 vascular targeted photodynamic therapy (VTP) using imaging-pathology correlation. METHODS: Renal adenocarcinoma cells were injected into the hindlimb of 13 BalB/c mice resulting in tumors ranging from 9.8 to 194.3mm3. US guidance was used to place a laser fiber into the tumor, and VTP was performed. CEUS was performed prior to animal sacrifice, 24h post-VTP. Whole tumors were extracted for histopathologic analysis using H&E and TUNEL staining. Pathology samples corresponding to the CEUS imaging plane were prepared in order to compare the size and extents of tumor necrosis. RESULTS: Tumor necrosis following VTP appeared as a central region of non-enhancement on CEUS, while viable tumor appeared as patchy regions of enhancement in the tumor periphery. The region of tumor necrosis measured in mean 66% and 64.8% of total tumor area on CEUS and pathology respectively (p=0.2). The size and location of the necrosis on CEUS images and pathology samples were found correlative with no inter-observer difference (weighted kappa of 0.771 and 0.823, respectively). CONCLUSION: CEUS allows accurate monitoring of VTP induced tumor necrosis in a small animal model.

Comparison of CT Fluoroscopy-Guided Manual and CT-Guided Robotic Positioning System for In Vivo Needle Placements in Swine Liver.

PURPOSE: To compare CT fluoroscopy-guided manual and CT-guided robotic positioning system (RPS)-assisted needle placement by experienced IR physicians to targets in swine liver. MATERIALS AND METHODS: Manual and RPS-assisted needle placement was performed by six experienced IR physicians to four 5 mm fiducial seeds placed in swine liver (n = 6). Placement performance was assessed for placement accuracy, procedure time, number of confirmatory scans, needle manipulations, and procedure radiation dose. Intra-modality difference in performance for each physician was assessed using paired t test. Inter-physician performance variation for each modality was analyzed using Kruskal-Wallis test. RESULTS: Paired comparison of manual and RPS-assisted placements to a target by the same physician indicated accuracy outcomes was not statistically different (manual: 4.53 mm; RPS: 4.66 mm; p = 0.41), but manual placement resulted in higher total radiation dose (manual: 1075.77 mGy/cm; RPS: 636.4 mGy/cm; p = 0.03), required more confirmation scans (manual: 6.6; RPS: 1.6; p < 0.0001) and needle manipulations (manual: 4.6; RPS: 0.4; p < 0.0001). Procedure time for RPS was longer than manual placement (manual: 6.12 min; RPS: 9.7 min; p = 0.0003). Comparison of inter-physician performance during manual placement indicated significant differences in the time taken to complete placements (p = 0.008) and number of repositions (p = 0.04) but not in other study measures (p > 0.05). Comparison of inter-physician performance during RPS-assisted placement suggested statistically significant differences in procedure time (p = 0.02) and not in other study measures (p > 0.05). CONCLUSIONS: CT-guided RPS-assisted needle placement reduced radiation dose, number of confirmatory scans, and needle manipulations when compared to manual needle placement by experienced IR physicians, with equivalent accuracy.

A study of porcine liver motion during respiration for improving targeting in image-guided needle placements.

PURPOSE: Liver motion due to respiration restricts targeting and needle placement accuracy during image-guided interventional procedures. Breath holds, imaging techniques, and navigation systems are used to improve targeting accuracy. Data of in-vivo liver behavior under respiration can enhance these approaches. METHODS: An experimental study was performed using the swine model to capture the dynamics of liver motion during respiration using needles tipped with electromagnetic sensors. The swine liver was segmented into four lobes (right lateral, right medial, left medial and left lateral), and two sensor-tipped needles were placed in each location to acquire representative displacement data. RESULTS: Maximum displacement was found to occur in the left medial and left lateral lobes, in the anterior-posterior direction. Significant lobe-dependent variation in motion behavior was recorded, but a variation within a lobe was minimal and independent of needle approach. Magnitude of displacement in all lobes was found to be monotonically correlated to breathing volume. Displacement of liver was found to be out of phase with breathing by approximately 2 Hz. The positioning of the animal was also found to influence direction and magnitude of liver displacement in different lobes. CONCLUSIONS: We have presented previously unavailable data and insight into the role of easily controllable parameters such as breathing volume, patient positioning, and lobe-specific heterogeneity in the displacement of liver due to respiration.