Directional microwave ablation in spine: experimental assessment of computational modeling.

BACKGROUND: Despite the theoretical advantages of treating metastatic bone disease with microwave ablation (MWA), there are few reports characterizing microwave absorption and bioheat transfer in bone. This report describes a computational modeling-based approach to simulate directional microwave ablation (dMWA) in spine, supported by ex vivo and pilot in vivo experiments in porcine vertebral bodies. MATERIALS AND METHODS: A 3D computational model of microwave ablation within porcine vertebral bodies was developed. Ex vivo porcine vertebra experiments using a dMWA applicator measured temperatures approximately 10.1 mm radially from the applicator in the direction of MW radiation (T1) and approximately 2.4 mm in the contra-lateral direction (T2). Histologic assessment of ablated ex vivo tissue was conducted and experimental results compared to simulations. Pilot in vivo experiments in porcine vertebral bodies assessed ablation zones histologically and with CT and MRI. RESULTS: Experimental T1 and T2 temperatures were within 3-7% and 11-33% of simulated temperature values. Visible ablation zones, as indicated by grayed tissue, were smaller than those typical in other soft tissues. Posthumous MRI images of in vivo ablations showed hyperintensity. In vivo experiments illustrated the technical feasibility of creating directional microwave ablation zones in porcine vertebral body. CONCLUSION: Computational models and experimental studies illustrate the feasibility of controlled dMWA in bone tissue.

Evolution of the imaging features of osteoid osteoma treated with RFA or MRgFUS during a long-term follow-up: a pictorial review with clinical correlations.

Interventional radiology is today considered the first-line treatment for osteoid osteoma both in the form of needle-guided technique of ablation (Radiofrequency) and of needleless technique (magnetic resonance-guided focused ultrasound surgery). The follow-up study of the procedures is mainly clinical, since the disappearance of pain is consistent with the success of the procedure. However, due to the minimally invasive and innovative nature of the approach, interpretation of the follow-up imaging could be ambiguous and misleading. Aim of our review was to define the main findings on the imaging that can best describe the regular evolution of these types of treatment. In particular, four findings were considered: (1) bone marrow oedema; (2) reactive phenomena (perilesional inflammatory reaction for extra-articular lesions or synovial reaction for intra-articular lesions); (3) bone remodelling (disappearance of the nidus and bone healing); (4) ring sign (considered as the granulation tissue around the nidus treated). These findings were evaluated using MRI and CT with a follow-up study that lasted up to 24 months.

Effect of Sonication Duration and Power on Ablation Depth During MR-Guided Focused Ultrasound of Bone.

PURPOSE: To evaluate the effect of differences in sonication duration and power on the size of postcontrast ablation zone following magnetic resonance-guided focused ultrasound (MRgFUS) of bone in a swine femoral bone model. MATERIALS AND METHODS: Experimental procedures received approval from the Institutional Committee on Animal Research. MRgFUS was used to create two thermal lesions in the left femur of six pigs. Each target was subjected to six sonications. 400J of energy was used for each sonication. However, the distal target received the standard sonication duration of 20 seconds (20W), while the proximal target received a longer sonication duration of 40 seconds (10W). MRgFUS lesions were imaged with fat-saturated spoiled gradient echo sequence at 3.0T MRI 10 minutes following the administration of contrast. Maximum three-plane dimensions of the hypoenhanced ablation area were measured. RESULTS: Postcontrast MR images demonstrated ovoid regions of hypoenhancement at each target. The average depth of ablation was significantly greater for the shorter high-power sonications (7.3 mm), compared to the longer lower-power sonications (4.5 mm), P = 0.026. The craniocaudal dimension was also greater for the shorter ablations 26.7 mm compared to the longer sonications 21.0 mm, P = 0.006. CONCLUSION: Contrary to anecdotal clinical experience, this preclinical model suggests that during MRgFUS of bone, standard duration, higher-power sonications resulted in deeper ablation volumes compared to long duration, lower-power sonications. These results suggest that to achieve deeper ablations, if longer sonications are used, then the power should be relatively maintained, for a net energy increase. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:1418-1422.

MRI-guided high-intensity focused ultrasound ablation of bone: evaluation of acute findings with MR and CT imaging in a swine model.

PURPOSE: To evaluate hyperacute (<1 hour) changes on magnetic resonance (MR) and computed tomography (CT) imaging following MR-guided high-intensity focused ultrasound (MRgHIFU) in a swine bone model as a function of sonication number and energy. MATERIALS AND METHODS: Experimental procedures received approval from the local Institutional Animal Care and Use Committee. MRgHIFU was used to create distal and proximal ablations in the right femur of eight pigs. Each target was dosed with four or six sonications within similar volumes. The energy dosed to the distal target was higher (419 ± 19 J) than the proximal target (324 ± 17 J). The targeted femur and contralateral control were imaged before and after ablation using MR at 3T. Qualitative changes in signal on T1-weighted, T2-weighted, and T1-weighted postcontrast images were assessed. Ablation dimensions were calculated from postcontrast MRI. The 64-slice CT images were also obtained before and after ablation and qualitative changes were assessed. RESULTS: MRgHIFU bone ablation size measured on average 8.5 × 21.1 × 16.2 mm (transverse × craniocaudal × anteroposterior). Interestingly, within similar prescribed volumes, increasing the number of sonications from 4 to 6 increased the depth of the intramedullary hypoenhanced zone from 2.9 mm to 6.5 mm (P < 0.001). There was no difference in the appearance of low versus high energy ablations. CT imaging did not show structural abnormalities. CONCLUSION: The number of MRgHIFU focal sonications can be used to increase the depth of treatment within the targeted bone. Unlike CT, T2-weighted and contrast-enhanced MR demonstrated the hyperacute structural changes in the femur and surrounding soft tissue.

Augmented Reality Navigation System (SIRIO) for Neuroprotection in Vertebral Tumoral Ablation.

(1) This study evaluates the impact of the CT-guided SIRIO augmented reality navigation system on the procedural efficacy and clinical outcomes of neuroprotection in vertebral thermal ablation (RTA) for primary and metastatic bone tumors. (2) Methods: A retrospective non-randomized analysis of 28 vertebral RTA procedures was conducted, comparing 12 SIRIO-assisted and 16 non-SIRIO-assisted procedures. The primary outcomes included dose-length product (DLP) and epidural dissection time. The secondary outcomes included technical success, complication rates, and pain scores at procedural time (VAS Time 0) and three months post-procedure (VAS Time 1). The statistical analyses included t-tests, Mann-Whitney U tests, and multiple regression. (3) Results: SIRIO-assisted procedures significantly reduced DLP (307.42 mGycm vs. 460.31 mGycm, p = 2.23 × 10-8) and procedural epidural dissection time (13.48 min vs. 32.26 min, p = 2.61 × 10-12) compared to non-SIRIO-assisted procedures. Multiple regression confirmed these reductions were significant (DLP: ß = -162.38, p < 0.001; time: ß = -18.25, p < 0.001). Pain scores (VAS Time 1) did not differ significantly between groups, and tumor type did not significantly influence outcomes. (4) Conclusions: The SIRIO system enhances neuroprotection efficacy and safety, reducing radiation dose and procedural time during spine tumoral ablation while maintaining consistent pain management outcomes.

Comprehensive and Sequential Gene Expression Analysis of Bone Healing Process Following Er:YAG Laser Ablation.

Objective: This study evaluated the comprehensive and sequential gene expression in laser-ablated bone compared with that in nontreated control bone. Background: Bone ablation by Er:YAG laser has shown positive effects on bone healing; however, the gene expression responses that occur during bone healing remain unclear. Materials and methods: The calvarial bone of male, 10-week-old Wistar rats was ablated by Er:YAG laser. Gene expression in the laser-ablated bone and nontreated control bone was evaluated at 6, 24, and 72 h using microarray analysis. Messenger RNA (mRNA) expression levels were validated by quantitative reverse transcription-polymerase chain reaction. Results: Gene expression of BCAR1/p130Cas (breast cancer anti-estrogen resistance 1/p130 Crk-associated substrate), a mechanotransducer, was gradually increased. Additionally, upstream of the Hippo signaling pathway was enriched according to Kyoto Encyclopedia of Genes and Genomes pathway analysis at 6 h. F-actin mRNA expression was also gradually increased, whereas the Hippo signaling pathway was downregulated from 6 to 24 h. Enrichment of bone formation-related Gene Ontology (GO) terms was observed from an early stage, whereas inflammation-related GO terms, gene sets, and mRNA expression of Nfkb1, Tnf, and Il1b were gradually enriched after 24 h. Conclusions: Bone ablation by Er:YAG laser regulated the expression of Bcar1 and Actg1, the main regulators of mechanotransduction in the bone tissue. Additionally, inflammation was gradually increased up to 72 h following bone ablation with Er:YAG laser. Laser influences the expression of genes associated with bone formation immediately after irradiation. Therefore, mechanical stress and the biological effects caused by Er:YAG laser irradiation potentially contribute to wound healing in the laser-ablated bone tissue.

Optical fibers for endoscopic high-power Er:YAG laserosteotomy.

SIGNIFICANCE: The highest absorption peaks of the main components of bone are in the mid-infrared region, making Er:YAG and CO2 lasers the most efficient lasers for cutting bone. Yet, studies of deep bone ablation in minimally invasive settings are very limited, as finding suitable materials for coupling high-power laser light with low attenuation beyond 2 µm is not trivial. AIM: The first aim of this study was to compare the performance of different optical fibers in terms of transmitting Er:YAG laser light with a 2.94-µm wavelength at high pulse energy close to 1 J. The second aim was to achieve deep bone ablation using the best-performing fiber, as determined by our experiments. APPROACH: In our study, various optical fibers with low attenuation (λ = 2.94 µm) were used to couple the Er:YAG laser. The fibers were made of germanium oxide, sapphire, zirconium fluoride, and hollow-core silica, respectively. We compared the fibers in terms of transmission efficiency, resistance to high Er:YAG laser energy, and bending flexibility. The best-performing fiber was used to achieve deep bone ablation in a minimally invasive setting. To do this, we adapted the optimal settings for free-space deep bone ablation with an Er:YAG laser found in a previous study. RESULTS: Three of the fibers endured energy per pulse as high as 820 mJ at a repetition rate of 10 Hz. The best-performing fiber, made of germanium oxide, provided higher transmission efficiency and greater bending flexibility than the other fibers. With an output energy of 370 mJ per pulse at 10 Hz repetition rate, we reached a cutting depth of 6.82 ± 0.99 mm in sheep bone. Histology image analysis was performed on the bone tissue adjacent to the laser ablation crater; the images did not show any structural damage. CONCLUSIONS: The findings suggest that our prototype could be used in future generations of endoscopic devices for minimally invasive laserosteotomy.

Influence of environmental conditions in bovine bone ablation by ultrafast laser.

Ultrafast lasers are promising tools for surgical applications requiring precise tissue cutting. Shallow ablation depth and slow rate as well as collateral damage are common barriers limiting the use of laser in clinical applications. Localized cooling with water and/or air jet is known to reduce collateral thermal damage. We studied the influence of environmental conditions including air, compressed air flow, still water and water jet on ablation depth, ablation rate and surface morphology on bovine bone samples with an 800 nm femtosecond laser. At 15 J/cm2 , no thermal effect was observed by electron microscopy and Raman spectroscopy. The experimental results indicate that environmental conditions play a significant role in laser ablation. The deepest cavity and highest ablation rate were achieved under the compressed air flow condition, which is attributed to debris removal during the ablation process. The shallowest ablation depth and lowest ablation rates were associated with water flushing. For surface morphology, smooth surface and the absence of microcracks were observed under air flow conditions, while rougher surfaces and minor microcracks were observed under other conditions. These results suggest that ultrafast ablation of bone can be more efficient and with better surface qualities if assisted with blowing air jet.

Evaluation of bone healing following Er:YAG laser ablation in rat calvaria compared with bur drilling.

The Er:YAG laser is currently used for bone ablation. However, the effect of Er:YAG laser irradiation on bone healing remains unclear. The aim of this study was to investigate bone healing following ablation by laser irradiation as compared with bur drilling. Rat calvarial bone was ablated using Er:YAG laser or bur with water coolant. Er:YAG laser effectively ablated bone without major thermal changes. In vivo micro-computed tomography analysis revealed that laser irradiation showed significantly higher bone repair ratios than bur drilling. Scanning electron microscope analysis showed more fibrin deposition on laser-ablated bone surfaces. Microarray analysis followed by gene set enrichment analysis revealed that IL6/JAK/STAT3 signaling and inflammatory response gene sets were enriched in bur-drilled bone at 6 hours, whereas the E2F targets gene set was enriched in laser-irradiated bone. Additionally, Hspa1a and Dmp1 expressions were increased and Sost expression was decreased in laser-irradiated bone compared with bur-drilled bone. In granulation tissue formed after laser ablation, Alpl and Gblap expressions increased compared to bur-drilled site. Immunohistochemistry showed that osteocalcin-positive area was increased in the laser-ablated site. These results suggest that Er:YAG laser might accelerate early new bone formation with advantageous surface changes and cellular responses for wound healing, compared with bur-drilling.

CT-guided radiofrequency ablation in osteoid osteoma: Result from a tertiary cancer centre in India.

AIMS: The aim of this study is to evaluate the clinical efficacy of computed tomography (CT)-guided radiofrequency (RF) ablation as a minimally invasive therapy for osteoid osteoma. MATERIALS AND METHODS: This is a retrospective analysis of prospectively maintained data of 43 symptomatic osteoid osteoma patients who were treated by radiofrequency ablation (RFA). Forty out of 43 patients were naive cases and underwent primary treatment for osteoid osteoma with RFA, whereas 3 patients included in the study underwent RFA for local recurrence after having undergone surgical treatment. Diagnosis was based on clinical and characteristic imaging findings, and biopsy was done for cases with atypical presentation. Pre and post procedure Visual Analog Score (VAS) was documented in all cases. Monopolar RFA system was used in all patients, and the electrode was placed within the lesion nidus under CT guidance coaxially through 11G introducer needle. Ablation was performed at 90° C for 5 min. RESULTS: Technical success rate of intranidal placement of electrode was 100%. The primary clinical success in our study was 97.7% (42 of 43), and the secondary clinical success was 100%. Pre and postprocedure VAS score in our study group was 7.8 and 0.4, respectively. Mean follow-up period in our study was 48 months (Range: 4-129 months). One patient had recurrence of pain 4 years after treatment and was treated successfully by a second session. Minor complications were seen in 3 patients with two cases of RF pad burns and one case of skin burn at the treatment site, and these were managed conservatively. No patients developed temporary/permanent neurological deficits, and no procedure-related mortality was seen in our study. CONCLUSION: CT-guided percutaneous RFA is a simple, safe, minimally invasive, and highly effective treatment option for osteoid osteoma with good long-term pain control and potentially low disease recurrence.

Bone ablation without thermal or acoustic mechanical injury via a novel picosecond infrared laser (PIRL).

BACKGROUND AND OBJECTIVE: A precise means to cut bone without significant thermal or mechanical injury has thus far remained elusive. A novel non-ionizing ultrafast pulsed picosecond infrared laser (PIRL) may provide the solution. Tissue ablation with the PIRL occurs via a photothermal process with thermal and stress confinement, resulting in efficient material ejection greatly enhanced through front surface spallation photomechanical effects. By comparison, the Er:YAG laser (EYL) ablates via photothermal and cavitation-induced photomechanical effects without thermal or acoustic confinement, leading to significant collateral tissue injury. This study compared PIRL and EYL bone ablation by infrared thermography (IRT), environmental scanning electron microscopy (ESEM), and histology. STUDY DESIGN: Prospective, comparative, ex vivo animal model. SETTING: Optics laboratory. SUBJECTS AND METHODS: Ten circular area defects were ablated in ex vivo chicken humeral cortex using PIRL and EYL at similar average power (~70 mW) under IRT. Following fixation, ESEM and undecalcified light microscopy images were obtained and examined for signs of cellular injury. RESULTS: Peak rise in surface temperature was negligible and lower for PIRL (1.56 °C; 95% CI, 0.762-2.366) compared to EYL ablation (12.99 °C; 95% CI, 12.189-13.792) (P < .001). ESEM and light microscopy demonstrated preserved cortical microstructure following PIRL ablation in contrast to diffuse thermal injury seen with EYL ablation. Microfractures were not observed. CONCLUSION: Ablation of cortical bone using the PIRL generates negligible and significantly less heat than EYL ablation while preserving cortical microstructure. This novel laser has great potential in advancing surgical techniques where precision osseous manipulation is required.