Evaluation of MRI T1-based treatment monitoring during laser-induced thermotherapy of liver metastases for necrotic size prediction

Microfocusing sapphire capillary needle for laser surgery and therapy: Fabrication and characterization

A sapphire shaped capillary needle designed for collimating and focusing of laser radiation was proposed and fabricated by the edge-defined film-fed growth technique. It features an as-grown surface quality, high transparency for visible and near-infrared radiation, high thermal and chemical resistance and the complex shape of the tip, which protects silica fibers. The needle's geometrical parameters can be adjusted for use in various situations, such as type of tissue, modality of therapy and treatment protocol. The focusing effect was demonstrated numerically and observed experimentally during coagulation of the ex vivo porcine liver samples. This needle in combination with 0.22NA optical fiber allows intensive and uniform coagulation of 150 mm³ volume interstitially and 30 mm³ superficially by laser exposure with 280 J without tissue carbonization and fiber damaging along with delicate treatment of small areas. The demonstrated results reveal the perspectives of the proposed sapphire microfocusing needle for laser surgery and therapy.

Effects of Different 980-nm Diode Laser Parameters in Hepatectomy

BACKGROUND AND OBJECTIVE

Despite the successful application of laser in animal experiments and clinics, the adjustment of laser parameters during surgery is still unclear. This study aimed to investigate the effect of different 980-nm diode laser parameters in hepatectomy. This could provide a clear protocol for using 980-nm diode laser in hepatectomy.

STUDY DESIGN/MATERIALS AND METHODS

In total, 48 Sprague-Dawley rats were used to explore the effects of different 980-nm diode laser parameters in hepatectomy, by setting different parameter combinations. The rats were randomly divided into eight groups, including the continuous wave group and quasi-continuous wave group. The effects were assessed in terms of liver resection speed, extent of intraoperative bleeding, and thermal damage.

RESULTS

In the quasi-continuous wave group, there was a significant difference in resection speed at the different laser parameters (P < 0.001); however, there was no significant difference in intraoperative bleeding and thermal damage. In the continuous wave group, there was a significant difference in resection speed, intraoperative bleeding, and thermal damage at different parameters.

CONCLUSION

The study showed that the average power determined hemostasis efficiency and thermal damage, and peak power determined the liver resection speed, whereas the pulse width and repetition frequency are not independent factors. When using 980-nm diode laser in hepatectomy, the average power should be decreased to prove hemostasis efficiency in delicate operations, and the peak power should be decreased to accelerate the procedure without worsening thermal damage. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Theoretical model for laser ablation outcome predictions in brain: calibration and validation on clinical MR thermometry images

PURPOSE

Neurosurgical laser ablation is experiencing a renaissance. Computational tools for ablation planning aim to further improve the intervention. Here, global optimisation and inverse problems are demonstrated to train a model that predicts maximum laser ablation extent.

METHODS

A closed-form steady state model is trained on and then subsequently compared to N = 20 retrospective clinical MR thermometry datasets. Dice similarity coefficient (DSC) is calculated to provide a measure of region overlap between the 57 °C isotherms of the thermometry data and the model-predicted ablation regions; 57 °C is a tissue death surrogate at thermal steady state. A global optimisation scheme samples the dominant model parameter sensitivities, blood perfusion (ω) and optical parameter (μ_eff) values, throughout a parameter space totalling 11 440 value-pairs. This represents a lookup table of μ_eff-ω pairs with the corresponding DSC value for each patient dataset. The μ_eff-ω pair with the maximum DSC calibrates the model parameters, maximising predictive value for each patient. Finally, leave-one-out cross-validation with global optimisation information trains the model on the entire clinical dataset, and compares against the model naïvely using literature values for ω and μ_eff.

RESULTS

When using naïve literature values, the model's mean DSC is 0.67 whereas the calibrated model produces 0.82 during cross-validation, an improvement of 0.15 in overlap with the patient data. The 95% confidence interval of the mean difference is 0.083-0.23 (p < 0.001).

CONCLUSIONS

During cross-validation, the calibrated model is superior to the naïve model as measured by DSC, with +22% mean prediction accuracy. Calibration empowers a relatively simple model to become more predictive.