Computer-assisted needle trajectory planning and mathematical modeling for liver tumor thermal ablation: A review.

Radiofrequency ablation (RFA) and microwave ablation (MWA) have become an important means for treating liver tumors. RFA and MWA are a minimally invasive therapy which involves an ablation applicator or needle (i.e., radiofrequency electrode or microwave antenna) inserted percutaneously into a tumor under the guidance of medical imaging, so as to destroy the tumor in situ by heating-induced coagulation necrosis. Treatment planning, particularly needle trajectory planning, is crucial to RFA and MWA. In clinical procedures, however, needle trajectory planning still relies on the personal experience of clinicians. Manual needle trajectory planning is tedious and may cause inter-operator difference. Therefore, computer-assisted needle trajectory planning techniques are of clinical value and have been extensively explored. However, a literature review that focuses on computer-assisted needle trajectory planning for liver tumor RFA and MWA has not been reported. In this paper, we conducted an extensive review on computer-assisted needle trajectory planning for RFA and MWA of liver tumors. Fundamentals of needle trajectory planning are summarized. Algorithms for single-needle and multi-needle trajectory planning are analyzed. Shortcomings of current computer-assisted needle trajectory planning algorithms are discussed and future developments are suggested.

A review of ultrasound detection methods for breast microcalcification.

Breast microcalcifications are one of the important imaging features of early breast cancer and are a key to early breast cancer diagnosis. Ultrasound imaging has been widely used in the detection and diagnosis of breast diseases because of its low cost, nonionizing radiation, and real-time capability. However, due to factors such as limited spatial resolution and speckle noise, it is difficult to detect breast microcalcifications using conventional B-mode ultrasound imaging. Recent studies show that new ultrasound technologies improved the visualization of microcalcifications over conventional B-mode ultrasound imaging. In this paper, a review of the literature on the ultrasonic detection methods of microcalcifications was conducted. The reviewed methods were broadly divided into high-frequency B-mode ultrasound imaging techniques, B-mode ultrasound image processing techniques, ultrasound elastography techniques, time reversal techniques, high spatial frequency techniques, second-order ultrasound field imaging techniques, and photoacoustic imaging techniques. The related principles and research status of these methods were introduced, and the characteristics and limitations of the various methods were discussed and analyzed. Future developments of ultrasonic breast microcalcification detection are suggested.

Numerical evaluation of ablation zone under different tip temperatures during radiofrequency ablation.

The present study aimed at investigating the relationship between the shape and size of ablation zone and the ablation time during radiofrequency ablation (RFA) at different tip temperatures (80, 85, 90, and 95 °C). A two-dimensional simulation model of liver RFA using single-electrode was first built by finite element method (FEM). A closed-loop proportional-integral (PI) controller was employed in the FEM model. The heat transfer issues were solved based on Pennes biological equation. To improve simulation accuracy of the FEM models, temperature-dependent forms of the electrical conductivity and the thermal conductivity were adopted in the model. The ablation zone was assessed by 54 °C isothermal contour (IT54). The ablation zone sizes obtained from the numerical simulations and ex vivo experiments were compared to evaluate the validity of the numerical model. All the four tip temperatures (80, 85, 90, and 95 °C) were tested using 3 ex vivo porcine livers respectively. According to numerical simulation results, the characterization functions of the ablation volume and the ablative margin (AM) were derived. The proposed curve functions could precisely characterize the shape and size of ablation zone at different preset tip values, and the statistical results showed that the prediction curves had a good consistency with simulation curves. This paper proposed the prediction models of the ablation zone in the RFA process, which could be used to achieve accurate planning of RFA needle placements and optimize patient care during temperature-controlled RFA therapy.