Influence of the bridging effect by sequential laser application on tissue ablation in an ex vivo model, taking organ perfusion into account

MR-guided laser-induced thermotherapy in ex vivo porcine kidney: comparison of four different imaging sequences

PURPOSE

To evaluate the clinical value of different magnetic resonance imaging (MRI) sequences for a real-time thermo-monitoring during laser-induced thermotherapy (LITT) in kidneys.

METHODS

Twenty-eight ex vivo pig kidneys were treated with laser ablation under MR guidance in a high-field MR scanner (Magnetom Espree or Avanto Fit, Siemens, Germany). For the thermal ablation of the kidney, a neodymium yttrium-aluminum-garnet (Nd:YAG) laser was used in combination with a special protective catheter (length 43 cm, 4 French) which is sealed at the distal end. First, ablation was performed for 7, 10, and 13 minutes using FLASH sequences for investigation of time-dependent growth of lesion size. In the second step, we evaluated the optimal imaging sequence during a 7 minutes ablation of the kidney and after cooling using four different MR sequences (Haste, FLASH, radial VIBE, and Caipirinha DIXON).

RESULTS

Macroscopic lesion volume increased from 3,784 ± 1,525 mm(3) to 7,683 ± 5,756 mm(3) after the ablation from 7 to 13 minutes and MR volume ranged from 2,107 ± 1,674 mm(3) to 2,934 ± 1,549 mm(3) after the ablation from 7 to 13 minutes. During ablation, FLASH (132 ± 34%) and radial VIBE (120 ± 43%) sequences displayed lesion volumes most efficiently with a trend to overestimation. The Caipirinha DIXON (323 ± 24%) sequence overestimated the volumes significantly during real-time monitoring. The volumes measured by MRI with FLASH (61 ± 30%), Haste (67 ± 28%), or radial VIBE (48 ± 14%) sequences after cooling of the kidney after ablation were always underestimated. The Caipirinha DIXON (142 ± 2%) sequence still overestimated the lesion volume after cooling of the kidney.

CONCLUSION

LITT is a feasible ablation modality in kidney tissue. Moreover, macroscopic and MR lesion volume increases time-dependently. For online monitoring, radial VIBE and FLASH sequences seem to be most efficient.

Bipolar and Multipolar Radio Frequency Ablation With Resistance Controlled Power Output: Standardized Ex Vivo Kidney Tissue Evaluation

PURPOSE

We investigated a newly developed bipolar and multipolar RF ablation system with an internally cooled electrode and resistance controlled power output in a standardized model of perfused ex vivo kidney tissue.

MATERIALS AND METHODS

RF energy was applied at different power levels (20, 30 and 60 W) for 1, 3, 5 and 9 minutes. Each treatment parameter was repeated 5 times. For the 20/30 W levels a bipolar electrode with an active conducting part of 20/30 mm was selected. At 60 W 2 bipolar electrodes with an active conducting part (30 mm each) were connected. Lesion volumes and shapes were calculated by measuring the maximum vertical, long axis and short axis diameters of the macroscopic lesion.

RESULTS

Lesion volume increased significantly with the treatment time and generator power applied (p < 0.0001). Lesion size in multipolar ablated zones was larger than that in bipolar ablated zones. A reliable dose-effect relationship existed between the generator power/applied treatment time and ablated tissue lesion size. All lesions were elliptical.

CONCLUSIONS

Bipolar and multipolar RF ablation with an internally cooled electrode and tissue resistance control represent an interesting advance in RF technology. The development of lesion size and volume is predictable, while a uniform lesion shape can be achieved in perfused ex vivo kidney tissue. Further in vivo trials are required to test whether complete and reliable tumor tissue ablation is possible with this system.

Multiple high-intensity focused ultrasound probes for kidney-tissue ablation

BACKGROUND AND PURPOSE

To investigate kidney-tissue ablation by high-intensity focused ultrasound (HIFU) using multiple and single probes.

MATERIALS AND METHODS

Ultrasound beams (1.75 MHz) produced by a piezoceramic element (focal distance 80 mm) were focused at the center of renal parenchyma. One of the three probes (mounted on a jig) could also be used for comparison with a single probe at comparable power ratings. Lesion dimensions were examined in perfused and unperfused ex vivo porcine kidneys at different power levels (40, 60, and 80 W) and treatment times (4, 6, and 8 seconds).

RESULTS

At identical power levels, the lesions induced by multiple probes were larger than those induced by a single probe. Lesion size increased with increasing pulse duration and generator power. The sizes and shapes of the lesions were predictably repeatable in all samples. Lesions in perfused kidneys were smaller than those in unperfused kidneys.

CONCLUSIONS

Ex vivo, kidney-tissue ablation by means of multiple HIFU probes offers significant advantages over single HIFU probes in respect of lesion size and formation. These advantages need to be confirmed by tests in vivo at higher energy levels.

Durability of Probes for Interstitial Laser Coagulation: Impact of Power Setting and Probe Design

BACKGROUND AND PURPOSE

Interstitial laser coagulation (ILC) is a well-established treatment option for patients suffering from benign prostatic hyperplasia (BPH). The vulnerability of the current fibers adds to the high cost of the procedure. The objective was to study the impact of different time-power modes and novel probe designs on tissue effects and fiber durability.

MATERIALS AND METHODS

Standardized interstitial laser (Nd:YAG) applications utilizing different fiber types and power settings were performed in vitro on fresh bovine liver in a fluid medium. The resulting effects on tissue coagulation were evaluated. Additionally, the durability of contemporary probes as well as novel designs was examined.

RESULTS

High-intensity application protocols of 1750 J within 60 seconds were significantly (p < 0.001) more effective in coagulating tissue (4.22 cm3) than the 90 seconds (3.68 cm3) and 120 seconds (3.06 cm3) time-power modes but significantly (p < 0.001) decreased the durability of fibers. Prototype probes significantly improved durability (p < 0.001), whereas efficacy remained unchanged (p > 0.5).

CONCLUSIONS

Using a laboratory model, we could demonstrate that high-intensity time-power settings are more effective in creating tissue coagulation in ILC. The resulting deterioration of the probes can be reduced by applying new fiber designs.