Biomedical subjects

Andrew S Wright

Publications and source records attributed to Andrew S Wright.

4 recordsLinked to original sources

PubMed2003

Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size.

Radiofrequency (RF) ablation is a minimally invasive method for treatment of primary and metastatic liver tumors. One of the currently commercially available devices employs an internally cooled 17-gauge needle probe. Within the probe, cool water is circulated during ablation, which cools tissue close to the probe resulting in larger lesions. We evaluated the effect of different cooling water temperatures on lesion size. We created a finite-element method model, simulated 12 min impedance-controlled ablation and determined temperature distribution for three water temperatures. Lesion diameters in the model were 33.8, 33.4, and 32.8 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. We solved a simplified model geometry analytically and present dependence of lesion diameter on cooling temperature. We further performed ex vivo experiments in fresh bovine liver. We created four lesions for each water temperature, with the same water temperatures as used in the finite-element method (FEM) model. Average lesion diameters were 28.3, 30, and 29.5 mm for water temperatures of 5 degrees C, 15 degrees C, and 25 degrees C, respectively. Water temperature did not have a significant effect on lesion size in the ex vivo experiments (p = 0.76), the FEM model, and the analytical solution.

Animals↗

PubMed2003

Hepatic microwave ablation with multiple antennae results in synergistically larger zones of coagulation necrosis.

BACKGROUND: Microwave ablation is a promising treatment for unresectable liver tumors. Unlike radiofrequency ablation, microwave ablation may be performed with multiple simultaneously active antennae. METHODS: Microwave ablation was performed in an in vivo porcine liver model by using a single antenna (n = 11) or three antennae in a triangular array, activated either sequentially (n = 11) or simultaneously (n = 13). Lesions were measured and assigned a qualitative shape score. RESULTS: Single-antenna microwave lesions had a mean volume of 7.4 +/- 3.9 cm(3), compared with 14.6 +/- 5.2 cm(3) and 43.1 +/- 4.3 cm(3) for sequential and simultaneous multiple-probe ablations, respectively (P <.001; analysis of variance). Simultaneous lesions were rounder than sequential ablations and were more effective near blood vessels. Simultaneous lesions created with probe separation of < or =1.7 cm were round and confluent, whereas clefts were present with distances >1.7 cm (P <.001). CONCLUSIONS: Microwave ablation has several theoretical advantages over currently available radiofrequency devices. Simultaneous three-probe microwave ablation lesions were three times larger than sequential lesions and nearly six times greater in volume than single-probe lesions. Additionally, simultaneous multiple-probe ablation results in qualitatively better lesions, with more uniform coagulation and better performance near blood vessels. Simultaneous multiple-probe ablation may decrease inadequate treatment of large tumors and decrease recurrence rates after tumor ablation.

Animals↗

PubMed2003

Minimally invasive approaches in management of hepatic tumors.

Traditionally, the only curative option for patients with liver tumors has been hepatic resection. Unfortunately, only 10%-20% of patients with liver tumors can undergo surgical resection due to limited hepatic reserve, high surgical risk, or unfavorable tumor location. Ablation of liver tumors is currently the main alternative to formal liver resection. Tumor cell death is achieved through a number of technologies, which may be separated into three categories: chemical (percutaneous ethanol injection), cold-based (cryotherapy), and heat-based (radiofrequency and microwave ablation or laser hyperthermia). Although long-term data are limited, ablation may be curative in some patients with a three- and five-year survival rate approaching that of resection. The main factors to success include proper patient selection, excellent diagnostic and procedural imaging, and careful post-procedure management and follow up. Long-term success following tumor ablation will be most dependent on the underlying tumor biology and the ability to achieve a negative margin. Future directions in ablation will include the use of adjunctive agents such as chemotherapeutics, further advances in energy delivery, improved imaging and lesion targeting, and continued refinements of current technology and technique.

Carcinoma, Hepatocellular↗

PubMed2002

Development and initial testing of a multimedia program for computer-assisted cognitive therapy.

A multimedia program for computer-assisted psychotherapy has been developed to help patients learn cognitive therapy skills. The program is designed to provide psychoeducation, teach self-help methods, and give information to clinicians on the patient's progress in using the software. Multimedia technology is utilized to engage users in the learning process and to make the program accessible for persons who do not have computer or keyboard skills. A preliminary study with 96 subjects who used the software along with treatment as usual found that 75 (78.1%) completed the entire program. Users indicated a high rate of acceptance of this form of computer-assisted therapy, and mean scores on a measure of cognitive therapy knowledge were significantly improved.

Adult↗