Computed Tomography Thermography for Ablation Zone Prediction in Microwave Ablation and Cryoablation: Advantages and Challenges in an Ex Vivo Porcine Liver Model.

PURPOSE: The aim of this study was to investigate the diagnostic accuracy of computed tomography (CT) for the prediction of ablation zones from microwave ablation (MWA) and cryoablation (CA) in an ex vivo porcine liver model. METHODS: Sequential (30 seconds) CT scans were acquired during and after MWA and CA in an ex vivo porcine liver model. We generated 120-kVp equivalent reconstructions of generic dual-energy CT data sets, and comprehensive region-of-interest measurements were statistically correlated with invasive temperature monitoring using Pearson correlation coefficient. Binary logistic regression was performed for prediction of successful ablation. RESULTS: With the use of pooled data from 6 lesions in 2 separate experiments, correlation analysis of attenuation in Hounsfield units (HU) and temperature yielded r = -0.79 [confidence interval (CI), -0.85 to -0.71] for MWA and r = 0.62 (CI, 0.55 to 0.67) for CA.For MWA, there was a linear association between attenuation and temperature up to 75°C; thus, linear regression yielded a slope of -2.00 HU/°C (95% CI, -1.58 to -2.41). For CA, a linear association between attenuation and temperature was observed in the cooling phase with a slope of 2.11 HU/°C (95% CI, 1.79 to 2.58). In MWA treatment, binary logistic regression separated less than 70°C and greater than 70°C with 89.2% accuracy. Within the ice ball, temperatures above and below -20°C were distinguished with 65.3% accuracy. CONCLUSIONS: Our experiments reveal several difficulties in predicting ablation zone temperature from CT attenuation. Microwave ablation leads to gas production in the tissue, which degrades the accuracy of noninvasive temperature measurement, especially at higher temperatures. In CA, CT thermometry is limited by ice ball formation, which leads to homogeneous attenuation, nearly independent of temperature. Further research is needed to define the role of CT thermography in ablation zone monitoring in liver malignancies.

Laser Guidance in C-Arm Cone-Beam CT-Guided Radiofrequency Ablation of Osteoid Osteoma Reduces Fluoroscopy Time.

PURPOSE: To assess whether laser guidance can reduce fluoroscopy and procedure time of cone-beam computed tomography (CBCT)-guided radiofrequency (RF) ablations of osteoid osteoma compared to freehand CBCT guidance. MATERIALS AND METHODS: 32 RF ablations were retrospectively analyzed, 17 laser-guided and 15 procedures using the freehand technique. Subgroup selection of 18 ablations in the hip-pelvic region with a similar degree of difficulty was used for a direct comparison. Data are presented as median (ranges). RESULTS: Comparison of all 32 ablations resulted in fluoroscopy times of 365 s (193-878 s) for freehand and 186 s (75-587 s) for laser-guided procedures (p = 0.004). Corresponding procedure times were 56 min (35-97 min) and 52 min (30-85 min) (p = 0.355). The subgroup showed comparable target sizes, needle path lengths, and number of scans between groups. Fluoroscopy times were lower for laser-guided procedures, 215 s (75-413 s), compared to 384 s (193-878 s) for freehand (p = 0.012). Procedure times were comparable between groups, 51 min (30-72 min) for laser guidance and 58 min (35-79 min) for freehand (p = 0.172). CONCLUSION: Adding laser guidance to CBCT-guided osteoid osteoma RF ablations significantly reduced fluoroscopy time without increasing procedure time. LEVEL OF EVIDENCE: Level 4, case series.

The Use of Laser Guidance Reduces Fluoroscopy Time for C-Arm Cone-Beam Computed Tomography-Guided Biopsies.

PURPOSE: When using laser guidance for cone-beam computed tomography (CBCT)-guided needle interventions, planned needle paths are visualized to the operator without the need to switch between entry- and progress-view during needle placement. The current study assesses the effect of laser guidance during CBCT-guided biopsies on fluoroscopy and procedure times. MATERIALS AND METHODS: Prospective data from 15 CBCT-guided biopsies of 8-65 mm thoracic and abdominal lesions assisted by a ceiling-mounted laser guidance technique were compared to retrospective data of 36 performed CBCT-guided biopsies of lesions >20 mm using the freehand technique. Fluoroscopy time, procedure time, and number of CBCT-scans were recorded. All data are presented as median (ranges). RESULTS: For biopsies using the freehand technique, more fluoroscopy time was necessary to guide the needle onto the target, 165 s (83-333 s) compared to 87 s (44-190 s) for laser guidance (p < 0.001). Procedure times were shorter for freehand-guided biopsies, 24 min versus 30 min for laser guidance (p < 0.001). CONCLUSION: The use of laser guidance during CBCT-guided biopsies significantly reduces fluoroscopy time.

Assessment of needle guidance devices for their potential to reduce fluoroscopy time and operator hand dose during C-arm cone-beam computed tomography-guided needle interventions.

PURPOSE: To assess whether the use of needle guidance devices can reduce fluoroscopy time and operator hand dose during cone-beam computed tomography-guided needle interventions. MATERIALS AND METHODS: The freehand technique was compared with techniques employing two distinct needle holders and a ceiling-mounted laser guidance technique. Laser guidance was used either alone or in combination with needle holders. Four interventional radiologists were instructed to reach predetermined targets in an abdominal phantom using these techniques. Each operator used all six techniques three times. Fluoroscopy time, procedure time, operator hand dose, and needle tip deviation were obtained for all simulated needle interventions. All data are presented as median (ranges). RESULTS: All procedures were successfully completed within 2-4 minutes, resulting in a deviation from target of 0.8 mm (0-4.7). In freehand procedures, the fluoroscopy time to reach the target was 50 seconds (31-98 s). Laser guidance, used alone or in combination with needle holders, reduced fluoroscopy time to 31 seconds (14-68 s) (P<.02). The operator hand dose in freehand procedures was 275 µSv (20-603 µSv). Laser guidance alone or in combination with needle holders resulted in a reduction of the hand dose to<36 µSv (5-82 µSv) per procedure (P<.001). There were no statistically significant effects on hand dose levels or fluoroscopy time when the needle holders were employed alone. CONCLUSIONS: Compared with the freehand technique, all three tested needle guidance devices performed with equivalent efficiency in terms of accuracy and procedure time. Only the addition of laser guidance was found to reduce both fluoroscopy time and operator hand dose.