Assessment of automated cone-beam CT vessel identification software during transarterial hepatic embolisation: radiation dose, contrast medium volume, processing time, and operator perspectives compared to digital subtraction angiography.

AIM: To evaluate arterial cone-beam computed tomography (A-CBCT) automated analysis software for identification of vessels supplying tumours during transarterial hepatic embolisation (TAE). MATERIALS AND METHODS: This study was approved by the institutional review board, with waiver of consent. Consecutive TAE procedures using arterial mapping software (AMS), and performed between February 2014 and August 2014, were reviewed. Hepatic arteries were imaged using digital subtraction angiography (DSA) as well as A-CBCT processed with AMS. Interventional radiologists reported1 potential embolisation target vessels computed using AMS versus DSA alone,2 modification of the embolisation plan based on AMS, and3 operator confidence related to technical success. Imaging set-up, processing time, radiation dose, and contrast media volume were recorded. RESULTS: Thirty of 34 consecutive procedures were evaluated retrospectively. At least one additional embolisation target vessel was identified using AMS in 13 procedures (43%, 95% confidence interval [CI]: 26-61%) and embolisation plan modified in 11 (37%, 95% CI: 19-54%). Radiologists reported AMS increased operator confidence and reduced the number of DSA acquisitions in 25 (83%, 95% CI: 70-97%) and 15 cases (50%, 95% CI: 32-68%), respectively. The average A-CBCT acquisition and processing time was 4 minutes 53 seconds and 3 minutes 45 seconds, respectively. A-CBCT contributed to 11% of the radiation dose and 18% of the contrast media volume. CONCLUSION: Physicians report increased tumour supplying vessel detection and intraprocedural confidence using AMS during TAE without substantial impact on radiation dose, contrast media volume, and procedure time.

Transfusion of recently donated (fresh) red blood cells (RBCs) does not improve survival in comparison with current practice, while safety of the oldest stored units is yet to be established: a meta-analysis.

BACKGROUND AND OBJECTIVES: Preclinical studies generated the hypothesis that older stored red blood cells (RBCs) can increase transfusion risks. To examine the most updated and complete clinical evidence and compare results between two trial designs, we assessed both observational studies and randomized controlled trials (RCTs) studying the effect of RBC storage age on mortality. MATERIALS AND METHODS: Five databases were searched through December 2014 for studies comparing mortality using transfused RBCs having longer and shorter storage times. RESULTS: Analysis of six RCTs found no significant differences in survival comparing current practice (average storage age of 2 to 3 weeks) to transfusion of 1- to 10-day-old RBCs (OR 0·91, 95% CI 0·77-1·07). RBC storage age was lower in RCTs vs. observational studies (P = 0·01). The 31 observational studies found an increased risk of death (OR 1·13, 95% CI 1·03-1·24) (P = 0·01) with increasing age of RBCs, a different mortality effect than RCTs (P = 0·02). CONCLUSION: RCTs established that transfusion of 1- to 10-day-old stored RBCs is not superior to current practice. The apparent discrepancy in mortality between analyses of RCTs and observational studies may in part relate to differences in hypotheses tested and ages of stored RBCs studied. Further trials investigating 1- to 10-day-old stored RBC benefits would seem of lower priority than studies to determine whether 4- to 6-week stored units have safety and efficacy equivalent to the 2- to 3-week-old stored RBCs commonly transfused today.

Performance of intra-procedural 18-fluorodeoxyglucose PET/CT-guided biopsies for lesions suspected of malignancy but poorly visualized with other modalities.

PURPOSE: We sought to evaluate the safety and the diagnostic success rate of percutaneous biopsies performed under intra-procedural (18)F-deoxyglucose (FDG) positron-emission tomography/computed tomography (PET/CT) guidance for lesions difficult to see with conventional cross-sectional imaging. METHODS: From 2011 to 2013, consecutive clinically indicated percutaneous PET/CT-guided biopsies of 106 masses (mean size, 3.3 cm; range, 0.7-15.9 cm; SD, 2.9 cm) in bones (n = 33), liver (n = 26), soft tissues (n = 18), lung (n = 15) and abdomen (n = 14) were reviewed. The biopsy procedures were performed following injection of a mean of 255 MBq (SD, 74) FDG. Mean maximal standardized uptake value (SUV) of lesions was 8.8 (SD, 6.3). A systematic review of the histopathological results and outcomes was performed. RESULTS: Biopsies were positive for malignancy in 76 cases (71.7%, 76/106) and for benign tissue in 30 cases (28.3%, 30/106). Immediate results were considered adequate for 100 PET/CT biopsies (94.3%, 100/106) requiring no further exploration, and for the six others (5.7%, 6/106) benign diagnoses were confirmed after surgery (n = 4) or follow-up (n = 2). The consequent overall sensitivity and the diagnostic success of biopsy were therefore 100%. No significant differences in terms of detection of malignancy were observed between the different locations. Lesions > 2 cm or with SUV > 4 were not significantly more likely to be malignant. Complications occurred after four biopsies (3.7%, 4/106). CONCLUSION: Intra-procedural PET/CT guidance appears as a safe and effective method and allows high diagnostic success of percutaneous biopsies for metabolically active lesions.

KRAS mutation effects on the 2-[18F]FDG PET uptake of colorectal adenocarcinoma metastases in the liver.

BACKGROUND: Deriving individual tumor genomic characteristics from patient imaging analysis is desirable. We explore the predictive value of 2-[18F]FDG uptake with regard to the KRAS mutational status of colorectal adenocarcinoma liver metastases (CLM). METHODS: 2-[18F]FDG PET/CT images, surgical pathology and molecular diagnostic reports of 37 patients who underwent PET/CT-guided biopsy of CLM were reviewed under an IRB-approved retrospective research protocol. Sixty CLM in 39 interventional PET scans of the 37 patients were segmented using two different auto-segmentation tools implemented in different commercially available software packages. PET standard uptake values (SUV) were corrected for: (1) partial volume effect (PVE) using cold wall-corrected contrast recovery coefficients derived from phantom spheres with variable diameter and (2) variability of arterial tracer supply and variability of uptake time after injection until start of PET scan derived from the tumor-to-blood standard uptake ratio (SUR) approach. The correlations between the KRAS mutational status and the mean, peak and maximum SUV were investigated using Student's t test, Wilcoxon rank sum test with continuity correction, logistic regression and receiver operation characteristic (ROC) analysis. These correlation analyses were also performed for the ratios of the mean, peak and maximum tumor uptake to the mean blood activity concentration at the time of scan: SURMEAN, SURPEAK and SURMAX, respectively. RESULTS: Fifteen patients harbored KRAS missense mutations (KRAS+), while another 3 harbored KRAS gene amplification. For 31 lesions, the mutational status was derived from the PET/CT-guided biopsy. The Student's t test p values for separating KRAS mutant cases decreased after applying PVE correction to all uptake metrics of each lesion and when applying correction for uptake time variability to the SUR metrics. The observed correlations were strongest when both corrections were applied to SURMAX and when the patients harboring gene amplification were grouped with the wild type: p ≤ 0.001; ROC area under the curve = 0.77 and 0.75 for the two different segmentations, respectively, with a mean specificity of 0.69 and sensitivity of 0.85. CONCLUSION: The correlations observed after applying the described corrections show potential for assigning probabilities for the KRAS missense mutation status in CLM using 2-[18F]FDG PET images.

REASSESSMENT OF INHALATION DOSES TO WORKERS IN AUSTRALIAN SHOW CAVES.

Exposure to radon in show caves is an existing exposure situation. A survey of radon levels in underground show caves around Australia, carried out in 1994, found that most of the show caves located in South-Eastern Australia had yearly average radon levels exceeding the Australian radon reference level of 1000 Bq m-3. At the time of the original survey, the radiation doses from exposure to radon progeny of the tour guides in these caves were estimated using the epidemiologically based dose conversion factors and all dose were assessed to be less than 10 mSv per year. In February 2018, the International Commission for Radiological Protection (ICRP) published updated radon and radon progeny dose conversion factors (DCF) applicable to worker exposure to radon in show caves. These updated DCF values are based on dosimetric modelling and are sensitive to the radon progeny activity size distribution. The recommended DCF values are up to a factor four times higher than the previous ICRP recommendations. The ICRP has published data that allows for the estimation of site-specific radon progeny dose coefficients if required. A reassessment of the radiation doses to workers in Australian show caves has been made using these updated ICRP DCF values and the historical measurements of radon progeny activity size distributions in Australian show caves. Using the site-specific DCF values, it is estimated that 15% of the workers exceeded 10 mSv y-1 and 6% exceeded 20 mSv y-1. Although the total number of show cave workers in Australia is very small, the updated radon progeny dose estimates are a significant radiation protection issue for the affected individuals and their employers.

Temporal evaluation of the microwave ablation zone and comparison of CT and gross sizes during the first month post-ablation in swine lung.

PURPOSE: The purpose of this study was to investigate the development and evolution of the microwave ablation (MWA) lesion in the normal lung by using a swine model at various time points and to compare post-procedural computed tomography (CT) and gross pathologic findings during the first month post-ablation. MATERIALS AND METHODS: Twenty-seven percutaneous MWA procedures were performed on swine lungs at 100W for either 2min (low dose, 18 ablations) or 10min (high dose, 9 ablations). Animals were sacrificed at either 2 days (n=5) or 28 days (n=5) after ablation. All animals underwent CT imaging immediate post-treatment and prior to sacrifice, with additional imaging at 7 and 14 days for the 28-day cohort. After euthanasia, lungs and trachea were removed en bloc and underwent gross pathology analysis. RESULTS: In both dose treatment groups, CT measurements of the ablation zone were maximum at Day 7 (low dose: 7.50±3.08 cm3; high dose: 24.87±11.34 cm3) and significantly larger compared to the immediate post-ablation measurements (low dose: 2.54±1.81 cm3; P=0.00011; high dose: 9.14±3.42 cm3; P=0.00374). No significant differences in dimensions were observed between CT and gross pathologic images for both high and low dose ablations in both cohorts. CONCLUSION: The treatment zone following MWA in the lung can vary in the sub-acute setting, achieving largest size at 7 days post-treatment. Furthermore, measurements from CT closely matched with gross pathologic ablation size.

Hepatic Arterial Embolization Using Cone Beam CT with Tumor Feeding Vessel Detection Software: Impact on Hepatocellular Carcinoma Response.

PURPOSE: Dedicated tumor feeding vessel detection software (TFVDS) using cone beam CT has shown a higher sensitivity to detect tumor feeding vessels during hepatic arterial embolization (HAE) of hepatocellular carcinoma (HCC) compared to 2D imaging. Our primary hypothesis was that HCC tumors treated with HAE guided by a TFVDS would show more complete response (CR) than when treated with 2D imaging alone. Secondary analysis of the impact on X-ray exposure was performed. MATERIALS AND METHODS: Nineteen males and 8 females (median age: 69 year, 46-85) with 44 tumors (median size: 38 mm, 6-100) treated with selective HAE between January 2013 and December 2014 were included. Exclusion criteria were: extra-hepatic supply, >4 tumors, tumor size >10 cm, and adjunctive local therapy. Baseline patient and procedure characteristics were reviewed. Differences in CR per modified Response Evaluation Criteria in Solid Tumors were assessed by univariate and multivariate analyses for tumor size, number, location, particles size, and use of TFVDS. RESULTS: Median imaging follow-up was 20.1 months (2-33). Use of TFVDS (13 patients, 19 tumors) was the only factor predictive of CR (OR = 3.85 [CI95%: 1.09, 13.67], p = 0.04) on univariate analysis but not on multivariate analysis (OR = 3.26 [0.87, 12.23], p = 0.08). A higher rate of CR was observed for HAE using TFVDS guidance versus 2D imaging alone (68.4%, 13-19, vs. 36%, 9-25, p = 0.03). Median dose area product was lower when TFVDS was used (149.7 Gy.cm2, 38-365, vs. 227.8 Gy.cm2, 85.3-468.6, p = 0.05). CONCLUSIONS: HCC embolized with TFVDS may result in improved local tumor response without increasing the dose exposure.

Microwave Ablation in the Management of Colorectal Cancer Pulmonary Metastases.

PURPOSE: To review outcomes following microwave ablation (MWA) of colorectal cancer pulmonary metastases and assess predictors of oncologic outcomes. METHODS: Technical success, primary and secondary technique efficacy rates were evaluated for 50 patients with 90 colorectal cancer pulmonary metastases at immediate, 4-8 weeks post-MWA and subsequent follow-up CT and/or 18F-FDG PET/CT. Local tumor progression (LTP) rate, LTP-free survival (LTPFS), cancer-specific and overall survivals were assessed. Complications were recorded according to SIR classification. RESULTS: Median follow-up was 25.6 months. Median tumor size was 1 cm (0.3-3.2 cm). Technical success, primary and secondary technique efficacy rates were 99, 90 and 92%, respectively. LTP rate was 10%. One-, 2- and 3-year LTPFS were: 93, 86 and 86%, respectively, with median LTPFS not reached. Median overall survival was 58.6 months, and median cancer-specific survival (CSS) was not reached. One-, 2- and 3-year overall and CSS were 94% and 98, 82 and 90%, 61 and 70%, respectively. On univariate analysis, minimal ablation margin (p < 0.001) and tumor size (p = 0.001) predicted LTPFS, with no LTP for minimal margin ≥ 5 mm and/or tumor size < 1 cm. Pleural-based metastases were associated with increased LTP risk (p = 0.002, SHR = 7.7). Pre-MWA CEA level > 10 ng/ml (p = 0.046) and ≥ 3 prior chemotherapy lines predicted decreased CSS (p = 0.02). There was no 90-day death. Major complications rate was 13%. CONCLUSIONS: MWA with minimal ablation margin ≥ 5 mm is essential for local control of colorectal cancer pulmonary metastases. Pleural-based metastases and larger tumor size were associated with higher risk of LTP. CEA level and pre-MWA chemotherapy impacted CSS.

Irreversible electroporation and thermal ablation of tumors in the liver, lung, kidney and bone: What are the differences?

Focal treatment with radiofrequency, microwave and cryoablation has been increasingly used for the treatment of tumors in patients who cannot undergo surgical resection and in select patients with early stage or oligometastatic disease. Each of these ablation modalities has a unique working principle and biophysics underlying the ablative effect, which largely determines the clinical indication for its application. Irreversible electroporation, a relatively new ablation technique with a predominantly nonthermal cell killing mechanism has emerged as an alternative treatment technique for tumors that are contraindicated for thermal ablation because of safety or efficacy considerations. Here, established thermal ablation techniques are compared with irreversible electroporation for treatment of tumors in the lung, liver, kidney and bone, and rationale is provided to guide selection of the most appropriate technique for each clinical setting.

Left atrial relaxation and left ventricular systolic function determine left atrial reservoir function.

BACKGROUND: Determinants of left atrial (LA) reservoir function and its influence on left ventricular (LV) function have not been quantified. METHODS AND RESULTS: In an open-pericardium, paced (70 and 90 bpm) pig model of LV regional ischemia (left anterior descending coronary constriction), with high-fidelity LV, LA, and RV pressure recordings, we obtained the LA area with 2D automated border detection echocardiography, LA pressure-area loops, and Doppler transmitral flow. We calculated LV tau, LA relaxation (a-x pressure difference divided by time, normalized by a pressure), and stiffness (slope between x and v pressure points of v loop). Determinants of total LA reservoir (maximum-minimum area, cm(2)) were identified by multiple regression analysis. Different mean rates of LA area increase identified 2 consecutive (early rapid and late slow) reservoir phases. During ischemia, LV long-axis shortening (LAS, LV base systolic descent) and LA reservoir area change decreased (7.3+/-0.3 [SEM] versus 5.6+/-0.3 cm(2), P<0.001) and LA stiffness increased (1.6+/-0.3 versus 3.1+/-0.3 mm Hg/cm(2), P=0.009). Early reservoir area change depended on LA mean ejection rate (LA area at ECG P wave minus minimum area divided by time; multiple regression coefficient=0.9; P<0.001) and relaxation (coefficient=4.9 cm(2)xms/s; P<0.001). Late reservoir area change depended on LAS (coefficient=8 cm/s; P<0.001). Total reservoir filling depended on LA stiffness (coefficient=-0.31 cm(4)/mm Hg; P=0. 001) and cardiac output (coefficient=0.001 cm(2)xmin/L; P=0.002). The strongest predictor of cardiac output was LA reservoir filling (coefficient=301 L/minxcm(2); P<0.001). The v loop area was determined by cardiac output, LV ejection time, tau, and early transmitral flow. CONCLUSIONS: Two (early and late) reservoir phases are determined by LA contraction and relaxation and LV base descent. Acute LV regional ischemia increases LA stiffness and impairs LA reservoir function by reducing LV base descent.

Changes in porcine transmitral flow velocity pattern and its diastolic determinants during partial coronary occlusion.

OBJECTIVES: To define the mechanical determinants of transmitral flow and the effect of heart rate during regional ischemia. BACKGROUND: Myocardial ischemia changes the transmitral flow velocity pattern due to disease-induced changes in the heart's diastolic properties. METHODS: Regional ischemia was produced in 12 pigs by partially occluding the left anterior descending coronary artery until segment-length shortening in the ischemic region fell by 20%. Transmitral flow velocity patterns and their determinants were measured under two conditions, baseline and ischemia, at two heart rates, 70 and 90 beats/min. RESULTS: Regional ischemia had a significant effect on two determinants of filling: relaxation, which was slower, and chamber stiffness, which increased. These changes were associated with reduced contractility and increased myocardial stiffness, resulting in an early transmitral flow pattern that was flatter and narrower, but no change in the late flow pattern. Moderate increases in heart rate accelerated relaxation and decreased atrioventricular pressure gradient but had no effect on contractility or myocardial or chamber stiffness, resulting in an early transmitral flow pattern that was flatter and narrower and an increased late flow velocity. CONCLUSIONS: This model of regional ischemia leads to a flatter and narrower early transmitral flow velocity pattern and no change in late flow due to a combination of slowed left ventricular relaxation and increased chamber stiffness. Reflex increases in heart rate that accompany ischemia tend to mask this effect.

Comparison of CT Fluoroscopy-Guided Manual and CT-Guided Robotic Positioning System for In Vivo Needle Placements in Swine Liver.

PURPOSE: To compare CT fluoroscopy-guided manual and CT-guided robotic positioning system (RPS)-assisted needle placement by experienced IR physicians to targets in swine liver. MATERIALS AND METHODS: Manual and RPS-assisted needle placement was performed by six experienced IR physicians to four 5 mm fiducial seeds placed in swine liver (n = 6). Placement performance was assessed for placement accuracy, procedure time, number of confirmatory scans, needle manipulations, and procedure radiation dose. Intra-modality difference in performance for each physician was assessed using paired t test. Inter-physician performance variation for each modality was analyzed using Kruskal-Wallis test. RESULTS: Paired comparison of manual and RPS-assisted placements to a target by the same physician indicated accuracy outcomes was not statistically different (manual: 4.53 mm; RPS: 4.66 mm; p = 0.41), but manual placement resulted in higher total radiation dose (manual: 1075.77 mGy/cm; RPS: 636.4 mGy/cm; p = 0.03), required more confirmation scans (manual: 6.6; RPS: 1.6; p < 0.0001) and needle manipulations (manual: 4.6; RPS: 0.4; p < 0.0001). Procedure time for RPS was longer than manual placement (manual: 6.12 min; RPS: 9.7 min; p = 0.0003). Comparison of inter-physician performance during manual placement indicated significant differences in the time taken to complete placements (p = 0.008) and number of repositions (p = 0.04) but not in other study measures (p > 0.05). Comparison of inter-physician performance during RPS-assisted placement suggested statistically significant differences in procedure time (p = 0.02) and not in other study measures (p > 0.05). CONCLUSIONS: CT-guided RPS-assisted needle placement reduced radiation dose, number of confirmatory scans, and needle manipulations when compared to manual needle placement by experienced IR physicians, with equivalent accuracy.

Three-dimensional CT-guided bronchoscopy with a real-time electromagnetic position sensor: a comparison of two image registration methods.

STUDY OBJECTIVES: To compare two different image registration methods for accurately displaying the position of a flexible bronchoscope on a previously acquired three-dimensional CT scan during bronchoscopy. SETTING: Bronchoscopy suite of a university hospital. PATIENTS: Fifteen adult patients scheduled for nonemergent bronchoscopy. METHODS: A miniature electromagnetic position sensor was placed at the tip of a flexible bronchoscope. Previously acquired three-dimensional CT scans were registered with the patient in the bronchoscopy suite. Registration method 1 used multiple skin fiducial markers. Registration method 2 used the inner surface of the trachea itself for registration. Method 1 was objectively assessed by measuring the error distance between the real skin marker position and the computer display position. Methods 1 and 2 were subjectively assessed by the bronchoscopist correlating visual bronchoscopic anatomic location with the computer display position on the CT image. RESULTS: The error distance (+/- SD) from known points for registration method 1 was 5.6 +/- 2.7 mm. Objective error distances were not measured for method 2 because no accurate placement of the bronchoscope sensor could be correlated with CT position. Subjectively, method 2 was judged more accurate than method 1 when compared with the fiberoptic view of the airways through the bronchoscope. Additionally, method 2 had the advantage of not requiring placement of fiducial markers before the CT scan. Respiratory motion contributed an error of 3.6 +/- 2.6 mm, which was partially compensated for by a second tracking sensor placed on the patient's chest. CONCLUSION: Image registration method 2 of surface fitting the trachea rather than method 1 of fiducial markers was subjectively judged to be superior for registering the position of a flexible bronchoscope during bronchoscopy. Method 2 was also more practical inasmuch as no special CT scanning technique was required before bronchoscopy.

Real-time bronchoscope tip localization enables three-dimensional CT image guidance for transbronchial needle aspiration in swine.

STUDY OBJECTIVE: To determine the feasibility of using real-time bronchoscope position technology coupled with previously acquired three-dimensional CT data to enhance transbronchial needle aspiration (TBNA). DESIGN: Eight swine were given percutaneously created target lesions for TBNA. A miniature position sensor was placed at the tip of a bronchoscope, and real-time position information during bronchoscopy was presented on a monitor simultaneously displaying previously acquired three-dimensional CT data. INTERVENTIONS: TBNA of target lesions and submucosal ink-spot injection of computer-generated targets. MEASUREMENTS AND RESULTS: TBNA specimens revealed successful aspiration of target material. Distances between ink marks made at computer-generated tracheal targets varied, on average (+/- SD), 4.2 mm +/- 2.6 mm from predetermined computer-distance coordinates. CONCLUSION: Real-time bronchoscope position technology coupled with previously acquired CT images may aid with TBNA of nonvisible extrabronchial lesions.

Focal hepatic ablation using interstitial photon radiation energy.

BACKGROUND: Intratumoral ablative therapy is being used increasingly for the treatment of primary and secondary hepatic malignancies. The interstitial point-source photon radiosurgery system (PRS) is a novel ablative technique that uses radiation therapy similar in dosimetry to interstitial brachytherapy. STUDY DESIGN: To determine the feasibility, toxicity, and local tissue destructive capabilities of the PRS in the liver, preliminary studies in a nontumor-bearing canine model were examined. A 6-month survival study was conducted. Each animal received three radiation treatments, in the right, central, and left hepatic regions. Three low-dose treatments were delivered to each of six animals (group A), generating a 2.0-cm-diameter radiated sphere with a dose of 20 Gy at the lesion edge. Three high-dose treatments were delivered to each of six animals (group B), generating a 3.0-cm-diameter radiated sphere with 20 Gy at the lesion edge. RESULTS: The treatment reproducibly generated sharply demarcated hepatic ablative lesions proportional to the administered dose. Mean lesion diameter at 1 month was 1.6+/-0.2 cm in group A and 3.4+/-1.0 cm in group B. Lesion size was independent of intrahepatic location, including near vascular structures. PRS therapy, when applied to portal structures, resulted in hilar damage. Hilar damage appeared to be associated with arteriolar thrombosis and bile duct injury. Treatment of regions adjacent to large hepatic veins and the IVC was not associated with vessel thrombosis or stricture. CONCLUSIONS: PRS ablation is a generally well-tolerated method that results in consistent, well-demarcated, symmetric lesions of complete necrosis with minimal adjacent parenchymal injury. Application of such an approach for the treatment of liver tumors is promising.

Noninvasive vasectomy using a focused ultrasound clip: thermal measurements and simulations.

INTRODUCTION: Conventional surgical vasectomy may lead to complications including bleeding, infection, and scrotal pain. Noninvasive transcutaneous delivery of therapeutic focused ultrasound has previously been shown to thermally occlude the vas deferens. However, skin burns and inconsistent vas occlusion have presented complications. This study uses bio-heat transfer simulations and thermocouple measurements to determine the optimal ablation dosimetry for vas occlusion without skin burns. METHODS: A 2-rad ultrasound transducer mounted on a vasectomy-clip-delivered ultrasound energy at 4 MHz to the canine vas deferens co-located at the focus between the clip jaws. Chilled degassed water was circulated through an attached latex balloon, providing efficient ultrasound coupling into the tissue and active skin cooling to prevent skin burns. Thermocouples placed at the vas, intradermal, and skin surface locations recorded temperatures during ablation. Procedures were performed with transducer acoustic powers of 3-7 W and sonication times of 60-120 s on both the left and right vas deferens (n = 2) in a total of four dogs (precooling control, 3 W/120 s, 5 W/90 s, 7 W/60 s). Measurements were compared with bio-heat transfer simulations modeling the effects of variations in power and sonication time on tissue temperatures and coagulation zones. RESULTS: Active skin cooling produces a thermal gradient in the tissue during ablation, allowing sufficient thermal doses to be delivered to the vas without skin burns. However, low-power, long-duration heating produced excessive tissue necrosis due to thermal diffusion, while high power and short heating times reduced the therapeutic window and produced skin burns presumably due to direct ultrasound absorption. CONCLUSIONS: Both simulations and experiments suggest that a therapeutic window exists in which thermal occlusion of the vas may be achieved without the formation of skin burns in the canine model (power = 5-7 W, surface intensity = 1.4-1.9 W/cm2, time = 20-50 s). This range of ablation parameters will help guide future experiments to refine incisionless vasectomy using focused ultrasound.

Interactive images in the operating room.

Fluoroscopy has made endourology possible, but its two dimensionality and poor tissue contrast limit its applications. Recent advances in computer technology are making it possible for surgeons to interact with three-dimensional CT and MR images. Initial interactive navigation systems tracked the position of surgical instruments on previously acquired images using optical, ultrasonic, or electromagnetic devices. More recently, real-time imaging and instrument tracking have become possible, such as with the open interventional MR scanners. The problems created by patient motion and tissue deformation during manipulation may thereby be overcome.

Field tests of a radon progeny sampler for the determination of effective dose.

A two-screen sampler (an effective dosimeter), with a collection efficiency matched to the particle size response of the radon progeny dose conversion factors (DCF), obtained from the ICRP respiratory tract model as implemented in the computer code RADEP, has been developed to assess the inhalation dose from exposure to radon progeny. In order to evaluate the performance of this sampler, the second stage of a six-stage wire screen diffusion battery was designed to operate as an Effective Dosimeter. This hybrid system allowed two methods for the determination of the radon progeny DCF. For the first method, the activity size distributions, measured using the diffusion battery, were used to obtain a size-weighted DCF. A second determination of DCF was obtained directly from the fraction collected by the Effective Dosimeter. The hybrid diffusion battery was used to measure radon progeny in the Fairy Cave, Buchan, Victoria at 20-min intervals over a 30-h period. This cave had radon concentrations exceeding 2000 Bq m(-3), with low aerosol concentration and low ventilation rates. The measurements were analysed for the radon progeny PAEC, the activity size distribution, the size-weighted DCF and the effective dosimeter collected fraction. The Effective Dosimeter DCFs were determined from the collected fraction using firstly a simple linear function and then using a more complex polynomial function to correct for residual errors. For the linear factor alone, the calculated Effective Dosimeter DCFs were on average 11% lower than the equivalent size-weighted DCF values. The agreement using the polynomial function was improved markedly, with a linear regression of the DCF yielding a fitted ratio of 0.965, with an R value of 0.99. For this study, the use of the ICRP conversion convention to estimate the occupational exposure to the tour guides working in the Fairy Cave would under estimate the effective dose by up to a factor of 2.

Standardization of Rn-222 at the Australian Radiation Laboratory.

The standardization of Rn-222 at the Australian Radiation Laboratory involves the calibration of scintillation cells by two methods using standard Ra-226 solutions traceable to the National Institute of Standards and Technology. One of these methods, namely the injection method, involves direct transfer of Rn-222 into a scintillation cell. In the other method, known as the volumetric method, the Rn-222 is flushed into a large container and the scintillation cell calibrated by sampling from this container. A comparison of the two methods showed that similar results were obtained, with the overall random uncertainty being 3.4% for one standard deviation. Using better estimates of the true calibration factors, the overall random uncertainty was reduced to 1.8% for one standard deviation.