Sensitivity of microwave ablation models to tissue biophysical properties: A first step toward probabilistic modeling and treatment planning.

PURPOSE: Computational models of microwave ablation (MWA) are widely used during the design optimization of novel devices and are under consideration for patient-specific treatment planning. The objective of this study was to assess the sensitivity of computational models of MWA to tissue biophysical properties. METHODS: The Morris method was employed to assess the global sensitivity of the coupled electromagnetic-thermal model, which was implemented with the finite element method (FEM). The FEM model incorporated temperature dependencies of tissue physical properties. The variability of the model was studied using six different outputs to characterize the size and shape of the ablation zone, as well as impedance matching of the ablation antenna. Furthermore, the sensitivity results were statistically analyzed and absolute influence of each input parameter was quantified. A framework for systematically incorporating model uncertainties for treatment planning was suggested. RESULTS: A total of 1221 simulations, incorporating 111 randomly sampled starting points, were performed. Tissue dielectric parameters, specifically relative permittivity, effective conductivity, and the threshold temperature at which they transitioned to lower values (i.e., signifying desiccation), were identified as the most influential parameters for the shape of the ablation zone and antenna impedance matching. Of the thermal parameters considered in this study, the nominal blood perfusion rate and the temperature interval across which the tissue changes phase were identified as the most influential. The latent heat of tissue water vaporization and the volumetric heat capacity of the vaporized tissue were recognized as the least influential parameters. Based on the evaluation of absolute changes, the most important parameter (perfusion) had approximately 40.23 times greater influence on ablation area than the least important parameter (volumetric heat capacity of vaporized tissue). Another significant input parameter (permittivity) had 22.26 times higher influence on the deviation of ablation edge shape from a sphere than one of the less important parameters (latent heat of liver tissue vaporization). CONCLUSIONS: Dielectric parameters, blood perfusion rate, and the temperature interval across which the tissue changes phase were found to have the most significant impact on MWA model outputs. The latent heat of tissue water vaporization and the volumetric heat capacity of the vaporized tissue were recognized as the least influential parameters. Uncertainties in model outputs identified in this study can be incorporated to provide probabilistic maps of expected ablation outcome for patient-specific treatment planning.

Design projects motivated and informed by the needs of severely disabled autistic children.

Technology can positively impact the lives of severely disabled autistic children if used to (a) gather situational awareness data regarding their health, development, and behavior and (b) assist them with learning and day-to-day activities. This paper summarizes student design projects in the Kansas State University (KSU) College of Engineering that are motivated and informed by the needs of severely disabled children at Heartspring, Wichita, KS. These efforts are supported through the National Science Foundation's General and Age-Related Disabilities Engineering (GARDE) program. Projects relate thematically to (1) facets of a bed sensor system that unobtrusively tracks nighttime health parameters and child activity and (2) miscellaneous resources geared toward paraeducator ("para") and child well-being and development.

Bed-based instrumentation for unobtrusive sleep quality assessment in severely disabled autistic children.

The relationship between sleep quality and daytime wellness and performance in severely disabled, autistic children is not well understood. While polysomnography and, more recently, actigraphy serve as means to obtain sleep assessment data from neurotypical children and adults, these techniques are not well-suited to severely autistic children. This paper presents recent progress on a bed sensor suite that can unobtrusively track physiological and behavioral parameters used to assess sleep quality. Electromechanical films and load cells provide data that yield heart rate, respiration rate, center of position, in-and-out-of-bed activity, and general movement, while thermocouples are used to detect bed-wetting events.

Proposed classification of pseudomyxoma peritonei: influence of signet ring cells on survival.

The nomenclature and classification of pseudomyxoma peritonei (PMP) is confusing and controversial. Numerous classification systems have been proposed, none of which are easily reproducible or a useful guide for treatment. Patients with PMP of appendiceal origin were identified from our institution's database. Kaplan-Meier analyses were performed based on a proposed new PMP classification, a three-tiered grading system designated PMP1, PMP2, and PMP3. These results were compared with the established schemes by Ronnett and Bradley et al. There were 211 patients included in the analysis with a mean age of 51 ± 12 years at diagnosis. For PMP1, 86 patients (40.8%) included cases with abundant extracellular mucin and columnar nonstratified epithelium without dysplasia or atypia. For PMP3, 50 patients (23.7%) consisted of PMP with any percentage of signet ring cells (SRCs), For PMP2, 75 patients (35.5%) included all other patients. The mean age (± standard deviation) for PMP 1, 2, and 3 were 51 ± 12, 51 ± 12, and 51 ± 10 years, respectively (P = 0.90). The three groups had similar sex distribution (P = 0.24) and resection status (P = 0.47). Kaplan-Meier analyses showed median survivals of 120, 88, and 40 months and 5-year survival rates of 85.7, 63.05, and 32.2 per cent (P < 0.0001) for PMP 1, 2, and 3, respectively. Three distinct categories, PMP1, 2, and 3, were identified, which provide better stratification in terms of overall survival and represent differences in tumor biology that may impact treatment recommendations.

Predictive factors for mortality after open repair of paravisceral abdominal aortic aneurysm.

OBJECTIVE: The use of fenestrated and branched stent graft technology for paravisceral abdominal aortic aneurysms (PAAA) is on the rise; however, its application is limited in the United States to only a few selected centers. Most PAAAs are currently repaired using an open approach. The objective of this study was to determine which patients are at highest risk with open PAAA repair and might benefit most from endovascular repair using fenestrated or branched stent grafts. METHODS: This was a retrospective cohort study using data from American College of Surgeons National Surgical Quality Improvement Program (NSQIP) hospitals. We identified 598 patients (27.5% women) who underwent elective open PAAA repair from the 2007 to 2009 NSQIP, a prospective database maintained at >250 centers. The main outcome measure was 30-day postoperative mortality. RESULTS: The median patient age was 73 years. The 30-day major morbidity rate was 30.1%, and the mortality rate was 4.5%. Major complications included reintubation (10.0%), sepsis (10.7%), return to operating room (9.2%), new dialysis requirement (5.9%), cardiac arrest or myocardial infarction (4.5%), and stroke (1.2%). Multivariate analyses identified four predictors of postoperative mortality after open PAAA repair: peripheral arterial disease (PAD) requiring revascularization or amputation, chronic obstructive pulmonary disease (COPD), anesthesia time, and female sex. PAD and COPD were present in only 5.2% and 20.4% of patients but were associated with a 16.1% and 9.0% mortality rate, respectively. The mortality rate in women was 7.3% vs 3.5% for men (P = .045). CONCLUSIONS: PAD, COPD, and female sex are major risk factors for postoperative mortality after open PAAA repair. Fenestrated or branched stent graft repair may be a more valuable alternative to open repair for patients with one or more of these characteristics who have suitable access vessels.

Postoperative respiratory failure after thyroid and parathyroid surgery: analysis of national surgical quality improvement program.

BACKGROUND: The risk-benefit analysis of any operation is influenced by its perioperative complications. Our objective was to examine the relationship between preoperative clinical characteristics and postoperative respiratory failure (PRF: mechanical ventilation for >48 hours after surgery or reintubation) within 30 days of thyroid and parathyroid surgeries. METHODS: American College of Surgeons' multicenter, prospective, National Surgical Quality Improvement Program (NSQIP) datasets (2007/2008) were used. Multivariable logistic regression was performed. RESULTS: Eighty-three of 20,778 (0.4%) patients developed PRF. Comparing patients who developed PRF to those who did not, 30-day mortality was seen in 13 of 83 versus 11 of 20,695 patients (p < .0001); and mean length of stay (LOS) was 9.1 (±9.5) days versus 1.1 (±1.6) days (p < .0001). Multivariable analysis demonstrated preoperative pneumonia, dependent functional status, dyspnea, dialysis dependence, hypertension, advanced age, and combined thyroid and parathyroid surgery as risk factors for PRF. CONCLUSION: PRF after thyroid and parathyroid surgeries is uncommon, but associated with significantly increased 30-day morbidity and mortality.

Wireless slips and falls prediction system.

Accidental slips and falls due to decreased strength and stability are a concern for the elderly. A method to detect and ideally predict these falls can reduce their occurrence and allow these individuals to regain a degree of independence. This paper presents the design and assessment of a wireless, wearable device that continuously samples accelerometer and gyroscope data with a goal to detect and predict falls. Lyapunov-based analyses of these time series data indicate that wearer instability can be detected and predicted in real time, implying the ability to predict impending incidents.

Morbidity and mortality after bowel resection for acute mesenteric ischemia.

BACKGROUND: Patients presenting with acute mesenteric ischemia (AMI) sufficiently advanced to require bowel resection have a high morbidity and mortality. The objective of this study was to analyze these patients to determine if certain pre- or intraoperative variables are predictive of death or complications which could then be used to develop a predictive model to aid in surgical decision-making. METHODS: Patients undergoing bowel resection for AMI were identified from the American College of Surgeons' National Surgical Quality Improvement Program database (2007-2008). Multiple logistic regression analysis was performed. RESULTS: The 861 patients identified had a median age of 69 years. Thirty-day postoperative morbidity and mortality were 56.6% and 27.9%, respectively. Pre- and intraoperative variables significantly associated with postoperative mortality (C statistic, 0.84) included preoperative do not resuscitate order, open wound, low albumin, dirty vs clean-contaminated case, and poor functional status. Pre- and intraoperative variables significantly associated with postoperative morbidity (C statistic, 0.79) included admission from chronic care facility, recent myocardial infarction, chronic obstructive pulmonary disease, requiring ventilator support, preoperative renal failure, previous cardiac surgery, and prolonged operative time. A predictive risk calculator was developed using these variables. CONCLUSION: Mortality and morbidity rates after bowel resection for AMI are high. A risk calculator for prediction of postoperative mortality and morbidity has been developed and awaits validation in subsequent studies.

Outcomes after laparoscopic adrenalectomy.

BACKGROUND: Laparoscopic adrenalectomy (LA) has become the standard of care for many conditions requiring removal of the adrenal gland. Previous studies on outcomes after LA have had limitations. This report describes the 30-day morbidity and mortality rates after LA and analyzes factors affecting operative time, hospital length of stay (LOS), and postoperative morbidity. METHODS: Patients undergoing LA in 2007 and 2008 were identified from the American College of Surgeons' National Surgical Quality Improvement Program (NSQIP). Using multivariate analysis of variance (ANOVA) and logistic regression, 52 demographic/comorbidity variables were analyzed to ascertain factors affecting operative time, LOS, and morbidity. RESULTS: The mean age of the 988 patients was 53.5 ± 13.7 years, and 60% of the patients were women. The mean body mass index (BMI) of the patients was 31.8 ± 7.9 kg/m(2). The 30-day morbidity and mortality rates were 6.8% and 0.5%, respectively. The mean and median operative times were 146.7 ± 66.8 min and 134 min, respectively. The mean and median hospital stays were 2.6 ± 3.1 days and 2 days, respectively. Compared with independent status, totally dependent functional status was associated with a 9.5-day increase in LOS (P = 0.0006) and an increased risk for postoperative morbidity (odds ratio [OR], 14.7; 95% confidence interval [CI], 2.4-91.9; P < 0.0001). Peripheral vascular disease (OR, 7.3; 95% CI, 1.7-31.7; P = 0.008) also was associated with increased 30-day morbidity. Neurologic and respiratory comorbidities were associated with increased LOS (P < 0.05). American Society of Anesthesiology (ASA) class 4 patients had a longer operative time than ASA class 1 patients (P = 0.002). CONCLUSIONS: The morbidity and mortality rates after LA are low. Dependent functional status and peripheral vascular disease predispose to postoperative morbidity. Dependent status, higher ASA class, and respiratory and neurologic comorbidities are associated with longer operative time and LOS.

FAST scan: is it worth doing in hemodynamically stable blunt trauma patients?

BACKGROUND: During the last decade, focused assessment with sonography for trauma increasingly has become the initial diagnostic modality of choice in trauma patients. It is still questionable, however, whether its use results in the underdiagnosis of intra-abdominal injury. It also remains doubtful whether a positive focused assessment with sonography for trauma affects clinical decision making in hemodynamically stable blunt trauma patients as evidenced through abdominal computerized tomography use. The aim of this study was to evaluate the results of focused assessment with sonography for trauma in hemodynamically stable blunt trauma patients and to determine its role in the diagnostic evaluation of these patients. METHODS: We reviewed our prospectively maintained trauma database. In trauma patients at our institute, focused assessment with sonography for trauma examinations are performed by surgery residents and are considered positive when free intra-abdominal fluid is visualized. Abdominal computerized tomography, diagnostic peritoneal lavage, or exploratory laparotomy findings were used as confirmation of intra-abdominal injury. RESULTS: In our 7-year study period, 2,980 trauma patients were evaluated at our institute, of which 2,130 patients underwent a focused assessment with sonography for trauma. In all, 18 patients had an inconclusive focused assessment with sonography for trauma, whereas 7 patients died on arrival, leaving 2,105 patients for our analysis. A total 88 true positive focused assessment with sonography for trauma were conducted. All hemodynamically stable blunt trauma patients who had a positive focused assessment with sonography for trauma (70/88) were confirmed by computerized tomography. Patients who underwent exploratory laparotomy directly (17/88) or diagnostic peritoneal lavage (1/88) as confirmation either had penetrating trauma or became hemodynamically unstable. A total of 1,894 true negative focused assessments with sonography for trauma scans were conducted, with 1,201 confirmed by computerized tomography and the rest by observation. In all, 118 false negative focused assessment with sonography for trauma were performed, of which 44 (37.3%) subsequently required exploratory laparotomy. Five patients had false positive focused assessment with sonography for trauma scans. Focused assessment with sonography for trauma scan had an overall sensitivity of 43%, a specificity of 99%, and positive and negative predictive values of 95% and 94%, respectively. Accuracy was 94.1%. In the hemodynamically stable blunt trauma group, there were 60 patients with true positive focused assessment with sonography for trauma examinations and 87 patients with false negative focused assessment with sonography for trauma examinations. In this group of patients, focused assessment with sonography for trauma had a sensitivity of 41%, specificity of 99%, and positive and negative predictive values of 94% and 95%, respectively. The overall accuracy was 95%. CONCLUSION: Given the low sensitivity, a negative focused assessment with sonography for trauma without confirmation by computerized tomography may result in missed intra-abdominal injuries. It is also observed in all focused assessment with sonography for trauma positive hemodynamically stable blunt trauma patients, confirmation is preferred through the use of a computerized tomography for better understanding of the intra-abdominal injuries and to decide on operative versus no-operative management. Thus, the use of focused assessment with sonography for trauma in hemodynamically stable blunt trauma patients seems not worthwhile. It should be reserved for hemodynamically unstable patients with blunt trauma.

Early experience in the application of distal protection devices in treatment of peripheral vascular disease of the lower extremities.

The objectives of this study were to reduce the risk of showering distal vessels with thromboemboli created during percutaneous interventions of the arteries in the lower extremities. Distal protection devices have been used in coronary and carotid interventions. Hence, using similar techniques, these filters and occlusion balloons were advanced past the targeted lesions and distally into femoral and popliteal arteries. Once opened, these devices allowed standard angioplasty and stent placement and captured the dislodged thromboemboli. Five cases were performed with the distal protection devices. One case used the distal occlusion balloon and four with the filter system. All five passed the lesion and were deployed. All five devices were retrieved without incident and were retrieved with substantial debris. There were no adverse events. The use of distal protection to treat high-risk or unstable lesions in the lower extremities shows great promise. Further case will be needed to evaluate the device for feasibility and safety.