UltraPulse--simulating a human arterial pulse with focussed airborne ultrasound.

Medical simulators provide a risk-free environment for trainee doctors to practice and improve their skills. UltraPulse is a new tactile system designed to utilise focussed airborne ultrasound to mimic a pulsation effect such as that of a human arterial pulse. In this paper, we focus on the construction of the haptics component, which can later be integrated into a variety of medical procedure training simulators.

A stable and real-time nonlinear elastic approach to simulating guidewire and catheter insertions based on Cosserat rod.

Interventional Radiology procedures (e.g., angioplasty, embolization, stent graft placement) provide minimally invasive therapy to treat a wide range of conditions. These procedures involve the use of flexible tipped guidewires to advance diagnostic or therapeutic catheters into a patient's vascular or visceral anatomy. This paper presents a real-time physically based hybrid modeling approach to simulating guidewire insertions. The long, slender body of the guidewire shaft is simulated using nonlinear elastic Cosserat rods, and the shorter flexible tip composed of a straight, curved, or angled design is modeled using a more efficient generalized bending model. Therefore, the proposed approach efficiently computes intrinsic dynamic behaviors of guidewire interactions within vascular structures. The efficacy of the proposed method is demonstrated using detailed numerical simulations inside 3-D blood vessel structures derived from preprocedural volumetric data. A validation study compares positions of four physical guidewires deployed within a vascular phantom, with the co-ordinates of the corresponding simulated guidewires within a virtual model of the phantom. An optimization algorithm is also implemented to further improve the accuracy of the simulation. The presented simulation model is suitable for interactive virtual reality-based training and for treatment planning.

Virtual reality, ultrasound-guided liver biopsy simulator: development and performance discrimination.

OBJECTIVES: The aim of this article was to identify and prospectively investigate simulated ultrasound-guided targeted liver biopsy performance metrics as differentiators between levels of expertise in interventional radiology. METHODS: Task analysis produced detailed procedural step documentation allowing identification of critical procedure steps and performance metrics for use in a virtual reality ultrasound-guided targeted liver biopsy procedure. Consultant (n=14; male=11, female=3) and trainee (n=26; male=19, female=7) scores on the performance metrics were compared. Ethical approval was granted by the Liverpool Research Ethics Committee (UK). Independent t-tests and analysis of variance (ANOVA) investigated differences between groups. RESULTS: Independent t-tests revealed significant differences between trainees and consultants on three performance metrics: targeting, p=0.018, t=-2.487 (-2.040 to -0.207); probe usage time, p = 0.040, t=2.132 (11.064 to 427.983); mean needle length in beam, p=0.029, t=-2.272 (-0.028 to -0.002). ANOVA reported significant differences across years of experience (0-1, 1-2, 3+ years) on seven performance metrics: no-go area touched, p=0.012; targeting, p=0.025; length of session, p=0.024; probe usage time, p=0.025; total needle distance moved, p=0.038; number of skin contacts, p<0.001; total time in no-go area, p=0.008. More experienced participants consistently received better performance scores on all 19 performance metrics. CONCLUSION: It is possible to measure and monitor performance using simulation, with performance metrics providing feedback on skill level and differentiating levels of expertise. However, a transfer of training study is required.

Off label use of devices and drugs in interventional radiology.

AIM: To establish how often off-label device and drug use occurs in interventional radiology (IR) in a UK tertiary referral hospital and consider the wider implications for the interventional radiologist. MATERIALS AND METHODS: Prospective data were collected during interventional procedures for 1 working week in a university hospital. Out-of-hours procedures and procedures outside the department were excluded. Operators were asked to record the drugs and devices used, the indication, and method of use. The instructions for use/summary of product characteristics were then studied for each device/drug used to assess if the use was on or off-label. RESULTS: During the study period 52 cases were performed and data were available on 26 cases (50%). In 22 of the 26 cases (84%) there was evidence of off-label use of devices or drugs. Off-label use of drugs included treatment of venous malformations with Fibrovein(©) (sodium tetradecyl sulphate), which is licensed for the treatment of varicose veins in the leg, and intra-arterial injection of heparin, which is licensed for intravenous and subcutaneous use. Off-label device use included placing vascular sheaths in the urinary tract, using angiographic catheters to guide wires in the urinary tract, using sheaths for thrombosuction, reshaping of the tip of most guidewires, and using angioplasty balloons to dislodge the arterial plug at fistula thrombectomy. CONCLUSION: Off-label device and drugs use is common in a UK tertiary hospital IR department and literature suggests this is common in the wider IR community. There are important clinical and legal implications for off-label use for patients and physicians.

A prototype percutaneous transhepatic cholangiography training simulator with real-time breathing motion.

PURPOSE: We present here a simulator for interventional radiology focusing on percutaneous transhepatic cholangiography (PTC). This procedure consists of inserting a needle into the biliary tree using fluoroscopy for guidance. METHODS: The requirements of the simulator have been driven by a task analysis. The three main components have been identified: the respiration, the real-time X-ray display (fluoroscopy) and the haptic rendering (sense of touch). The framework for modelling the respiratory motion is based on kinematics laws and on the Chainmail algorithm. The fluoroscopic simulation is performed on the graphic card and makes use of the Beer-Lambert law to compute the X-ray attenuation. Finally, the haptic rendering is integrated to the virtual environment and takes into account the soft-tissue reaction force feedback and maintenance of the initial direction of the needle during the insertion. RESULTS: Five training scenarios have been created using patient-specific data. Each of these provides the user with variable breathing behaviour, fluoroscopic display tuneable to any device parameters and needle force feedback. CONCLUSIONS: A detailed task analysis has been used to design and build the PTC simulator described in this paper. The simulator includes real-time respiratory motion with two independent parameters (rib kinematics and diaphragm action), on-line fluoroscopy implemented on the Graphics Processing Unit and haptic feedback to feel the soft-tissue behaviour of the organs during the needle insertion.

Physics-based virtual environment for training core skills in vascular interventional radiological procedures.

Recent years have seen a significant increase in the use of Interventional Radiology (IR) as an alternative to open surgery. A large number of IR procedures commences with needle puncture of a vessel to insert guidewires and catheters: these clinical skills are acquired by all radiologists during training on patients, associated with some discomfort and occasionally, complications. While some visual skills can be acquired using models such as the ones used in surgery, these have limitations for IR which relies heavily on a sense of touch. Both patients and trainees would benefit from a virtual environment (VE) conveying touch sensation to realistically mimic procedures. The authors are developing a high fidelity VE providing a validated alternative to the traditional apprenticeship model used for teaching the core skills. The current version of the CRaIVE simulator combines home made software, haptic devices and commercial equipments.

Simulators in catheter-based interventional radiology: training or computer games?

Training in interventional radiology (IR) relies on a traditional apprenticeship; to protect patients, expert supervision is mandatory until knowledge, attitudes and practical skills have been certified as satisfactory. However, the current quality of IR training is threatened by reduced time for trainees to learn, as well as a loss of basic diagnostic, training cases to non-invasive imaging. At the same time, IR techniques are becoming a focus of interest to a range of other clinical specialities. To address this training shortfall there is a need to develop novel training alternatives such as simulator models. Few simulator models in any medical field have been successfully validated to show improved clinical skills in treating patients. To date no endovascular simulator has met this standard. A good simulator must be based around key performance measures (metrics) derived from careful analysis of the procedure to be replicated. Metrics can be determined by trained psychologists from a direct analysis of the content of the job or task to be tested. The identification of these critical measures of performance is a complex process which must be tailored to a training curriculum to be effective. Simulators based on flawed metrics will invariably lead to unsatisfactory assessment. It follows that simulator development must involve the statutory licensing authorities. Equally it is essential that we do not assume that training on a particular simulator will correlate with the ability to perform the task in the real world. This "transfer of training" must be rigorously proven by validation studies.

Aortic side branch perfusion alone does not account for high intra-sac pressure after endovascular repair (EVAR) in the absence of graft-related endoleak.

OBJECTIVE: to examine the effect of stent-graft deployment on pressure within an aneurysm sac and to investigate the potential sources of intra-sac pressure. MATERIAL AND METHODS: intra-sac pressure was monitored during and immediately after endovascular repair via an indwelling catheter. Intra-sac pressure was also monitored during conventional open repair and was compared with the pressure measured within patent lumbar and inferior mesenteric side-branches, both before and after restoration of iliac arterial blood flow. Intra-sac and side-branch pressures were recorded and expressed as ratios of simultaneously measured radial artery pressure. RESULTS: in the absence of a graft-related endoleak (23/25 patients), endovascular repair resulted in a significant reduction in intra-sac pulse pressure (median ratio 0.31 IQR 0.10-0.46). There was no corresponding reduction in mean intra-sac pressure (median ratio 0.91; IQR 0.83-1.00). Application of clamps at conventional open repair resulted in a fall in both intra-sac pressure (median ratio 0.39, IQR 0.32-0.64) and pressure within side-branches (median ratio 0.45, IQR 0.33-0.64). Restoration of iliac blood flow resulted in a modest recovery of the side-branch pressure (median ratio 0.63, IQR 0.57-0.81), which nonetheless remained significantly less than the intra-sac pressure recorded after EVAR (p=0.01). CONCLUSION: reperfusion of the aneurysm sac through patent side-branches seems insufficient to account for persistent pressurisation of the aneurysm after endovascular repair. This finding supports the hypothesis that pressure may be transmitted directly through stent-graft fabric.

Perianeurysmal fibrosis: a relative contra-indication to endovascular repair.

OBJECTIVE: Perianeurysmal fibrosis (PAF) with involvement of neighbouring viscera can render open repair of inflammatory aneurysms technically difficult and therefore hazardous. For this reason, endovascular repair (EVAR) has been advocated as the preferred approach for this condition. EVAR is known to induce a systemic inflammatory response in patients but the nature of the local response remains unknown. If significant, such a response could exacerbate rather than ameliorate PAF. The aim of the study was to examine the incidence, course and consequences of perianeurysmal fibrosis detected by computerised tomography (CT) before and after EVAR. MATERIAL AND METHODS: The clinical records of patients treated by EVAR and followed for at least 6 months were reviewed. Pre and post-operative CT images were independently graded for PAF by three radiologists according to a standard protocol. RESULTS: PAF was documented preoperatively in six out of a total of 61 patients. In two of these PAF worsened after EVAR resulting in ureteric obstruction and hydronephrosis requiring ureteric stents. In the remaining 4 patients PAF did not reduce postoperatively. PAF of low grade developed postoperatively in 10 out of 55 patients (18%) in whom there was no evidence of PAF on preoperative imaging. Median follow-up was 18 months (range 6-36 months). The development of periaortic fibrosis de novopostoperatively was statistically significant (McNemar's test p=0.002). CONCLUSION: EVAR does not seem to reverse PAF if this is present preoperatively and it induces this condition in approximately one sixth of patients without evidence of preoperative PAF. The potential for this adverse inflammatory local response should be taken into account when considering EVAR for treatment of aneurysms with perianeurysmal fibrosis and must be weighed against the perceived benefits of this approach.

The experiences and challenges of informal caregivers: common themes and differences among whites, blacks, and hispanics.

PURPOSE: This study examined commonalities and differences in the experiences and challenges of White, Black, and Hispanic informal caregivers in New York, NY. DESIGN AND METHODS: A randomly selected representative cross-section of 2,241 households was contacted through telephone interviews. Complete data were available for 380 eligible participants, who were classified as White (n = 164), Black (n = 129) and Hispanic (n = 87). Descriptive, bivariate, and multivariate analyses were conducted to examine differences in caregiving intensity, reported difficulty with providing care, and having unmet needs with care provision. RESULTS: Over 70% of caregivers had no help from formal caregivers, even though over 80% had been providing care for at least 1 year, and 40% had been providing this care for 20 or more hr per week. Compared with White caregivers, Black caregivers were more likely to provide higher intensity care, to report having unmet needs with care provision, and to experience increased religiosity since becoming caregivers, but were less likely to report difficulty with providing care. Hispanic caregivers were more likely than White caregivers to have help from formal caregivers and to experience increased religiosity since becoming caregivers. IMPLICATIONS: Although many similarities exist in the experiences and challenges of informal caregivers, gaining insight from different populations of family caregivers would help program planners, policy makers, and formal caregivers to develop and implement culturally sensitive programs and policies that are supportive of the needs of these caregivers in their ever-expanding roles. Future efforts also should focus on exploring the potentially significant role that community resources, in particular, religious institutions, could play in providing outreach and support to racial/ethnic minority caregivers.

Aortic side branch embolization before endovascular aneurysm repair: incidence of type II endoleak.

PURPOSE: To assess the feasibility of embolization of aortic side branches and its impact on the incidence of type II endoleak after endovascular aneurysm repair. MATERIALS AND METHODS: Endovascular aneurysm repair was performed in 74 patients. Aortic side branch vessels were evaluated on the preoperative angiogram and computed tomography (CT) and, where embolization of lumbar and inferior mesenteric vessels was considered technically possible, this was attempted prior to endovascular repair. Follow-up CT was used to assess the presence of type II endoleak. RESULTS: Seventy-two patients were followed up for longer than 1 month. Embolization was attempted in 25 cases, successfully in 10, with partial success in 11, and failure in four. Twenty patients with successful or partly successful preoperative embolization were discharged and followed-up. Four (20%) had demonstrable type II endoleak during follow-up, with two of these persisting at latest follow-up. Of 43 patients without previous embolization, there were 10 (23.3%) type II endoleaks during the follow-up period, four of these persisting. In cases with type II endoleak, mean sac diameter change was -0.5 mm in the cases with previous embolization and +3.1 mm without. The mean period to onset of type II endoleak was 6.9 months without, and 15.3 months with, previous embolization. CONCLUSION: Although the cohort size is below a level that would confer significance, the trend of these findings is such as to suggest a lack of influence of aortic side branch embolization on the incidence of type II endoleak during the follow-up period.

Decision analysis for small, asymptomatic intracranial arteriovenous malformations.

OBJECT: Asymptomatic intracranial arteriovenous malformations (AVMs) represent a clinically challenging problem because of the complex decision making that must be undertaken prior to beginning any type of treatment. In addition, the relative infrequency of these lesions means that there is relatively little experience reported in the literature. The authors use a decision-analysis technique to model the considerations that go into determining the treatment of these lesions in an effort to quantify the various risks and overall benefits conferred by the following three treatment strategies: observation/natural history, microsurgery, and stereotactic radiosurgery. METHODS: The authors conducted a thorough literature search to elucidate the risks and outcomes associated with each treatment option. These values were used to build and run a comprehensive Markov model to determine a base-case analysis. All of the input variables were also subjected to sensitivity analysis to identify the most influential input variables and the crossover points in which favored strategies changed. The base-case analysis suggested that microsurgery was the favored treatment option because this hypothetical cohort accumulated 21.53 quality-adjusted life years (QALYs) over the course of the model compared with the 16.97 QALYs and 16.40 QALYs for stereotctic radiosurgery and observation, respectively. Sensitivity analysis demonstrated that overall major neurological morbidity and mortality were the most influential input variables both perioperatively and during the radiosurgical "latent" period (that is, up to 2 years posttreatment). The maximum acceptable perioperative combined major neurological morbidity and mortality rate was 6.8%. The latent period combined major neurological morbidity and mortality would need to be 0.7% to make radiosurgery favorable in this analysis. CONCLUSIONS: Results of this decision analysis model suggest that microsurgery in the hands of experienced cerebrovascular surgeons, who can expect a less than 6.8% combined rate of major neurological morbidity and mortality, offers patients a greater overall quality of life over time.

Graft distortion after endovascular repair of abdominal aortic aneurysm: association with sac morphology and mid-term complications.

PURPOSE: To investigate the incidence, significance, and mechanism of stent-graft distortion after endovascular repair (EVR) of abdominal aortic aneurysm. METHODS: EVR of abdominal aortic aneurysm was performed in 51 cases (49 modular, bifurcated; 2 tube). Thirty-two patients were followed for 6 or more months and had equivalent baseline and follow-up images which could be used to determine changes in graft configuration. Sac dimensions were measured using computed tomographic (CT) images and graft-related complications were recorded. RESULTS: Amongst 32 patients evaluated on follow-up, there was graft distortion in 24. Distorted grafts were significantly (p = 0.002) associated with sac diameter reduction (mean 5 mm) and sac length reduction (mean 8.1 mm). All graft-related complications occurred in the limbs of eight distorted grafts, with a mean reduction of sac length in this group of 7.8 mm on reformatted CT images. CONCLUSION: There was a highly significant association between graft distortion and limb complications, and reduced sac dimensions.

Freedom from endoleak after endovascular aneurysm repair does not equal treatment success.

OBJECTIVE: To determine whether freedom from endoleak after endovascular repair of abdominal aortic aneurysm (EVAR) is a reliable guide to freedom from persistent or recurrent pressurisation of the aneurysm sac (endotension) and therefore freedom from risk of rupture. PATIENTS AND METHODS: The records of 55 patients followed for more than 3 months after EVAR were reviewed to correlate the presence or absence of endoleak on contrast-enhanced CT and/or angiography with changes in maximum aneurysm diameter (DMAX). RESULTS: in 22 (40%) patients there was no significant change in DMAX during follow-up. In 21 of these no endoleak was observed on CT or angiography. One patient developed a secondary side-branch endoleak which remains under observation. In 18 (33%) patients, DMAX decreased during follow-up. Thirteen of these remained free of endoleak. Four patients developed secondary endoleaks which were treated by secondary intervention. One patient with persistent primary endoleak suffered fatal aneurysm rupture three days before planned intervention. DMAX increased in 15 (27%) patients. In only five of these could an endoleak be identified on CT and/or angiography. One primary side-branch endoleak persists following failed embolisation. Four secondary endoleaks have been corrected by secondary intervention. Four of the remaining 10 patients died suddenly from unknown cause. All had DMAX greater than 65 mm at last follow-up. One patient underwent late conversion, which suggested continued pressurisation through thrombus at the site of a "sealed" primary proximal endoleak. Two patients are scheduled to undergo embolisation of patent side-branches revealed only by Levovist enhanced Duplex scanning and three patients remain under observation. CONCLUSION: Freedom from endoleak on conventional imaging incorrectly suggested freedom from endotension in 10 (18%) of our patients. Follow-up after endovascular repair must include regular measurement of DMAX and/or aneurysm sac volume to identify those patients who remain at risk of rupture.

Human first trimester fetal ovaries express oncofetal antigens and steroid receptors.

OBJECTIVE: To document the expression of oncofetal antigens and steroid receptors in first trimester human fetal ovaries and to determine the effect of advancing gestation on expression patterns. METHODS: Fetal gonads were collected from surgical terminations of pregnancy, and fetal sex was determined by fluorescence in situ hybridization. Immunocytochemical analysis was performed on paraffin sections of microdissected fetal ovaries using antibodies to carcinoembryonic antigen (CEA), placental alkaline phosphatase (PLAP), hCG, alpha fetoprotein (AFP), CA 125, estrogen receptor (ER) and progesterone receptor (PR) in 12 first trimester human fetal ovaries. Expression was quantified objectively by measuring percentage area of immunoreactivity (PAI) on whole sections of the ovary using an interactive image analysis system. Two pathologists, blinded to the antibodies used, independently viewed and scored all sections. RESULTS: PLAP, PR, ER and CEA were expressed in all 12 ovaries (31%, 28%, 21%, and 16% mean PAI, respectively). A diffuse staining pattern was observed at 8 weeks' gestation, which was more focal and confined to the cortical regions of the gonad by 12 weeks' gestation. Putative primordial germ cells were positive for PLAP, PR and ER but rarely for CEA. The expression (PAI) of PLAP and PR was unchanged during the first trimester, whereas that of ER decreased from 28% to 12%. The expression of CEA and hCG decreased from 8 to 11 weeks and then increased markedly by 13 weeks. AFP had a medullary distribution and was expressed in nine of 12 ovaries (mean PAI 18%). CA 125 expression was minimal or undetected. CONCLUSION: PLAP, ER and PR were the most extensively expressed protein antigens, particularly in fetal ovarian cortex. These variable patterns of expression suggest levels of differentiation in the immature first trimester human fetal ovary.

Cost-effectiveness of surgery for small abdominal aortic aneurysms on the basis of data from the United Kingdom small aneurysm trial.

PURPOSE: Although the United Kingdom small aneurysm trial reported no survival benefit for early operation in patients with small (4. 0-5.5 cm) abdominal aortic aneurysms (AAAs), the trial lacked statistical power to detect small but potentially meaningful gains in life expectancy, particularly for specific subgroups. We used decision analysis to better characterize the potential benefits and cost-effectiveness of early surgery. METHODS: We used a Markov model to assess the marginal cost-effectiveness (incremental cost per quality-adjusted life year [QALY] saved) of early surgery relative to surveillance for small AAAs, using data from the UK Trial. Subgroup analyses were performed by patient age and AAA diameter. Sensitivity analysis was used to evaluate the effect of elective operative mortality on cost-effectiveness. RESULTS: In our baseline analysis, early operations provided a small survival advantage (0.14 QALYs) at a small incremental cost of $1510. Thus, despite a small survival benefit, early surgery appeared cost-effective ($10, 800/QALY). The small cost differential resulted from the large proportion of patients who underwent surveillance, who eventually underwent AAA repair, and therefore incurred the cost of the surgical procedures. The survival advantage and cost-effectiveness of early operation increased with lower operative mortality, younger age, and larger AAA diameter. CONCLUSION: Despite the negative conclusions of the UK trial, early surgery may be cost-effective for patients with small AAAs, particularly younger patients (<72 years of age) with larger AAAs (> or = 4.5 cm). Because the gains in life expectancy are relatively small, however, clinical decision making should be strongly guided by patient preferences.

The role of the pulmonary afferent receptors in producing hemodynamic changes during hyperinflation and endotracheal suctioning in an oleic acid-injured animal model of acute respiratory failure.

The purpose of this study was to examine the role of the pulmonary afferent receptors in producing hemodynamic changes during hyperinflation and endotracheal suctioning (ETS) in an oleic acid-injured animal model of acute respiratory failure. Previous investigations of hyperinflation as a method to prevent hypoxia-induced sequelae of ETS have demonstrated unrecognized hemodynamic consequences. In this within-subject, repeated-measures study, instrumented, oleic acid-injured dogs had continuous measurements of heart rate (HR), mean aortic blood pressure (MAP), left ventricular pressure (Plv), pulmonary artery pressure (Ppa), right ventricular afterload (Ppa(tm)), right atrial pressure (Pra), and right ventricular filling pressure (Pra(tm)) during hyperinflation and ETS when the vagi were intact and after the pulmonary branches of the vagus nerves had been severed. After severing the vagi, MAP and Plv were decreased and HR and Ppa were increased. With the vagi severed, there was less variation in MAP and Ppa but increased variation in HR. These findings suggest that vagally mediated reflexes from the lungs produce some, but not all, of the hemodynamic effects associated with hyperinflation and ETS. Continued research is necessary to discover a method of hyperoxygenation and suctioning that does not produce potentially harmful hemodynamic effects.

Use of contrast-enhanced ultrasound in follow-up after endovascular aortic aneurysm repair.

PURPOSE: To investigate the use of contrast-enhanced ultrasound in the detection of endoleak after endovascular repair of abdominal aortic aneurysm. MATERIALS AND METHODS: Eighteen patients underwent follow-up on 20 occasions after endovascular aortic aneurysm repair by arterial-phase contrast-enhanced spiral computed tomography (CT). All patients had unenhanced color Doppler ultrasound and Levovist-enhanced ultrasound on the same day. The ultrasound examinations were reported in a manner that was blind to the CT results. CT was regarded as the gold standard for the purposes of the study. RESULTS: There were three endoleaks shown by CT. Unenhanced ultrasound detected only one endoleak (sensitivity, 33%). Levovist-enhanced ultrasound detected all three endoleaks (sensitivity, 100%). Levovist-enhanced ultrasound indicated an additional six endoleaks that were not confirmed by CT (specificity, 67%; positive predictive value, 33%). In one of these six cases, the aneurysm increased in size, which indicates a likelihood of endoleak. Two of the remaining false-positive results occurred in patients known to have a distal implantation leak at completion angiography. CONCLUSION: In this small group of patients, contrast-enhanced ultrasound appears to be a reliable screening test for endoleak. The false-positive results with enhanced ultrasound may be due to the failure of CT to detect slow flow collateral pathways. Although the number of patients in this study is small, enhanced ultrasound may be more reliable than CT in detecting endoleak.