Factors associated with persistent opioid use 6-12 months after primary total knee arthroplasty.

Persistent pain following knee arthroplasty occurs in up to 20% of patients and may require ongoing analgesia, including extended opioid administration. A comprehensive secondary analysis was performed from results of a study that considered persistent postoperative pain in 242 patients who underwent unilateral knee arthroplasty using a standardised enhanced recovery programme. Opioid prescribing for 12 months before and 12 months after surgery was evaluated and converted to oral morphine equivalents. Demographic, functional, psychological and pain questionnaires were completed along with quantitative sensory testing and genetic analysis. Forty-nine percent of patients had at least one opioid prescription in the 12 months before surgery. Opioid prescriptions were filled in 93% of patients from discharge to 3 months and in 27% of patients ≥6 months after surgery. Persistent opioid use ≥6 months after surgery was strongly associated with pre-operative opioid use (RR 3.2, p < 0.001 (95%CI 1.9-5.4)). The median (IQR [range]) oral morphine equivalent daily dose was 3.6 (0.9-10.5 [0-100.0]) mg pre-operatively, 35.0 (22.5-52.5 [4.6-180.0]) mg in hospital, 12.8 (5.1-24.8 [0-57.9]) mg from discharge to 3 months and 5.9 (4.5-12.0 [0-44.5]) mg at ≥6 months following surgery. Predictors of increased daily oral morphine equivalent ≥6 months after surgery included increased average daily oral morphine equivalent dose compared with previous values (lag), increased body mass index and three or more comorbid pain sites. Persistent opioid use was not associated with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain (RR 1.003, p = 0.655, 95%CI 0.65-1.002) or WOMAC function (RR 1.001, p = 0.99, 95%CI 0.99-1.03) outcomes 6 months after surgery. There was no association between persistent opioid use and pre-operative quantitative sensory testing results or psychological distress. Pre-operatively, patients with a higher body mass index, more comorbid pain sites and those who had filled an opioid prescription in the last 12 months, were at increased risk of persistent opioid use and a higher oral morphine equivalent daily dose ≥ 6 months after surgery. Strategies need to be developed to limit dose and duration of persistent opioid use in patients following knee arthroplasty surgery.

Comparison of manual and semi-automatic registration in augmented reality image-guided liver surgery: a clinical feasibility study.

BACKGROUND: The laparoscopic approach to liver resection may reduce morbidity and hospital stay. However, uptake has been slow due to concerns about patient safety and oncological radicality. Image guidance systems may improve patient safety by enabling 3D visualisation of critical intra- and extrahepatic structures. Current systems suffer from non-intuitive visualisation and a complicated setup process. A novel image guidance system (SmartLiver), offering augmented reality visualisation and semi-automatic registration has been developed to address these issues. A clinical feasibility study evaluated the performance and usability of SmartLiver with either manual or semi-automatic registration. METHODS: Intraoperative image guidance data were recorded and analysed in patients undergoing laparoscopic liver resection or cancer staging. Stereoscopic surface reconstruction and iterative closest point matching facilitated semi-automatic registration. The primary endpoint was defined as successful registration as determined by the operating surgeon. Secondary endpoints were system usability as assessed by a surgeon questionnaire and comparison of manual vs. semi-automatic registration accuracy. Since SmartLiver is still in development no attempt was made to evaluate its impact on perioperative outcomes. RESULTS: The primary endpoint was achieved in 16 out of 18 patients. Initially semi-automatic registration failed because the IGS could not distinguish the liver surface from surrounding structures. Implementation of a deep learning algorithm enabled the IGS to overcome this issue and facilitate semi-automatic registration. Mean registration accuracy was 10.9 ± 4.2 mm (manual) vs. 13.9 ± 4.4 mm (semi-automatic) (Mean difference - 3 mm; p = 0.158). Surgeon feedback was positive about IGS handling and improved intraoperative orientation but also highlighted the need for a simpler setup process and better integration with laparoscopic ultrasound. CONCLUSION: The technical feasibility of using SmartLiver intraoperatively has been demonstrated. With further improvements semi-automatic registration may enhance user friendliness and workflow of SmartLiver. Manual and semi-automatic registration accuracy were comparable but evaluation on a larger patient cohort is required to confirm these findings.

Interactive 3D U-net for the segmentation of the pancreas in computed tomography scans.

The increasing incidence of pancreatic cancer will make it the second deadliest cancer in 2030. Imaging based early diagnosis and image guided treatment are emerging potential solutions. Artificial intelligence (AI) can help provide and improve widespread diagnostic expertise and accurate interventional image interpretation. Accurate segmentation of the pancreas is essential to create annotated data sets to train AI, and for computer assisted interventional guidance. Automated deep learning segmentation performance in pancreas computed tomography (CT) imaging is low due to poor grey value contrast and complex anatomy. A good solution seemed a recent interactive deep learning segmentation framework for brain CT that helped strongly improve initial automated segmentation with minimal user input. This method yielded no satisfactory results for pancreas CT, possibly due to a sub-optimal neural network architecture. We hypothesize that a state-of-the-art U-net neural network architecture is better because it can produce a better initial segmentation and is likely to be extended to work in a similar interactive approach. We implemented the existing interactive method, iFCN, and developed an interactive version of U-net method we call iUnet. The iUnet is fully trained to produce the best possible initial segmentation. In interactive mode it is additionally trained on a partial set of layers on user generated scribbles. We compare initial segmentation performance of iFCN and iUnet on a 100CT dataset using dice similarity coefficient analysis. Secondly, we assessed the performance gain in interactive use with three observers on segmentation quality and time. Average automated baseline performance was 78% (iUnet) versus 72% (FCN). Manual and semi-automatic segmentation performance was: 87% in 15 min. for manual, and 86% in 8 min. for iUNet. We conclude that iUnet provides a better baseline than iFCN and can reach expert manual performance significantly faster than manual segmentation in case of pancreas CT. Our novel iUnet architecture is modality and organ agnostic and can be a potential novel solution for semi-automatic medical imaging segmentation in general.

Persistent postoperative pain after total knee arthroplasty: a prospective cohort study of potential risk factors.

BACKGROUND: Persistent postoperative pain (PPP) is common after total knee arthroplasty (TKA). The primary aim of this prospective cohort study was to identify important predictors of moderate to severe PPP 6 and 12 months after TKA. METHODS: Consenting patients (n=300) undergoing primary unilateral TKA attended a preoperative session to collect clinical information (age, gender, BMI, preoperative knee pain, comorbid pain, likely neuropathic pain) and psychological variables (depression, anxiety, catastrophising, expected pain). Quantitative sensory testing (pressure pain thresholds, temporal summation, conditioned pain modulation) was performed, and blood samples were obtained for subsequent genotyping of OPRM1 and COMT. Acute postoperative pain was measured at rest and during movement. Surgical factors (surgery time, patella resurfacing, anaesthetic type) were collected after operation. Follow-up questionnaires were sent 6 and 12 months after surgery. Multivariate logistic regression was used to identify predictors of PPP. RESULTS: The prevalence of moderate to severe PPP was 21% (n=60) and 16% (n=45) 6 and 12 months after surgery, with 55% (n=33) and 60% (n=31) of PPP likely neuropathic in nature. At 6 months, a combination of preoperative pain intensity, expected pain, trait anxiety, and temporal summation (Akaike information criterion, 309.9; area under receiver operating characteristic (ROC) curve, 0.70) was able to correctly classify 66% of patients into moderate to severe PPP and no to mild PPP groups. At 12 months, preoperative pain intensity, expected pain, and trait anxiety (Akaike information criterion, 286.8; area under ROC curve, 0.66) correctly classified 66% of patients. CONCLUSIONS: Findings from this study highlight several factors that may be targeted in future intervention studies to reduce the development of PPP. TRIAL REGISTRY NUMBER: ACTRN12612001089820.

Beam distortion due to gold fiducial markers during salvage high-intensity focused ultrasound in the prostate.

PURPOSE: High intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option for patients with recurrence after external beam radiation therapy (EBRT). As part of EBRT the prostate is frequently implanted with permanent fiducial markers. To date, the impact of these markers on subsequent HIFU treatment is unknown. The objective of this work was to systematically investigate, using computational simulations, how these fiducial markers affect the delivery of HIFU treatment. METHODS: A series of simulations was performed modelling the propagation of ultrasound pressure waves in the prostate with a single spherical or cylindrical gold marker at different positions and orientations. For each marker configuration, a set of metrics (spatial-peak temporal-average intensity, focus shift, focal volume) was evaluated to quantify the distortion introduced at the focus. An analytical model was also developed describing the marker effect on the intensity at the focus. The model was used to examine the marker's impact in a clinical setting through case studies. RESULTS: The simulations show that the presence of the marker in the pre-focal region causes reflections which induce a decrease in the focal intensity and focal volume, and a shift of the maximum pressure point away from the transducer's focus. These effects depend on the shape and orientation of the marker and become more pronounced as its distance from the transducer's focus decreases, with the distortion introduced by the marker greatly increasing when placed within 5 mm of the focus. The analytical model approximates the marker's effect and can be used as an alternative method to the computationally intensive and time consuming simulations for quickly estimating the intensity at the focus. A retrospective review of a small patient cohort selected for focal HIFU after failed EBRT indicates that the presence of the marker may affect HIFU treatment delivery. CONCLUSIONS: The distortion introduced by the marker to the HIFU beam when positioned close to the focus may result in an undertreated region beyond the marker due to less energy arriving at the focus, and an overtreated region due to reflections. Further work is necessary to investigate whether the results presented here justify the revision of the patient selection criteria or the markers' placement protocol.

The concordance between the volume hotspot and the grade hotspot: a 3-D reconstructive model using the pathology outputs from the PROMIS trial.

OBJECTIVES: The rationale for directing targeted biopsy towards the centre of lesions has been questioned in light of prostate cancer grade heterogeneity. In this study, we assess the assumption that the maximum cancer Gleason grade (Gleason grade hotspot) lies within the maximum dimension (volume hotspot) of a prostate cancer lesion. METHODS: 3-D histopathological models were reconstructed using the outputs of the 5-mm transperineal mapping (TPM) biopsies used as the reference test in the pilot phase of Prostate Mri Imaging Study (PROMIS), a paired validating cohort study investigating the performance of multi-parametric magnetic resonance imaging (MRI) against transrectal ultrasound (TRUS) biopsies. The prostate was fully sampled with 5 mm intervals; each core was separately labelled, inked and orientated in space to register 3-D cancer lesions location. The data from the histopathology results were used to create a 3-D interpolated reconstruction of each lesion and identify the spatial coordinates of the largest dimension (volume hot spot) and highest Gleason grade (Gleason grade hotspot) and assess their concordance. RESULTS: Ninety-four men, with median age 62 years (interquartile range, IQR= 58-68) and median PSA 6.5 ng ml(-1) (4.6-8.8), had a median of 80 (I69-89) cores each with a median of 4.5 positive cores (0-12). In the primary analysis, the prevalence of homogeneous lesions was 148 (76%; 95% confidence interval (CI) ±6.0%). In all, 184 (94±3.2%) lesions showed concordant hotspots and 11/47 (23±12.1%) of heterogeneous lesions showed discordant hotspots. The median 3-D distance between discordant hotspots was 12.8 mm (9.9-15.5). These figures remained stable on secondary analyses using alternative reconstructive assumptions. Limitations include a certain degree of error within reconstructed models. CONCLUSIONS: Guiding one biopsy needle to the maximum cancer diameter would lead to correct Gleason grade attribution in 94% of all lesions and 79% of heterogeneous ones if a true hit was obtained. Further correlation of histological lesions, their MRI appearance and the detectability of these hotspots on MRI will be undertaken once PROMIS results are released.

Pharmacogenetics of opioid response.

For opioids requiring CYP2D6 O-demethylation to active metabolites, poor metabolizers have reduced metabolite formation and minimal pain reduction. Clinically, this has only reliably been shown for tramadol. Ultra-rapid metabolizers have an increased risk of toxicity especially for codeine. ABCB1 genetics show no consistent findings. In Asian populations, the high OPRM1 118A>G frequency associates with higher opioid dosage requirements. Clinical translation of opioid genetics is premature because many important pain and addiction phenotype factors contribute.

Using the unbiased perspectives of people living with a spinal cord injury in assessments of mobility.

STUDY DESIGN: Clinometrics study. OBJECTIVE: To devise a way of capturing the unbiased perspectives of people living with a spinal cord injury (SCI) in assessments of mobility. SETTING: SCI unit and community. METHODS: Three groups of raters used the Global Impression of Change Scale (GICS) to rate change in mobility of a cohort of patients with a recent SCI. The three groups of raters were as follows: 10 people with a recent SCI, 10 people with an established SCI and 10 physiotherapists. The ratings were done after viewing 51 pairs of videos depicting one of three motor tasks: sitting unsupported, transferring and walking. Each pair of videos showed the same person performing the same motor task on two occasions. The videos were taken between 1 h and 5 months apart and presented side by side, randomly left or right, on the screen. Raters were asked to score the amount of change in performance between the two videos on a 7-point Global Impression of Change Scale (GICS). Intra-rater reliability for the three motor tasks and three groups of raters was determined using intra-class correlation coefficients. RESULTS: People with an SCI were reliable at rating change in patients' abilities to transfer and walk with ICC's ranging from 0.66 to 0.81 (95% Confidence interval bounds ranging from 0.51 to 0.94). Physiotherapists were consistently but only marginally more reliable at rating than people with an SCI. CONCLUSIONS: Videos and the GICS may provide a way of using the unbiased perspectives of people living with spinal cord injury in assessments of mobility.

The use of bronchodilators in people with recently acquired tetraplegia: a randomised cross-over trial.

STUDY DESIGN: A within-participant, double-blind, cross-over, randomised control trial. OBJECTIVES: To determine the short-term effects of bronchodilator therapy on respiratory function in people with recently acquired motor complete tetraplegia. SETTING: Hospital, Australia. METHODS: A total of 12 people with recently acquired tetraplegia were randomised to receive either a one-off dose of a bronchodilator followed by an equivalent dose of a placebo propellant between 1 day and 1 week later or visa versa. The three outcomes were forced expiratory volume in 1 s (FEV1), peak expiratory flow rate (PEF) and forced vital capacity (FVC). These were measured while supine by a blinded assessor 10 and 30 min after treatment. Data were analysed on 11 participants and reported as percentage of predicted. RESULTS: The FEV1, FVC and PEF mean between-group differences (95% confidence interval) at 10 min post treatment were 7.3% (2.7-11.9%; P=0.003), 5.5% (1.6-9.4%; P=0.008) and 20.1% (1.1-40.4%; P=0.039). Similar effects were observed at 30 min for FVC and FEV1 but not for PEF. CONCLUSION: Bronchodilator therapy has a beneficial effect on FEV1, FVC and PEF in participants with recently acquired tetraplegia.

How much equipment is prescribed for people with spinal cord injury in Australia, do they use it and are they satisfied 1 year later?

BACKGROUND AND PURPOSE: The purpose of this study was to determine the amount and type of equipment prescribed to aid mobility and self-care for patients with spinal cord injuries (SCI) in Australia and to determine how frequently the equipment is used 1 year later and whether patients are satisfied with it. METHODS: A consecutive series of 61 patients admitted for rehabilitation to two Sydney SCI units were recruited. All mobility and self-care equipment worth more than $AU50 prescribed by therapists before patients' discharge was recorded. This included wheelchairs, commodes, shower chairs, hoists, electric beds, pressure-relieving cushions, bed mattresses, slideboards, walking aids, orthoses, electrical stimulation systems and other pieces of notable exercise equipment. Patients were interviewed 1 year later and asked about each piece of equipment they had been prescribed. Specifically, they were asked about how frequently they had used each piece of equipment and whether they were satisfied with it. Data were analysed using descriptive statistics. RESULTS: Three hundred and fourteen pieces of equipment, including 68 wheelchairs, were prescribed for the 61 patients. Most of the equipment (226/314) was used more than 20 times in the 2 months preceding the 1-year review. Most patients were satisfied or highly satisfied with the majority of equipment prescribed, although patients were very dissatisfied or only partly dissatisfied with 18/314 pieces of equipment. DISCUSSION: Patients were generally satisfied with the equipment they were prescribed. There was a small amount of equipment prescribed that was not used 1 year later or with which patients were dissatisfied.

A comparison of patients' and physiotherapists' expectations about walking post spinal cord injury: a longitudinal cohort study.

STUDY DESIGN: A longitudinal cohort study. OBJECTIVE: The primary objective of this study was to compare the expectations that patients with recent spinal cord injury (SCI) had about walking 1 year from injury with the expectations of their physiotherapists. SETTING: Two Sydney SCI units. METHODS: A consecutive series of 47 patients admitted to the metropolitan SCI units was recruited. Using the mobility scale, expectations of the patients and their physiotherapists about walking at 1 year from SCI were recorded at the time of admission to rehabilitation. Ability to walk was then assessed at 1 year from the SCI. RESULTS: On admission to rehabilitation, 31 patients expected to walk about their homes at 1 year post SCI, but only 18 (58%) of these patients did so. In contrast, physiotherapists expected 21 patients to be able to walk about their homes at 1 year post SCI, with 17 (81%) of these patients doing so. Similarly, whereas 21 patients expected to walk about the community at 1 year post SCI, only 11 (52%) of these patients did so. Physiotherapists expected 8 patients to walk about the community at 1 year post SCI and 7 (88%) of these patients did so. The differences between patients' and physiotherapists' expectations about walking were statistically significant (P<0.001). CONCLUSION: There is a high degree of disagreement between patients' and physiotherapists' expectations about walking at 1 year post SCI. Differences between patients' and physiotherapists' expectations about walking are potentially problematic and requires research to identify appropriate management strategies.

Clinicians' and patients' impressions of change in motor performance as potential outcome measures for clinical trials.

STUDY DESIGN: A cross-sectional descriptive study was undertaken. OBJECTIVES: The overall objective was to explore the potential usefulness of clinicians' and patients' impressions of change in motor performance for clinical trials. Specifically, the aim was to compare clinicians' and patients' impressions of change in motor performance with standardized outcome measures in people with spinal cord injury (SCI). SETTING: Spinal injury units, Sydney, Australia. METHODS: Thirty people undergoing rehabilitation after recent SCI were recruited. They were assessed on two occasions separated by between 1 and 5 months. On both occasions, patients were assessed sitting unsupported (n = 25), transferring (n = 23) and walking (n = 12) using standardized outcome measures. On the second occasion, patients rated their impressions of change in each of the three motor tasks since their initial assessment. A 15-point scale was used. In addition, patients were videoed performing the three motor tasks on the two occasions. Two clinicians with SCI experience independently viewed the pairs of videos and rated their impressions of change using the same 15-point scale. Clinicians' and patients' impressions of change were compared with each other and to the standardized objective measures. RESULTS: Clinicians' and patients' impressions of change were greater than change measured with standardized objective measures for all three motor tasks (P<0.01). In addition, patients' impressions of change were greater than clinicians' impressions of change for transferring, but comparable for unsupported sitting and walking. CONCLUSION: Clinicians' and patients' impressions of change in motor performance may have potential for evaluating treatment effectiveness in clinical trials.

Callose synthase GSL7 is necessary for normal phloem transport and inflorescence growth in Arabidopsis.

One isoform of callose synthase, Glucan Synthase-Like7 (GSL7), is tightly coexpressed with two isoforms of sucrose synthase (SUS5 and SUS6) known to be confined to phloem sieve elements in Arabidopsis (Arabidopsis thaliana). Investigation of the phenotype of gsl7 mutants of Arabidopsis revealed that the sieve plate pores of stems and roots lack the callose lining seen in wild-type plants. Callose synthesis in other tissues of the plant appears to be unaffected. Although gsl7 plants show only minor phenotypic alterations during vegetative growth, flowering stems are reduced in height and all floral parts are smaller than those of wild-type plants. Several lines of evidence suggest that the reduced growth of the inflorescence is a result of carbohydrate starvation. Levels of sucrose, hexoses, and starch are lower in the terminal bud clusters of gsl7 than in those of wild-type plants. Transcript levels of "starvation" genes expressed in response to low sugars are elevated in the terminal bud clusters of gsl7 plants, at the end of the night, and during an extended night. Pulse-chase experiments with (14)CO(2) show that transport of assimilate in the flowering stem is much slower in gsl7 mutants than in wild-type plants. We suggest that the callose lining of sieve plate pores is essential for normal phloem transport because it confers favorable flow characteristics on the pores.

Normal growth of Arabidopsis requires cytosolic invertase but not sucrose synthase.

The entry of carbon from sucrose into cellular metabolism in plants can potentially be catalyzed by either sucrose synthase (SUS) or invertase (INV). These 2 routes have different implications for cellular metabolism in general and for the production of key metabolites, including the cell-wall precursor UDPglucose. To examine the importance of these 2 routes of sucrose catabolism in Arabidopsis thaliana (L.), we generated mutant plants that lack 4 of the 6 isoforms of SUS. These mutants (sus1/sus2/sus3/sus4 mutants) lack SUS activity in all cell types except the phloem. Surprisingly, the mutant plants are normal with respect to starch and sugar content, seed weight and lipid content, cellulose content, and cell-wall structure. Plants lacking the remaining 2 isoforms of SUS (sus5/sus6 mutants), which are expressed specifically in the phloem, have reduced amounts of callose in the sieve plates of the sieve elements. To discover whether sucrose catabolism in Arabidopsis requires INVs rather than SUSs, we further generated plants deficient in 2 closely related isoforms of neutral INV predicted to be the main cytosolic forms in the root (cinv1/cinv2 mutants). The mutant plants have severely reduced growth rates. We discuss the implications of these findings for our understanding of carbon supply to the nonphotosynthetic cells of plants.

Quantification of blood flow from rotational angiography.

For assessment of cerebrovascular diseases, it is beneficial to obtain three-dimensional (3D) information on vessel morphology and hemodynamics. Rotational angiography is routinely used to determine the 3D geometry and we propose a method to exploit the same acquisition to determine the blood flow waveform and the mean volumetric flow rate. The method uses a model of contrast agent dispersion to determine the flow parameters from the spatial and temporal development of the contrast agent concentration, represented by a flow map. Furthermore, it also overcomes artifacts due to the rotation of the c-arm using a newly introduced reliability map. The method was validated on images from a computer simulation and from a phantom experiment. With a mean error of 11.0% for the mean volumetric flow rate and 15.3% for the blood flow waveform from the phantom experiments, we conclude that the method has the potential to give quantitative estimates of blood flow parameters during cerebrovascular interventions.

Analysis of the sucrose synthase gene family in Arabidopsis.

The properties and expression patterns of the six isoforms of sucrose synthase in Arabidopsis are described, and their functions are explored through analysis of T-DNA insertion mutants. The isoforms have generally similar kinetic properties. Although there is variation in sensitivity to substrate inhibition by fructose this is unlikely to be of major physiological significance. No two isoforms have the same spatial and temporal expression patterns. Some are highly expressed in specific locations, whereas others are more generally expressed. More than one isoform is expressed in all organs examined. Mutant plants lacking individual isoforms have no obvious growth phenotypes, and are not significantly different from wild-type plants in starch, sugar and cellulose content, seed weight or seed composition under the growth conditions employed. Double mutants lacking the pairs of similar isoforms sus2 and sus3, and sus5 and sus6, are also not significantly different in these respects from wild-type plants. These results are surprising in the light of the marked phenotypes observed when individual isoforms are eliminated in crop plants including pea, maize, potato and cotton. A sus1/sus4 double mutant grows normally in well-aerated conditions, but shows marked growth retardation and accumulation of sugars when roots are subjected to hypoxia. The sucrose synthase activity in roots of this mutant is 3% or less of wild-type activity. Thus under well-aerated conditions sucrose mobilization in the root can proceed almost entirely via invertases without obvious detriment to the plant, but under hypoxia there is a specific requirement for sucrose synthase activity.

Cadaver validation of intensity-based ultrasound to CT registration.

A method is presented for the rigid registration of tracked B-mode ultrasound images to a CT volume of a femur and pelvis. This registration can allow tracked surgical instruments to be aligned with the CT image or an associated preoperative plan. Our method is fully automatic and requires no manual segmentation of either the ultrasound images or the CT volume. The parameter which is directly related to the speed of sound through tissue has also been included in the registration optimisation process. Experiments have been carried out on six cadaveric femurs and three cadaveric pelves. Registration results were compared with a "gold standard" registration acquired using bone implanted fiducial markers. Results show the registration method to be accurate, on average, to 1.6 mm root-mean-square target registration error.

Tissue deformation and shape models in image-guided interventions: a discussion paper.

This paper promotes the concept of active models in image-guided interventions. We outline the limitations of the rigid body assumption in image-guided interventions and describe how intraoperative imaging provides a rich source of information on spatial location of anatomical structures and therapy devices, allowing a preoperative plan to be updated during an intervention. Soft tissue deformation and variation from an atlas to a particular individual can both be determined using non-rigid registration. Established methods using free-form deformations have a very large number of degrees of freedom. Three examples of deformable models--motion models, biomechanical models and statistical shape models--are used to illustrate how prior information can be used to restrict the number of degrees of freedom of the registration algorithm and thus provide active models for image-guided interventions. We provide preliminary results from applications for each type of model.

Influence of head position on carotid hemodynamics in young adults.

Studies in adults have shown marked changes in geometry and relative positions of the carotid arteries when rotating the head. The aim of this study was to quantify the change in geometry and analyze its effect on carotid hemodynamics as a result of head rotation. The right carotid arteries of nine young adult subjects were investigated in supine position with straight and left turned head positions, respectively. The three-dimensional (3D) carotid geometry was reconstructed by using 3D ultrasound (3D US), and the carotid hemodynamics were calculated by combining 3D US with computational fluid dynamics. It was observed that cross-sectional areas and shapes did not change markedly with head rotation, but carotid vessel center lines altered with planarification of the common carotid artery as a main feature (P < 0.05). Measured common carotid flow rates changed significantly at the individual level when the head was turned, but on the average, the change in mean common carotid flow rate was relatively small (0.37 +/- 1.11 ml/s). The effect of the altered center lines and flow rates on the atherogenic nature of the carotid bifurcation was evaluated by using calculated hemodynamic wall parameters, such as wall shear stress (WSS) and oscillatory shear index (OSI). It was found that WSS and OSI patterns changed significantly with head rotation, but the variations were very subject dependent and could not have been predicted without assessing the altered geometry and flow of the carotid bifurcation for individual cases. This study suggests that there is a need for standardization of the choice of head position in the 3D US scan protocol, and that carotid stents and emboli diverters should be studied in different head positions.