Elevated Wall Shear Stress in Aortic Type B Dissection May Relate to Retrograde Aortic Type A Dissection: A Computational Fluid Dynamics Pilot Study.

OBJECTIVE: Retrograde aortic type A dissection (RTAD) is a known complication in patients with aortic type B dissection. The purpose of this computational fluid dynamics (CFD) study was to identify haemodynamic risk factors for the occurrence of RTAD. METHODS: Computed tomographic angiography (CTA) images of 10 patients with type B dissections, who subsequently developed a RTAD, were retrospectively analysed together with patients constituting a control group (n = 10) where no further vascular events after the initial type B dissection occurred. CFD simulations were conducted based on 3D surface models of the aortic lumen derived from CTA datasets. For both groups, pressures, velocity magnitudes and wall shear stress (WSS) were compared at the site of the future RTAD entry tear and the surrounding aortic wall. RESULTS: WSS at the site of the future entry tear was significantly elevated compared with the surrounding wall (15.10 Pa vs. 5.15 Pa, p < .001) and was significantly higher in the RTAD group than in the control group (6.05 Pa, p < .002). Pressures and velocity magnitudes were not significantly elevated at the entry tear (3825.8 Pa, 0.63 m/s) compared with the aortic arch (3549.8 Pa, 0.50 m/s) or control group (3501.7 Pa, 0.62 m/s). CONCLUSIONS: Increased WSS accompanies the occurrence of RTAD. The results merit the design for a prospective study to confirm whether WSS is a risk factor for the occurrence of RTAD.

MR-based in vivo follow-up study of Achilles tendon volume and hydration state after ankle-loading activity.

The purpose of this study was to evaluate temporal alterations of the Achilles tendon volume and hydration state after cross-country-running. Achilles tendons of six untrained participants were examined on a 3T MR-scanner before running, immediately afterwards, and in the following 24, 48, and 72 h. Using a 3D-UTE sequence, caudal (CA) and cranial (CR) mid-portion tendon areas were examined with off-resonance saturation ratios (OSR) and T2* relaxation times. Tendon volume was measured with a self-written Matlab-based automated contour detection algorithm (AVAT) in submillimeter T2-weighted MR images. A significant influence of running in caudal (P = 0.017) and cranial OSR values (P = 0.001), tendon volume (P = 0.024), and cranial T2* measurements (P = 0.046), but not in caudal T2* values (P = 0.298) were found. In detail, mean individual OSR and tendon volume measurements demonstrated a similar but inverted course in their values after exercise: initially, OSR values increased after running (and tendon volume decreased), while subsequently a decrease of OSR values (with an increase of tendon volume) could be observed. OSR and tendon volume measurements are able to detect a physiological response of tendons to a mechanical stimulus. After a transient decrease of free water in the Achilles tendon, an increase with a maximum free water content 48 h after ankle loading and a tendency toward normalization after 72 h was found.

Relationships and redundancies of selected hemodynamic and structural parameters for characterizing virtual treatment of cerebral aneurysms with flow diverter devices.

BACKGROUND AND PURPOSE: To quantify the relationship and to demonstrate redundancies between hemodynamic and structural parameters before and after virtual treatment with a flow diverter device (FDD) in cerebral aneurysms. METHODS: Steady computational fluid dynamics (CFD) simulations were performed for 10 cerebral aneurysms where FDD treatment with the SILK device was simulated by virtually reducing the porosity at the aneurysm ostium. Velocity and pressure values proximal and distal to and at the aneurysm ostium as well as inside the aneurysm were quantified. In addition, dome-to-neck ratios and size ratios were determined. Multiple correlation analysis (MCA) and hierarchical cluster analysis (HCA) were conducted to demonstrate dependencies between both structural and hemodynamic parameters. RESULTS: Velocities in the aneurysm were reduced by 0.14m/s on average and correlated significantly (p<0.05) with velocity values in the parent artery (average correlation coefficient: 0.70). Pressure changes in the aneurysm correlated significantly with pressure values in the parent artery and aneurysm (average correlation coefficient: 0.87). MCA found statistically significant correlations between velocity values and between pressure values, respectively. HCA sorted velocity parameters, pressure parameters and structural parameters into different hierarchical clusters. HCA of aneurysms based on the parameter values yielded similar results by either including all (n=22) or only non-redundant parameters (n=2, 3 and 4). CONCLUSION: Hemodynamic and structural parameters before and after virtual FDD treatment show strong inter-correlations. Redundancy of parameters was demonstrated with hierarchical cluster analysis.

Intradiurnal Fluctuations of Off-Resonance Saturation Effects in Healthy Human Achilles Tendons Assessed with a 3D Ultrashort Echo Time MRI Sequence at 3 Tesla.

PURPOSE: The purpose of this study was to evaluate whether gravitational interstitial fluid accumulation in healthy subjects has an impact on off-resonance saturation ratios (OSR) or the volume of the Achilles tendon after a prolonged time of reduced levels of physical activity. MATERIALS AND METHODS: 7 healthy volunteers were repeatedly investigated on 3 consecutive days on a 3 T whole body MR scanner using an ultrashort echo time (UTE) imaging sequence with a Gaussian off-resonance saturation pulse at a frequency offset of 2000 Hz to calculate OSR values. For accurate volumetric quantification of the Achilles tendon, a newly developed contour detection snake algorithm was applied on high-resolution isotropic T2-weighted SPACE sequence datasets. Single-measure intraclass correlation coefficients (ICC) were calculated to estimate test-retest reliability. RESULTS: For OSR and tendon volume measurements on three consecutive days, excellent reproducibility could be achieved with ICC values above 0.96 and 0.97, respectively. Comparing the results of all three days, a statistically significant mean individual percentage decrease (- 4.1  ±â€Š1.5 %; p = 0.001) of calculated tendon OSR values was found for the evening measurements. No statistically significant difference between tendon volumes in the morning and the evening could be detected (p = 0.589). CONCLUSION: The results of this in-vivo study demonstrate a significant influence of gravitational interstitial fluid accumulation after reduced physical activity on OSR values in the Achilles tendon, but not on tendon volume. Taken together with the demonstrated excellent reproducibility, these findings are important for future studies investigating temporal changes of the Achilles tendon microstructure.

Comparison of morphological and rheological conditions between conventional and eversion carotid endarterectomy using computational fluid dynamics--a pilot study.

PURPOSE: To compare postoperative morphological and rheological conditions after eversion carotid endarterectomy versus conventional carotid endarterectomy using computational fluid dynamics. BASIC METHODS: Hemodynamic metrics (velocity, wall shear stress, time-averaged wall shear stress and temporal gradient wall shear stress) in the carotid arteries were simulated in one patient after conventional carotid endarterectomy and one patient after eversion carotid endarterectomy by computational fluid dynamics analysis based on patient specific data. PRINCIPAL FINDINGS: Systolic peak of the eversion carotid endarterectomy model showed a gradually decreased pressure along the stream path, the conventional carotid endarterectomy model revealed high pressure (about 180 Pa) at the carotid bulb. Regions of low wall shear stress in the conventional carotid endarterectomy model were much larger than that in the eversion carotid endarterectomy model and with lower time-averaged wall shear stress values (conventional carotid endarterectomy: 0.03-5.46 Pa vs. eversion carotid endarterectomy: 0.12-5.22 Pa). CONCLUSIONS: Computational fluid dynamics after conventional carotid endarterectomy and eversion carotid endarterectomy disclosed differences in hemodynamic patterns. Larger studies are necessary to assess whether these differences are consistent and might explain different rates of restenosis in both techniques.

Qualitative and quantitative performance of ¹8F-FDG-PET/MRI versus ¹8F-FDG-PET/CT in patients with head and neck cancer.

BACKGROUND AND PURPOSE: MR imaging and PET/CT are integrated in the work-up of head and neck cancer patients. The hybrid imaging technology (18)F-FDG-PET/MR imaging combining morphological and functional information might be attractive in this patient population. The aim of the study was to compare whole-body (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT in patients with head and neck cancer, both qualitatively in terms of lymph node and distant metastases detection and quantitatively in terms of standardized uptake values measured in (18)F-FDG-avid lesions. MATERIALS AND METHODS: Fourteen patients with head and neck cancer underwent both whole-body PET/CT and PET/MR imaging after a single injection of (18)F-FDG. Two groups of readers counted the number of lesions on PET/CT and PET/MR imaging scans. A consensus reading was performed in those cases in which the groups disagreed. Quantitative standardized uptake value measurements were performed by placing spheric ROIs over the lesions in 3 different planes. Weighted and unweighted κ statistics, correlation analysis, and the Wilcoxon signed rank test were used for statistical analysis. RESULTS: κ statistics for the number of head and neck lesion lesions counted (pooled across regions) revealed interreader agreement between groups 1 and 2 of 0.47 and 0.56, respectively. Intrareader agreement was 0.67 and 0.63. The consensus reading provided an intrareader agreement of 0.63. For the presence or absence of metastasis, interreader agreement was 0.85 and 0.70. The consensus reading provided an intrareader agreement of 0.72. The correlations between the maximum standardized uptake value in (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT for primary tumors and lymph node and metastatic lesions were very high (Spearman r = 1.00, 0.93, and 0.92, respectively). CONCLUSIONS: In patients with head and neck cancer, (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT provide comparable results in the detection of lymph node and distant metastases. Standardized uptake values derived from (18)F-FDG-PET/MR imaging can be used reliably in this patient population.

Multimodality imaging of primary CNS lymphoma in immunocompetent patients.

Primary central nervous system lymphoma (PCNSL) belongs to the group of extranodal non-Hodgkin's lymphoma, and the management of the disease is radically different from other central nervous system neoplasms. Owing to its varied appearance on imaging, diagnosis of PCNSL can be challenging. The purpose of this pictorial review is to depict the brain findings of PCNSL during initial diagnosis in immunocompetent individuals. Multimodal imaging integrating advanced sequences can facilitate differentiation of PCNSL from other CNS neoplasms.

N staging of lung cancer patients with PET/MRI using a three-segment model attenuation correction algorithm: initial experience.

OBJECTIVES: Evaluate the performance of PET/MRI at tissue interfaces with different attenuation values for detecting lymph node (LN) metastases and for accurately measuring maximum standardised uptake values (SUVmax) in lung cancer patients. MATERIALS AND METHOD: Eleven patients underwent PET/CT and PET/MRI for staging, restaging or follow-up of suspected or known lung cancer. Four experienced readers determined the N stage of the patients for each imaging method in a randomised blinded way. Concerning metastases, SUVmax of FDG-avid LNs were measured in PET/CT and PET/MRI in all patients. A standard of reference was created with a fifth experienced independent reader in combination with a chart review. Results were analysed to determine interobserver agreement, SUVmax correlation between CT and MRI (three-segment model) attenuation correction and diagnostic performance of the two techniques. RESULTS: Overall interobserver agreement was high (κ = 0.86) for PET/CT and substantial (κ = 0.70) for PET/MRI. SUVmax showed strong positive correlation (Spearman's correlation coefficient = 0.93, P < 0.001) between the two techniques. Diagnostic performance of PET/MRI was slightly inferior to that of PET/CT, without statistical significance (P > 0.05). CONCLUSIONS: PET/MRI using three-segment model attenuation correction for LN staging in lung cancer shows a strong parallel to PET/CT in terms of SUVmax, interobserver agreement and diagnostic performance. KEY POINTS: •F18-FDG PET/MRI shows similar performance to F18-FDG PET/CT in lung cancer N staging. •PET/MRI has substantial interobserver agreement in N staging. •A three-segment model attenuation correction is reliable for assessing the mediastinum.

Accuracy and variability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR.

OBJECTIVES: This study aims to test whether inter-observer variability and time of diameter measurements for thoracic endovascular aortic repair (TEVAR) are improved by semiautomatic centerline analysis compared to manual assessment. METHODS: Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 males) were retrospectively analysed by two blinded experts in vascular radiology. Maximum aortic diameters at three positions relevant to TEVAR were assessed (P1, distal to left common carotid artery; P2, distal to left subclavian artery; and P3, proximal to coeliac trunk) using three measurement techniques: manual axial slices (axial), manual double-oblique multiplanar reformations (MPRs) and semiautomatic centerline analysis. RESULTS: Diameter measurements by both centerline analysis and the axial technique did not significantly differ from MPR (p = 0.17 and p = 0.37). Total deviation index for 0.9 was for P1 2.7 mm (axial), 3.7 mm (MPR), 1.8 mm (centerline); for P2 2.0 mm (axial), 3.6 mm (MPR), 1.8 mm (centerline); and for P3 3.0 mm (axial), 3.5 mm (MPR), 2.5 mm (centerline). Measurement time using centerline analysis was significantly shorter than for assessment by MPR. CONCLUSIONS: Centerline analysis provides the least variable and fast diameter measurements in TEVAR patients with the same accuracy as the current reference standard MPR.

Bloodless lung transplantation in Jehovah's Witnesses: impact on perioperative parameters and outcome compared with a matched control group.

BACKGROUND: Jehovah's Witnesses (JW) refuse to receive blood products due to their religious beliefs. Bloodless transplantation programs have made the successful transplantation of solid organs like heart, liver, kidney, and pancreas in JW feasible. In this study we present the third and fourth case of a successful bloodless lung transplantation and analyze perioperative parameters and outcome with a strictly selected matched control group (CG). METHODS: Two JW patients suffering from idiopathic pulmonary fibrosis had single lung transplantation in the transfusion-free program. Ten of 113 patients (8.8%) undergoing lung transplantation fulfilled the matching criteria and served as CG. Perioperative parameters including blood loss and transfusions were collected from the charts. Regarding outcome parameters arterial blood gas, lung function testing, length of stay, and survival were analyzed. RESULTS: Concerning perioperative parameters no significant differences could be found between both groups except for the creatinine level, which was significantly lower in the JW group on postoperative day 0 (P = .037), and the hemoglobin and hematocrit levels, which were significantly higher in the JW group on postoperative day 3 (P = .032 and P = .041, respectively). The analysis of the outcome parameters revealed significantly higher postoperative lung functional testing values forced expiratory volume after 1 second (FEV1) and forced vital capacity (FVC) in the JW group compared with the CG (P = .037 and P = .036, respectively). CONCLUSION: Bloodless lung transplantation is feasible in carefully selected JW recipients. Comparing JW to CG, no statistically significant difference in the perioperative course and a trend towards a favorable postoperative lung function outcome were detected.

Clinical standardized fMRI reveals altered language lateralization in patients with brain tumor.

BACKGROUND AND PURPOSE: Brain tumors affecting language-relevant areas may influence language lateralization. The purpose of this study was to systematically investigate language lateralization in brain tumor patients using clinical language fMRI, comparing the results with a group of healthy volunteers. MATERIALS AND METHODS: Fifty-seven strictly right-handed patients with left-hemispheric-space intracranial masses (mainly neoplastic) affecting either the Broca area (n = 19) or Wernicke area (n = 38) were prospectively enrolled in this study. Fourteen healthy volunteers served as a control group. Standardized clinical language fMRI, using visually triggered sentence- and word-generation paradigms, was performed on a 1.5T MR scanner. Semiautomated analyses of all functional data were conducted on an individual basis using BrainVoyager. A regional lateralization index was calculated for Broca and Wernicke areas separately versus their corresponding right-hemisphere homologs. RESULTS: In masses affecting the Broca area, a significant decrease in the lateralization index was found when performing word generation (P = .0017), whereas when applying sentence generation, the decrease did not reach statistical significance (P = .851). Masses affecting the Wernicke area induced a significant decrease of the lateralization index when performing sentence generation (P = .0007), whereas when applying word generation, the decrease was not statistically significant (P = .310). CONCLUSIONS: Clinical language fMRI was feasible for patients with brain tumors and provided relevant presurgical information by localizing essential language areas and determining language dominance. A significant effect of the brain masses on language lateralization was observed, with a shift toward the contralesional, nondominant hemisphere. This may reflect compensatory mechanisms of the brain to maintain communicative abilities.

Gadofosveset enhanced MR phlebography for detecting pelvic and deep vein leg thrombosis.

BACKGROUND: Deep venous thrombosis is mainly diagnosed by ultrasound today. In some instances diagnosis is challenging and magnetic resonance angiography could be an attractive alternative. Gadofosveset is a blood pool contrast agent with some favourable properties for this purpose. PATIENTS AND METHODS: We investigated eight patients with proven deep venous thrombosis by Gadofosveset enhanced MR phlebography. We performed a 3D gradient-echo sequence with an overall measurement time of 9 minutes and 6 seconds. One minute after injection of Gadofosveset in a concentration of 0.12 ml/kg body weight images were acquired. Thrombi were visualised by their lack of luminal contrast filling. RESULTS: Thrombi were visualised in all patients. In one patient with extended thrombosis a previously undiagnosed ovarian adenocarcinoma was detected additionally. CONCLUSIONS: Deep venous thromboses in lower extremities can be visualised reliably by performing MR phlebography with blood pool contrast agent Gadofosveset. Visualisation of the complete venous system is feasible. This investigation method may be performed in patients difficult to investigate with ultrasound or may be used for planning interventional procedures.

Reliability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR among non-experts.

OBJECTIVES: The study aimed to test whether reliability and inter-observer variability of preoperative measurements for thoracic endovascular aortic repair (TEVAR) among non-experts are improved by semiautomatic centerline analysis compared with manual assessment. METHODS: Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 men) were retrospectively analysed in randomised order by one blinded vascular expert (reference standard) and three blinded non-expert readers. Aortic diameters were measured at four positions relevant to TEVAR using three measurement techniques (manual axial slices, manual multiplanar reformations (MPRs) and semiautomatic centerline analysis). Length measurements were performed using centerline analysis. Reliability was calculated as absolute measurement deviation (AMD) from reference standard and inter-observer variability as coefficient of variance (CV) among non-expert readers. RESULTS: For axial, MPR and centerline techniques, mean AMD was 7.3 ± 7.7%, 6.7 ± 4.5% and 4.7 ± 4.8% and mean CV was 5.2 ± 4.2%, 5.8 ± 4.8% and 3.9 ± 5.4%. Both AMD and CV were significantly lower for centerline analysis compared with axial technique (p = 0.001/0.042) and MPR (p = 0.009/0.003). AMD and CV for length measurements by centerline analysis were 3.2 ± 2.8% and 2.6 ± 2.4%, respectively. Centerline analysis was significantly faster than MPR (p < 0.001). CONCLUSIONS: Semiautomatic centerline analysis provides the most reliable and least variable diameter and length measurements among non-experts in candidates for TEVAR.

Noninvasive imaging of treated cerebral aneurysms, Part II: CT angiographic follow-up of surgically clipped aneurysms.

Although not useful for the evaluation of coiled aneurysms, CT angiography (CTA) is far superior to MR angiography (MRA) for the evaluation of aneurysms after surgical clipping. Using the latest multidetector row scanners and optimized imaging parameters, CTA can often effectively depict and follow small aneurysm remnants; demonstrate patency, stenosis, or vasospasm in the adjacent parent vessels; and provide surveillance of the entire cerebrovasculature for de novo aneurysms after surgical clipping. Despite these advances, conventional angiography remains the gold standard for the evaluation of surgically treated aneurysms and should be liberally used to resolve any cases of diagnostic uncertainty on noninvasive imaging.

Noninvasive imaging of treated cerebral aneurysms, part I: MR angiographic follow-up of coiled aneurysms.

MRA is emerging as an alternative to conventional catheter based angiography for the assessment of aneurysms after endovascular treatment. Short TE and contrast enhanced MRA techniques can be applied to optimize image quality. We review the available data regarding the application of MR for the assessment of cerebral aneurysms after endovascular therapy.

tPA by telephone: extending the benefits of a comprehensive stroke center.

The use of tissue plasminogen activator (tPA) in community hospitals has been limited by a lack of neurologic support. The authors developed a telephone network to support community emergency departments (EDs) in the use of tPA. Their experience demonstrates equivalent results for patients treated by telephone and those treated in-house. Their number of tPA-treated patients increased 72%. Requirements included willingness of community EDs to use tPA and willingness of the stroke center to provide support.

Faculty triage shortens emergency department length of stay.

OBJECTIVE: To determine whether faculty triage (FT) activities can shorten emergency department (ED) length of stay (LOS). METHODS: This was a comparison study measuring the impact of faculty triage vs no faculty triage on ED LOS. It was set in an urban county teaching hospital. Subjects were patients presenting to the registration desk between 9 AM and 9 PM on 16 consecutive Mondays (August 2 to November 15, 1999). On eight Mondays, an additional faculty member was stationed at the triage desk. He or she was asked to expedite care by rapid evaluation orders for diagnostic studies and basic therapeutic interventions, and by moving serious patients to the patient care areas. He or she was not provided with detailed instructions or protocols. The ED LOS, time of registration (TIMEREG), inpatient admission status (ADMIT), x-ray utilization (XRAY), total patients registered each day between 9 AM and 9 PM (TOTREG), and patients who left without being seen (LWBS) were determined using an ED information system. The LOS was analyzed in relation to FT, ADMIT, and XRAY by the Mann-Whitney U test. The LOS was related to TIMEREG and TOTREG by simple linear regression. Stepwise multiple linear regression models to predict LOS were generated using all the variables. RESULTS: Patients without FT (n = 814) had a mean LOS of 445 minutes. Patients with FT (n = 920) had a mean LOS of 363 minutes. Mean difference in LOS was -82 minutes (95% CI = -111 to -53), a reduction of 18%. The LOS was also related to: ADMIT +203 minutes (95% CI = 168 to 238), TOTREG -2.7 min/additional patient registered (95% CI = -1.15 to -4.3), and TIMEREG +0.14 min/min since 9 AM (95% CI = 0.07 to 0.21). The LWBS was reduced by 46% with FT. In multiple regression analysis, ADMIT, FT, TIMEREG, and XRAY were all related to LOS, but the model explained only a small part of variance (adjusted R(2) = 0.093). The faculty cost is estimated to be $11.98/patient. CONCLUSIONS: Faculty triage offers a moderate increase in efficiency at this ED, albeit with relatively high cost.