Preoperative mapping of arterial spinal supply using 3.0-T MR angiography with an intravasal contrast medium and high-spatial-resolution steady-state

Preoperative mapping of the arterial spinal supply prior to thoracoabdominal aortic aneurysm repair is highly relevant because of high risk for postoperative ischemic spinal cord injuries such as paraparesis or paraplegia.

Hydrodynamic correlation functions of a driven granular fluid in steady state

We study a homogeneously driven granular fluid of hard spheres at intermediate volume fractions and focus on time-delayed correlation functions in the stationary state. Inelastic collisions are modeled by incomplete normal restitution, allowing for efficient simulations with an event-driven algorithm. The incoherent scattering function Fincoh(q,t ) is seen to follow time-density superposition with a relaxation time that increases significantly as the volume fraction increases. The statistics of particle displacements is approximately Gaussian. For the coherent scattering function S(q,ω), we compare our results to the predictions of generalized fluctuating hydrodynamics, which takes into account that temperature fluctuations decay either diffusively or with a finite relaxation rate, depending on wave number and inelasticity. For sufficiently small wave number q we observe sound waves in the coherent scattering function S(q,ω) and the longitudinal current correlation function Cl(q,ω). We determine the speed of sound and the transport coefficients and compare them to the results of kinetic theory.

Morphological and biochemical T2 evaluation of cartilage repair tissue based on a hybrid double echo at steady state (DESS-T2d) approach

To use a new approach which provides, based on the widely used three-dimensional double-echo steady-state (DESS) sequence, in addition to the morphological information, the generation of biochemical T2 maps in one hybrid sequence.

Advanced morphological 3D magnetic resonance observation of cartilage repair tissue (MOCART) scoring using a new isotropic 3D proton-density, turbo spin echo sequence with variable flip angle distribution (PD-SPACE) compared to an isotropic 3D steady-state free precession sequence (True-FISP) and standard 2D sequences

To evaluate a new isotropic 3D proton-density, turbo-spin-echo sequence with variable flip-angle distribution (PD-SPACE) sequence compared to an isotropic 3D true-fast-imaging with steady-state-precession (True-FISP) sequence and 2D standard MR sequences with regard to the new 3D magnetic resonance observation of cartilage repair tissue (MOCART) score.

Differential requirement for ROCK in dendritic cell migration within lymphatic capillaries in steady-state and inflammation

Dendritic cell (DC) migration via lymphatic vessels to draining lymph nodes (dLNs) is crucial for the initiation of adaptive immunity. We imaged this process by intravital microscopy (IVM) in the ear skin of transgenic mice bearing red-fluorescent vasculature and yellow-fluorescent DCs. DCs within lymphatic capillaries were rarely transported by flow, but actively migrated within lymphatics and were significantly faster than in the interstitium. Pharmacologic blockade of the Rho-associated protein kinase (ROCK), which mediates nuclear contraction and de-adhesion from integrin ligands, significantly reduced DC migration from skin to dLNs in steady-state. IVM revealed that ROCK blockade strongly reduced the velocity of interstitial DC migration, but only marginally affected intralymphatic DC migration. By contrast, during tissue inflammation, ROCK blockade profoundly decreased both interstitial and intralymphatic DC migration. Inhibition of intralymphatic migration was paralleled by a strong up-regulation of ICAM-1 in lymphatic endothelium, suggesting that during inflammation ROCK mediates de-adhesion of DC-expressed integrins from lymphatic-expressed ICAM-1. Flow chamber assays confirmed an involvement of lymphatic-expressed ICAM-1 and DC-expressed ROCK in DC crawling on lymphatic endothelium. Overall, our findings further define the role of ROCK in DC migration to dLNs and reveal a differential requirement for ROCK in intralymphatic DC crawling during steady-state and inflammation.

On the modeling of drug induced respiratory depression in the non-steady-state

The ability of anesthetic agents to provide adequate analgesia and sedation is limited by the ventilatory depression associated with overdosing in spontaneously breathing patients. Therefore, quantitation of drug induced ventilatory depression is a pharmacokinetic-pharmacodynamic problem relevant to the practice of anesthesia. Although several studies describe the effect of respiratory depressant drugs on isolated endpoints, an integrated description of drug induced respiratory depression with parameters identifiable from clinically available data is not available. This study proposes a physiological model of CO2 disposition, ventilatory regulation, and the effects of anesthetic agents on the control of breathing. The predictive performance of the model is evaluated through simulations aimed at reproducing experimental observations of drug induced hypercarbia and hypoventilation associated with intravenous administration of a fast-onset, highly potent anesthetic mu agonist (including previously unpublished experimental data determined after administration of 1 mg alfentanil bolus). The proposed model structure has substantial descriptive capability and can provide clinically relevant predictions of respiratory inhibition in the non-steady-state to enhance safety of drug delivery in the anesthetic practice.

Steady-state diffusion imaging for MR in-vivo evaluation of reparative cartilage after matrix-associated autologous chondrocyte transplantation at 3 tesla--preliminary results

OBJECTIVES: To demonstrate the feasibility of time-reversed fast imaging with steady-state precession (FISP) called PSIF for diffusion-weighted imaging of cartilage and cartilage transplants in a clinical study. MATERIAL AND METHODS: In a cross-sectional study 15 patients underwent MRI using a 3D partially balanced steady-state gradient echo pulse sequence with and without diffusion weighting at two different time points after matrix-associated autologous cartilage transplantation (MACT). Mean diffusion quotients (signal intensity without diffusion-weighting divided by signal intensity with diffusion weighting) within the cartilage transplants were compared to diffusion quotients found in normal cartilage. RESULTS: The global diffusion quotient found in repair cartilage was significantly higher than diffusion values in normal cartilage (p<0.05). There was a decrease between the earlier and the later time point after surgery. CONCLUSIONS: In-vivo diffusion-weighted imaging based on the PSIF technique is possible. Our preliminary results show follow-up of cartilage transplant maturation in patients may provide additional information to morphological assessment.

Renal artery assessment with nonenhanced steady-state free precession versus contrast-enhanced MR angiography

PURPOSE: To prospectively assess the diagnostic accuracy of nonenhanced three-dimensional (3D) steady-state free precession (SSFP) magnetic resonance (MR) angiography for detection of renal artery stenosis (RAS), with breath-hold contrast material-enhanced MR angiography performed as the reference standard. MATERIALS AND METHODS: The study was local ethics committee approved; all patients gave written informed consent. Fifty-three patients (30 male, 23 female; mean age, 58 years) with arterial hypertension and suspected of having RAS were examined with 1.5-T 3D SSFP renal MR angiography. Stenosis grade, maximal visible vessel length, and subjective image quality were compared. Sensitivity, specificity, accuracy, and negative predictive value (NPV) were calculated on artery-by-artery and patient-by-patient bases. The significance of the results was assessed with the paired two-sided t test for continuous variables and with the marginal homogeneity test for categorical variables. Cohen kappa statistics were used to estimate interobserver agreement. RESULTS: One hundred eight renal arteries with 20 significant (>or=50%) stenoses were detected with contrast-enhanced MR angiography. At artery-by-artery analysis, sensitivity, specificity, accuracy, and NPV of nonenhanced SSFP MR angiography for RAS detection were 100%, 93%, 94%, and 100%, respectively, for observer 1 and 95%, 95%, 95%, and 99%, respectively, for observer 2. Corresponding patient-by-patient values were 100%, 92%, 94%, and 100%, respectively, for observer 1 and 100%, 95%, 96%, and 100%, respectively, for observer 2. Overestimation of stenosis grade with SSFP MR angiography resulted in six and four false-positive findings for readers 1 and 2, respectively. Mean maximal visible lengths of the renal arteries were 69.9 mm at contrast-enhanced MR angiography and 61.1 mm at SSFP MR angiography (P<.001). Both techniques yielded good to excellent image quality. CONCLUSION: Slab-selective inversion-prepared 3D SSFP MR angiography had high sensitivity, specificity, accuracy, and NPV for RAS detection, without the need for contrast material. However, RAS severity was overestimated in some patients.

Rapid estimation of cartilage T2 based on double echo at steady state (DESS) with 3 Tesla

The double-echo-steady-state (DESS) sequence generates two signal echoes that are characterized by a different contrast behavior. Based on these two contrasts, the underlying T2 can be calculated. For a flip-angle of 90 degrees , the calculated T2 becomes independent of T1, but with very low signal-to-noise ratio. In the present study, the estimation of cartilage T2, based on DESS with a reduced flip-angle, was investigated, with the goal of optimizing SNR, and simultaneously minimizing the error in T2. This approach was validated in phantoms and on volunteers. T2 estimations based on DESS at different flip-angles were compared with standard multiecho, spin-echo T2. Furthermore, DESS-T2 estimations were used in a volunteer and in an initial study on patients after cartilage repair of the knee. A flip-angle of 33 degrees was the best compromise for the combination of DESS-T2 mapping and morphological imaging. For this flip angle, the Pearson correlation was 0.993 in the phantom study (approximately 20% relative difference between SE-T2 and DESS-T2); and varied between 0.429 and 0.514 in the volunteer study. Measurements in patients showed comparable results for both techniques with regard to zonal assessment. This DESS-T2 approach represents an opportunity to combine morphological and quantitative cartilage MRI in a rapid one-step examination.