Time efficient design of multi dimensional RF pulses: Application of a multi shift CGLS algorithm

Designing multi dimensional ratio frequency excitation pulses in the small flip angle regime commonly reduces to the solution of a least squares problem, which requires regularization to be solved numerically. Usually, regularization is carried out by the introduction of a penalty, λ, on the solution norm. In most cases, the optimal regularization parameter is not known a priori and the problem needs to be solved for several values of λ. The optimal value can be selected, typically by plotting the L‐curve. In this article, a conjugate gradients‐based algorithm is applied to design ratio frequency pulses in a time‐efficient way without a priori knowledge of the optimal regularization parameter. The computation time is reduced considerably (by a factor 10 in a typical set up) with respect to the standard conjugate gradients for least square since just one run of the algorithm is required. Simulations are shown and the performance is compared to that of conjugate gradients for least square. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Positive end-expiratory pressure induces liver congestion in living donor liver transplant patients: myth or fact

Living-donated liver transplant (LDLT) patients may develop lung edema during reperfusion, requiring higher positive end-expiratory pressure (PEEP) levels, which may impair liver outflow. The aim of the study was to assess the effect of increased PEEP levels on venous liver outflow and systemic hemodynamics in patients after LDLT. Thirty-nine LDLT recipients were enrolled in this study. All patients were postoperatively pressure-controlled ventilated and three different PEEP levels (0, 5 and 10 mbar) were randomly set. Systemic hemodynamic parameters and flow velocities of the hepatic artery, portal vein, and right hepatic vein were recorded at each PEEP level. PEEP of 10 mbar increased significantly central venous and pulmonary capillary pressure. Flow velocities in the right hepatic vein, the portal vein, the hepatic artery, mean arterial pressure, pulmonary arterial pressure, and cardiac index were not influenced by PEEP. Our study demonstrated that PEEP up to 10 mbar did not impair liver outflow in LDLT recipients.     

Haematopoietic and endothelial progenitor cells are deficient in quiescent systemic lupus erythematosus

BACKGROUND: Systemic lupus erythematosus (SLE) is associated with a high prevalence of cardiovascular disease. Circulating endothelial progenitor cells (EPCs) contribute to vascular regeneration and repair, thereby protecting against atherosclerotic disease. EPCs are derived from CD34+ haematopoietic stem cells (HSCs), which have an increased propensity for apoptosis in the bone marrow of patients with SLE. AIM: To determine whether circulating HSCs and EPCs are reduced in SLE, contributing to an increased cardiovascular risk. METHODS: Progenitor cells were sampled from 15 female patients with SLE in prolonged clinical remission from their disease and 15 matched healthy controls. HSC and CD34+KDR+ EPCs were quantified by flow cytometry. Annexin V staining was used to identify apoptotic cells. RESULTS: Patients with SLE had reduced levels of circulating CD34+ HSCs and CD34+KDR+ EPCs, associated with increased HSC apoptosis. Compared with controls, the fraction of HSCs that could be identified as EPCs was higher in patients with SLE, consistent with a primary defect of HSCs. EPC outgrowth from mononuclear cells, which depends mainly on CD34- cells, was unaffected. CONCLUSIONS: Patients with SLE have lower levels of circulating HSCs and EPCs, even during clinical remission. The data suggest that increased HSC apoptosis is the underlying cause for this depletion. These observations indicate that progenitor cell-mediated endogenous vascular repair is impaired in SLE, which may contribute to the accelerated development of atherosclerosis.     

Progression from MCI to AD: Predictive value of CSF Aβ42 is modified by APOE genotype

Objective

To study CSF biomarkers amyloid-beta 1-42 (Aβ42) and total tau (tau) in relation to APOE genotype in their ability to predict progression from mild cognitive impairment (MCI) to Alzheimer's disease (AD).

Methods

In 100 MCI patients CSF Aβ42, tau and APOE genotype were determined. At follow-up of 18 (13-24) months 58 patients remained non-progressive and 42 progressed to AD.

Results

Cox proportional hazards models showed an interaction between Aβ42 and APOE genotype (p < 0.05). Stratification for APOE revealed HR (95% CI) for abnormal Aβ42 of 8.2 (2.1-31.9) for ε4 non-carriers, 3.9 (0.8-18.5) for heterozygotes and 0.3 (0.0-1.7) for homozygotes. Inversely, stratification for Aβ42 revealed that in patients with normal levels of Aβ42, ε4 homozygotes had a strongly increased risk of progression to AD with HR (95% CI) 20.8 (2.4-182.8). Tau and APOE independently predicted progression to AD.

Conclusions

Aβ42 was a stronger predictor of progression to AD in APOE ε4 non-carriers than in carriers. Furthermore, the risk of progression for ε4 homozygotes was very high, also in patients with normal levels of Aβ42.     

Spontaneous blood oxygenation level-dependent fMRI signal is modulated by behavioral state and correlates with evoked response in sensorimotor cortex: a 7.0-T fMRI study

Synchrony measurements of spontaneous low-frequency blood oxygenation level-dependent (BOLD) fluctuations are increasingly being used to investigate spatial regions of functional connectivity. Although information regarding BOLD-BOLD synchrony between different regions is frequently reported, the relationship between spontaneous activity and behavioral state, and the association of spontaneous signal synchrony and evoked response, are less well characterized. The purpose of this study is to exploit the higher signal-to-noise ratio and in turn available spatial resolution at 7.0 T to understand the relationship between synchrony, measured as Pearson's R value, and amplitude, measured as signal standard deviation over time, in sensorimotor cortex for four separate behavioral states: eyes closed resting (EC), eyes open fixation (EO), EO with constant right hand fist clench (EO-F) and EO with 6 s off/6 s on (0.083 Hz) right hand finger tapping (EO-T). BOLD (TE/TR = 25/3,000 ms; 100 time points) scans were performed in healthy volunteers (7.0 T; 4 M/3 F; right-handed) at high spatial resolution = 1.6 × 1.6 × 1.6 mm3 . Results (z > 5; P < 0.05; low-pass filtering <0.067 Hz) reveal that synchrony is highest in the EC state (R = 0.35 ± 0.07) and reduces for EO (R = 0.26 ± 0.07), EO-F (R = 0.23 ± 0.07; P < 0.05), and EO-T (R = 0.12 ± 0.04; P < 0.05) conditions. Amplitude was highest in the EC condition and only reduced significantly (P < 0.05) for the EO-T condition. Synchrony within sensorimotor cortex correlated with evoked finger-tapping response magnitude (R = 0.81; P = 0.03), suggesting that spontaneous signal synchrony may be a predictor of evoked BOLD response magnitude and may account for intersubject variability in sensorimotor cortex.     

Tract-based magnetic resonance spectroscopy of the cingulum bundles at 7 T

The cingulum bundle is a white matter fiber bundle in the human brain that is believed to be implicated in various neurological and psychiatric diseases. Subtle disease-related differences in metabolite concentrations in the cingulum tracts that may underlie these diseases may be detected using MR spectroscopic information. However, to date, limited signal to noise and lack of spatial resolution have prevented a reliable and reproducible measurement of metabolites in the cingulum bundle in vivo. Here we propose a new method that combines MR spectroscopic imaging at 7 T with fiber tracking to select only those MR spectroscopy voxels that are actually part of the cingulum bundles. The spectra of the selected spectroscopy voxels are processed per voxel and then combined yielding one spectrum at high spectral resolution for each cingulum bundle. In this way sensitivity is increased, as large parts of the cingulum are included while partial volume effects with both gray matter and white matter from other tracts is kept to a minimum. Three healthy volunteers were scanned to assess the feasibility of the method. For all three healthy volunteers spectra for the left and right cingulum tracts were computed, partial volume fractions calculated and metabolite fractions were quantified yielding similar results suggesting that tract-based MR spectroscopy allows us to study metabolic concentrations of individual white matter fiber bundles with high sensitivity and high specificity.