Perfusion imaging of the human lung using flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER)

Pulmonary perfusion is an important parameter in the evaluation of lung diseases such as pulmonary embolism. A noninvasive MR perfusion imaging technique of the lung is presented in which magnetically labeled blood water is used as an endogenous, freely diffusible tracer. The perfusion imaging technique is an arterial spin tagging method called Flow sensitive Alternating Inversion Recovery with an Extra Radiofrequency pulse (FAIRER). Seven healthy human volunteers were studied. High-resolution perfusion-weighted images with negligible artifacts were acquired within a single breathhold. Different patterns of signal enhancement were observed between the pulmonary vessels and parenchyma, which persists up to TI = 1400 ms. The T1s of blood and lung parenchyma were determined to be 1.46s and 1.35 s, respectively.     

Quantitative multi-modal functional MRI with blood oxygenation level dependent exponential decays adjusted for flow attenuated inversion recovery (BOLDED AFFAIR)

A magnetic resonance imaging (MRI) method is described that allows interleaved measurements of transverse (R(2)(*) and R(2)) and longitudinal (R(1)) relaxation rates of tissue water in conjunction with spin labeling. The image-contrasts are intrinsically blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) weighted, but each contrast is made quantitative by two echo time (TE) and inversion recovery time (TIR) acquisitions with gradient echo (GE) and spin echo (SE) weighted echo-planar imaging (EPI). The EPI data were acquired at 7 Tesla with nominal spatial resolution of 430 x 430 x 1000 microm(3) in rat brain in vivo. The method is termed as blood oxygenation level dependent exponential decays adjusted for flow attenuated inversion recovery (BOLDED AFFAIR) and allows acquisition of R(2)(*), R(2), and CBF maps in an interleaved manner within approximately 12 minute. The basic theory of the method, associated experimental/systematic errors, and temporal restrictions are discussed. The method is validated by comparison of multi-modal maps obtained by BOLDED AFFAIR (i.e., two TE and TIR values with GE and SE sequences) and conventional approach (i.e., multiple TE and TIR values with GE and SE sequences) during varied levels of whole brain activity. Preliminary functional data from a rat forepaw stimulation model demonstrate the feasibility of this method for functional MRI (fMRI) studies. It is expected that with appropriate precautions this method in conjunction with contrast agent-based MRI has great potential for quantitative fMRI studies of mammalian cortex.     

An investigation of motion correction algorithms for pediatric spinal cord DTI in healthy subjects and patients with spinal cord injury

Patient and physiological motion can cause artifacts in DTI of the spinal cord which can impact image quality and diffusion indices. The purpose of this investigation was to determine a reliable motion correction method for pediatric spinal cord DTI and show effects of motion correction on DTI parameters in healthy subjects and patients with spinal cord injury. Ten healthy subjects and ten subjects with spinal cord injury were scanned using a 3 T scanner. Images were acquired with an inner field-of-view DTI sequence covering cervical spine levels C1 to C7. Images were corrected for motion using two types of transformation (rigid and affine) and three cost functions. Corrected images and transformations were examined qualitatively and quantitatively using in-house developed code. Fractional anisotropy (FA) and mean diffusivity (MD) indices were calculated and tested for statistical significance pre- and post- motion correction. Images corrected using rigid methods showed improvements in image quality, while affine methods frequently showed residual distortions in corrected images. Blinded evaluation of pre and post correction images showed significant improvement in cord homogeneity and edge conspicuity in corrected images (p < 0.0001). The average FA changes were statistically significant (p < 0.0001) in the spinal cord injury group, while healthy subjects showed less FA change and were not significant. In both healthy subjects and subjects with spinal cord injury, quantitative and qualitative analysis showed the rigid scaled-least-squares registration technique to be the most reliable and effective in improving image quality.     

partially saturated fluid attenuated inversion recovery (FLAIR) sequences in multiple sclerosis: Comparison with fully relaxed FLAIR and conventional spin-echo

Fluid attenuated inversion recovery (FLAIR) sequences produce selective cerebrospinal fluid (CSF) suppression by employing a very long inversion time (TI). We used the FLAIR sequence to study patients with multiple sclerosis (MS) at 0.6 T. So far, a very long TR (and long acquisition time) has been used in a fully relaxed (FR-FLAIR) system. To speed up the FLAIR sequences, we used a shorter TR, and demonstrated that complete CSF suppression can be maintained with partial saturation (PS-FLAIR) by reducing TI at the same time. The introduction of partial saturation, however, reduced the contrast between lesions and normal appearing white matter (NAWM). Suboptimal CSF suppression therefore had to be accepted to maintain sufficient lesion to NAWM contrast. Using a TE of 60 ms, the PS-FLAIR and FR-FLAIR performed equally well in the detection of MS-lesions, although the former provided poorer CSF suppression. Both FLAIR sequences, however, provided poorer contrast between lesions and NAWM compared to conventional spin-echo sequences. Although the long acquisition time of the FLAIR sequence can be reduced by using partial saturation, complete CSF suppression and good lesion to NAWM contrast are incompatible at short TRs. Using a TE of 60 ms, conventional spin-echo sequences detect more lesions and provide better contrast between lesions and NAWM than FLAIR sequences in MS patients.     

The influence of hyperoxia on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and cerebral blood flow velocity in the middle cerebral artery (CBFVMCA) in human volunteers

Conflicting results reported on the effects of hyperoxia on cerebral hemodynamics have been attributed mainly to methodical and species differences. In the present study contrast-enhanced magnetic resonance imaging (MRI) perfusion measurement was used to analyze the influence of hyperoxia (fraction of inspired oxygen (FiO2) = 1.0) on regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) in awake, normoventilating volunteers (n = 19). Furthermore, the experiment was repeated in 20 volunteers for transcranial Doppler sonography (TCD) measurement of cerebral blood flow velocity in the middle cerebral artery (CBFV(MCA)). When compared to normoxia (FiO2 = 0.21), hyperoxia heterogeneously influenced rCBV (4.95 +/- 0.02 to 12.87 +/- 0.08 mL/100g (FiO2 = 0.21) vs. 4.50 +/- 0.02 to 13.09 +/- 0.09 mL/100g (FiO2 = 1.0). In contrast, hyperoxia diminished rCBF in all regions (68.08 +/- 0.38 to 199.58 +/- 1.58 mL/100g/min (FiO2 = 0.21) vs. 58.63 +/- 0.32 to 175.16 +/- 1.51 mL/100g/min (FiO2 = 1.0)) except in parietal and left frontal gray matter. CBFV(MCA) remained unchanged regardless of the inspired oxygen fraction (62 +/- 9 cm/s (FiO2 = 0.21) vs. 64 +/- 8 cm/s (FiO2 = 1.0)). Finding CBFV(MCA) unchanged during hyperoxia is consistent with the present study's unchanged rCBF in parietal and left frontal gray matter. In these fronto-parietal regions predominantly fed by the middle cerebral artery, the vasoconstrictor effect of oxygen was probably counteracted by increased perfusion of foci of neuronal activity controlling general behavior and arousal.     

Effect of vasodilator hydralazine on tumor microvascular random flow and blood volume as measured by intravoxel incoherent motion (IVIM) weighted MRI in conjunction with Gd-DTPA-Albumin enhanced MRI.

We studied the effect of hydralazine on tumor blood volume fraction and microvascular random flow velocity magnitude by IVIM weighted MRI in conjunction with dynamic Gd-DTPA-Albumin enhanced MRI. Blood volume fraction maps were obtained from the dynamic Gd-DTPA-Albumin enhanced MRI measurements. The average blood volume fraction of R3230 AC adenocarcinoma decreased from 0.125 +/- 0.022 (s.d.) ml/g to 0.105 +/- 0.018 (s.d.) ml/g (p < 0.001) after the administration of hydralazine at a dose of 5 mg/kg. The microvascular random flow velocity magnitude maps were obtained from the IVIM weighted MRI signals by utilizing the Gd-DTPA-Albumin measured blood volume fractions as an input in the compartmental modeling analysis of the IVIM weighted MRI signal. The random-directional microvascular flow induced MRI signal attenuation was separated from the molecular diffusion induced signal attenuation. Flow induced attenuation was more significant after the administration of hydralazine. The mean microvascular random flow velocity magnitude increased from 0.52 +/- 0.15 (s.d.) mm/sec to 0.73 +/- 0.23 (s.d.) mm/sec (p < 0.05) in the presence of the above blood volume fraction change.     

Renal plasma flow (RPF) measured with multiple-inversion-time arterial spin labeling (ASL) and tracer kinetic analysis: Validation against a dynamic contrast-enhancement method

PurposeTo propose and validate a method for accurately quantifying renal plasma flow (RPF) with arterial spin labeling (ASL).Materials and methodsThe proposed method employs a tracer-kinetic approach and derives perfusion from the slope of the ASL difference signal sampled at multiple inversion-times (TIs). To validate the method's accuracy, we performed a HIPAA-compliant and IRB-approved study with 15 subjects (9 male, 6 female; age range 24–73) to compare RPF estimates obtained from ASL to those from a more established dynamic contrast-enhanced (DCE) MRI method. We also investigated the impact of TI-sampling density on the accuracy of estimated RPF.ResultsGood agreement was found between ASL- and DCE-measured RPF, with a mean difference of 9 ± 30 ml/min and a correlation coefficient R = 0.92 when ASL signals were acquired at 16 TIs and a mean difference of 9 ± 57 ml/min and R = 0.81 when ASL signals were acquired at 5 TIs. RPF estimated from ASL signals acquired at only 2 TIs (400 and 1200 ms) showed a low correlation with DCE-measured values (R = 0.30).ConclusionThe proposed ASL method is capable of measuring RPF with an accuracy that is comparable to DCE MRI. At least 5 TIs are recommended for the ASL acquisition to ensure reliability of RPF measurements.     

Sevoflurane and nitrous oxide increase regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) in a drug-specific manner in human volunteers

Anesthesia for diagnostic procedures, e.g., MRI measurements, has increasingly used sevoflurane and nitrous oxide in recent years. Sevoflurane and nitrous oxide are known cerebrovasodilatators, however, which potentially interferes with MRI examination of cerebral hemodynamics. To compare the effects of relevant equianesthetic concentrations (0.4 MAC) of both drugs on regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) we used contrast-enhanced magnetic resonance imaging (MRI) perfusion measurement, which has the advantage of providing regional anatomic resolution.

Sevoflurane increased rCBF more than did nitrous oxide in all regions except in parietal and frontal gray matter. Nitrous oxide, by contrast, increased rCBV in most of the gray matter regions more than did sevoflurane. In summary we show that, in contrast to nitrous oxide, sevoflurane supratentorially reversed the anterior-posterior gradient in rCBF and typically redistributed rCBF to infratentorial gray matter. In contrast, nitrous oxide increased rCBV more than did sevoflurane. Both inhalational anesthetics had a drug-specific influence on cerebral hemodynamics, which is of importance when interpreting MRI studies of cerebral hemodynamics in anesthetized patients.     

Correlation between spinal cord diffusion tensor imaging and postural response latencies in persons with multiple sclerosis: A pilot study

PurposeLonger latency of postural response in multiple sclerosis (MS) may be linked to imbalance and increased likelihood of falls. It may be caused by the compromised microstructural integrity in the spinal cord, as evidenced by slowed somatosensory conduction in the spinal cord. Thus, the purpose of this study is to investigate the correlation between latency of postural responses and microstructural integrity of the cervical spinal cord, the region particularly related to the disease severity in MS, using diffusion tensor imaging (DTI) metrics.MethodsSeventeen persons with MS with mild-to-moderate disease severity were enrolled in this study. Postural response latencies of each patient were measured using electromyography of the tibialis anterior muscle (TA) and gastrocnemius muscle (GN) in response to surface perturbations. Cervical spinal cord DTI images were obtained from each patient. DTI mean, radial, axial diffusivity, and fractional anisotropy (FA) were measured between segments C4 and C6. Correlations of DTI metrics with postural response latencies, expanded disability status scale (EDSS) scores, and 25-foot walk (T25FW) were assessed using the Spearman's rank correlation coefficient at α = 0.05.ResultsLower FA was significantly correlated with longer latencies measured on right TA in response to forward postural perturbations (r = −0.51, p = .04). DTI metrics showed no significant correlations with EDSS scores (r = −0.06–0.09, p = .73–0.95) or T25FW (r = −0.1–0.14, p = .6–0.94). DTI metrics showed no significant differences between subjects with and without spinal cord lesions (p = .2–0.7).ConclusionsOur results showed a significant correlation between lower FA in the cervical spinal cord and longer latencies measured on right TA in response to forward postural perturbations in persons with MS, suggesting that impaired cervical spinal cord microstructure assessed by DTI may be associated with the delayed postural responses.     

N-Acetylaspartate concentrations in the thalami of neuropathic pain patients and healthy comparison subjects measured with (1)H-MRS

We investigated the absolute concentration of N-acetylaspartate (NAA) in the thalami of neuropathic pain patients and healthy comparison subjects by single-voxel proton magnetic resonance spectroscopy ((1)H-MRS). (1)H-MRS was performed with a 1.5-T MR system on a voxel in the thalamus bilaterally in 9 neuropathic pain patients and 14 healthy control subjects. We measured the absolute concentration of NAA using a linear combination model. The NAA concentration in the thalamus decreased significantly on the contralateral side in seven patients and on the ipsilateral side in two patients, as compared with the mean NAA concentration of the healthy control subjects. The NAA concentrations in two patients who did not respond to standard pain treatments were extremely decreased. Our results using (1)H-MRS suggest that neuropathic pain seems to be associated with an abnormal balance of the neural activity in the thalamus. The NAA concentration of the thalamus may be related to the efficacy of therapy. (1)H-MRS may serve as a useful noninvasive tool for evaluating thalamic neural activity in neuropathic pain patients.     

Entropy generation (irreversibility) associated with flow and heat transport mechanism in Sisko nanomaterial

Here a novel applications of entropy generation optimization is presented for nonlinear Sisko nanomaterial flow by rotating stretchable disk. Flow is examined in the absence of magnetohydrodynamics and Joule heating. Total irreversibility rate (entropy generation rate) is investigated for different flow parameters. Heat source/sink and viscous dissipation effects are considered. Impacts of Brownian motion and thermophoresis on irreversibility have been analyzed. Governing flow equations comprise momentum, energy and nanoparticle concentration. Von Karman's similarity variables are implemented for reduction of PDEs into ODEs. Homotopy analysis technique for series solutions is implemented. Attention is given to the irreversibility. The impacts of different flow parameters on velocity, nanoparticle concentration, temperature and irreversibility rate are graphically presented. From obtained results it is examined that irreversibility rate enhances for larger estimation of Brinkman number and diffusion. Furthermore it is also examined that temperature and nanoparticle concentration show contrast behavior through Prandtl number and Brownian motion.     

Comparison between Si(100) and Si(111) in the reaction with oxygen at high temperatures

In this Letter, both the dynamics and kinetics of the reaction of oxygen molecules on Si(100)p2 × 1 and Si(111)7 × 7 and 1× 1 surfaces are compared. In all three cases, two distinct adsorption channels were observed. For oxygen molecules with translational energies less than 0.08 eV, the initial sticking is not sensitive to the energy or the angle of incidence, but displays a high sensitivity to the surface structure. At higher energies, a second channel becomes effective. The initial sticking coefficient increases rapidly and scales with the normal component of the translational energy, but the dependence on surface structure is greatly diminished. The kinetics of SiO formation are qualitatively similar on all surfaces with slightly higher rates on Si(111).     

Conditions and instability in f(R) gravity with non-minimal coupling between matter and geometry

In this paper, on the basis of the generalized f(R) gravity model with arbitrary coupling between geometry and matter, four classes of f(R) gravity models with non-minimal coupling between geometry and matter will be studied. By means of conditions of power-law expansion and the equation of state of matter less than ?1/3, the relationship among p, w and n, the conditions and the candidate for late-time cosmic accelerated expansion will be discussed in the four classes of f(R) gravity models with non-minimal coupling. Furthermore, in order to keep to considering models that are realistic ones, the Dolgov–Kawasaki instability will be investigated in each of them.     

Gravitational constant in f(R) theories of gravity with non-minimal coupling between matter and geometry

We study the effect of the non-minimal coupling between matter and geometry on the gravitational constant in the context of f(R) theories of gravity on cosmic scales. For a class of f(R) models,the result shows that the value of the gravitational constant not only changes over time but also has the dampened oscillation behavior.Compared with the result of the standard ACDM model, the consequence suggests that the coupling between matter and geometry should be weak.     

Relationships between occurrence of superconductivity and crystal structure in new equiatomic ternary silicides MTSi (M = Ti,Zr, Hf and T = Ru,Os, Rh)

With the preparation of the new ternary equiatomic silicides HfRuSi, TiOsSi, HfOsSi, ZrRhSi and HfRhSi, the complete series of the MTSi compounds (with M = Ti,Zr,Hf and T = Fe,Ru,Os,Co,Rh,Ir) has now been obtained. The TiNiSitype structure favors the appearance of superconductivity for the ternary silicides in contrast to what is observed for ternary equiatomic phosphides and arsenides for which the ordered Fe₂Ptype is more favorable than the TiNiSi-type. The presence of 3d-elements such as Ti, Fe or Co cancels the superconductivity whatever the ternary compounds considered, silicides, phosphides or arsenides.     

Assessment of the amount of body water in the Red Knot (Calidris canutus): an evaluation of the principle of isotope dilution with 2H, (17)O, and (18)O as measured with laser spectrometry and isotope ratio mass spectrometry

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2H, (17)O, and (18)O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2H and (18)O only) and a stable isotope ratio infrared laser spectrometry (2H, (17)O, and (18)O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the (17)O and (18)O measurements.