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Spin Labeling (spin + labeling)
Kinds of Spin Labeling Selected AbstractsImaging brain activity during natural vision using CASL perfusion fMRIHUMAN BRAIN MAPPING, Issue 7 2007Hengyi Rao Abstract Functional MRI (fMRI) has begun to be used to explore human brain activity during ecological and natural conditions. Arterial spin labeling (ASL) perfusion fMRI provides an appealing approach for imaging sustained brain activity during natural conditions because of its long-term temporal stability and ability to noninvasively quantify absolute cerebral blood flow (CBF). The present study used ASL perfusion fMRI to measure brain activation patterns associated with natural vision by concurrently recording CBF and blood oxygen level-dependent (BOLD) contrasts while subjects were freely viewing a cartoon movie. Reliable quantitative whole-brain CBF values (,60 mL/100g/min) as well as regional CBF values (45,80 mL/100g/min) were measured during movie viewing and resting states. The perfusion contrast revealed CBF increases in multiple visual pathway areas and frontal areas, and CBF decreases in ventromedial frontal cortex and superior temporal cortex during movie viewing compared to resting states. Concurrent BOLD contrast revealed similar but weaker activation and deactivation patterns. Regression analyses of both CBF data and BOLD data showed significant associations between activation in the middle temporal (MT) region and subjects' perception of motion. Region of interest analysis based on a priori literature-defined MT demonstrated significant monotonic stepwise associations between the intensity of motion perception and the CBF and BOLD signal changes. These results demonstrate the feasibility of using ASL perfusion fMRI for imaging both sustained and dynamic effects in neural activation during natural and ecologically valid situations, and support the notion of maintained functional segregation and specialization during natural vision. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source] PDK1 and PKB/Akt: Ideal Targets for Development of New Strategies to Structure-Based Drug DesignIUBMB LIFE, Issue 3 2003Thomas Harris Abstract Growth factor binding events to receptor tyrosine kinases result in activation of phosphatidylinositol 3-kinase (PI3K), and activated PI3K generates the membrane-bound second messengers phosphatidylinositol 3,4-diphosphate [PI(3,4)P2] and PI(3,4,5)P3, which mediate membrane translocation of the phosphoinositide-dependent kinase-1 (PDK1) and protein kinase B (PKB, also known as Akt). In addition to the kinase domain, PDK1 and PKB contain a pleckstrin homology (PH) domain that binds to the second messenger, resulting in the phosphorylation and activation of PKB by PDK1. Recent evidence indicates that constitutive activation of PKB contributes to cancer progression by promoting proliferation and increased cell survival. The indicating of PDK1 and PKB as primary targets for discovery of anticancer drugs, together with the observations that both PDK1 and PKB contain small-molecule regulatory binding sites that may be in proximity to the kinase active site, make PDK1 and PKB ideal targets for the development of new strategies to structure-based drug design. While X-ray structures have been reported for the kinase domains of PDK1 and PKB, no suitable crystals have been obtained for either PDK1 or PKB with their PH domains intact. In this regard, a novel structure-based strategy is proposed, which utilizes segmental isotopic labeling of the PH domain in combination with site-directed spin labeling of the kinase active site. Then, long-range distance restraints between the 15N-labeled backbone amide groups of the PH domain and the unpaired electron of the active site spin label can be determined from magnetic resonance studies of the enhancement effect that the paramagnetic spin label has on the nuclear relaxation rates of the amide protons. The determination of the structure and position of the PH domain with respect to the known X-ray structure of the kinase active site could be useful in the rational design of potent and selective inhibitors of PDK1 and PKB by 'linking' the free energies of binding of substrate (ATP) analogs with analogs of the inositol polar head group of the phospholipid second messenger. The combined use of X-ray crystallography, segmental isotopic and spin labeling, and magnetic resonance studies can be further extended to the study of other dynamic multidomain proteins and targets for structure-based drug design. IUBMB Life, 55: 117-126, 2003 [source] Continuous arterial spin labeling using a train of adiabatic inversion pulses,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2005Bradford A. Moffat PhD Abstract Purpose To develop a simple and robust magnetic resonance imaging (MRI) pulse sequence for the quantitative measurement of blood flow in the brain and cerebral tumors that has practical implementation advantages over currently used continuous arterial spin labeling (CASL) schemes. Materials and Methods Presented here is a single-coil protocol that uses a train of hyperbolic secant inversion pulses to produce continuous arterial spin inversion for perfusion weighting of fast spin echo images. Flow maps of normal rat brains and those containing a 9L gliosarcoma orthotopic tumor model conditions were acquired with and without carbogen. Results The perfusion-weighted images have reduced magnetization transfer signal degradation as compared to the traditional single-coil CASL while avoiding the use of a more complex two-coil CASL technique. Blood flow measurements in tumor and normal brain tissue were consistent with those previously reported by other CASL techniques. Contralateral and normal brain showed increased blood flow with carbogen breathing, while tumor tissue lacked the same CO2 reactivity. Conclusion This variation of the CASL technique is a quantitative, robust, and practical single-coil method for measuring blood flow. This CASL method does not require specialized radiofrequency coils or amplifiers that are not routinely used for anatomic imaging of the brain, therefore allowing these flow measurements to be easily incorporated into traditional rodent neuroimaging protocols. J. Magn. Reson. Imaging 2005;21:290,296. © 2005 Wiley-Liss, Inc. [source] Methodology of brain perfusion imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2001Emmanuel L. Barbier PhD Abstract Numerous techniques have been proposed in the last 15 years to measure various perfusion-related parameters in the brain. In particular, two approaches have proven extremely successful: injection of paramagnetic contrast agents for measuring cerebral blood volumes (CBV) and arterial spin labeling (ASL) for measuring cerebral blood flows (CBF). This review presents the methodology of the different magnetic resonance imaging (MRI) techniques in use for CBV and CBF measurements and briefly discusses their limitations and potentials. J. Magn. Reson. Imaging 2001;13:496,520. © 2001 Wiley-Liss, Inc. [source] Quantitative lung perfusion mapping at 0.2 T using FAIR True-FISP MRIMAGNETIC RESONANCE IN MEDICINE, Issue 5 2006Petros Martirosian Abstract Perfusion measurements in lung tissue using arterial spin labeling (ASL) techniques are hampered by strong microscopic field gradients induced by susceptibility differences between the alveolar air and the lung parenchyma. A true fast imaging with steady precession (True-FISP) sequence was adapted for applications in flow-sensitive alternating inversion recovery (FAIR) lung perfusion imaging at 0.2 Tesla and 1.5 Tesla. Conditions of microscopic static field distribution were assessed in four healthy volunteers at both field strengths using multiecho gradient-echo sequences. The full width at half maximum (FWHM) values of the frequency distribution for 180,277 Hz at 1.5 Tesla were more than threefold higher compared to 39,109 Hz at 0.2 Tesla. The influence of microscopic field inhomogeneities on the True-FISP signal yield was simulated numerically. Conditions allowed for the development of a FAIR True-FISP sequence for lung perfusion measurement at 0.2 Tesla, whereas at 1.5 Tesla microscopic field inhomogeneities appeared too distinct. Perfusion measurements of lung tissue were performed on eight healthy volunteers and two patients at 0.2 Tesla using the optimized FAIR True-FISP sequence. The average perfusion rates in peripheral lung regions in transverse, sagittal, and coronal slices of the left/right lung were 418/400, 398/416, and 370/368 ml/100 g/min, respectively. This work suggests that FAIR True-FISP sequences can be considered appropriate for noninvasive lung perfusion examinations at low field strength. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Normal cerebral perfusion measurements using arterial spin labeling: Reproducibility, stability, and age and gender effectsMAGNETIC RESONANCE IN MEDICINE, Issue 4 2004Laura M. Parkes Abstract Before meaningful conclusions can be drawn from clinical measures of cerebral blood perfusion, the precision of the measurement must be determined and set in the context of inter- and intrasubject sources of variability. This work establishes the reproducibility of perfusion measurements using the noninvasive MRI technique of continuous arterial spin labeling (CASL). Perfusion was measured in 34 healthy normal subjects. Intersubject variability was assessed, and age and gender contributions were estimated. Intersubject variation was found to be large, with up to 100% perfusion difference for subjects of the same age and gender. Repeated measurements in one subject showed that perfusion remains remarkably stable in the short term when compared with intersubject variation and the large capacity for perfusion change in the brain. A significant decrease in the ratio of gray-matter to white-matter perfusion was found with increasing age (0.79% per year (P < 0.0005)). This appears to be due mainly to a reduction in gray-matter perfusion, which was found to decrease by 0.45% per year (P = 0.04). Regional analysis suggested that the gray-matter age-related changes were predominantly localized in the frontal cortex. Whole-brain perfusion was 13% higher (P = 0.02) in females compared to males. Magn Reson Med 51:736,743, 2004. © 2004 Wiley-Liss, Inc. [source] Functional perfusion imaging using continuous arterial spin labeling with separate labeling and imaging coils at 3 TMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Toralf Mildner Abstract Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin-echo echo-planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger-tapping task. Signal differences between the condition of finger tapping and the resting state were between ,0.5% and ,1.1 % among the subjects. The imaging protocol included a long post-label delay (PLD) to reduce transit time effects. Labeling was applied for all repetitions of the functional run to reduce the sampling interval. Magn Reson Med 49:791,795, 2003. © 2003 Wiley-Liss, Inc. [source] Improved perfusion quantification in FAIR imaging by offset correctionMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001Karam Sidaros Abstract Perfusion quantification using pulsed arterial spin labeling has been shown to be sensitive to the RF pulse slice profiles. Therefore, in Flow-sensitive Alternating-Inversion Recovery (FAIR) imaging the slice selective (ss) inversion slab is usually three to four times thicker than the imaging slice. However, this reduces perfusion sensitivity due to the increased transit delay of the incoming blood with unperturbed spins. In the present article, the dependence of the magnetization on the RF pulse slice profiles is inspected both theoretically and experimentally. A perfusion quantification model is presented that allows the use of thinner ss inversion slabs by taking into account the offset of RF slice profiles between ss and nonselective inversion slabs. This model was tested in both phantom and human studies. Magn Reson Med 46:193,197, 2001. © 2001 Wiley-Liss, Inc. [source] Quantitative ASL muscle perfusion imaging using a FAIR-TrueFISP technique at 3.0,TNMR IN BIOMEDICINE, Issue 1 2006Andreas Boss Abstract The feasibility of muscle perfusion imaging with diagnostic image quality was demonstrated using the FAIR-TrueFISP arterial spin labeling technique on a clinical 3.0,T whole-body scanner. In eight healthy volunteers (24 to 42 years old), quantitative perfusion maps of the forearm musculature were acquired before and after intense exercise. All measurements were carried out in a 3.0,T whole-body MR unit in combination with an eight-channel head coil. Pulsed arterial spin labeling and data recording were performed with an adapted FAIR-TrueFISP technique and quantitative perfusion maps were calculated on a pixel-by-pixel basis by means of the extended Bloch equations. Perfusion images with an in-plane resolution of 1,mm showed no significant distortions or blurring. Perfusion,time curves could be recorded with a temporal resolution of 6.4,s. Maximum perfusion in the musculature was found ,2,min after exercise, reaching values of up to 220,mL/min per 100,g of tissue with good delineation between the active muscles and the musculature not involved in the exercise. In conclusion, the TrueFISP pulsed arterial spin labeling technique allows patient-friendly assessment of muscular perfusion in a clinical whole-body scanner. Copyright © 2006 John Wiley & Sons, Ltd. [source] Continuous arterial spin labeling at the human common carotid artery: the influence of transit timesNMR IN BIOMEDICINE, Issue 1 2005Toralf Mildner Abstract In evaluating the sensitivity of arterial spin labeling (CASL) and for quantification of perfusion, knowledge of the transit time from the labeling plane to the imaging slice is crucial. The purpose of the current study was to obtain estimates of transit times relevant under the specific experimental conditions of CASL in human subjects using a separate local labeling coil at the neck. Specifically, the post-label delay (PLD), i.e. the time between the end of the labeling period and the image acquisition, was varied either with or without additional application of crusher gradients to suppress intravascular signal contributions. The overall sensitivity change for varying the PLD between 1000 and 1700,ms was low. A tissue transit time from the neck to an axial supraventricular section through Broca's knee was obtained by fitting the PLD dependence to a two-compartment model. Averaging over subjects yielded 1930,±,110,ms for the tissue transit time, and 73,±,5,ml,min,1 100,g,1 for the cerebral blood flow. Small areas that exhibited a very high signal change upon labeling were indicative of regional variation in cerebral blood flow related to vascular anatomy. Copyright © 2004 John Wiley & Sons, Ltd. [source] Arterial spin-labeled perfusion combined with segmentation techniques to evaluate cerebral blood flow in white and gray matter of children with sickle cell anemia,PEDIATRIC BLOOD & CANCER, Issue 1 2009Kathleen J. Helton MD Abstract Background Changes in cerebral perfusion are an important feature of the pathophysiology of sickle cell anemia (SCA); cerebrovascular ischemia occurs frequently and leads to neurocognitive deficits, silent infarcts, and overt stroke. Non-invasive MRI methods to measure cerebral blood flow (CBF) by arterial spin labeling (ASL) afford new opportunities to characterize disease- and therapy-induced changes in cerebral hemodynamics in patients with SCA. Recent studies have documented elevated gray matter (GM) CBF in untreated children with SCA, but no measurements of white matter (WM) CBF have been reported. Procedures Pulsed ASL with automated brain image segmentation-classification techniques were used to determine the CBF in GM, WM, and abnormal white matter (ABWM) of 21 children with SCA, 18 of whom were receiving hydroxyurea therapy. Results GM and WM CBF were highly associated (R2,=,0.76, P,<,0.0001) and the GM to WM CBF ratio was 1.6 (95% confidence interval: 1.43,1.83). Global GM CBF in our treated cohort was 87,±,24 mL/min/100 g, a value lower than previously reported in untreated patients with SCA. CBF was elevated in normal appearing WM (43,±,14 mL/min/100 g) but decreased in ABWM (6,±,12 mL/min/100 g), compared to published normal pediatric controls. Hemispheric asymmetry in CBF was noted in most patients. Conclusions These perfusion measurements suggest that hydroxyurea may normalize GM CBF in children with SCA, but altered perfusion in WM may persist. This novel combined approach for CBF quantification will facilitate prospective studies of cerebral vasculopathy in SCA, particularly regarding the effects of treatments such as hydroxyurea. Pediatr Blood Cancer 2009;52:85,91. © 2008 Wiley-Liss, Inc. [source] Arterial spin labeling demonstrates that focal amygdalar glutamatergic agonist infusion leads to rapid diffuse cerebral activationACTA NEUROLOGICA SCANDINAVICA, Issue 3 2010J. P. Munasinghe Munasinghe JP, Banerjee M, Acosta MT, Banks M, Heffer A, Silva AC, Koretsky A, Theodore WH. Arterial spin labeling demonstrates that focal amygdalar glutamatergic agonist infusion leads to rapid diffuse cerebral activation. Acta Neurol Scand: 2010: 121: 209,216. © 2009 The Authors Journal compilation © 2009 Blackwell Munksgaard. Objectives,,, To investigate acute effects of intra-amygdalar excitatory amino acid administration on blood flow, relaxation time and apparent diffusion coefficient in rat brain. Materials and methods,,, Several days after MR-compatible cannula placement in right basolateral amygdala, anesthetized rats were imaged at 7 T. Relative cerebral blood flow (CBF) was measured before and 60 min after infusion of 10 nmol KA, cAMPA, ATPA, or normal saline using arterial spin labeling. Quantitative T2 and diffusion-weighted images were acquired. rCBF, T2 and ADC values were evaluated in bilateral basolateral amygdala, hippocampus, basal ganglia, frontal and parietal regions. Results,,, KA led to the highest, and ATPA lowest bilateral rCBF increases. Time courses varied among drugs. T2 for KA and AMPA was higher while ADC was lower for KA. Conclusions,,, Intra-amygdalar injection of GluR agonists evoked bilateral seizure activity and increased rCBF, greater for KA and AMPA than selective ATPA GluR5 activation. [source] | |||||||||||||