Acquisition time and reproducibility of continuous arterial spin-labeling perfusion imaging at 3 T

SUMMARY: Arterial spin-labeling (ASL) is a relatively new and noninvasive MR imaging technique, used to measure cerebral blood flow (CBF). Scanning time and reproducibility remain important issues in the clinical applicability of ASL. We expected both to benefit from higher field strengths. We describe that when performing ASL at 3T, 20 averages suffice to obtain steady and reproducible CBF values. Scanning time can be as short as 3 minutes. A rterial spin labeling (ASL) is a noninvasive MR imaging technique, used for visualization and quantification of cerebral perfusion. Cerebral blood flow (CBF) values measured by ASL are comparable with CBF values measured by conventional techniques (eg, positron-emission tomography or susceptibility-weighted MR imaging). ASL is based on magnetic labeling of arterial blood water protons, which are used as an endogenous tracer of flow. Magnetic inversion takes place in a plane proximal to the brain. The decay rate of the labeled spins is sufficiently long to visualize perfusion of brain vasculature and microvasculature. Perfusion images are obtained by subtraction of successively acquired labeled and nonlabeled control images. In general, 40 to 60 paired acquisitions are averaged to improve perfusion signal intensity. ASL sequences differ in the way magnetic labeling is applied and are commonly classified as continuous or pulsed ASL (CASL or PASL, respectively). In CASL, continuous adiabatic inversion of spins is applied. In PASL, labeling is performed at once over a wide spatial range. Pseudocontinuous ASL (pCASL) has been introduced recently and uses a series of discrete labeling pulses. 1-8 Despite its advantages, scanning time and reproducibility remain important issues in the clinical applicability of ASL. The use of higher-field strengths could overcome these issues because of increased signal-to-noise ratio, prolonged T1-weighted relaxation time of labeled blood, and better spatial and temporal resolution. Also, we hypothesized that acquisition-related reproducibility of ASL will improve at higher-field strengths, whereas physiology-related reproducibility will not change. Previous CASL reproducibility studies were performed at 1.5T with test-retest timeframes of at least 1 hour. Technique After approval of the local ethics committee and written informed consent from all volunteers, we scanned 10 volunteers (5 men; age range, 25-33 years) without known cerebrovascular disease during 3 different sessions within 3 weeks. Each session protocol consisted of 2 CASL sequences preceded by MR angiography. All scans were performed on a 3T Intera MR scanner with a transmit-receive head coil from the manufacturer (Philips Medical Systems, Best, the Netherlands). The 3D time-of-flight MR angiography was obtained to allow for careful planning of the labeling plane perpendicular to the distal ascending portion of the internal carotid and basilar arteries, 10 -20 mm below the circle of Willis. For the ASL sequences, we implemented the amplitude-modulated CASL approach described by Alsop and Detre 5 , without compromising clinical specific absorption rate levels. We used spin-echo single-shot echo-planar imaging. The imaging volume was positioned parallel to the labeling plane with its center 60 mm above the labeling plane. ASL parameters were TR, 4500 ms; TE, 32ms; flip angle, 90°; FOV, 210 ϫ 210; section thickness, 7 mm with 1-mm gap; matrix size, 64 ϫ 45 (reconstructed to 64 ϫ 64); 50 averages; labeling duration, 2.0 s; radiofrequency pulse amplitude, 3.5 T; gradient strength, 2.5 mT/m; modulation frequency, 250 Hz; and postlabeling delay, 1.2 to 2.2 s. FSL (FMRIB-Software-Library, Functional Magnetic Resonance Imaging of the Brain Centre, Department of Clinical Neurology, University of Oxford, Oxford, UK) was used for off-line data processing. f ϭ ⌬MR 1a 2␣M con {e ϪwR1a Ϫ e Ϫ(ϩW)R1a } in which f is CBF (mL/g/s), ␣ is the labeling efficiency at 3T (0.68), 7 is the blood-brain partition coefficient (0.98 mL/g), ⌬M is the difference between labeled image and control image intensity, R 1a is the longitudinal relaxation time of blood (0.67 s Ϫ1 ), M con is the average control image intensity, ⌻ is the labeling duration (2 s), and w is the postlabeling delay (1.2-2.2 s)

Degradation of haloaromatic compounds

An ever increasing number of halogenated organic compounds has been produced by industry in the last few decades. These compounds are employed as biocides, for synthetic polymers, as solvents, and as synthetic intermediates. Production figures are often incomplete, and total production has frequently to be extrapolated from estimates for individual countries. Compounds of this type as a rule are highly persistent against biodegradation and belong, as "recalcitrant" chemicals, to the class of so-called xenobiotics. This term is used to characterise chemical substances which have no or limited structural analogy to natural compounds for which degradation pathways have evolved over billions of years. Xenobiotics frequently have some common features. e.g. high octanol/water partitioning coefficients and low water solubility which makes for a high accumulation ratio in the biosphere (bioaccumulation potential). Recalcitrant compounds therefore are found accumulated in mammals, especially in fat tissue, animal milk supplies and also in human milk. Highly sophisticated analytical techniques have been developed for the detection of organochlorines at the trace and ultratrace level

Herkenning van kinderen met sikkelcelziekte in Nederland

Timely recognition of clinical signs and symptoms of sickle cell disease remains of great importance because the neonatal PKU screening program in The Netherlands that was introduced in January 1st 2007 will not reach all children with this disease. Of children that have been diagnosed in the Emma Children's Hospital AMC, Amsterdam, 20% would not have been reached by this new program: immigrant's children born abroad and adopted children. It goes without saying that also in children that have been born in the Netherlands before January 1st 2007 the diagnosis sickle cell disease should be considered in cases of disease-specific clinical symptoms. The initial clinical manifestation of sickle cell disease in children born in the Netherlands is potentially life-threatening in 8% (7/88), e.g. a pneumococcal infection or an acute splenic sequestration. Painful crisis, paleness and jaundice are the most common presenting symptoms. The median age at diagnosis of the group of Amsterdam children was 25 months. In view of the potential health benefit it is advised to test children from populations at risk, that are under the medical attention of a hospital for any reason, for the presence of sickle cell disease. This applies especially to children with a pneumococcal infectio

Een jaar neonatale screening op sikkelcelziekte in het Emma Kinderziekenhuis/Academisch Medisch Centrum te Amsterdam

Early detection of children with sickle cell disease, determination of carriership frequency as well as evaluation of the knowledge regarding this haemoglobinopathy in various ethnic risk groups. Prospective. From 1 November 1998 through to 31 October 1999, the ethnic background was recorded for consecutive pregnant women under care of the Academic Medical Centre, Amsterdam, the Netherlands, and the presence of carriership for sickle cell disease was evaluated. Carriers were asked about their knowledge of sickle cell disease. A diagnostic blood test of cord blood was also performed using a PCR which could detect both haemoglobin S and C mutations. Fifty-five carriers were detected in a group of 1,016 investigated pregnant women (5.4%). The carriership frequencies in Surinam and African women were 12 and 15.7%, respectively. Knowledge of sickle cell disease, its occurrence in populations at risk, as well as the terms 'inheritance' and 'carriership', differed substantially between Surinam and African women, with awareness being lower in the latter group. In six cases informed consent was not asked. All other 49 carriers consented to a diagnostic test. Two intrauterine deaths occurred. Four children had sickle cell disease: three had HbSS, one had HbSC. Nineteen children proved to be carriers for sickle cell disease, 18 were heterozygotes for HbS, one for HbC. This targeted neonatal screening for sickle cell disease was feasible in a hospital setting. The number of children diagnosed with the disease supports the wider implementation of this method of early detectio

Acquisition Time and Reproducibility of Continuous Arterial Spin-Labeling Perfusion Imaging at 3T

Arterial spin-labeling (ASL) is a relatively new and noninvasive MR imaging technique, used to measure cerebral blood flow (CBF). Scanning time and reproducibility remain important issues in the clinical applicability of ASL. We expected both to benefit from higher field strengths. We describe that when performing ASL at 3T, 20 averages suffice to obtain steady and reproducible CBF values. Scanning time can be as short as 3 minute

Preinduction of HSP70 promotes hypoxic tolerance and facilitates acclimatization to acute hypobaric hypoxia in mouse brain

It has been shown that induction of HSP70 by administration of geranylgeranylacetone (GGA) leads to protection against ischemia/reperfusion injury. The present study was performed to determine the effect of GGA on the survival of mice and on brain damage under acute hypobaric hypoxia. The data showed that the mice injected with GGA survived significantly longer than control animals (survival time of 9.55 ± 3.12 min, n = 16 vs. controls at 4.28 ± 4.29 min, n = 15, P < 0.005). Accordingly, the cellular necrosis or degeneration of the hippocampus and the cortex induced by sublethal hypoxia for 6 h could be attenuated by preinjection with GGA, especially in the CA2 and CA3 regions of the hippocampus. In addition, the activity of nitric oxide synthase (NOS) of the hippocampus and the cortex was increased after exposure to sublethal hypoxia for 6 h but could be inhibited by the preinjection of GGA. Furthermore, the expression of HSP70 was significantly increased at 1 h after GGA injection. These results suggest that administration of GGA improved survival rate and prevented acute hypoxic damage to the brain and that the underlying mechanism involved induction of HSP70 and inhibition of NOS activity