Spin Labeling Technique Research Articles

Overview and Critical Appraisal of Arterial Spin Labelling Technique in Brain Perfusion Imaging.

Arterial spin labelling (ASL) allows absolute quantification of CBF via a diffusible intrinsic tracer (magnetically labelled blood water) that disperses from the vascular system into neighbouring tissue. Thus, it can provide absolute CBF quantification, which eliminates the need for the contrast agent, and can be performed repeatedly. This review will focus on the common ASL acquisition techniques (continuous, pulsed, and pseudocontinuous ASL) and how ASL image quality might be affected by intrinsic factors that may bias the CBF measurements. We also provide suggestions to mitigate these risks, model appropriately the acquired signal, increase the image quality, and hence estimate the reliability of the CBF, which consists an important noninvasive biomarker. Emerging methodologies for extraction of new ASL-based biomarkers, such as arterial arrival time (AAT) and arterial blood volume (aBV), will be also briefly discussed.

Transit time corrected arterial spin labeling technique aids to overcome delayed transit time effect

This study aimed to evaluate the usefulness of transit time corrected cerebral blood flow (CBF) maps based on multi-phase arterial spin labeling MR perfusion imaging (ASL-MRP). The Institutional Review Board of our hospital approved this retrospective study. Written informed consent was waived. Conventional and multi-phase ASL-MRPs and dynamic susceptibility contrast MR perfusion imaging (DSC-MRP) were acquired for 108 consecutive patients. Vascular territory-based volumes of interest were applied to CBF and time to peak (TTP) maps obtained from DSC-MRP and CBF maps obtained from conventional and multi-phase ASL-MRPs. The concordances between normalized CBF (nCBF) from DSC-MRP and nCBF from conventional and transition time corrected CBF maps from multi-phase ASL-MRP were evaluated using Bland-Altman analysis. In addition, the dependence of difference between nCBF (ΔnCBF) values obtained from DSC-MRP and conventional ASL-MRP (or multi-phase ASL-MRP) on TTP obtained from DSC-MRP was also analyzed using regression analysis. The values of nCBFs from conventional and multi-phase ASL-MRPs had lower values than nCBF based on DSC-MRP (mean differences, 0.08 and 0.07, respectively). The values of ΔnCBF were dependent on TTP values from conventional ASL-MRP technique (F = 5.5679, P = 0.0384). No dependency of ΔnCBF on TTP values from multi-phase ASL-MRP technique was revealed (F = 0.1433, P > 0.05). The use of transit time corrected CBF maps based on multi-phase ASL-MRP technique can overcome the effect of delayed transit time on perfusion maps based on conventional ASL-MRP.

Positron Emission Tomographic Imaging Elucidates the Complex Relationship Between Glucose Uptake and Tissue Blood Flow Mechanism in Squamous Cell Oral Cancer Patients.

BackgroundThrough the clinical use of positron emission tomography, we aimed to elucidate the complex relationship between glucose uptake and squamous cell oral cancer (ScOC) growth, along with its mechanism with respect to tissue blood flow (tBF).Material/MethodsWe retrospectively reviewed a total of 69 newly diagnosed ScOC patients by Fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography (PET). Maximum and mean standard uptake values (SUV↑ and ) were recorded to assess glucose uptake. Multi-shot spin-echo echo-planar imaging-based pseudo-continuous arterial spin labeling (pcASL) technique at 3.0 T MRI was used to obtain tBF values in ScOC (tBF-ScOC). Patients were divided according to T-stage and location. Pearson’s correlation coefficients were calculated between both SUV and tBF-ScOC for significant correlations.ResultsForty-one (59.4%) patients had oropharynx and the other 28 (40.6%) patients had laryngopharynx. Significant positive correlations were detected between SUV↑, , tBF-ScOC and non-advanced T-stage (T1a, T1b, T2 and T3), while a negative correlation was observed in the advanced T-stage (T4a and T4b).ConclusionsUsing PET imaging, we established the relationship between glucose uptake and ScOC growth on the basis of the division of T-stage and tumor location of ScOC, thereby elucidating the underlying mechanism. Our findings provide insights important to the diagnosis, treatment, and care of ScOC patients.

Aberrant patterns of brain cerebral blood flow in Chinese han first-episode drug-naïve depressive patients with and without a family history of depression.

A positive family history plays a key role in the brain pathology of depression patients and previous research has confirmed that disturbed mood maintenance may be related to abnormal regional cerebral blood flow (rCBF). However, little is known about whether the rCBF is different between depression patients with and without family histories. To address this question, we examined the rCBF in drug-naïve, first-episode depression patients with and without family histories of depression using a 3D pseudo-continuous arterial spin-labelling technique. We found that decreased rCBF was predominantly observed in the patients without family histories, while decreased and increased rCBF co-existed in patients with family histories. The observed brain regions with altered rCBF were associated with affection processing, such as the prefrontal, occipital and insular areas. However the patterns of rCBF alteration observed in the present study were different from those found in previous studies where patients were compared with healthy controls. Our present findings, together with the findings from previous studies have prompted the need of a long-term follow-up study to characterize the brain features of the developmental trajectory of depression and investigate the targets for precise, personalized treatments.

Maximization of photocatalytic activity of Bi2S3/TiO2/Au ternary heterostructures by proper epitaxy formation and plasmonic sensitization

Ternary Bi2S3/TiO2/Au heterostructure has been successfully synthesized by decorationg Au nanoparticls onto binary Bi2S3/TiO2 heterostructure. Structural analysis suggests that the heterostructure consists of orthorhombic Bi2S3, tetragonal anatase TiO2 and face centered cubic Au. The appearance of extra Raman peak at 123cm−1 and the modification of Raman peaks of Bi2S3 and TiO2 phases indicates a significant molecular interaction during growth of TiO2 nanocrystals (NCs) on the surface of Bi2S3 nanorods. Self assembly of nanorods triggered by oleic acid results in urchin like morphology of pure Bi2S3. The {011} facet of TiO2 nanocrystals grow epiaxially on {013} facet of Bi2S3 nanorods. Periodic arrangement of (111) plane of Au and (011) plane of Bi2S3 favors epitaxial growth in Bi2S3/TiO2/Au heterostructure. Unique design of the ternary heterostructure makes a preferable pathway for the photogenerated electrons by suppressing the electron-hole recombination. The observation of decreased electron spin resonance signal intensity based on spin label technique confirms the electron transfer from photoexcited heterostructure. Favorable energetic positions of conduction and valence band edges of semiconductors (Bi2S3 and TiO2) and Fermi level of metal (Au) are the key factors to enhance the photo catalytic activity of ternary heterostructure. Plasmonic phenomenon of metal (Au) nanoparticles by changing their size and shape was also investigated to remove organic pollutants from waste water.

The evolution of biomedical EPR (ESR)

Since the first EPR/ESR spectrum of a paramagnetic substance was published over 70 years ago, the technical improvements did not occur until after/during World War II with the advent of radar technology. The approaches to biomedical problems started somewhat later with the real burst of activity starting after the birth of the spin label technique about 50 years ago. The applications to proteins, then membranes and nucleic acids, and later applications to cells and eventually in-vivo on small animals and now humans has led EPR/ESR to finally being recognized as a uniquely powerful technique in the toolbox of techniques probing macromolecules and their interactions, free radical biology and its eventual value as a diagnostic technique. This article gives an overview of EPR/ESR studies of biomedically related systems, including proteins and enzymes. It presents a very personal historical perspective, briefly reviews the origins of the technique and reflects on possible future directions. As with NMR, advances in molecular biology and technology drastically changed the nature and focus of the technique, particularly the site directed spin labeling method that has been invaluable in determining protein and macromolecular structure by both EPR and NMR.

Functional assessment of prefrontal lobes in patients with major depression disorder using a dual-mode technique of 3D-arterial spin labeling and 18F-fluorodeoxyglucose positron emission tomography/computed tomography.

The aim of this study was to explore the functions of cerebral blood perfusion and glucose metabolism in the prefrontal lobe of patients with major depression disorder (MDD), and to analyze the correlations between these functional changes and depressive symptoms. 3D-arterial spin labeling (ASL) and 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) were successfully performed in 17 patients with MDD and 16 healthy controls in a resting state. The depressive symptoms of the patients were classified into seven factors and scored with the Hamilton Depression Rating Scale. Regional cerebral blood flow (CBF) values and standardized uptake values (SUV) of 18F-FDG in the whole brain were respectively compared between the patients and healthy controls using a two-sample t-test, and the correlations between the CBF and SUV in the prefrontal cerebral regions with the patients' Hamilton scores were evaluated using Pearson correlation analysis. Decreased regional CBF was indicated in the bilateral middle and the right superior frontal gyri, and decreased regional SUV was indicated in the bilateral superior, middle and inferior frontal gyri in the MDD patients compared with the controls. Positive correlations were observed between CBF values and aggregate Hamilton scores in the left middle and right middle frontal gyri of the patients. Positive correlations were also observed between SUVs and aggregate Hamilton scores in the left middle and right middle frontal gyri. 18F-FDG PET/CT was indicated to be more sensitive than 3D-ASL in identifying the functional abnormalities in the prefrontal lobe. Decreased CBF and SUV in the prefrontal lobe were closely correlated with Hamilton score. The left middle frontal gyrus may be a key functional region in MDD.

EPR Studies on the Properties of Model Photoreceptor Membranes Made of Natural and Synthetic Lipids

The membranes of retina photoreceptors have unique lipid composition. They contain a high concentration of polyunsaturated docosahexaenoic acid, with six double bonds, and are enriched in phosphatidylethanolamines. Based on their phospholipid composition and cholesterol content, membranes of photoreceptors can be divided into three types: plasma membrane, young disks membranes, and old disks membranes. High amount of docosahexaenoic acid, abundant illumination, and high respiratory demands make these membranes sensitive to oxidative stress and lipid peroxidation. Human retinas are not easily available for research, therefore most research is done on bovine retinas. However, to follow, in a controlled manner, the changes in membrane properties caused by different factors it seems advisable to apply carefully prepared models of photoreceptor membranes. Using synthetic lipids we prepared liposome models of three types of photoreceptor membranes, and by means of electron paramagnetic resonance spectroscopy and spin labeling technique we compared polarity and fluidity of those model membranes with the properties of membranes consisting of natural lipids extracted from photoreceptor outer segments of bovine retinas. Additionally, we studied the effect of oxidation on the membrane properties in the presence and in the absence of zeaxanthin, which is an antioxidant naturally present in the human retina. The results show that there are significant differences in polarity and fluidity between all investigated membranes, which reflect differences in their lipid composition. The properties of the membranes made of natural photoreceptor outer segment lipids are most similar to the ones of the models of old disks membranes. Oxidation did not change the membrane properties significantly; however, a slight ordering effect was observed in liposomes made of natural photoreceptor outer segment lipids and in the model of old disks membranes. Zeaxanthin affected polarity and fluidity mostly in the model of old disks membranes. The results show that by careful selection and appropriate proportions of lipid mixtures, it is possible to obtain synthetic membranes of the properties similar to the natural ones.

Apathy in depression: An arterial spin labeling study

IntroductionApathy is usually defined as a lack of goal-directed behavior. Although it is observed in about 30% of depressed patients, neurovascular mechanisms underpinning apathy remain little-known.ObjectivesThe main objective of this study was to compare the cerebral perfusion of apathetic depressed patients with non-apathetic depressed patients by arterial spin labeling (ASL), a quantitative and non-invasive perfusion magnetic resonance imaging (MRI) technique. The secondary objectives were to study their clinical profile and their correlation with cerebral perfusion data.MethodsThis study was conducted from a cohort of depressed patients in Rennes, France. Eighty-three depressed patients were included, of whom 22 were apathetic (AES≥42), 61 non-apathetic (AES < 42). Everyone got a clinical evaluation with scale screenings, especially for apathy (AES), anxiety (STAI) and anhedonia (SHAPS) as well as a cerebral MRI, including a pseudo-continuous ASL sequence.ResultsApathetic depressed patients were significantly less anxious and less anhedonic. Apathetic perfused better than non-apathetic in the inferior frontal gyrus (P = 0.022). We found a significant positive relationship between apathy and perfusion of the left frontal inferior gyrus (P = 0.05, r = 0.21). State-anxiety was positively correlated with perfusion of the cingulate cortex, the insula and the left amygdala. Anhedonia was positively correlated with the perfusion of the ventromedial prefrontal cortex, the cingulate cortex and the insula.ConclusionsWe have shown that the clinical and perfusional profiles of apathetic depressed and non-apathetic differ. This study suggests the existence of two distinct neurobiological networks for depressed patients; one involving motivational networks for apathetic patients, and another one involving emotional networks for more anhedonic patients.Disclosure of interestThe authors have not supplied their declaration of competing interest.

Enhanced task-related brain activation and resting perfusion in healthy older adults after chronic blueberry supplementation.

Blueberries are rich in flavonoids, which possess antioxidant and anti-inflammatory properties. High flavonoid intakes attenuate age-related cognitive decline, but data from human intervention studies are sparse. We investigated whether 12 weeks of blueberry concentrate supplementation improved brain perfusion, task-related activation, and cognitive function in healthy older adults. Participants were randomised to consume either 30 mL blueberry concentrate providing 387 mg anthocyanidins (5 female, 7 male; age 67.5 ± 3.0 y; body mass index, 25.9 ± 3.3 kg·m-2) or isoenergetic placebo (8 female, 6 male; age 69.0 ± 3.3 y; body mass index, 27.1 ± 4.0 kg·m-2). Pre- and postsupplementation, participants undertook a battery of cognitive function tests and a numerical Stroop test within a 1.5T magnetic resonance imaging scanner while functional magnetic resonance images were continuously acquired. Quantitative resting brain perfusion was determined using an arterial spin labelling technique, and blood biomarkers of inflammation and oxidative stress were measured. Significant increases in brain activity were observed in response to blueberry supplementation relative to the placebo group within Brodmann areas 4/6/10/21/40/44/45, precuneus, anterior cingulate, and insula/thalamus (p < 0.001) as well as significant improvements in grey matter perfusion in the parietal (5.0 ± 1.8 vs -2.9 ± 2.4%, p = 0.013) and occipital (8.0 ± 2.6 vs -0.7 ± 3.2%, p = 0.031) lobes. There was also evidence suggesting improvement in working memory (2-back test) after blueberry versus placebo supplementation (p = 0.05). Supplementation with an anthocyanin-rich blueberry concentrate improved brain perfusion and activation in brain areas associated with cognitive function in healthy older adults.

Antifreeze Mechanism Study of Ice Growth Inhibition by Spin Labeled Ice Binding Proteins

Ice binding proteins (IBPs) were found to play critical role for various organisms to survive in extreme cold climates. We carried out the study on spin labeled type 1 IBPs whose sequence is from that of the Pseudopleuronectes americanus (winter flounder). The spin labeled sites involved in our study have undergone a manipulation on different directions along the α-helical structure. Site directed spin labeling technique was used to make the spin labeled peptides. Combination of the EPR spectra at low temperatures and observation of their inhibition to the growth of ice crystals gives us insight into their antifreeze mechanism on both molecular scale and microscopic scale. This poster will focus on presenting the experimental result of ice crystal inhibition, while another poster of my fellow student researchers will focus on the EPR result. Osmometer-microscopy technique was used to observe the ice crystals. The changes in antifreeze activities, kinetics of ice crystals’ growths and shapes of the ice crystals by these spin labeled IBPs compared with the wild type IBP were observed and will be discussed in this poster. Results include observations of IBP binding on both sides of the basal plane and prism faces of ice seed crystals. Significant differences between thermal hysteresis and crystal structured due to the binding of the Spin labeled IBPs were observed which is correlated to the EPR spectra at molecular level. Single cystal growth on the horizontal axis is observed within the hysteresis gap of the spin labeled IBPs while the wild type IBP showed no crystal growth during the hysteresis gap. There were various differences between thermal hysteresis values between the different spin labeled IBPs.

Cerebral blood flow and vasoreactivity in aging: an arterial spin labeling study.

Regional cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) in young and elderly participants were assessed using pulsed arterial spin labeling (ASL) and blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) techniques in combination with inhalation of CO2. Pulsed ASL and BOLD-MRI were acquired in seventeen asymptomatic volunteers (10 young adults, age: 30±7 years; 7 elderly adults, age: 64±8 years) with no history of diabetes, hypertension, and neurological diseases. Data from one elderly participant was excluded due to the incorrigible head motion. Average baseline CBF in gray matter was significantly reduced in elderly (46±9 mL·100 g-1·min-1) compared to young adults (57±8 mL·100 g-1·min-1; P=0.02). Decreased pulsed ASL-CVR and BOLD-CVR in gray matter were also observed in elderly (2.12±1.30 and 0.13±0.06 %/mmHg, respectively) compared to young adults (3.28±1.43 and 0.28±0.11 %/mmHg, respectively; P<0.05), suggesting some degree of vascular impairment with aging. Moreover, age-related decrease in baseline CBF was observed in different brain regions (inferior, middle and superior frontal gyri; precentral and postcentral gyri; superior temporal gyrus; cingulate gyri; insula, putamen, caudate, and supramarginal gyrus). In conclusion, CBF and CVR were successfully investigated using a protocol that causes minimal or no discomfort for the participants. Age-related decreases in baseline CBF and CVR were observed in the cerebral cortex, which may be related to the vulnerability for neurological disorders in aging.

APPLICATION OF ESR-SPECTROSCOPY FOR DIAGNOSIS AND PROGNOSIS OF CANCER

Diagnostic medicine has significantly changed during the past decade. The emergence of proteomics and genomics has significantly increased our understanding of disease. These fields have also revealed the vast array of proteins that are expressed in various disease processes, such as cancer. Measurement of these unique proteins expressed in certain diseases may offer diagnostic clues or allow patient prognosis to be assessed. Another approach is to measure the effects that these ligands have on the structure and function of albumin. Albumin is known to play an important role in modulating the serum concentrations of various proteins produced by tumor cells. In this review, we introduce the reader to the technique of spin labeling followed by electron paramagnetic resonance spectroscopy. This method is a powerful tool for evaluating the structural and functional changes that can occur to albumin following the binding of various ligands. We describe the utility of this technique for the diagnosis of cancer and sepsis, as well as some other novel potential applications.

Cerebral blood flow, blood supply, and cognition in Type 2 Diabetes Mellitus.

We investigated whether type 2 diabetes (T2DM) and the presence of cognitive impairment are associated with altered cerebral blood flow (CBF). Forty-one participants with and thirty-nine without T2DM underwent 3-Tesla MRI, including a quantitative technique measuring (macrovascular) blood flow in the internal carotid artery and an arterial spin labeling technique measuring (microvascular) perfusion in the grey matter (GM). Three analysis methods were used to quantify the CBF: a region of interest analysis, a voxel-based statistical parametric mapping technique, and a ‘distributed deviating voxels’ method. Participants with T2DM exhibited significantly more tissue with low CBF values in the cerebral cortex and the subcortical GM (3.8-fold increase). The latter was the only region where the hypoperfusion remained after correcting for atrophy, indicating that the effect of T2DM on CBF, independent of atrophy, is small. Subcortical CBF was associated with depression. No associations were observed for CBF in other regions with diabetes status, for carotid blood flow with diabetes status, or for CBF or flow in relation with cognitive function. To conclude, a novel method that tallies total ‘distributed deviating voxels’ demonstrates T2DM-associated hypoperfusion in the subcortical GM, not associated with cognitive performance. Whether a vascular mechanism underlies cognitive decrements remains inconclusive.

Support vector machine classification of arterial volume-weighted arterial spin tagging images.

IntroductionIn recent years, machine‐learning techniques have gained growing popularity in medical image analysis. Temporal brain‐state classification is one of the major applications of machine‐learning techniques in functional magnetic resonance imaging (fMRI) brain data. This article explores the use of support vector machine (SVM) classification technique with motor‐visual activation paradigm to perform brain‐state classification into activation and rest with an emphasis on different acquisition techniques.MethodsImages were acquired using a recently developed variant of traditional pseudocontinuous arterial spin labeling technique called arterial volume‐weighted arterial spin tagging (AVAST). The classification scheme is also performed on images acquired using blood oxygenation–level dependent (BOLD) and traditional perfusion‐weighted arterial spin labeling (ASL) techniques for comparison.ResultsThe AVAST technique outperforms traditional pseudocontinuous ASL, achieving classification accuracy comparable to that of BOLD contrast images.ConclusionThis study demonstrates that AVAST has superior signal‐to‐noise ratio and improved temporal resolution as compared with traditional perfusion‐weighted ASL and reduced sensitivity to scanner drift as compared with BOLD. Owing to these characteristics, AVAST lends itself as an ideal choice for dynamic fMRI and real‐time neurofeedback experiments with sustained activation periods.

Assessment of glioma response to radiotherapy using 3D pulsed-continuous arterial spin labeling and 3D segmented volume

BackgroundGliomas are the most common primary brain tumors in adults, in some cases, radiotherapy may be the preferred treatment option especially for elderly people who cannot endure surgery. Therefore, it is necessary to evaluate the effects of radiotherapy on glioma. Arterial spin labeling (ASL) is an MR imaging technique that allows for a quantitative determination of cerebral blood flow (CBF) noninvasively. Tumor volume is still an important determinant for evaluating treatment response. The purpose of this study was to investigate the relationship between the tumor perfusion parameters and tumor volume and assess the effects of radiotherapy on glioma using pulsed-continuous arterial spin labeling (pcASL) technique. Methods35 patients with gliomas, histologically classified as low-grade group (n=16) and high-grade group (n=19), treated with radiotherapy only or before using other therapies were included in this study. MR examinations, including T1 weighted image and pcASL, were performed before and 4, 8, 12, 16 weeks after radiotherapy. Regional CBF of normal tissue, mean tumor blood flow (TBFmean), maximum tumor blood flow (TBFmax), and tumor volume were evaluated at each time point. Both the percentage change in CBF (CBF ratio), TBFmean (TBFmean ratio), TBFmax (TBFmax ratio) and the percentage change in tumor volume (volume ratio) were calculated using values obtained before and after radiotherapy. The correlation between the volume ratio and CBF ratio, TBFmean ratio, TBFmax ratio was assessed using linear regression analysis and Pearson’s correlation. ResultsThe TBFmean and TBFmax of high-grade gliomas were significantly higher than that of low-grade group. In high-grade group, a strong correlation was demonstrated between the tumor volume and the TBFmax before radiotherapy (R2=0.35, rs=0.59, p<0.05). There was also a significant correlation between the TBFmax before radiotherapy and the tumor volume ratio before and 8 weeks after radiotherapy (R2=0.56, rs=−0.74, p<0.05). ConclusionThe TBFmax measured using pcASL could assess tumoral grade and also could become a potential tool for evaluating the therapeutic effects of radiation.

Optimization of simultaneous multislice EPI for concurrent functional perfusion and BOLD signal measurements at 7T.

PurposeTo overcome limitations of previous ultra‐high‐field arterial spin labeling (ASL) techniques concerning temporal resolution and brain coverage by utilizing the simultaneous multi‐slice (SMS) approach.MethodsAn optimized, flow‐alternating inversion recovery quantitative imaging of perfusion using a single subtraction II scheme was developed that tackles the challenges of 7 tesla (T) ASL. The implementation of tailored labeling radiofrequency pulses reduced the effect of transmit field ( B1+) inhomogeneities. The proposed approach utilizes an SMS echo‐planar imaging (EPI) readout to efficiently achieve large brain coverage.ResultsA pulsed ASL (PASL) technique with large brain coverage is described and optimized that can be applied at temporal resolutions below 2.5 s, similar to those achievable at 1.5 and 3T magnetic field strength. The influences of within‐ and through‐slice acceleration factors and reconstruction parameters on perfusion and blood‐oxygenation‐level‐dependent (BOLD)‐signal image and temporal signal‐to‐noise ratio (SNR) are presented. The proposed approach yielded twice the brain coverage as compared to conventional PASL at 7T, without notable loss in image quality.ConclusionThe presented SMS EPI PASL at 7T overcomes current limitations in SNR, temporal resolution, and spatial coverage for functional perfusion and BOLD signal as well as baseline perfusion measurements. Magn Reson Med 78:121–129, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

Comparison between dynamic susceptibility contrast magnetic resonance imaging and arterial spin labeling techniques in distinguishing malignant from benign brain tumors

ObjectivesThe purpose of this study was to preliminarily compare unenhanced arterial spin-labeled (ASL) imaging, dynamic susceptibility contrast-enhanced cerebral blood volume (DSCE-CBV) magnetic resonance imaging (MRI) for evaluation of tumor perfusion in patients with brain tumors. Materials and methodsA total of 27 patients with brain tumors were examined in 1,5T MRI. Single phase and multiphase ASL, DSCE-CBV examinations were assessed by both qualitative and quantitative analysis for the detection of malignancy. Imaging results were correlated with a histopathology or follow-up. ResultsBased on 31 studies in 27 patients with brain tumors, the visual inspection sensitivities for ASL and dynamic DSC perfusion imaging were 88% and 94%, respectively, with 100% specificity for both. On qualitative evaluation, sensitivities for ASL and DSC perfusion imaging perfusions were 88% and 94%, respectively, with 100% specificity for both. The highest sensitivity values for quantitative ASL imaging were obtained using a normalized cut-off ratio of 1.65, resulting in sensitivity of 94% for ASL imaging and cut-off ratio of 1.95 and sensitivity 94% for DSCE-CBV imaging. ConclusionThe present study revealed similar sensitivity and specificity for both multhiphase ASL and DSC MRI. Thus, we suggest that ASL perfusion can be used in daily clinical practice.

Feasibility of Quantifying Arterial Cerebral Blood Volume Using Multiphase Alternate Ascending/Descending Directional Navigation (ALADDIN).

Arterial cerebral blood volume (aCBV) is associated with many physiologic and pathologic conditions. Recently, multiphase balanced steady state free precession (bSSFP) readout was introduced to measure labeled blood signals in the arterial compartment, based on the fact that signal difference between labeled and unlabeled blood decreases with the number of RF pulses that is affected by blood velocity. In this study, we evaluated the feasibility of a new 2D inter-slice bSSFP-based arterial spin labeling (ASL) technique termed, alternate ascending/descending directional navigation (ALADDIN), to quantify aCBV using multiphase acquisition in six healthy subjects. A new kinetic model considering bSSFP RF perturbations was proposed to describe the multiphase data and thus to quantify aCBV. Since the inter-slice time delay (TD) and gap affected the distribution of labeled blood spins in the arterial and tissue compartments, we performed the experiments with two TDs (0 and 500 ms) and two gaps (300% and 450% of slice thickness) to evaluate their roles in quantifying aCBV. Comparison studies using our technique and an existing method termed arterial volume using arterial spin tagging (AVAST) were also separately performed in five subjects. At 300% gap or 500-ms TD, significant tissue perfusion signals were demonstrated, while tissue perfusion signals were minimized and arterial signals were maximized at 450% gap and 0-ms TD. ALADDIN has an advantage of visualizing bi-directional flow effects (ascending/descending) in a single experiment. Labeling efficiency (α) of inter-slice blood flow effects could be measured in the superior sagittal sinus (SSS) (20.8±3.7%.) and was used for aCBV quantification. As a result of fitting to the proposed model, aCBV values in gray matter (1.4–2.3 mL/100 mL) were in good agreement with those from literature. Our technique showed high correlation with AVAST, especially when arterial signals were accentuated (i.e., when TD = 0 ms) (r = 0.53). The bi-directional perfusion imaging with multiphase ALADDIN approach can be an alternative to existing techniques for quantification of aCBV.

Pulsed arterial spin labelling at ultra-high field with a B 1 (+) -optimised adiabatic labelling pulse.

Arterial spin labelling (ASL) techniques benefit from the increased signal-to-noise ratio and the longer T 1 relaxation times available at ultra-high field. Previous pulsed ASL studies at 7T concentrated on the superior regions of the brain because of the larger transmit radiofrequency inhomogeneity experienced at ultra-high field that hinders an adequate inversion of the blood bolus when labelling in the neck. Recently, researchers have proposed to overcome this problem with either the use of dielectric pads, through dedicated transmit labelling coils, or special adiabatic inversion pulses. We investigate the performance of an optimised time-resampled frequency-offset corrected inversion (TR-FOCI) pulse designed to cause inversion at much lower peak B 1 (+) . In combination with a PICORE labelling, the perfusion signal obtained with this pulse is compared against that obtained with a FOCI pulse, with and without dielectric pads. Mean grey matter perfusion with the TR-FOCI was 52.5±10.3mL/100g/min, being significantly higher than the 34.6±2.6mL/100g/min obtained with the FOCI pulse. No significant effect of the dielectric pads was observed. The usage of the B 1 (+) -optimised TR-FOCI pulse results in a significantly higher perfusion signal. PICORE-ASL is feasible at ultra-high field with no changes to operating conditions.