Spin Labeling Technique Research Articles

Perfusion deficit to cholinergic challenge in veterans with Gulf War Illness

A highly plausible etiology for Gulf War Illness (GWI) is that the neural damage and cognitive deficits are associated with excessive exposure to cholinesterase-inhibiting cholinergic stimulants. Our previous SPECT study provided strong indication that cerebral blood flow (CBF) in veterans with GWI may be different from those of unaffected control veterans. The present study confirmed and extended previous findings that patients with GWI have abnormal response to an inhibitory cholinergic challenge, physostigmine infusion, when compared to age–gender–education matched control veterans. The MRI-based arterial spin labeling (ASL) and phase-contrast techniques have several key advantages over SPECT, including shorter experiment duration, complete non-invasiveness, and higher spatial and temporal resolutions, and therefore may provide a cost-effective biomarker for characterization of GWI.

Lung perfusion measured using magnetic resonance imaging: New tools for physiological insights into the pulmonary circulation

Since the lung receives the entire cardiac output, sophisticated imaging techniques are not required in order to measure total organ perfusion. However, for many years studying lung function has required physiologists to consider the lung as a single entity: in imaging terms as a single voxel. Since imaging, and in particular functional imaging, allows the acquisition of spatial information important for studying lung function, these techniques provide considerable promise and are of great interest for pulmonary physiologists. In particular, despite the challenges of low proton density and short T2* in the lung, noncontrast MRI techniques to measure pulmonary perfusion have several advantages including high reliability and the ability to make repeated measurements under a number of physiologic conditions. This brief review focuses on the application of a particular arterial spin labeling (ASL) technique, ASL-FAIRER (flow sensitive inversion recovery with an extra radiofrequency pulse), to answer physiologic questions related to pulmonary function in health and disease. The associated measurement of regional proton density to correct for gravitational-based lung deformation (the "Slinky" effect (Slinky is a registered trademark of Pauf-Slinky incorporated)) and issues related to absolute quantification are also discussed.

Conformational distributions at the N-peptide/boxB RNA interface studied using site-directed spin labeling

In bacteriophage λ, interactions between a 22-amino acid peptide (called the N-peptide) and a stem-loop RNA element (called boxB) play a critical role in transcription anti-termination. The N-peptide/boxB complex has been extensively studied, and serves as a paradigm for understanding mechanisms of protein/RNA recognition. Particularly, ultrafast spectroscopy techniques have been applied to monitor picosecond fluorescence decay behaviors of 2-aminopurines embedded at various positions of the boxB RNA. The studies have led to a model in which the bound N-peptide exists in dynamic equilibrium between two states, with peptide C-terminal fragment either stacking on (i.e., the stacked state) or peeling away from (i.e., the unstacked state) the RNA loop. The function of the N-peptide/boxB complex seems to correlate with the fraction of the stacked state. Here, the N-peptide/boxB system is studied using the site-directed spin labeling technique, in which X-band electron paramagnetic resonance spectroscopy is applied to monitor nanosecond rotational behaviors of stable nitroxide radicals covalently attached to different positions of the N-peptide. The data reveal that in the nanosecond regime the C-terminal fragment of bound N-peptide adopts multiple discrete conformations within the complex. The characteristics of these conformations are consistent with the proposed stacked and unstacked states, and their distributions vary upon mutations within the N-peptide. These results suggest that the dynamic two-state model remains valid in the nanosecond regime, and represents a unique mode of function in the N-peptide/boxB RNA complex. It also demonstrates a connection between picosecond and nanosecond dynamics in a biological complex.

Effects of large-scale nonstationarity on parametric maps. A study of rest perfusion CASL data

This study investigates the emergence of characteristic patterns in clusters thresholded at uncorrected significance levels, using as a case study rest perfusion images obtained with the continuous arterial spin labelling technique (CASL). The origin of these patterns is traced back to the existence of large-scale spatial covariance, a violation of the stationarity assumption on the spatial distribution of residual errors. It is shown that in the presence of large-scale covariance, several principles or intuitions common among experimenters when evaluating the inferential strength of their analyses are not applicable. Thresholded maps and clusters are confounded by the spatial patterns of large-scale covariance, irrespective of the existence of a true effect, as shown in t maps constructed by resampling groups at random from a large pool of volumes. Filtering clusters according to their size made the problem worse, and corrections on cluster size based on random field theory models of smoothness had only a minor impact on their tendency to appear in characteristic locations. A formal analysis shows that the large-scale covariance at the origin of these problems is retained in the parametric map irrespective of sample size. Therefore, neither sample independence nor sample size protect from replications of effects being confounded by replications of the spatial covariance of residual errors. In contrast, cluster peaks were not affected by large-scale covariance but only by local differences in smoothness levels, as predicted by random field theory for the distribution of maxima, highlighting the different inferential robustness of cluster-based and maxima-based statistics. A framework is provided to generalize these results to mixed effects models with nested random effects, applicable also to activation studies. Large-scale nonstationarity is most problematic when the variance source at the origin of the characteristic patterns is not specific to a function or variable involved in the inferential process, as typically in observational studies of individual differences. These results raise the question of the existence and impact of large-scale nonstationarity in studies with data obtained with other techniques.

A Nucleotide-Independent Nitroxide Probe Reports on Site-Specific Stereomeric Environment in DNA

In this report, stereospecific structural and dynamic features in DNA are studied using the site-directed spin labeling technique. A stable nitroxide radical, 1-oxyl-4-bromo-2,2,5,5-tetramethylpyrroline (R5a), was attached postsynthetically to phosphorothioates that were chemically introduced, one at a time, at five sites of a DNA duplex. The two phosphorothioate diastereomers (R p or S p ) were separated, and nitroxide rotational motions were monitored using electron paramagnetic resonance spectroscopy. The resulting spectra vary according to diastereomer identity and location of the labeling site, with R p -R5a spectra effectively reporting on local DNA structural features and S p -R5a spectra sensing variations in local DNA motions. This establishes R p - and S p -R5a as unique probes for investigating nucleic acids in a site- and stereospecific manner, which may aid studies of stereospecific DNA/protein interactions. In addition, weighted averages of individual R p and S p spectra match those of R5a attached to mixed diastereomers. This suggests that R5a linked to mixed diastereomers reports on the composite behaviors of R p - and S p -R5a and is useful in initial probing of the DNA local environment. This work advances understanding of R5a/DNA coupling, and is a key step forward in developing a nucleotide-independent spectroscopic probe for studying nucleic acids.

Comparison of selective arterial spin labeling using 1D and 2D tagging RF pulses

Generic arterial spin labeling (ASL) techniques label all brain feeding arteries. In this work, we used two different selective ASL (SASL) methods to show the perfusion of one single artery. A slice selective inversion of an area including the desired vessel was compared to a multidimensional RF pulse with Gaussian profile to label only the artery of interest. Perfusion images with a resolution of 2 x 2 x 5 mm 3 are shown that were acquired after tagging only the internal carotid artery of healthy volunteers. In addition, both techniques were applied to a patient with an extra-intracranial bypass to illustrate its perfusion territory. These perfusion images are consistent with a standard angiography. SASL imaging with a resolution of 2 x 2 x 5 mm 3 is possible in a total scan time of 5 min. The presented MR techniques may in part replace the assessment of revascularization success by conventional angiography.

Brain MR perfusion‐weighted imaging with alternate ascending/descending directional navigation

In this study, a new arterial spin labeling technique that requires no separate spin preparation pulse was developed. Sequential two-dimensional slices were acquired in ascending and descending orders by turns using balanced steady state free precession for pair-wise subtraction. Simulation studies showed this new technique, alternate ascending/descending directional navigation (ALADDIN), has high sensitivity to both slow- (1-10 cm/sec) and fast-moving (>10 cm/sec) blood because of the presence of multiple labeling planes proximal to imaging planes and sensitivity of balanced steady state free precession to initial magnetization differences. ALADDIN provided high-resolution multislice perfusion-weighted images in ∼ 3 min. About 80-90% of signals in a slice were ascribed to spins saturated in the four prior slices. Three to five edge slices on each side of imaging group were affected by transient magnetization transfer effects and incomplete T(1) recovery between successive acquisitions. ALADDIN signals were dependent on many imaging parameters, implying room for improvement. Sagittal and coronal ALADDIN images demonstrated perfusion direction in gray matter regions was mostly from center to lateral, anterior, or posterior, whereas that in some white matter regions was reversed. ALADDIN is likely useful for many studies requiring perfusion-weighted imaging with short scan time, insensitiveness to arterial transit time, directional information, high resolution, and/or wide coverage.

Arterial spin labeling MRI for assessment of perfusion in native and transplanted kidneys

PurposeTo apply a magnetic resonance arterial spin labeling (ASL) technique to evaluate kidney perfusion in native and transplanted kidneys. Materials and MethodsThis study was compliant with the Health Insurance Portability and Accountability Act and approved by the institutional review board. Informed consent was obtained from all subjects. Renal perfusion exams were performed at 1.5 T in a total of 25 subjects: 10 with native and 15 with transplanted kidneys. A flow-sensitive alternating inversion recovery (FAIR) ASL sequence was performed with respiratory triggering in all subjects and under free-breathing conditions in five transplant subjects. Thirty-two control/tag pairs were acquired and processed using a single-compartment model. Perfusion in native and transplanted kidneys was compared above and below an estimated glomerular filtration rate (eGFR) threshold of 60 ml/min per 1.73 m2 and correlations with eGFR were determined. ResultsIn many of the transplanted kidneys, major feeding vessels in the coronal plane required a slice orientation sagittal to the kidney. Renal motion during the examination was observed in native and transplant subjects and was corrected with registration. Cortical perfusion correlated with eGFR in native (r=0.85, P=.002) and transplant subjects (r=0.61, P=.02). For subjects with eGFR >60 ml/min per 1.73 m2, native kidneys demonstrated greater cortical (P=.01) and medullary (P=.04) perfusion than transplanted kidneys. For subjects with eGFR <60 ml/min per 1.73 m2, native kidneys demonstrated greater medullary perfusion (P=.04) compared to transplanted kidneys. Free-breathing acquisitions provided renal perfusion measurements that were slightly lower compared to the coached/triggered technique, although no statistical differences were observed. ConclusionIn conclusion, FAIR-ASL was able to measure renal perfusion in subjects with native and transplanted kidneys, potentially providing a clinically viable technique for monitoring kidney function.

Limitation of pulsed arterial spin labeling technique in the measurement of normal white matter perfusion

Objective To investigate the limitation of quantitative measurement of cerebral blood flow (CBF) of normal white matter by using a single subtraction with thin-slice TI1 periodic saturation (Q2TIPS Ⅱ ) pulsed arterial spin labeling (PASL)technique. Methods Thirty-one patients with brain tumors were examined at 3.0 T MRI system . A second version of quantitative imaging of perfusion using a single subtraction with additional thin-section periodic saturation after inversion and a time delay (Q2TIPS) technique of pulsed arterial spin labeling in the multisection mode and T2* dynamic susceptibility-weighted contrast-enhanced (T2* DSC)MR imaging were both implemented. Cerebral blood flow map obtained from PASL and DSC were reviewed. The regions of interest( ROI )were placed in the region of normal white matter contralateral to the lesion in the proximal and distal slices. In regions of interest, the signal intensity (SI)was measured from the maps of cerebral blood flow map obtained from PASL and DSC. Pair-t test was performed to determine if there were significant signal differences between proximal and distal slices. Pearson linear correlation analysis of signal intensity was performed for values from the same slices of PASL-CBF and DSC-CBF maps. Results In the deep white matter of distal slice, PASL-CBF map showed perfusion deficit while DSC-CBF map showed low CBF in the corresponding brain area. With the increased inversion time,the PASL-CBF map showed obviously improved perfusion signal in deep white matter (but still some perfusion deficit)and slightly decreased perfusion signal in grey matter. The mean signal of normal white matter measured from distal slices of PASL-CBF maps was( -22.1 ±55.5) ml· 100 g-1 · min-1 while it was (89.5 ±45.5) ml. 100 g-1 · min-1 in proximal slices. There was a significant difference of signal intensity from PASL-CBF maps between distal and proximal slices ( t = - 9. 512, P ＜ 0. 01 ＝, while no difference of signal intensity between distal[ (62. 8 ± 29.9) ml · 100 g-1 · min-1] and proximal slices [(57. 1 ±29.6) ml · 100 g-1 · min-1 ]was obtained from DSC-CBF maps(t= -1.607,P＞0.05). There was no significant correlation between PASL-CBF and DSC-CBF in both distal ( r = 0. 093, P ＞ 0. 05 ) and proximal slices ( r = - 0. 234, P ＞ 0. 05). Conclusions PASL has limitation in the accurate quantification of cerebral blood flow of normal white matter. The quantification of CBF was affected by the limitations of the technique itself and the different parameters chosen.. Key words: Brain; Perfusion; Magnetic resonance imaging

High-field continuous arterial spin labeling with long labeling duration: reduced confounds from blood transit time and postlabeling delay.

In quantitative perfusion imaging using arterial spin labeling, variable blood transit times and postlabeling delays are two confounding factors that may compromise the accuracy of perfusion quantifications. In this study, theoretical analyses and experimental data at 9.4 T demonstrate that increasing labeling duration not only enhances the contrast of the arterial spin labeling signal but also minimizes the effect of variable postlabeling delays in multislice arterial spin labeling acquisitions. With a labeling duration of 6.4 sec, arterial spin labeling signal acquired in multislice mode (11 slices) is very similar to that acquired in single-slice mode. Previous studies have shown that inserting a delay between the spin labeling pulse and the image acquisition pulse could reduce confounds resulting from variable blood transit times at the expense of arterial spin labeling sensitivity. Our simulations suggest that enhancing the contrast of arterial spin labeling signal offers the opportunity for extending the postlabeling delay to a longer duration, minimizing systematic errors associated with a wide range of blood transit times, which could have significant implications for applying arterial spin labeling techniques to perfusion imaging of pathological conditions in animal models.

EPR investigation of clomipramine interaction with phosphatidylcholine membranes in presence and absence of cholesterol

The effects of tricylic antidepressant clomipramine (CLO) on the membrane properties of saturated dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine as well as on unsaturated egg yolk phosphatidylcholine liposomes were investigated by the electron paramagnetic resonance spin-labeling technique, in combination with the simulation of the spectra, taking into account that the membrane is heterogeneous and composed of the regions with different fluidity characteristics. Different spin labels, monitoring membrane properties in the upper and inner parts of the membrane, were used. In general, two spectral components, having different motional characteristics, were detected in all liposomes investigated. In liposomes with saturated chains, CLO decreased the phase-transition temperature, disordered the membrane, and increased polarity in the upper part of the membrane. However, less impact was observed in liposomes with unsaturated chains. In dipalmitoyl phosphatidylcholine liposomes, it also induced molecular rearrangements near the pretransition temperature. The presence of 30 mol% cholesterol increased the fluidizing effect of CLO and modified the lateral diffusion of nitroxide in the inner part of the membrane. A unique anomalous increase in diffusion of nitroxide, dependent on CLO concentration, was detected in the temperature region where the phosphatidylcholine membrane without cholesterol experiences the phase transitions. Since the changes in the central part of the membrane were even more pronounced than in the upper part of the membrane, it could be concluded that CLO incorporates into the membrane with its hydrophobic ring parallel to the phospholipid chains.

Tissue ACE inhibition improves microcirculation in remote myocardium after coronary stenosis: MR imaging study in rats

ACE inhibition has been shown to improve left ventricular (LV) and myocardial blood flow. Previous data regarding changes in capillary density and angiogenesis during ACE inhibition are controversial. The aim of the following study was to determine myocardial microcirculation and heart function in the rat after coronary stenosis using non invasive MR imaging techniques. MR spin labeling and cine techniques have been performed in female Wistar rats 2 weeks after coronary artery stenosis. In one group, animals were treated with quinapril in a dose of 6 mg/kg/day. Perfusion, relative blood volume (RBV), LV mass and function were determined non-invasively 2 weeks after treatment. Finally, fibrosis and capillary density were analyzed histologically. Additionally, hemodynamic measurements were realized in a further group in order to calculate systemic vascular resistance (SVR). Quinapril resulted in a significant increase in perfusion at rest in the remote and the poststenotic myocardium with improved systolic function and a decrease in SVR compared to the non treated control group. Additionally, maximum perfusion and RBV were slightly elevated whereas capillary density was unchanged among the groups. MRI allows for non-invasive quantification of functional microcirculation and heart function. In addition to the well known effect of ACE inhibition on systolic function, treatment with the tissue specific ACE inhibitor quinapril revealed an important microvascular improvement, especially at arteriolar level. These findings may support the use of tissue ACE inhibitors to improve cardiac microcirculation after ischemia.

Quantitative analysis of arterial spin labeling FMRI data using a general linear model

Arterial spin labeling techniques can yield quantitative measures of perfusion by fitting a kinetic model to difference images (tagged-control). Because of the noisy nature of the difference images investigators typically average a large number of tagged versus control difference measurements over long periods of time. This averaging requires that the perfusion signal be at a steady state and not at the transitions between active and baseline states in order to quantitatively estimate activation induced perfusion. This can be an impediment for functional magnetic resonance imaging task experiments. In this work, we introduce a general linear model (GLM) that specifies Blood Oxygenation Level Dependent (BOLD) effects and arterial spin labeling modulation effects and translate them into meaningful, quantitative measures of perfusion by using standard tracer kinetic models. We show that there is a strong association between the perfusion values using our GLM method and the traditional subtraction method, but that our GLM method is more robust to noise.

A novel copper(II) coordination at His186 in full-length murine prion protein

To explore Cu(II) ion coordination by His 186 in the C-terminal domain of full-length prion protein (moPrP), we utilized the magnetic dipolar interaction between a paramagnetic metal, Cu(II) ion, and a spin probe introduced in the neighborhood of the postulated binding site by the spin labeling technique (SDSL technique). Six moPrP mutants, moPrP(D143C), moPrP(Y148C), moPrP(E151C), moPrP(Y156C), moPrP(T189C), and moPrP(Y156C,H186A), were reacted with a methane thiosulfonate spin probe and a nitroxide residue (R1) was created in the binding site of each one. Line broadening of the ESR spectra was induced in the presence of Cu(II) ions in moPrP(Y148R1), moPrP(Y151R1), moPrP(Y156R1), and moPrP(T189R1) but not moPrP(D143R1). This line broadening indicated the presence of electron–electron dipolar interaction between Cu(II) and the nitroxide spin probe, suggesting that each interspin distance was within 20 Å. The interspin distance ranges between Cu(II) and the spin probes of moPrP(Y148R1), moPrP(Y151R1), moPrP(Y156R1), and moPrP(T189R1) were estimated to be 12.1 Å, 18.1 Å, 10.7 Å, and 8.4 Å, respectively. In moPrP(Y156R1,H186A), line broadening between Cu(II) and the spin probe was not observed. These results suggest that a novel Cu(II) binding site is involved in His186 in the Helix2 region of the C-terminal domain of moPrP C.

Components of acquisition-to-acquisition variance in continuous arterial spin labelling (CASL) imaging

BackgroundImages of perfusion estimates obtained with the continuous arterial spin labelling technique are characterized by variation between single acquisitions. Little is known about the spatial determinants of this variation during the acquisition process and their impact on voxel-by-voxel estimates of effects.ResultsWe show here that the spatial patterns of covariance between voxels arising during the acquisition of these images uncover distinct mechanisms through which this variance arises: through variation in global perfusion levels; through the action of large vessels and other, less well characterized, large anatomical structures; and through the effect of noisy areas such as the edges of the brain.ConclusionsKnowledge of these covariance patterns is important to experimenters for a correct interpretation of findings, especially for studies where relatively few acquisitions are made.

Estimation of labeling efficiency in pseudocontinuous arterial spin labeling

Pseudocontinuous arterial spin labeling MRI is a new arterial spin labeling technique that has the potential of combining advantages of continuous arterial spin labeling and pulsed arterial spin labeling. However, unlike continuous arterial spin labeling, the labeling process of pseudocontinuous arterial spin labeling is not strictly an adiabatic inversion and the efficiency of labeling may be subject specific. Here, three experiments were performed to study the labeling efficiency in pseudocontinuous arterial spin labeling MRI. First, the optimal labeling position was determined empirically to be approximately 84 mm below the anterior commissure-posterior commissure line in order to achieve the highest sensitivity. Second, an experimental method was developed to utilize phase-contrast velocity MRI as a normalization factor and to estimate the labeling efficiency in vivo, which was founded to be 0.86 +/- 0.06 (n = 10, mean +/- standard deviation). Third, we compared the labeling efficiency of pseudocontinuous arterial spin labeling MRI under normocapnic and hypercapnic (inhalation of 5% CO(2)) conditions and showed that a higher flow velocity in the feeding arteries resulted in a reduction in the labeling efficiency. In summary, our results suggest that labeling efficiency is a critical parameter in pseudocontinuous arterial spin labeling MRI not only in terms of achieving highest sensitivity but also in quantification of absolute cerebral blood flow in milliliters per minute per 100 g. We propose that the labeling efficiency should be estimated using phase-contrast velocity MRI on a subject-specific basis.

Effects of CBV, CBF, and blood-brain barrier permeability on accuracy of PASL and VASO measurement

Cerebral blood flow, cerebral blood volume (CBV), and water permeability through blood-brain barrier are important hemodynamic parameters in brain physiology. Pulsed arterial spin labeling and vascular-space occupancy techniques have been used to measure regional cerebral blood flow and CBV, respectively. However, these techniques generally ignore the effects of one hemodynamic parameter on the measurement of others. For instance, the influences of CBV changes on arterial spin labeling or the permeability effects on vascular-space occupancy typically were not accounted for in the quantification of blood flow or volume. In the current work, the biophysical effects of CBV on pulsed arterial spin labeling and permeability on vascular-space occupancy signals are evaluated using a general two-compartment model. The dependence of these effects on the T(1) at various field strengths is also assessed by simulations. Results indicate that CBV has negligible to small influences on pulsed arterial spin labeling signal (<6.6% at 3 T) and permeability effects are negligible on vascular-space occupancy signal (<0.1% at 3 T) under normal physiologic conditions. In addition, CBV effect on pulsed arterial spin labeling is further diminished at high field strengths, but residual blood contamination in vascular-space occupancy signal may be enhanced at high fields due to the reduced difference between extra- and intravascular T(1) values.

Spin-spoiler: a novel arterial spin labeling technique without the need of subtraction

Introdudction Arterial Spin Labeling (ASL) has been successfully used for the visualization of the renal and coronary arteries without the need of a contrast agent [1,2]. The classical approach of ASL consists of the acquisition of two image datasets with and without a spatially selective labeling prepulse. The disadvantages of this methodology include the need for two acquisitions and image subtraction resulting in increased sensitivity to motion. Alternative techniques not requiring image subtraction have been proposed and successfully applied for renal and coronary angiography [3]. In this work we propose a novel ASL technique (Spin-Spoiler) without the need for image subtraction. It is based on the application of a spatially selective labeling pulse followed by a non-selective refocusing and a tip up pulse resulting in localized spin tagging and simultaneous background tissue suppression over a wide range of T1 values. We sought to evaluate this technique in a T1 phantom and in healthy subjects for selective renal artery visualization.

Theoretical and experimental evaluation of continuous arterial spin labeling techniques

Continuous arterial spin labeling is known to be the most sensitive arterial spin labeling technique. To avoid magnetization transfer effects and to overcome hardware limitations, several sequences have been proposed that adiabatically label the inflowing blood. Four of these methods are examined with respect to their sensitivity both theoretically by Bloch equation simulations and experimentally. All sequences were optimized carefully by adjusting their measurement parameters based exclusively on the results of simulations. Perfusion measurements on the human brain obtained at 3 T result in excellent images from all techniques, while differences in sensitivity are similar to those expected from the simulations.

Perfusion MRI of brain tumours: a comparative study of pseudo-continuous arterial spin labelling and dynamic susceptibility contrast imaging

The purpose of this study was to compare the non-invasive 3D pseudo-continuous arterial spin labelling (PC ASL) technique with the clinically established dynamic susceptibility contrast perfusion magnetic resonance imaging (DSC-MRI) for evaluation of brain tumours. A prospective study of 28 patients with contrast-enhancing brain tumours was performed at 3 T using DSC-MRI and PC ASL with whole-brain coverage. The visual qualitative evaluation of signal enhancement in tumour was scored from 0 to 3 (0 = no signal enhancement compared with white matter, 3 = pronounced signal enhancement with equal or higher signal intensity than in grey matter/basal ganglia). The extent of susceptibility artefacts in the tumour was scored from 0 to 2 (0 = no susceptibility artefacts and 2 = extensive susceptibility artefacts (maximum diameter > 2 cm)). A quantitative analysis was performed with normalised tumour blood flow values (ASL nTBF, DSC nTBF): mean value for region of interest (ROI) in an area with maximum signal enhancement/the mean value for ROIs in cerebellum. There was no difference in total visual score for signal enhancement between PC ASL and DSC relative cerebral blood flow (p = 0.12). ASL had a lower susceptibility-artefact score than DSC-MRI (p = 0.03). There was good correlation between DSC nTBF and ASL nTBF values with a correlation coefficient of 0.82. PC ASL is an alternative to DSC-MRI for the evaluation of perfusion in brain tumours. The method has fewer susceptibility artefacts than DSC-MRI and can be used in patients with renal failure because no contrast injection is needed.