The POST trial: initial post-market experience of the Penumbra system: revascularization of large vessel occlusion in acute ischemic stroke in the United States and Europe.

BACKGROUND AND PURPOSE: The purpose of this study was to assess the initial post-market experience of the device and how it is compared with the Penumbra Pivotal trial used to support the 510k application. METHODS: A retrospective case review of 157 consecutive patients treated with the Penumbra system at seven international centers was performed. Primary endpoints were revascularization of the target vessel (TIMI score of 2 or 3), good functional outcome as defined by a modified Rankin scale (mRS) score of ≤2 and incidence of procedural serious adverse events. Results were compared with those of the Penumbra pivotal trial. RESULTS: A total of 157 vessels were treated. Mean baseline values at enrollment were: age 65 years, NIHSS score 16. After use of the Penumbra system, 87% of the treated vessels were revascularized to TIMI 2 (54%) or 3 (33%) as compared with 82% reported in the Pivotal trial. Nine procedural serious adverse events were reported in 157 patients (5.7%). All-cause mortality was 20% (32/157), and 41% had a mRS of ≤2 at 90-day follow-up as compared with only 25% in the Pivotal trial. Patients who were successfully revascularized by the Penumbra system had significantly better outcomes than those who were not. CONCLUSION: Initial post-market experience of the Penumbra system revealed that the revascularization rate and safety profile of the device are comparable to those reported in the Pivotal trial. However, the proportion of patients who had good functional outcome was higher than expected.

Superselective arterial spin labeling applied for flow territory mapping in various cerebrovascular diseases.

In three example patients suffering from internal carotid artery occlusion, intracranial steno-occlusive disease, and symptomatic arteriovenous malformation (AVM), a new method named superselective pseudo-continuous arterial spin labeling (pCASL) was used in addition to clinical routine measurements. The capabilities of this method are demonstrated to gain important information in diagnosis, risk analysis, and treatment monitoring that are neither accessible by digital subtraction angiography nor by existing selective arterial spin labeling methods and thus to propose future applications in clinical routine. In all cases superselective pCASL enabled the assessment of tissue viability and of territorial brain perfusion at different levels starting from major brain feeding vessels to collateral circulation at the level of the Circle of Willis to even distal branching arteries. This made it possible to estimate the contribution of an extracranial-intracranial bypass to the brain perfusion; to depict individual arteries to important functional brain areas; to identify en-passant feeding vessels of an AVM and to track possible changes in their perfusion territories after intervention.

Perfusion territory imaging of intracranial branching arteries - optimization of continuous artery-selective spin labeling (CASSL).

Continuous artery-selective spin labeling (CASSL) is based on a standard continuous arterial spin labeling sequence with adiabatic flow-driven inversion and an amplitude-modulated control experiment, and has been proposed recently as a new method for the noninvasive flow territory mapping of cerebral arteries. Spatial selectivity is achieved by the rotation of a tilted labeling plane about the axis of a selected artery, which restricts the tagging pulses to the same spatial position for the vessel of interest but, for any other adjacent and parallel artery, the locus of resonance will vary in time and saturates the blood at a certain distance to the labeling focus. In numerical simulations and in a volunteer study, the key labeling parameters of CASSL were investigated with the goal of increasing the spatial selectivity whilst maintaining sufficient labeling efficiency, in order to selectively label the blood in small intracranial arteries distal to the circle of Willis. The optimized labeling parameters were employed in vivo and adapted to different vascular geometries. The labeling of small intracranial branches of the anterior, middle and posterior cerebral arteries in close vicinity to other vessels yielded clearly delineated perfusion territories and demonstrated the method's capability for highly selective perfusion measurements.

Superselective pseudocontinuous arterial spin labeling.

A new technique for the imaging of flow territories of individual extra- and intracranial arteries is presented. The method is based on balanced pseudocontinuous arterial spin labeling but employs additional time-varying gradients in between the radiofrequency pulses of the long labeling train. The direction of the additional gradient vector is perpendicular to the selected artery and its azimuthal angle is switched after every radiofrequency pulse. The phases of the radiofrequency pulses are adopted to cancel out the phase accrual of the spins at the center of the target vessel due to the extra applied gradients. This results in efficient inversion at the targeted position, whereas elsewhere time-varying phase changes will result in marginal inversion efficiency. By changing the moment of the added gradients, the size of the labeling focus can be adjusted. Influence of the temporal order of the additional gradients on the labeling efficiency and on the selectivity was investigated by simulations and experimental measurements. In a volunteer study, the acquisition of high signal-to-noise ratio flow territory images of small branches of the anterior cerebral artery distal to the circle of Willis was demonstrated. This shows the method's flexibility for dealing with complicated arterial geometries and its ability to superselectively label small intracranial arteries.

Assessment of thrombus in acute middle cerebral artery occlusion using thin-slice nonenhanced Computed Tomography reconstructions.

BACKGROUND AND PURPOSE: We sought to evaluate how accurately length and volume of thrombotic clots occluding cerebral arteries of patients with acute ischemic stroke can be assessed from nonenhanced CT (NECT) scans reconstructed with different slice widths. METHODS: NECT image data of 58 patients with acute ischemic stroke with vascular occlusion proven by CT angiography were reconstructed with slice widths of 1.25 mm, 2.5 mm, 3.75 mm, and 5 mm. Thrombus lengths and volumes were quantified based on these NECT images by detecting and segmenting intra-arterial hyperdensities. The results were compared with reference values of thrombus length and volume obtained from CT angiography images using Bland-Altman analysis and predefined levels or tolerance to find NECT slice thicknesses that allow for sufficiently accurate thrombus quantification. RESULTS: Thrombus length can be measured with high accuracy using the hyperdense middle cerebral artery sign detected in NECT images with slice thicknesses of 1.25 mm and 2.5 mm. We found mean deviations from the reference values and limits of agreement of -0.1 mm+/-0.6 mm with slice widths of 1.25 mm and 0.1 mm+/-0.7 mm for slice widths of 2.5 mm. Thrombus length measurements in NECT images with higher slice width and all evaluated thrombus volume measurements exhibited severe dependence on the level and did not match the accuracy criteria. CONCLUSIONS: The length of the hyperdense middle cerebral artery sign as detected on thin-slice NECT reconstructions in patients with acute ischemic stroke can be used to quantify thrombotic burden accurately. Thus, it might qualify as a new diagnostic parameter in acute stroke management that indicates and quantifies the extent of vascular obliteration.

Four patients with speech delay, seizures and variable corpus callosum thickness sharing a 0.440 Mb deletion in region 1q44 containing the HNRPU gene.

Structural genome aberrations are frequently associated with highly variable congenital phenotypes involving mental retardation and developmental delay. Although some of these aberrations may result in recognizable phenotypes, a high degree of phenotypic variability often complicates a comprehensive clinical and genetic diagnosis. We describe four patients with overlapping deletions in chromosomal region 1q44, who show developmental delay, in particular of expressive speech, seizures, hypotonia, CNS anomalies, including variable thickness of the abnormal corpus callosum in three of them. High resolution oligonucleotide and SNP array-based segmental aneuploidy profiling showed that these three patients share a 0.440 Mb interstitial deletion, which does not overlap with previously published consensus regions of 1q44 deletions. Two copies of AKT3 and ZNF238, two previously proposed dosage sensitive candidate genes for microcephaly and agenesis of the corpus callosum, were retained in two of our patients. The deletion shared by our patients encompassed the FAM36A, HNRPU, EFCAB2 and KIF26B genes. Since HNRPU is involved in the regulation of embryonic brain development, this represents a novel plausible candidate gene for the combination of developmental delay, speech delay, hypotonia, hypo- or agenesis of the corpus callosum, and seizures in patients with 1q44 deletions. Since only one of the two patients with deletions including the ZNF124 gene showed a vermis hypoplasia, mere hemizygosity for this gene is not sufficient to cause this anomaly. Moreover, to reconcile the variability in the corpus callosum thickness, additional mechanisms, such as unmasking of hemizygous mutations, position effects and possible interactions with other loci need consideration.

Complication rate in unprotected carotid artery stenting with closed-cell stents.

INTRODUCTION: The discussion on the use of protection devices (PDs) in carotid artery stenting (CAS) is gaining an increasing role in lowering the periprocedural complication rates. While many reviews and reports with retrospective data analysis do promote the use of PDs the most recent multi-centre trials are showing advantages for unprotected CAS combined with closed-cell stent designs. METHODS: We retrospectively analysed 358 unprotected CAS procedures performed from January 2003 to June 2009 in our clinic. Male/female ratio was 2.68/1. The average age was 69.3 years. Seventy-three percent (261/358) showed initial neurological symptoms. All patients were treated on a standardised interventional protocol. A closed and small-sized cell designed stent was implanted in most cases (85.2%). One hundred seventy-one (47.8%) were controlled by Doppler ultrasonography usually at first in a 3-month and later in 6-month intervals. RESULTS: The peri-interventional and 30-day mortality/stroke rate was 4.19% (15/358). These events included three deaths, five hyperperfusion syndromes (comprising one death by a secondary fatal intracranial haemorrhage), one subarachnoid haemorrhage and seven ischaemic strokes. Only 20% (3/15) of all complications occurred directly peri-interventional. The overall peri-interventional complication rate was 0.8% (3/358). Most complications occurred in initial symptomatic patients (5.36%). The in-stent restenosis rate for more than 70% was 7% (12/171) detected at an average of 9.8 month. CONCLUSION: Our clinical outcome demonstrates that unprotected CAS with small cell designed stents results in a very low procedural complication rate, which makes the use of a protection device dispensable.

Dyschromatosis ptychotropica: an unusual pigmentary disorder in a boy with epileptic encephalopathy and progressive atrophy of the central nervous system-a novel entity?

The skin and the central nervous system are tissues of common ectodermal origin and share a close ontogenetic relationship. Genetic diseases primarily affecting both organ systems are regularly encountered in both dermatological and neurological settings. Here, we report on a boy with epileptic encephalopathy, severe intellectual disability, optic atrophy, and progressive cerebellar and supratentorial atrophy, reminiscent of progressive encephalopathy with edema and hypsarrythmia (PEHO) syndrome displaying a previously undescribed dyschromatosis in the form of progressive reticulate and mottled hyper- and hypopigmentation of the neck and the inguinal and axillary regions. We hypothesised that this combination of neurological and cutaneous findings has a common aetiology and represents a novel recognisable entity. Because of the unusual dermatological findings, we suggest the term dyschromatosis ptychotropica. Recognition of further cases may help elucidate the aetiology of this condition and give insight into the pathophysiology of both pigmentation disorders and epileptic encephalopathies.

The POST trial: initial post-market experience of the Penumbra system: revascularization of large vessel occlusion in acute ischemic stroke in the United States and Europe.

BACKGROUND AND PURPOSE: The purpose of this study was to assess the initial post-market experience of the device and how it is compared with the Penumbra Pivotal trial used to support the 510k application. METHODS: A retrospective case review of 157 consecutive patients treated with the Penumbra system at seven international centers was performed. Primary endpoints were revascularization of the target vessel (TIMI score of 2 or 3), good functional outcome as defined by a modified Rankin scale (mRS) score of ≤2 and incidence of procedural serious adverse events. Results were compared with those of the Penumbra pivotal trial. RESULTS: A total of 157 vessels were treated. Mean baseline values at enrollment were: age 65 years, NIHSS score 16. After use of the Penumbra system, 87% of the treated vessels were revascularized to TIMI 2 (54%) or 3 (33%) as compared with 82% reported in the Pivotal trial. Nine procedural serious adverse events were reported in 157 patients (5.7%). All-cause mortality was 20% (32/157), and 41% had a mRS of ≤2 at 90-day follow-up as compared with only 25% in the Pivotal trial. Patients who were successfully revascularized by the Penumbra system had significantly better outcomes than those who were not. CONCLUSION: Initial post-market experience of the Penumbra system revealed that the revascularization rate and safety profile of the device are comparable to those reported in the Pivotal trial. However, the proportion of patients who had good functional outcome was higher than expected.

Subacute stent thrombosis in intracranial stenting.

BACKGROUND AND PURPOSE: We sought to determine the safety of intracranial stenting with respect to subacute stent thrombosis in patients being treated with standardized antiplatelet therapy. METHODS: We retrospectively evaluated the outcome of primary intracranial stenting of atherosclerotic stenoses and of stenting in coil embolization procedures in 67 patients. We focused on those cases that led to subacute stent thrombosis even though the patients had been treated with standardized antiplatelet therapy before, during, and after stent placement. Patient age ranged from 19 to 78 years. In 33 patients, stents were placed for treatment of atherosclerotic stenoses; in the remaining 34 patients, stents were placed to assist coiling of aneurysms. The patients in this study were treated between January 2003 and August 2007. RESULTS: Of the total 67 patients initially treated successfully by intracranial stenting, 7 patients developed subacute stent thrombosis. Of these 7 patients, 3 received stent placement into the basilar artery because of an underlying stenosis; in 1 patient, a stenosis of the M1 segment of the middle cerebral artery was treated. In 3 patients, aneurysms of the anterior cerebral artery, the posterior inferior cerebellar artery, and the basilar artery were treated by stent-assisted coil embolization. In 4 of the 7 patients with subacute thrombosis, recanalization of stents by local application of recombinant tissue-type plasminogen activator was successful. CONCLUSIONS: Intracranial stenting can lead to subacute stent thrombosis, even in patients who are treated with standardized antiplatelet therapy. Such complications have been described for patients after coronary artery stenting, but to our knowledge, no one has reported on a comparable number of cases of intracranial stenting procedures. In certain clinical scenarios, local thrombolysis with recombinant tissue-type plasminogen activator is an important treatment option to deal with subacute stent thrombosis.

Association of right-to-left shunt with frontal white matter lesions in T2-weighted MR imaging of stroke patients.

INTRODUCTION: Cardiac right-to-left shunt (RLS), mainly due to patent foramen ovale (PFO), is a risk factor for paradoxical embolism and stroke. Results of studies about brain lesions in diffusion-weighted imaging (DWI) in PFO patients were controversial. DWI only detects acute ischemic lesions. We assessed the hypothesis that, in T2-weighted magnetic resonance imaging (T2WI) of stroke patients, RLS is associated with a typical distribution of small white matter lesions. MATERIALS AND METHODS: In this retrospective case-control study, T2WI images of 162 stroke patients were evaluated. From stroke patients admitted between 1999 and 2003, 81 stroke patients with RLS were identified with contrast-enhanced transcranial Doppler (bubble test). Controls were 81 age-matched stroke patients without RLS (negative bubble test). In T2WI images, small lesions (<2 cm) were categorized depending on their location in subcortical white matter, peritrigonal white matter, deep and paraventricular white matter, and basal ganglia. Additionally, larger territorial infarcts were rated. RESULTS: In T2WI frontal or predominantly frontal-located subcortical small white matter, lesions are significantly associated with RLS (p < 0.0001, chi-square test). Forty-three patients with RLS (53%) and only 19 control patients (23%) showed this frontal dominance. Odds ratio is 3.7 (95% confidence interval = 1.9-7.1) for having a RLS when T2WI shows this lesion pattern in a stroke patient. No patient of the RLS group and 6% of the control group had parietal dominance. Distribution of small lesions in other locations like basal ganglia or deep white matter showed no significant difference for the groups. CONCLUSION: A distribution of mainly frontal subcortical small white matter lesions in T2WI is significantly associated with RLS in stroke patients.

Hemodynamic assessment of carotid stenosis by functional magnetic resonance imaging.

BACKGROUND: Functional magnetic resonance imaging (fMRI) is a method usually used to identify cortical representations of cerebral functions. Some studies and case reports suggest that stenoses of the brain-supplying arteries influence the BOLD (blood-oxygenation-level-dependent) signal. The objective of this study was to find out whether the BOLD signal differs in the ipsilateral hemisphere of patients with hemodynamically relevant and those with irrelevant stenosis of the internal carotid artery (ICA) and if a successful treatment might have an influence on the BOLD signal. METHODS: We included 10 patients with hemodynamically relevant stenosis in group 1; another 10 patients with hemodynamically irrelevant stenosis of the ICA were included in group 2. Patients underwent recanalization by either stenting or operation of the ICA. fMRI with a hand-tapping task was performed before and after treatment. Data were analyzed with 'Statistical Parametric Mapping' 2 for both hemispheres. An asymmetry index (AI, range 0-2) was calculated for the hand motor areas. RESULTS: All data are given as means +/- SD. The mean preinterventional AI in group 1 was 1.08 +/- 0.87 and 0.30 +/- 0.54 in group 2 (p = 0.029). The mean postinterventional AI was 0.32 +/- 0.29 in group 1 and 0.25 +/- 0.21 in group 2 (p = 0.599). CONCLUSION: fMRI is not only capable of delivering spatial information, but also of distinguishing a hemodynamically relevant from an irrelevant stenosis of the ICA.

Clinical and angiographic risk factors for stroke and death within 30 days after carotid endarterectomy and stent-protected angioplasty: a subanalysis of the SPACE study.

BACKGROUND: Carotid endarterectomy (CEA) and carotid artery stenting (CAS) are used to prevent ischaemic stroke in patients with stenosis of the internal carotid artery. Better knowledge of risk factors could improve assignment of patients to these procedures and reduce overall risk. We aimed to assess the risk of stroke or death associated with CEA and CAS in patients with different risk factors. METHODS: We analysed data from 1196 patients randomised to CAS or CEA in the Stent-Protected Angioplasty versus Carotid Endarterectomy in Symptomatic Patients (SPACE) trial. The primary outcome event was death or ipsilateral stroke (ischaemic or haemorrhagic) with symptoms that lasted more than 24 h between randomisation and 30 days after therapy. Six predefined variables were assessed as potential risk factors for this outcome: age, sex, type of qualifying event, side of intervention, degree of stenosis, and presence of high-grade contralateral stenosis or occlusion. The SPACE trial is registered at Current Controlled Trials, with the international standard randomised controlled trial number ISRCTN57874028. FINDINGS: Risk of ipsilateral stroke or death increased significantly with age in the CAS group (p=0.001) but not in the CEA group (p=0.534). Classification and regression tree analysis showed that the age that gave the greatest separation between high-risk and low-risk populations who had CAS was 68 years: the rate of primary outcome events was 2.7% (8/293) in patients who were 68 years old or younger and 10.8% (34/314) in older patients. Other variables did not differ between the CEA and CAS groups. INTERPRETATION: Of the predefined covariates, only age was significantly associated with the risk of stroke and death. The lower risk after CAS versus CEA in patients up to 68 years of age was not detectable in older patients. This finding should be interpreted with caution because of the drawbacks of post-hoc analyses.

Magnetic resonance imaging of individual cerebral perfusion territories improves the diagnosis of embolic stroke.

This case study demonstrates the feasibility and diagnostic value of the oblique-plane arterial spin labeling method to visualize individual perfusion territories in a patient with embolic stroke. The perfusion territories obtained with this technique differed significantly from the standard anatomical situation. Imaging findings suggested that all acute embolic lesions in both hemispheres had arisen from one symptomatic internal carotid artery stenosis.

Evolution of hippocampal CA-1 diffusion lesions in transient global amnesia.

OBJECTIVE: Selective focal MR-Signal (diffusion-) changes in the CA-1 sector of the hippocampus have been described in transient global amnesia (TGA), but the pathophysiological substrate of these lesions is largely unknown. As several imaging and epidemiological findings point to a vascular origin an analysis of the temporal evolution of the hippocampal apparent diffusion coefficient (ADC) changes may offer new understanding of the pathomechanisms of TGA. METHODS: The time course of the ADC of hippocampal DWI lesions in TGA patients was studied using serial 3 T high-resolution MR-imaging within 1-10 days as well as 4-6 months after TGA. ADC values from 76 MR-studies were analyzed and expressed as ratio ADC (rADC) in reference to the unaffected hemisphere. RESULTS: Twenty-nine patients with TGA showed 34 DWI lesions with corresponding T2 lesions in the CA-1 sector of the hippocampal cornu ammonis within a time window of 24-72 h after onset. Ratio ADC decreased below 1.0 (0.66 +/- 0.08) 24 h after the acute TGA episode and did show a further significant decrease to 0.57 +/- 0.1 after 3 days (p < 0.05). After 72 h, rADC increased and normalized around day 10 with rADC values of 1.0 (p < 0.05). INTERPRETATION: The temporal evolution of the rADC in hippocampal signal changes in TGA shows a time course previously described for ischemic lesions in human stroke patients. This might imply a vascular origin of diffusion changes leading to a transient perturbation of memory relevant circuits in the hippocampus.

Neuropsychological consequences of endarterectomy and endovascular angioplasty with stent placement for treatment of symptomatic carotid stenosis: a prospective randomised study.

BACKGROUND AND PURPOSE: Previous studies compared carotid endarterectomy (CEA) and carotid artery stent placement (CAS) for treatment of symptomatic carotid artery stenosis. Whereas most previous studies showed both treatment modalities to be associated with a comparable risk of periprocedural cerebrovascular complications, these previous studies have shown significantly more microemboli and significantly more lesions in diffusion-weighted MR imaging after CAS compared to CEA. The clinical relevance of these differences remains unknown. We therefore compared the neuropsychological consequences of CAS and CEA and additionally measured the S100beta protein, a marker of cerebral damage. METHODS: A total of 48 patients with symptomatic carotid artery stenosis greater than 70 % (according to ECST criteria) were enrolled and 45 patients participated in the follow-up. The patients were randomly assigned for CEA (24 patients) or CAS (21 patients). S100beta protein values were evaluated 2 hours before the procedure, as well as one and two hours thereafter. Patients were assessed before treatment, and again 6 and 30 days after treatment using a comprehensive neuropsychological test battery. RESULTS: Patients of the CAS and the CEA groups did not significantly differ in terms of age, gender, education, degree of carotid artery stenosis, cerebrovascular symptoms and vascular risk factors. Following previously used criteria, a cognitive change in patients was assumed to have occurred when there was a decline of more than one standard deviation in two or more tests assessing various cognitive domains. Six days and 30 days after the treatment both groups showed a comparable number of patients with cognitive changes compared to baseline. There were no significant differences in S100beta protein values. CONCLUSION: These results provide some reassurance that CAS is not associated with greater cognitive deterioration than CEA is.

Aggressive therapy with intravenous abciximab and intra-arterial rtPA and additional PTA/stenting improves clinical outcome in acute vertebrobasilar occlusion: combined local fibrinolysis and intravenous abciximab in acute vertebrobasilar stroke treatment (FAST): results of a multicenter study.

BACKGROUND AND PURPOSE: A combined therapy of local recombinant tissue plasminogen activator (rtPA) fibrinolysis and intravenous Abciximab platelet inhibition with additional percutaneous transluminal angioplasty (PTA)/stenting may improve recanalization and neurological outcome in patients with acute vertebrobasilar occlusion. METHODS: Combined FAST therapy consisted on intravenous bolus of Abciximab (0.25 mg/kg) followed by a 12-hour infusion therapy (0.125 microg/kg per minute) and low-dose intra-arterial rtPA (median dosage: 20 mg, FAST cohort: N=47). The results were compared with a retrospective cohort, treated by intraarterial rtPA monotherapy (median dosage: 40 mg, rtPA cohort, N=41). Additional PTA/stenting was performed in case of severe residual stenosis. Recanalization success was classified according to the Trials in Myocardial Infarction (TIMI) criteria: TIMI0/1, failed recanalization; TIMI2/3, successful recanalization. Bleeding complications were evaluated according to severe extracerebral hemorrhage (ECH), asymptomatic intracerebral hemorrhage (AIH), and symptomatic intracerebral hemorrhage (SIH). RESULTS: Overall bleeding rate was higher under the combined therapy, but the SIH rate did not differ (FAST versus rtPA: ECH, 3% versus 0%; AIH, 32% versus 22%; SIH 13% versus 12%). Additional PTA/stenting was performed in 14 (FAST) versus 5 (rtPA) patients. TIMI2/3 recanalization rate was similar (FAST, 72%; rtPA, 68%), but TIMI3 rate was remarkably higher under combined therapy (FAST, 45%; rtPA, N=22%). Neurologic outcome appeared better under combined therapy (FAST versus rtPA: favorable outcome rate: 34% versus 17%) with a significantly lower mortality rate (FAST versus rtPA: 38% versus 68%; P=0.006). These results were consistent for embolic and atherothrombotic occlusions. CONCLUSIONS: Combined therapy of intravenous Abciximab and half dose intra-arterial rtPA with additional PTA/stenting appears to improve neurologic outcome in acute vertebrobasilar occlusion despite an increase of overall bleeding complications.

Improving the amplitude-modulated control experiment for multislice continuous arterial spin labeling.

The use of an amplitude-modulated radiofrequency (RF) pulse for a control experiment is a proven method to control for off-resonance effects in multislice continuous arterial spin labeling (CASL) experiments. This method is also known as double adiabatic inversion. The adiabaticity factor of a single half-pulse, beta(1/2), and a new dimensionless parameter alpha, which is obtained from the labeling parameters and the flow velocity, are introduced. This makes it possible to distinguish three distinct cases: 1) With low alpha, a double inversion occurs. 2) With alpha > or = approximately 4, the efficiency with which the longitudinal magnetization is returned to the z-axis depends on the phase of the amplitude modulation at the time the spins cross the center of the labeling plane. 3) In the intermediate region, the efficiency shows undesirable fluctuations. In a Bloch equation simulation, three optimized parameter sets are determined. Near ideal performance should always be achieved by combinations of parameters for which beta(1/2) > or = approximately 2 and alpha approximately pi/beta(1/2). The efficiency increases were realized in a volunteer study, showing the practical application of the suggested optimization.

Continuous artery-selective spin labeling (CASSL).

A new technique for selective spin labeling of individual arteries is presented. It is based on continuous arterial spin labeling (CASL) with an amplitude-modulated control experiment. Precessionary motion of the labeling gradient about the axis of the artery, combined with an appropriate frequency modulation of the labeling RF pulse, restricts the adiabatic inversion to the desired artery. In phantom studies, it was found that the level of selectivity could be controlled by the sequence parameters, and that the achievable labeling efficiency was at a level of approximately 80% compared to a regular, nonselective CASL experiment. In a volunteer study we acquired high-quality images of the perfusion territories of the internal carotid artery (ICA), the basilar artery (BA), the middle cerebral artery (MCA), and both anterior cerebral arteries (ACAs). The results show the method's flexibility for different geometries and flow velocities. Potential applications include perfusion territory imaging of smaller cerebral arteries, and selective angiography techniques.

Brain perfusion territory imaging applying oblique-plane arterial spin labeling with a standard send/receive head coil.

A new method for the selective spin labeling of left- or right-sided supplying arteries of the brain without the need for additional RF coils is demonstrated. A clinical 1.5 T scanner was used. The spatial selectivity of the labeling process is based on the limited coverage of the excitation field of a standard send/receive head coil together with an oblique positioning of the labeling plane. A computer simulation was used to optimize key labeling parameters under the condition of laminar flow. The validity of the computer model results was confirmed by MRI measurements with a flow model. For human studies, a double-inversion continuous arterial spin labeling (CASL) sequence was modified to allow for arbitrary positioning of the labeling plane. The obtained perfusion-weighted images showed a clear delineation of the perfusion territories of the selected arteries in the anterior circulation of the brain and good gray/white matter contrast.