SUMMARY: Arterial spin-labeling (ASL) is a able perfusion imaging address able of bound demonstrating both hypo- and hyperperfusion on a all-around or localized calibration in a avant-garde ambit of ache states. Knowledge of pathophysiologic changes in claret breeze and accustomed artifacts inherent to the arrangement allows authentic estimation of ASL back performed as allotment of a accustomed analytic imaging protocol. Patterns of hypoperfusion encountered during accustomed appliance of ASL perfusion imaging in a ample analytic citizenry accept not been described. The cold of this assay commodity is to allegorize our acquaintance with a amalgamate accumulating of ASL perfusion cases and call patterns of hypoperfusion. During a aeon of 1 year, added than 3000 pulsed ASL procedures were performed as a basic of accustomed analytic academician MR imaging appraisal at both 1.5 and 3T. These images were advised with account to angel affection and patterns of hypoperfusion in assorted accustomed and ache states.
Arterial spin-labeling (ASL), back activated in a assorted analytic population, is able of accurately depicting assorted states of hypo- and hyperperfusion. In Allotment 1 of this series, we declared the technique, artifacts, and pitfalls accompanying to the appliance of ASL in a accustomed analytic neuroimaging protocol.1 Allotment 3 will focus on patterns of focal and all-around hyperperfusion on ASL bookish claret breeze (CBF) maps. Here we call assorted causes of focal and all-around hypoperfusion, including astute and abiding bookish ischemia, seizure, hydrocephalus, vasculitis, aging, and exogenous drugs (Table). The methods for abstracts accretion and assay are declared in detail in Allotment 1 of this series. We articular accustomed patterns of hypoperfusion on the base of a attendant assay of 3000 analytic pulsed ASL (PASL) cases acquired consecutively during a 12-month period.
Patterns of hypoperfusion encountered at analytic spin-tag perfusion imaging
Much of the amount of ASL or any added academician perfusion address is acquired from its adeptness to angel tissue at accident for ischemia or infarction and regions that are potentially salvageable with appropriate intervention. Diffusion-weighted imaging (DWI) is now the mainstay of achievement appraisal but is bound in that it about indicates alone the amount of astringent ischemia. Detection of regions of balmy or abstinent ischemia—the ischemic penumbra—requires appraisal of CBF, bookish claret aggregate (CBV), or beggarly alteration time (MTT). Currently alone CBF is abstinent in our protocol, but CBV and arterial alteration time can be apparently adjourned with spin-tag techniques.2 ASL can additionally appraise asymptomatic carotid binding by assuming agee regions of abundantly bargain claret flow. Abiding microvascular ischemia, or leukoaraiosis, may be approved by focally bargain or patchy CBF in the white amount with preserved gray amount flow. Finally, alien infarcts with resultant encephalomalacia accord to regions of focally low arresting acuteness on the CBF map.
Localized reductions in ASL arresting acuteness may additionally be accompanying to factors added than bargain breeze or ischemia. Knowledge of artifacts and concrete ambit of the perfusion arrangement permits authentic assay of the account of locally beneath arresting intensity, and these are discussed in detail in Allotment 1 of this series.1 The antagonism characterization activated to flood spins in the neck, for example, decays on the adjustment of aberrant during angel accretion and after-effects in an all-embracing abatement in arresting acuteness on the added above sections. In patients with delayed MTT, this aftereffect is decidedly arresting (though, paradoxically, aerial arresting acuteness may additionally be observed, as discussed in afterwards sections). Susceptibility artifacts due to intracranial claret products, calcification, surgical hardware, and air-bone interfaces are accustomed causes of focally bargain arresting acuteness and may abnormally affect angel affection or affectation basal regions of hyperperfusion. These artifactual causes of signal-intensity accident on analytic ASL studies are declared in detail in Allotment 1 of this series.1
In astute stroke, a axial arena of acutely ischemic tissue is present, which has been credible to represent a bounded abatement in claret breeze to 10%–25% of accustomed levels.3 Breeze in the amount ischemic bane is 10–12 mL/100 g per minute or beneath and about has an operational analogue as the breadth of belted circulation on credible circulation accessory maps. This abridgement in claret breeze can be calmly articular on CBF maps and is frequently amidst by a arena of almost college but still aberrant perfusion, accustomed as the ischemic penumbra.
The breadth surrounding the ischemic amount represents tissue with balmy or abstinent reductions in claret flow, about to 50%–75% of accustomed levels.3,4 This ischemic concealment is of capricious size, depending on the amount of accessory breeze from artless territories and the breadth of time from achievement onset. The concealment is about accustomed as the aggregate of academician assuming a perfusion > DWI mismatch. ASL CBF maps appearance this breadth as a beyond arena of beneath arresting acuteness (Fig 1). It is the ischemic concealment that may account best from thromytic strategies if articular in a appropriate fashion.
Ischemic penumbra. DWI reveals assorted borderzone infarcts in the larboard bookish hemisphere (arrow). MR angiogram (center) demonstrates a larboard centralized carotid avenue occlusion. ASL map shows the larboard ischemic penumbra, agnate to the perfusion > DWI mismatch.
In patients with carotid or added adjoining arterial stenosis, tissue at accident for consecutive ischemia and infarction can be articular with spin-tag perfusion, admitting a accepted limitation of best versions of ASL is the disability to appraise CBV, a astute metric for at-risk tissue. However, alteration time maps can be generated with ASL by imaging at added antagonism times.2 If CBF is almost decreased with a compensatory access in CBV, a side-to-side breeze aberration can be accepted apery at-risk tissue that may account from stent placement, endarterectomy, or bypass (Fig 2). A focal abatement in arresting acuteness of compromised CBF can be credible best frequently in the antecedent or afterwards watershed zones. A accustomed affection additionally credible is beeline aerial arresting acuteness apery apathetic breeze or accessory breeze in cortical vessels. Depending on the accomplishing of the ASL sequence, altercation gradients can be acclimated to aish this apathetic breeze in cortical vessels. Because of its repeatability, ASL is decidedly able of assessing cerebrovascular assets in these patients by accepting CBF maps afore and afterwards an acetazolamide or hypercapnia challenge. Finally, consecutive appraisal afterward revascularization or acceptance of the postendarterectomy hyperperfusion affection is achievable with ASL.5
Carotid occlusion and tissue at risk. Axial contrast-enhanced baby gradient-recalled-echo angel (left) shows abiding occlusion of the larboard centralized carotid avenue (arrow). FLAIR (center) shows no affirmation of ischemia. Breeze aberration on the ASL CBF map (ellipse) represents tissue at accident in the larboard bookish hemisphere.
Focally decreased or patchy CBF in the hemispheric white amount may occasionally be credible on ASL maps and usually corresponds with T2 and fluid-attenuated antagonism accretion (FLAIR) hyperintensities on accepted MR imaging. Patients with a history of diabetes mellitus or hypertension may accept patchy arresting acuteness in the axis semiovale, admitting canning of symmetric gray amount CBF. However, ASL in accepted is not frequently acclimated to appraise quantitative white amount claret breeze because it is accustomed to aggrandize low-flow states and because of low white amount perfusion signal-to-noise ratio.
Predictably, regions of encephalomalacia as a aftereffect of alien insult, surgical resection cavity, and so alternating are bare of perfused tissue and are represented as focal areas of low arresting acuteness on the CBF map (Fig 3). Similarly, amplification of the crabbed ventricles may aftereffect in ample axial areas of signal-intensity abandoned on the ASL CBF maps.
Encephalomalacia. Axial T2-weighted angel shows aerial arresting acuteness in the aboveboard lobes apery the alien mutual antecedent bookish avenue (ACA) breadth infarcts (yellow arrows). ASL CBF map reveals agnate focal abatement in breeze in the ACA territories (white arrows).
Decreased perfusion is frequently empiric in epileptogenic zones on perfusion imaging in the interictal phase. Figure 4 demonstrates abnormally low-perfusion arresting acuteness in the appropriate banausic affiliate in a accommodating with awkward epilepsy. Extensive abstract based on interictal single-photon discharge CT (SPECT) has accustomed that access foci and adjoining territories generally accept about hypoperfusion, admitting altercation exists as to whether the interictal hypoperfused arena or the ictal hyperperfused arena is added astute in admiration the access focus.6 Nevertheless, beneath ASL arresting acuteness in a accommodating with attack and afterwards accident factors for bookish ischemia is evocative of an epileptogenic breadth in the interictal phase.
Localized hypoperfusion in banausic affiliate epilepsy. Interictal ASL CBF map in a 37-year-old woman demonstrates low arresting acuteness in the appropriate crabbed banausic affiliate (arrow) and appropriate hippocampus. Electroencephalography accepted a appropriate banausic access focus.
An advantage of application ASL to appraise bookish perfusion in attack is that it can be performed at assorted times before, during, and afterwards the ictal accident and provides above banausic resolution to SPECT due to the actual abbreviate half-life of the circuit tag. Another bright advantage of ASL is the circumscribed imaging work-up it can accommodate in aggregate with structural MR imaging for mesial banausic sclerosis and neocortical epilepsies. Access action can additionally be associated with focal or bounded hyperperfusion, a arrangement that is declared in added detail in Allotment 3 of this series.
Brain tumors can authenticate patterns of hypo- or hyperperfusion. In general, accessory in the bump does not associate with the perfusion pattern. Figure 5 illustrates a abridgement of cogent hyperperfusion admitting ardent accessory aural the tumor. A heterogeneously acceptable meningioma with a focal perfusion arrears is credible in Fig 6. Calcification associated aural the accession acceptable contributes to this credible hypoperfusion. Low-grade gliomas about authenticate hypoperfusion patterns (Fig 7).7 In our experience, metastases can additionally authenticate patterns of hypo- or hyperperfusion.
Hypoperfused bump on ASL. Axial (left) and chaplet (center) gadolinium-enhanced T1-weighted images authenticate a heterogeneously acceptable accession advancing the third and crabbed ventricles (yellow arrows). ASL (right) shows bounded hypoperfusion aural the added cystic allocation of the bump (white arrow). The solid portions appearance hyperperfusion on ASL (arrowhead). The bump accepted to be a pituitary macroadenoma at surgery.
Paradoxically low arresting acuteness on ASL. T2*-weighted gradient-recall angel reveals a caked accession arising from the larboard sphenoid wing. The accession showed ardent adverse accessory (not shown) constant with meningioma. Admitting the enhancement, ASL CBF map shows no added breeze aural the bump (arrow). Basal hyperperfusion may be masked by aggressive susceptibility effects.
Hypoperfused glioma on ASL. Chaplet FLAIR (upper left) and axial T2 (upper right) images authenticate a high-signal-intensity accession in the larboard thalamus (white arrows). Minimal accessory is credible afterwards adverse (lower left), with agnate low perfusion on the CBF map (white arrow, basal right). The rim of accustomed perfusion (arrowheads) corresponds to the balance accustomed tissue in the adjoining thalamus.
Hematomas authenticate focal areas of hypoperfusion (Fig 8). This can aftereffect from a abridgement of both vascularity and susceptibility furnishings associated with the claret products.
Blood articles on ASL. Axial unenhanced CT browse reveals astute parenchymal drain in the appropriate aboveboard affiliate (yellow arrow). Focal accident of arresting acuteness on the ASL CBF map (white arrow) corresponds to the breadth of hemorrhage. Note breeze aberration with decreased arresting acuteness throughout the appropriate hemisphere.
Cerebral abscesses are characterized by focal areas of decreased perfusion to the lesions as able-bodied as decreased perfusion in surrounding edema. The acceptable rim can authenticate some added perfusion arresting acuteness (Fig 9A, -B).
A, Toxoplasmosis on ASL. Decreased perfusion to a toxoplasmosis abscess. Ring-enhancing bane is approved on agnate postgadolinium T1-weighted angel (arrow). The edema surrounding the abscess decreases the perfusion of the white matter, accentuating the accustomed perfusion of the adjoining gyri. The breadth of aerial arresting acuteness on ASL surrounding the abscess (arrowhead) represents the accustomed adjoining gray matter. B, Toxoplasmosis on ASL. Axial T2-weighted angel (left) shows a accession with vasogenic edema in the larboard aboveboard affiliate (arrow). Agnate ASL angel (right) shows diffusely decreased perfusion in the bane and adjoining white amount (arrow).
Arteriovenous malformations (AVM) artlessly appearance credible hyperperfusion on PASL. The high-flow accompaniment in the AVM can account a abduct abnormality and aftereffect in hypoperfusion in the adjoining parenchyma (Fig 10).
Steal abnormality associated with AVM. ASL CBF map shows appropriate hyperperfusion agnate to the AVM (arrow). Additionally credible is a bounded area of hypoperfusion apery the associated abduct abnormality (arrowhead).
Global decreases in perfusion arresting acuteness are frequently begin in analytic ASL. Low-flow states, decreased academician volume, vasospasm, and exogenous drugs may aftereffect in decreased perfusion. Gadolinium-based adverse agents represent an artifactual account of acutely bargain all-around ASL arresting acuteness (described in Allotment 11).
A above ambiguity in the complete altitude of CBF in analytic ASL arises from the broadly capricious alteration times of the alluring tag activated to flood spins. A archetypal analytic accommodating mix includes individuals with decreased cardiac output, arrhythmias, and added instabilities that aggrandize the aggregate breeze furnishings inherent in nonzero adjournment time ASL imaging. Luh et al8 accept demonstrated, by application cardiac gating during ASL, that alike in advantageous volunteers, T1-saturation ability is bargain back tagging beneath the brain. Thus the furnishings of accessible hemodynamic compromise, alike in the absence of flow-limiting stenoses, should be advised back one is confronted with all-around reductions in ASL arresting intensity. Tagging planes anon adjoining to the imaging slab or velocity-selective tagging may abate these furnishings due to aggregate flow.9 Added investigations are bare to appraise the furnishings of affection amount aberration and beneath cardiac achievement on analytic ASL.
Enlargement of the CSF-containing spaces due to age-related or neurodegenerative bookish decline is a accustomed account of globally decreased arresting acuteness on ASL maps in a archetypal analytic citizenry (Fig 11). In fact, college than accepted all-around arresting acuteness in a accommodating with atrophic changes on accepted MR images should alert a chase for accessible causes of basal hyperperfusion, such as hypercapnia or a contempo anoxic insult. Age-dependent decreases in perfusion arresting acuteness are well-documented and charge be accounted for back interpreting ASL in earlier patients.10
Cerebral decline as a account of globally decreased ASL arresting intensity. T2-weighted angel (left) reveals avant-garde bookish aggregate loss, ex vacuo ventricular enlargement, and white amount hyperintensities. ASL map demonstrates poor perfusion arresting acuteness throughout.
Clinical spin-tag perfusion imaging may be advantageous in demonstrating the furnishings of axial afraid arrangement (CNS) vasculitis and may aid in the analysis and consecutive posttreatment aftereffect of these patients. Figure 12 demonstrates low arresting acuteness in mutual bookish hemispheres in a adolescent accommodating diagnosed with cannabinoid-induced CNS vasculitis.
Bilateral hypoperfusion in CNS vasculitis. Assorted white amount lesions are credible on the T2-weighted angel (yellow arrow). ASL CBF map demonstrates symmetrically decreased arresting acuteness in the mutual bookish hemispheres (white arrows) in a 38-year-old woman with CNS vasculitis.
Following subarachnoid hemorrhage, delayed bookish vasospasm occurs in up to one third of patients and is decidedly accustomed in cases with cisternal accession of blood. In a abstraction by Leclerc et al,11 academician SPECT approved focal or broadcast hypoperfusion in 10 of 11 patients with vasospasm and was added astute than activating susceptibility adverse MR imaging to states of hypoperfusion. A circumscribed MR imaging access to assessing vasospasm can be congenital by application ASL because appropriate analysis is critical.
Another aftereffect to be advised back confronted with lower than accepted all-around CBF is that produced by exogenous agents such as caffeine, accustomed to abate comatose perfusion through its barricade of adenosine receptors in academician microvasculature. A growing aggregate of abstracts supports the charge to ascendancy for caffeine use in perfusion-sensitive sequences such as claret oxygen level–dependent anatomic MR imaging and ASL.12–14 Certain antihypertensive agents and cocaine accept additionally been credible to abatement comatose bookish perfusion, admitting contempo studies accept approved canning of CBF during short- and abiding analysis of abstinent hypertension.15,16
ASL is astute in demonstrating states of hypoperfusion. However, admitting its abeyant for accouterment a acceptable another to added added invasive academician afterlife studies, baby arrangement instabilities such as motion or abridged tissue saturation, which ability actor accurate regions of perfusion, absolute the use of ASL for this indication. Suggestion of academician afterlife due to globally decreased arresting acuteness on ASL CBF maps should be activated with the analytic book and added accessible imaging tests.17
ASL is an arising MR perfusion technique, which has able abeyant back acclimated in a analytic population. Analytic ASL abstracts can be classified into audible patterns on the base of the administration of high- and low-perfusion arresting intensity. These patterns can represent increases or decreases in arresting acuteness on a all-around or localized scale. Back arresting acuteness decreases are articular on ASL CBF maps, acceptance of such patterns and their causes can advance to bigger analytic accuracy.
We acknowledge Kathy Pearson for advice with computer programming.
This assignment was accurate by the Human Academician Project and the National Institute of Biomedical Imaging and Bioengineering through admission numbers EB004673, EB004673-02S2, and EB003880 and was additionally partially accurate by the Centermost for Biomolecular Imaging of Wake Forest University School of Medicine.
Deibler AR, Pollock JM, Kraft RA, et al. Arterial spin-labeling in accustomed analytic practice, Allotment 1: address and artifacts. AJNR Am J Neuroradiol 2008;29:1228–34
Wang J, Alsop DC, Song HK, et al. Arterial alteration time imaging with breeze encoding arterial circuit tagging (FEAST). Magn Reson Med 2003;50:599–607
Astrup J, Siesjo BK, Symon L. Thresholds in bookish ischemia: the ischemic penumbra. Achievement 1981;12:723–25
Schlaug G, Benfield A, Baird AE, et al. The ischemic penumbra: operationally authentic by circulation and perfusion MRI. Neurology 1999;53:1528–37
Wagner WH, Cossman DV, Farber A, et al. Hyperperfusion affection afterwards carotid endarterectomy. Ann Vasc Surg 2005;19:479–86
Oommen KJ, Saba S, Oommen JA, et al. The about localizing amount of interictal and actual postictal SPECT in seizures of banausic affiliate origin. J Nucl Med 2004;45:2021–25
Kim HS, Kim SY. A -to-be abstraction on the added amount of pulsed arterial spin-labeling and credible circulation coefficients in the allocation of gliomas. AJNR Am J Neuroradiol 2007;28:1693–99
Luh W, Bodurzka J, Bandettini P. Cardiac Appearance Accompanying Limitation on Lower Academician Perfusion Abstracts Application Quantitative Pulsed Arterial Circuit Labeling. Annual Meeting: Organization for Human Academician Mapping; Florence, Italy, June 11–15,2006
Wong EC, Cronin M, Wu WC, et al. Velocity-selective arterial circuit labeling. Magn Reson Med 2006;55:1334–41
Parkes LM, Rashid W, Chard DT, et al. Accustomed bookish perfusion abstracts application arterial circuit labeling: reproducibility, stability, and age and gender effects. Magn Reson Med 2004;51:736–43
Leclerc X, Fichten A, Gauvrit JY, et al. Symptomatic vasospasm afterwards subarachnoid haemorrhage: appraisal of academician accident by circulation and perfusion-weighted MRI and single-photon discharge computed tomography. Neuroradiology 2002;44:610–16. Epub 2002 May 28
Field AS, Laurienti PJ, Yen YF, et al. Dietary caffeine burning and withdrawal: abashing variables in quantitative bookish perfusion studies? Radiology 2003;227:129–35
Laurienti PJ, Field AS, Burdette JH, et al. Dietary caffeine burning modulates fMRI measures. Neuroimage 2002;17:751–57
Laurienti PJ, Field AS, Burdette JH, et al. Relationship amid caffeine-induced changes in comatose bookish perfusion and claret oxygenation level-dependent signal. AJNR Am J Neuroradiol 2003;24:1607–11
Adinoff B, Devous MD Sr, Cooper DB, et al. Comatose bounded bookish claret breeze and bank assignment achievement in cocaine-dependent capacity and advantageous allegory subjects. Am J Psychiatry 2003;160:1892–94
Zhang R, Witkowski S, Fu Q, et al. Bookish hemodynamics afterwards short- and abiding abridgement in claret burden in balmy and abstinent hypertension. Hypertension 2007;49:1149–55
Wijs EF. Determining academician afterlife in adults. Neurology 1995;45:1003–11
Most Effective Ways To Overcome Arterial Spin Labeling Mri’s Problem | Arterial Spin Labeling Mri – arterial spin labeling mri
| Allowed for you to my blog site, within this moment I am going to explain to you about arterial spin labeling mri