Arterial spin-labeling MR imaging in moyamoya disease compared with clinical assessments and other MR imaging finings
Introduction
Moyamoya disease (MMD) is a slowly progressive intracranial vascular steno-occlusive disease of unknown etiology that was first reported in 1957 by Takeuchi et al. [1]. MMD is characterized by bilateral progressive occlusion of the distal part of the internal carotid artery (ICA), and the proximal part of the middle (MCA) and anterior cerebral arteries (ACA), in association with irregular vascular networks, referred to as moyamoya vessels, around steno-occlusive regions [2].
Digital subtraction angiography (DSA) is a standard method for evaluating blood vessels that provides useful information for treatment. However, DSA is relatively invasive and requires careful management, especially of pediatric MMD patients, who often require general anesthesia. After magnetic resonance imaging (MRI) and three-dimensional time-of-flight MR angiography (MRA) guidelines were established for the diagnosis and treatment of MMD [3], MRI and MRA have been well accepted as standard diagnostic and follow-up procedures for MMD [4], [5], [6], [7].
On the other hand, estimations of the brain perfusion are still based on nuclear medicine brain perfusion studies such as positron emission tomography (PET) or single-photon emission computed tomography (SPECT) imaging [8], [9], [10]. Although PET and SPECT are the gold-standard examinations for brain perfusion information, they cannot be performed frequently in clinical practice because they require special facilities, expensive agents, and invasive examination methods. While new methods of dynamic susceptibility contrast MRI (DSC-MRI) and dynamic helical computed tomography (CT) have been developed for brain perfusion studies [11], [12], these modalities have disadvantages, including the need to administer contrast material and procedural difficulties such as with the bolus injection technique. These disadvantages are exacerbated in cases involving pediatric patients.
Arterial spin-labeling (ASL) is a non-invasive imaging technique of acquiring blood flow information by MRI [13], and ASL-MRI has been applied to measure flow rates in various CNS disorders [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. Recently, CBF values obtained by ASL-MRI in MMD patients were reported to be more strongly correlated with SPECT imaging with iodine-123-N-isopropyl-p-iodoamphetamine (123I-IMP) with acetazolamide challenge than without [21]. Therefore, ASL-MRI could indicate potentially ischemic areas, in addition to unequivocally damaged regions of interest. However, the causal factors for the results remain to be clarified. Our purpose with this study was to account for the results obtained with ASL-MRI in MMD patients by comparatively assessing ASL-MRI, clinical information, and other MRI findings.
Section snippets
Materials and methods
The current retrospective research was approved by our institutional review board (No. 2011-07-01).
Magnetic resonance imaging
ASL-MRI and other MRI scans were carried out as part of the routine clinical brain MR examinations performed on a clinical 3.0-Tesla MR imaging unit (MAGNETOM Trio, A Tim System, Siemens AG, Erlangen, Germany) with a 12-channel head coil.
Hemispheric CBF value of ASL-MRI (ASL value)
The details regarding these processing methods have been reported previously [14], [21]. The hemispheric CBF values of ASL-MRI (ASL values) were calculated on both sides of the cerebrum in each patient (see Appendix 2).
MRA score
Houkin's grading system for MRA on MMD was adopted to evaluate the steno-occlusive severity of intracranial vessels on MRA (Table 1) [6]. The related anatomical hallmarks were added to the definitions, as Houkin's grading system presents some judgmental difficulties [7]. The MRA
Image evaluation methods
All images were observed on a computer viewer system (ViewR version 1.09.15, Yokogawa Electric Corporation, Tokyo, Japan) with a 54-cm class color LCD monitor (Radioforce R22, Eizo Nanao, Ishikawa, Japan). MR imaging was evaluated by two observers (MN, with 2 years of experience in neuroradiology, and TN, with 7 years of experience in neuroradiology) in consensus fashion.
Statistical analysis
The relevance of ASL values in 142 hemispheres was assessed in relation to five clinical factors (sex, family history, revascularization surgery, age at MR exam, and age at onset) and four MR imaging factors (MRA score, CVA score, BMV score, and ivy score). Student's t-test was performed to estimate differences in ASL values between males and females, and the presence and absence of family history and revascularization surgery. Spearman's signed-rank tests were performed to estimate the
Results
Table 2 shows the results of the univariate analyses of ASL values with clinical and MR imaging factors.
Patients with a family history of the disease had significantly higher ASL values than those without such a history. This result may indicate that cerebral perfusion tended to be salvaged in patients with a family history. There were significant negative correlations with age at MR exam (Fig. 1A), ASL values vs. MRA scores (Fig. 1B), and CVA scores. This finding may suggest that ASL values in
Discussion
In a previous study of ASL-MRI in patients with Moyamoya disease compared with SPECT imaging of patients with the disease, it was reported that CBF values measured by ASL-MRI were correlated with SPECT imaging on 123I-IMP in patients at rest and after an acetazolamide challenge [21]. In particular, CBF values on ASL-MRI were more strongly correlated with those obtained by 123I-IMP after an acetazolamide challenge than with values obtained with a non-challenged group. This result suggests that
Disclosure of funding
Nothing to disclose.
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