Abstract
BackgroundTo evaluate ungated nonenhanced hybridized arterial spin labeling (hASL) magnetic resonance angiography (MRA) of the extracranial carotid arteries using a fast low angle shot (FLASH) readout at 3 Tesla.MethodsIn this retrospective, institutional review board-approved and HIPAA-compliant study, we evaluated the image quality (4-point scale) of nonenhanced hASL MRA using a FLASH readout with respect to contrast-enhanced MRA (CEMRA) in 37 patients presenting with neurologic symptoms. Two certified neuroradiologists independently evaluated 407 arterial segments (11 per patient) for image quality. The presence of vascular pathology was determined by consensus reading. Gwet’s AC1 was used to assess inter-rater agreement in image quality scores, and image quality scores were correlated with age and body mass index. Objective measurements of arterial lumen area and sharpness in the carotid arteries were compared to values obtained with CEMRA. Comparisons were also made with conventional nonenhanced 2D time-of-flight (TOF) MRA.ResultsCEMRA provided the best image quality, while nonenhanced hASL FLASH MRA provided image quality that exceeded 2D TOF at the carotid bifurcation and in the internal and external carotid arteries. All nine vascular abnormalities of the carotid and intracranial arteries detected by CEMRA were depicted with hASL MRA, with no false positives. Inter-rater agreement of image quality scores was highest for CEMRA (AC1 = 0.87), followed by hASL (AC1 = 0.61) and TOF (AC1 = 0.43) (P < 0.001, all comparisons). With respect to CEMRA, agreement in cross-sectional lumen area was significantly better with hASL than TOF in the common carotid artery (intraclass correlation (ICC) = 0.90 versus 0.66; P < 0.05) and at the carotid bifurcation (ICC = 0.87 versus 0.54; P < 0.05). Nonenhanced hASL MRA provided superior arterial sharpness with respect to CEMRA and 2D TOF (P < 0.001).ConclusionAlthough inferior to CEMRA in terms of image quality and inter-rater agreement, hASL FLASH MRA offers an alternative to 2D TOF for the nonenhanced evaluation of the extracranial carotid arteries at 3 Tesla. Compared with 2D TOF, nonenhanced hASL FLASH MRA provides improved quantification of arterial cross-sectional area, vessel sharpness, inter-rater agreement and image quality.
Highlights
To evaluate ungated nonenhanced hybridized arterial spin labeling magnetic resonance angiography (MRA) of the extracranial carotid arteries using a fast low angle shot (FLASH) readout at 3 Tesla
Nonenhanced 3D hybridized arterial spin labeling (hASL) MRA was acquired as a clinical scout scan prior to injection of contrast media in consecutive patients who were referred for neck MRA with and without contrast material
Excluding arterial locations outside the field of view (3 of 407 for contrast-enhanced magnetic resonance angiography (CEMRA), 14 of 407 for hASL MRA, and 89 of 407 for TOF MRA), a total of 318 locations were portrayed by all three techniques
Summary
To evaluate ungated nonenhanced hybridized arterial spin labeling (hASL) magnetic resonance angiography (MRA) of the extracranial carotid arteries using a fast low angle shot (FLASH) readout at 3 Tesla. Time-of-flight (TOF) magnetic resonance angiography (MRA) is a well-established and easy-to-use method for diagnosing disorders of the extracranial carotid arteries without the use of contrast agents [6,7,8,9,10]. It is often used in clinical practice, TOF has well-known drawbacks including artifacts from saturation and dephasing of flowing spins, as well as limited vascular coverage with respect to CEMRA [11]. Raoult and colleagues [13] postulated that better suppression of static background tissue would likely improve the clinical utility of nonenhanced MRA of the extracranial carotid arteries, and mentioned that arterial spin labeling (ASL) methods, initially described long ago [16, 17], might achieve this
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