High‐resolution anatomic, diffusion tensor, and magnetization transfer magnetic resonance imaging of the optic chiasm at 3T

Abstract

Purpose: To evaluate techniques for anatomical and physiological imaging of the intracranial optic nerve (ON), optic chiasm (OC), and optic tract (OT) at 3T with the aim of visualizing axonal damage in multiple sclerosis (MS). Materials and Methods:Imaging was performed on a 3T scanner employing a custom-designed head coil that consisted of a coil array with four coils (30 ϫ 30 cm 2 ). Oblique fast spin echo (FSE) images, magnetization transfer (MT)-enhanced 3D gradient-echo (GRE) time-of-flight (TOF) images, and line scan diffusion images (LSDI) were obtained. Full diffusion tensor (DT) analysis was performed, and apparent diffusion coefficient (ADC), fractional anisotropy (FA), and fiber direction maps were obtained.Results: FSE anatomic images were obtained with an inplane resolution of 0.39 ϫ 0.52 mm 2 . The in-plane resolution of the MT and LSDI images was 0.78 ϫ 0.78 mm 2 . The OC, intracranial ON, and OT can be seen on these images. The dominant fiber orientations in the OC, ON, and OT, as derived from the DT images, are displayed. Conclusion:This study shows that by using 3T and a customdesigned, four-channel head coil, it is possible to acquire highresolution anatomical and physiological images of the OC, ON, and OT. The pilot results presented here pave the way for imaging the anterior visual pathway in patients with MS. IMAGING OF THE OPTIC NERVE (ON) and the optic pathway can assist in the assessment of many causes of injury, such as trauma, inflammation, infection, and tumor. Many patients with multiple sclerosis (MS) exhibit optic neuritis as the first symptom of the disease. Previous MS studies conducted at 1.5T (1-4) demonstrated the potential value of MRI of the ON in MS. However, routine imaging remains a difficult task due to the complexity of the ON and surrounding structures. The main difficulties are the small size of the optic tract (OT); nerve movement; signal from surrounding fat, bone, and cerebrospinal fluid (CSF); and susceptibility effects caused by air in nearby structures.Despite these difficulties, clinical MRI of the ON and optic pathway is promising. Several studies have shown the usefulness of both qualitative (1,5-9) and quantitative (2-4,10,11) MR techniques for diagnosing optic neuritis. One of the criteria for the successful application of these techniques is obtaining high-resolution images. Higher fields (i.e., 3T) and dedicated RF coils may provide better high-resolution imaging. With this in mind, we conducted a study of the ON, optic chiasm (OC), and OT at 3T using a custom-designed phasedarray coil. The combination of these two approaches provides an excellent signal-to-noise ratio (SNR) and allows the acquisition of outstanding high-resolution anatomic images. The SNR achieved offers the opportunity to carry out MRI-based physiological measurements on the OC. In this study we employed two methods: magnetization transfer (MT) imaging and diffusion tensor imaging (DTI).MT imaging is a quantitative technique that involves selective presaturation of the broad macromolecu...

High resolution MRI anatomy of the cat brain at 3Tesla

“…For example, 3T assessment of the integrity of the lateral lemniscus and acoustic radiation can lead to diagnosis of sensorineural hearing loss; and tinnitus can also be diagnosed using MRI modalities (Smits et al, 2007, Johansen-Berg et al, 2009). Additionally, high field MRI can detect optic neuritis, which is often the first diagnostic sign in multiple sclerosis (Vinogradov et al, 2005). …”

Distinguishing and quantification of the human visual pathways using high-spatial-resolution diffusion tensor tractography

“…Even with higher SNR at 3T magnetic field strength, visual pathways including the optic tracts and small branches such as the pretectal fibers could not be traced without contamination from neighboring white matter tracts [6, 16]. Because of the larger voxels, though the SNR was enhanced, partial volume averaging was exacerbated which proved detrimental to the mapping of crossing fibers, especially the optic chiasm [6, 16, 19, 20, 21]. Effects of partial volume averaging in DTT due to slice thickness were studied previously in the context of crossing fibers and few attempts were made to quantify the entire human visual pathways [6, 16, 58], especially the optic radiations at high spatial resolution [59].…”

“…Diffusion-sensitized MRI methods applied to the human visual pathways have utilized regions-of-interest [9, 10], deterministic [11, 12, 13, 14] and probabilistic tractography [15, 16, 17] on separate components of the visual system including optic nerves [9, 18], optic chiasm [19, 20, 21], optic tracts [10], and optic radiations [11–14] including Meyer loop [7, 8]. Qualitatively, the methods adopted to-date to quantify components of the human visual system using diffusion-weighted imaging were different on several aspects including spin history preparation (i.e.…”

3T in der Neuroradiologie—Spannungsfeld zwischen Wunsch und Wirklichkeit

“…Die überwiegende Zahl der bisherigen Arbeiten zu DTI und Fibertracking wurde an Kernspintomographen mit einer Feldstärke von 1,5T durchgeführt, nur wenige Untersuchungen bei einer Feldstärke von 3T [86][87][88][89][90][91].…”

“…In Anbetracht der doppelten Magnetfeldstärke von 3T gegenüber 1,5T ergibt sich theoretisch zwar eine Verdopplung des SNR und damit verbunden auch die Möglichkeit einer höheren Auflösung [87,88,90,91], wobei jedoch sowohl durch makroskopische als auch Figures 14a and 14b. T1 contrast of the spine at 3T.…”