* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Clinical Investigative Study Detectability of Neural Tracts and Nuclei
Brain morphometry wikipedia , lookup
Neuroeconomics wikipedia , lookup
Cortical cooling wikipedia , lookup
Optogenetics wikipedia , lookup
Synaptic gating wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Diffusion MRI wikipedia , lookup
Neuroesthetics wikipedia , lookup
Nervous system network models wikipedia , lookup
Convolutional neural network wikipedia , lookup
Artificial neural network wikipedia , lookup
Types of artificial neural networks wikipedia , lookup
Metastability in the brain wikipedia , lookup
History of neuroimaging wikipedia , lookup
Recurrent neural network wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Hypothalamus wikipedia , lookup
Anatomy of the cerebellum wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Eyeblink conditioning wikipedia , lookup
Clinical Investigative Study Detectability of Neural Tracts and Nuclei in the Brainstem Utilizing 3DAC-PROPELLER Taro Nishikawa, MD, PhD, Kouichirou Okamoto, MD, PhD, Hitoshi Matsuzawa, MD, PhD, Makoto Terumitsu, DDS, PhD, Tsutomu Nakada, MD, PhD, Yukihiko Fujii, MD, PhD From the Department of Neurosurgery, Brain Research Institute, University of Niigata, Niigata, Japan (TN, KO, YF); Center for Integrated Human Brain Science, Brain Research Institute, University of Niigata, Niigata, Japan (HM, MT, TN, YF). ABSTRACT Despite clinical importance of identifying exact anatomical location of neural tracts and nuclei in the brainstem, no neuroimaging studies have validated the detectability of these structures. The aim of this study was to assess the detectability of the structures using three-dimensional anisotropy contrast-periodically rotated overlapping parallel lines with enhanced reconstruction (3DAC-PROPELLER) imaging. Forty healthy volunteers (21 males, 19 females; 19-53 years, average 23.4 years) participated in this study. 3DAC-PROPELLER axial images were obtained with a 3T-MR system at four levels of the brainstem: the lower midbrain, upper and lower pons, and medulla oblongata. Three experts independently judged whether five tracts (corticospinal tract, medial lemniscus, medial longitudinal fasciculus, central tegmental and spinothalamic tracts) and 10 nuclei (oculomotor and trochlear nuclei, spinal trigeminal, abducens, facial, vestibular, hypoglossal, prepositus, and solitary nuclei, locus ceruleus, superior and inferior olives) on each side could be identified. In total, 240 assessments were made. The five tracts and eight nuclei were identified in all the corresponding assessments, whereas the locus ceruleus and superior olive could not be identified in 3 (1.3%) and 16 (6.7%) assessments, respectively. 3DACPROPELLER seems extremely valuable imaging method for mapping out surgical strategies for brainstem lesions. Introduction Even a tiny lesion in the brainstem is likely to cause significant and critical neurological deterioration because neural tracts and nuclei as well as reticular formation important in maintaining fundamental brain functions such as consciousness, respiratory regulation, and motor functions are densely packed within this small part of the brain. Although surgery for brainstem lesions is challenging, advancements in technologies such as neuroimaging, navigation systems, and intraoperative functional monitoring have made it is possible to be safely perform brainstem surgery without worsening of neurological symptoms and signs.1–3 When diagnosing and treating patients with lesions in the brainstem, especially with surgical intervention, it is quite important to precisely map the anatomical relationships between the lesions and neural structures such as neural tracts and nuclei. However, no studies have validated a neuroimaging method that can detect a number of unspecific neural tracts and nuclei, including thin tracts and small nuclei, in the brainstem. Magnetic resonance imaging (MRI) is clearly the best method for imaging brain structures in clinical settings. Among various MRI contrast imaging modalities, three-dimensional anisotropy contrast-periodically rotated overlapping parallel lines with enhanced reconstruction (3DAC-PROPELLER) on 238 Copyright Keywords: 3DAC-PROPELLER, MRI, neural tract, nucleus, brainstem. Acceptance: Received June 11, 2012, and in revised form March 4, 2013. Accepted for publication March 11, 2013. Correspondence: Yukihiko Fujii, MD, PhD, Department of Neurosurgery, Brain Research Institute, University of Niigata, 1-757 Asahimachi-dori, Niigata 9518585, Japan. E-mail: [email protected]. ac.jp. J Neuroimaging 2014;24:238-244. DOI: 10.1111/jon.12027 a high-field system seems a suitable method for demonstrating the neural structures, including neural tracts and nuclei, in all areas of the human brain, especially in the brainstem.4, 5 In this study we aimed to verify the detectability of neural tracts and nuclei in the brainstem using 3DAC-PROPELLER imaging on a 3 Tesla MRI system. Subjects and Methods Forty healthy volunteers (21 males and 19 females; 19-53 years, median 23 years) participated in this study. Informed consent was obtained from all participants according to the human research guidelines of the Internal Review Board of the University of Niigata. A General Electric (Waukesha, WI, USA) Signa 3.0T system with an eight-channel phased-array head coil was used to perform all the imaging studies. Axial diffusion-weighted images (DWI) with the PROPELLER method were obtained using the following parameter settings: FOV 22 cm × 22 cm; matrix 256 × 256; slice thickness 5 mm; intersection gap 2.5 mm; echo train length 12; TR 4,000 milliseconds; TE 78.7 milliseconds; NEX 5. The b-value was 1,100 seconds/mm2 for each axis, with the three combinations of diffusion gradient vectors ◦ 2013 by the American Society of Neuroimaging C 㸫㸫 Table 1. A List of Assessed Neural Tracts in the Brainstem 1. Corticospinal tract 2. Medial lemniscus 3. Medial longitudinal fasciculus 4. Central tegmental tract 5. Spinothalamic tract 3DAC-PROPELLER, three-dimensional anisotropy contrast-periodically rotated overlapping parallel lines with enhanced reconstruction. Table 2. A List of Assessed Nuclei in the Brainstem a. Oculomotor nucleus/trochlear nucleus b. Spinal trigeminal nucleus c. Abducens nucleus d. Facial nucleus e. Vestibular nucleus f. Hypoglossal nucleus/prepositus nucleus g. Solitary nucleus h. Locus ceruleus i. Superior olive j. Inferior olive 3DAC-PROPELLER, three-dimensional anisotropy contrast-periodically rotated overlapping parallel lines with enhanced reconstruction. as follows: (1, 0, 0), (0, 1, 0), (0, 0, 1), where the (x, y, z) direction corresponds to (right to left, anterior to posterior, superior to inferior) of the brain in the supine position. Considering the specific absorption rate, the number of slices was limited to 4. From each participant, DWI images were obtained at four levels of the brainstem: lower midbrain, upper pons, lower pons, and medulla oblongata. The total scanning time necessary to obtain images of four slices was approximately 17 minutes. PROPELLER is an ingenious method of motion correction found to be useful for eliminating artifacts on rapid-DWI images by acquiring data in a series of rotating strips (blades) in kspace.6 In 3DAC image processing, three primary colors—red, green, and blue—are respectively assigned to the gray scale of the three anisotropic DWI PROPELLER images: x-, y-, and zaxes. These three primary color images are then combined pixel by pixel to form a single-color image in full-color spectrum. The final images are displayed negatively to obtain a one-to-one correlation between each of the three colors (red, green, and blue) and their respective axes (x, y, and z).7 For details of 3DAC processing and further mathematical formulations, readers are referred to references 4, 19, and 20. Evaluation of Neural Tracts and Nuclei in the Brainstem 3DAC imaging is a type of fiber orientation-weighted imaging. On axial 3DAC-PROPELLER images, neural fibers running in the right-left direction (x-axis) appear as red, whereas fibers running in the anterior-posterior direction (y-axis) and in the direction of the body axis (ie, up-down, z-axis) appear as green and blue, respectively. Nuclei appear as light colors, nearly white. Because of their clinical importance, five neural tracts (Table 1) and 10 cranial nerve nuclei (Table 2) were selected and evaluated on each side of the brainstem. In several anatomical textbooks and atlases,8–11 three experts (two neurosurgeons Fig 1. Representative axial 3DAC-PROPELLER image at the level of the lower midbrain. The dense blue region between the frontopontine tract (12) located anteromedially and the occipitaltemporopontine tract (13) located posterolaterally in the cerebral peduncle is the corticospinal tract (1). The medial lemniscus (2) is located in the tegmentum on the boundary with the cerebral peduncle and is depicted as a thin blue region adjacent to the substantia nigra (l). The oculomotor/trochlear nuclei (a) can be observed as a pale and small region medially located on the front edge of the central gray matter (k). The small blue region lateral to the central gray matter (k) is the mesencephalic tract and nucleus of the trigeminal nerve (6). The medial longitudinal fasciculus (3) is displayed as a blue region anterolateral to the oculomotor/trochlear nuclei (a). The central tegmental tract (4), albeit a main ascending tract of reticular formation, is observed as a blue area lateral to the medial longitudinal fasciculus (3). The spinothalamic tract (5) is identified as a blue area just posterior to the medial lemniscus (2) in the lateral margin of the tegmentum. The decussation of superior cerebellar peduncles (11) is also observed as a red structure in the center. In the interpeducular cistern between the cerebral peduncles the oculomotor nerves (III) are seen. and a neuroradiologist) independently identified the five neural tracts, first as blue regions clearly demonstrated on 3DACPROPELLER images; they marked these regions on the images with arrows. Next, they identified the nuclei as light-colored, nearly white areas in the vicinity of the neural tracts, which served as anatomical indices for identifying nuclei. On the basis of the aforementioned anatomical textbooks and atlases,8–11 diagrams showing the four levels of brainstem structures were also created (Figures 1–4). Detailed mapping of the neural structures on 3DAC-PROPELLER images of each level of the brainstem were described in the figure legends. Nishikawa et al: Detecting Brainstem Neural Tracts and Nuclei with 3DAC-PROPELLER 㸫㸫 239 Fig 2. Representative axial 3DAC-PROPELLER image at the level of the upper pons. The corticospinal tract (1) is observed as multilayered dark blue regions among the transverse pontine fibers displayed in red. The medial lemniscus (2) is shown as a transverse blue region in the middle of the upper pons. The medial longitudinal fasciculus (3) is seen as a small blue area on the paramedian floor of the fourth ventricle. On the lateral side of the fasciculus, the central tegmental tract (4) is observed as a round dark blue area. In the margin of the pontine tegmentum, the spinothalamic tract (5) is depicted as a blue region located adjacent and posterolateral to the medial lemniscus (2). The locus ceruleus (h) can be observed as a small pale area anterolateral and adjacent to the central gray matter (k). The raphe nucleus (n) is shown as a light green longitudinal region on the midline. The superior cerebellar peduncle (8) appears as a light blue area lateral to the fourth ventricle and central tegmental tract (4). The middle cerebellar peduncle (9) is observed as a green large region in the lateral margin of the pontine base. The mesencephalic trigeminal tract and nucleus (6) are depicted as a small dark blue area posterior to the locus ceruleus (h) on the boundary between the central gray matter (k) and superior cerebellar peduncle (8). The neural tracts and nuclei on a 3DAC-PROPELLER image were classified into one of three groups: (1) excellent, structure could be easily identified without any references; (2) good, identification required reference to anatomical structures on the other side or the adjacent images; and (3) poor, identification was difficult or impossible. Tracts and nuclei classified as excellent and good were regarded as detectable and those as poor as undetectable. In total, 240 assessments of each neural tract or nucleus were made (ie, 40 subjects × 2 sides × 3 experts). These assessments based on 3DAC-PROPELLER images also estimated the reproducibility and accuracy of the experts’ findings for each structure (neural tract or nucleus), defined as 240 Fig 3. Representative axial 3DAC-PROPELLER image at the level of the lower pons. The corticospinal tract (1) is depicted as a large dark blue region between two red compartments (ie, the superficial layer and the deep layer of the transverse pontine fibers in the middle of the ventral part of the pons). The medial lemniscus (2) is observed as a blue transverse structure behind the deep layer of the transverse pontine fibers. The medial longitudinal fasciculi (3) are depicted in the form of inverted V on the midline of the floor of the fourth ventricle. The central tegmental tract (4) is shown a blue region in the reticular formation located behind the medial lemniscus (2). The spinothalamic tract (5) is displayed as a light blue region lateral to the medial lemniscus (2). The abducens nucleus (c) is shown as a pale oval region anterolateral to the medial longitudinal fasciculus (3). The spinal trigeminal nucleus nerve (b) is shown as a pale region adjacent to the spinal trigeminal tract (7) depicted in blue. The vestibular nucleus (e) is observed as pale region lateral to the lateral wall of the fourth ventricle, which is in contact with the inner surface of the inferior cerebellar peduncle (10). The superior olive (i) is displayed as a tiny pale area anterolateral to the central tegmental tract and behind the medial lemniscus (2). The facial nucleus (d) is a pale round area posterolateral to the superior olive (i). The raphe nucleus (n) is observed as a green region on the midline. The cochlear nucleus (m) composed of anterior and posterior parts (ie, ventral and dorsal nuclei) is depicted as a pale region lateral to the inferior cerebellar peduncle (10). The abducens nerve (VI) emerges from the anterior aspect of the pons and is depicted in a greenish color. The facial nerves (VII) and vestibulocochlear nerve (VIII) run through the brainstem and appear from the lateral side of the pons and are depicted in red. the concordance percentage among assessments (detectable or undetectable) of the three experts and the percentage of truepositives and true-negatives, respectively. In this study, truepositives, true-negatives, false-positives, and false-negatives corresponded to detectable assessment of the structure of interest; detectable assessment of the structure closest to the structure of interest, which was the closest neural tract if the structure of interest was a neural tract or the closest nucleus if it was a Journal of Neuroimaging Vol 24 No 3 May/June 2014 㸫㸫 shown in Figures 1–4, respectively. Numbers, letters, and abbreviations representing anatomical structures in the figures are listed in Tables 1 and 2. Detectability of Neural Tracts and Nuclei The five neural tracts, displayed as blue structures, were all judged as detectable (ie, excellent or good) on all four slices in all assessments (Table 3). In all five tracts, the reproducibility and accuracy were also 100%, ie, none of the five neural tracts were difficult to identify (ie, poor) and none were misinterpreted as another neural tract (no false-positive). Among the 10 nuclei, displayed as light color areas, eight were judged as detectable in all assessments (Table 4). The remaining two, the locus ceruleus and superior olive, were judged as difficult to identify in 3 (1.3%) and 16 (6.7%) assessments, respectively. For the majority of the nuclei, reproducibility and accuracy were 100% (Table 4). Discussion Fig 4. Representative axial 3DAC-PROPELLER image at the level of the medulla oblongata. The corticospinal tract (1) is shown as a dark blue area in the anterior margin of the medulla oblongata. The inferior olive (j) is displayed as a green oval region posterior to the tract. Between both the inferior olives (j), the medial lemniscus (2) is shown as a paramedian and longitudinal blue structure, behind which the medial longitudinal fasciculus (3) is also shown as a paramedian blue region adjacent to the floor of fourth ventricle. The central tegmental tract (4) is displayed as a dark blue and round structure abutting the dorsal side of the inferior olive (j), behind which the spinothalamic tract (5) is depicted as a dark blue area lateral to the central tegmental tract (4) and on the margin of the retro-olivary groove. Posterior to the groove, the spinal trigeminal tract (7) and nucleus (b) are shown as blue and pale areas, respectively. The pale small region observed lateral to the medial longitudinal fasciculus (3) is the hypoglossal nucleus/prepositus nucleus (f), behind which the dorsal longitudinal fasciculus (14) is observed as a small blue region beneath the fourth ventricle floor. The vestibular nuclei (e) composed of medial vestibular nucleus and inferior vestibular nucleus are observed as pale regions beneath the floor of the fourth ventricle and medial to the inferior cerebellar peduncle (10). On the ventral side of the nuclei, the solitary nucleus (g) around the solitary tract is displayed as a pale small area. The tectospinal tract (15), which connects the quadrigeminal body and the spinal cord, is shown as the blue region between the medial lemniscus (2) and the medial longitudinal fasciculus (3). On the lateral margin of the inferior cerebellar peduncle (10), the cochlear nucleus (m) is depicted as a light-colored region. Outside the medulla, the glossopharyngeal nerve (IX) and vestibulocochlear nerve (VIII) are shown as red streak structures. nucleus; misinterpretation of the structure of interest as its closest structure; and undetectable assessment of the structure of interest, respectively. Results Representative axial 3DAC-PROPELLER images of the lower midbrain, upper pons, lower pons, and medulla oblongata are This study utilizing 3DAC-PROPELLER images4, 5 revealed that the five neural tracts assessed were detectable at all four levels of the brainstem in all subjects and the 10 nuclei assessed were detectable in most subjects, although the locus ceruleus and superior olive were undetectable in a few subjects (Table 4). Hence, 3DAC-PROPELLER imaging is capable of detecting a significant number of the nuclei and neural tracts in the brainstem. 3DAC-PROPELLER On conventional MRI images, the majority of neural tracts and nuclei in the brainstem are difficult to detect, although the locus ceruleus can be imaged with a specialized high-resolution T1TSE MR sequence as a small area of elevated signal intensity adjacent to the fourth ventricle.12 In various pathological conditions or diseases, the degenerated neural tracts or nuclei can be depicted as areas of high signal intensity on conventional T2WI images.13–16 However, the depiction of these anatomical structures in the brainstem is limited to specific pathological conditions. The contrast based on water diffusion in MRI imaging may be capable of depicting fine structures in the brainstem. The anisotropy of the diffusion of water molecules in human brains, which is noninvasively measurable using MRI, arises almost exclusively from neural fibers, principally axons. There are many applications for neuroimaging methods based on diffusion anisotropy, known as diffusion tensor imaging (DTI), including 3DAC imaging, fiber tracking (ie, tractography), and fractional anisotropy imaging.17, 18 The main drawback of DTIs other than 3DAC imaging is the need to use algorithms to calculate eigenvalues and to determine eigenvectors based on these numerical estimations, which lead to potential degradation of image quality and difficulty in detecting fine neural tracts and nuclei in the brainstem.7 The quality of the reconstructed images—based on estimated parameter values such as eigenvalues of the apparent diffusion tensor—has been disappointing.19 This can be understood intuitively by considering the difference between T1 images (ie, images reconstructed on the basis Nishikawa et al: Detecting Brainstem Neural Tracts and Nuclei with 3DAC-PROPELLER 㸫㸫 241 Table 3. Detectability of the Five Neural Tracts Assessed in the Brainstem Detection, n (%) Yes Neural Tracts (Label in Figures) Lower midbrain Corticospinal tract (1) Medial lemniscus (2) Medial longitudinal fasciculus (3) Central tegmental tract (4) Spinothalamic tract (5) Upper pons Corticospinal tract (1) Medial lemniscus (2) Medial longitudinal fasciculus (3) Central tegmental tract (4) Spinothalamic tract (5) Lower pons Corticospinal tract (1) Medial lemniscus (2) Medial longitudinal fasciculus (3) Central tegmental tract (4) Spinothalamic tract (5) Medulla oblongata Corticospinal tract (1) Medial lemniscus (2) Medial longitudinal fasciculus (3) Central tegmental tract (4) Spinothalamic tract (5) No Excellent Good Poor Overall Detectability, n (%) 240 (100) 240 (100) 240 (100) 237 (98.7) 240 (100) 0 (.0) 0 (.0) 0 (.0) 3 (1.3) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 100 100 100 100 100 100 100 100 100 100 240 (100) 240 (100) 240 (100) 237 (98.7) 240 (100) 0 (.0) 0 (.0) 0 (.0) 3 (1.3) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 100 100 100 100 100 100 100 100 100 100 240 (100) 240 (100) 240 (100) 224 (93.3) 221 (87.5) 0 (.0) 0 (.0) 0 (.0) 16 (6.7) 19 (8.1) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 100 100 100 100 100 100 100 100 100 100 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 100 100 100 100 100 100 100 100 100 100 Reproducibility, % Accuracy, % Table 4. Detectability of the 10 Nuclei Assessed in the Brainstem Detection, n (%) Excellent Good Poor Overall Detectability, n (%) 233 (97.1) 7 (2.9) 0 (.0) 240 (100) Yes Nuclei (Label in Figures) Lower midbrain Oculomotor Nucleus/trochlear nucleus (a) Upper pons Locus ceruleus (h) Lower pons Spinal trigeminal nucleus (b) Abducens nucleus (c) Facial nucleus (d) Vestibular nucleus (e) Superior olive (i) Medulla oblongata Spinal trigeminal nucleus (b) Vestibular nucleus (e) Solitary nucleus (g) Hypoglossal nucleus/prepositus nucleus (f) Inferior olive (j) No Reproducibility, % Accuracy, % 100 NA 225 (93.7) 12 (5.0) 3 (1.3) 237 (98.7) 100 NA 224 (93.3) 240 (100) 227 (94.6) 240 (100) 211 (87.9) 16 (6.7) 0 (.0) 13 (5.4) 0 (.0) 13 (5.4) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 16 (6.7) 240 (100) 240 (100) 240 (100) 240 (100) 224 (93.3) 100 100 100 100 98.8 100 100 96.7 100 96.7 224 (93.3) 240 (100) 224 (93.3) 240 (100) 240 (100) 16 (6.7) 0 (.0) 16 (6.7) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 0 (.0) 240 (100) 240 (100) 240 (100) 240 (100) 240 (100) 100 100 100 100 100 100 100 100 100 100 NA = not available (no nucleus to compare with the nucleus in this study). of estimated T1 values) and T1-weighted images (ie, images obtained using a spin-echo sequence without numerical estimations). However, 3DAC is an algorithm introduced to avoid the difficulties of performing full tensor analysis.7, 19, 20 In the 3DAC algorithm, the mathematical process is performed in im- 242 age form, effectively preventing unwanted degradation of image quality. Consequently, 3DAC images have exquisitely high anatomical resolution sensitive to physiological perturbations, resulting in the potential capability of identifying thin neural tracts and nuclei.7, 19, 20 Journal of Neuroimaging Vol 24 No 3 May/June 2014 㸫㸫 When trying to detect microstructures in the brainstem, higher signal-to-noise ratio (S/N) obtained using high-field MRI systems is undoubtedly advantageous, but the higher susceptibility effect remains a significant trade-off. The high susceptibility effect is likely to produce a susceptibility artifact resulting in degradation of image quality, especially on echo-planar imaging (EPI), which is usually used to obtain DTI. EPI is inherently subject to susceptibility artifacts, particularly at the skull base or brainstem region. Accordingly, several methods have been proposed to reduce or correct image distortion caused by the susceptibility effect.17, 18, 21, 22 Among them, the PROPELLER sequence is a suitable method to effectively eliminate these undesired artifacts. Because PROPELLER is a spin-echo sequence, a motion probing gradient can be readily implemented for DWI and can eliminate the susceptibility artifacts inherent in DWI.23 Therefore, PROPELLER is especially effective for application to DWI with high-field systems. Hence, a combination of 3DAC and PROPELLER with a 3 Tesla MRI system seems an optimal imaging method in the clinical setting for depicting anatomical microstructures such as neural tracts and nuclei in the whole brainstem.4 Detectability of Neural Tracts and Nuclei in the Brainstem In this study utilizing 3DAC-PROPELLER images, the five neural tracts were clearly visualized as blue regions because of strong diffusion anisotropy in the direction of the body axis (z-axis). The 10 nuclei were well depicted as light-colored structures because of both weak diffusion anisotropy and the existence of neural tracts clearly identified in their vicinity, which serve as anatomical indices for identifying nuclei. The oculomotor nucleus/trochlear nucleus, spinal trigeminal nucleus, abducens nucleus, facial nucleus, vestibular nucleus, hypoglossal nucleus/prepositus nucleus, solitary nucleus, and inferior olive could be identified in all subjects. In several subjects, however, the locus ceruleus and superior olive were difficult to detect because they are smaller than the other nuclei assessed and their signal contrast decreases because of the partial volume effect in thick slices. Indeed, thinner slices seem preferable for identifying smaller neural structures because they reduce the partial volume effect. That leads, however, to decreased signal-to-noise ratio, resulting in reduced signal contrast or longer examination time to allow for more NEX to avoid loss of contrast. Furthermore, the locus ceruleus and superior olive are poorly demarcated nuclei intermingled with numerous scattered neurons in the reticular formation, leading to the difficulty in identifying them as clusters of neurons (ie, nuclei).24, 25 Reproducibility and Accuracy Reproducibility and accuracy were 100% for the majority of neural structures of the brainstem assessed in this study— especially for all the five neural tracts, even the medial longitudinal fasciculus and the central tegmental tract (Tables 3 and 4). These two are small tracts running very close together in a similar direction. Their high reproducibility and accuracy seems to be plausibly explained by the fact that 3DAC-PROPELLER images can clearly demonstrate a distinction between the two tracts: the former appears as oval, blue structures running in the Fig 5. Axial 3DAC-PROPELLER images of four levels of the brainstem in three subjects demonstrate the reproducibility of assessments of the neural tracts and nuclei. paramedian region and close to the forth ventricle and the latter as round, blue structures running laterally in the deep portion of the brainstem (Figures 1–5). Clinical Application Based on normal anatomical structures of the brainstem, several safe entry zones, where incision and retraction of the brainstem could be safely made without significant neurological deficits due to the absence of important neural tracts and nuclei, have been proposed.26, 27 However, it may be difficult to apply these safe entry zones to patients with large intra-axial mass lesions in the brainstem because of the displacement of neural tracts and nuclei. For these patients, it seems feasible to identify neural tracts and nuclei directly and precisely and to determine real safe entry zones using 3DAC-PROPELLER preoperatively. Conclusion Using 3DAC-PROPELLER images, five neural tracts in the brainstem were identified in all subjects and 10 nuclei were identified in most subjects. According to our results, 3DACPROPELLER imaging is helpful for identifying both neural tracts and nuclei in the brainstem, which seems to be an extremely valuable imaging method for mapping out surgical strategies for brainstem lesions. References 1. Bertalanffy H, Gilsbach JM, Eggert HR, et al. Microsurgery of deep-seated cavernous angiomas: report of 26 cases. Acta Neurochir (Wien) 1991;108:91-99. Nishikawa et al: Detecting Brainstem Neural Tracts and Nuclei with 3DAC-PROPELLER 㸫㸫 243 2. Wang C, Zhang J, Liu A, et al. Surgical management of medullary hemangioblastoma: report of 47 cases. Surg Neurol 2001;56:218226. 3. Wang C, Zhang J, Liu A, et al. Surgical treatment of primary midbrain gliomas. Surg Neurol 2000;53:41-51. 4. Nakada T, Matsuzawa H, Fujii Y, et al. Three-dimensional anisotropy contrast periodically rotated overlapping parallel lines with enhanced reconstruction (3DAC PROPELLER) on a 3.0T system: a new modality for routine clinical neuroimaging. J Neuroimaging 2006;16:206-211. 5. Terajima K, Matsuzawa H, Shimohata T, et al. Tract-by-tract morphometric and diffusivity analyses in vivo of spinocerebellar degeneration. J Neuroimaging 2009;19:220-226. 6. Pipe JG. Motion correction with PROPELLER MRI: application to head motion and free breathing cardia imaging. Magn Reson Med 1999;103:963-969. 7. Nakada T, Nakayama N, Fujii Y, et al. Clinical application of magnetic resonance axonography. J Neurosurg 1999;90:791-795. 8. Martin JH. Atlas II: myelin-stained sections through the central nervous system. In: Martin JH, ed. Neuroanatomy, Text and Atlas. New York: McGraw-Hill; 1989:425-488. 9. Paxinos G, Huang XF. Atlas of the Human Brainstem. Waltham, MA: Academic Press; 1995. 10. Haines DE. Neuroanatomy. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2007. 11. Naidich TP, Duvernoy HM, Delman BN, et al. Duvernoy’s Atlas of the Human Brain Stem and Cerebellum. Berlin, Germany: Springer; 2008. 12. Keren NI, Lozar CT, Harris KC, et al. In vivo mapping of the human locus coeruleus. NeuroImage 2009;47:1261-1267. 13. Kuhn MJ, Johnson KA, Davis KR. Wallerian degeneration: evaluation with MR imaging. Radiology 1988;168:199-202. 14. Kitajima M, Korogi Y, Shimomura O, et al. Hypertrophic olivary degeneration: MR imaging and pathologic findings. Radiology 1994;192:539-543. 244 15. Okamoto K, Furusawa T, Ishikawa K, et al. Focal T2 hyperintensity in the dorsal brain stem in patients with vestibular schwanoma. AJNR Am J Neuroradiol 2006;27:1307-1311. 16. Yagishita A, Oda M. Progressive supranuclear palsy: MRI and pathological findings. Neuroradiology 1996;38(Supple 1):S60S66. 17. Finsterbusch J. High-resolution diffusion tensor imaging with inner field-of-view EPI. J Magn Reson Imaging 2009;29:987-993. 18. Nagae-Poetscher LM, Jiang H, Wakana S, et al. High-resolution diffusion tensor imaging of the brain stem at 3 T. AJNR Am J Neuroradiol 2004;25:1325-1330. 19. Nakada T, Matsuzawa H. Three-dimensional anisotropy magnetic resonance imaging of the rat nervous system. Neurosci Res 1995;22:389-398. 20. Nakada T, Matsuzawa H, Kwee IL. Magnetic resonance axonography of the rat spinal cord. NeuroReport 1994;5:2053-2056. 21. Mangin JF, Poupon C, Clark C, et al. Distortion correction and robust tensor estimation for MR diffusion imaging. Med Image Anal 2002;6:191-198. 22. Heidemann RM, Anwander A, Feiweier T, et al. k-space and qspace: combining ultra-high spatial and angular resolution in diffusion imaging using ZOOPPA at 7T. NeuroImage 2012;967-978. 23. Pipe JG. Motion correction with PROPELLER MRI: application to head motion and free breathing cardiac imaging. Magn Reson Med 1999;103:963-969. 24. Brodal A. Neurological Anatomy in Relation to Clinical Medicine. 3rd ed. New York: Oxford University Press; 1981:394-447. 25. Wang D. Reticular formation and spinal cord injury. Spinal Cord 2009;47:204-212. 26. Cantore G, Missori P, Santoro A. Cavernous angiomas of the brain stem: intra-axial anatomical pitfalls and surgical strategies. Surg Neurol 1999;52:84-93. 27. Kyoshima K, Kobayashi S, Gibo H, et al. A study of safe entry zones via the floor of the fourth ventricle for brain-stem lesions: report of three cases. J Neurosurg 1993;78:987-993. Journal of Neuroimaging Vol 24 No 3 May/June 2014 㸫㸫