Human subthalamic nucleus: evaluation with high-resolution MR imaging at 3.0 T. Neuroradiology. 2008;50:675-681. [PMID: 18443775 DOI: 10.1007/s00234-008-0388-4]

Improved visualization of the subthalamic nucleus on synthetic MRI with optimized parameters: initial study

BACKGROUND

Synthetic magnetic resonance imaging (SyMRI) enables to reformat various images by adjusting the MR parameters.

PURPOSE

To investigate whether customization of the repetition time (TR), echo time (TE), and inversion time (TI) in SyMRI could improve the visualization of subthalamic nucleus (STN).

MATERIAL AND METHODS

We examined five healthy volunteers using both coronal SyMRI and quantitative susceptibility mapping (QSM), seven patients with Parkinson's disease (PD) using coronal SyMRI, and 15 patients with PD using coronal QSM. Two neuroradiologists reformatted SyMRI (optimized SyMRI) by adjusting TR, TE, and TI to achieve maximum tissue contrast between the STN and the adjacent brain parenchyma. The optimized MR parameters in the PD patients varied according to the individual. For regular SyMRI (T2-weighted imaging [T2WI] and STIR), optimized SyMRI, and QSM, qualitative visualization scores of the STN (STN score) were recorded. The contrast-to-noise ratio (CNR) of the STN was also measured.

RESULTS

For the STN scores in both groups, the optimized SyMRI were significantly higher than the regular SyMRI (P < 0.05), and there were no significant differences between optimized SyMRI and QSM. For the CNR of differentiation of the STN from the substantia nigra, the optimized SyMRI was higher than the regular SyMRI (volunteer: T2WI P = 0.10 and STIR P = 0.26; PD patient: T2WI P = 0.43 and STIR P = 0.25), but the optimized SyMRI was lower than the QSM (volunteer: P = 0.26; PD patient: P = 0.03).

CONCLUSIONS

On SyMRI, optimization of MR parameters (TR, TE, and TI) on an individual basis may be useful to increase the conspicuity of the STN.

Charting human subcortical maturation across the adult lifespan with in vivo 7 T MRI

The human subcortex comprises hundreds of unique structures. Subcortical functioning is crucial for behavior, and disrupted function is observed in common neurodegenerative diseases. Despite their importance, human subcortical structures continue to be difficult to study in vivo. Here we provide a detailed account of 17 prominent subcortical structures and ventricles, describing their approximate iron and myelin contents, morphometry, and their age-related changes across the normal adult lifespan. The results provide compelling insights into the heterogeneity and intricate age-related alterations of these structures. They also show that the locations of many structures shift across the lifespan, which is of direct relevance for the use of standard magnetic resonance imaging atlases. The results further our understanding of subcortical morphometry and neuroimaging properties, and of normal aging processes which ultimately can improve our understanding of neurodegeneration.

A literature review of magnetic resonance imaging sequence advancements in visualizing functional neurosurgery targets

OBJECTIVE

Historically, preoperative planning for functional neurosurgery has depended on the indirect localization of target brain structures using visible anatomical landmarks. However, recent technological advances in neuroimaging have permitted marked improvements in MRI-based direct target visualization, allowing for refinement of "first-pass" targeting. The authors reviewed studies relating to direct MRI visualization of the most common functional neurosurgery targets (subthalamic nucleus, globus pallidus, and thalamus) and summarize sequence specifications for the various approaches described in this literature.

METHODS

The peer-reviewed literature on MRI visualization of the subthalamic nucleus, globus pallidus, and thalamus was obtained by searching MEDLINE. Publications examining direct MRI visualization of these deep brain stimulation targets were included for review.

RESULTS

A variety of specialized sequences and postprocessing methods for enhanced MRI visualization are in current use. These include susceptibility-based techniques such as quantitative susceptibility mapping, which exploit the amount of tissue iron in target structures, and white matter attenuated inversion recovery, which suppresses the signal from white matter to improve the distinction between gray matter nuclei. However, evidence confirming the superiority of these sequences over indirect targeting with respect to clinical outcome is sparse. Future targeting may utilize information about functional and structural networks, necessitating the use of resting-state functional MRI and diffusion-weighted imaging.

CONCLUSIONS

Specialized MRI sequences have enabled considerable improvement in the visualization of common deep brain stimulation targets. With further validation of their ability to improve clinical outcomes and advances in imaging techniques, direct visualization of targets may play an increasingly important role in preoperative planning.

Image Guidance in Deep Brain Stimulation Surgery to Treat Parkinson's Disease: A Comprehensive Review

Deep brain stimulation (DBS) is an effective therapy as an alternative to pharmaceutical treatments for Parkinson's disease (PD). Aside from factors such as instrumentation, treatment plans, and surgical protocols, the success of the procedure depends heavily on the accurate placement of the electrode within the optimal therapeutic targets while avoiding vital structures that can cause surgical complications and adverse neurologic effects. Although specific surgical techniques for DBS can vary, interventional guidance with medical imaging has greatly contributed to the development, outcomes, and safety of the procedure. With rapid development in novel imaging techniques, computational methods, and surgical navigation software, as well as growing insights into the disease and mechanism of action of DBS, modern image guidance is expected to further enhance the capacity and efficacy of the procedure in treating PD. This article surveys the state-of-the-art techniques in image-guided DBS surgery to treat PD, and discusses their benefits and drawbacks, as well as future directions on the topic.

Cortico-basal white matter alterations occurring in Parkinson's disease

Magnetic resonance imaging studies typically use standard anatomical atlases for identification and analyses of (patho-)physiological effects on specific brain areas; these atlases often fail to incorporate neuroanatomical alterations that may occur with both age and disease. The present study utilizes Parkinson's disease and age-specific anatomical atlases of the subthalamic nucleus for diffusion tractography, assessing tracts that run between the subthalamic nucleus and a-priori defined cortical areas known to be affected by Parkinson's disease. The results show that the strength of white matter fiber tracts appear to remain structurally unaffected by disease. Contrary to that, Fractional Anisotropy values were shown to decrease in Parkinson's disease patients for connections between the subthalamic nucleus and the pars opercularis of the inferior frontal gyrus, anterior cingulate cortex, the dorsolateral prefrontal cortex and the pre-supplementary motor, collectively involved in preparatory motor control, decision making and task monitoring. While the biological underpinnings of fractional anisotropy alterations remain elusive, they may nonetheless be used as an index of Parkinson's disease. Moreover, we find that failing to account for structural changes occurring in the subthalamic nucleus with age and disease reduce the accuracy and influence the results of tractography, highlighting the importance of using appropriate atlases for tractography.

Evaluating the role of 1.5T quantitative susceptibility mapping for subthalamic nucleus targeting in deep brain stimulation surgery

BACKGROUND AND PURPOSE

Quantitative susceptibility mapping (QSM) has been shown to be valuable in direct targeting for subthalamic nucleus (STN) DBS, given its higher quality of contrast between the STN border and adjacent anatomical structures. The objective is to demonstrate the feasibility of using 1.5T QSM for direct targeting in STN DBS planning.

MATERIAL AND METHODS

Eleven patients underwent MRI acquisitions using a 1.5T scanner, including multi-echo gradient echo sequences for generating QSM images. 22 STN targets were planned with direct targeting method using QSM images by one stereotactic neurosurgeon and indirect targeting method using standard protocol by a second stereotactic neurosurgeon. The two physicians were blinded to each other's results.

RESULTS

The mean coordinates for the STN using direct targeting relative to the mid-commissural point (MCP) was 11.41±2.43mm lateral, 2.48±0.53mm posterior and 4.45±0.95mm inferior. The mean coordinates for the STN using indirect targeting was 11.79±2.51mm lateral, 2.55±0.54mm posterior, and 4.84±1.03mm inferior. The mean (±SEM) radial error between the direct and indirect target was 0.67±0.14mm. In cases where DBS electrodes were implanted, the radial difference between the indirect and actual target (1.19±0.30mm) was statistically equivalent to the radial difference between the direct and actual target (1.0±0.27mm).

CONCLUSIONS

Direct targeting of the STN for DBS implantation using 1.5T QSM was found to be statistically equivalent to standard protocol surgery planning. This may offer a simpler, more intuitive alternative for DBS surgery planning at centers with 1.5T MRIs.

Visualizing the Human Subcortex Using Ultra-high Field Magnetic Resonance Imaging

With the recent increased availability of ultra-high field (UHF) magnetic resonance imaging (MRI), substantial progress has been made in visualizing the human brain, which can now be done in extraordinary detail. This review provides an extensive overview of the use of UHF MRI in visualizing the human subcortex for both healthy and patient populations. The high inter-subject variability in size and location of subcortical structures limits the usability of atlases in the midbrain. Fortunately, the combined results of this review indicate that a large number of subcortical areas can be visualized in individual space using UHF MRI. Current limitations and potential solutions of UHF MRI for visualizing the subcortex are also discussed.

Effects of aging on T₁, T₂*, and QSM MRI values in the subcortex

The aging brain undergoes several anatomical changes that can be measured with Magnetic Resonance Imaging (MRI). Early studies using lower field strengths have assessed changes in tissue properties mainly qualitatively, using [Formula: see text]- or [Formula: see text]- weighted images to provide image contrast. With the development of higher field strengths (7 T and above) and more advanced MRI contrasts, quantitative measures can be acquired even of small subcortical structures. This study investigates volumetric, spatial, and quantitative MRI parameter changes associated with healthy aging in a range of subcortical nuclei, including the basal ganglia, red nucleus, and the periaqueductal grey. The results show that aging has a heterogenous effects across regions. Across the subcortical areas an increase of [Formula: see text] values is observed, most likely indicating a loss of myelin. Only for a number of areas, a decrease of [Formula: see text] and increase of QSM is found, indicating an increase of iron. Aging also results in a location shift for a number of structures indicating the need for visualization of the anatomy of individual brains.

Toward defining deep brain stimulation targets in MNI space: A subcortical atlas based on multimodal MRI, histology and structural connectivity

Three-dimensional atlases of subcortical brain structures are valuable tools to reference anatomy in neuroscience and neurology. For instance, they can be used to study the position and shape of the three most common deep brain stimulation (DBS) targets, the subthalamic nucleus (STN), internal part of the pallidum (GPi) and ventral intermediate nucleus of the thalamus (VIM) in spatial relationship to DBS electrodes. Here, we present a composite atlas based on manual segmentations of a multimodal high resolution brain template, histology and structural connectivity. In a first step, four key structures were defined on the template itself using a combination of multispectral image analysis and manual segmentation. Second, these structures were used as anchor points to coregister a detailed histological atlas into standard space. Results show that this approach significantly improved coregistration accuracy over previously published methods. Finally, a sub-segmentation of STN and GPi into functional zones was achieved based on structural connectivity. The result is a composite atlas that defines key nuclei on the template itself, fills the gaps between them using histology and further subdivides them using structural connectivity. We show that the atlas can be used to segment DBS targets in single subjects, yielding more accurate results compared to priorly published atlases. The atlas will be made publicly available and constitutes a resource to study DBS electrode localizations in combination with modern neuroimaging methods.

Subthalamic nucleus volumes are highly consistent but decrease age-dependently-a combined magnetic resonance imaging and stereology approach in humans

The subthalamic nucleus (STN) is a main target structure of deep brain stimulation (DBS) in idiopathic Parkinson's disease. Nevertheless, there is an ongoing discussion regarding human STN volumes and neuron count, which could potentially have an impact on STN-DBS. Moreover, a suspected functional subdivision forms the basis of the tripartite hypothesis, which has not yet been morphologically substantiated. In this study, it was aimed to investigate the human STN by means of combined magnetic resonance imaging (MRI) and stereology. STN volumes were obtained from 14 individuals (ranging from 65 to 96 years, 25 hemispheres) in 3 T MRI and in luxol-stained histology slices. Neuron number and cell densities were investigated stereologically over the entire STN and in pre-defined subregions in anti-human neuronal protein HuC/D-stained slices. STN volumes measured with MRI were smaller than in stereology but appeared to be highly consistent, measuring on average 99 ± 6 mm³ (MRI) and 132 ± 20 mm³ (stereology). The neuron count was 431,088 ± 72,172. Both STN volumes and cell count decreased age-dependently. Neuron density was different for the dorsal, medial and ventral subregion with significantly higher values ventrally than dorsally. Small variations in STN volumes in both MRI and stereology contradict previous findings of large variations in STN size. Age-dependent decreases in STN volumes and neuron numbers might influence the efficacy of STN-DBS in a geriatric population. Though the study is limited in sample size, site-dependent differences for the STN subregions form a morphological basis for the tripartite theory. Hum Brain Mapp 38:909-922, 2017. © 2016 Wiley Periodicals, Inc.

Assessment of Age-Related Morphometric Changes of Subcortical Structures in Healthy People Using Ultra-High Field 7 Tesla Magnetic Resonance Imaging

Objective: To assess the age-related morphometric changes of subcortical structures in healthy people.

Materials and Methods: Ultra-high field 7 tesla magnetic resonance (MR) imaging in humans was used to visualize the subcortical structures of healthy young, middle-aged and elderly participants. Using the magnetization-prepared two rapid acquisition gradient echo (MP2RAGE) sequence, we assessed the visibility of the margins of the thalamus and white matter in the thalamus, as well as the anterior commissure (AC) and posterior commissure (PC) length, the maximal height of the thalamus, the half width of the third ventricle and the distance between the AC and the center of the mammillothalamic tract (MTT) at the level of the AC-PC plane. All quantitative data were statistically evaluated.

Results: The AC-PC length did not differ significantly among the three groups. The maximal height of the thalamus decreased with age (r_s(53) = −0.719, p < 0.001). The half width of the third ventricle (r_s(53) = 0.705, p < 0.001) and the distance between the AC and the center of the MTT (r_s(53) = 0.485, p < 0.001) increased with age. The distance between the AC and the center of the MTT of the young and the elderly participants differed significantly (p = 0.007).

Conclusion: The AC-PC length is not a good candidate for proportional correction during atlas-to-patient registration. The maximal height of the thalamus and the half width of the third ventricle correlated strongly with age, and the MTT position in relation to the AC shifted posteriorly as age increased. These age-related morphometric changes of subcortical structures should be considered in targeting for functional neurosurgery.

Modeling Laterality of the Globus Pallidus Internus in Patients With Parkinson's Disease

OBJECTIVE

Neurosurgical interventions such as deep brain stimulation surgery of the globus pallidus internus (GPi) play an important role in the treatment of medically refractory Parkinson's disease (PD), and require high targeting accuracy. Variability in the laterality of the GPi across patients with PD has not been well characterized. The aim of this report is to identify factors that may contribute to differences in position of the motor region of GPi.

MATERIALS AND METHODS

The charts and operative reports of 101 PD patients following deep brain stimulation surgery (70 males, aged 11-78 years) representing 201 GPi were retrospectively reviewed. Data extracted for each subject include age, gender, anterior and posterior commissures (AC-PC) distance, and third ventricular width. Multiple linear regression, stepwise regression, and relative importance of regressors analysis were performed to assess the predictive ability of these variables on GPi laterality.

RESULTS

Multiple linear regression for target vs. third ventricular width, gender, AC-PC distance, and age were significant for normalized linear regression coefficients of 0.333 (p < 0.0001), 0.206 (p = 0.00219), 0.168 (p = 0.0119), and 0.159 (p = 0.0136), respectively. Third ventricular width, gender, AC-PC distance, and age each account for 44.06% (21.38-65.69%, 95% CI), 20.82% (10.51-35.88%), 21.46% (8.28-37.05%), and 13.66% (2.62-28.64%) of the R² value, respectively. Effect size calculation was significant for a change in the GPi laterality of 0.19 mm per mm of ventricular width, 0.11 mm per mm of AC-PC distance, 0.017 mm per year in age, and 0.54 mm increase for male gender.

CONCLUSION

This variability highlights the limitations of indirect targeting alone, and argues for the continued use of MRI as well as intraoperative physiological testing to account for such factors that contribute to patient-specific variability in GPi localization.

Lateralization of the Subthalamic Nucleus with Age in Parkinson's Disease

Age-related changes in subthalamic nucleus (STN) position have not been well characterized in patients with Parkinson's disease (PD). We report a systematic retrospective analysis of age-related changes in radiographic and final deep brain stimulator (DBS) STN coordinates in PD patients. The charts of 134 PD patients (97 males, 28-84 years) representing 255 STN were reviewed. Multiple linear regression, stepwise regression, and relative importance of regressors analysis was performed to determine the significance of the relationship between STN position and age. Across all subjects, both radiographic STN localization and final DBS position within the STN showed a lateralization of the STN target with age (R²=0.1096,p=6.9×10^-8 and R²=0.0433,p=8.7×10^-4, respectively). Lateralization with age was observed regardless of MR field strength (1.5T and 3.0T) (R²=0.0946,p=7.6×10^-6 and R²=0.2687,p=9.2×10^-5, respectively). No other consistent or clinically significant age-related changes were identified. Multiple linear regression revealed that the third ventricle width and age are statistically significant predictors of radiographic STN lateralization (R² = 0.2404, p = 1.51×10^-5 and p = .00784 respectively). Step-wise regression demonstrated that age is a non-redundant predictor of STN lateralization relative to third ventricle width. Similar to healthy controls, STN position appears to shift laterally with age in PD. This highlights limitations of indirect targeting and atlas-based stereotactic surgery and argues for reliance on patient specific anatomy since factors such as age and 3^rd ventricular width can contribute to patient-specific variability in STN localization.

Anatomic characterization of prelemniscal radiations by probabilistic tractography: implications in Parkinson's disease

To characterize the anatomical connectivity of the prelemniscal radiations (Raprl), a white matter region within the posterior subthalamic area (PSA) that is an effective neurosurgical target for treating motor symptoms of Parkinson's disease (PD). Diffusion-weighted images were acquired from twelve healthy subjects using a 3T scanner. Constrained spherical deconvolution, a method that allows the distinction of crossing fibers within a voxel, was used to compute track-density images with sufficient resolution to accurately delineate distinct PSA regions and probabilistic tractography of Raprl in both hemispheres. Raprl connectivity was reproducible across all subjects and showed fibers traversing through this region towards primary and supplementary motor cortices, the orbitofrontal cortex, ventrolateral thalamus, and the globus pallidus, cerebellum and dorsal brainstem. All brain regions reached by Raprl fibers are part of motor circuits involved in the pathophysiology of PD; while these fiber systems converge at the level of the PSA, they can be spatially segregated. Fibers of distinct and specific motor control networks are identified within Raprl. The description of this anatomical crossroad suggests that, in the future, tractography could allow deep brain stimulation or lesional therapies in white matter targets according to individual patient's symptoms.

Magnetic resonance imaging of the subthalamic nucleus for deep brain stimulation

The subthalamic nucleus (STN) is one of the most important stereotactic targets in neurosurgery, and its accurate imaging is crucial. With improving MRI sequences there is impetus for direct targeting of the STN. High-quality, distortion-free images are paramount. Image reconstruction techniques appear to show the greatest promise in balancing the issue of geometrical distortion and STN edge detection. Existing spin echo- and susceptibility-based MRI sequences are compared with new image reconstruction methods. Quantitative susceptibility mapping is the most promising technique for stereotactic imaging of the STN.

A probabilistic atlas of the basal ganglia using 7 T MRI

A common localization procedure in functional imaging studies includes the overlay of statistical parametric functional magnetic resonance imaging (fMRI) maps or coordinates with neuroanatomical atlases in standard space, e.g., MNI-space. This procedure allows the identification of specific brain regions. Most standard MRI software packages include a wide range of atlases but have a poor coverage of the subcortex. We estimated that approximately 7% of the known subcortical structures are mapped in standard MRI-compatible atlases [1]. Here we provide a data description of a subcortical probabilistic atlas based on ultra-high resolution in-vivo anatomical imaging using 7 T (T) MRI. The atlas includes six subcortical nuclei: the striatum (STR), the globus pallidus internal and external segment (GPi/e), the subthalamic nucleus (STN), the substantia nigra (SN), and the red nucleus (RN). These probabilistic atlases are shared on freely available platforms such as NITRC and NeuroVault and are published in NeuroImage “Quantifying inter-individual anatomical variability in the subcortex using 7 T structural MRI” [2].

The subcortical cocktail problem; mixed signals from the subthalamic nucleus and substantia nigra

The subthalamic nucleus and the directly adjacent substantia nigra are small and important structures in the basal ganglia. Functional magnetic resonance imaging studies have shown that the subthalamic nucleus and substantia nigra are selectively involved in response inhibition, conflict processing, and adjusting global and selective response thresholds. However, imaging these nuclei is complex, because they are in such close proximity, they can vary in location, and are very small relative to the resolution of most fMRI sequences. Here, we investigated the consistency in localization of these nuclei in BOLD fMRI studies, comparing reported coordinates with probabilistic atlas maps of young human participants derived from ultra-high resolution 7T MRI scanning. We show that the fMRI signal reported in previous studies is likely not unequivocally arising from the subthalamic nucleus but represents a mixture of subthalamic nucleus, substantia nigra, and surrounding tissue. Using a simulation study, we also tested to what extent spatial smoothing, often used in fMRI preprocessing pipelines, influences the mixture of BOLD signals. We propose concrete steps how to analyze fMRI BOLD data to allow inferences about the functional role of small subcortical nuclei like the subthalamic nucleus and substantia nigra.

Comparison of magnetic resonance imaging sequences for depicting the subthalamic nucleus for deep brain stimulation

Electrodes are surgically implanted into the subthalamic nucleus (STN) of Parkinson’s disease patients to provide deep brain stimulation. For ensuring correct positioning, the anatomic location of the STN must be determined preoperatively. Magnetic resonance imaging has been used for pinpointing the location of the STN. To identify the optimal imaging sequence for identifying the STN, we compared images produced with T₂ star-weighted angiography (SWAN), gradient echo T₂*-weighted imaging, and fast spin echo T₂-weighted imaging in 6 healthy volunteers. Our comparison involved measurement of the contrast-to-noise ratio (CNR) for the STN and substantia nigra and a radiologist’s interpretations of the images. Of the sequences examined, the CNR and qualitative scores were significantly higher on SWAN images than on other images (p < 0.01) for STN visualization. Kappa value (0.74) on SWAN images was the highest in three sequences for visualizing the STN. SWAN is the sequence best suited for identifying the STN at the present time.

Low-power inversion recovery MRI preserves brain tissue contrast for patients with Parkinson disease with deep brain stimulators

BACKGROUND AND PURPOSE

Fast spin-echo short τ inversion recovery sequences have been very useful for MR imaging-guided deep brain stimulation procedures in Parkinson disease. However, high-quality fast spin-echo imaging deposits significant heat, exceeding FDA-approved limits when patients already have undergone deep brain stimulation and need a second one or a routine brain MR imaging for neurologic indications. We have developed a STIR sequence with an ultra-low specific absorption rate that meets hardware limitations and produces adequate tissue contrast in cortical and subcortical brain tissues for deep brain stimulation recipients.

MATERIALS AND METHODS

Thirteen patients with medically refractory Parkinson disease who qualified for deep brain stimulation were imaged at 1.5T with a fast spin-echo short τ inversion recovery sequence modified to meet conditional MR imaging hardware and specific absorption rate restrictions. Tissue contrast-to-noise ratios and implant localization were objectively and subjectively compared by 2 neuroradiologists, and image quality for surgical planning was assessed by a neurosurgeon for high and low specific absorption rate images.

RESULTS

The mean contrast-to-noise ratio for cerebral tissues without including the contrast-to-noise ratio for ventricular fluid was 35 and 31 for high and low specific absorption rate images. Subjective ratings for low specific absorption rate tissue contrast in 77% of patients were identical to (and in a few cases higher than) those of high specific absorption rate contrast, while the neurosurgical coordinates for fusing the stereotactic atlas with low specific absorption rate MR imaging were equivalent to those of the high specific absorption rate for 69% of patients.

CONCLUSIONS

Patients with Parkinson disease who have already had a deep brain stimulation face a risk of neural injury if routine, high specific absorption rate MR imaging is performed. Our modified fast spin-echo short τ inversion recovery sequence conforms to very conservative radiofrequency safety limits, while it maintains high tissue contrast for presurgical planning, postsurgical assessment, and radiologic evaluations with greater confidence for radiofrequency safety.

Investigation of morphometric variability of subthalamic nucleus, red nucleus, and substantia nigra in advanced Parkinson's disease patients using automatic segmentation and PCA-based analysis

Subthalamic nucleus (STN) deep brain stimulation (DBS) is an effective surgical therapy to treat Parkinson's disease (PD). Conventional methods employ standard atlas coordinates to target the STN, which, along with the adjacent red nucleus (RN) and substantia nigra (SN), are not well visualized on conventional T1w MRIs. However, the positions and sizes of the nuclei may be more variable than the standard atlas, thus making the pre-surgical plans inaccurate. We investigated the morphometric variability of the STN, RN and SN by using label-fusion segmentation results from 3T high resolution T2w MRIs of 33 advanced PD patients. In addition to comparing the size and position measurements of the cohort to the Talairach atlas, principal component analysis (PCA) was performed to acquire more intuitive and detailed perspectives of the measured variability. Lastly, the potential correlation between the variability shown by PCA results and the clinical scores was explored.

Volumetric analysis of the subthalamic and red nuclei based on magnetic resonance imaging in patients with Parkinson's disease

Parkinson's disease (PD) is associated with degeneration of the dopaminergic neurons in the substantia nigra. The subthalamic nucleus (STN) plays a pivotal role in the pathogenesis. However, there is not much known about the morphological changes in the STN. The red nucleus (RN) has many connections with the motor coordinating pathways although it is not primarily involved in the pathogenesis. In this study we aimed to compare the volumes of the STN and RN measured by magnetic resonance imaging in PD patients and controls to investigate how these structures are affected at the morphological level. Twenty patients with PD and twenty age/sex matched controls were enrolled in this study. Severity score was determined by Hoehn & Yahr staging: 6 at stage II and 14 at stage III in med-off state. Imaging was performed by a 1.5 Tesla (T) MR scanner. Measurements of total brain and normalized STN and RN volumes were performed by manual planimetry using Image J software. No statistically significant differences were observed between two groups based on age or gender and disease stage and nuclei volumes. The total estimated brain volumes were not different between PD patients and controls. However, normalized volumes of the STN and RN were 14% and 16% larger, respectively, in PD patients compared to the controls (p < 0.05). Our findings suggest that the volumes of the STN and RN are increased in patients with PD. These changes possibly reflect the altered metabolic activity of these regions demonstrated by neurophysiological studies.

Ultra-high 7T MRI of structural age-related changes of the subthalamic nucleus

The subthalamic nucleus (STh) is a small subcortical structure which is involved in regulating motor as well as cognitive functions. Due to its small size and close proximity to other small subcortical structures, it has been a challenge to localize and visualize it using magnetic resonance imaging (MRI). Currently there are several standard atlases available that are used to localize the STh in functional MRI studies and clinical procedures such as deep brain stimulation (DBS). DBS is an increasingly common neurosurgical procedure that has been successfully used to alleviate motor symptoms present in Parkinson's disease. However, current atlases are based on low sample sizes and restricted age ranges (Schaltenbrand and Wahren, 1977), and hence the use of these atlases effectively ignores the substantial structural brain changes that are associated with aging. In the present study, ultra-high field 7 tesla (T) magnetic resonance imaging (MRI) in humans was used to visualize and segment the STh in young, middle-aged, and elderly participants. The resulting probabilistic atlas maps for all age groups show that the STh shifts in the lateral direction with increasing age. In sum, the results of the present study suggest that age has to be taken into account in atlases for the optimal localization of the STh in healthy and diseased brains.

Imaging for deep brain stimulation: The zona incerta at 7 Tesla

AIM: To evaluate different promising magnetic resonance imaging (MRI) methods at 7.0 Tesla (T) for the pre-stereotactic visualization of the zona incerta (ZI).

METHODS: Two neuroradiologists qualitatively and quantitatively examined T2-turbo spin-echo (T2-TSE), T1-weighted gradient-echo, as well as FLASH2D-T2Star and susceptibility-weighted imaging (SWI) for the visualization of the ZI at 7.0 T MRI. Delineation and image quality for the ZI were independently examined using a 6-scale grading system. Inter-rater reliability using Cohen’s kappa coefficient (κ) were assessed. Contrast-to-noise ratios (CNR), and signal-to-noise ratios (SNR) for the ZI were calculated for all sequences. Differences in delineation, SNR, and CNR between the sequences were statistically assessed using a paired t-test. For the anatomic validation the coronal FLASH2D-T2Star images were co-registered with a stereotactic atlas (Schaltenbrand-Wahren).

RESULTS: The rostral part of the ZI (rZI) could easily be identified and was best and reliably visualized in the coronal FLASH2D-T2Star images. The caudal part was not definable in any of the sequences. No major artifacts in the rZI were observed in any of the scans. FLASH2D-T2Star and SWI imaging offered significant higher CNR values for the rZI compared to T2-TSE images (P > 0.05). The co-registration of the coronal FLASH2D-T2Star images with the stereotactic atlas schema (Schaltenbrand-Wahren) confirmed the correct localization of the ZI in all cases.

CONCLUSION: FLASH2D-T2Star imaging (particularly coronal view) provides the reliable and currently optimal visualization of the rZI at 7.0 T. These results can facilitate a better and more precise targeting of the caudal part of the ZI than ever before.

The subthalamic nucleus at 7.0 Tesla: evaluation of sequence and orientation for deep-brain stimulation

BACKGROUND

Deep-brain stimulation (DBS) of the subthalamic nucleus (STN) is an accepted neurosurgical technique for the treatment of medication-resistant Parkinson's disease and other neurological disorders. The accurate targeting of the STN is facilitated by precise and reliable identification in pre-stereotactic magnetic resonance imaging (MRI). The aim of the study was to compare and evaluate different promising MRI methods at 7.0 T for the pre-stereotactic visualisation of the STN METHODS: MRI (T2-turbo spin-echo [TSE], T1-gradient echo [GRE], fast low-angle shot [FLASH] two-dimensional [2D] T2* and susceptibility-weighted imaging [SWI]) was performed in nine healthy volunteers. Delineation and image quality for the STN were independently evaluated by two neuroradiologists using a six-point grading system. Inter-rater reliability, contrast-to-noise ratios (CNRs) and signal-to-noise ratios (SNRs) for the STN were calculated. For the anatomical validation, the coronal FLASH 2D T2* images were co-registered with a stereotactic atlas (Schaltenbrand-Wahren).

RESULTS

The STN was clearly and reliably visualised in FLASH 2D T2* imaging (particularly coronal view), with a sharp delineation between the STN, the substantia nigra and the zona incerta. No major artefacts in the STN were observed in any of the sequences. FLASH 2D T2* and SWI images offered significantly higher CNR for the STN compared with T2-TSE. The co-registration of the coronal FLASH 2D T2* images with the stereotactic atlas affirmed the correct localisation of the STN in all cases.

CONCLUSION

The STN is best and reliably visualised in FLASH 2D T2* imaging (particularly coronal orientation) at 7.0-T MRI.

The subthalamic nucleus at 3.0 Tesla: choice of optimal sequence and orientation for deep brain stimulation using a standard installation protocol: clinical article

OBJECT

Reliable visualization of the subthalamic nucleus (STN) is indispensable for accurate placement of electrodes in deep brain stimulation (DBS) surgery for patients with Parkinson disease (PD). The aim of the study was to evaluate different promising new MRI methods at 3.0 T for preoperative visualization of the STN using a standard installation protocol.

METHODS

Magnetic resonance imaging studies (T2-FLAIR, T1-MPRAGE, T2*-FLASH2D, T2-SPACE, and susceptibility-weighted imaging sequences) obtained in 9 healthy volunteers and in 1 patient with PD were acquired. Two neuroradiologists independently analyzed image quality and visualization of the STN using a 6-point scale. Interrater reliability, contrast-to-noise ratios, and signal-to-noise ratios for the STN were calculated. For illustration of the anatomical accuracy, coronal T2*-FLASH2D images were fused with the corresponding coronal section schema of the Schaltenbrand and Wahren stereotactic atlas.

RESULTS

The STN was best and reliably visualized on T2*-FLASH2D imaging (in particular, the coronal view). No major artifacts in the STN were observed in any of the sequences. Susceptibility-weighted, T2-SPACE, and T2*-FLASH2D imaging provided significantly higher contrast-to-noise ratio values for the STN than standard T2-weighted imaging. Fusion of the coronal T2*-FLASH2D and the digitized coronal atlas view projected the STN clearly within the boundaries of the STN found in anatomical sections.

CONCLUSIONS

For 3.0-T MRI, T2*-FLASH2D (particularly the coronal view) provides optimal delineation of the STN using a standard installation protocol.

Toward in vivo histology: a comparison of quantitative susceptibility mapping (QSM) with magnitude-, phase-, and R2*-imaging at ultra-high magnetic field strength

Quantitative magnetic susceptibility mapping (QSM) has recently been introduced to provide a novel quantitative and local MRI contrast. However, the anatomical contrast represented by in vivo susceptibility maps has not yet been compared systematically and comprehensively with gradient (recalled) echo (GRE) magnitude, frequency, and R(2)(*) images. Therefore, this study compares high-resolution quantitative susceptibility maps with conventional GRE imaging approaches (magnitude, frequency, R(2)(*)) in healthy individuals at 7 T with respect to anatomic tissue contrast. Volumes-of-interest were analyzed in deep and cortical gray matter (GM) as well as in white matter (WM) on R(2)(*) and susceptibility maps. High-resolution magnetic susceptibility maps of the human brain exhibited superb contrast that allowed the identification of substructures of the thalamus, midbrain and basal ganglia, as well as of the cerebral cortex. These were consistent with histology but not generally visible on magnitude, frequency or R(2)(*)-maps. Common target structures for deep brain stimulation, including substantia nigra pars reticulata, ventral intermediate nucleus, subthalamic nucleus, and the substructure of the internal globus pallidus, were clearly distinguishable from surrounding tissue on magnetic susceptibility maps. The laminar substructure of the cortical GM differed depending on the anatomical region, i.e., a cortical layer with increased magnetic susceptibility, corresponding to the Stria of Gennari, was found in the GM of the primary visual cortex, V1, whereas a layer with reduced magnetic susceptibility was observed in the GM of the temporal cortex. Both magnetic susceptibility and R(2)(*) values differed substantially in cortical GM depending on the anatomic regions. Regression analysis between magnetic susceptibility and R(2)(*) values of WM and GM structures suggested that variations in myelin content cause the overall contrast between gray and white matter on susceptibility maps and that both R(2)(*) and susceptibility values provide linear measures for iron content in GM. In conclusion, quantitative magnetic susceptibility mapping provides a non-invasive and spatially specific contrast that opens the door to the assessment of diseases characterized by variation in iron and/or myelin concentrations. Its ability to reflect anatomy of deep GM structures with superb delineation may be useful for neurosurgical applications.

Visualization of the internal globus pallidus: sequence and orientation for deep brain stimulation using a standard installation protocol at 3.0 Tesla

BACKGROUND

Deep-brain stimulation (DBS) of the internal globus pallidus (GPi) has shown remarkable therapeutic benefits for treatment-resistant neurological disorders including dystonia and Parkinson's disease (PD). The success of the DBS is critically dependent on the reliable visualization of the GPi. The aim of the study was to evaluate promising 3.0 Tesla magnetic resonance imaging (MRI) methods for pre-stereotactic visualization of the GPi using a standard installation protocol.

METHODS

MRI at 3.0 T of nine healthy individuals and of one patient with PD was acquired (FLAIR, T1-MPRAGE, T2-SPACE, T2*-FLASH2D, susceptibility-weighted imaging mapping (SWI)). Image quality and visualization of the GPi for each sequence were assessed by two neuroradiologists independently using a 6-point scale. Axial, coronal, and sagittal planes of the T2*-FLASH2D images were compared. Inter-rater reliability, contrast-to-noise ratios (CNR) and signal-to-noise ratios (SNR) for the GPi were determined. For illustration, axial T2*-FLASH2D images were fused with a section schema of the Schaltenbrand-Wahren stereotactic atlas.

RESULTS

The GPi was best and reliably visualized in axial and to a lesser degree on coronal T2*-FLASH2D images. No major artifacts in the GPi were observed in any of the sequences. SWI offered a significantly higher CNR for the GPi compared to standard T2-weighted imaging using the standard parameters. The fusion of the axial T2*-FLASH2D images and the atlas projected the GPi clearly in the boundaries of the section schema.

CONCLUSIONS

Using a standard installation protocol at 3.0 T T2*-FLASH2D imaging (particularly axial view) provides optimal and reliable delineation of the GPi.

Visualisation of the zona incerta for deep brain stimulation at 3.0 Tesla

PURPOSE

Deep-brain stimulation (DBS) of the zona incerta (ZI) has shown promising results for medication-refractory neurological disorders including Parkinson's disease (PD) and essential tremor (ET). The success of the intervention is indispensably dependent on the reliable visualisation of the ZI. The aim of the study was to evaluate different promising new magnetic resonance imaging (MRI) methods at 3.0 Tesla for pre-stereotactic visualisation of the ZI using a standard installation the protocol.

METHODS

MRI of nine healthy volunteers was acquired (T1-MPRAGE, T2-FLAIR, T2*-FLASH2D, T2-SPACE and susceptibility-weighted imaging (SWI). Image quality and visualisation of the ZI for each sequence were analysed independently by two neuroradiologists using a 6-point scale. For T2*-FLASH2D the axial, coronal and sagittal planes were compared. The delineation of the ZI versus the internal capsule, the subthalamic nucleus and the pallidofugal fibres was evaluated in all sequences and compared to T2-FLAIR using a paired t-test. Inter-rater reliability, contrast-to-noise ratios (CNR), and signal-to-noise ratios (SNR) for the ZI were computed. For illustration, coronal T2*-FLASH2D images were co-registered with the corresponding section schema of the Schaltenbrand-Wahren stereotactic atlas.

RESULTS

Only the rostral part of the ZI (rZI) could be identified. The rZI was best and reliably visualised in T2*-FLASH2D (particularly coronal orientation; p < 0.05). No major artifacts in the rZI were observed in any of the sequences. SWI, T2-SPACE, and T2*-FLASH imaging offered significant higher CNR values for the rZI compared to T2-FLAIR imaging using standard parameters. The co-registration of the coronal T2*-FLASH2D images projected the ZI clearly into the boundaries of the anatomical sections.

CONCLUSIONS

The delineation of the rZI is best possible in T2*-FLASH2D (particularly coronal view) using a standard installation protocol at 3.0 T. The caudal ZI could not be discerned in any of the sequences.

Direct visualization of the subthalamic nucleus and its iron distribution using high-resolution susceptibility mapping

Histological studies have shown a relatively high iron concentration in the subthalamic nucleus (STN). T2- and T2*-weighted sequences have previously been used to visualize the STN in vivo. The phase information of gradient-echo images reflects the magnetic tissue properties more directly, e.g., iron is more paramagnetic than water. Unfortunately, phase images suffer from non-local effects and orientation dependency. The goal of this study is to delineate the STN more precisely using susceptibility maps, calculated from phase images, which directly index magnetic tissue properties while removing the non-local effects and orientation dependency. Use of 7T MRI enables high spatial resolution with good signal to noise ratio (SNR). Eight healthy subjects were scanned at 7T using a high-resolution 3D gradient-echo sequence. Susceptibility maps were calculated from phase data using a thresholding Fourier approach and a regularization approach using spatial priors. The susceptibility maps clearly distinguish the STN from the adjacent substantia nigra (SN). Their susceptibilities are quantitatively different (0.06 and 0.1 ppm for the STN and SN, respectively). These maps allowed the STN, SN, and the red nucleus to be manually segmented, thus providing 3D visualization of their boundaries. In sum, the STN can be more clearly distinguished from adjacent structures in susceptibility maps than in T2*-weighted images or phase images.

The regional distribution of T2-relaxation times in MR images of the substantia nigra and crus cerebri

INTRODUCTION

When scanning the size of the substantia nigra (SN), for example in Parkinson's disease, it is important to precisely locate its true anatomic location. The hypointense areas on T2-weighted magnetic resonance images (T2w) at the level of the upper midbrain are usually labeled as the SN. Recent studies showed that the line of demarcation between the SN and the crus cerebri (CC) in T2w images seems not to be clear. The purpose of our study was to evaluate the depiction of the SN and the CC on calculated R2 maps by analyzing the regional distribution of T2 values in both regions.

METHODS

In 36 healthy subjects, triple echo turbo spin echo were obtained at 1.5 T and R2 maps calculated. Proton density-weighted turbo spin echo images (PDw) were used as reference. The CC and SN were manually traced on PDw sections (CCP and SNP) and also the hyperintense areas on the R2 maps, suggestive of the SN (DT2). The obtained volumes were evaluated in terms of total size, intersections size, and residual areas, as well as the corresponding T2 values.

RESULTS

DT2 corresponded to anterolateral parts of the SNP and showed an extension to anteromedial part of the CC. The intersections between DT2 and CCP and DT2 and SNP presented both decreased but different T2 values (102 +/- 5 and 95 +/- 4 ms).

CONCLUSION

An exact differentiation of the SN from the CC is not possible on the basis of T2w images but rather on the basis of the underlying calculated T2 values from the triple echo sequence.

Automated optimization of subcortical cerebral MR imaging-atlas coregistration for improved postoperative electrode localization in deep brain stimulation

BACKGROUND AND PURPOSE

The efficacy of deep brain stimulation in treating movement disorders depends critically on electrode localization, which is conventionally described by using coordinates relative to the midcommissural point. This approach requires manual measurement and lacks spatial normalization of anatomic variances. Normalization is based on intersubject spatial alignment (coregistration) of corresponding brain structures by using different geometric transformations. Here, we have devised and evaluated a scheme for automated subcortical optimization of coregistration (ASOC), which maximizes patient-to-atlas normalization accuracy of postoperative structural MR imaging into the standard Montreal Neurologic Institute (MNI) space for the basal ganglia.

MATERIALS AND METHODS

Postoperative T2-weighted MR imaging data from 39 patients with Parkinson disease and 32 patients with dystonia were globally normalized, representing the standard registration (control). The global transformations were regionally refined by 2 successive linear registration stages (RSs) (ASOC-1 and 2), focusing progressively on the basal ganglia with 2 anatomically selective brain masks, which specify the reference volume (weighted cost function). Accuracy of the RSs was quantified by spatial dispersion of 16 anatomic landmarks and their root-mean-square errors (RMSEs) with respect to predefined MNI-based reference points. The effects of CSF volume, age, and sex on RMSEs were calculated.

RESULTS

Mean RMSEs differed significantly (P < .001) between the global control (4.2 +/- 2.0 mm), ASOC-1 (1.92 +/- 1.02 mm), and ASOC-2 (1.29 +/- 0.78 mm).

CONCLUSIONS

The present method improves the registration accuracy of postoperative structural MR imaging data into MNI space within the basal ganglia, allowing automated normalization with increased precision at stereotactic targets, and enables lead-contact localization in MNI coordinates for quantitative group analysis.

Localization of the subthalamic nucleus: optimization with susceptibility-weighted phase MR imaging

BACKGROUND AND PURPOSE

On clinical MR images, the subthalamic nuclei (STN) are poorly delineated from adjacent structures, impeding safe direct targeting for placement of electrodes in the treatment of Parkinson disease. Susceptibility-weighted MR phase imaging offers improved contrast and spatial resolution at reduced imaging times relative to clinically used T2-weighted spin-echo imaging for STN visualization. Our purpose was to assess STN visibility by using phase imaging, comparing phase and magnitude images obtained concurrently by using susceptibility-weighted imaging (SWI). The goal was to identify an efficient scanning protocol for high-quality phase images of STN.

MATERIALS AND METHODS

Seventy-eight SWI scans were acquired at 3T by using different TEs and acceleration factors. STN visibility and delimitation from adjacent structures were scored from 0 (not interpretable) to 5 (excellent). Regression analyses assessed the relationship of STN visibility to scanning parameters

RESULTS

STN were identified at all studied TEs on phase images. Visibility and delimitation of STN were consistently superior on phase images compared with magnitude images. Good visualization (score of >or=4) of STN on phase imaging occurred at a mean TE of 20.0 ms and a sensitivity encoding (SENSE) of 1.40. Scores of STN visualization on phase images were dependent on SENSE (P < .002) and TE (P < .031). Good delimitation of the STN on phase imaging occurred at a mean TE of 21.6 ms and a SENSE of 1.36.

CONCLUSIONS

Visualization and delimitation of STN was superior on phase images and was achieved at 3T in <2.5 minutes. A TE of 20 ms and an acceleration factor of <or=1.5 are recommended to visualize STN by using this method.