High-resolution 3D MR Imaging Research Articles

Anterior cruciate ligament reconstruction related complications: 2D and 3D high-resolution magnetic resonance imaging evaluation.

Anterior cruciate ligament (ACL) injury is a common indication for sports-related major surgery and accounts for a large proportion of ligamentous injuries in athletes. The advancements in 2D and 3D MR imaging have provided considerable potential for a one-stop shop radiation-free assessment with an all-in-one modality examination of the knee, for both soft-tissue and bone evaluations. This article reviews ACL injuries and types of surgical managements with illustrative examples using high resolution 2D and 3D MR imaging. Various complications of ACL reconstruction procedures are highlighted with a focus on the use of advanced MR imaging and relevant arthroscopic correlations.

Simultaneous super-resolution and contrast synthesis of routine clinical magnetic resonance images of the knee for improving automatic segmentation of joint cartilage: data from the Osteoarthritis Initiative.

High resolution three-dimensional (3D) magnetic resonance (MR) images are well suited for automated cartilage segmentation in the human knee joint. However, volumetric scans such as 3D Double-Echo Steady-State (DESS) images are not routinely acquired in clinical practice which limits opportunities for reliable cartilage segmentation using (fully) automated algorithms. In this work, a method for generating synthetic 3D MR (syn3D-DESS) images with better contrast and higher spatial resolution from routine, low resolution, two-dimensional (2D) Turbo-Spin Echo (TSE) clinical knee scans is proposed. A UNet convolutional neural network is employed for synthesizing enhanced artificial MR images suitable for automated knee cartilage segmentation. Training of the model was performed on a large, publically available dataset from the OAI, consisting of 578 MR examinations of knee joints from 102 healthy individuals and patients with knee osteoarthritis. The generated synthetic images have higher spatial resolution and better tissue contrast than the original 2D TSE, which allow high quality automated 3D segmentations of the cartilage. The proposed approach was evaluated on a separate set of MR images from 88 subjects with manual cartilage segmentations. It provided a significant improvement in automated segmentation of knee cartilages when using the syn3D-DESS images compared to the original 2D TSE images. The proposed method can successfully synthesize 3D DESS images from 2D TSE images to provide images suitable for automated cartilage segmentation.

High-Resolution MRI for Evaluation of Ventriculostomy Tubes: Assessment of Positioning and Proximal Patency.

Imaging evaluation of ventriculostomy tubes, despite the frequency of malfunction, has remained inadequate due to the absence of a systematic way of assessing the catheter itself. In this retrospective review, we assessed the utility of high-resolution 3D MR imaging techniques, including CISS and volumetric interpolated breath-hold examination sequences, in the evaluation of ventriculostomy catheters. We performed a retrospective review of 23 clinical MR imaging cases of shunted hydrocephalus spanning a 3-year period, all depicting ventriculostomy catheters. The MR imaging examinations included isotropic CISS and volumetric interpolated breath-hold examination sequences performed with and without contrast. These were independently evaluated by 2 neuroradiologists with respect to the catheter course, side hole position, relationship of the side holes to the ventricles, patency, and the presence or absence of intraluminal debris. The catheter tip was best seen on isotropic CISS sequences reformatted in an oblique plane, and side holes were visualized as CSF signal defects along the catheter wall in 10/23 (43%) cases. The relationship of the catheter side holes to the ventricles was seen in 47% of cases and was best visualized on the coronal CISS sequences. Catheter patency was confirmed in 12/23 (52%) cases, while the other 48% were notable for T2 hypointense filling defects compatible with luminal obstruction. Enhancement of some of these filling defects on imaging is suggestive of choroid plexus ingrowth rather than debris. High-resolution 3D MR imaging using isotropic CISS sequences allows systematic evaluation of catheter positioning, patency, and potential etiologic differentiation of filling defects when shunt dysfunction is suspected.

NIMG-45. 3D SINGLE-SCAN FOR MULTI-CONTRAST-WEIGHTED MRI FOR LESION DETECTION IN PATIENTS WITH GLIOMAS

Abstract INTRODUCTION Multi-contrast-weighted (MCW) MRI allows derivation of T1-weighted, T2-weighted, and T2-FLAIR images and their parametric maps. Under current practice, these high-resolution 3D MR images are acquired separately with a total scan time is approximately 30 minutes. The goal of this study was to develop a novel sequence and processing strategy for MCW MRI and lesion detection of gliomas with 1mm isotropic resolution in 6 minutes, which can significantly improve clinical imaging workflow. The proposed whole brain, single-scan method enables the generation of segmented tumor regions that correspond the hyperintense lesion on T2-weighted or T2-FLAIR images (T2L). METHODS Our strategy involves using a highly accelerated 3D MRI sequence to achieve whole brain, MCW images that can be jointly segmented with modified k-means clustering. Six patients with enhancing gliomas were scanned with this sequence before the injection of gadolinium, 4 of which also received a repeat scan post-gadolinium. Our automatic segmentation of the T2L and manual definition of the contrast-enhancing lesion (CEL) was compared against manually segmented lesions drawn from conventional anatomical imaging. RESULTS Whole-brain MCW MRI was achieved with 1mm isotropic resolution in 6 mins. Grey-matter, white-matter, CSF, and the T2L could be automatically segmented with our clustering method. The resulting automatically-segmented T2L volume was not significantly different between our new sequence and clinically defined regions (average Dice Coefficient=0.81(+/-0.05); p=0.95). CONCLUSIONS Our novel, 6-minute scan and processing strategy was able to generate MCW anatomical images and automatically segment grey-matter, white-matter, and T2L volumes that were similar to manual segmentation of conventional anatomical imaging. We are currently extending the automatic segmentation to the CEL. This approach has the potential to improve clinical workflow by allowing time for therapy-specific advanced imaging and providing a noninvasive tool for monitoring tumor evolution. Validation is currently being performed in a larger cohort.

Metabolic regional and network changes in Alzheimer's disease subtypes

Clinical variants of Alzheimer's disease (AD) include the common amnestic subtype as well as subtypes characterised by leading visual processing impairments or by multimodal neurocognitive deficits. We investigated regional metabolic patterns and networks between AD subtypes. The study comprised 9 age-matched controls and 25 patients with mild to moderate AD. Methods included clinical and neuropsychological assessment, high-resolution FDG PET and T1-weighted 3D MR imaging with PET-MR coregistration, grey matter segmentation, atlas-based regions-of-interest, linear mixed effects and regional correlation analysis. Regional metabolic patterns differed significantly between groups, but significant hypometabolism in the posterior cingulate cortex (PCC) was common to all subtypes. The most distinctive regional abnormality was occipital hypometabolism in the visual subtype. In controls, two large clusters of positive regional metabolic correlations were observed. The most pronounced breakdown of the normal correlation pattern was found in amnestic patients who, in contrast, showed the least regional focal metabolic deficits. The normal positive correlation between PCC and hippocampus was lost in all subtypes. In conclusion, PCC hypometabolism and metabolic correlation breakdown between PCC and hippocampus are the common functional core of all AD subtypes. Network alterations exceed focal regional impairment and are most prominent in the amnestic subtype.

Normal Magnetic Resonance Imaging Anatomy of the Anterolateral Knee Ligament With a T2/T1-Weighted 3-Dimensional Sequence: A Feasibility Study

PurposeThe anatomy of the lateral knee compartment has been recently further explored with description of the anterolateral knee ligament (ALL). The purpose of this study was to confirm the presence of ALL on cadaveric knees and to describe its normal anatomy in young healthy volunteers, utilizing a high-resolution 3-dimensional (3D) pulse sequence. MethodsDissection was performed on 9 cadaveric knees in order to confirm the presence of ALL. Conventional 2-dimensional sequences of 10 knees at 1.5 T and 10 knees at 3 T, with a slice thickness of 2-4 mm, were reviewed for the presence of ALL. A 3D T2/T1-weighted gradient echo sequence (constructive interference in steady state [CISS]), yielding in-plane resolution of 0.4 mm × 0.4 mm × 0.4 mm, was applied in 14 healthy volunteers (26 knees). All 3D images were manipulated using multiplanar reconstruction (MPR) and the presence and width of ALL were recorded. ResultsCadaveric dissection disclosed the presence of ALL in 8 of 9 knees. Conventional knee MR imaging depicted ALL only on coronal images (18 of 20) whereas the CISS revealed ALL on 24 of 26 studied knees (92.3%). ALL has a mean thickness of 1.1 ± 0.27 mm measured on coronal MR images. ConclusionsALL can be thoroughly assessed in young healthy individuals with the use of high-resolution 3D MR imaging with MPR at 1.5 T.

MRI-detectable changes in mouse brain structure induced by voluntary exercise

Physical exercise, besides improving cognitive and mental health, is known to cause structural changes in the brain. Understanding the structural changes that occur with exercise as well as the neuroanatomical correlates of a predisposition for exercise is important for understanding human health. This study used high-resolution 3D MR imaging, in combination with deformation-based morphometry, to investigate the macroscopic changes in brain structure that occur in healthy adult mice following four weeks of voluntary exercise. We found that exercise induced changes in multiple brain structures that are involved in motor function and learning and memory including the hippocampus, dentate gyrus, stratum granulosum of the dentate gyrus, cingulate cortex, olivary complex, inferior cerebellar peduncle and regions of the cerebellum. In addition, a number of brain structures, including the hippocampus, striatum and pons, when measured on MRI prior to the start of exercise were highly predictive of subsequent exercise activity. Exercise tended to normalize these pre-existing differences between mice.

Validation and application of an intervertebral disc finite element model utilizing independently constructed tissue-level constitutive formulations that are nonlinear, anisotropic, and time-dependent

Finite element (FE) models are advantageous in the study of intervertebral disc mechanics as the stress–strain distributions can be determined throughout the tissue and the applied loading and material properties can be controlled and modified. However, the complicated nature of the disc presents a challenge in developing an accurate and predictive disc model, which has led to limitations in FE geometry, material constitutive models and properties, and model validation. The objective of this study was to develop a new FE model of the intervertebral disc, to validate the model׳s nonlinear and time-dependent responses without tuning or calibration, and to evaluate the effect of changes in nucleus pulposus (NP), cartilaginous endplate (CEP), and annulus fibrosus (AF) material properties on the disc mechanical response. The new FE disc model utilized an analytically-based geometry. The model was created from the mean shape of human L4/L5 discs, measured from high-resolution 3D MR images and averaged using signed distance functions. Structural hyperelastic constitutive models were used in conjunction with biphasic-swelling theory to obtain material properties from recent tissue tests in confined compression and uniaxial tension. The FE disc model predictions fit within the experimental range (mean±95% confidence interval) of the disc׳s nonlinear response for compressive slow loading ramp, creep, and stress-relaxation simulations. Changes in NP and CEP properties affected the neutral-zone displacement but had little effect on the final stiffness during slow-ramp compression loading. These results highlight the need to validate FE models using the disc׳s full nonlinear response in multiple loading scenarios.

High Resolution 3D MR Imaging Using 3x Acceleration Wideband MRI Technique

High Resolution 3D MR Imaging Using 3x Acceleration Wideband MRI Technique

Frequency and Location of Dilated Virchow-Robin Spaces in Elderly People: A Population-Based 3D MR Imaging Study

dVRS have been previously associated with aging and cerebrovascular diseases. However, little is known about their prevalence and topographic distribution in the general elderly population. dVRS were evaluated by using high-resolution 3D MR imaging in 1826 subjects enrolled in the 3C-Dijon MR imaging study. On T1-weighted MR imaging, dVRS were detected according to 3D imaging criteria and rated by using 4-level severity scores based in the BG or in the WM. The number and anatomic location of large dVRS (≥3 mm) were recorded. dVRS were observed in the BG or WM in every subject. The severity of dVRS was significantly associated with higher age in both the BG and WM, whereas sex was related to the severity of dVRS only in the BG. Large dVRS were detected in 33.2% of participants. Status cribrosum was found in 1.3% of participants. dVRS were also highly prevalent within the hippocampus (44.5%) and hypothalamus (11.6%). dVRS are always detected in the BG or WM in elderly people, and large dVRS are also prevalent. The topographic distribution of dVRS is not uniform within the brain and may depend on anatomic or pathologic characteristics interacting with aging and sex.

Simulation of High-Resolution Magnetic Resonance Images on the IBM Blue Gene/L Supercomputer Using SIMRI

Medical imaging system simulators are tools that provide a means to evaluate system architecture and create artificial image sets that are appropriate for specific applications. We have modified SIMRI, a Bloch equation-based magnetic resonance image simulator, in order to successfully generate high-resolution 3D MR images of the Montreal brain phantom using Blue Gene/L systems. Results show that redistribution of the workload allows an anatomically accurate 2563 voxel spin-echo simulation in less than 5 hours when executed on an 8192-node partition of a Blue Gene/L system.

High-Resolution 3D MR Imaging of the Trochlear Nerve

The cisternal segment of the trochlear nerve is difficult to identify reliably by routine MR imaging. We investigated the visibility and anatomic features of the trochlear nerve by using high-resolution 3D-bTFE imaging in healthy subjects. This study was conducted with 32 healthy subjects without ocular movement disorders. For us to visualize the cisternal segment of the trochlear nerve, all subjects underwent 3D-bTFE imaging at 3T with 2 different resolutions: conventional resolution (voxel size, 0.67 x 0.45 x 1.4 mm) and high resolution (voxel size, 0.3 x 0.3 x 0.25 mm). Visibility of the trochlear nerve was graded with the use of a qualitative scale of certainty as follows: definite, probable, and indeterminate. The diameter of the trochlear nerve was measured. On conventional-resolution images, the visibility of the trochlear nerve was definite in 3 nerves, probable in 12 nerves, and indeterminate in 49 nerves. On high-resolution images, visibility was definite in 63 nerves and probable in 1 nerve. The mean diameter of the trochlear nerve was 0.54 mm (range, 0.35-0.96 mm). The trochlear nerve was visualized 100% of the time on high-resolution imaging with a voxel smaller than the nerve diameter. High-resolution imaging should have an important role in investigating the pathogenic mechanism of neuropathic strabismus, such as congenital superior oblique palsy.

Topographic Analysis of the Inferior Parietal Lobule in High-Resolution 3D MR Imaging

Recent functional MR imaging studies have revealed that the inferior parietal lobule (IPL) supports numerous functions; however, the precise organization of the IPL remains unclear. It has been previously reported that the individual components of the IPL show variable morphologic features; thus, any investigations of IPL function must take into account the variable topography of the IPL. However, it is difficult to understand the topography of the IPL only in transaxial and/or sagittal MR images. We generated volume rendering (VR) images of the brain from high-resolution 3D MR imaging data and analyzed the topography of the IPL. Forty healthy volunteers were examined with 1.5T MR imaging, and VR images were generated. Sulcal continuity, sulcal connections, and the gyral pattern of the IPL were investigated. The main sulci and gyri were able to be identified excellently on VR images of all volunteers. One long, continuous postcentral sulcus (postCS) was seen in 47.5% and 40% in the right and left hemisphere, respectively. The frequency with which the postCS connected with the anterior end of the IPS was 72.5% and 75% in the right and left, respectively. The gyral pattern of the IPL showed variable morphology. VR images can depict the sulcal continuity and connections of the IPL accurately. VR imaging is a very useful noninvasive technique to observe the topography of the IPL and should contribute to the investigation of functional localization.

Tumor-Volume Changes after Radiosurgery for Vestibular Schwannoma: Implications for Follow-Up MR Imaging Protocol

The outcome of radiosurgery for vestibular schwannoma (VS) is assessed by posttreatment measurement of tumor size and could be influenced by the timing and quality of the assessment. This study evaluates the volumetric changes of VS after radiosurgery and proposes a radiologic follow-up program. Of 142 patients with VS treated with radiosurgery, we selected patients who were followed at least 3 times during a minimum of 32 months with a T1-weighted gadolinium-enhanced high-resolution 3D MR imaging examination identical to the pretreatment MR imaging. Forty-five patients were identified with a mean follow-up of 50 months (range, 32-78 months). Pre- and posttreatment tumor volumes were calculated by using BrainSCAN software by manually contouring tumors on each MR imaging study. Volume changes of >13% were defined as events. At last follow-up MR imaging, volumes were smaller in 37 (82.2%) of the 45 patients. Eleven (29.7%) of these 37 tumors showed transient swelling preceding regression, with a median time to regression of 34 months (range, 20-55 months). Seven (15.6%) of the 45 tumors had volume progression compared with the tumor on pretreatment MR imaging studies. Of these 7 tumors, 3, however, had volume regression compared with the preceding MR imaging study, and in 4, volume progression was ongoing. One tumor remained the same. Tumor-volume measurements by standardized T1-weighted gadolinium-enhanced high-resolution 3D MR imaging follow-up protocols revealed good local control of VS after radiosurgery. The first-follow-up MR imaging at 2 years and the second at 5 years postradiosurgery differentiated transient progression from ongoing progression and may prevent unnecessary therapeutic interventions.

MRI guidance improves accuracy of stereotaxic targeting for cell transplantation in parkinsonian monkeys

Accuracy of targeting is critical for the success of cell transplantation in the central nervous system. We compared the accuracy of conventional atlas-guided stereotaxis to magnetic resonance imaging (MRI)-guided stereotaxic targeting in various basal ganglia nuclei in parkinsonian monkeys. 28 monkeys underwent unilateral striatal transplantation. High-resolution 3D MR images of the brain were used in 15 monkeys fitted with a MRI-compatible stereotaxic frame for target localization. This was immediately followed by cranial surgery with the frame “in situ”. 13 additional monkeys underwent stereotaxic atlas-guided cranial surgery for placement of cell transplants. Following extensive behavioral testing and microelectrode recordings, all animals were perfused. The brains were sectioned coronally and stained to determine the morphology of needle tracts as an accuracy measure of stereotaxic placements. MRI-guided stereotaxy was completely accurate in 80% as compared to 38.5% in atlas-guided stereotaxis. The chance of missing a target completely was as high as 38.5% in atlas-guided stereotaxis, which was reduced to 6.67% when MRI was used for guidance. Targeting error occurred mostly in the anterior caudate and posterior putamen as against better accuracy in the anterior putamen. These results suggest that accuracy of stereotaxic unilateral cranial targeting into the putamen and the caudate in monkeys can be improved with high-resolution 3D MR imaging.

Quantitative visualization of ictal subdural EEG changes in children with neocortical focal seizures

Objective To quantify the ictal subdural electroencephalogram (EEG) changes using spectral analysis, and to delineate the quantitatively defined ictal onset zones on high-resolution 3D MR images in children with intractable neocortical epilepsy. Methods Fourteen children with intractable neocortical epilepsy (age: 1–16 years) who had subsequent resective surgery were retrospectively studied. The subjects underwent a high-resolution MRI and prolonged subdural EEG recording. Spectral analysis was applied to 3 habitual focal seizures. After fast Fourier transformation of the EEG epoch at ictal onset, an amplitude spectral curve (square root of the power spectral curve) was created for each electrode. The EEG magnitude of ictal rhythmic discharges was defined as the area under the amplitude spectral curve within a preset frequency band including the ictal discharge frequency, and calculated for each electrode. The topography mapping of ictal EEG magnitude was subsequently displayed on a surface-rendered MRI. Finally, receiver operating characteristic (ROC) analysis was performed to evaluate the consistency between quantitatively and visually defined ictal onset zones. Results The electrode showing the maximum of the averaged ictal EEG magnitude was part of the visually defined ictal onset zone in all cases. ROC analyses demonstrated that electrodes showing >30% of the maximum of the averaged ictal EEG magnitude had a specificity of 0.90 and a sensitivity of 0.74 for the concordance with visually defined ictal onset zones. Significance Quantitative ictal subdural EEG analysis using spectral analysis may supplement conventional visual inspection in children with neocortical epilepsy by providing an objective definition of the onset zone and its simple visualization on the patient's MRI.

Voxel-Based Morphometry Reveals Increased Gray Matter Density in Broca's Area in Male Symphony Orchestra Musicians

Broca's area is a major neuroanatomical substrate for spoken language and various musically relevant abilities, including visuospatial and audiospatial localization. Sight reading is a musician-specific visuospatial analysis task, and spatial ability is known to be amenable to training effects. Musicians have been reported to perform significantly better than nonmusicians on spatial ability tests, which is supported by our findings with the Benton judgement of line orientation (JOL) test ( P < 0.001). We hypothesised that use-dependent adaptation would lead to increased gray matter density in Broca's area in musicians. Voxel-based morphometry (VBM) and stereological analyses were applied to high-resolution 3D MR images in male orchestral musicians ( n = 26) and sex, handedness, and IQ-matched nonmusicians ( n = 26). The wide age range (26 to 66 years) of volunteers permitted a secondary analysis of age-related effects. VBM with small volume correction (SVC) revealed a significant ( P = 0.002) region of increased gray matter in Broca's area in the left inferior frontal gyrus in musicians. We observed significant age-related volume reductions in cerebral hemispheres, dorsolateral prefrontal cortex subfields bilaterally and gray matter density in the left inferior frontal gyrus in controls but not musicians; a positive correlation between JOL test score and age in musicians but not controls; a positive correlation between years of playing and the volume of gray matter in a significant region identified by VBM in under-50-year-old musicians. We suggest that orchestral musical performance promotes use-dependent retention, and possibly expansion, of gray matter involving Broca's area and that this provides further support for shared neural substrates underpinning expressive output in music and language.

Anesthetic protocol: propofol use in Rhesus macaques (Macaca mulatta) during magnetic resonance imaging with stereotactic head frame application

Magnetic resonance image (MRI) guidance is often necessary for accurate targeting for stereotactic intracranial surgery in animals used for experimental research studies. The magnetic field created by the MR imaging equipment, logistics of the use of stereotactic head frame in confined space and the need to limit movement of the subject during the imaging creates unique challenges. We demonstrate in this study the usefulness of intravenous propofol to anesthetize adult Rhesus monkeys to obtain high resolution 3D MR images immediately followed by conversion to inhalation anesthesia and stereotactic intracranial surgery with the head frame ‘in situ.’ There was minimal morbidity with achieving a high degree of precision for the stereotactic targeting.