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1.
Magn Reson Med ; 85(3): 1237-1247, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-32869349

RESUMO

PURPOSE: The goal of this study was to determine the accuracy of displacement-encoding with stimulated echoes (DENSE) MRI in a tissue motion phantom with displacements representative of those observed in human brain tissue. METHODS: The phantom was comprised of a plastic shaft rotated at a constant speed. The rotational motion was converted to a vertical displacement through a camshaft. The phantom generated repeatable cyclical displacement waveforms with a peak displacement ranging from 92 µm to 1.04 mm at 1-Hz frequency. The surface displacement of the tissue was obtained using a laser Doppler vibrometer (LDV) before and after the DENSE MRI scans to check for repeatability. The accuracy of DENSE MRI displacement was assessed by comparing the laser Doppler vibrometer and DENSE MRI waveforms. RESULTS: Laser Doppler vibrometer measurements of the tissue motion demonstrated excellent cycle-to-cycle repeatability with a maximum root mean square error of 9 µm between the ensemble-averaged displacement waveform and the individual waveforms over 180 cycles. The maximum difference between DENSE MRI and the laser Doppler vibrometer waveforms ranged from 15 to 50 µm. Additionally, the peak-to-peak difference between the 2 waveforms ranged from 1 to 18 µm. CONCLUSION: Using a tissue phantom undergoing cyclical motion, we demonstrated the percent accuracy of DENSE MRI to measure displacement similar to that observed for in vivo cardiac-induced brain tissue.


Assuntos
Algoritmos , Imageamento por Ressonância Magnética , Encéfalo/diagnóstico por imagem , Humanos , Movimento (Física) , Imagens de Fantasmas
2.
J Biomech Eng ; 140(8)2018 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-30003253

RESUMO

Intrinsic cardiac-induced deformation of brain tissue is thought to be important in the pathophysiology of various neurological disorders. In this study, we evaluated the feasibility of utilizing displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify two-dimensional (2D) neural tissue strain using cardiac-driven brain pulsations. We examined eight adult healthy volunteers with an electrocardiogram-gated spiral DENSE sequence performed at the midsagittal plane on a 3 Tesla MRI scanner. Displacement, pixel-wise trajectories, and principal strains were determined in seven regions of interest (ROI): the brain stem, cerebellum, corpus callosum, and four cerebral lobes. Quantification of small neural tissue motion and strain along with their spatial and temporal variations in different brain regions was found to be feasible using DENSE. The medial and inferior brain structures (brain stem, cerebellum, and corpus callosum) had significantly larger motion and strain compared to structures located more peripherally. The brain stem had the largest peak mean displacement (PMD) (187 ± 50 µm, mean ± SD). The largest mean principal strains in compression and extension were observed in the brain stem (0.38 ± 0.08%) and the corpus callosum (0.37 ± 0.08%), respectively. Measured values in percent strain were altered by as much as 0.1 between repeated scans. This study showed that DENSE can quantify regional variations in brain tissue motion and strain and has the potential to be utilized as a tool to evaluate the changes in brain tissue dynamics resulting from alterations in biomechanical stresses and tissue properties.


Assuntos
Encéfalo/diagnóstico por imagem , Imageamento por Ressonância Magnética , Estresse Mecânico , Adulto , Fenômenos Biomecânicos , Encéfalo/citologia , Estudos de Viabilidade , Feminino , Humanos , Masculino
3.
J Neuroradiol ; 45(1): 23-31, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28826656

RESUMO

PURPOSE: Type I Chiari malformation (CMI) is a radiologically-defined structural dysmorphism of the hindbrain and posterior cranial fossa (PCF). Traditional radiographic identification of CMI relies on the measurement of the cerebellar tonsils in relation to the foramen magnum with or without associated abnormalities of the neuraxis. The primary goal of this retrospective study was to comprehensively assess morphometric parameters above the McRea line in a group of female CMI patients and normal controls. MATERIAL AND METHODS: Twenty-nine morphological measurements were taken on 302 mid-sagittal MR images of adult female CMI patients (n=162) and healthy controls (n=140). All MR images were voluntarily provided by CMI subjects through an online database and control participant images were obtained through the Human Connectome Project and a local hospital system. RESULTS: Analyses were performed on the full dataset of adult female MR images and a restricted dataset of 229 participants that were equated for age, race, and body mass index. Eighteen group differences were identified in the PCF area that we grouped into three clusters; PCF structures heights, clivus angulation, and odontoid process irregularity. Fourteen group differences persisted after equating our CMI and control groups on demographic characteristics. CONCLUSION: PCF structures reliably differ in adult female CMI patients relative to healthy controls. These differences reflect structural abnormalities in the osseous and soft tissue structures of the clivus, odontoid process, and cerebellum. Clinical and pathophysiological implications are discussed.


Assuntos
Malformação de Arnold-Chiari/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Adulto , Pontos de Referência Anatômicos , Estudos de Casos e Controles , Fossa Craniana Posterior/anormalidades , Fossa Craniana Posterior/diagnóstico por imagem , Feminino , Humanos , Estudos Retrospectivos , Rombencéfalo/anormalidades , Rombencéfalo/diagnóstico por imagem
4.
Int J Radiat Oncol Biol Phys ; 118(1): 242-252, 2024 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-37607642

RESUMO

PURPOSE: A novel form of lung functional imaging applied for functional avoidance radiation therapy has been developed that uses 4-dimensional computed tomography (4DCT) data and image processing techniques to calculate lung ventilation (4DCT-ventilation). Lung segmentation is a common step to define a region of interest for 4DCT-ventilation generation. The purpose of this study was to quantitatively evaluate the sensitivity of 4DCT-ventilation imaging using different lung segmentation methods. METHODS AND MATERIALS: The 4DCT data of 350 patients from 2 institutions were used. Lung contours were generated using 3 methods: (1) reference segmentations that removed airways and pulmonary vasculature manually (Lung-Manual), (2) standard lung contours used for planning (Lung-RadOnc), and (3) artificial intelligence (AI)-based contours that removed the airways and pulmonary vasculature (Lung-AI). The AI model was based on a residual 3-dimensional U-Net and was trained using the Lung-Manual contours of 279 patients. We compared the Lung-RadOnc or Lung-AI with Lung-Manual contours for the entire 4DCT-ventilation functional avoidance process including lung segmentation (surface Dice similarity coefficient [Surface DSC]), 4DCT-ventilation generation (correlation), and subanalysis of 10 patients on a dosimetric endpoint (percentage of high functional volume of lung receiving ≥20 Gy [fV20{%}]). RESULTS: Surface DSC comparing Lung-Manual/Lung-RadOnc and Lung-Manual/Lung-AI contours was 0.40 ± 0.06 and 0.86 ± 0.04, respectively. The correlation between 4DCT-ventilation images generated with Lung-Manual/Lung-RadOnc and Lung-Manual/Lung-AI were 0.48 ± 0.14 and 0.85 ± 0.14, respectively. The difference in fV20[%] between 4DCT-ventilation generated with Lung-Manual/Lung-RadOnc and Lung-Manual/Lung-AI was 2.5% ± 4.1% and 0.3% ± 0.5%, respectively. CONCLUSIONS: Our work showed that using standard planning lung contours can result in significantly variable 4DCT-ventilation images. The study demonstrated that AI-based segmentations generate lung contours and 4DCT-ventilation images that are similar to those generated using manual methods. The significance of the study is that it characterizes the lung segmentation sensitivity of the 4DCT-ventilation process and develops methods that can facilitate the integration of this novel imaging in busy clinics.


Assuntos
Neoplasias Pulmonares , Ventilação Pulmonar , Humanos , Neoplasias Pulmonares/diagnóstico por imagem , Neoplasias Pulmonares/radioterapia , Inteligência Artificial , Pulmão/diagnóstico por imagem , Tomografia Computadorizada Quadridimensional/métodos
5.
Ann Biomed Eng ; 49(6): 1462-1476, 2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-33398617

RESUMO

While the degree of cerebellar tonsillar descent is considered the primary radiologic marker of Chiari malformation type I (CMI), biomechanical forces acting on the brain tissue in CMI subjects are less studied and poorly understood. In this study, regional brain tissue displacement and principal strains in 43 CMI subjects and 25 controls were quantified using a magnetic resonance imaging (MRI) methodology known as displacement encoding with stimulated echoes (DENSE). Measurements from MRI were obtained for seven different brain regions-the brainstem, cerebellum, cingulate gyrus, corpus callosum, frontal lobe, occipital lobe, and parietal lobe. Mean displacements in the cerebellum and brainstem were found to be 106 and 64% higher, respectively, for CMI subjects than controls (p < .001). Mean compression and extension strains in the cerebellum were 52 and 50% higher, respectively, in CMI subjects (p < .001). Brainstem mean extension strain was 41% higher in CMI subjects (p < .001), but no significant difference in compression strain was observed. The other brain structures revealed no significant differences between CMI and controls. These findings demonstrate that brain tissue displacement and strain in the cerebellum and brainstem might represent two new biomarkers to distinguish between CMI subjects and controls.


Assuntos
Malformação de Arnold-Chiari/diagnóstico por imagem , Malformação de Arnold-Chiari/fisiopatologia , Encéfalo/diagnóstico por imagem , Encéfalo/fisiopatologia , Adulto , Fenômenos Biomecânicos , Feminino , Humanos , Imageamento por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-Idade , Estresse Mecânico , Adulto Jovem
6.
IEEE Trans Biomed Eng ; 65(7): 1516-1523, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-28961100

RESUMO

GOAL: Develop and test an MRI-compatible hydrodynamic simulator of cerebrospinal fluid (CSF) motion in the cervical spinal subarachnoid space. Four anatomically realistic subject-specific models were created based on a 22-year-old healthy volunteer and a five-year-old patient diagnosed with Chiari I malformation. METHODS: The in vitro models were based on manual segmentation of high-resolution T2-weighted MRI of the cervical spine. Anatomically realistic dorsal and ventral spinal cord nerve rootlets (NR) were added. Models were three dimensional (3-D) printed by stereolithography with 50-µm layer thickness. A computer controlled pump system was used to replicate the shape of the subject specific in vivo CSF flow measured by phase-contrast MRI. Each model was then scanned by T2-weighted and 4-D phase contrast MRI (4D flow). RESULTS: Cross-sectional area, wetted perimeter, and hydraulic diameter were quantified for each model. The oscillatory CSF velocity field (flow jets near NR, velocity profile shape, and magnitude) had similar characteristics to previously reported studies in the literature measured by in vivo MRI. CONCLUSION: This study describes the first MRI-compatible hydrodynamic simulator of CSF motion in the cervical spine with anatomically realistic NR. NR were found to impact CSF velocity profiles to a great degree. SIGNIFICANCE: CSF hydrodynamics are thought to be altered in craniospinal disorders such as Chiari I malformation. MRI scanning techniques and protocols can be used to quantify CSF flow alterations in disease states. The provided in vitro models can be used to test the reliability of these protocols across MRI scanner manufacturers and machines.


Assuntos
Líquido Cefalorraquidiano , Vértebras Cervicais , Impressão Tridimensional , Medula Espinal , Adulto , Líquido Cefalorraquidiano/diagnóstico por imagem , Líquido Cefalorraquidiano/fisiologia , Vértebras Cervicais/anatomia & histologia , Vértebras Cervicais/diagnóstico por imagem , Vértebras Cervicais/fisiologia , Pré-Escolar , Humanos , Imageamento por Ressonância Magnética , Masculino , Modelos Biológicos , Fluxo Pulsátil/fisiologia , Medula Espinal/anatomia & histologia , Medula Espinal/diagnóstico por imagem , Medula Espinal/fisiologia , Adulto Jovem
7.
PLoS One ; 12(3): e0173680, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28296953

RESUMO

Intrathecal drug and gene vector delivery is a procedure to release a solute within the cerebrospinal fluid. This procedure is currently used in clinical practice and shows promise for treatment of several central nervous system pathologies. However, intrathecal delivery protocols and systems are not yet optimized. The aim of this study was to investigate the effects of injection parameters on solute distribution within the cervical subarachnoid space using a numerical platform. We developed a numerical model based on a patient-specific three dimensional geometry of the cervical subarachnoid space with idealized dorsal and ventral nerve roots and denticulate ligament anatomy. We considered the drug as massless particles within the flow field and with similar properties as the CSF, and we analyzed the effects of anatomy, catheter position, angle and injection flow rate on solute distribution within the cerebrospinal fluid by performing a series of numerical simulations. Results were compared quantitatively in terms of drug peak concentration, spread, accumulation rate and appearance instant over 15 seconds following the injection. Results indicated that solute distribution within the cervical spine was altered by all parameters investigated within the time range analyzed following the injection. The presence of spinal cord nerve roots and denticulate ligaments increased drug spread by 60% compared to simulations without these anatomical features. Catheter position and angle were both found to alter spread rate up to 86%, and catheter flow rate altered drug peak concentration up to 78%. The presented numerical platform fills a first gap towards the realization of a tool to parametrically assess and optimize intrathecal drug and gene vector delivery protocols and systems. Further investigation is needed to analyze drug spread over a longer clinically relevant time frame.


Assuntos
Vértebras Cervicais , Espaço Subaracnóideo/efeitos dos fármacos , Humanos
8.
Ann Biomed Eng ; 44(5): 1524-37, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26446009

RESUMO

For the first time, inter-operator dependence of MRI based computational fluid dynamics (CFD) modeling of cerebrospinal fluid (CSF) in the cervical spinal subarachnoid space (SSS) is evaluated. In vivo MRI flow measurements and anatomy MRI images were obtained at the cervico-medullary junction of a healthy subject and a Chiari I malformation patient. 3D anatomies of the SSS were reconstructed by manual segmentation by four independent operators for both cases. CFD results were compared at nine axial locations along the SSS in terms of hydrodynamic and geometric parameters. Intraclass correlation (ICC) assessed the inter-operator agreement for each parameter over the axial locations and coefficient of variance (CV) compared the percentage of variance for each parameter between the operators. Greater operator dependence was found for the patient (0.19 < ICC < 0.99) near the craniovertebral junction compared to the healthy subject (ICC > 0.78). For the healthy subject, hydraulic diameter and Womersley number had the least variance (CV = ~2%). For the patient, peak diastolic velocity and Reynolds number had the smallest variance (CV = ~3%). These results show a high degree of inter-operator reliability for MRI-based CFD simulations of CSF flow in the cervical spine for healthy subjects and a lower degree of reliability for patients with Type I Chiari malformation.


Assuntos
Malformação de Arnold-Chiari , Líquido Cefalorraquidiano , Medula Cervical , Imageamento por Ressonância Magnética , Malformação de Arnold-Chiari/diagnóstico por imagem , Malformação de Arnold-Chiari/fisiopatologia , Medula Cervical/diagnóstico por imagem , Medula Cervical/fisiopatologia , Feminino , Humanos , Masculino , Movimento (Física) , Variações Dependentes do Observador
9.
Ann Biomed Eng ; 43(12): 2911-23, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26108203

RESUMO

Central nervous system (CNS) tissue motion of the brain occurs over 30 million cardiac cycles per year due to intracranial pressure differences caused by the pulsatile blood flow and cerebrospinal fluid (CSF) motion within the intracranial space. This motion has been found to be elevated in type 1 Chiari malformation. The impact of CNS tissue motion on CSF dynamics was assessed using a moving-boundary computational fluid dynamics (CFD) model of the cervical-medullary junction (CMJ). The cerebellar tonsils and spinal cord were modeled as rigid surfaces moving in the caudocranial direction over the cardiac cycle. The CFD boundary conditions were based on in vivo MR imaging of a 35-year old female Chiari malformation patient with ~150-300 µm motion of the cerebellar tonsils and spinal cord, respectively. Results showed that tissue motion increased CSF pressure dissociation across the CMJ and peak velocities up to 120 and 60%, respectively. Alterations in CSF dynamics were most pronounced near the CMJ and during peak tonsillar velocity. These results show a small CNS tissue motion at the CMJ can alter CSF dynamics for a portion of the cardiac cycle and demonstrate the utility of CFD modeling coupled with MR imaging to help understand CSF dynamics.


Assuntos
Malformação de Arnold-Chiari/fisiopatologia , Líquido Cefalorraquidiano/fisiologia , Modelos Biológicos , Movimento/fisiologia , Adulto , Cerebelo/fisiologia , Vértebras Cervicais/fisiologia , Feminino , Humanos , Hidrodinâmica , Medula Espinal/fisiologia
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