RESUMO
BACKGROUND: Impaired cerebrovascular reactivity (CVR) has been correlated with recurrent ischemic stroke. However, for clinical purposes, most CVR techniques are rather complex, time-consuming, and lack validation for quantitative measurements. The recent adaptation of a standardized hypercapnic stimulus in combination with a blood-oxygenation-level-dependent (BOLD) magnetic resonance imaging signal as a surrogate for cerebral blood flow offers a potential universally comparable CVR assessment. We investigated the association between impaired BOLD-CVR and risk for recurrent ischemic events. METHODS: We conducted a retrospective analysis of patients with symptomatic cerebrovascular large vessel disease who had undergone a prospective hypercapnic-challenged BOLD-CVR protocol at a single tertiary stroke referral center between June 2014 and April 2020. These patients were followed up for recurrent acute ischemic events for up to 3 years. BOLD-CVR (%BOLD signal change per mmâ Hg CO2) was calculated on a voxel-by-voxel basis. Impaired BOLD-CVR of the affected (ipsilateral to the vascular pathology) hemisphere was defined as an average BOLD-CVR, falling 2 SD below the mean BOLD-CVR of the right hemisphere in a healthy age-matched reference cohort (n=20). Using a multivariate Cox proportional hazards model, the association between impaired BOLD-CVR and ischemic stroke recurrence was assessed and Kaplan-Meier survival curves to visualize the acute ischemic stroke event rate. RESULTS: Of 130 eligible patients, 28 experienced recurrent strokes (median, 85 days, interquartile range, 5-166 days). Risk factors associated with an increased recurrent stroke rate included impaired BOLD-CVR, a history of atrial fibrillation, and heart insufficiency. After adjusting for sex, age group, and atrial fibrillation, impaired BOLD-CVR exhibited a hazard ratio of 10.73 (95% CI, 4.14-27.81; P<0.001) for recurrent ischemic stroke. CONCLUSIONS: Among patients with symptomatic cerebrovascular large vessel disease, those exhibiting impaired BOLD-CVR in the affected hemisphere had a 10.7-fold higher risk of recurrent ischemic stroke events compared with individuals with nonimpaired BOLD-CVR.
Assuntos
Fibrilação Atrial , Transtornos Cerebrovasculares , AVC Isquêmico , Acidente Vascular Cerebral , Humanos , Estudos Retrospectivos , Estudos Prospectivos , Imageamento por Ressonância Magnética/métodos , Acidente Vascular Cerebral/diagnóstico por imagem , Infarto Cerebral , Hipercapnia/diagnóstico por imagem , Circulação Cerebrovascular/fisiologiaRESUMO
OBJECTIVES: To assess the lingual nerve (LN) visualization using a 3D double-echo steady-state MRI sequence (3D-DESS). MATERIALS AND METHODS: Three readers prospectively evaluated the LN for its continuous visibility in 3D-DESS MRI in 19 patients with an indication for removal of mandibular impacted third molars, using a 5-point scale (4 = excellent to 0 = none). Six LN anatomical intermediate points (IP) were selected and checked for their detectability by a 4-point scale (4 = yes to1 = no). Inter- and intra-rater agreement was evaluated using intraclass correlation coefficient and percentage of agreement. RESULTS: The average nerve continuity score was 3.3 ± 0.46. In 35% of the cases, the entire course was continuously visible. In 10%, the proximal and 60%, the distal part of the nerve was not continuously visible. Inter- and intra-reader agreement was good (ICC = 0.76, ICC = 0.75). The average detectability score of all IP was 3.7 ± 0.41. From IP1 to IP5, the detectability was excellent; meanwhile, IP6 had lower visibility. The inter- and intra-reader percentage of agreement was 77% and 87%. CONCLUSIONS: The 3D-DESS sequence allowed accurate and continuous visualization of the LN with high reproducibility in more than one-third of the patients. This could improve the preoperative clarification of the LN position and thereby reduce complications during dentoalveolar surgical interventions. CLINICAL RELEVANCE: 3D-DESS MRI might be beneficial in clinical scenarios where the second molar is elongated or presents a difficult rotational position while simultaneously having a close positional relationship to the third molar. Thereby, osteotomy performed more lingually, indicating extended lingual flap detachment may increase the risk of LN damage.
Assuntos
Nervo Lingual , Dente Serotino , Humanos , Imageamento por Ressonância Magnética , Mandíbula/diagnóstico por imagem , Mandíbula/cirurgia , Dente Serotino/diagnóstico por imagem , Dente Serotino/cirurgia , Reprodutibilidade dos Testes , Extração DentáriaRESUMO
BACKGROUND: In patients with steno-occlusive disease, recent findings suggest that hemodynamic alterations may also be associated with crossed cerebellar diaschisis (CCD) rather than a functional disruption alone. PURPOSE: To use a quantitative multiparametric hemodynamic MRI to gain a better understanding of hemodynamic changes related to CCD in patients with unilateral anterior circulation stroke. STUDY TYPE: Prospective cohort study. POPULATION: Twenty-four patients (25 datasets) with symptomatic unilateral anterior circulation stroke. FIELD STRENGTH/SEQUENCE: 3T/two sequences: single-shot (echo-planar imaging) EPI sequence and T2* gradient echo perfusion-weighted imaging study. ASSESSMENT: The presence of CCD was inferred from the cerebellar asymmetry index (CAI) of the blood oxygenation-level dependent cerebrovascular reactivity (BOLD-CVR) exam, which was calculated from the mean BOLD-CVR and standard deviation of the CAI of the healthy control group. For all perfusion-weighted (PW)-MRI parameters, the cerebellar and middle cerebral artery (MCA) territory asymmetry indices were calculated. STATISTICAL TESTS: Independent Student's t-test to compare the variables from the CCD positive(+) and CCD negative(-) groups and analysis of covariance (ANCOVA) to statistically control the effect of covariates (infarct volume and time since ischemia onset). RESULTS: CCD was present in 33% of patients. In the MCA territory of the affected hemisphere, BOLD-CVR was significantly more impaired in the CCD(+) group as compared to the CCD(-) group (mean BOLD-CVR ± SD [%BOLD signal/ΔmmHgCO2 ]: -0.03 ± 0.12 vs. 0.11 ± 0.13, P < 0.05). Moreover, the mean transit time (MTT) (asymmetry index (%) CCD(+) vs. CCD(-): 28 ± 23 vs. 4 ± 11, P < 0.05) and time to peak (TTP) (10 ± 10 vs. 2 ± 5, P < 0.05) in the MCA territory of the affected hemisphere were significantly prolonged, while cerebral blood volume was, on average, increased in the CCD(+) group (25 ± 15 vs. 4 ± 19, P < 0.05). DATA CONCLUSION: Our findings show that, in patients with symptomatic unilateral anterior circulation stroke, CCD is associated with hemodynamic impairment in the ipsilateral MCA territory, which further supports the concept of a vascular component of CCD. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 3.
Assuntos
Artéria Cerebral Média , Acidente Vascular Cerebral , Circulação Cerebrovascular , Hemodinâmica , Humanos , Imageamento por Ressonância Magnética , Estudos Prospectivos , Acidente Vascular Cerebral/diagnóstico por imagemRESUMO
BACKGROUND: To assess changes of the craniocervical junction (CCJ), computed tomography (CT) is considered the reference standard. Recent advances in bone depiction on magnetic resonance imaging (MRI) enable high-quality visualization of osseous structures. Consequently, MRI may serve as an alternative to CT, without the use of ionizing radiation. PURPOSE: To compare two MRI sequences optimized for bone visualization to the CT reference standard in the assessment of the osseous CCJ. STUDY TYPE: Prospective. POPULATION/SUBJECTS: Twenty-seven decedents and five healthy volunteers. FIELD STRENGTH/SEQUENCE: 3T/ultrashort-echo time gradient echo (UTE) and optimized 3D-multiecho in-phase gradient echo sequences (FRACTURE). ASSESSMENT: All decedents were scanned with both MRI sequences and CT. Three observers rated degeneration to obtain a score for the upper (atlanto-dental and left/right atlanto-occipital joint) and for the lower part of the CCJ (left and right atlanto-axial joint). Two reader rated the following quantitative parameters: basion-axial-interval, atlanto-dental-interval, atlanto-occipital-interval, Powers-ratio, and signal/contrast-to-noise-ratio. As a proof of concept, five healthy volunteers were scanned with both MRI sequences. STATISTICAL TESTS: Degeneration was assessed on a Likert scale by three independent observers. Interrater and intermodality reliability were calculated using an intraclass correlation coefficient. To compare distance measurements between examination methods, a Friedman test, between-degenerative ratings, and a Kruskal-Wallis test were performed. RESULTS: Degenerative ratings of the CCJ between MRI sequences and CT showed a good interrater and intermodality agreement. MRI sequences tended to underestimate the degree of degeneration compared to CT, and this became more marked with increasing degeneration severity. There were no significant relationships between distance measurements and the degree of degeneration (PCT = 0.62, PUTE = 0.64, PFRACTURE = 0.67). The in vivo examination proved the feasibility of both MRI methods in a clinical setting. DATA CONCLUSION: Quantitative and qualitative ratings on MR images were comparable to CT images; thus, MRI may be a valid alternative to CT assessing the CCJ. LEVEL OF EVIDENCE: 1. TECHNICAL EFFICACY STAGE: 3.
Assuntos
Imageamento Tridimensional , Imageamento por Ressonância Magnética , Humanos , Estudos Prospectivos , Reprodutibilidade dos Testes , Tomografia Computadorizada por Raios XRESUMO
BACKGROUND AND PURPOSE: Clinical outcomes vary substantially among individuals with large vessel occlusion (LVO) stroke. A small infarct core and large imaging mismatch were found to be associated with good recovery. The aim of this study was to investigate whether those imaging variables would improve individual prediction of functional outcome after early (<6 h) endovascular treatment (EVT) in LVO stroke. METHODS: We included 222 patients with acute ischemic stroke due to middle cerebral artery (MCA)-M1 occlusion who received EVT. As predictors, we used clinical variables and region of interest (ROI)-based magnetic resonance imaging features. We developed different machine-learning models and quantified their prediction performance according to the area under the receiver-operating characteristic curves and the Brier score. RESULTS: The rate of successful recanalization was 78%, with 54% patients having a favorable outcome (modified Rankin scale score 0-2). Small infarct core was associated with favorable functional outcome. Outcome prediction improved only slightly when imaging was added to patient variables. Age was the driving factor, with a sharp decrease in likelihood of favorable functional outcome above the age of 78 years. CONCLUSIONS: In patients with MCA-M1 occlusion strokes referred to EVT within 6 h of symptom onset, infarct core volume was associated with outcome. However, ROI-based imaging variables led to no significant improvement in outcome prediction at an individual patient level when added to a set of clinical predictors. Our study is in concordance with current practice, where imaging mismatch or collateral readouts are not recommended as factors for excluding patients with MCA-M1 occlusion for early EVT.
Assuntos
Isquemia Encefálica , Procedimentos Endovasculares , Acidente Vascular Cerebral , Idoso , Isquemia Encefálica/diagnóstico por imagem , Humanos , Infarto da Artéria Cerebral Média/diagnóstico por imagem , Infarto da Artéria Cerebral Média/cirurgia , Aprendizado de Máquina , Artéria Cerebral Média , Estudos Retrospectivos , Acidente Vascular Cerebral/diagnóstico por imagem , Acidente Vascular Cerebral/terapia , Trombectomia , Resultado do TratamentoRESUMO
PURPOSE OF REVIEW: Visual snow is considered a disorder of central visual processing resulting in a perturbed perception of constant bilateral whole-visual field flickering or pixelation. When associated with additional visual symptoms, it is referred to as visual snow syndrome. Its pathophysiology remains elusive. This review highlights the visual snow literature focusing on recent clinical studies that add to our understanding of its clinical picture, pathophysiology, and treatment. RECENT FINDINGS: Clinical characterization of visual snow syndrome is evolving, including a suggested modification of diagnostic criteria. Regarding pathophysiology, two recent studies tested the hypothesis of dysfunctional visual processing and occipital cortex hyperexcitability using electrophysiology. Likewise, advanced functional imaging shows promise to allow further insights into disease mechanisms. A retrospective study now provides Class IV evidence for a possible benefit of lamotrigine in a minority of patients. SUMMARY: Scientific understanding of visual snow syndrome is growing. Major challenges remain the subjective nature of the disease, its overlap with migraine, and the lack of quantifiable outcome measures, which are necessary for clinical trials. In that context, refined perceptual assessment, objective electrophysiological parameters, as well as advanced functional brain imaging studies, are promising tools in the pipeline.
Assuntos
Encéfalo/diagnóstico por imagem , Transtornos da Percepção/diagnóstico , Transtornos da Visão/diagnóstico , Percepção Visual/fisiologia , Encéfalo/fisiopatologia , Neuroimagem Funcional , Humanos , Transtornos da Percepção/diagnóstico por imagem , Transtornos da Percepção/fisiopatologia , Estudos Retrospectivos , Transtornos da Visão/diagnóstico por imagem , Transtornos da Visão/fisiopatologiaRESUMO
BACKGROUND: The optimization of magnetic resonance spectroscopy (MRS) sequences allows improved diagnosis and prognosis of neurological and psychological disorders. Thus, to assess the test-retest and intersequence reliability of such MRS sequences in quantifying metabolite concentrations is of clinical relevance. PURPOSE: To evaluate the test-retest and intersequence reliability of three MRS sequences to estimate GABA and Glx = Glutamine+Glutamate concentrations in the human brain. STUDY TYPE: Prospective. SUBJECTS: Eighteen healthy participants were scanned twice (range: 1 day to 1 week between the two sessions) with identical protocols. FIELD STRENGTH/SEQUENCE: 3T using a 32-channel SENSE head coil in the PCC region; PRESS, JPRESS, and MEGA-PRESS sequences. ASSESSMENT: Metabolite concentrations were estimated using LCModel (for PRESS and MEGA-PRESS) and ProFit2 (for JPRESS). STATISTICAL TESTS: The test-retest reliability was evaluated by Wilcoxon signed-rank tests, Pearson's r correlation coefficients, intraclass-correlation coefficients (ICC), coefficients of variation (CV), and by Bland-Altman (BA) plots. The intersequence reliability was assessed with Wilcoxon signed-rank tests, Pearson's r correlation coefficients, and BA plots. RESULTS: For GABA, only the MEGA-PRESS sequence showed a moderate test-retest correlation (r = 0.54, ICC = 0.5, CV = 8.8%) and the BA plots indicated good agreement (P > 0.05) for all sequences. JPRESS provided less precise results and PRESS was insensitive to GABA. For Glx, the r and ICC values for PRESS (r = 0.87, ICC = 0.9, CV = 2.9%) and MEGA-PRESS (r = 0.70, ICC = 0.7, CV = 5.3%) reflect higher correlations, compared with JPRESS (r = 0.39, ICC = 0.4, CV = 20.1%). DATA CONCLUSION: MEGA-PRESS and JPRESS are suitable for the reliable detection of GABA, the first being more precise. The three sequences included in the study can measure Glx concentrations. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:1181-1191.
Assuntos
Regiões de Interação com a Matriz , Ácido gama-Aminobutírico , Encéfalo/diagnóstico por imagem , Humanos , Imageamento por Ressonância Magnética , Espectroscopia de Ressonância Magnética , Estudos Prospectivos , Reprodutibilidade dos TestesRESUMO
PURPOSE: The lateral geniculate nucleus (LGN) is an essential nucleus of the visual pathway, occupying a small volume (60-160â¯mm3) among the other thalamic nuclei. The reported LGN volumes vary greatly across studies due to technical limitations and due to methodological differences of volume assessment. Yet, structural and anatomical alterations in ophthalmologic and neurodegenerative pathologies can only be revealed by a precise and reliable LGN representation. To improve LGN volume assessment, we first implemented a reference acquisition for LGN volume determination with optimized Contrast to Noise Ratio (CNR) and high spatial resolution. Next, we compared CNR efficiency and rating reliability of 3D Magnetization Prepared Rapid Gradient Echo (MPRAGE) images using white matter nulled (WMn) and grey matter nulled (GMn) sequences and its subtraction (WMn-GMn) relative to the clinical standard Proton Density Turbo Spin Echo (PD 2D TSE) and the reference acquisition. We hypothesized that 3D MPRAGE should provide a higher CNR and volume determination accuracy than the currently used 2D sequences. MATERIALS AND METHODS: In 31 healthy subjects, we obtained at 3 and 7â¯T the following MR sequences: PD-TSE, MPRAGE with white/grey matter signal nulled (WMn/GMn), and a motion-corrected segmented MPRAGE sequence with a resolution of 0.4â¯×â¯0.4â¯×â¯0.4â¯mm3 (reference acquisition). To increase CNR, GMn were subtracted from WMn (WMn-GMn). Four investigators manually segmented the LGN independently. RESULTS: The reference acquisition provided a very sharp depiction of the LGN and an estimated mean LGN volume of 124⯱â¯3.3â¯mm3. WMn-GMn had the highest CNR and gave the most reproducible LGN volume estimations between field strengths. Even with the highest CNR efficiency, PD-TSE gave inconsistent LGN volumes with the weakest reference acquisition correlation. The LGN WM rim induced a significant difference between LGN volumes estimated from WMn and GMn. WMn and GMn LGN volume estimations explained most of the reference acquisition volumes' variance. For all sequences, the volume rating reliability were good. On the other hand, the best CNR rating reliability, LGN volume and CNR correlations with the reference acquisition were obtained with GMn at 7â¯T. CONCLUSION: WMn and GMn MPRAGE allow reliable LGN volume determination at both field strengths. The precise location and identification of the LGN (volume) can help to optimize neuroanatomical and neurophysiological studies, which involve the LGN structure. Our optimized imaging protocol may be used for clinical applications aiming at small nuclei volumetric and CNR quantification.
Assuntos
Corpos Geniculados/anatomia & histologia , Corpos Geniculados/diagnóstico por imagem , Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Adolescente , Adulto , Feminino , Humanos , Aumento da Imagem , Masculino , Pessoa de Meia-Idade , Padrões de Referência , Reprodutibilidade dos Testes , Razão Sinal-Ruído , Adulto JovemRESUMO
Blood oxygenation level-dependent functional MRI cerebrovascular reactivity (BOLD-CVR) is a contemporary technique to assess brain tissue hemodynamic changes after extracranial- intracranial (EC-IC) bypass flow augmentation surgery. The authors conducted a preliminary study to investigate the feasibility and safety of intraoperative 3-T MRI BOLD-CVR after EC-IC bypass flow augmentation surgery. Five consecutive patients selected for EC-IC bypass revascularization underwent an intraoperative BOLD-CVR examination to assess early hemodynamic changes after revascularization and to confirm the safety of this technique. All patients had a normal postoperative course, and none of the patients exhibited complications or radiological alterations related to prolonged anesthesia time. In addition to intraoperative flow measurements of the bypass graft, BOLD-CVR maps added information on the hemodynamic status and changes at the brain tissue level. Intraoperative BOLD-CVR is feasible and safe in patients undergoing EC-IC bypass revascularization. This technique can offer immediate hemodynamic feedback on brain tissue revascularization after bypass flow augmentation surgery.
Assuntos
Revascularização Cerebral/métodos , Transtornos Cerebrovasculares/diagnóstico por imagem , Transtornos Cerebrovasculares/metabolismo , Monitorização Neurofisiológica Intraoperatória/métodos , Imageamento por Ressonância Magnética/métodos , Consumo de Oxigênio/fisiologia , Idoso , Circulação Cerebrovascular/fisiologia , Transtornos Cerebrovasculares/cirurgia , Estudos de Viabilidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Resultado do TratamentoRESUMO
BACKGROUND AND PURPOSE: Increased stroke risk correlates with hemodynamic failure, which can be assessed with (15O-)H2O positron emission tomography (PET) cerebral blood flow (CBF) measurements. This gold standard technique, however, is not established for routine clinical imaging. Standardized blood oxygen-level-dependent (BOLD) functional magnetic resonance imaging+CO2 is a noninvasive and potentially widely applicable tool to assess whole-brain quantitative cerebrovascular reactivity (CVR). We examined the agreement between the 2 imaging modalities and hypothesized that quantitative CVR can be a surrogate imaging marker to assess hemodynamic failure. METHODS: Nineteen data sets of subjects with chronic cerebrovascular steno-occlusive disease (age, 60±11 years; 4 women) and unilaterally impaired perfusion reserve on Diamox-challenged (15O-)H2O PET were studied and compared with a standardized BOLD functional magnetic resonance imaging+CO2 examination within 6 weeks (8±19 days). Agreement between quantitative CBF- and CVR-based perfusion reserve was assessed. Hemodynamic failure was staged according to PET findings: stage 0: normal CBF, normal perfusion reserve; stage I: normal CBF, decreased perfusion reserve; and stage II: decreased CBF, decreased perfusion reserve. The BOLD CVR data set of the same subjects was then matched to the corresponding stage of hemodynamic failure. RESULTS: PET-based stage I versus stage II could also be clearly separated with BOLD CVR measurements (CVR for stage I 0.11 versus CVR for stage II -0.03; P<0.01). Hemispheric and middle cerebral artery territory difference analyses (ie, affected versus unaffected side) showed a significant correlation for CVR impairment in the affected hemisphere and middle cerebral artery territory (P<0.01, R2=0.47 and P=0.02, R2= 0.25, respectively). CONCLUSIONS: BOLD CVR corresponded well to CBF perfusion reserve measurements obtained with (15O-)H2O-PET, especially for detecting hemodynamic failure in the affected hemisphere and middle cerebral artery territory and for identifying hemodynamic failure stage II. BOLD CVR may, therefore, be considered for prospective studies assessing stroke risk in patients with chronic cerebrovascular steno-occlusive disease, in particular because it can potentially be implemented in routine clinical imaging.
Assuntos
Isquemia Encefálica/diagnóstico por imagem , Hemodinâmica , Angiografia por Ressonância Magnética/métodos , Tomografia por Emissão de Pósitrons/métodos , Acidente Vascular Cerebral/diagnóstico por imagem , Idoso , Isquemia Encefálica/sangue , Dióxido de Carbono/sangue , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Oxigênio/sangue , Acidente Vascular Cerebral/sangueRESUMO
PURPOSE: To assess the feasibility of functional blood oxygen-level dependent (BOLD) MRI to evaluate intraoperative cerebrovascular reactivity (CVR) at 3 Tesla field strength. METHODS: Ten consecutive neurosurgical subjects scheduled for a clinical intraoperative MRI examination were enrolled in this study. In addition to the clinical protocol a BOLD sequence was implemented with three cycles of 44 s apnea to calculate CVR values on a voxel-by-voxel basis throughout the brain. The CVR range was then color-coded and superimposed on an anatomical volume to create high spatial resolution CVR maps. RESULTS: Ten subjects (mean age 34.8 ± 13.4; 2 females) uneventfully underwent the intraoperative BOLD protocol, with no complications occurring. Whole-brain CVR for all subjects was (mean ± SD) 0.69 ± 0.42, whereas CVR was markedly higher for tumor subjects as compared to vascular subjects, 0.81 ± 0.44 versus 0.33 ± 0.10, respectively. Furthermore, color-coded functional maps could be robustly interpreted for a whole-brain assessment of CVR. CONCLUSION: We demonstrate that intraoperative BOLD MRI is feasible in creating functional maps to assess cerebrovascular reactivity throughout the brain in subjects undergoing a neurosurgical procedure. Magn Reson Med 77:806-813, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Assuntos
Encéfalo , Circulação Cerebrovascular/fisiologia , Monitorização Neurofisiológica Intraoperatória/métodos , Imageamento por Ressonância Magnética/métodos , Adulto , Encéfalo/irrigação sanguínea , Encéfalo/diagnóstico por imagem , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Oxigênio/sangue , Oxigênio/metabolismo , Adulto JovemRESUMO
PURPOSE: To assess the feasibility of diffusion tensor imaging (DTI) using simultaneous multislice (SMS) acquisition with blipped controlled aliasing in parallel imaging (CAIPI) for accelerated readout-segmented echo planar imaging (rs-EPI) of the mandibular nerves. DTI of the mandibular nerves using EPI is challenging due to susceptibility artifacts. Rs-EPI is less prone to artifacts but associated with longer scan durations. MATERIALS AND METHODS: Eight asymptomatic volunteers were imaged at 3T using a 64-channel head/neck coil. Conventional, 2-fold (2xSMS) and 3-fold (3xSMS) slice-accelerated rs-EPI sequences were acquired. Tractography of the mandibular nerves was performed. Signal-to-noise ratio (SNR), fractional anisotropy (FA), mean diffusivity (MD), and number of tracts were calculated. Artifacts were evaluated qualitatively on Likert scales. Parameters were compared statistically. Clinical feasibility of 2xSMS rs-EPI was tested in four patients. RESULTS: SNR was similar for conventional (mean ± SD; 8.55 ± 3.90) and 2xSMS rs-EPI (7.83 ± 3.15) but lower for 3xSMS rs-EPI (5.42 ± 2.93; analysis of variance, P = 0.004). FA was similar for all sequences (rs-EPI, 0.42 ± 0.08; 2xSMS rs-EPI, 0.43 ± 0.08; 3xSMS rs-EPI, 0.44 ± 0.06), while 3xSMS rs-EPI showed lower MD (rs-EPI, 0.0015 ± 0.0003; 2xSMS rs-EPI, 0.0014 ± 0.0001; 3xSMS rs-EPI, 0.0013 ± 0.0003) and lower number of tracts (rs-EPI, 66.56 ± 51.31; 2xSMS rs-EPI, 65.75 ± 55.40; 3xSMS rs-EPI, 37.93 ± 52.42) compared to rs-EPI and 2xSMS rs-EPI. Additionally, 2xSMS rs-EPI was feasible in four clinical patients and provided robust imaging results. CONCLUSION: 2xSMS rs-EPI yielded similar SNR, FA, and MD values compared to conventional rs-EPI at reduced scan time and is feasible in clinical patients. These findings suggest the potential clinical applicability of rs-EPI for DTI of the mandibular nerve. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:663-677.
Assuntos
Imagem de Tensor de Difusão/métodos , Imagem Ecoplanar/métodos , Processamento de Imagem Assistida por Computador/métodos , Nervo Mandibular/diagnóstico por imagem , Adulto , Estudos de Viabilidade , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Adulto JovemRESUMO
PURPOSE: To investigate the feasibility of MR diffusion tensor imaging (DTI) of the median nerve using simultaneous multi-slice echo planar imaging (EPI) with blipped CAIPIRINHA. MATERIALS AND METHODS: After federal ethics board approval, MR imaging of the median nerves of eight healthy volunteers (mean age, 29.4 years; range, 25-32) was performed at 3 T using a 16-channel hand/wrist coil. An EPI sequence (b-value, 1,000 s/mm(2); 20 gradient directions) was acquired without acceleration as well as with twofold and threefold slice acceleration. Fractional anisotropy (FA), mean diffusivity (MD) and quality of nerve tractography (number of tracks, average track length, track homogeneity, anatomical accuracy) were compared between the acquisitions using multivariate ANOVA and the Kruskal-Wallis test. RESULTS: Acquisition time was 6:08 min for standard DTI, 3:38 min for twofold and 2:31 min for threefold acceleration. No differences were found regarding FA (standard DTI: 0.620 ± 0.058; twofold acceleration: 0.642 ± 0.058; threefold acceleration: 0.644 ± 0.061; p ≥ 0.217) and MD (standard DTI: 1.076 ± 0.080 mm(2)/s; twofold acceleration: 1.016 ± 0.123 mm(2)/s; threefold acceleration: 0.979 ± 0.153 mm(2)/s; p ≥ 0.074). Twofold acceleration yielded similar tractography quality compared to standard DTI (p > 0.05). With threefold acceleration, however, average track length and track homogeneity decreased (p = 0.004-0.021). CONCLUSION: Accelerated DTI of the median nerve is feasible. Twofold acceleration yields similar results to standard DTI. KEY POINTS: ⢠Standard DTI of the median nerve is limited by its long acquisition time. ⢠Simultaneous multi-slice acquisition is a new technique for accelerated DTI. ⢠Accelerated DTI of the median nerve yields similar results to standard DTI.
Assuntos
Imagem de Difusão por Ressonância Magnética/métodos , Imagem de Tensor de Difusão/métodos , Imagem Ecoplanar/métodos , Nervo Mediano/diagnóstico por imagem , Adulto , Anisotropia , Feminino , Voluntários Saudáveis , Humanos , MasculinoRESUMO
Numerous technical advances in magnetic resonance imaging have opened up promising new approaches in dentomaxillofacial radiology in recent years. With its ability to simultaneously visualize soft and hard tissues, MRI has the potential to become an innovative method for accurate diagnosis and planning of dental implants. Dental MRI is already a valuable and useful complement to conventional X-ray imaging techniques and could further minimize the risks of surgery by optimizing existing treatment protocols. Considering current efforts in dentistry to reduce radiation exposure and take a further step toward personalized oral diagnostics that consider patient-specific factors, this article reviews the capabilities of dentomaxillofacial MR imaging in implant surgery. It highlights the various applications of MRI in dental implant surgery and evaluates both the benefits and the clinical challenges. Overall, considering the specific indications and limitations of MR sequences, dental MRI represents a further significant advance in individualized treatment planning in dentistry. It allows consideration of parameters not visualized by conventional imaging techniques and is particularly useful for evaluating surgically relevant parameters, especially those related to soft tissue.
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Imageamento por Ressonância Magnética , Humanos , Imageamento por Ressonância Magnética/métodos , Implantação Dentária Endóssea/métodos , Implantes Dentários , Planejamento de Assistência ao PacienteRESUMO
This study aimed to compare preoperative data relevant to third molar surgery based on radiographic orthopantomography (OPG) and orthopantomogram-like MR images (MR-OPG), using five different MR protocols. X-ray-based OPG and OPG-like MRI reconstructions from DESS, SPACE-STIR, SPACE-SPAIR, T1-VIBE-Dixon, and UTE sequences were acquired in 11 patients undergoing third molar surgery, using a 15-channel mandibular coil. Qualitative (image quality, susceptibility to artifacts, positional relationship, contact/non-contact of the inferior alveolar nerve (IAN), relationship to maxillary sinus, IAN continuity, root morphology) and quantitative (tooth length, retromolar distance, distance to the IAN, and distance to the mandible margin) parameters of the maxillary and mandibular third molars were assessed regarding inter-reader agreement and quantitative discrepancies by three calibrated readers. Radiation-free MR-OPGs generated within clinically tolerable acquisition times, which exhibited high image quality and low susceptibility to artifacts, showed no significant differences compared with X-ray-based OPGs regarding the assessment of quantitative parameters. UTE MR-OPGs provided radiographic-like images and were best suited for assessing qualitative preoperative data (positional relationship, nerve contact/non-contact, and dental root morphology) relevant to third molar surgery. For continuous and focal nerve imaging, DESS MR-OPG was superior. MR-OPGs could represent a shift towards indication-specific and modality-oriented perioperative imaging in high-risk oral and maxillofacial surgery.
Assuntos
Dente Impactado , Traumatismos do Nervo Trigêmeo , Humanos , Dente Serotino/diagnóstico por imagem , Dente Serotino/cirurgia , Raios X , Radiografia Panorâmica/métodos , Imageamento por Ressonância Magnética/métodos , Dente Impactado/cirurgia , Extração Dentária , Espectroscopia de Ressonância Magnética , Nervo Mandibular , Mandíbula/diagnóstico por imagem , Mandíbula/cirurgia , Mandíbula/inervação , Traumatismos do Nervo Trigêmeo/diagnóstico por imagemRESUMO
PURPOSE: To comprehensively assess the existing literature regarding the rapidly evolving in vivo application of magnetic resonance imaging (MRI) for potential applications, benefits, and challenges in dental implant surgery. METHODS: Electronic and manual searches were conducted in PubMed MEDLINE, EMBASE, Biosis, and Cochrane databases by two reviewers following the PICOS search strategy. This involved using medical subject headings (MeSH) terms, keywords, and their combinations. RESULTS: Sixteen studies were included in this systematic review. Of the 16, nine studies focused on preoperative planning and follow-up phases, four evaluated image-guided implant surgery, while three examined artifact reduction techniques. The current literature highlights several MRI protocols that have recently investigated and evaluated the in vivo feasibility and accuracy, focusing on its potential to provide surgically relevant quantitative and qualitative parameters in the assessment of osseointegration, peri-implant soft tissues, surrounding anatomical structures, reduction of artifacts caused by dental implants, and geometric accuracy relevant to implant placement. Black Bone and MSVAT-SPACE MRI, acquired within a short time, demonstrate improved hard and soft tissue resolution and offer high sensitivity in detecting pathological changes, making them a valuable alternative in targeted cases where CBCT is insufficient. Given the data heterogeneity, a meta-analysis was not possible. CONCLUSIONS: The results of this systematic review highlight the potential of dental MRI, within its indications and limitations, to provide perioperative surgically relevant parameters for accurate placement of dental implants.
Assuntos
Implantação Dentária Endóssea , Implantes Dentários , Imageamento por Ressonância Magnética , Humanos , Imageamento por Ressonância Magnética/métodos , Implantação Dentária Endóssea/métodos , Cirurgia Assistida por Computador/métodos , ArtefatosRESUMO
Effective attention control is essential for behavioral adaptation to different environmental contexts. In Post-traumatic Stress Disorder (PTSD) altered attention has been described in trauma-related and other emotional contexts. Nevertheless, atypical attention is also seen with neutral stimuli. The mechanisms of attention alterations in PTSD associated with neutral stimuli are poorly understood. The present study investigates alerting and orienting responses in PTSD participants using emotionally neutral stimuli in a saccade eye movement task incorporating both spatially predictable and temporally unpredictable conditions. We studied 23 PTSD patients and 27 Non-PTSD controls, using repeated-measures mixed modeling to estimate group and task condition differences in behavioral and psychophysiological measures. We explored the relationships among saccade characteristics, pupil size, and PTSD symptoms, including CAPS hypervigilance scores. PTSD, compared to Non-PTSD, participants showed differences in their saccade 'main sequence', reflected by higher peak velocities adjusted for amplitude. PTSD participants had smaller primary position errors in the unpredictable saccade condition. They also exhibited greater hyperarousal, reflected by larger pupil size during fixation that was greater in the unpredictable condition. Our results suggest that a heightened state of arousal and hypervigilance in PTSD leads to a state of atypical attention bias, even in emotionally neutral contexts. These differences may reflect higher saccade vigor. The observed differences suggest atypical attention in PTSD, which goes beyond possible distraction associated with emotional or threat-related stimuli.
Assuntos
Atenção , Movimentos Sacádicos , Transtornos de Estresse Pós-Traumáticos , Humanos , Transtornos de Estresse Pós-Traumáticos/fisiopatologia , Movimentos Sacádicos/fisiologia , Feminino , Masculino , Adulto , Atenção/fisiologia , Pessoa de Meia-Idade , Adulto Jovem , Pupila/fisiologia , Nível de Alerta/fisiologiaRESUMO
Background and Purpose: The feasibility of acquiring diffusion-weighted imaging (DWI) images on an MR-Linac for quantitative response assessment during radiotherapy was explored. DWI data obtained with a Spin Echo Echo Planar Imaging sequence adapted for a 0.35 T MR-Linac were examined and compared with DWI data from a conventional 3 T scanner. Materials and Methods: Apparent diffusion coefficient (ADC) measurements and a distortion correction technique were investigated using DWI-calibrated phantoms and in the brains of seven volunteers. All DWI utilized two phase-encoding directions for distortion correction and off-resonance field estimation. ADC maps in the brain were analyzed for automatically segmented normal tissues. Results: Phantom ADC measurements on the MR-Linac were within a 3 % margin of those recorded by the 3 T scanner. The maximum distortion observed in the phantom was 2.0 mm prior to correction and 1.1 mm post-correction on the MR-Linac, compared to 6.0 mm before correction and 3.6 mm after correction at 3 T. In vivo, the average ADC values for gray and white matter exhibited variations of 14 % and 4 %, respectively, for different selections of b-values on the MR-Linac. Distortions in brain images before correction, estimated through the off-resonance field, reached 2.7 mm on the MR-Linac and 12 mm at 3 T. Conclusion: Accurate ADC measurements are achievable on a 0.35 T MR-Linac, both in phantom and in vivo. The selection of b-values significantly influences ADC values in vivo. DWI on the MR-Linac demonstrated lower distortion levels, with a maximum distortion reduced to 1.1 mm after correction.
RESUMO
BACKGROUND AND PURPOSE: Assessing treatment success of intracranial aneurysms treated with Woven EndoBridge (WEB) devices using MRI is important in follow-up imaging. Depicting both the device configuration as well as reperfusion is challenging due to susceptibility artefacts. We evaluated the usefulness of contrast-enhanced 3D-Ultrashort Echo-Time (UTE) sequence in this setting. MATERIALS AND METHODS: In this prospective study, 12 patients (9 female) with 15 treated aneurysms were included. These 12 patients underwent 18 MRI examinations. Follow-up UTE-MRI controls were performed on the same 3-Tesla scanner. We compared the visualization of device configuration, artifact-related virtual stenosis of the parent vessel and WEB occlusion scale in 3D isotropic UTE-MRI post-contrast with standard time-of-flight (TOF) MR-angiography with (CE) and without intravenous contrast as well as DSA. Two interventional neuroradiologists rated the images separately and in consensus. RESULTS: Visualization of the WEB device position and configuration was rated superior or highly superior using the UTE sequence in 17/18 MRIs compared to TOF-MRA. Artifact-related virtual stenosis of the parent vessel was significantly lower in UTE-MRI compared to TOF and CE-TOF. Reperfusion was visible in 8/18 controls in DSA. TOF was able to grade reperfusion correctly in 16 cases, CE-TOF in 16 cases and UTE in 17 cases. CONCLUSIONS: Contrast-enhanced UTE is a novel MRI sequence that shows benefit compared to standard sequences in non-invasive and radiation-free follow-up imaging of intracranial aneurysms treated using the WEB-device. ABBREVIATIONS: ACoA = anterior communicating artery, BA = basilar artery, CEA = contrast enhanced angiography, ICA = internal carotid artery, MCA = middle cerebral artery, PCom = posterior communicating artery TOF-CE = contrast enhanced time-of-flight angiography, UTE = ultra-short echo time, WEB = woven endobridge.
RESUMO
HYPOTHESIS: This study investigates the impact of different diffusion magnetic imaging (dMRI) acquisition settings and mathematical fiber models on tractography performance for depicting cranial nerve (CN) VII in healthy young adults. BACKGROUND: The aim of this study is to optimize visualization of CN VII for preoperative assessment in surgeries near the nerve in the cerebellopontine angle, reducing surgery-associated complications. The study analyzes 100 CN VII in dMRI images from the Human Connectome Project, using three separate sets with different b values (b = 1,000 s/mm2, b =2,000 s/mm2, b =3,000 s/mm2) and four different tractography methods, resulting in 1,200 tractographies analyzed. RESULTS: The results show that multifiber and free water (FW) compartment models produce significantly more streamlines than single-fiber tractography. The addition of an FW compartment significantly increases the mean streamline fractional anisotropy (FA). Expert quality ratings showed that the highest rated tractography was the 1 tensor (1T) method without FW at b values of 1,000 s/mm2. CONCLUSIONS: In this young and healthy cohort, best tractography results are obtained by using a 1T model without a FW compartment in b =1,000 diffusion MR images. The FW compartment increased the contrast between streamlines and cerebrospinal fluid (higher mean streamline FA). This finding may help ongoing research to improve CN VII tractography results in tumor cases where the nerve is often stretched and thinned by the tumor.