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Metal artifact reduction by virtual monoenergetic reconstructions from spectral brain CT. Eur J Radiol Open 2023; 10:100479. [PMID: 36819113 PMCID: PMC9932346 DOI: 10.1016/j.ejro.2023.100479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Accepted: 01/29/2023] [Indexed: 02/05/2023] Open
Abstract
Purpose Conventional computed tomography (CT) images are severely affected by metal artifacts in patients with intracranial coils. Monoenergetic images have been suggested to reduce metal artifacts.The aim of this study was to assess metal artifacts in virtual monoenergetic images (VMIs) reconstructed from spectral brain CT. Methods Thirty-two consecutive patients with intracranial coils examined by spectral non contrast brain CT (NCCT) at our center between November 2017 and April 2019 were included. Attenuation and standard deviations were measured in regions of interest (ROIs) at predefined areas in artifact-free and artifact-affected areas. Measurements were performed in conventional polyenergetic images (CIs) and the corresponding data for VMIs were retrieved through spectral diagrams for the each ROI. Subjective analysis was performed by visual grading of CIs and specific VMIs by two neuroradiologists, independently. Results In artefact-affected image areas distal from the metal objects, the attenuation values decreased with higher energy level VMIs. The same effect was not seen for artefact-affected image areas close to the metal.Subjective rating of the artefact severity was significantly better in VMIs at 50 keV for one of the two reviewers compared to the CIs. Overall image quality and tissue differentiation scores were significantly higher for both reviewers in VMIs at 60 and 70 keV compared to CIs. Conclusion Our quantitative and qualitative image analysis shown that there is a small significant reduction of intracranial coils artifacts severity by all monoenergetic reconstructions from 50 to 200 keV with preserved or increased overall subjective image quality compared to conventional images.
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Key Words
- Aneurysm
- CIs, conventional images
- CSF, cerebrospinal fluid
- CT, computed tomography
- DECT, dual energy computed tomography
- DLP, dose length product
- DSA, digital subtraction angiography
- Diagnostic imaging
- HU, Hounsfield units
- IQR, interquartile range
- MRI, magnetic resonance imaging
- Metal artifacts
- Monoenergetic imaging
- PACS, Picture Archiving and Communication System
- ROI, region of interest
- SD, standard deviation
- SNR, signal-to-noise ratio
- VMIs, virtual monoenergetic images
- WM, white matter
- X-ray computed tomography
- keV, kiloelectron volt
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Putting on molecular weight: Enabling cryo-EM structure determination of sub-100-kDa proteins. Curr Res Struct Biol 2022; 4:332-337. [PMID: 36248264 PMCID: PMC9562432 DOI: 10.1016/j.crstbi.2022.09.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 09/22/2022] [Accepted: 09/25/2022] [Indexed: 11/17/2022] Open
Abstract
Significant advances in the past decade have enabled high-resolution structure determination of a vast variety of proteins by cryogenic electron microscopy single particle analysis. Despite improved sample preparation, next-generation imaging hardware, and advanced single particle analysis algorithms, small proteins remain elusive for reconstruction due to low signal-to-noise and lack of distinctive structural features. Multiple efforts have therefore been directed at the development of size-increase techniques for small proteins. Here we review the latest methods for increasing effective molecular weight of proteins <100 kDa through target protein binding or target protein fusion - specifically by using nanobody-based assemblies, fusion tags, and symmetric scaffolds. Finally, we summarize these state-of-the-art techniques into a decision-tree to facilitate the design of tailored future approaches, and thus for further exploration of ever-smaller proteins that make up the largest part of the human genome.
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Key Words
- BRIL, cytochromeb562 RIL
- DARPin, Design Ankyrin Repeat Protein
- Fab, antigen binding fragment
- GFP, Green Fluorecent Protein
- GPCR, G protein-coupled receptor
- MW, molecular weight
- Mb, megabody
- Nb, nanobody
- SNR, signal-to-noise ratio
- SPA, single particle analysis
- TM, transmembrane
- cryo-EM, cryogenic electron microscopy
- kDa, kiloDalton
- κOR ICL3, κ-opiod receptor intracellular loop 3
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Clinical Evaluation of an Instrument-Integrated OCT-Based Distance Sensor for Robotic Vitreoretinal Surgery. OPHTHALMOLOGY SCIENCE 2021; 1:100085. [PMID: 36246942 PMCID: PMC9560530 DOI: 10.1016/j.xops.2021.100085] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 10/11/2021] [Accepted: 11/08/2021] [Indexed: 04/29/2023]
Abstract
PURPOSE To assess the efficacy of an instrument-integrated OCT (iiOCT)-based distance sensor during robotic vitreoretinal surgery using the Preceyes Surgical System (PSS; Preceyes B.V.). DESIGN Single-center interventional study. PARTICIPANTS Patients requiring vitreoretinal surgery. METHODS Five patients were enrolled. Standard preoperative OCT images were obtained. After vitrectomy, a predefined set of actions was performed using the iiOCT-based sensor. Images then were processed to assess the signal-to-noise ratio (SNR) at various angles to the retina and at different distances between the instrument tip and the retinal surface. Preoperative and intraoperative OCT images were compared qualitatively and quantitatively. MAIN OUTCOMES MEASURES The feasibility in performing surgical tasks using the iiOCT-based sensor during vitreoretinal surgery, the SNR when imaging the retina, differences among intraoperative and preoperative OCT images, and characteristics of intraoperative retinal movements detected with the iiOCT-based probe. RESULTS Surgeons were able to perform all the tasks but one. The PSS was able to maintain a fixed distance. The SNR of the iiOCT-based sensor signal was adequate to determine the distance to the retina and to control the PSS. Analysis of iiOCT-based sensor A-scans identified 3 clearly distinguishable retinal layers, including the inner retinal boundary and the interface at the retinal pigment epithelium-Bruch's membrane. Thickness values differed by less than 5% from that measured by preoperative OCT, indicating its accuracy. The Fourier analysis of iiOCT-based sensor recordings identified anteroposterior retinal movements attributed to heartbeat and respiration. CONCLUSIONS This iiOCT-based sensor was tested successfully and promises reliable use during robot-assisted surgery. An iiOCT-based sensor is a promising step toward OCT-guided robotic retinal surgery.
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Deep Learning-Based Automatic Detection of Ellipsoid Zone Loss in Spectral-Domain OCT for Hydroxychloroquine Retinal Toxicity Screening. OPHTHALMOLOGY SCIENCE 2021; 1:100060. [PMID: 36246938 PMCID: PMC9560656 DOI: 10.1016/j.xops.2021.100060] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 09/15/2021] [Accepted: 09/16/2021] [Indexed: 05/01/2023]
Abstract
PURPOSE Retinal toxicity resulting from hydroxychloroquine use manifests photoreceptor loss and disruption of the ellipsoid zone (EZ) reflectivity band detectable on spectral-domain (SD) OCT imaging. This study investigated whether an automatic deep learning-based algorithm can detect and quantitate EZ loss on SD OCT images with an accuracy comparable with that of human annotations. DESIGN Retrospective analysis of data acquired in a prospective, single-center, case-control study. PARTICIPANTS Eighty-five patients (168 eyes) who were long-term hydroxychloroquine users (average exposure time, 14 ± 7.2 years). METHODS A mask region-based convolutional neural network (M-RCNN) was implemented and trained on individual OCT B-scans. Scan-by-scan detections were aggregated to produce an en face map of EZ loss per 3-dimensional SD OCT volume image. To improve the accuracy and robustness of the EZ loss map, a dual network architecture was proposed that learns to detect EZ loss in parallel using horizontal (horizontal mask region-based convolutional neural network [M-RCNNH]) and vertical (vertical mask region-based convolutional neural network [M-RCNNV]) B-scans independently. To quantify accuracy, 10-fold cross-validation was performed. MAIN OUTCOME MEASURES Precision, recall, intersection over union (IOU), F1-score metrics, and measured total EZ loss area were compared against human grader annotations and with the determination of toxicity based on the recommended screening guidelines. RESULTS The combined projection network demonstrated the best overall performance: precision, 0.90 ± 0.09; recall, 0.88 ± 0.08; and F1 score, 0.89 ± 0.07. The combined model performed superiorly to the M-RCNNH only model (precision, 0.79 ± 0.17; recall, 0.96 ± 0.04; IOU, 0.78 ± 0.15; and F1 score, 0.86 ± 0.12) and M-RCNNV only model (precision, 0.71 ± 0.21; recall, 0.94 ± 0.06; IOU, 0.69 ± 0.21; and F1 score, 0.79 ± 0.16). The accuracy was comparable with the variability of human experts: precision, 0.85 ± 0.09; recall, 0.98 ± 0.01; IOU, 0.82 ± 0.12; and F1 score, 0.91 ± 0.06. Automatically generated en face EZ loss maps provide quantitative SD OCT metrics for accurate toxicity determination combined with other functional testing. CONCLUSIONS The algorithm can provide a fast, objective, automatic method for measuring areas with EZ loss and can serve as a quantitative assistance tool to screen patients for the presence and extent of toxicity.
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Key Words
- 2D, 2-dimensional
- 3D, 3-dimensional
- AAO, American Academy of Ophthalmology
- Automatic detection
- CPN, combined projection network
- Deep learning
- EZ, ellipsoid zone
- Ellipsoid zone loss
- Hydroxychloroquine toxicity
- IOU, intersection over union
- M-RCNN, mask region-based convolutional neural network
- M-RCNNH, horizontal mask region-based convolutional neural network
- M-RCNNV, vertical mask region-based convolutional neural network
- SD, spectral-domain
- SNR, signal-to-noise ratio
- mfERG, multifocal electroretinography
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Direct measurement of neuronal ensemble activity using photoacoustic imaging in the stimulated Fos-LacZ transgenic rat brain: A proof-of-principle study. PHOTOACOUSTICS 2021; 24:100297. [PMID: 34522608 PMCID: PMC8426561 DOI: 10.1016/j.pacs.2021.100297] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 07/28/2021] [Accepted: 08/28/2021] [Indexed: 05/16/2023]
Abstract
Measuring neuroactivity underlying complex behaviors facilitates understanding the microcircuitry that supports these behaviors. We have developed a functional and molecular photoacoustic tomography (F/M-PAT) system which allows direct imaging of Fos-expressing neuronal ensembles in Fos-LacZ transgenic rats with a large field-of-view and high spatial resolution. F/M-PAT measures the beta-galactosidase catalyzed enzymatic product of exogenous chromophore X-gal within ensemble neurons. We used an ex vivo imaging method in the Wistar Fos-LacZ transgenic rat, to detect neuronal ensembles in medial prefrontal cortex (mPFC) following cocaine administration or a shock-tone paired stimulus. Robust and selective F/M-PAT signal was detected in mPFC neurons after both conditions (compare to naive controls) demonstrating successful and direct detection of Fos-expressing neuronal ensembles using this approach. The results of this study indicate that F/M-PAT can be used in conjunction with Fos-LacZ rats to monitor neuronal ensembles that underlie a range of behavioral processes, such as fear learning or addiction.
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Key Words
- ANSI, American national standards institute
- AP, anterior-posterior
- Brain
- CNR, contrast-to-noise ratio
- Cocaine
- DMSO, dimethyl sulfoxide
- DV, dorsal-ventral
- F/M-PAT, functional molecular photoacoustic tomography
- FOV, field-of-view
- Fear conditioning
- Fos
- GRIN, gradient-index
- IL, infralimbic cortex
- ML, medial-lateral
- Neuronal ensemble
- OCT, optical coherence tomography
- OPO, optical parametric oscillator
- PA, photoacoustic
- PBS, phosphate buffer saline
- PL, prelimbic cortex
- Photoacoustic imaging
- SNR, signal-to-noise ratio
- US, ultrasound
- X-gal
- X-gal, beta-D-galactosidase
- fMRI, functional magnetic resonance imaging
- mPFC, medial prefrontal cortex
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Multi-band whole-body diffusion-weighted imaging with inversion recovery fat saturation: Effects of respiratory compensation. Eur J Radiol Open 2021; 8:100374. [PMID: 34485628 PMCID: PMC8403743 DOI: 10.1016/j.ejro.2021.100374] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Revised: 08/20/2021] [Accepted: 08/22/2021] [Indexed: 10/25/2022] Open
Abstract
Purpose To prospectively compare artefacts and image quality in testicular stage I cancer patients using different combinations of breathing schemes and Multi-band (MB) in whole-body DWIBS at 1.5 T.Diffusion-Weighted whole-body Imaging with Background body signal Suppression (DWIBS) using inversion recovery (IR) fat saturation is a cornerstone in oncologic whole-body MRI, but implementation is restrained by long acquisition times. The new Multi-Band (MB) technique reduces scan time which can be reinvested in respiratory compensation. Methods Thirty testicular cancer stage I patients were included. Three variations of whole-body DWIBS were tested: Standard free Breathing (FB)-DWIBS, FB-MB-DWIBS and Respiratory triggered (RT)-MB-DWIBS. Artefacts and image quality of b = 800 s/mm2 images were evaluated using a Likert scale. No pathology was revealed. SNR was calculated in a healthy volunteer. Results RT-MB-DWIBS was rated significantly better than FB-DWIBS in the thorax (p < 0.001) and abdomen (p < 0.001), but not in the pelvis (p = 0.569). FB-MB-DWIBS was ranked significantly lower than both FB-DWIBS (p < 0.001) and RT-MB-DWIBS (p < 0.001) at all locations. However, FB-MB-DWIBS was scanned in half the time without being less than "satisfactory". Few artefacts were encountered. SNR was similar for low-intensity tissues, but the SNR in high-intensity and respiratory-prone tissue (spleen) was slightly lower for FB-DWIBS than the other sequences. Conclusion Images produced by the sequences were similar. MB enables the use of respiratory trigger or can be used to produce very fast free-breathing DWI with acceptable image quality.
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Key Words
- ADC, apparent diffusion coefficient
- CT, computed tomography
- DWI, diffusion-weighted imaging
- DWIBS, diffusion-weighted whole-body imaging with background body signal suppression
- Diffusion magnetic resonance imaging
- EPI, echo planar imaging
- FB, free-breathing
- IR, inversion recovery
- MB, multi-band
- MRI, magnetic resonance imaging
- Multi-band
- NSA, number of signal averages
- Pet, positron emission tomography
- RF, radio frequency
- ROI, region of interest
- RT, respiratory triggered
- Respiratory compensation
- SAR, specific absorption rate
- SMS, simultaneous multislice
- SNR, signal-to-noise ratio
- SPAIR, spectral attenuated inversion recovery
- T, tesla
- TE, echo time
- TR, repetition time
- Testicular neoplasm
- WB, whole-body
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Non-contrast versus contrast-enhanced MR in the diagnosis of spondylitis: A quantitative concordance-analysis. Eur J Radiol Open 2020; 7:100306. [PMID: 33335952 PMCID: PMC7733015 DOI: 10.1016/j.ejro.2020.100306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Revised: 12/03/2020] [Accepted: 12/04/2020] [Indexed: 11/03/2022] Open
Abstract
Introduction : Magnetic Resonance (MR) imaging using gadolinium contrast media is an essential imaging modality in diagnosing spondylitis. However, gadolinium contrast is not widely available in Indonesia and relatively expensive. Many MR studies in Indonesia are performed without contrast administration. It is unclear how confident non-contrast MR can diagnose tuberculous spondylitis in comparison to standard contrast MR. Purposes : This study aims to evaluate the concordance between the contrast MR and non-contrast spine MR in diagnosing tuberculous spondylitis. We also evaluate the interobserver agreement between the general radiologist and musculoskeletal radiologist in interpreting non-contrast MR of spondylitis. Materials and Methods : A cross-sectional study using secondary data was performed to evaluate the concordance between the MR results regarding the usage of contrast media in diagnosing spondylitis. The inclusion criteria were patients over 17 years old who underwent complete sequences of contrast-enhanced MR examination of the spine, referred to radiology with the clinical diagnosis of suspected tuberculous spondylitis, spondylodiscitis, or both. All of the non-contrast and contrast-enhanced MR results were read and interpreted by two independent observers, a musculoskeletal radiologist and a general radiologist, blindly. The interobserver agreement analysis of the MR examination was conducted using Kappa and McNemar test. Results : There was no significant difference between the contrast and non-contrast MR in diagnosing spondylitis (P= 0.368) and no significant difference in the interpretation of MR between the first and the second observer (P = 0.343). The concordance between the contrast and non-contrast spine MR in diagnosing spondylitis (R: 0.88, P < 0.001) and the interpretation of MR between both observers (R: 0.65, P < 0.001) were showed in this study. Conclusion : There is a high concordance between the contrast and non-contrast MR in diagnosing tuberculous spondylitis. Although contrast MR is preferred as the standard imaging method of spondylitis, in case gadolinium contrast is unavailable, non-contrast MR can still provide valuable information in diagnosing spondylitis.
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Combustion in the future: The importance of chemistry. PROCEEDINGS OF THE COMBUSTION INSTITUTE. INTERNATIONAL SYMPOSIUM ON COMBUSTION 2020; 38:S1540-7489(20)30501-0. [PMID: 33013234 PMCID: PMC7518234 DOI: 10.1016/j.proci.2020.06.375] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2019] [Revised: 05/18/2020] [Accepted: 06/28/2020] [Indexed: 06/11/2023]
Abstract
Combustion involves chemical reactions that are often highly exothermic. Combustion systems utilize the energy of chemical compounds released during this reactive process for transportation, to generate electric power, or to provide heat for various applications. Chemistry and combustion are interlinked in several ways. The outcome of a combustion process in terms of its energy and material balance, regarding the delivery of useful work as well as the generation of harmful emissions, depends sensitively on the molecular nature of the respective fuel. The design of efficient, low-emission combustion processes in compliance with air quality and climate goals suggests a closer inspection of the molecular properties and reactions of conventional, bio-derived, and synthetic fuels. Information about flammability, reaction intensity, and potentially hazardous combustion by-products is important also for safety considerations. Moreover, some of the compounds that serve as fuels can assume important roles in chemical energy storage and conversion. Combustion processes can furthermore be used to synthesize materials with attractive properties. A systematic understanding of the combustion behavior thus demands chemical knowledge. Desirable information includes properties of the thermodynamic states before and after the combustion reactions and relevant details about the dynamic processes that occur during the reactive transformations from the fuel and oxidizer to the products under the given boundary conditions. Combustion systems can be described, tailored, and improved by taking chemical knowledge into account. Combining theory, experiment, model development, simulation, and a systematic analysis of uncertainties enables qualitative or even quantitative predictions for many combustion situations of practical relevance. This article can highlight only a few of the numerous investigations on chemical processes for combustion and combustion-related science and applications, with a main focus on gas-phase reaction systems. It attempts to provide a snapshot of recent progress and a guide to exciting opportunities that drive such research beyond fossil combustion.
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Key Words
- 2M2B, 2-methyl-2-butene
- AFM, atomic force microscopy
- ALS, Advanced Light Source
- APCI, atmospheric pressure chemical ionization
- ARAS, atomic resonance absorption spectroscopy
- ATcT, Active Thermochemical Tables
- BC, black carbon
- BEV, battery electric vehicle
- BTL, biomass-to-liquid
- Biofuels
- CA, crank angle
- CCS, carbon capture and storage
- CEAS, cavity-enhanced absorption spectroscopy
- CFD, computational fluid dynamics
- CI, compression ignition
- CRDS, cavity ring-down spectroscopy
- CTL, coal-to-liquid
- Combustion
- Combustion chemistry
- Combustion diagnostics
- Combustion kinetics
- Combustion modeling
- Combustion synthesis
- DBE, di-n-butyl ether
- DCN, derived cetane number
- DEE, diethyl ether
- DFT, density functional theory
- DFWM, degenerate four-wave mixing
- DMC, dimethyl carbonate
- DME, dimethyl ether
- DMM, dimethoxy methane
- DRIFTS, diffuse reflectance infrared Fourier transform spectroscopy
- EGR, exhaust gas recirculation
- EI, electron ionization
- Emissions
- Energy
- Energy conversion
- FC, fuel cell
- FCEV, fuel cell electric vehicle
- FRET, fluorescence resonance energy transfer
- FT, Fischer-Tropsch
- FTIR, Fourier-transform infrared
- Fuels
- GC, gas chromatography
- GHG, greenhouse gas
- GTL, gas-to-liquid
- GW, global warming
- HAB, height above the burner
- HACA, hydrogen abstraction acetylene addition
- HCCI, homogeneous charge compression ignition
- HFO, heavy fuel oil
- HRTEM, high-resolution transmission electron microscopy
- IC, internal combustion
- ICEV, internal combustion engine vehicle
- IE, ionization energy
- IPCC, Intergovernmental Panel on Climate Change
- IR, infrared
- JSR, jet-stirred reactor
- KDE, kernel density estimation
- KHP, ketohydroperoxide
- LCA, lifecycle analysis
- LH2, liquid hydrogen
- LIF, laser-induced fluorescence
- LIGS, laser-induced grating spectroscopy
- LII, laser-induced incandescence
- LNG, liquefied natural gas
- LOHC, liquid organic hydrogen carrier
- LT, low-temperature
- LTC, low-temperature combustion
- MBMS, molecular-beam MS
- MDO, marine diesel oil
- MS, mass spectrometry
- MTO, methanol-to-olefins
- MVK, methyl vinyl ketone
- NOx, nitrogen oxides
- NTC, negative temperature coefficient
- OME, oxymethylene ether
- OTMS, Orbitrap MS
- PACT, predictive automated computational thermochemistry
- PAH, polycyclic aromatic hydrocarbon
- PDF, probability density function
- PEM, polymer electrolyte membrane
- PEPICO, photoelectron photoion coincidence
- PES, photoelectron spectrum/spectra
- PFR, plug-flow reactor
- PI, photoionization
- PIE, photoionization efficiency
- PIV, particle imaging velocimetry
- PLIF, planar laser-induced fluorescence
- PM, particulate matter
- PM10 PM2,5, sampled fractions with sizes up to ∼10 and ∼2,5 µm
- PRF, primary reference fuel
- QCL, quantum cascade laser
- RCCI, reactivity-controlled compression ignition
- RCM, rapid compression machine
- REMPI, resonance-enhanced multi-photon ionization
- RMG, reaction mechanism generator
- RON, research octane number
- Reaction mechanisms
- SI, spark ignition
- SIMS, secondary ion mass spectrometry
- SNG, synthetic natural gas
- SNR, signal-to-noise ratio
- SOA, secondary organic aerosol
- SOEC, solid-oxide electrolysis cell
- SOFC, solid-oxide fuel cell
- SOx, sulfur oxides
- STM, scanning tunneling microscopy
- SVO, straight vegetable oil
- Synthetic fuels
- TDLAS, tunable diode laser absorption spectroscopy
- TOF-MS, time-of-flight MS
- TPES, threshold photoelectron spectrum/spectra
- TPRF, toluene primary reference fuel
- TSI, threshold sooting index
- TiRe-LII, time-resolved LII
- UFP, ultrafine particle
- VOC, volatile organic compound
- VUV, vacuum ultraviolet
- WLTP, Worldwide Harmonized Light Vehicle Test Procedure
- XAS, X-ray absorption spectroscopy
- YSI, yield sooting index
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Estimation of diffusion, perfusion and fractional volumes using a multi-compartment relaxation-compensated intravoxel incoherent motion (IVIM) signal model. Eur J Radiol Open 2019; 6:198-205. [PMID: 31193664 PMCID: PMC6538803 DOI: 10.1016/j.ejro.2019.05.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 05/14/2019] [Indexed: 12/12/2022] Open
Abstract
Compartmental diffusion MRI models that account for intravoxel incoherent motion (IVIM) of blood perfusion allow for estimation of the fractional volume of the microvascular compartment. Conventional IVIM models are known to be biased by not accounting for partial volume effects caused by free water and cerebrospinal fluid (CSF), or for tissue-dependent relaxation effects. In this work, a three-compartment model (tissue, free water and blood) that includes relaxation terms is introduced. To estimate the model parameters, in vivo human data were collected with multiple echo times (TE), inversion times (TI) and b-values, which allowed a direct relaxation estimate alongside estimation of perfusion, diffusion and fractional volume parameters. Compared to conventional two-compartment models (with and without relaxation compensation), the three-compartment model showed less effects of CSF contamination. The proposed model yielded significantly different volume fractions of blood and tissue compared to the non-relaxation-compensated model, as well as to the conventional two-compartment model, suggesting that previously reported parameter ranges, using models that do not account for relaxation, should be reconsidered.
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Key Words
- CSF, cerebrospinal fluid
- Diffusion
- GM, grey matter
- IR, inversion recovery
- IVIM, intravoxel incoherent motion
- Intravoxel incoherent motion
- PVE, partial volume effect
- Perfusion fraction
- Pseudo-diffusion
- ROI, region of interest
- Relaxation
- SNR, signal-to-noise ratio
- T1, longitudinal relaxation time
- T2, transverse relaxation time
- TE, echo time
- TI, inversion time
- TR, repetition time
- WM, white matter
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Optimizing diffusion-weighted magnetic resonance imaging for evaluation of lung tumors: A comparison of respiratory triggered and free breathing techniques. Eur J Radiol Open 2018; 5:189-193. [PMID: 30450371 PMCID: PMC6222289 DOI: 10.1016/j.ejro.2018.10.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 10/09/2018] [Accepted: 10/21/2018] [Indexed: 12/17/2022] Open
Abstract
Purpose The aim of this study was to compare respiratory-triggered (RT) and free breathing (FB) diffusion weighted imaging (DWI) techniques regarding apparent diffusion coefficient (ADC) measurements and repeatability in non-squamous non-small cell lung cancer (NSCLC) measuring the total tumor volume. Material and Methods A total of 57 magnetic resonance imaging (MRI) examinations were analyzed. DWI was obtained by a single-shot spin-echo echo-planar imaging sequence, and for each MRI examination 2 consecutive RT and 2 consecutive FB DWI sequences were performed. Two radiologists independently read the images and made measurements. For each tumor the mean ADC value of the whole tumor volume was calculated. The difference in mean ADCs between FB and RT DWI was evaluated using the paired-sample t-test. The repeatability of ADC measurements related to imaging method was evaluated by intra class correlations (ICC) for each of the FB and RT DWI pairs. Results There were no significant differences in mean ADCs between FB and RT (Reader 1 p = 0.346, Reader 2 p = 0.583). The overall repeatability of ADC measurement was good for both acquisition methods, with ICCs > 0.9. Subgroup analysis showed somewhat poorer repeatability in small tumors (50 ml or less) and tumors in the lower lung zones for the RT acquisition, with ICC as low as 0.72. Conclusions No difference in ADC measurement or repeatability between FB and RT DWI in whole lesion ADC measurements of adenocarcinomas in the lung was demonstrated. The results imply that in this setting the FB acquisition method is accurate and possibly more robust than the RT acquisition technique.
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Key Words
- ADC, apparent diffusion coefficient
- BH, breath-hold
- DWI, diffusion weighted imaging
- Diffusion weighted imaging
- FB, free breathing
- ICC, intra class correlations
- MRI, magnetic resonance imaging
- Magnetic resonance imaging
- NSCLC, non-squamous non-small cell lung cancer
- ROI, region of interest
- RT, respiratory-triggered
- SNR, signal-to-noise ratio
- non-Small cell lung cancer
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Autosomal dominant cerebellar ataxias: Imaging biomarkers with high effect sizes. NEUROIMAGE-CLINICAL 2018; 19:858-867. [PMID: 29922574 PMCID: PMC6005808 DOI: 10.1016/j.nicl.2018.06.011] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 05/19/2018] [Accepted: 06/07/2018] [Indexed: 12/13/2022]
Abstract
Objective As gene-based therapies may soon arise for patients with spinocerebellar ataxia (SCA), there is a critical need to identify biomarkers of disease progression with effect sizes greater than clinical scores, enabling trials with smaller sample sizes. Methods We enrolled a unique cohort of patients with SCA1 (n = 15), SCA2 (n = 12), SCA3 (n = 20) and SCA7 (n = 10) and 24 healthy controls of similar age, sex and body mass index. We collected longitudinal clinical and imaging data at baseline and follow-up (mean interval of 24 months). We performed both manual and automated volumetric analyses. Diffusion tensor imaging (DTI) and a novel tractography method, called fixel-based analysis (FBA), were assessed at follow-up. Effect sizes were calculated for clinical scores and imaging parameters. Results Clinical scores worsened as atrophy increased over time (p < 0.05). However, atrophy of cerebellum and pons showed very large effect sizes (>1.2) compared to clinical scores (<0.8). FBA, applied for the first time to SCA, was sensitive to microstructural cross-sectional differences that were not captured by conventional DTI metrics, especially in the less studied SCA7 group. FBA also showed larger effect sizes than DTI metrics. Conclusion This study showed that volumetry outperformed clinical scores to measure disease progression in SCA1, SCA2, SCA3 and SCA7. Therefore, we advocate the use of volumetric biomarkers in therapeutic trials of autosomal dominant ataxias. In addition, FBA showed larger effect size than DTI to detect cross-sectional microstructural alterations in patients relative to controls. Biomarkers are needed to test upcoming therapies for spinocerebellar ataxia. As spinocerebellar ataxias are rare, biomarkers with high effect sizes are needed. We identified imaging biomarkers with higher effect sizes than clinical scores.
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Key Words
- Apparent fiber density
- CCFS, composite cerebellar functional severity score
- CFE, connectivity-based fixel enhancement
- CSD, constrained spherical deconvolution
- CST, corticospinal tract
- DTI, diffusion tensor imaging
- Diffusion imaging.
- FA, fractional anisotropy
- FBA, fixel-based analysis
- FC, fiber cross-section
- FD, fiber density
- FDC, fiber density and cross-section
- FOD, fiber orientation distribution
- FOV, Field of view
- Fixel analysis
- GRAPPA, generalized autocalibrating partial parallel acquisition
- Imaging biomarkers
- MPRAGE, magnetization-prepared rapid gradient-echo
- MRI, magnetic resonance imaging
- RD, radial diffusivity
- SARA, scale for the assessment and rating of ataxia
- SCA, spinocerebellar ataxias
- SNR, signal-to-noise ratio
- Spinocerebellar ataxia
- TBSS, tract-based spatial statistics
- TE, echo time
- TR, repetition time
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Continuous wave laser diodes enable fast optoacoustic imaging. PHOTOACOUSTICS 2018; 9:31-38. [PMID: 29387537 PMCID: PMC5772504 DOI: 10.1016/j.pacs.2017.12.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 11/22/2017] [Accepted: 12/14/2017] [Indexed: 05/18/2023]
Abstract
Pulsed laser diodes may offer a smaller, less expensive alternative to conventional optoacoustic laser sources; however they do not provide pulse rates faster than a few tens of kHz and emit at wavelengths only within the near-infrared region. We investigated whether continuous wave (CW) laser diodes, which are available in visible and near-infrared regions, can be good optoacoustic light sources when overdriven with a peak current >40-fold higher than the CW absolute maximum. We found that overdriven CW diodes provided ∼10 ns pulses of ∼200 nJ/pulse and repetition rates higher than 600 kHz without being damaged, outperforming many pulsed laser diodes. Using this system, we obtained images of phantoms and mouse ear and human arm in vivo, confirming their use in optoacoustic imaging and sensing.
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Key Words
- CNR, contrast to background ration
- COD, catastrophic optical damage
- CW, continuous wave
- Current drivers
- DAQ, data acquisition card
- FWHM, full width at half maximum
- Light sources
- Light-emitting diodes
- MIP, maximum intensity projection
- NIR, near-infrared
- Near-infrared
- OPO, optical parametric oscillator
- PLD, pulsed laser diode
- Photoacoustic
- SNR, signal-to-noise ratio
- TTL, transistor-transistor-logic
- UST, ultrasound transducer
- VIS, visible
- Visible
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Connectivity derived thalamic segmentation in deep brain stimulation for tremor. Neuroimage Clin 2018; 18:130-142. [PMID: 29387530 PMCID: PMC5790021 DOI: 10.1016/j.nicl.2018.01.008] [Citation(s) in RCA: 113] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2017] [Revised: 12/23/2017] [Accepted: 01/13/2018] [Indexed: 02/02/2023]
Abstract
The ventral intermediate nucleus (VIM) of the thalamus is an established surgical target for stereotactic ablation and deep brain stimulation (DBS) in the treatment of tremor in Parkinson's disease (PD) and essential tremor (ET). It is centrally placed on a cerebello-thalamo-cortical network connecting the primary motor cortex, to the dentate nucleus of the contralateral cerebellum through the dentato-rubro-thalamic tract (DRT). The VIM is not readily visible on conventional MR imaging, so identifying the surgical target traditionally involved indirect targeting that relies on atlas-defined coordinates. Unfortunately, this approach does not fully account for individual variability and requires surgery to be performed with the patient awake to allow for intraoperative targeting confirmation. The aim of this study is to identify the VIM and the DRT using probabilistic tractography in patients that will undergo thalamic DBS for tremor. Four male patients with tremor dominant PD and five patients (three female) with ET underwent high angular resolution diffusion imaging (HARDI) (128 diffusion directions, 1.5 mm isotropic voxels and b value = 1500) preoperatively. Patients received VIM-DBS using an MR image guided and MR image verified approach with indirect targeting. Postoperatively, using parallel Graphical Processing Unit (GPU) processing, thalamic areas with the highest diffusion connectivity to the primary motor area (M1), supplementary motor area (SMA), primary sensory area (S1) and contralateral dentate nucleus were identified. Additionally, volume of tissue activation (VTA) corresponding to active DBS contacts were modelled. Response to treatment was defined as 40% reduction in the total Fahn-Tolosa-Martin Tremor Rating Score (FTMTRS) with DBS-ON, one year from surgery. Three out of nine patients had a suboptimal, long-term response to treatment. The segmented thalamic areas corresponded well to anatomically known counterparts in the ventrolateral (VL) and ventroposterior (VP) thalamus. The dentate-thalamic area, lay within the M1-thalamic area in a ventral and lateral location. Streamlines corresponding to the DRT connected M1 to the contralateral dentate nucleus via the dentate-thalamic area, clearly crossing the midline in the mesencephalon. Good response was seen when the active contact VTA was in the thalamic area with highest connectivity to the contralateral dentate nucleus. Non-responders had active contact VTAs outside the dentate-thalamic area. We conclude that probabilistic tractography techniques can be used to segment the VL and VP thalamus based on cortical and cerebellar connectivity. The thalamic area, best representing the VIM, is connected to the contralateral dentate cerebellar nucleus. Connectivity based segmentation of the VIM can be achieved in individual patients in a clinically feasible timescale, using HARDI and high performance computing with parallel GPU processing. This same technique can map out the DRT tract with clear mesencephalic crossing.
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Key Words
- AC, anterior commissure
- BEDPOSTX, Bayesian estimation of diffusion parameters obtained using sampling techniques X
- BET, brain extraction tool
- CI, confidence interval
- CON, connectivity
- Connectivity
- DBS
- DBS, deep brain stimulation
- DF, degrees of freedom
- DICOM, digital imaging and communications in medicine
- DRT
- DWI
- DWI, diffusion weighted imaging
- Deep brain stimulation
- Dentate nucleus
- Dentato-rubro-thalamic tract
- Diffusion weighted imaging
- EV, explanatory variable
- FLIRT, FMRIB's linear image registration tool
- FMRIB, Oxford centre for functional MRI of the brain
- FNIRT, FMRIB's non-linear image registration tool
- FSL, FMRIB's software library
- FoV, field of view
- GLM, general linear model
- HARDI, high angular resolution diffusion imaging
- HFS, high frequency stimulation
- IPG, implantable pulse generator
- LC, Levodopa challenge
- LEDD, l-DOPA equivalent daily dose
- M1, primary motor cortex
- MMS, mini-mental score
- MNI, Montreal neurological institute
- MPRAGE, magnetization-prepared rapid gradient-echo
- MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine
- NHNN, National Hospital for Neurology and Neurosurgery
- NIfTI, neuroimaging informatics technology initiative
- PC, posterior commissure
- PD
- PFC, prefrontal cortex
- PMC, premotor cortex
- Parkinson's disease
- S1, primary sensory cortex
- SAR, specific absorption rate
- SD, standard deviation
- SE, standard error
- SMA, supplementary motor area
- SNR, signal-to-noise ratio
- SSEPI, single-shot echo planar imaging
- STN, subthalamic nucleus
- TFCE, threshold-free cluster enhancement
- TMS, transcranial magnetic stimulation
- Tremor
- UPDRS, unified Parkinson's disease rating scale
- VBM, voxel based morphometry
- VIM
- VL
- VL, ventral lateral
- VP, ventral posterior
- VTA, volume of tissue activated
- Ventrointermedialis
- Ventrolateral nucleus
- cZI, caudal zona incerta
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Simultaneous investigation of microvasculature and parenchyma in cerebral small vessel disease using intravoxel incoherent motion imaging. NEUROIMAGE-CLINICAL 2017; 14:216-221. [PMID: 28180080 PMCID: PMC5288390 DOI: 10.1016/j.nicl.2017.01.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 11/28/2016] [Accepted: 01/16/2017] [Indexed: 01/01/2023]
Abstract
INTRODUCTION Cerebral small vessel disease (cSVD) is associated with microvascular and parenchymal alterations. Intravoxel incoherent motion (IVIM) MRI has been proposed to simultaneously measure both the microvascular perfusion and parenchymal diffusivity. This study aimed to evaluate the application of IVIM in cSVD to assess the microvasculature and parenchymal microstructure. METHODS Seventy-three patients with cSVD (age 70 ± 11 y) and thirty-nine controls (age 69 ± 12 y) underwent IVIM imaging (3T). Group differences of the perfusion volume fraction f and the parenchymal diffusivity D were investigated using multivariable linear regression accounted for age, sex and cardiovascular factors. To examine the relation between the IVIM measures and the disease severity on structural MRI, white matter hyperintensity (WMH) load served as surrogate measure of the disease severity. RESULTS Patients had a larger f (p < 0.024) in the normal appearing white matter (NAWM) than controls. Higher D (p < 0.031) was also observed for patients compared with controls in the NAWM and grey matter. Both f (p < 0.024) and D (p < 0.001) in the NAWM and grey matter increased with WMH load. CONCLUSIONS The increased diffusivity reflects the predicted microstructural tissue impairment in cSVD. Unexpectedly, an increased perfusion volume fraction was observed in patients. Future studies are needed to reveal the precise nature of the increased perfusion volume fraction. IVIM imaging showed that the increases of f and D in cSVD were both related to disease severity, which suggests the potential of IVIM imaging to provide a surrogate marker for the progression of cSVD.
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Key Words
- BMI, body mass index
- Brain parenchyma
- Cerebral small vessel disease
- DGM, deep grey matter
- DW, diffusion weighted
- Diffusion weighted imaging
- FLAIR, fluid attenuated inversion recovery
- FOV, field of view
- IVIM, intravoxel incoherent motion imaging
- Intravoxel incoherent motion imaging
- LS, lacunar stroke
- Microvasculature
- NAWM, normal appearing white matter
- PVS, perivascular spaces
- Perfusion MR imaging
- ROI, region of interest
- SNR, signal-to-noise ratio
- WMH, white matter hyperintensity
- cSVD, cerebral small vessel disease
- mVCI, mild vascular cognitive impairment
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Diffusion-weighted MR imaging of non-complicated hepatic cysts: Value of 3T computed diffusion-weighted imaging. Eur J Radiol Open 2016; 3:138-44. [PMID: 27489867 PMCID: PMC4959945 DOI: 10.1016/j.ejro.2016.07.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 06/30/2016] [Accepted: 07/02/2016] [Indexed: 12/16/2022] Open
Abstract
Purpose To investigate the utility of computed 3T diffusion-weighted imaging (c-DWI) for the diagnosis of non-complicated hepatic cysts with a focus on the T2 shine-through effect. Materials and methods In 50 patients with non-complicated hepatic cysts we acquired one set of DWIs (b-value 0 and 1000 s/mm2) at 1.5T, and two sets at 3T (b-value 0 and 1000 s/mm2, TE 70 ms; b-value 0 and 600 s/mm2, TE 60 ms). We defined the original DWIs acquired with b = 1000 s/mm2 at 1.5T and 3T as “o-1.5T-1000” and “o-3T-1000”. c-DWIs were calculated with 3T DWI at b-values of 0 and 600 s/mm2. c-DWI with b = 1000 and 1500 s/mm2 were defined as “c-1000” and “c-1500”. Radiologists evaluated the signal intensity (SI) of the cysts using a 3-point score where 1 = not visible, 2 = discernible, and 3 = clearly visible. They calculated the contrast ratio (CR) between the cysts and the surrounding liver parenchyma on each DWIs and recorded the apparent diffusion coefficient (ADC) with a b-value = 0 and 1000 s/mm2 on 1.5T- and 3T DWIs. Results Compared with o-1.5T-1000 DWI, the visual scores of all but the c-1500 DWIs were higher (p = 0.07 for c-1500- and p < 0.01 for the other DWIs). The CR at b = 1000 s/mm2 was higher on o-3T-1000- than on o-1.5T-1000- (p < 0.01) but not higher than on c-1500 DWIs (p = 0.96). The CR at b = 0 s/mm2 on 3T images with TE 70 ms was higher than on 1.5T images (p < 0.01). The ADC value was higher for 3T- than 1.5T images (p < 0.01). Conclusions Non-complicated hepatic cysts showed higher SI on o-3T-1000- than o-1.5T-1000 DWIs due to the T2-shine through effect. This high SI was suppressed on c-1500 DWIs.
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Key Words
- ADC, apparent diffusion coefficient
- CR, contrast ratio
- Computed diffusion-weighted imaging
- DWI, diffusion-weighted imaging
- Diffusion-weighted imaging
- Field strength
- HCC, hepatocellular carcinoma
- MRI, magnetic resonance imaging
- Non-complicated hepatic cysts
- SI, signal intensity
- SNR, signal-to-noise ratio
- T1-WI, T1-weighted MRI
- T2 shine-through effect
- T2-WI, T2-weighted MRI
- c-DWI, computed diffusion-weighted imaging
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Hyperpolarized (13)C MR imaging detects no lactate production in mutant IDH1 gliomas: Implications for diagnosis and response monitoring. Neuroimage Clin 2016; 12:180-9. [PMID: 27437179 PMCID: PMC4939422 DOI: 10.1016/j.nicl.2016.06.018] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 10/26/2022]
Abstract
Metabolic imaging of brain tumors using (13)C Magnetic Resonance Spectroscopy (MRS) of hyperpolarized [1-(13)C] pyruvate is a promising neuroimaging strategy which, after a decade of preclinical success in glioblastoma (GBM) models, is now entering clinical trials in multiple centers. Typically, the presence of GBM has been associated with elevated hyperpolarized [1-(13)C] lactate produced from [1-(13)C] pyruvate, and response to therapy has been associated with a drop in hyperpolarized [1-(13)C] lactate. However, to date, lower grade gliomas had not been investigated using this approach. The most prevalent mutation in lower grade gliomas is the isocitrate dehydrogenase 1 (IDH1) mutation, which, in addition to initiating tumor development, also induces metabolic reprogramming. In particular, mutant IDH1 gliomas are associated with low levels of lactate dehydrogenase A (LDHA) and monocarboxylate transporters 1 and 4 (MCT1, MCT4), three proteins involved in pyruvate metabolism to lactate. We therefore investigated the potential of (13)C MRS of hyperpolarized [1-(13)C] pyruvate for detection of mutant IDH1 gliomas and for monitoring of their therapeutic response. We studied patient-derived mutant IDH1 glioma cells that underexpress LDHA, MCT1 and MCT4, and wild-type IDH1 GBM cells that express high levels of these proteins. Mutant IDH1 cells and tumors produced significantly less hyperpolarized [1-(13)C] lactate compared to GBM, consistent with their metabolic reprogramming. Furthermore, hyperpolarized [1-(13)C] lactate production was not affected by chemotherapeutic treatment with temozolomide (TMZ) in mutant IDH1 tumors, in contrast to previous reports in GBM. Our results demonstrate the unusual metabolic imaging profile of mutant IDH1 gliomas, which, when combined with other clinically available imaging methods, could be used to detect the presence of the IDH1 mutation in vivo.
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Key Words
- 2-HG, 2-hydroxyglutarate
- AIF, arterial input function
- AUC, area under the curve
- DNP, dynamic nuclear polarization
- DNP-MR, dynamic nuclear polarization magnetic resonance
- EGF, epidermal growth factor
- EGFR, epidermal growth factor receptor
- FA, flip angle
- FGF, fibroblast growth factor
- FLAIR, fluid attenuated inversion recovery
- FOV, field of view
- GBM, glioblastoma
- Glioma
- Hyperpolarized 13C Magnetic Resonance Spectroscopy (MRS)
- IDH1, isocitrate dehydrogenase 1
- Isocitrate dehydrogenase 1 (IDH1) mutation
- LDHA, lactate dehydrogenase A
- MCT1, monocarboxylate transporter 1
- MCT4, monocarboxylate transporter 4
- MR, magnetic resonance
- MRI, magnetic resonance imaging
- MRS, magnetic resonance spectroscopic imaging
- MRS, magnetic resonance spectroscopy
- Metabolic reprogramming
- NA, number of averages
- NT, number of transients
- PBS, phosphate-buffer saline
- PDGF, platelet-derived growth factor
- PET, positron emission tomography
- PI3K, phosphoinositide 3-kinase
- PTEN, phosphatase and tensin homolog
- RB1, retinoblastoma protein 1
- SLC16A1, solute carrier family 16 member 1
- SLC16A3, solute carrier family 16 member 3
- SNR, signal-to-noise ratio
- SW, spectral width
- TCGA, The Cancer Genome Atlas
- TE, echo time
- TMZ, temozolomide
- TP53, tumor protein p53
- TR, repetition time
- Tacq, acquisition time
- VOI, voxel of interest
- mTOR, mammalian target of rapamycin
- α-KG, α-ketoglutarate
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Magnetic Resonance Imaging: Principles and Techniques: Lessons for Clinicians. J Clin Exp Hepatol 2015; 5:246-55. [PMID: 26628842 PMCID: PMC4632105 DOI: 10.1016/j.jceh.2015.08.001] [Citation(s) in RCA: 144] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 08/10/2015] [Indexed: 12/12/2022] Open
Abstract
The development of magnetic resonance imaging (MRI) for use in medical investigation has provided a huge forward leap in the field of diagnosis, particularly with avoidance of exposure to potentially dangerous ionizing radiation. With decreasing costs and better availability, the use of MRI is becoming ever more pervasive throughout clinical practice. Understanding the principles underlying this imaging modality and its multiple applications can be used to appreciate the benefits and limitations of its use, further informing clinical decision-making. In this article, the principles of MRI are reviewed, with further discussion of specific clinical applications such as parallel, diffusion-weighted, and magnetization transfer imaging. MR spectroscopy is also considered, with an overview of key metabolites and how they may be interpreted. Finally, a brief view on how the use of MRI will change over the coming years is presented.
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Key Words
- ADC, apparent diffusion coefficient
- CSI, Chemical shift imaging
- DTI, diffusion tensor imaging
- DWI, Diffusion-weighted imaging
- FA, Fractional anisotropy
- FID, free induction decay
- MRI, magnetic resonance imaging
- MTR, MT ratios
- NMR, nuclear magnetic resonance
- PRESS, Point-resolved spectroscopy
- RA, relative anisotropy
- RF, radiofrequency
- SNR, signal-to-noise ratio
- STEAM, Stimulated echo acquisition mode
- TR, repetition time
- magnetic resonance imaging
- magnetic resonance spectroscopy
- medical physics
- nuclear magnetic resonance
- nuclear medicine
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Objective and subjective image quality with prospectively gated versus ECG-controlled tube current modulation using 256-slice computed tomographic angiography. J Saudi Heart Assoc 2015; 27:256-63. [PMID: 26557743 PMCID: PMC4614896 DOI: 10.1016/j.jsha.2015.03.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2014] [Revised: 03/24/2015] [Accepted: 03/26/2015] [Indexed: 11/23/2022] Open
Abstract
Introduction Radiation exposure is one of the major limitations of computed tomographic coronary angiography (CTA). The purpose of this study was to compare the objective and subjective image quality and radiation dose using prospective ECG gating (PGA) versus ECG-controlled tube current modulation (ECTCM) scanning techniques. Methods A prospective, single-center study was performed at Prince Sultan Cardiac Centre, Qassim, Saudi Arabia. A total of 104 patients with low-to- intermediate probability of coronary artery disease (CAD) underwent CTA with either PGA or ECTCM acquisition. PGA was performed during the study period and compared with the last 50 CTAs previously done using ECTCM. A 4-point scale was used to assess the image quality subjectively. Objective image quality was assessed using image signal, noise, and signal-to-noise ratio (SNR). Results Patient‘s Baseline characteristics were not different between the two scanning protocols. The 4-point score of subjective image quality showed no significant differences between the PGA and ECTCM scans (2.9 ± 0.7, 2.96 ± 0.7, respectively; p = 0.87). The objective image quality showed significantly higher noise and lower SNR with PGA compared with ECTCM (31 ± 9, 27 ± 9, respectively; p < 0.001 for noise) and (15 ± 5, 17 ± 7, respectively; p < 0.001 for SNR), with no statistical difference in the image signal (434 ± 123, 425 ± 103 HU, respectively, p = 0.7). Radiation exposure was significantly lower with PGA than with ECTCM. The dose-length product (DLP) for PGA was 334 ± 130 mGy, compared with 822 ± 286 mGy for the ECTCM. This corresponds to a 59% reduction in radiation exposure (p < 0.0001). Conclusions Although prospective ECG-triggered axial scanning increased image noise, it maintained subjective image quality and was associated with a 59% reduction in radiation exposure when compared with ECTCM.
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Key Words
- BMI, body mass index
- CAD, coronary artery disease
- CTA, computed tomographic coronary angiography
- Coronary angiography
- DLP, dose-length product
- ECTCM, ECG-controlled tube current modulation
- HR, heart rate
- HU, Hounsfield unit
- Image noise
- MPR, multi-planar reconstruction
- PGA, prospective gated axial
- RGH, retrospectively-gated helical
- Radiation exposure
- SNR, signal-to-noise ratio
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Measurement of brain perfusion in newborns: pulsed arterial spin labeling (PASL) versus pseudo-continuous arterial spin labeling (pCASL). NEUROIMAGE-CLINICAL 2014; 6:126-33. [PMID: 25379424 PMCID: PMC4215516 DOI: 10.1016/j.nicl.2014.08.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 07/31/2014] [Accepted: 08/16/2014] [Indexed: 11/25/2022]
Abstract
BACKGROUND Arterial spin labeling (ASL) perfusion-weighted imaging (PWI) by magnetic resonance imaging (MRI) has been shown to be useful for identifying asphyxiated newborns at risk of developing brain injury, whether or not therapeutic hypothermia was administered. However, this technique has been only rarely used in newborns until now, because of the challenges to obtain sufficient signal-to-noise ratio (SNR) and spatial resolution in newborns. OBJECTIVE To compare two methods of ASL-PWI (i.e., single inversion-time pulsed arterial spin labeling [single TI PASL], and pseudo-continuous arterial spin labeling [pCASL]) to assess brain perfusion in asphyxiated newborns treated with therapeutic hypothermia and in healthy newborns. DESIGN/METHODS We conducted a prospective cohort study of term asphyxiated newborns meeting the criteria for therapeutic hypothermia; four additional healthy term newborns were also included as controls. Each of the enrolled newborns was scanned at least once during the first month of life. Each MRI scan included conventional anatomical imaging, as well as PASL and pCASL PWI-MRI. Control and labeled images were registered separately to reduce the effect of motion artifacts. For each scan, the axial slice at the level of the basal ganglia was used for comparisons. Each scan was scored for its image quality. Quantification of whole-slice cerebral blood flow (CBF) was done afterwards using previously described formulas. RESULTS A total number of 61 concomitant PASL and pCASL scans were obtained in nineteen asphyxiated newborns treated with therapeutic hypothermia and four healthy newborns. After discarding the scans with very poor image quality, 75% (46/61) remained for comparison between the two ASL methods. pCASL images presented a significantly superior image quality score compared to PASL images (p < 0.0001). Strong correlation was found between the CBF measured by PASL and pCASL (r = 0.61, p < 0.0001). CONCLUSION This study demonstrates that both ASL methods are feasible to assess brain perfusion in healthy and sick newborns. However, pCASL might be a better choice over PASL in newborns, as pCASL perfusion maps had a superior image quality that allowed a more detailed identification of the different brain structures.
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Gray matter contamination in arterial spin labeling white matter perfusion measurements in patients with dementia. NEUROIMAGE-CLINICAL 2013; 4:139-44. [PMID: 24371796 PMCID: PMC3871287 DOI: 10.1016/j.nicl.2013.11.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/20/2013] [Revised: 11/05/2013] [Accepted: 11/06/2013] [Indexed: 01/28/2023]
Abstract
Introduction White matter (WM) perfusion measurements with arterial spin labeling can be severely contaminated by gray matter (GM) perfusion signal, especially in the elderly. The current study investigates the spatial extent of GM contamination by comparing perfusion signal measured in the WM with signal measured outside the brain. Material and methods Four minute 3T pseudo-continuous arterial spin labeling scans were performed in 41 elderly subjects with cognitive impairment. Outward and inward geodesic distance maps were created, based on dilations and erosions of GM and WM masks. For all outward and inward geodesic distances, the mean CBF was calculated and compared. Results GM contamination was mainly found in the first 3 subcortical WM voxels and had only minor influence on the deep WM signal (distances 4 to 7 voxels). Perfusion signal in the WM was significantly higher than perfusion signal outside the brain, indicating the presence of WM signal. Conclusion These findings indicate that WM perfusion signal can be measured unaffected by GM contamination in elderly patients with cognitive impairment. GM contamination can be avoided by the erosion of WM masks, removing subcortical WM voxels from the analysis. These results should be taken into account when exploring the use of WM perfusion as micro-vascular biomarker. A single slice distance analysis was performed. Perfusion signal in the white matter was compared with signal outside the brain. The application of erosion was compared with removal of partial volume voxels. White matter perfusion signal can be distinguished from gray matter contamination. The erosion of three voxels is warranted to avoid gray matter contamination.
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