scholarly journals MRI-Based Quantification of Magnetic Susceptibility in Gel Phantoms: Assessment of Measurement and Calculation Accuracy

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Emma Olsson ◽  
Ronnie Wirestam ◽  
Emelie Lind
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Contrast Agent ◽  
Calculated Data ◽  
Local Magnetic Field ◽  
Main Magnetic Field ◽  
Magic Angle ◽  
Venous Oxygen Saturation ◽  
Tissue Contrast ◽  
Concentration Of Contrast Agent

The local magnetic field inside and around an object in a magnetic resonance imaging unit depends on the magnetic susceptibility of the object being magnetized, in combination with its geometry/orientation. Magnetic susceptibility can thus be exploited as a source of tissue contrast, and susceptibility imaging may also become a useful tool in contrast agent quantification and for assessment of venous oxygen saturation levels. In this study, the accuracy of an established procedure for quantitative susceptibility mapping (QSM) was investigated. Three gel phantoms were constructed with cylinders of varying susceptibility and geometry. Experimental results were compared with simulated and analytically calculated data. An expected linear relationship between estimated susceptibility and concentration of contrast agent was observed. Less accurate QSM-based susceptibility values were observed for cylindrical objects at angles, relative to the main magnetic field, that were close to or larger than the magic angle. Results generally improved for large objects/high spatial resolution and large volume coverage. For simulated phase maps, accurate susceptibility quantification by QSM was achieved also for more challenging geometries. The investigated QSM algorithm was generally robust to changes in measurement and calculation parameters, but experimental phase data of sufficient quality may be difficult to obtain in certain geometries.

scholarly journals Pemetaan batuan penyusun candi di bawah permukaan berdasarkan metode geomagnetik studi kasus: cagar budaya candi Songgiriti desa Songgokerto kecamatan Batu kota Batu

2021 ◽  
Vol 2 (1) ◽  
pp. 11-18
Author(s):  
Agus Riyanto ◽  
Siti Zulaikah ◽  
Daeng Achmad Suaidi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Cultural Heritage ◽  
Mineral Exploration ◽  
Analysis Data ◽  
Local Magnetic Field ◽  
Cross Sectional ◽  
Sample Number ◽  
Magnetometer Data ◽  
Archaeological Objects

The geomagnetic method is often used in petroleum, geothermal and mineral exploration and can be applied to searching prospect archaeological objects (Siahaan, 2009). Several studies has been used the geomagnetic method to seek for archaeological objects by Ariani (2012) in Losari Temples and Sismanto et al (1997) in Kedulan Temple. In Batu City there is one of the cultural heritage that have not been intact called Songgoriti Temple. So, in this research we expected the existence of temple’s rocks using geomagnetic method. The de sign of the research using geomagnetic methods begins with the study of litera ture. This research was conducted with two methods there is calculating the val ue of the magnetic susceptibility of samples Temple’s rock using Bartington Susceptibility Meter MS2B and retrieving data field using the Proton magneto meter type ENVI SCINTREX. In the end of this research, we accepted the re sults of the two methods were compared to find out the site rock of temple. In magnetometer data analysis, data is processed using Magpick software, surfer 9.0 software and Mag2dc software. The results of the research show that a local magnetic field patterns of rocks in the area of cultural heritage Songgoriti Tem ple is divided into three parts namely high local magnetic field (yellow to red), the moderate local magnetic field (green to yellow) and low local magnetic field (blue). Furthermore based on five cross-sectional modeling using Mag2dc, we obtained the prediction the site of temple Songgoriti that is the sample number 1 found on the 2 position i.e at coordinates 49S 664547.5m 9130115m and coor dinate 49S 664585m 9130105m; sample number 3 found on the 2 position i.e at coordinates 49S 664583m 9130100m and coordinate 49S 664585m 9130100m; sample number 4 found on the 2 position i.e. at coordinates 49S 664577.5m 9130115m and coordinate 49S 664577.5m 9130110m; sample number 5 found on the 3 position i.e. at coordinates 49S 664566m 9130095m, coordinates 49S 664573m 9130095m and coordinate 49S 664582.5 m 9130095m; sample num ber 6 is found in 5 position i.e. at coordinates 49S 664545.5 m 9130110m, coordinates 49S 664550m 9130110m, coordinates 49S 664546m 9130105m, coordinates 49S 664565m 9130105m and coordinates 49S 664562.5 m 9130100m. For sample number 2 that is not found at all in the five models cross section. This may be caused by the value of the magnetic susceptibility sample number 2 is minor when compared to another samples that is 0.86 x 10-6 m3/kg

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

2020 ◽  
Vol 1 (3) ◽  
Author(s):  
Maysam Abedi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Least Squares ◽  
Minimization Problem ◽  
Potential Field ◽  
Field Data ◽  
Least Squares Method ◽  
Porphyry Copper ◽  
Magnetic Data ◽  
Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit.  The real case study located in  Semnan province of  Iran  consists  of  an arc-shaped  porphyry  andesite  covered  by  sedimentary  units  which  may  have  potential  of  mineral  occurrences, especially  porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

Technology of creation of digital charts of the Earth's main magnetic field

2009 ◽  
Vol 11 (2) ◽  
pp. 1-6
Author(s):  
E. A. Zhalkovsky ◽  
V. I. Nikiforov ◽  
A. M. Merzly ◽  
A. E. Beriozko ◽  
A. A. Soloviev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Main Magnetic Field

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

scholarly journals Quantitative dual contrast photon-counting computed tomography for assessment of articular cartilage health

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Petri Paakkari ◽  
Satu I. Inkinen ◽  
Miitu K. M. Honkanen ◽  
Mithilesh Prakash ◽  
Rubina Shaikh ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Articular Cartilage ◽  
Contrast Agent ◽  
Contrast Agents ◽  
Photon Counting ◽  
Spectral Imaging ◽  
Ct Scanning ◽  
Photon Counting Detector ◽  
Tissue Contrast ◽  
Reference Parameters

AbstractPhoton-counting detector computed tomography (PCD-CT) is a modern spectral imaging technique utilizing photon-counting detectors (PCDs). PCDs detect individual photons and classify them into fixed energy bins, thus enabling energy selective imaging, contrary to energy integrating detectors that detects and sums the total energy from all photons during acquisition. The structure and composition of the articular cartilage cannot be detected with native CT imaging but can be assessed using contrast-enhancement. Spectral imaging allows simultaneous decomposition of multiple contrast agents, which can be used to target and highlight discrete cartilage properties. Here we report, for the first time, the use of PCD-CT to quantify a cationic iodinated CA4+ (targeting proteoglycans) and a non-ionic gadolinium-based gadoteridol (reflecting water content) contrast agents inside human osteochondral tissue (n = 53). We performed PCD-CT scanning at diffusion equilibrium and compared the results against reference data of biomechanical and optical density measurements, and Mankin scoring. PCD-CT enables simultaneous quantification of the two contrast agent concentrations inside cartilage and the results correlate with the structural and functional reference parameters. With improved soft tissue contrast and assessment of proteoglycan and water contents, PCD-CT with the dual contrast agent method is of potential use for the detection and monitoring of osteoarthritis.

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