Biomedical Image Processing / Medical Image Processing
Mohamad reza Rezaeian
Volume 16, Issue 4 , March 2023, , Pages 300-310
Abstract
The chemical exchange due to saturation transfer by applying an electromagnetic radio frequency (RF) pulse to a magnetic resonance scanner is called the CEST effect. The CEST effect depends mainly on relaxation times, chemical exchange rate, concentration of the contrast agent and RF pulse properties. ...
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The chemical exchange due to saturation transfer by applying an electromagnetic radio frequency (RF) pulse to a magnetic resonance scanner is called the CEST effect. The CEST effect depends mainly on relaxation times, chemical exchange rate, concentration of the contrast agent and RF pulse properties. Dependence of chemical exchange rate on some clinical indicators such as pH, temperature and glucose consumption, allows diagnosis diseases non-invasively. The chemical exchange rate is determined through presenting new objective function of the CEST effect in the mathematical closed form quantitatively. A new description of the optimal amplitude of the rectangular RF pulse is obtained by applying gradient-based methods on the proposed convex objective function. Chemical exchange rate is proposed at the simple representation form independent to contrast agent by reversing the optimal amplitude description for large shift frequency contrast agents. Evaluation of the objective function and the proposed relations are performed by comparing them with valid methods derived solving Bloch-McConnell equations through parametric and real data. The mean relative square error of the objective function based on the parametric data is 7.25% and for the proposed the optimal amplitude and chemical exchange rate based on the real data are 6.3% and 4.2%, respectively.
Biomedical Image Processing / Medical Image Processing
Mohamad Reza Rezaeian
Volume 15, Issue 1 , May 2021, , Pages 47-58
Abstract
Molecular magnetic resonance imaging by tracking contrast agents based on magnetic resonance of the nucleus is considered a novel anatomical and functional diagnostic method in various medical applications due to its good spatial resolution and safe technology. In a magnetic resonance scanner, a spectroscopic ...
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Molecular magnetic resonance imaging by tracking contrast agents based on magnetic resonance of the nucleus is considered a novel anatomical and functional diagnostic method in various medical applications due to its good spatial resolution and safe technology. In a magnetic resonance scanner, a spectroscopic spectrum known as the Z-spectrum is obtained by applying a predominantly rectangular electromagnetic saturation pulse. At frequencies corresponding to the Larmor frequency, some amplitudes due to water saturation contrast factors are formed, representing saturation transfer’s effect due to chemical exchange (CEST). Chemical shifts, magnetic field heterogeneity and imaging process’s noise, while shifting the Larmore frequencies position, distorts the CEST effect. This noise is mainly modeled by the raisin distribution, which is an extent of Gaussian distribution. In this paper, an efficient method for reducing noise from the Z-spectrum and detecting the CEST effect is presented. Deionization is performed using the analytical model’s output resulting from solving the Bloch-McCannell equations and detecting the CEST effect by calculating the Bayesian likelihood function. The proposed method’s effectiveness for noise cancellation and detection the CEST effect was performed on real Z-spectra which is obtained from magnetic resonance scanners and data obtained from human tissue. The average performance of the proposed method is measured by relative mean square error between the real Z-spectrum and the noise in the signal to noise 10dB and the number of observations 5 was about four percent. The value of the first type of error (p-value) based on parametric data was less than 5% when the noise variance was more than 0.008 and the number of observations was more than 5. In this paper, a criterion for detecting the effect of CEST based on the mediation operator is proposed to evaluate the efficiency of the proposed method in proportion to the noise power and the number of observations.
