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RISS 인기검색어
- 검색키워드
- 저자 : Munish Chauhan (검색결과 7 건)
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Chauhan, Munish,Jeong, Woo Chul,Kim, Hyung Joong,Kwon, Oh In,Woo, Eung Je Informa UK Ltd. 2013 International journal of hyperthermia Vol.29 No.7
<P><I>Purpose</I>: The aim of this study was to show the potential of magnetic resonance electrical impedance tomography (MREIT) conductivity imaging in terms of its capability to detect ablated lesions and differentiate tissue conditions in liver radiofrequency (RF) ablation. <I>Materials and methods</I>: RF ablation procedures were performed in bovine livers using a LeVeen RF needle electrode. Ablation lesions were created using a power-controlled mode at 30, 50, and 70 W for 1, 3, and 5 min of exposure time, respectively. After the ablation, the liver was cut into several blocks including the ablated lesion, and positioned inside a phantom filled with agarose gel. Electrodes were attached on the side of the phantom and it was placed inside the MRI bore. For MREIT imaging, multi-spin-echo pulse sequence was used to obtain the magnetic flux density data according to the injection currents. <I>Results</I>: The conductivity of ablation lesions was significantly changed with the increase of exposure time (pKW < 0.01, Kruskal-Wallis test). With RF powers of 30 and 50 W, significant differences between the coagulation necrosis and hyperaemic rim were observed for more than 5 min and 3 min, respectively (pMW < 0.01, Mann-Whitney test). At 70 W, all cases showed significant differences except 3 min (pMW < 0.01). The positive correlation between the exposure time and tissue conductivity was observed in both two ablation areas (pSC < 0.01, Spearman correlation). <I>Conclusions</I>: This <I>ex vivo</I> feasibility study demonstrates that current MREIT conductivity imaging can detect liver RF ablation lesions without using any contrast media or additional MR scan.</P>
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Kwon, Oh In,Chauhan, Munish,Kim, Hyung Joong,Jeong, Woo Chul,Wi, Hun,Oh, Tong In,Woo, Eung Je Informa UK Ltd. 2014 International journal of hyperthermia Vol.30 No.7
<P><I>Purpose</I>: This study shows the potential of magnetic resonance electrical impedance tomography (MREIT) as a non-invasive RF ablation monitoring technique.</P><P><I>Materials and methods</I>: We prepared bovine muscle tissue with a pair of needle electrodes for RF ablation, a temperature sensor, and two pairs of surface electrodes for conductivity image reconstructions. We used the injected current non-linear encoding with multi-echo gradient recalled echo (ICNE-MGRE) pulse sequence in a series of MREIT scans for conductivity imaging. We acquired magnetic flux density data induced by externally injected currents, while suppressing other phase artefacts. We used an 8-channel RF head coil and 8 echoes to improve the signal-to-noise ratio (SNR) in measured magnetic flux density data. Using the measured data, we reconstructed a time series of 180 conductivity images at every 10.24 s during and after RF ablation.</P><P><I>Results</I>: Tissue conductivity values in the lesion increased with temperature during RF ablation. After reaching 60 °C, a steep increase in tissue conductivity values occurred with relatively little temperature increase. After RF ablation, tissue conductivity values in the lesion decreased with temperature, but to values different from those before ablation due to permanent structural changes of tissue by RF ablation.</P><P><I>Conclusion</I>: We could monitor temperature and also structural changes in tissue during RF ablation by producing spatio-temporal maps of tissue conductivity values using a fast MREIT conductivity imaging method. We expect that the new monitoring method could be used to estimate lesions during RF ablation and improve the efficacy of the treatment.</P>
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Dong-Hyun Kim,Chauhan, Munish,Min-Oh Kim,Woo Chul Jeong,Hyung Joong Kim,Sersa, Igor,Oh In Kwon,Eung Je Woo IEEE 2015 IEEE transactions on medical imaging Vol.34 No.2
<P>Electrical conductivities of biological tissues show frequency-dependent behaviors, and these values at different frequencies may provide clinically useful diagnostic information. MR-based tissue property mapping techniques such as magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance electrical property tomography (MREPT) are widely used and provide unique conductivity contrast information over different frequency ranges. Recently, a new method for data acquisition and reconstruction for low- and high-frequency conductivity images from a single MR scan was proposed. In this study, we applied this simultaneous dual-frequency range conductivity mapping MR method to evaluate its utility in a designed phantom and two in vivo animal disease models. Magnetic flux density and B1<SUP>+</SUP> phase map for dual-frequency conductivity images were acquired using a modified spin-echo pulse sequence. Low-frequency conductivity was reconstructed from MREIT data by the projected current density method, while high-frequency conductivity was reconstructed from MREPT data by B1<SUP>+</SUP> mapping. Two different conductivity phantoms comprising varying ion concentrations separated by insulating films with or without holes were used to study the contrast mechanism of the frequency-dependent conductivities related to ion concentration and mobility. Canine brain abscess and ischemia were used as in vivo models to evaluate the capability of the proposed method to identify new electrical properties-based contrast at two different frequencies. The simultaneous dual-frequency range conductivity mapping MR method provides unique contrast information related to the concentration and mobility of ions inside tissues. This method has potential to monitor dynamic changes of the state of disease.</P>
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Accelerating acquisition strategies for low-frequency conductivity imaging using MREIT
Song, Yizhuang,Seo, Jin Keun,Chauhan, Munish,Indahlastari, Aprinda,Ashok Kumar, Neeta,Sadleir, Rosalind IOP 2018 Physics in medicine & biology Vol.63 No.4
<P>We sought to improve efficiency of magnetic resonance electrical impedance tomography data acquisition so that fast conductivity changes or electric field variations could be monitored. Undersampling of k-space was used to decrease acquisition times in spin-echo-based sequences by a factor of two. Full MREIT data were reconstructed using continuity assumptions and preliminary scans gathered without current. We found that phase data were reconstructed faithfully from undersampled data. Conductivity reconstructions of phantom data were also possible. Therefore, undersampled k-space methods can potentially be used to accelerate MREIT acquisition. This method could be an advantage in imaging real-time conductivity changes with MREIT.</P>
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Zijun Meng,김형중,Saurav ZK Sajib,Munish Chauhan,Woo Chul Jeong,Young Tae Kim,우응제 대한의용생체공학회 2012 Biomedical Engineering Letters (BMEL) Vol.2 No.1
Purpose In performing human MREIT imaging experiments,we addressed two technical issues of the chemical shift artifact and measurement noise. In this study, we present improved conductivity images of in vivo human lower extremity using the chemical shift artifact correction and multi-echo methods. Methods To remove the chemical shift artifact in both MR magnitude and phase images, the three-point Dixon’s waterfat separation technique was modified for MREIT. Since the knee is more sensitive to injection currents, we limited the current amplitude in knee experiments to 3 mA to avoid painful sensation. We implemented this technique by incorporating a lately developed multi-echo based MREIT pulse sequence to enhance MR signals themselves and also by prolonging the total current injection time. Results Experimental results clearly show that the correction method effectively eliminates artifacts related with the chemical shift phenomenon in reconstructed conductivity images. The multi-echo method is advantageous in terms of SNR of MR magnitude, noise level of Bz compared with single-echo. The chemical shift artifact correction using multi-echo method allowed conductivity image reconstruction of the knee with 3 mA injection currents. Conclusions We expect that MREIT conductivity imaging incorporating both the chemical shift artifact correction and multi-echo pulse sequence would accelerate further experimental MREIT studies.
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Numerical Simulations of MREIT Conductivity Imaging for Brain Tumor Detection
Meng, Zi Jun,Sajib, Saurav Z. K.,Chauhan, Munish,Sadleir, Rosalind J.,Kim, Hyung Joong,Kwon, Oh In,Woo, Eung Je Hindawi Publishing Corporation 2013 Computational and mathematical methods in medicine Vol.2013 No.-
<P>Magnetic resonance electrical impedance tomography (MREIT) is a new modality capable of imaging the electrical properties of human body using MRI phase information in conjunction with external current injection. Recent <I>in vivo</I> animal and human MREIT studies have revealed unique conductivity contrasts related to different physiological and pathological conditions of tissues or organs. When performing <I>in vivo</I> brain imaging, small imaging currents must be injected so as not to stimulate peripheral nerves in the skin, while delivery of imaging currents to the brain is relatively small due to the skull's low conductivity. As a result, injected imaging currents may induce small phase signals and the overall low phase SNR in brain tissues. In this study, we present numerical simulation results of the use of head MREIT for brain tumor detection. We used a realistic three-dimensional head model to compute signal levels produced as a consequence of a predicted doubling of conductivity occurring within simulated tumorous brain tissues. We determined the feasibility of measuring these changes in a time acceptable to human subjects by adding realistic noise levels measured from a candidate 3 T system. We also reconstructed conductivity contrast images, showing that such conductivity differences can be both detected and imaged. </P>
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