1
|
Çan MK, Ider YZ. Bias correction for phase-based cr-MREPT using low resolution B1+ magnitude. Phys Med Biol 2024; 69:125020. [PMID: 38830364 DOI: 10.1088/1361-6560/ad53a1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 06/03/2024] [Indexed: 06/05/2024]
Abstract
ObjectiveFull-form Magnetic Resonance Electrical Properties Tomography (MREPT) requires bothB1+magnitude and phase information. SinceB1+phase can be obtained faster and with higher SNR compared toB1+magnitude, several phase-based methods have been developed for conductivity imaging. However, phase-based methods suffer from a concave bias due to the assumption that∇|B1+|is negligible in the ROI.ApproachIn this paper, we re-derive the central equation of phase-based cr-MREPT without assuming that∇|B1+|is negligible and thus propose a correction method directly integrated into the equation system.Main resultsProposed method successfully corrects the concave bias on both simulated and experimental data and significantly increases image quality.SignificanceThe proposed correction method depends on a very low-resolution|B1+|map, and therefore the imaging time does not increase significantly for obtainingB1+magnitude. Moreover, correction can be achieved using simulatedB1+magnitude, hence completely removing the additional imaging requirement.
Collapse
Affiliation(s)
- Mustafa Kaan Çan
- Department of Electrical and Electronics Engineering, Bilkent University, 06800 Ankara, Turkey
| | - Yusuf Ziya Ider
- Department of Biomedical Engineering, Başkent University, 06790 Ankara, Turkey
| |
Collapse
|
2
|
Yildiz G, Ider YZ. Use of dielectric padding to eliminate low convective field artifact in cr-MREPT conductivity images. Magn Reson Med 2019; 81:3168-3184. [PMID: 30693565 DOI: 10.1002/mrm.27648] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Revised: 12/05/2018] [Accepted: 12/05/2018] [Indexed: 11/07/2022]
Abstract
PURPOSE Convection-reaction equation-based magnetic resonance electrical properties tomography (cr-MREPT) provides conductivity images that are boundary artifact-free and robust against noise. However, these images suffer from the low convective field (LCF) artifact. We propose to use dielectric pads to alter the transmit magnetic field (B1 + ), shift the LCF region, and eliminate the LCF artifact. METHODS Computer simulations were conducted to analyze the effects of pad electrical properties, pad thickness, pad height, arc angle, and thickness of the pad-object gap. In 3T MR experiments, water pads and BaTiO3 pads were used with agar-saline phantoms. Two data sets (e.g., with the pad located on the left or on the right of the object [phantom]) were acquired, and the corresponding linear systems were simultaneously solved to get LCF artifact-free conductivity images. RESULTS A pad needed to have 180° arc angle and the same height with the phantom for maximum benefit. Increasing the pad thickness and/or the relative permittivity of the pad increased the LCF shift, whereas excessive amounts of these parameters caused errors in conductivity reconstructions because the effect of neglected Bz terms became noticeable. Conductivity of the pad, on the other hand, had minimal effect on elimination of the LCF artifact. Combining 2 data sets (i.e., with 2 different dielectric pad positions) resulted in more accurate conductivity maps (low L2 -errors) as opposed to no pad or single pad cases in experiments and simulations. CONCLUSIONS Using the proposed technique, LCF artifact is significantly removed, and the reconstructed conductivity values are improved.
Collapse
Affiliation(s)
- Gulsah Yildiz
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Yusuf Ziya Ider
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| |
Collapse
|
3
|
Song Y, Seo JK, Chauhan M, Indahlastari A, Ashok Kumar N, Sadleir R. Accelerating acquisition strategies for low-frequency conductivity imaging using MREIT. Phys Med Biol 2018; 63:045011. [PMID: 29345626 DOI: 10.1088/1361-6560/aaa8d2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
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.
Collapse
Affiliation(s)
- Yizhuang Song
- School of Mathematics and Statistics, Institute of Data Science and Technology, Shandong Normal University, Jinan, Shandong, 250014, People's Republic of China
| | | | | | | | | | | |
Collapse
|
4
|
Lee H, Sohn CH, Park J. Current-induced alternating reversed dual-echo-steady-state for joint estimation of tissue relaxation and electrical properties. Magn Reson Med 2016; 78:107-120. [DOI: 10.1002/mrm.26350] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 06/27/2016] [Accepted: 06/29/2016] [Indexed: 11/05/2022]
Affiliation(s)
- Hyunyeol Lee
- Biomedical Imaging and Engineering Lab, Department of Biomedical Engineering; Sungkyunkwan University; Suwon Republic of Korea
| | - Chul-Ho Sohn
- Department of Radiology; Seoul National University Hospital; Seoul Republic of Korea
| | - Jaeseok Park
- Biomedical Imaging and Engineering Lab, Department of Biomedical Engineering; Sungkyunkwan University; Suwon Republic of Korea
| |
Collapse
|
5
|
Oran OF, Ider YZ. Feasibility of conductivity imaging using subject eddy currents induced by switching of MRI gradients. Magn Reson Med 2016; 77:1926-1937. [PMID: 27364521 DOI: 10.1002/mrm.26283] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Revised: 04/28/2016] [Accepted: 04/28/2016] [Indexed: 01/19/2023]
Abstract
PURPOSE To investigate the feasibility of low-frequency conductivity imaging based on measuring the magnetic field due to subject eddy currents induced by switching of MRI z-gradients. METHODS We developed a simulation model for calculating subject eddy currents and the magnetic fields they generate (subject eddy fields). The inverse problem of obtaining conductivity distribution from subject eddy fields was formulated as a convection-reaction partial differential equation. For measuring subject eddy fields, a modified spin-echo pulse sequence was used to determine the contribution of subject eddy fields to MR phase images. RESULTS In the simulations, successful conductivity reconstructions were obtained by solving the derived convection-reaction equation, suggesting that the proposed reconstruction algorithm performs well under ideal conditions. However, the level of the calculated phase due to the subject eddy field in a representative object indicates that this phase is below the noise level and cannot be measured with an uncertainty sufficiently low for accurate conductivity reconstruction. Furthermore, some artifacts other than random noise were observed in the measured phases, which are discussed in relation to the effects of system imperfections during readout. CONCLUSION Low-frequency conductivity imaging does not seem feasible using basic pulse sequences such as spin-echo on a clinical MRI scanner. Magn Reson Med 77:1926-1937, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Omer Faruk Oran
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Yusuf Ziya Ider
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| |
Collapse
|
6
|
Balidemaj E, Kok HP, Schooneveldt G, van Lier ALHMW, Remis RF, Stalpers LJA, Westerveld H, Nederveen AJ, van den Berg CAT, Crezee J. Hyperthermia treatment planning for cervical cancer patients based on electrical conductivity tissue properties acquired in vivo with EPT at 3 T MRI. Int J Hyperthermia 2016; 32:558-68. [PMID: 26982889 DOI: 10.3109/02656736.2015.1129440] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Introduction The reliability of hyperthermia treatment planning (HTP) is strongly dependent on the accuracy of the electric properties of each tissue. The values currently used are mostly based on ex vivo measurements. In this study, in vivo conductivity of human muscle, bladder content and cervical tumours, acquired with magnetic resonance-based electric properties tomography (MR-EPT), are exploited to investigate the effect on HTP for cervical cancer patients. Methods Temperature-based optimisation of five different patients was performed using literature-based conductivity values yielding certain antenna settings, which are then used to compute the temperature distribution of the patient models with EPT-based conductivity values. Furthermore, the effects of altered bladder and muscle conductivity were studied separately. Finally, the temperature-based optimisation was performed with patient models based on EPT conductivity values. Results The tumour temperatures for all EPT-based dielectric patient models were lower compared to the optimal tumour temperatures based on literature values. The largest deviation was observed for patient 1 with ΔT90 = -1.37 °C. A negative impact was also observed when the treatment was optimised based on the EPT values. For four patients ΔT90 was less than 0.6 °C; for one patient it was 1.5 °C. Conclusions Electric conductivity values acquired by EPT are higher than commonly used from literature. This difference has a substantial impact on cervical tumour temperatures achieved during hyperthermia. A higher conductivity in the bladder and in the muscle tissue surrounding the tumour leads to higher power dissipation in the bladder and muscle, and therefore to lower tumour temperatures.
Collapse
Affiliation(s)
- Edmond Balidemaj
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | - Henny Petra Kok
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | - Gerben Schooneveldt
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | | | - Rob F Remis
- c Circuits and Systems Group, Delft Technical University Technical University , Delft , Netherlands
| | - Lukas J A Stalpers
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | - Henrike Westerveld
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | - Aart J Nederveen
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| | | | - Johannes Crezee
- a Department of Radiation Oncology , Academic Medical Centre , Meibergdreef 9 , Amsterdam , 1105 AZ Netherlands
| |
Collapse
|
7
|
Gurler N, Ider YZ. Gradient-based electrical conductivity imaging using MR phase. Magn Reson Med 2016; 77:137-150. [PMID: 26762771 DOI: 10.1002/mrm.26097] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Revised: 11/27/2015] [Accepted: 11/27/2015] [Indexed: 11/07/2022]
Abstract
PURPOSE To develop a fast, practically applicable, and boundary artifact free electrical conductivity imaging method that does not use transceive phase assumption, and that is more robust against the noise. THEORY Starting from the Maxwell's equations, a new electrical conductivity imaging method that is based solely on the MR transceive phase has been proposed. Different from the previous phase based electrical properties tomography (EPT) method, a new formulation was derived by including the gradients of the conductivity into the equations. METHODS The governing partial differential equation, which is in the form of a convection-reaction-diffusion equation, was solved using a three-dimensional finite-difference scheme. To evaluate the performance of the proposed method numerical simulations, phantom and in vivo human experiments have been conducted at 3T. RESULTS Simulation and experimental results of the proposed method and the conventional phase-based EPT method were illustrated to show the superiority of the proposed method over the conventional method, especially in the transition regions and under noisy data. CONCLUSION With the contributions of the proposed method to the phase-based EPT approach, a fast and reliable electrical conductivity imaging appears to be feasible, which is promising for clinical diagnoses and local SAR estimation. Magn Reson Med 77:137-150, 2017. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Necip Gurler
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Yusuf Ziya Ider
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| |
Collapse
|
8
|
Current density imaging sequence for monitoring current distribution during delivery of electric pulses in irreversible electroporation. Biomed Eng Online 2015; 14 Suppl 3:S6. [PMID: 26356233 PMCID: PMC4565567 DOI: 10.1186/1475-925x-14-s3-s6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Background Electroporation is gaining its importance in everyday clinical practice of cancer treatment. For its success it is extremely important that coverage of the target tissue, i.e. treated tumor, with electric field is within the specified range. Therefore, an efficient tool for the electric field monitoring in the tumor during delivery of electroporation pulses is needed. The electric field can be reconstructed by the magnetic resonance electric impedance tomography method from current density distribution data. In this study, the use of current density imaging with MRI for monitoring current density distribution during delivery of irreversible electroporation pulses was demonstrated. Methods Using a modified single-shot RARE sequence, where four 3000 V and 100 μs long pulses were included at the start, current distribution between a pair of electrodes inserted in a liver tissue sample was imaged. Two repetitions of the sequence with phases of refocusing radiofrequency pulses 90° apart were needed to acquire one current density image. For each sample in total 45 current density images were acquired to follow a standard protocol for irreversible electroporation where 90 electric pulses are delivered at 1 Hz. Results Acquired current density images showed that the current density in the middle of the sample increased from first to last electric pulses by 60%, i.e. from 8 kA/m2 to 13 kA/m2 and that direction of the current path did not change with repeated electric pulses significantly. Conclusions The presented single-shot RARE-based current density imaging sequence was used successfully to image current distribution during delivery of short high-voltage electric pulses. The method has a potential to enable monitoring of tumor coverage by electric field during irreversible electroporation tissue ablation.
Collapse
|
9
|
Rossmann C, Haemmerich D. Review of temperature dependence of thermal properties, dielectric properties, and perfusion of biological tissues at hyperthermic and ablation temperatures. Crit Rev Biomed Eng 2014; 42:467-92. [PMID: 25955712 PMCID: PMC4859435 DOI: 10.1615/critrevbiomedeng.2015012486] [Citation(s) in RCA: 156] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The application of supraphysiological temperatures (>40°C) to biological tissues causes changes at the molecular, cellular, and structural level, with corresponding changes in tissue function and in thermal, mechanical and dielectric tissue properties. This is particularly relevant for image-guided thermal treatments (e.g. hyperthermia and thermal ablation) delivering heat via focused ultrasound (FUS), radiofrequency (RF), microwave (MW), or laser energy; temperature induced changes in tissue properties are of relevance in relation to predicting tissue temperature profile, monitoring during treatment, and evaluation of treatment results. This paper presents a literature survey of temperature dependence of electrical (electrical conductivity, resistivity, permittivity) and thermal tissue properties (thermal conductivity, specific heat, diffusivity). Data of soft tissues (liver, prostate, muscle, kidney, uterus, collagen, myocardium and spleen) for temperatures between 5 to 90°C, and dielectric properties in the frequency range between 460 kHz and 3 GHz are reported. Furthermore, perfusion changes in tumors including carcinomas, sarcomas, rhabdomyosarcoma, adenocarcinoma and ependymoblastoma in response to hyperthmic temperatures up to 46°C are presented. Where appropriate, mathematical models to describe temperature dependence of properties are presented. The presented data is valuable for mathematical models that predict tissue temperature during thermal therapies (e.g. hyperthermia or thermal ablation), as well as for applications related to prediction and monitoring of temperature induced tissue changes.
Collapse
Affiliation(s)
- Christian Rossmann
- Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina, USA
| | - Dieter Haemmerich
- Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina, USA; Department of Bioengineering, Clemson University, Clemson, South Carolina, USA
| |
Collapse
|