1
|
Odéen H, Hofstetter LW, Payne AH, Guiraud L, Dumont E, Parker DL. Simultaneous proton resonance frequency T 1 - MR shear wave elastography for MR-guided focused ultrasound multiparametric treatment monitoring. Magn Reson Med 2023; 89:2171-2185. [PMID: 36656135 PMCID: PMC10940047 DOI: 10.1002/mrm.29587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 12/21/2022] [Accepted: 12/30/2022] [Indexed: 01/20/2023]
Abstract
PURPOSE To develop an efficient MRI pulse sequence to simultaneously measure multiple parameters that have been shown to correlate with tissue nonviability following thermal therapies. METHODS A 3D segmented EPI pulse sequence was used to simultaneously measure proton resonance frequency shift (PRFS) MR thermometry (MRT), T1 relaxation time, and shear wave velocity induced by focused ultrasound (FUS) push pulses. Experiments were performed in tissue mimicking gelatin phantoms and ex vivo bovine liver. Using a carefully designed FUS triggering scheme, a heating duty cycle of approximately 65% was achieved by interleaving FUS ablation pulses with FUS push pulses to induce shear waves in the tissue. RESULTS In phantom studies, temperature increases measured with PRFS MRT and increases in T1 correlated with decreased shear wave velocity, consistent with material softening with increasing temperature. During ablation in ex vivo liver, temperature increase measured with PRFS MRT initially correlated with increasing T1 and decreasing shear wave velocity, and after tissue coagulation with decreasing T1 and increasing shear wave velocity. This is consistent with a previously described hysteresis in T1 versus PRFS curves and increased tissue stiffness with tissue coagulation. CONCLUSION An efficient approach for simultaneous and dynamic measurements of PRSF, T1 , and shear wave velocity during treatment is presented. This approach holds promise for providing co-registered dynamic measures of multiple parameters, which correlates to tissue nonviability during and following thermal therapies, such as FUS.
Collapse
Affiliation(s)
- Henrik Odéen
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, USA
| | - Lorne W. Hofstetter
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, USA
| | - Allison H. Payne
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, USA
| | | | | | - Dennis L. Parker
- Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, USA
| |
Collapse
|
2
|
Parker DL, Payne A, Odéen H. A k-space-based method to measure and correct for temporal B 0 field variations in MR temperature imaging. Magn Reson Med 2022; 88:1098-1111. [PMID: 35576148 PMCID: PMC11034809 DOI: 10.1002/mrm.29275] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 03/29/2022] [Accepted: 04/01/2022] [Indexed: 11/10/2022]
Abstract
PURPOSE Present a method to use change in phase in repeated Cartesian k-space measurements to monitor the change in magnetic field for dynamic MR temperature imaging. METHODS The method is applied to focused ultrasound heating experiments in a gelatin phantom and an ex vivo salt pork sample, without and with simulated respiratory motion. RESULTS In each experiment, phase variations due to B0 field drift and respiration were readily apparent in the measured phase difference. With correction, the SD of the temperature over time was reduced from 0.18°C to 0.14°C (no breathing) and from 0.81°C to 0.22°C (with breathing) for the gelatin phantom, and from 0.68°C to 0.13°C (no breathing) and from 1.06°C to 0.17°C (with breathing) for the pork sample. The accuracy in nonheated regions, assessed as the RMS error deviation from 0°C, improved from 1.70°C to 1.11°C (no breathing) and from 4.73°C to 1.47°C (with breathing) for the gelatin phantom, and from 5.95°C to 0.88°C (no breathing) and from 13.40°C to 1.73°C (with breathing) for the pork sample. The correction did not affect the temperature measurement accuracy in the heated regions. CONCLUSION This work demonstrates that phase changes resulting from variations in B0 due to drift and respiration, commonly seen in MR thermometry applications, can be measured directly from 3D Cartesian acquisition methods. The correction of temporal field variations using the presented technique improved temperature accuracy, reduced variability in nonheated regions, and did not reduce accuracy in heated regions.
Collapse
Affiliation(s)
- Dennis L Parker
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, United States
| | - Allison Payne
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, United States
| | - Henrik Odéen
- Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, University of Utah, Salt Lake City, Utah, United States
| |
Collapse
|
3
|
McLean M, Parker DL, Odéen H, Payne A. A T1-based correction method for proton resonance frequency shift thermometry in breast tissue. Med Phys 2021; 48:4719-4729. [PMID: 34265109 DOI: 10.1002/mp.15085] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 05/30/2021] [Accepted: 06/01/2021] [Indexed: 11/06/2022] Open
Abstract
PURPOSE Develop and evaluate the effectiveness of a T1-based correction method for errors in proton resonant frequency shift thermometry due to non-local field effects caused by heating in fatty breast tissues. METHODS Computational models of human breast tissue were created by segmenting MRI data from a healthy human volunteer. MR-guided focused ultrasound (MRgFUS) heating and MR thermometry measurements were simulated in several locations in the heterogeneous segmented breast models. A T1-based correction method for PRF thermometry errors was applied and the maximum positive and negative errors and the root mean squared error (RMSE) in a region around each heating location was evaluated with and without correction. The method uses T1 measurements to estimate the temperature change in fatty tissues and correct for their influence. Experimental data from a heating study in cadaver breast tissue were analyzed, and the expected PRFS error computed. RESULTS The simulated MR thermometry had maximum single voxel errors ranging between 10% and 18% when no correction was applied. Applying the correction led to a considerable improvement, lowering the maximum error range to 2%-5%. The 5th to 95th percentile interval of the temperature error distribution was also lowered with correction, from approximately 3.5 to 1°C. This correction worked even when T1 times were uniformly raised or lowered by 5%-10%. The experimental data showed predicted errors of 15%. CONCLUSIONS This simulation study demonstrates that the T1-based correction method reduces MR thermometry errors due to non-local effects from heating in fatty tissues, potentially improving the accuracy of thermometry measurements during MRgFUS treatments. The presented correction method is reliant on having a patient-specific 3D model of the breast, and may be limited by the accuracy of the fat temperatures which in turn may be limited by noise or bias present in the T1 measurements.
Collapse
|
4
|
Zhang Y, Guo S, Zhang P, Zhong J, Liu W. Iron oxide magnetic nanoparticles based low-field MR thermometry. NANOTECHNOLOGY 2020; 31:345101. [PMID: 32408274 DOI: 10.1088/1361-6528/ab932b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
This paper reports on a highly accurate approach of magnetic resonance (MR) thermometry using iron oxide magnetic nanoparticles (MNPs) as temperature sensors. An empirical model for the description of the temperature dependent R 2 relaxation rate is proposed by taking into account the temperature sensitivity of the MNP magnetization. The temperature sensitivity of the MNP magnetization (η) and the temperature sensitivity of the R 2 relaxation rate (κ) are simulated with the proposed empirical models to investigate their dependence on the magnetic field and the particle size. Simulation results show the existence of optimal magnetic fields Hoη and Hoκ that maximize the temperature sensitivities η and κ. Furthermore, simulations and experiments demonstrate that the optimal magnetic field Hoη (Hoκ ) decreases with increasing the particle size. Experiments on temperature dependent R 2 relaxation rate are performed at different magnetic fields for MNP samples with different iron concentrations. Experimental results show that the proposed MR thermometry using MNPs as temperature sensors allows a temperature estimation accuracy of about 0.05 °C. We believe that the achieved approach of highly accurate MR thermometry is of great interest and significance to biomedicine and biology.
Collapse
Affiliation(s)
- Yapeng Zhang
- School of Artificial Intelligence and Automation, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China. Key Laboratory of Image Processing and Intelligent Control (Huazhong University of Science and Technology), Ministry of Education, Wuhan 430074, People's Republic of China
| | | | | | | | | |
Collapse
|
5
|
Faller TL, Trotier AJ, Rousseau AF, Franconi JM, Miraux S, Ribot EJ. 2D multislice MP2RAGE sequence for fast T 1 mapping at 7 T: Application to mouse imaging and MR thermometry. Magn Reson Med 2020; 84:1430-1440. [PMID: 32083341 DOI: 10.1002/mrm.28220] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 12/24/2019] [Accepted: 01/29/2020] [Indexed: 11/08/2022]
Abstract
PURPOSE To develop a 2D radial multislice MP2RAGE sequence for fast and reliable T1 mapping at 7 T in mice and for MR thermometry. METHODS The 2D-MP2RAGE sequence was performed with the following parameters: TI1 -TI2 -MP2RAGETR = 1000-3000-9000 ms. The multiple dead times within the sequence were used for interleaved multislice acquisition, enabling one to acquire six slices in 9 seconds. The excitation pulse shape, inversion selectivity, and interslice gap were optimized. In vitro comparison with the inversion-recovery sequence was performed. The T1 variations with temperature were measured on tubes with T1 ranging from 800 ms to 2000 ms. The sequence was used to acquire T1 maps continuously during 30 minutes on the brain and abdomen of healthy mice. RESULTS A three-lobe cardinal sine excitation pulse, combined with an inversion slice thickness and an interslice gap of respectively 150% and 50% of the imaging slice thickness, led to a SD and bias of the T1 measurements below 1% and 2%, respectively. A linear dependence of T1 with temperature was measured between 10°C and 60°C. In vivo, less than 1% variation was measured between successive T1 maps in the mouse brain. In the abdomen, no obvious in-plane motion artifacts were observed but respiratory motion in the slice dimension led to 6% T1 underestimation. CONCLUSION The multislice MP2RAGE sequence could be used for fast whole-body T1 mapping and MR thermometry. Its reconstruction method would enable on-the-fly reconstruction.
Collapse
Affiliation(s)
- Thibaut L Faller
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| | - Aurélien J Trotier
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| | - Alice F Rousseau
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| | - Jean-Michel Franconi
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| | - Sylvain Miraux
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| | - Emeline J Ribot
- Centre de Résonance Magnétique des Systèmes Biologiques, UMR 5536, CNRS/Université de Bordeaux, Bordeaux, France
| |
Collapse
|
6
|
Zhang L, Armstrong T, Li X, Wu HH. A variable flip angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonant frequency shift and T 1 -based thermometry. Magn Reson Med 2019; 82:2062-2076. [PMID: 31257639 DOI: 10.1002/mrm.27883] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 06/02/2019] [Accepted: 06/07/2019] [Indexed: 02/06/2023]
Abstract
PURPOSE To develop and evaluate a variable-flip-angle golden-angle-ordered 3D stack-of-radial MRI technique for simultaneous proton resonance frequency shift (PRF) and T1 -based thermometry in aqueous and adipose tissues, respectively. METHODS The proposed technique acquires multiecho radial k-space data in segments with alternating flip angles to measure 3D temperature maps dynamically on the basis of PRF and T1 . A sliding-window k-space weighted image contrast filter is used to increase temporal resolution. PRF is measured in aqueous tissues and T1 in adipose tissues using fat/water masks. The accuracy for T1 quantification was evaluated in a reference T1 /T2 phantom. In vivo nonheating experiments were conducted in healthy subjects to evaluate the stability of PRF and T1 in the brain, prostate, and breast. The proposed technique was used to monitor high-intensity focused ultrasound (HIFU) ablation in ex vivo porcine fat/muscle tissues and compared to temperature probe readings. RESULTS The proposed technique achieved 3D coverage with 1.1-mm to 1.3-mm in-plane resolution and 2-s to 5-s temporal resolution. During 20 to 30 min of nonheating in vivo scans, the temporal coefficient of variation for T1 was <5% in the brain, prostate, and breast fatty tissues, while the standard deviation of relative PRF temperature change was within 3°C in aqueous tissues. During ex vivo HIFU ablation, the temperatures measured by PRF and T1 were consistent with temperature probe readings, with an absolute mean difference within 2°C. CONCLUSION The proposed technique achieves simultaneous PRF and T1 -based dynamic 3D MR temperature mapping in aqueous and adipose tissues. It may be used to improve MRI-guided thermal procedures.
Collapse
Affiliation(s)
- Le Zhang
- Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California
| | - Tess Armstrong
- Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.,Physics in Biology and Medicine Interdepartmental Graduate Program, University of California Los Angeles, Los Angeles, California
| | - Xinzhou Li
- Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.,Department of Bioengineering, University of California Los Angeles, Los Angeles, California
| | - Holden H Wu
- Department of Radiological Sciences, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California.,Physics in Biology and Medicine Interdepartmental Graduate Program, University of California Los Angeles, Los Angeles, California.,Department of Bioengineering, University of California Los Angeles, Los Angeles, California
| |
Collapse
|
7
|
Odéen H, Parker DL. Magnetic resonance thermometry and its biological applications - Physical principles and practical considerations. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2019; 110:34-61. [PMID: 30803693 PMCID: PMC6662927 DOI: 10.1016/j.pnmrs.2019.01.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 01/23/2019] [Indexed: 05/25/2023]
Abstract
Most parameters that influence the magnetic resonance imaging (MRI) signal experience a temperature dependence. The fact that MRI can be used for non-invasive measurements of temperature and temperature change deep inside the human body has been known for over 30 years. Today, MR temperature imaging is widely used to monitor and evaluate thermal therapies such as radio frequency, microwave, laser, and focused ultrasound therapy. In this paper we cover the physical principles underlying the biological applications of MR temperature imaging and discuss practical considerations and remaining challenges. For biological tissue, the MR signal of interest comes mostly from hydrogen protons of water molecules but also from protons in, e.g., adipose tissue and various metabolites. Most of the discussed methods, such as those using the proton resonance frequency (PRF) shift, T1, T2, and diffusion only measure temperature change, but measurements of absolute temperatures are also possible using spectroscopic imaging methods (taking advantage of various metabolite signals as internal references) or various types of contrast agents. Currently, the PRF method is the most used clinically due to good sensitivity, excellent linearity with temperature, and because it is largely independent of tissue type. Because the PRF method does not work in adipose tissues, T1- and T2-based methods have recently gained interest for monitoring temperature change in areas with high fat content such as the breast and abdomen. Absolute temperature measurement methods using spectroscopic imaging and contrast agents often offer too low spatial and temporal resolution for accurate monitoring of ablative thermal procedures, but have shown great promise in monitoring the slower and usually less spatially localized temperature change observed during hyperthermia procedures. Much of the current research effort for ablative procedures is aimed at providing faster measurements, larger field-of-view coverage, simultaneous monitoring in aqueous and adipose tissues, and more motion-insensitive acquisitions for better precision measurements in organs such as the heart, liver, and kidneys. For hyperthermia applications, larger coverage, motion insensitivity, and simultaneous aqueous and adipose monitoring are also important, but great effort is also aimed at solving the problem of long-term field drift which gets interpreted as temperature change when using the PRF method.
Collapse
Affiliation(s)
- Henrik Odéen
- University of Utah, Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, 729 Arapeen Drive, Salt Lake City, UT 84108-1217, USA.
| | - Dennis L Parker
- University of Utah, Utah Center for Advanced Imaging Research, Department of Radiology and Imaging Sciences, 729 Arapeen Drive, Salt Lake City, UT 84108-1217, USA.
| |
Collapse
|
8
|
Svedin BT, Payne A, Parker DL. Simultaneous proton resonance frequency shift thermometry and T 1 measurements using a single reference variable flip angle T 1 method. Magn Reson Med 2019; 81:3138-3152. [PMID: 30652347 DOI: 10.1002/mrm.27643] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Revised: 11/20/2018] [Accepted: 11/29/2018] [Indexed: 12/31/2022]
Abstract
PURPOSE Implement simultaneous proton resonance frequency (PRF) shift and T1 measurements with equivalent temporal resolution using a single reference variable flip angle method. This novel method allows for simultaneous thermometry in both aqueous and fatty tissue. METHODS This method acquires a single reference image at the lower flip angle and all dynamic images at the higher angle. T1 is calculated using a single reference variable flip angle method, which accounts for the reference image temperature remaining constant. Monte Carlo simulations determined the optimal dynamic flip angle for combined PRF and T1 measurements. This method was evaluated in MR-guided focused ultrasound heating experiments using a gelatin phantom and human cadaver breasts. In vivo measurement precision was demonstrated in healthy female volunteers under nonheating conditions. RESULTS Temperature rise during MR-guided focused ultrasound heating was measured in aqueous tissue with both PRF and T1 . Both measures show good qualitative agreement in both space and time in aqueous tissue. The T1 change due to temperature increase was measured in fat, demonstrating the expected temporal response. The dynamic flip angle that produces optimal SNR for PRF measurements is lower than the optimal angle for T1 measurements, necessitating the selection of a compromise angle. CONCLUSION The single reference variable flip angle method provides a reliable way to simultaneously measure PRF temperature and T1 change and overcomes PRF's inability to simultaneously monitor temperature in aqueous and adipose tissues. Future work will calibrate T1 change to temperature, enabling real-time temperature in fat and increasing patient safety and treatment efficacy during thermal interventional treatments.
Collapse
Affiliation(s)
- Bryant T Svedin
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah
| | - Allison Payne
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah
| |
Collapse
|
9
|
Tudorancea I, Porumb V, Trandabăţ A, Neaga D, Tamba B, Iliescu R, Dimofte GM. New experimental model for single liver lobe hyperthermia in small animals using non-directional microwaves. PLoS One 2017; 12:e0184810. [PMID: 28934251 PMCID: PMC5608293 DOI: 10.1371/journal.pone.0184810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 08/31/2017] [Indexed: 11/19/2022] Open
Abstract
PURPOSE Our aim was to develop a new experimental model for in vivo hyperthermia using non-directional microwaves, applicable to small experimental animals. We present an affordable approach for targeted microwave heat delivery to an isolated liver lobe in rat, which allows rapid, precise and stable tissue temperature control. MATERIALS AND METHODS A new experimental model is proposed. We used a commercial available magnetron generating 2450 MHz, with 4.4V and 14A in the filament and 4500V anodic voltage. Modifications were required in order to adjust tissue heating such as to prevent overheating and to allow for fine adjustments according to real-time target temperature. The heating is controlled using a virtual instrument application implemented in LabView® and responds to 0.1° C variations in the target. Ten healthy adult male Wistar rats, weighing 250-270 g were used in this study. The middle liver lobe was the target for controlled heating, while the rest of the living animal was protected. RESULTS In vivo microwave delivery using our experimental setting is safe for the animals. Target tissue temperature rises from 30°C to 40°C with 3.375°C / second (R2 = 0.9551), while the increment is lower it the next two intervals (40-42°C and 42-44°C) with 0.291°C/ s (R2 = 0.9337) and 0.136°C/ s (R2 = 0.7894) respectively, when testing in sequences. After reaching the desired temperature, controlled microwave delivery insures a very stable temperature during the experiments. CONCLUSIONS We have developed an inexpensive and easy to manufacture system for targeted hyperthermia using non-directional microwave radiation. This system allows for fine and stable temperature adjustments within the target tissue and is ideal for experimental models testing below or above threshold hyperthermia.
Collapse
Affiliation(s)
- Ionuț Tudorancea
- Department of Physiology, Grigore T. Popa University of Medicine and Pharmacy, Iasi, Romania
| | - Vlad Porumb
- Department of Surgery, Grigore T. Popa University of Medicine and Pharmacy, Iasi, Romania
- Department of Surgery, Regional Institute of Oncology, Iasi, Romania
- * E-mail:
| | - Alexandru Trandabăţ
- Faculty of Electrical Engineering, Gheorghe Asachi Technical University, Iaşi, Romania
| | - Decebal Neaga
- Department of Engineering, Regional Institute of Oncology, Iasi, Romania
| | - Bogdan Tamba
- Department of Pharmacology, Grigore T. Popa University of Medicine and Pharmacy, Iasi, Romania
| | - Radu Iliescu
- Department of Pharmacology, Grigore T. Popa University of Medicine and Pharmacy, Iasi, Romania
| | - Gabriel M. Dimofte
- Department of Surgery, Grigore T. Popa University of Medicine and Pharmacy, Iasi, Romania
- Department of Surgery, Regional Institute of Oncology, Iasi, Romania
| |
Collapse
|
10
|
Svedin BT, Parker DL. Technical Note: The effect of 2D excitation profile on T1 measurement accuracy using the variable flip angle method with an average flip angle assumption. Med Phys 2017; 44:5930-5937. [PMID: 28796308 DOI: 10.1002/mp.12513] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 07/26/2017] [Accepted: 07/26/2017] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To study the accuracy and precision of T1 estimates using the Variable Flip Angle (VFA) method in 2D and 3D acquisitions. METHODS Excitation profiles were simulated using numerical implementation of the Bloch equations for Hamming-windowed sinc excitation pulses with different time-bandwidth products (TBP) of 2, 6, and 10 and for T1 values of 295 ms and 1045 ms. Experimental data were collected in 5° increments from 5° to 90° for the same T1 and TBP values. T1 was calculated for every combination of flip angle with and without a correction for B1 and slice profile variation. Calculations were also made for flat slice profile such as obtained in 3D acquisition. Monte Carlo simulations were performed to obtain T1 measurement uncertainty. RESULTS VFA T1 measurements in 2D without correction can result in a 40-80% underestimation of true T1 . Flip angle correction can reduce the underestimation, but results in accurate measurements of T1 only within a narrow band of flip angle combinations. The narrow band of accuracy increases with TBP, but remains too narrow for any practical range of T1 values or B1 variation. Simulated noisy VFA T1 measurements in 3D were accurate as long as the two angles chosen are on either side of the Ernst angle. CONCLUSIONS Accurate T1 estimates from VFA 2D acquisitions are possible, but only a narrow range of T1 values within a narrow range of flip angle combinations can be accurately calculated using a 2D slice. Unless a better flip angle correction method is used, these results demonstrate that accurate measurements of T1 in 2D cannot be obtained robustly enough for practical use and are more likely obtained by a thin slab 3D VFA acquisition than from multiple-slice 2D acquisitions. VFA T1 measurements in 3D are accurate for wide ranges of flip angle combinations and T1 values.
Collapse
Affiliation(s)
- Bryant T Svedin
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, USA
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, USA
| |
Collapse
|
11
|
Kardoulaki EM, Syms RRA, Young IR, Choonee K, Rea M, Gedroyc WMW. Optothermal profile of an ablation catheter with integrated microcoil for MR-thermometry during Nd:YAG laser interstitial thermal therapies of the liver—an in-vitro experimental and theoretical study. Med Phys 2016; 42:1389-97. [PMID: 25735293 DOI: 10.1118/1.4908225] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Flexible microcoils integrated with ablation catheters can improve the temperature accuracy during local MR-thermometry in Nd:YAG laser interstitial thermal therapies. Here, the authors are concerned with obtaining a preliminary confirmation of the clinical utility of the modified catheter. They investigate whether the thin-film substrate and copper tracks of the printed coil inductor affect the symmetry of the thermal profile, and hence of the lesion produced. METHODS Transmission spectroscopy in the near infrared was performed to test for the attenuation at 1064 nm through the 25 μm thick Kapton substrate of the microcoil. The radial transmission profile of an infrared high-power, light emitting diode with >80% normalized power at 1064 nm was measured through a cross section of the modified applicator to assess the impact of the copper inductor on the optical profile. The measurements were performed in air, as well as with the applicator surrounded by two types of scattering media; crystals of NaCl and a layer of liver-mimicking gel phantom. A numerical model based on Huygens-Fresnel principle and finite element simulations, using a commercially available package (COMSOL Multiphysics), were employed to compare with the optical measurements. The impact of the modified optical profile on the thermal symmetry was assessed by examining the high resolution microcoil derived thermal maps from a Nd:YAG laser ablation performed on a liver-mimicking gel phantom. RESULTS Less than 30% attenuation through the Kapton film was verified. Shadowing behind the copper tracks was observed in air and the measured radial irradiation correlated well with the diffraction pattern calculated numerically using the Huygens-Fresnel principle. Both optical experiments and simulations, demonstrate that shadowing is mitigated by the scattering properties of a turbid medium. The microcoil derived thermal maps at the end of a Nd:YAG laser ablation performed on a gel phantom in a 3 T scanner confirm that the modified irradiation pattern does not disrupt the thermal symmetry, even though, unlike tissue, the gel is minimally scattering. CONCLUSIONS The results from this initial assessment indicate that microcoils can be safely integrated with ablation catheters and ensure that the complete necrosis of the liver tumor can still be achieved.
Collapse
Affiliation(s)
- Evdokia M Kardoulaki
- Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Richard R A Syms
- Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Ian R Young
- Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Kaushal Choonee
- Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Marc Rea
- Department of Radiology, Imperial College Healthcare NHS Trust, Paddington, London W2 1NY, United Kingdom
| | - Wladyslaw M W Gedroyc
- Department of Radiology, Imperial College Healthcare NHS Trust, Paddington, London W2 1NY, United Kingdom
| |
Collapse
|
12
|
Odéen H, de Bever J, Almquist S, Farrer A, Todd N, Payne A, Snell JW, Christensen DA, Parker DL. Treatment envelope evaluation in transcranial magnetic resonance-guided focused ultrasound utilizing 3D MR thermometry. J Ther Ultrasound 2014; 2:19. [PMID: 25343028 PMCID: PMC4199783 DOI: 10.1186/2050-5736-2-19] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Accepted: 09/17/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Current clinical targets for transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) are all located close to the geometric center of the skull convexity, which minimizes challenges related to focusing the ultrasound through the skull bone. Non-central targets will have to be reached to treat a wider variety of neurological disorders and solid tumors. Treatment envelope studies utilizing two-dimensional (2D) magnetic resonance (MR) thermometry have previously been performed to determine the regions in which therapeutic levels of FUS can currently be delivered. Since 2D MR thermometry was used, very limited information about unintended heating in near-field tissue/bone interfaces could be deduced. METHODS In this paper, we present a proof-of-concept treatment envelope study with three-dimensional (3D) MR thermometry monitoring of FUS heatings performed in a phantom and a lamb model. While the moderate-sized transducer used was not designed for transcranial geometries, the 3D temperature maps enable monitoring of the entire sonication field of view, including both the focal spot and near-field tissue/bone interfaces, for full characterization of all heating that may occur. 3D MR thermometry is achieved by a combination of k-space subsampling and a previously described temporally constrained reconstruction method. RESULTS We present two different types of treatment envelopes. The first is based only on the focal spot heating-the type that can be derived from 2D MR thermometry. The second type is based on the relative near-field heating and is calculated as the ratio between the focal spot heating and the near-field heating. This utilizes the full 3D MR thermometry data achieved in this study. CONCLUSIONS It is shown that 3D MR thermometry can be used to improve the safety assessment in treatment envelope evaluations. Using a non-optimal transducer, it is shown that some regions where therapeutic levels of FUS can be delivered, as suggested by the first type of envelope, are not necessarily safely treated due to the amount of unintended near-field heating occurring. The results presented in this study highlight the need for 3D MR thermometry in tcMRgFUS.
Collapse
Affiliation(s)
- Henrik Odéen
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah 84108, USA
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
| | - Joshua de Bever
- School of Computing, University of Utah, Salt Lake City, Utah 84112, USA
| | - Scott Almquist
- School of Computing, University of Utah, Salt Lake City, Utah 84112, USA
| | - Alexis Farrer
- Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112, USA
| | - Nick Todd
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah 84108, USA
| | - Allison Payne
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah 84108, USA
| | - John W Snell
- Focused Ultrasound Foundation, Charlottesville, Virginia 22903, USA
- Department of Neurological Surgery, University of Virginia, Charlottesville, Virginia 22908, USA
| | - Douglas A Christensen
- Department of Bioengineering, University of Utah, Salt Lake City, Utah 84112, USA
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA
| | - Dennis L Parker
- Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah 84108, USA
| |
Collapse
|
13
|
Todd N, Diakite M, Payne A, Parker DL. In vivo evaluation of multi-echo hybrid PRF/T1 approach for temperature monitoring during breast MR-guided focused ultrasound surgery treatments. Magn Reson Med 2013; 72:793-9. [PMID: 24259398 DOI: 10.1002/mrm.24976] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Revised: 08/15/2013] [Accepted: 09/10/2013] [Indexed: 12/18/2022]
Abstract
PURPOSE To evaluate the precision of in vivo temperature measurements in adipose and glandular breast tissue using a multi-echo hybrid PRF/T1 pulse sequence. METHODS A high-bandwidth, multi-echo hybrid PRF/T1 sequence was developed for monitoring temperature changes simultaneously in fat- and water-based tissues. The multiple echoes were combined with the optimal weightings for magnitude and phase images, allowing for precise measurement of both T1 and the proton resonance frequency (PRF) shift. The sequence was tested during in vivo imaging of 10 healthy volunteers in a breast-specific MR-guided focused ultrasound system and also during focused ultrasound heating of excised breast adipose tissue. RESULTS The in vivo results indicated that the sequence can measure PRF temperatures with 1.25 × 1.25 × 3.5 mm resolution, 1.9 s temporal resolution, and 1.0°C temperature precision, and can measure T1 values with 3.75 × 3.75 × 3.5 mm resolution, 3.8 s temporal resolution, and 2.5%-4.8% precision. The excised tissue heating experiments demonstrate the sequence's ability to monitor temperature changes simultaneously in water- and fat-based tissues. CONCLUSION The addition of a high-bandwidth, multi-echo readout to the hybrid PRF/T1 sequence improves the precision of each measurement, providing a sequence that will be beneficial to several MR-guided thermal therapies.
Collapse
Affiliation(s)
- Nick Todd
- Department of Radiology, University of Utah, Salt Lake City, Utah, USA
| | | | | | | |
Collapse
|
14
|
Parker DL, Payne A, Todd N, Hadley JR. Phase reconstruction from multiple coil data using a virtual reference coil. Magn Reson Med 2013; 72:563-9. [PMID: 24006172 DOI: 10.1002/mrm.24932] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 07/30/2013] [Accepted: 07/30/2013] [Indexed: 12/11/2022]
Abstract
PURPOSE This study develops a method to obtain optimal estimates of absolute magnetization phase from multiple-coil MRI data. THEORY AND METHODS The element-specific phases of a multi-element receiver coil array are accounted for by using the phase of a real or virtual reference coil that is sensitive over the entire imaged volume. The virtual-reference coil is generated as a weighted combination of measurements from all receiver coils. The phase-corrected multiple coil complex images are combined using the inverse covariance matrix. These methods are tested on images of an agar phantom, an in vivo breast, and an anesthetized rabbit obtained using combinations of four, nine, and three receiver channels, respectively. RESULTS The four- and three-channel acquisitions require formation of a virtual-reference receiver coil while one channel of the nine-channel receive array has a sensitivity profile covering the entire imaged volume. Referencing to a real or virtual coil gives receiver phases that are essentially identical except for the individual receiver channel noise. The resulting combined images, which account for receiver channel noise covariance, show the expected reduction in phase variance. CONCLUSION The proposed virtual reference coil method determines a phase distribution for each coil from which an optimal phase map can be obtained.
Collapse
Affiliation(s)
- Dennis L Parker
- Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, USA
| | | | | | | |
Collapse
|