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Perron S, Ouriadov A, Wawrzyn K, Hickling S, Fox MS, Serrai H, Santyr G. Application of a 2D frequency encoding sectoral approach to hyperpolarized 129Xe MRI at low field. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 336:107159. [PMID: 35183921 DOI: 10.1016/j.jmr.2022.107159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 01/05/2022] [Accepted: 01/27/2022] [Indexed: 06/14/2023]
Abstract
Inhaled hyperpolarized 129Xe MRI is a non-invasive and radiation risk free lung imaging method, which can directly measure the business unit of the lung where gas exchange occurs: the alveoli and acinar ducts (lung function). Currently, three imaging approaches have been demonstrated to be useful for hyperpolarized 129Xe MR in lungs: Fast Gradient Recalled Echo (FGRE), Radial Projection Reconstruction (PR), and spiral/cones. Typically, non-Cartesian acquisitions such as PR and spiral/cones require specific data post-processing, such as interpolating, regridding, and density-weighting procedures for image reconstruction, which often leads to smoothing effects and resolution degradation. On the other hand, Cartesian methods such as FGRE are not short-echo time (TE) methods; they suffer from imaging gradient-induced diffusion-weighting of the k-space center, and employ a significant number of radio-frequency (RF) pulses. Due to the non-renewable magnetization of the hyperpolarized media, the use of a large number of RF pulses (FGRE/PR) required for full k-space coverage is a significant limitation, especially for low field (<0.5 T) hyperpolarized gas MRI. We demonstrate an ultra-fast, purely frequency-encoded, Cartesian pulse sequence called Frequency-Encoding Sectoral (FES), which takes advantage of the long T2* of hyperpolarized 129Xe gas at low field strength (0.074 T). In contrast to PR/FGRE, it uses a much smaller number of RF pulses, and consequently maximizes image Signal-to-Noise Ratio (SNR) while shortening acquisition time. Additionally, FES does not suffer from non-uniform T2* decay leading to image blurring; a common issue with interleaved spirals/cones. The Cartesian k-space coverage of the proposed FES method does not require specific k-space data post-processing, unlike PR/FGRE and spiral/cones methods. Proton scans were used to compare the FES sequence to both FGRE and Phase Encoding Sectoral, in terms of their SNR values and imaging efficiency estimates. Using FES, proton and hyperpolarized 129Xe images were acquired from a custom hollow acrylic phantom (0.04L) and two normal rats (129Xe only), utilizing both single-breath and multiple-breath schemes. For the 129Xe phantom images, the apparent diffusion coefficient, T1, and T2* relaxation maps were acquired and generated. Blurring due to the T2* decay and B0 field variation were simulated to estimate dependence of the image resolution on the duration of the data acquisition windows (i.e. sector length), and temperature-induced resonance frequency shift from the low field magnet hardware.
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Affiliation(s)
- Samuel Perron
- Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada
| | - Alexei Ouriadov
- Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada; School of Biomedical Engineering, Faculty of Engineering, The University of Western Ontario, London, ON, Canada.
| | - Krzysztof Wawrzyn
- Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada
| | | | - Matthew S Fox
- Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada; Lawson Health Research Institute, London, Ontario, Canada
| | - Hacene Serrai
- Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada
| | - Giles Santyr
- Translational Medicine Program, Peter Gilgan Centre for Research and Learning, The Hospital for Sick Children, Toronto, ON, Canada; Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
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Abstract
The use of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the clinical setting enables the acquisition of valuable anatomical information in a rapid, non-invasive fashion. However, MRI applications for identifying disease-related biomarkers are limited due to low sensitivity at clinical magnetic field strengths. The development of hyperpolarized (hp) 129Xe MRI/MRS techniques as complements to traditional 1H-based imaging has been a burgeoning area of research over the past two decades. Pioneering experiments have shown that hp 129Xe can be encapsulated within host molecules to generate ultrasensitive biosensors. In particular, xenon has high affinity for cryptophanes, which are small organic cages that can be functionalized with affinity tags, fluorophores, solubilizing groups, and other moieties to identify biomedically relevant analytes. Cryptophane sensors designed for proteins, metal ions, nucleic acids, pH, and temperature have achieved nanomolar-to-femtomolar limits of detection via a combination of 129Xe hyperpolarization and chemical exchange saturation transfer (CEST) techniques. This review aims to summarize the development of cryptophane biosensors for 129Xe MRI applications, while highlighting innovative biosensor designs and the consequent enhancements in detection sensitivity, which will be invaluable in expanding the scope of 129Xe MRI. This review aims to summarize the development of cryptophane biosensors for 129Xe MRI applications, while highlighting innovative biosensor designs and the consequent enhancements in detection sensitivity, which will be invaluable in expanding the scope of 129Xe MRI.![]()
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Affiliation(s)
- Serge D Zemerov
- Department of Chemistry, University of Pennsylvania, 231 South 34 St., Philadelphia, PA 19104-6323, USA
| | - Ivan J Dmochowski
- Department of Chemistry, University of Pennsylvania, 231 South 34 St., Philadelphia, PA 19104-6323, USA
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Adams CJ, Capaldi DPI, Di Cesare R, McCormack DG, Parraga G. On the Potential Role of MRI Biomarkers of COPD to Guide Bronchoscopic Lung Volume Reduction. Acad Radiol 2018; 25:159-168. [PMID: 29051040 DOI: 10.1016/j.acra.2017.08.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 08/23/2017] [Accepted: 08/26/2017] [Indexed: 01/08/2023]
Abstract
RATIONALE AND OBJECTIVES In patients with severe emphysema and poor quality of life, bronchoscopic lung volume reduction (BLVR) may be considered and guided based on lobar emphysema severity. In particular, x-ray computed tomography (CT) emphysema measurements are used to identify the most diseased and the second-most diseased lobes as BLVR targets. Inhaled gas magnetic resonance imaging (MRI) also provides chronic obstructive pulmonary disease (COPD) biomarkers of lobar emphysema and ventilation abnormalities. Our objective was to retrospectively evaluate CT and MRI biomarkers of lobar emphysema and ventilation in patients with COPD eligible for BLVR. We hypothesized that MRI would provide complementary biomarkers of emphysema and ventilation that help determine the most appropriate lung lobar targets for BLVR in patients with COPD. MATERIALS AND METHODS We retrospectively evaluated 22 BLVR-eligible patients from the Thoracic Imaging Network of Canada cohort (diffusing capacity of the lung for carbon monoxide = 37 ± 12%predicted, forced expiratory volume in 1 second = 34 ± 7%predicted, total lung capacity = 131 ± 17%predicted, and residual volume = 216 ± 36%predicted). Lobar CT emphysema, measured using a relative area of <-950 Hounsfield units (RA950) and MRI ventilation defect percent, was independently used to rank lung lobe disease severity. RESULTS In 7 of 22 patients, there were different CT and MRI predictions of the most diseased lobe. In some patients, there were large ventilation defects in lobes not targeted by CT, indicative of a poorly ventilated lung. CT and MRI classification of the most diseased and the second-most diseased lobes showed a fair-to-moderate intermethod reliability (Cohen κ = 0.40-0.59). CONCLUSIONS In this proof-of-concept retrospective analysis, quantitative MRI ventilation and CT emphysema measurements provided different BLVR targets in over 30% of the patients. The presence of large MRI ventilation defects in lobes next to CT-targeted lobes might also change the decision to proceed or to guide BLVR to a different lobar target.
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Affiliation(s)
- Colin J Adams
- Robarts Research Institute, Western University, 1151 Richmond Street N, London, ON N6A 5B7, Canada; Department of Medicine, Western University, London, Ontario, Canada
| | - Dante P I Capaldi
- Robarts Research Institute, Western University, 1151 Richmond Street N, London, ON N6A 5B7, Canada; Department of Medical Biophysics, Western University, London, Ontario, Canada
| | - Robert Di Cesare
- Robarts Research Institute, Western University, 1151 Richmond Street N, London, ON N6A 5B7, Canada
| | | | - Grace Parraga
- Robarts Research Institute, Western University, 1151 Richmond Street N, London, ON N6A 5B7, Canada; Department of Medical Biophysics, Western University, London, Ontario, Canada.
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