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1.
Magn Reson Med ; 92(3): 967-981, 2024 Sep.
Article in English | MEDLINE | ID: mdl-38297511

ABSTRACT

PURPOSE: Hyperpolarized xenon MRI suffers from heterogeneous coil bias and magnetization decay that obscure pulmonary abnormalities. Non-physiological signal variability can be mitigated by measuring and mapping the nominal flip angle, and by rescaling the images to correct for signal bias and decay. While flip angle maps can be calculated from sequentially acquired images, scan time and breath-hold duration are doubled. Here, we exploit the low-frequency oversampling of 2D-spiral and keyhole reconstruction to measure flip angle maps from a single acquisition. METHODS: Flip angle maps were calculated from two images generated from a single dataset using keyhole reconstructions and a Bloch-equation-based model suitable for hyperpolarized substances. Artifacts resulting from acquisition and reconstruction schemes (e.g., keyhole reconstruction radius, slice-selection profile, spiral-ordering, and oversampling) were assessed using point-spread functions. Simulated flip angle maps generated using keyhole reconstruction were compared against the paired-image approach using RMS error (RMSE). Finally, feasibility was demonstrated for in vivo xenon ventilation imaging. RESULTS: Simulations demonstrated accurate flip angle maps and B1-inhomogeneity correction can be generated with only 1.25-fold central-oversampling and keyhole reconstruction radius = 5% (RMSE = 0.460°). These settings also generated accurate flip angle maps in a healthy control (RSME = 0.337°) and a person with cystic fibrosis (RMSE = 0.404°) in as little as 3.3 s. CONCLUSION: Regional lung ventilation images with reduced impact of B1-inhomogeneity can be acquired rapidly by combining 2D-spiral acquisition, Bloch-equation-based modeling, and keyhole reconstruction. This approach will be especially useful for breath-hold studies where short scan durations are necessary, such as dynamic imaging and applications in children or people with severely compromised respiratory function.


Subject(s)
Artifacts , Image Processing, Computer-Assisted , Lung , Magnetic Resonance Imaging , Xenon Isotopes , Humans , Magnetic Resonance Imaging/methods , Xenon Isotopes/chemistry , Image Processing, Computer-Assisted/methods , Lung/diagnostic imaging , Computer Simulation , Algorithms , Male , Female , Phantoms, Imaging , Adult , Breath Holding , Cystic Fibrosis/diagnostic imaging
2.
NMR Biomed ; 27(12): 1461-7, 2014 Dec.
Article in English | MEDLINE | ID: mdl-25208220

ABSTRACT

The purpose of this work was to assess the reproducibility of percentage of ventilated lung volume (PV) measured from hyperpolarized (HP) (3)He and (1)H anatomical images acquired in the same breath-hold when compared with PV measured from (3)He and (1)H images from separate breath-holds. Volumetric (3)He ventilation and (1)H anatomical images of the same resolution were acquired during the same breath-hold. To assess reproducibility, this procedure was performed twice with a short gap between acquisitions. In addition, (1)H images were also acquired in a separate breath for comparison. PV ((3)He ventilated volume divided by (1)H total lung volume) was calculated using the single-breath-hold images (PV(single)) and the separate-breath-hold images (PV(separate)). Short-term reproducibility of PV measurement was assessed for both single- and separate-breath acquisitions. Dice similarity coefficients (DSCs) were calculated to quantify spatial overlap between (3)He and (1)H segmentations for the single- and separate-breath-hold acquisitions. The efficacy of using the separate-breath method combined with image registration was also assessed. The mean magnitude difference between the two sets of PV values (±standard deviation) was 1.49 ± 1.32% for PV(single) and 4.19 ± 4.10% for PV(separate), with a significant difference (p < 0.01). The mean magnitude difference between the two PV values for the registered separate-breath technique (PV(sep-registered)) was 2.27 ± 2.23%. Bland-Altman analysis showed that PV measured with single-breath acquisitions was more repeatable than PV measured with separate-breath acquisitions, regardless of image registration. DSC values were significantly greater (p < 0.01) for single-breath acquisition than for separate-breath acquisition. Acquisition of HP gas ventilation and (1)H anatomical images in a single breath-hold provides a more reproducible means of percentage lung ventilation volume measurement than the previously used separate-breath-hold scan approach, and reduces errors.


Subject(s)
Helium , Lung Volume Measurements/methods , Magnetic Resonance Imaging , Protons , Pulmonary Ventilation/physiology , Respiration , Adult , Aged , Humans , Image Processing, Computer-Assisted , Middle Aged , Reproducibility of Results
3.
Magn Reson Med ; 69(2): 360-9, 2013 Feb.
Article in English | MEDLINE | ID: mdl-22473679

ABSTRACT

Adding prior knowledge to compressed sensing reconstruction can improve image reconstruction. In this work, two approaches are investigated to improve reconstruction of two-dimensional hyperpolarized (3)He lung ventilation images using prior knowledge. When compared against a standard compressed sensing reconstruction, the proposed methods allowed acquisition of images with higher under-sampling factors and reduction of the blurring effects that increase with higher reduction factors when fixed flip angles are used. These methods incorporate the prior knowledge of polarization decay of hyperpolarized (3)He and the mutual anatomical information from a registered (1)H image acquired in the same breath. Three times accelerated two-dimensional images reconstructed with compressed sensing and prior knowledge gave lower root-mean square error, than images reconstructed without introduction of any prior information. When introducing the polarization decay as prior knowledge, a significant improvement was achieved in the lung region, the root mean square value decreased by 45% and from the whole image by 36%. When introducing the mutual anatomical information as prior knowledge, the root mean square decreased by 21% over the lung region and by 15% over the whole image.


Subject(s)
Algorithms , Data Compression/methods , Helium , Image Interpretation, Computer-Assisted/methods , Lung/anatomy & histology , Magnetic Resonance Imaging/methods , Adult , Contrast Media , Female , Gases , Humans , Image Enhancement/methods , Isotopes , Male , Radiopharmaceuticals , Reproducibility of Results , Sensitivity and Specificity
4.
NMR Biomed ; 25(1): 44-51, 2012 Jan.
Article in English | MEDLINE | ID: mdl-22241670

ABSTRACT

In imaging of human lungs with hyperpolarised noble gases, measurements of apparent diffusion coefficient (ADC) and relaxation time provide valuable information for the assessment of lung microstructure. In this work, a sequence was developed for interleaved acquisition of ventilation images, ADC, T(2)* and flip angle maps in a single scan from the human lungs with a single dose of inhaled (3)He at 3 T. Spatially registered ventilation images with parametric maps were obtained. The total acquisition time was reduced by random undersampling of the k-space and reconstruction using compressed sensing (CS). The gain in speed was used for an increase in spatial resolution. Mean ADC values from the fully sampled and undersampled CS data exhibit no statistically significant difference in a given subject. The mean T(2)* values, however, were found to differ significantly, which is attributed to the combined effect of low signal-to-noise ratio (SNR) of the fully sampled data and the smoothing effect inherent in CS reconstruction.


Subject(s)
Helium , Image Processing, Computer-Assisted/methods , Magnetic Resonance Imaging/methods , Respiration , Adult , Anisotropy , Diffusion , Female , Health , Humans , Male
5.
Magn Reson Med ; 67(2): 322-5, 2012 Feb.
Article in English | MEDLINE | ID: mdl-22083758

ABSTRACT

The (3)He MR diffusion signal is sensitive to lung microstructure, but it is also affected by the presence of background field inhomogeneities induced by the magnetic susceptibility difference at the air-tissue interface. These susceptibility-induced gradients, which are dependent on field strength, have been assumed negligible in theoretical models used to extract airway morphometric information from (3)He MR diffusion data at field strengths up to 4.7 T. In this work, the effect of susceptibility gradients on (3)He apparent diffusion coefficient is demonstrated with experiments in healthy volunteers at two B(0) field strengths: 1.5 and 3 T. Apparent diffusion coefficient values obtained at 3 T were systematically larger than at 1.5 T, demonstrating that susceptibility effects are statistically significant even at clinical field strengths (B(0) ≤ 3 T) and introduce biases in the estimates of airway dimensions (e.g., mean linear intercept up to 17% larger at 3 T than 1.5 T). Susceptibility effects should be taken into account in the development of theoretical models of lung (3)He MR diffusion and considered when interpreting (3)He apparent diffusion coefficients obtained at different B(0).


Subject(s)
Diffusion Magnetic Resonance Imaging/methods , Image Processing, Computer-Assisted/methods , Lung/physiology , Administration, Inhalation , Adult , Algorithms , Artifacts , Computer Simulation , Gases , Helium , Humans , Isotopes , Lung Volume Measurements , Models, Theoretical , Reference Values , Signal-To-Noise Ratio
6.
J Magn Reson ; 204(2): 228-38, 2010 Jun.
Article in English | MEDLINE | ID: mdl-20347604

ABSTRACT

Models of lung acinar geometry have been proposed to analytically describe the diffusion of (3)He in the lung (as measured with pulsed gradient spin echo (PGSE) methods) as a possible means of characterizing lung microstructure from measurement of the (3)He ADC. In this work, major limitations in these analytical models are highlighted in simple diffusion weighted experiments with (3)He in cylindrical models of known geometry. The findings are substantiated with numerical simulations based on the same geometry using finite difference representation of the Bloch-Torrey equation. The validity of the existing "cylinder model" is discussed in terms of the physical diffusion regimes experienced and the basic reliance of the cylinder model and other ADC-based approaches on a Gaussian diffusion behaviour is highlighted. The results presented here demonstrate that physical assumptions of the cylinder model are not valid for large diffusion gradient strengths (above approximately 15 mT/m), which are commonly used for (3)He ADC measurements in human lungs.


Subject(s)
Helium/pharmacokinetics , Image Interpretation, Computer-Assisted/methods , Lung/anatomy & histology , Lung/metabolism , Magnetic Resonance Imaging/methods , Magnetic Resonance Spectroscopy/methods , Models, Biological , Computer Simulation , Helium/chemistry , Humans , Image Enhancement/methods , Isotopes/chemistry , Isotopes/pharmacokinetics , Magnetic Resonance Imaging/instrumentation , Phantoms, Imaging , Reproducibility of Results , Sensitivity and Specificity
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