To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE)... more To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice. Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison. An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1-4) and the...
Magnetic Resonance Materials in Physics, Biology and Medicine, 2015
This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might ... more This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might reach acoustic noise levels of over 100 dB(A) in clinical practice. A diffusion-weighted readout-segmented echo-planar imaging (EPI) sequence was optimized for acoustic noise by utilizing small readout segment widths to obtain low gradient slew rates and amplitudes instead of faster k-space coverage. In addition, all other gradients were optimized for low slew rates. Volunteer and patient imaging experiments were conducted to demonstrate the feasibility of the method. Acoustic noise measurements were performed and analyzed for four different DWI measurement protocols at 1.5T and 3T. An acoustic noise reduction of up to 20 dB(A) was achieved, which corresponds to a fourfold reduction in acoustic perception. The image quality was preserved at the level of a standard single-shot (ss)-EPI sequence, with a 27-54 % increase in scan time. The diffusion-weighted imaging technique proposed in this study allowed a substantial reduction in the level of acoustic noise compared to standard single-shot diffusion-weighted EPI. This is expected to afford considerably more patient comfort, but a larger study would be necessary to fully characterize the subjective changes in patient experience.
Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for... more Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for efficient banding artifact removal in bSSFP imaging. Based on a varying radiofrequency (RF) phase-increment in combination with a radial trajectory, DYPR-SSFP allows obtaining a banding-free image out of a single acquired k-space. The purpose of this work is to present an extension of this technique, enabling fast three-dimensional isotropic banding-free bSSFP imaging. While banding artifact removal with DYPR-SSFP relies on the applied dynamic phase-cycle, this aspect can lead to artifacts, at least when the number of acquired projections lies below a certain limit. However, by using a 3D radial trajectory with quasi-random view ordering for image acquisition, this problem is intrinsically solved, enabling 3D DYPR-SSFP imaging at or even below the Nyquist criterion. The approach is validated for brain and knee imaging at 3 Tesla. Volumetric, banding-free images were obtained in clinically acceptable scan times with an isotropic resolution up to 0.56mm. The combination of DYPR-SSFP with a 3D radial trajectory allows banding-free isotropic volumetric bSSFP imaging with no expense of scan time. Therefore, this is a promising candidate for clinical applications such as imaging of cranial nerves or articular cartilage.
Recently, the (Resolution Enhanced-) T1 insensitive steady-state imaging (TOSSI) approach has bee... more Recently, the (Resolution Enhanced-) T1 insensitive steady-state imaging (TOSSI) approach has been proposed for the fast acquisition of T2 -weighted images. This has been achieved by balanced steady-state free precession (bSSFP) imaging between unequally spaced inversion pulses. The purpose of this work is to present an extension of this technique, considerably increasing both the efficiency and possibilities of TOSSI. A radial trajectory in combination with an appropriate view-sharing reconstruction is used. Because each projection traverses the contrast defining k-space center, several different contrasts can be extracted from a single-shot measurement. These contrasts include various T2 -weightings and T2 /T1 -weighting if an even number of inversion pulses is used, while an odd number allow the generation of several images with predefined tissue types cancelled. The approach is validated for brain and abdominal imaging at 3.0 Tesla. Results are compared with RE-TOSSI, bSSFP, and...
Introduction: The application of the basic Cartesian GRAPPA [1] reconstruction algorithm requires... more Introduction: The application of the basic Cartesian GRAPPA [1] reconstruction algorithm requires regular, symmetric undersampled data. Non-Cartesian sampling schemes, such as radial or spiral trajectories, do not fulfill this requirement. Therefore, special reconstruction and/or data reordering procedures are necessary. In all previous methods, the GRAPPA reconstruction is performed first on the reordered data, followed by regridding of the reconstructed data onto a Cartesian grid [2-5]. However, if the undersampled non-Cartesian data are first regridded, the inherent symmetry of the acquisition scheme can be used to define several Cartesian patterns in the regridded data which can be used for reconstruction. Examining specifically the spiral case, the regridded undersampled k-space can be divided into several "sectors," where each sector can be reconstructed with a specific Cartesian pattern. The reconstruction for each sector is then identical to a Cartesian GRAPPA reco...
Introduction Since the first phased array design, the overlap decoupling became the most often us... more Introduction Since the first phased array design, the overlap decoupling became the most often used decoupling technique. At a certain amount of overlap, the mutual inductance between adjacent array coil elements is forced to be zero. Therefore the interaction between neighbouring coil elements is eliminated [1]. The hole-slotted coil design has been shown to provide a deeper RF penetration into the sample compared to a standard loop design. This hole-slotted geometry is based on the magnetron´s design theory and has already been shown to operate as an array, in which the elements are capacitive decoupled [2]. Generally, capacitive decoupling is associated with a larger number of variables increasing the array complexity. In order to simplify the array construction, the applicability of overlap decoupling in a hole-slotted loop-geometry array is investigated and compared with conventional loop coils at 1.5 and 7 Tesla. Methods At 1.5 T: All experiments were performed on a 1.5 T whol...
Introduction: One dimensional parallel imaging is limited to reduction factors of approximately R... more Introduction: One dimensional parallel imaging is limited to reduction factors of approximately R=4, due to intrinsic limitations on the sensitivity variations in one spatial dimension. Besides the high intrinsic SNR in 2D parallel imaging, due to the volume excitation, scan time reduction can be performed in two spatial dimensions simultaneously, thereby exploiting the sensitivity variations more efficiently, which results in significantly higher reduction factors. It has recently been shown that besides standard 2D SENSE reductions [1], 2D CAIPIRINHA–type [2] reductions are also applicable, which use sampling patterns with sample positions shifted from their normal positions. Thus, there are multiple 2D sampling patterns conceivable given a specific reduction factor. One central question to answer is which sampling pattern exploits the sensitivity variations provided by the underlying coil configuration most efficiently and therefore provides the best image quality after parallel ...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 4, 2015
Phase-constrained parallel MRI approaches have the potential for significantly improving the imag... more Phase-constrained parallel MRI approaches have the potential for significantly improving the image quality of accelerated MRI scans. The purpose of this study was to investigate the properties of two different phase-constrained parallel MRI formulations, namely the standard phase-constrained approach and the virtual conjugate coil (VCC) concept utilizing conjugate k-space symmetry. Both formulations were combined with image-domain algorithms (SENSE) and a mathematical analysis was performed. Furthermore, the VCC concept was combined with k-space algorithms (GRAPPA and ESPIRiT) for image reconstruction. In vivo experiments were conducted to illustrate analogies and differences between the individual methods. Furthermore, a simple method of improving the signal-to-noise ratio by modifying the sampling scheme was implemented. For SENSE, the VCC concept was mathematically equivalent to the standard phase-constrained formulation and therefore yielded identical results. In conjunction wit...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 11, 2015
In radial imaging, projections may become "miscentered" due to gradient errors such as ... more In radial imaging, projections may become "miscentered" due to gradient errors such as delays and eddy currents. These errors may result in image artifacts and can disrupt the reliability of direct current (DC) navigation. The proposed parallel imaging-based technique retrospectively estimates trajectory error from miscentered radial data without extra acquisitions, hardware, or sequence modification. After phase correction, self-calibrated GRAPPA operator gridding (GROG) weights are iteratively applied to shift-miscentered projections toward the center of k-space. A search algorithm identifies the shift that aligns the peak k-space signals by maximizing the sum-of-squares DC signal estimate of each projection. The algorithm returns a trajectory estimate and a corrected radial k-space signal. Data from a spherical phantom, the head, and the heart demonstrate that image reconstruction with the estimated trajectory restores image quality and reduces artifacts such as streaks...
This work is intended to demonstrate that T1 measured in the lungs depends on the echo time (TE) ... more This work is intended to demonstrate that T1 measured in the lungs depends on the echo time (TE) used. Measuring lung T1 can be used to gain quantitative morphological and functional information. It is also shown that this dependence is particularly visible when using an ultra-short TE (UTE) sequence with TE well below 1 ms for T1 quantification in lung tissue, rather than techniques with TE on the order of 1-2 ms. The lungs of 12 healthy volunteers (aged 22 to 33 years) were examined at 1.5 Tesla. A segmented inversion recovery Look-Locker multi-echo sequence based on two-dimensional UTE was used for independent T1 quantification at five TEs between TE1 = 70 μs and TE5 = 2.3 ms. The measured T1 was found to increase gradually with TE from 1060 ± 40 ms at TE1 to 1389 ± 53 ms at TE5 (P < 0.001). Measuring T1 at ultra-short echo times reveals a significant dependence of observed T1 on the echo time. Thus, any comparison of T1 values should also consider the TEs used. However, this dependence on TE could also be exploited to gain additional diagnostic information on the tissue compartments in the lung. J. Magn. Reson. Imaging 2015.
Fast imaging methods and the availability of required hardware for magnetic resonance tomography ... more Fast imaging methods and the availability of required hardware for magnetic resonance tomography (MRT) have significantly reduced acquisition times from about an hour down to several minutes or seconds. With this development over the last 20 years, magnetic resonance imaging (MRI) has become one of the most important instruments in clinical diagnosis. In recent years, the greatest progress in further increasing imaging speed has been the development of parallel MRI (pMRI). Within the last 3 years, parallel imaging methods have become commercially available, and therefore are now available for a broad clinical use. The basic feature of pMRI is a scan time reduction, applicable to nearly any available MRI method, while maintaining the contrast behavior without requiring higher gradient system performance. Because of its faster image acquisition, pMRI can in some cases even significantly improve image quality. In the last 10 years of pMRI development, several different pMRI reconstruct...
In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field streng... more In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field strength of 1.5 Tesla. Recently, an ongoing development to higher field strength can be observed and a new clinical standard at 3.0 Tesla seems to be established. High field MRI with its intrinsic higher signal to noise ratio (SNR) can enable new applications of MRI in medical diagnosis, or can serve to improve existing methods. It is important to note, that the use of high field MRI is not without its limitations. Besides the SNR, other unwanted effects increase with a higher field strength. Without correction, these high field problems cause a serious loss in image quality. An elegant way to address these problems is the use of parallel imaging. In many clinical applications, parallel MRI (pMRI) is part of the standard protocol, because pMRI can enhance virtually every MRI application, without necessarily affecting the contrast behavior of the underlying imaging sequence. In high field MRI, ...
Magnetic Resonance Materials in Physics, Biology and Medicine, 2014
To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imagin... more To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imaging and quantitative [Formula: see text] mapping in different breathing phases in order to assess the feasibility of oxygen-enhanced 3D functional lung imaging. A 3D sequence with ultrashort echo times and interleaved double readouts was implemented for oxygen-enhanced lung imaging at 1.5 T. Six healthy volunteers were examined while breathing room air as well as 100 % oxygen. Images from expiratory and inspiratory breathing phases were reconstructed and compared for the two breathing gases. The average [Formula: see text] value measured for room air was 2.10 ms, with a 95 % confidence interval (CI) of 1.95-2.25 ms, and the average for pure oxygen was 1.89 ms, with a 95 % CI of 1.76-2.01 ms, resulting in a difference of 10.1 % (95 % CI 8.9-11.3 %). An 11.2 % increase in signal intensity (95 % CI 10.4-12.1 %) in the T 1-weighted images was detected when subjects were breathing pure oxygen compared to room air. Furthermore, a significant change in signal intensity (26.5 %, 95 % CI 18.8-34.3 %) from expiration to inspiration was observed. This study demonstrated the feasibility of simultaneous [Formula: see text] mapping and T 1-weighted 3D imaging of the lung. This method has the potential to provide information about ventilation, oxygen transfer, and lung expansion within one experiment. Future studies are needed to investigate the clinical applicability and diagnostic value of this approach in various pulmonary diseases.
To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE)... more To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice. Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison. An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1-4) and the...
Magnetic Resonance Materials in Physics, Biology and Medicine, 2015
This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might ... more This work was aimed at reducing acoustic noise in diffusion-weighted MR imaging (DWI) that might reach acoustic noise levels of over 100 dB(A) in clinical practice. A diffusion-weighted readout-segmented echo-planar imaging (EPI) sequence was optimized for acoustic noise by utilizing small readout segment widths to obtain low gradient slew rates and amplitudes instead of faster k-space coverage. In addition, all other gradients were optimized for low slew rates. Volunteer and patient imaging experiments were conducted to demonstrate the feasibility of the method. Acoustic noise measurements were performed and analyzed for four different DWI measurement protocols at 1.5T and 3T. An acoustic noise reduction of up to 20 dB(A) was achieved, which corresponds to a fourfold reduction in acoustic perception. The image quality was preserved at the level of a standard single-shot (ss)-EPI sequence, with a 27-54 % increase in scan time. The diffusion-weighted imaging technique proposed in this study allowed a substantial reduction in the level of acoustic noise compared to standard single-shot diffusion-weighted EPI. This is expected to afford considerably more patient comfort, but a larger study would be necessary to fully characterize the subjective changes in patient experience.
Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for... more Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for efficient banding artifact removal in bSSFP imaging. Based on a varying radiofrequency (RF) phase-increment in combination with a radial trajectory, DYPR-SSFP allows obtaining a banding-free image out of a single acquired k-space. The purpose of this work is to present an extension of this technique, enabling fast three-dimensional isotropic banding-free bSSFP imaging. While banding artifact removal with DYPR-SSFP relies on the applied dynamic phase-cycle, this aspect can lead to artifacts, at least when the number of acquired projections lies below a certain limit. However, by using a 3D radial trajectory with quasi-random view ordering for image acquisition, this problem is intrinsically solved, enabling 3D DYPR-SSFP imaging at or even below the Nyquist criterion. The approach is validated for brain and knee imaging at 3 Tesla. Volumetric, banding-free images were obtained in clinically acceptable scan times with an isotropic resolution up to 0.56mm. The combination of DYPR-SSFP with a 3D radial trajectory allows banding-free isotropic volumetric bSSFP imaging with no expense of scan time. Therefore, this is a promising candidate for clinical applications such as imaging of cranial nerves or articular cartilage.
Recently, the (Resolution Enhanced-) T1 insensitive steady-state imaging (TOSSI) approach has bee... more Recently, the (Resolution Enhanced-) T1 insensitive steady-state imaging (TOSSI) approach has been proposed for the fast acquisition of T2 -weighted images. This has been achieved by balanced steady-state free precession (bSSFP) imaging between unequally spaced inversion pulses. The purpose of this work is to present an extension of this technique, considerably increasing both the efficiency and possibilities of TOSSI. A radial trajectory in combination with an appropriate view-sharing reconstruction is used. Because each projection traverses the contrast defining k-space center, several different contrasts can be extracted from a single-shot measurement. These contrasts include various T2 -weightings and T2 /T1 -weighting if an even number of inversion pulses is used, while an odd number allow the generation of several images with predefined tissue types cancelled. The approach is validated for brain and abdominal imaging at 3.0 Tesla. Results are compared with RE-TOSSI, bSSFP, and...
Introduction: The application of the basic Cartesian GRAPPA [1] reconstruction algorithm requires... more Introduction: The application of the basic Cartesian GRAPPA [1] reconstruction algorithm requires regular, symmetric undersampled data. Non-Cartesian sampling schemes, such as radial or spiral trajectories, do not fulfill this requirement. Therefore, special reconstruction and/or data reordering procedures are necessary. In all previous methods, the GRAPPA reconstruction is performed first on the reordered data, followed by regridding of the reconstructed data onto a Cartesian grid [2-5]. However, if the undersampled non-Cartesian data are first regridded, the inherent symmetry of the acquisition scheme can be used to define several Cartesian patterns in the regridded data which can be used for reconstruction. Examining specifically the spiral case, the regridded undersampled k-space can be divided into several "sectors," where each sector can be reconstructed with a specific Cartesian pattern. The reconstruction for each sector is then identical to a Cartesian GRAPPA reco...
Introduction Since the first phased array design, the overlap decoupling became the most often us... more Introduction Since the first phased array design, the overlap decoupling became the most often used decoupling technique. At a certain amount of overlap, the mutual inductance between adjacent array coil elements is forced to be zero. Therefore the interaction between neighbouring coil elements is eliminated [1]. The hole-slotted coil design has been shown to provide a deeper RF penetration into the sample compared to a standard loop design. This hole-slotted geometry is based on the magnetron´s design theory and has already been shown to operate as an array, in which the elements are capacitive decoupled [2]. Generally, capacitive decoupling is associated with a larger number of variables increasing the array complexity. In order to simplify the array construction, the applicability of overlap decoupling in a hole-slotted loop-geometry array is investigated and compared with conventional loop coils at 1.5 and 7 Tesla. Methods At 1.5 T: All experiments were performed on a 1.5 T whol...
Introduction: One dimensional parallel imaging is limited to reduction factors of approximately R... more Introduction: One dimensional parallel imaging is limited to reduction factors of approximately R=4, due to intrinsic limitations on the sensitivity variations in one spatial dimension. Besides the high intrinsic SNR in 2D parallel imaging, due to the volume excitation, scan time reduction can be performed in two spatial dimensions simultaneously, thereby exploiting the sensitivity variations more efficiently, which results in significantly higher reduction factors. It has recently been shown that besides standard 2D SENSE reductions [1], 2D CAIPIRINHA–type [2] reductions are also applicable, which use sampling patterns with sample positions shifted from their normal positions. Thus, there are multiple 2D sampling patterns conceivable given a specific reduction factor. One central question to answer is which sampling pattern exploits the sensitivity variations provided by the underlying coil configuration most efficiently and therefore provides the best image quality after parallel ...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 4, 2015
Phase-constrained parallel MRI approaches have the potential for significantly improving the imag... more Phase-constrained parallel MRI approaches have the potential for significantly improving the image quality of accelerated MRI scans. The purpose of this study was to investigate the properties of two different phase-constrained parallel MRI formulations, namely the standard phase-constrained approach and the virtual conjugate coil (VCC) concept utilizing conjugate k-space symmetry. Both formulations were combined with image-domain algorithms (SENSE) and a mathematical analysis was performed. Furthermore, the VCC concept was combined with k-space algorithms (GRAPPA and ESPIRiT) for image reconstruction. In vivo experiments were conducted to illustrate analogies and differences between the individual methods. Furthermore, a simple method of improving the signal-to-noise ratio by modifying the sampling scheme was implemented. For SENSE, the VCC concept was mathematically equivalent to the standard phase-constrained formulation and therefore yielded identical results. In conjunction wit...
Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine, Jan 11, 2015
In radial imaging, projections may become "miscentered" due to gradient errors such as ... more In radial imaging, projections may become "miscentered" due to gradient errors such as delays and eddy currents. These errors may result in image artifacts and can disrupt the reliability of direct current (DC) navigation. The proposed parallel imaging-based technique retrospectively estimates trajectory error from miscentered radial data without extra acquisitions, hardware, or sequence modification. After phase correction, self-calibrated GRAPPA operator gridding (GROG) weights are iteratively applied to shift-miscentered projections toward the center of k-space. A search algorithm identifies the shift that aligns the peak k-space signals by maximizing the sum-of-squares DC signal estimate of each projection. The algorithm returns a trajectory estimate and a corrected radial k-space signal. Data from a spherical phantom, the head, and the heart demonstrate that image reconstruction with the estimated trajectory restores image quality and reduces artifacts such as streaks...
This work is intended to demonstrate that T1 measured in the lungs depends on the echo time (TE) ... more This work is intended to demonstrate that T1 measured in the lungs depends on the echo time (TE) used. Measuring lung T1 can be used to gain quantitative morphological and functional information. It is also shown that this dependence is particularly visible when using an ultra-short TE (UTE) sequence with TE well below 1 ms for T1 quantification in lung tissue, rather than techniques with TE on the order of 1-2 ms. The lungs of 12 healthy volunteers (aged 22 to 33 years) were examined at 1.5 Tesla. A segmented inversion recovery Look-Locker multi-echo sequence based on two-dimensional UTE was used for independent T1 quantification at five TEs between TE1 = 70 μs and TE5 = 2.3 ms. The measured T1 was found to increase gradually with TE from 1060 ± 40 ms at TE1 to 1389 ± 53 ms at TE5 (P < 0.001). Measuring T1 at ultra-short echo times reveals a significant dependence of observed T1 on the echo time. Thus, any comparison of T1 values should also consider the TEs used. However, this dependence on TE could also be exploited to gain additional diagnostic information on the tissue compartments in the lung. J. Magn. Reson. Imaging 2015.
Fast imaging methods and the availability of required hardware for magnetic resonance tomography ... more Fast imaging methods and the availability of required hardware for magnetic resonance tomography (MRT) have significantly reduced acquisition times from about an hour down to several minutes or seconds. With this development over the last 20 years, magnetic resonance imaging (MRI) has become one of the most important instruments in clinical diagnosis. In recent years, the greatest progress in further increasing imaging speed has been the development of parallel MRI (pMRI). Within the last 3 years, parallel imaging methods have become commercially available, and therefore are now available for a broad clinical use. The basic feature of pMRI is a scan time reduction, applicable to nearly any available MRI method, while maintaining the contrast behavior without requiring higher gradient system performance. Because of its faster image acquisition, pMRI can in some cases even significantly improve image quality. In the last 10 years of pMRI development, several different pMRI reconstruct...
In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field streng... more In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field strength of 1.5 Tesla. Recently, an ongoing development to higher field strength can be observed and a new clinical standard at 3.0 Tesla seems to be established. High field MRI with its intrinsic higher signal to noise ratio (SNR) can enable new applications of MRI in medical diagnosis, or can serve to improve existing methods. It is important to note, that the use of high field MRI is not without its limitations. Besides the SNR, other unwanted effects increase with a higher field strength. Without correction, these high field problems cause a serious loss in image quality. An elegant way to address these problems is the use of parallel imaging. In many clinical applications, parallel MRI (pMRI) is part of the standard protocol, because pMRI can enhance virtually every MRI application, without necessarily affecting the contrast behavior of the underlying imaging sequence. In high field MRI, ...
Magnetic Resonance Materials in Physics, Biology and Medicine, 2014
To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imagin... more To develope a self-gated free-breathing 3D sequence allowing for simultaneous T 1-weighted imaging and quantitative [Formula: see text] mapping in different breathing phases in order to assess the feasibility of oxygen-enhanced 3D functional lung imaging. A 3D sequence with ultrashort echo times and interleaved double readouts was implemented for oxygen-enhanced lung imaging at 1.5 T. Six healthy volunteers were examined while breathing room air as well as 100 % oxygen. Images from expiratory and inspiratory breathing phases were reconstructed and compared for the two breathing gases. The average [Formula: see text] value measured for room air was 2.10 ms, with a 95 % confidence interval (CI) of 1.95-2.25 ms, and the average for pure oxygen was 1.89 ms, with a 95 % CI of 1.76-2.01 ms, resulting in a difference of 10.1 % (95 % CI 8.9-11.3 %). An 11.2 % increase in signal intensity (95 % CI 10.4-12.1 %) in the T 1-weighted images was detected when subjects were breathing pure oxygen compared to room air. Furthermore, a significant change in signal intensity (26.5 %, 95 % CI 18.8-34.3 %) from expiration to inspiration was observed. This study demonstrated the feasibility of simultaneous [Formula: see text] mapping and T 1-weighted 3D imaging of the lung. This method has the potential to provide information about ventilation, oxygen transfer, and lung expansion within one experiment. Future studies are needed to investigate the clinical applicability and diagnostic value of this approach in various pulmonary diseases.
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Papers by Felix Breuer