Magnetic Resonance Materials in Physics, Biology and Medicine最新文献

Objectives: Magnetic resonance imaging (MRI) is a complex medical imaging method where multiple technical and physiological factors may lead to undesired changes in image quality. The quality control methods utilizing test objects are useful in measuring technical performance, but they may not fully detect all factors present in clinical imaging. In this study, we developed methodologies to quantify observer-based image quality and to compare these observations with technical quality control (QC) parameters.

Materials and methods: We analysed 150 brain MRI 3D-FLAIR volumes from 15 scanners, measuring image quality both quantitatively and by visually ranking the images using forced-choice comparison.

Results: Significant differences were found between different scanners based on the forced choice comparison. In imaging study-specific analysis, a weak correlation was observed with contrast-to-noise ratio (CNR) (R² = 0.17) and brain white matter-gray matter (WM/GM) contrast (R² = 0.14). With device-specific median correlation, the CNR and WM/GM contrast R² were 0.21 and 0.34, respectively. Additionally, using device-specific median values, a correlation was found with image quality index (QI) (R² = 0.21) and some modulation transfer function (MTF) based resolution-specific parameters (MTF10 FH, R² = 0.19; MTF10 AP, R² = 0.20; MTF50 AP, R² = 0.17).

Discussion: The forced choice comparison can be effectively utilized to rank image quality across multiple MRI scanners. Technical image quality parameters, directly analysed from anatomical image volumes, can offer prospective maintenance value. Additionally, the quality of clinical image volumes can be assessed using both forced choice comparison and calculational image analysis methods.

Objective: Within gradient-spoiled transient-state MR sequences like Magnetic Resonance Fingerprinting or Magnetic Resonance Spin TomogrAphy in Time-domain (MR-STAT), it is examined whether an optimized RF phase modulation can help to improve the precision of the resulting relaxometry maps.

Methods: Using a Cramer-Rao based method called BLAKJac, optimized sequences of RF pulses have been generated for two scenarios (amplitude-only modulation and amplitude + phase modulation) and for several conditions. These sequences have been tested on a phantom, a healthy human brain and a healthy human leg, to reconstruct parametric maps ( $T_1$ and $T_2$ ) as well as their standard deviations.

Results: The amplitude + phase modulation scenario systematically resulted in lower noise levels than the amplitude-only modulation scenario. On average, the difference was around 34%, but it was substantially larger for scans acquired under SAR restrictions. Compared to amplitude-only, in the amplitude + phase modulation scenario, the relevance of an inversion pulse and of a pause were greatly reduced, at least considering overall precision and in-phantom accuracy.

Conclusion: The application of an optimized RF phase modulation in quantitative transient-states MRI is beneficial for almost all tested scenarios and conditions, in particular under SAR restrictions Furthermore, RF phase modulation reduces the need for inversions pulses and pauses.

Purpose: To reconstruct whole-heart images from free-running acquisitions through automated selection of data acceptance windows (ES: end-systole, MD: mid-diastole, ED: end-diastole) that account for heart rate variability (HRV).

Methods: SYMPHONIC was developed and validated in simulated (N = 1000) and volunteer (N = 14) data. To validate SYMPHONIC, the position of the detected acceptance windows, total duration, and resulting ventricular volume were compared to the simulated ground truth to establish metrics for temporal error, quiescent interval duration, and volumetric error, respectively. SYMPHONIC MD images and those using manually defined acceptance windows with fixed (MANUAL_FIXED) or adaptive (MANUAL_ADAPT) width were compared by measuring vessel sharpness (VS). The impact of HRV was assessed in patients (N = 6).

Results: Mean temporal error was larger for MD than for ED and ED in both simulations and volunteers. Mean volumetric errors were comparable. Interval duration differed for ES (p = 0.04) and ED (p < 10^-3), but not for MD (p = 0.08). In simulations, SYMPHONIC and MANUAL_ADAPT provided consistent VS for increasing HRV, while VS decreased for MANUAL_FIXED. In volunteers, VS differed between MANUAL_ADAPT and MANUAL_FIXED (p < 0.01), but not between SYMPHONIC and MANUAL_ADAPT (p = 0.03) or MANUAL_FIXED (p = 0.42).

Conclusion: SYMPHONIC accurately detected quiescent cardiac phases in free-running data and resulted in high-quality whole-heart images despite the presence of HRV.

Introduction: This study proposes a framework for determining the calculation error in online SAR supervision introduced by directional couplers.

Materials and methods: A mathematical framework is introduced showing how the error in the measured excitation vector compared to the actual excitation vector can be rewritten as a new set of virtual observation points (VOPs). By comparing the new set of VOPs to the original VOPs through an optimization, the maximum underestimation of SAR can be calculated. The framework is then applied to five different RF arrays.

Results: The results show that the error in SAR calculation is very dependent on the position of the reference plane of the directional coupler measurements and the S-parameters of the array. To have an error of less than 5%, directional couplers with a directivity better than 40 dB are necessary for the worst case of the investigated arrays.

Discussion: The framework presented in this paper provides an approach for calculating a safety factor to account for the inaccuracies introduced by directional coupler measurements in online SAR supervision. The framework can also be adapted to other types of measurements.

Objective: The Polar Fourier Transform (PFT) has been proposed as a direct alternative to gridding for reconstructing radially acquired MRI data. This study evaluates the feasibility of inline PFT implementation on a clinical MRI scanner and assesses its computational performance and image quality under acceleration.

Materials and methods: PFT was implemented as modular components within the Siemens Image Calculation Environment, using a recursive numerical Hankel transform. Phantom and in vivo brain datasets acquired with 2D radial trajectories were reconstructed using both PFT and vendor-supplied gridding. Reconstruction time, SNR, artifact behavior, and spatial resolution were assessed across multiple undersampling levels (up to 8 ×), using simulations and repeated scans.

Results: PFT was successfully integrated with a runtime of ~ 6-9 × acquisition time. It exhibited spatially variant behavior, concentrating resolution in central region while shifting undersampling-induced blurring outward. Compared to gridding, PFT reduced structured streaks and better preserved image quality under acceleration. Gradient delay artifacts were reduced by alternating spoke polarity. Notably, the pituitary gland and basilar artery remained visible at high acceleration, highlighting preserved central fidelity.

Discussion: PFT enables effective inline reconstruction for radial MRI and preserves image quality in small central regions of interest under aggressive undersampling-supporting dynamic and ROI-focused applications.

Objective: To evaluate if co-registering Diffusion-Weighted Imaging (DWI) before generating Apparent Diffusion Coefficient (ADC) maps can improve differentiating benign and malignant breast lesions in MRI based on the A6702 thresholds.

Materials and methods: This IRB-approved study involved an in-house dataset and the publicly available ACRIN-6698 dataset, both including multi b-value DWI. In phase one, 16 ANTs library-based co-registration methods were evaluated on a subset of n = 138 cases from our in-house cohort. The quantitative assessment included mean ADC values of manually segmented lesions (diagnostic metrics using individual and A6702-defined thresholds) and coefficient of Variation. In the second phase, the best-performing methods were tested for generalizability on an unseen set of 40 cases (20 from in-house and 20 from external dataset). Three blinded readers segmented lesions on co-registered and non-co-registered ADC maps. Agreement and consistency were evaluated via Bland-Altman, segmentation distance, and intraclass correlation coefficient.

Results: Rigid co-registration using DWI at b = 750 s/mm² as reference (b750-Rigid) improved accuracy of both optimal/conservative A6702 trial thresholds with sensitivity/specificity increasing from 93%/10% to 97%/30% and 100%/30% respectively. Mean ADC values were not significantly different after co-registration (p > 0.05).

Discussion: Co-registration of DWI images before ADC map generation, particularly using b750-Rigid registration, seems promising for improving lesion classification in breast MRI. Further validation is warranted.

The frequency response and transfer function of a system are closely related, but distinct concepts from a control system theory and signal processing perspective. Unfortunately, these concepts have been used inconsistently in the magnetic resonance imaging (MRI) literature for gradient characterization. This note highlights the differences, with the intention to establish a common naming convention, consistent with other engineering fields. This will facilitate communication between colleagues with a different research background, promoting knowledge transfer and potentially alleviate shortcomings that have resulted from the incorrect usage of the term "transfer function" for gradient characterization in the past.

Background: Deuterium metabolic imaging (DMI) has recently been established as a versatile MR-based technique for in vivo mapping of glucose and other metabolic pathways using safe, non-ionizing ²H-labeled tracers.

Objective: In this review, methodological advances in DMI over the past decade are summarized, spanning hardware, acquisition, reconstruction, and quantification.

Approach and outline: Developments in multinuclear system modifications and dual-tuned head and body coils that enable 3D DMI at clinical and ultra-high field strengths are outlined. Efficient spatial-spectral encoding strategies and balanced steady-state-free-precession-based MRSI, which improve SNR efficiency and spatiotemporal resolution, are reviewed together with temporally interleaved ¹H/²H acquisitions that integrate DMI into standard MRI workflows. Indirect ¹H-observed deuterium detection (QELT) is described as a complementary approach for sites without multinuclear hardware. On the reconstruction side, model-based, low-rank and AI-driven methods are highlighted for de-noising, accelerated sampling, and robust spectral-temporal fitting.

Outlook: Current strategies for concentration estimation, kinetic modeling, and treatment of label loss are discussed, positioning DMI as a promising complement to FDG-PET and ¹³C-MRS for studying metabolism in neurological, oncological and systemic disease.

Motivation: The twisted-pair (TP) coil design is a promising strategy for developing novel, flexible, wearable MRI detectors that can provide SNR gains in various clinical applications of high-field MRI. We hypothesize that the TP coil's receive (Rx) sensitivity can be significantly increased by combining it with two complementary elements, such as dielectric resonators (DRs) and dipole antennas.

Methods: TP coils were combined with DRs made of high-permittivity material (ε_r = 1070) and transceiver (TxRx) dipole antennas. The Tx and Rx performance of six different types of arrays (TP-only, dipole-only, TP with DRs, dipole with DRs, dipole with TPs, and dipole with TPs and DRs) was investigated through numerical simulations involving a cylindrical phantom suitable for lower extremity applications and two human voxel models. MR phantom experiments were conducted using a 7 Tesla whole-body MRI scanner to validate the Tx and Rx performance of all six array types.

Results: The array combining all three types of elements (TP coils, DRs, and dipole antennas) provided the highest overall Rx performance; MR phantom experiments showed that integrating DRs with TP coils increased peripheral SNR by 250% and central SNR by 23% (for a total 38% gain in the center when also using dipole antennas in Rx). Human voxel model simulations confirmed that similar SNR gains can be achieved in vivo. Integrating DRs into TP coils also increased central Tx field efficiency by 4.6% and reduced the peak SAR_10g by 25.8% in the human voxel model Hugo.

Conclusion: DRs and dipole antennas can significantly improve the overall Rx performance of TP coils. This concept can benefit MRI of the human lower extremity at 7 Tesla and encourage exploration of its utility for other clinical applications.