Magnetic Resonance Materials in Physics Biology and Medicine

Cardiovascular magnetic resonance (CMR) has become a key imaging modality in clinical cardiology practice due to its unique capabilities for non-invasive imaging of the cardiac chambers and great vessels. A wide range of CMR sequences have been developed to assess various aspects of cardiac structure and function, and significant advances have also been made in terms of imaging quality and acquisition times. A lot of research has been dedicated to the development of global and regional quantitative CMR indices that help the distinction between health and pathology. The goal of this review paper is to discuss the structural and functional CMR indices that have been proposed thus far for clinical assessment of the cardiac chambers. We include indices definitions, the requirements for the calculations, exemplar applications in cardiovascular diseases, and the corresponding normal ranges. Furthermore, we review the most recent state-of-the art techniques for the automatic segmentation of the cardiac boundaries, which are necessary for the calculation of the CMR indices. Finally, we provide a detailed discussion of the existing literature and of the future challenges that need to be addressed to enable a more robust and comprehensive assessment of the cardiac chambers in clinical practice.

In current combined PET/MR systems, PET attenuation correction is based on MRI, since the small bore inside MRI systems and the strong magnetic field do not permit a rotating PET transmission source or a CT device to be integrated. Unlike CT measurements in PET/CT scanners, the MR signal is not directly correlated to tissue density and thus cannot be converted by a simple transformation of intensity values. Various approaches have been developed based on templates, atlas information, direct segmentation of T1-weighted MR images, or segmentation of images from special MR sequences. The advantages and disadvantages of these approaches as well as additional challenges will be discussed in this review.

OBJECTIVE: To investigate how angiographic information can be obtained from proton density (PD) maps reconstructed with a fast 3D Magnetic Resonance Spin TomogrAphy in Time-domain (MR-STAT) protocol, focusing on intracranial vessels and aneurysms in a clinically relevant population. MATERIALS AND METHODS: This proof-of-concept study consisted of two experiments. First, a healthy volunteer underwent MR-STAT with selective and non-selective excitation to investigate the origin of elevated effective proton density in arteries. Second, ten patients with intracranial aneurysms underwent 3D MR-STAT and time-of-flight MR angiography (TOF MRA). Two neuroradiologists independently assessed vessel visibility, image quality, and aneurysm size. Intraclass correlation coefficients (ICC) were computed for aneurysm size measurements. RESULTS: Selective excitation amplified inflow effects and yielded increased artery-tissue contrast in PD maps. Major intracranial arteries were visible in all clinical MR-STAT angiographic datasets. Nine out of ten MR-STAT angiographies were rated as at least diagnostically acceptable. Aneurysm measurements showed strong agreement between conventional and MR-STAT angiographic modalities (ICC=0.86/ICC=0.71) and high inter-rater reliability (ICC=0.90/ICC=0.92). DISCUSSION: MR-STAT PD maps enable angiographic visualization as an intrinsic component of a single fast quantitative acquisition, demonstrating technical feasibility for vessel depiction. Future work should focus on optimizing MR-STAT acquisition strategies to improve vessel conspicuity and broader clinical validation.

INTRODUCTION: High-performance whole-body gradient systems show promise for breast diffusion-weighted imaging, but their performance is constrained by physiological limits. Although local nonlinear gradient coils can provide stronger gradients while remaining within these limits, they often exhibit a substantial reduction in the gradient amplitude of the z-component of the magnetic field near the chest wall. METHODS: We introduced an optimization framework incorporating a constraint on the anterior-posterior variation in the encoding gradient amplitude. A figure of merit combining coil efficiency and minimum wire width was defined to assess performance. A prototype was constructed to validate the design methodology. RESULTS: The optimized coil achieved a 2.35-fold efficiency increase over standard linear coils. Compared to previous nonlinear designs, the new constraint reduced spatial variation by 35.7% and improved minimum efficiency near the chest wall by 2.6-fold. Experimental field maps matched simulations with errors under 8%. DISCUSSION: The proposed method effectively mitigates the trade-off between gradient strength and spatial uniformity along anterior-posterior direction. By enhancing performance in the posterior breast region, the design addresses a critical limitation of previous local coils. CONCLUSION: This framework enables the development of high-performance, robust local gradient coils, facilitating the clinical implementation of advanced DWI protocols for breast cancer screening.

Abstract Purpose Investigating the feasibility of variable flip angle (VFA) T 1 mapping for quantitative liver imaging at 0.55 T and evaluating the impact of RF spoiling correction and deep learning-based (DL) reconstruction on accuracy. Methods A VFA protocol was developed and combined with DL reconstruction to improve quantitative robustness at 0.55 T. Phantom experiments validated T 1 estimates against multi-TI inversion-recovery spin-echo reference measurements. Bloch simulations characterized RF spoiling-induced bias and derived 0.55 T-specific calibration coefficients. Twelve healthy subjects were scanned to assess field-strength-dependent effects of B 1 + inhomogeneity. Results In vivo, DL reconstruction reduced noise-related variability of voxel-wise hepatic T 1 estimates compared to conventional reconstructions in the same subject. At 0.55 T, B 1 + maps showed the highest transmit homogeneity, with liver flip angle variation of 98.2 ± 2.9%, compared with 94.6 ± 7.4% at 1.5 T and 100.7 ± 9.8% at 3 T. Accordingly, B 1 + correction had minimal impact on hepatic T 1 distributions at 0.55 T, whereas more pronounced effects were observed at higher field strengths. Phantom experiments demonstrated improved agreement of VFA-derived T 1 values with the IR-SE reference after 0.55 T-specific RF spoiling correction, supporting the accuracy of the corrected VFA approach. Bland–Altman analysis confirmed that RF spoiling correction had a greater impact on phantom T 1 accuracy than B 1 + correction. Conclusion At 0.55 T, RF spoiling and reconstruction strategies are the main determinants of quantitative accuracy, while transmit field inhomogeneity plays a minor role. Combined RF spoiling correction and DL reconstruction enables robust VFA T 1 mapping without B 1 + correction. Reduced low-field T 1 values improve VFA model conditioning and reduce sensitivity to flip angle deviations, supporting VFA-based T 1 mapping for low-field MRI.

Glioma imaging remains constrained by the limited ability of conventional MRI to capture biologically relevant tumor features beyond blood-brain barrier disruption. Hypoxia-modulated blood oxygen level-dependent (BOLD) MRI has emerged as a potential contrast-agent-free approach to probe oxygenation-related tumor physiology, using deoxyhemoglobin as an endogenous susceptibility contrast mechanism. By altering blood oxygenation during acquisition, the technique generates signal changes that may provide physiological information beyond structural imaging and resting perfusion measures. We performed a narrative review of 29 human and animal studies using hypoxic oxygen challenges during BOLD MRI. Substantial heterogeneity was identified in gas delivery, carbon dioxide control, MRI acquisition and analytical approaches. A recurring methodological issue was carbon dioxide control, since carbon dioxide is the dominant vasoactive stimulus and hypoxia-induced hyperventilation with secondary hypocapnia can confound BOLD signal interpretation. Preclinical brain tumor studies suggest sensitivity to spatial heterogeneity between viable and necrotic tumor regions. Early human glioblastoma studies support the feasibility and tolerability of hypoxia-modulated BOLD acquisitions and show spatially heterogeneous signal- and perfusion-related maps without exogenous contrast. Current evidence supports hypoxia-modulated BOLD MRI as a promising translational imaging approach, but clinical data remain limited and prospective validation in glioblastoma cohorts is required.