To determine whether prototype integrated slice-specific shimming (iShim) diffusion-weighted imaging (DWI) combined with Boost diffusion sampling improves image quality and diagnostic performance for focal liver lesions compared with conventional DWI and alternative iShim sampling schemes.

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.

Perfusion MRI plays an important role in brain tumor assessment, especially for tumor grading and differentiation of tumor progression from pseudoprogression. Arterial spin labeling (ASL) MRI is a non-invasive method for measuring cerebral blood flow (CBF) using blood water as an endogenous tracer, which has great clinical potential for brain tumor imaging and might help to lower the use of gadolinium-based contrast agents. In this review, we discuss recent advances of the ASL method with a special focus on brain tumors, including multi-time point ASL which not only allows more accurate CBF quantification, but also yields arterial transit time (ATT) maps. Another method to reduce dependency on ATT is velocity-selective ASL, for which labeling is directly performed in the imaging volume. By performing a physiological challenge, like a hypercapnia breathing challenge, the reactivity of the tumor's neovasculature can be determined. More recent advances in ASL allow probing the blood-brain barrier (BBB) integrity by measuring the rate of water transport across the BBB (BBB-ASL). By labeling only a single artery, selective ASL sequences can help to identify what part of the tumor is fed by which artery. In conclusion, we see the future potential of ASL MRI not only in replacing contrast agents for perfusion assessment but also in providing additional information to the MRI exam, such as BBB integrity or the architecture of the vascular feeders.