Oxygen-enhanced MRI assessment of tumour hypoxia in head and neck cancer is feasible and well tolerated in the clinical setting.

BACKGROUND: Tumour hypoxia is a recognised cause of radiotherapy treatment resistance in head and neck squamous cell carcinoma (HNSCC). Current positron emission tomography-based hypoxia imaging techniques are not routinely available in many centres. We investigated if an alternative technique called oxygen-enhanced magnetic resonance imaging (OE-MRI) could be performed in HNSCC. METHODS: A volumetric OE-MRI protocol for dynamic T1 relaxation time mapping was implemented on 1.5-T clinical scanners. Participants were scanned breathing room air and during high-flow oxygen administration. Oxygen-induced changes in T1 times (ΔT1) and R2* rates (ΔR2*) were measured in malignant tissue and healthy organs. Unequal variance t-test was used. Patients were surveyed on their experience of the OE-MRI protocol. RESULTS: Fifteen patients with HNSCC (median age 59 years, range 38 to 76) and 10 non-HNSCC subjects (median age 46.5 years, range 32 to 62) were scanned; the OE-MRI acquisition took less than 10 min and was well tolerated. Fifteen histologically confirmed primary tumours and 41 malignant nodal masses were identified. Median (range) of ΔT1 times and hypoxic fraction estimates for primary tumours were -3.5% (-7.0 to -0.3%) and 30.7% (6.5 to 78.6%) respectively. Radiotherapy-responsive and radiotherapy-resistant primary tumours had mean estimated hypoxic fractions of 36.8% (95% confidence interval [CI] 17.4 to 56.2%) and 59.0% (95% CI 44.6 to 73.3%), respectively (p = 0.111). CONCLUSIONS: We present a well-tolerated implementation of dynamic, volumetric OE-MRI of the head and neck region allowing discernment of differing oxygen responses within biopsy-confirmed HNSCC. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04724096 . Registered on 26 January 2021. RELEVANCE STATEMENT: MRI of tumour hypoxia in head and neck cancer using routine clinical equipment is feasible and well tolerated and allows estimates of tumour hypoxic fractions in less than ten minutes. KEY POINTS: • Oxygen-enhanced MRI (OE-MRI) can estimate tumour hypoxic fractions in ten-minute scanning. • OE-MRI may be incorporable into routine clinical tumour imaging. • OE-MRI has the potential to predict outcomes after radiotherapy treatment.

Switching from linear to macrocyclic gadolinium-based contrast agents halts the relative T1 -Weighted signal increase in deep gray matter of children with brain tumors: A retrospective study.

BACKGROUND: Studies have shown signal intensity (SI) changes in the brains of children exposed to repeated doses of a gadolinium-based contrast agent (GBCA). HYPOTHESIS: The trajectory of changes in relative dentate nucleus (DN) and globus pallidus (GP) SI in children receiving multiple doses of GBCA will alter when switched from linear to macrocyclic agents. STUDY TYPE: Retrospective longitudinal. POPULATION: Thirty-five children, age range 0.5-17.0 years, undergoing brain tumor follow-up between 2006 and 2017. FIELD STRENGTH/SEQUENCE: Unenhanced T1 WI, serial scans at both 1.5T and 3T. ASSESSMENT: Regions of interest were drawn on DN, GP, and SIs normalized to middle cerebellar peduncle (DN/MCP) and cerebral white matter (GP/CWM), respectively. A change in SI ratios as a function of dose (slope gradient) calculated according to the type of contrast agent received: linear only, macrocyclic only, or switchover from linear to macrocyclic. For the latter, gradients were compared before and after switchover. The effect of anticancer treatment on slope gradient was tested. STATISTICAL TESTS: One-sample t-test or Mann-Whitney U-test for slope gradients differing from zero. Independent samples t-tests to compare slope gradient groups. Paired sample t-tests to compare slope gradients before and after switchover. RESULTS: A significant (P < 0.05) increase in SI ratio was observed following multiple doses of linear but not macrocyclic agents: mean percentage increase per dose in SI was 0.063% vs. -0.034% for DN/MCP, and 0.078% vs. 0.004% for GP/CWM ratios. A significant (P < 0.05) change of SI trajectory in the DN/MCP ratio was demonstrated when switching from a linear to macrocyclic agent. There was no difference in SI trajectory between patients who had anticancer therapies and those who did not, DN/MCP P = 0.740; GP/BWM P = 0.694. DATA CONCLUSION: Switching from linear to macrocyclic gadolinium-based contrast agents seems to halt the relative T1 signal increase in deep gray matter in children. Anticancer treatments appeared to have no impact on the trajectory of T1 SI. LEVEL OF EVIDENCE: 4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:288-295.