Quantitative brain T1 maps derived from T1-weighted MRI acquisitions: a proof-of-concept study

BACKGROUND

Longitudinal T1 relaxation time is a key imaging biomarker. In addition, T1 values are modulated by the administration of T1 contrast agents used in patients with tumors and metastases. However, in clinical practice, dedicated T1 mapping sequences are often not included in brain MRI protocols. The aim of this study is to address the absence of dedicated T1 mapping sequences in imaging protocol by deriving T1 maps from standard T1-weighted sequences.

METHODS

A phantom, composed of 144 solutions of paramagnetic agents at different concentrations, was imaged with a three-dimensional (3D) T1-weighed turbo spin-echo (TSE) sequence designed for brain imaging. The relationship between the T1 values and the signal intensities was established using this phantom acquisition. T1 mapping derived from 3D T1-weighted TSE acquisitions in four healthy volunteers and one patient with brain metastases were established and compared to reference T1 mapping technique. The concentration of Gd-based contrast agents in brain metastases were assessed from the derived T1 maps.

RESULTS

Based on the phantom acquisition, the relationship between T1 values and signal intensity (SI) was found equal to T1 = 0.35 × SI-1.11 (R2 = 0.97). TSE-derived T1 values measured in white matter and gray matter in healthy volunteers were equal to 0.997 ± 0.096 s and 1.358 ± 0.056 s (mean ± standard deviation), respectively. Mean Gd3+ concentration value in brain metastases was 94.7 ± 30.0 μM.

CONCLUSION

The in vivo results support the relevance of the phantom-based approach: brain T1 maps can be derived from T1-weighted acquisitions.

RELEVANCE STATEMENT

High-resolution brain T1 maps can be generated, and contrast agent concentration can be quantified and imaged in brain metastases using routine 3D T1-weighted TSE acquisitions.

KEY POINTS

Quantitative T1 mapping adds significant value to MRI diagnostics. T1 measurement sequences are rarely included in routine protocols. T1 mapping and concentration of contrast agents can be derived from routine standard scans. The diagnostic value of MRI can be improved without additional scan time.

NANO-GBM trial of AGuIX nanoparticles with radiotherapy and temozolomide in the treatment of newly diagnosed Glioblastoma: Phase 1b outcomes and MRI-based biodistribution

Background

In glioblastoma (GBM), tumor progression occurs mainly within the irradiated tumor volume. To address this challenge, a radiosensitization strategy with intravenous gadolinium-based theranostic nanoparticles (AGuIX) is being explored in the NANO-GBM phase1b/2R trial (NCT04881032). Here, we present the results of the phase 1b part, which is the first-in-human use of these nanoparticles with radiotherapy and chemotherapy for the treatment of newly diagnosed GBM.

Material and Methods

Eligible patients were aged 18 to 75 years with newly diagnosed and histologically confirmed GBM, with incomplete resection (biopsy or partial surgery). The phase 1b part was a dose escalation approach (Time-to-event Continuous Reassessment Method) with three dose levels: 50, 75, and 100 mg/kg. Patients were treated with RT (60 Gy), and concomitant and adjuvant TMZ, and 4 injections of AGuIX (D-3/-7, D1, D8, and D15). Dose-limiting-toxicity (DLT) was defined as any grade 3-4 adverse event (CTCAE v5.0), excluding alopecia, nausea, and rapidly controlled vomiting. Pharmacokinetic (PK), and biodistribution based on MRI were evaluated.

Results

Between March 2022 and March 2023, eight patients were enrolled: 1 at 50 mg/kg, 1 at 75 mg/kg, and 6 at 100 mg/kg. All patients received the four AGuIX injections. Only one patient experienced a DLT (at 100 mg/kg): a grade 3 lymphopenia (related to TMZ). The RP2D of AGuIX was determined as 100 mg/kg. AGuIX mean AUC increased with dose. Regions of GBM with moderate (36-123 µM), and high (123-291 µM) or very high (>291 µM) AGuIX concentrations accounted in average for 38.7 and 26.8 %, respectively.

Conclusion

These results confirm the lack of AGuIX-related toxicity and the widespread dispersion of nanoparticles throughout GBM. This supports progression to the randomized phase 2 part, utilizing an RP2D of AGuIX of 100 mg/kg (4 injections).