Assessment of T1 and T2 Relaxation-Time Changes in NMIBC Tissue After 5-ALA Photodynamic Therapy Using Quantitative Magnetic Resonance Imaging.

Background/Objectives: Non-muscle-invasive bladder cancer (NMIBC) accounts for the majority of newly diagnosed bladder cancers and is characterized by a high recurrence rate despite standard treatments. Photodynamic therapy (PDT) using 5-aminolevulinic acid (5-ALA) offers a promising alternative; however, objective methods for monitoring therapeutic response are needed. Quantitative magnetic resonance imaging (MRI), particularly T1 and T2 relaxation mapping, may provide non-invasive biomarkers of tissue response to PDT. Methods: In this ex vivo study, 50 samples obtained during transurethral electro-resection of bladder tumors were analyzed using a 1.5 Tesla MRI scanner. Twenty-five healthy control tissues (n = 25) served as the control group. Twenty-five NMIBC tissues were analyzed twice: before and after 5-ALA-PDT. T1 and T2 relaxation times were measured, and regions of interest (ROIs) were manually segmented to obtain quantitative values. Statistical analyses were performed to assess the significance of differences observed between study groups. Results: T1 relaxation times significantly differed between groups: 1351.7 ± 271.1 ms in healthy tissue, 727.7 ± 145.0 ms in untreated NMIBC, and 368.9 ± 65.2 ms in NMIBC after PDT (p < 0.0001). T2 values were 93.5 ± 20.3 ms (healthy), 78.5 ± 20.4 ms (NMIBC), and 55.7 ± 6.1 ms (NMIBC_PDT), with significant reduction after PDT (p < 0.01). Conclusions: Quantitative T1 and T2 mapping via MRI is a sensitive and non-invasive method for detecting structural and biochemical changes in bladder tissue following 5-ALA-PDT. These relaxation times may serve as reliable biomarkers for therapeutic response, facilitating in real-time monitoring and personalized treatment planning for NMIBC. Further in vivo studies are warranted to validate these findings and integrate them into clinical practice.