Data from: Quantitative multi-parametric magnetic resonance imaging of tumor response to photodynamic therapy

Objective: The aim of this study was to characterize response to
photodynamic therapy (PDT) in a mouse cancer model using a
multi-parametric quantitative MRI protocol and to identify MR parameters
as potential biomarkers for early assessment of treatment outcome.
Methods: CT26.WT colon carcinoma tumors were grown subcutaneously in the
hind limb of BALB/c mice. Therapy consisted of intravenous injection of
the photosensitizer Bremachlorin, followed by 10 min laser illumination
(200 mW/cm2) of the tumor 6 h post injection. MRI at 7 T was performed at
baseline, directly after PDT, as well as at 24 h, and 72 h. Tumor
relaxation time constants (T1 and T2) and apparent diffusion coefficient
(ADC) were quantified at each time point. Additionally, Gd-DOTA dynamic
contrast-enhanced (DCE) MRI was performed to estimate transfer constants
(Ktrans) and volume fractions of the extravascular extracellular space
(ve) using standard Tofts-Kermode tracer kinetic modeling. At the end of
the experiment, tumor viability was characterized by histology using
NADH-diaphorase staining. Results: The therapy induced extensive cell
death in the tumor and resulted in significant reduction in tumor growth,
as compared to untreated controls. Tumor T1 and T2 relaxation times
remained unchanged up to 24 h, but decreased at 72 h after treatment.
Tumor ADC values significantly increased at 24 h and 72 h. DCE-MRI derived
tracer kinetic parameters displayed an early response to the treatment.
Directly after PDT complete vascular shutdown was observed in large parts
of the tumors and reduced uptake (decreased Ktrans) in remaining tumor
tissue. At 24 h, contrast uptake in most tumors was essentially absent.
Out of 5 animals that were monitored for 2 weeks after treatment, 3 had
tumor recurrence, in locations that showed strong contrast uptake at 72 h.
Conclusion: DCE-MRI is an effective tool for visualization of vascular
effects directly after PDT. Endogenous contrast parameters T1, T2, and
ADC, measured at 24 to 72 h after PDT, are also potential biomarkers for
evaluation of therapy outcome.