Simultaneous R2*, R2, and R2' quantification by combining S0 estimation of the free induction decay with a single...

Area of Science:

• Magnetic Resonance Imaging
• Radiopharmaceutical Therapy
• Biomedical Engineering

Background:

• Accurate quantification of holmium microspheres (Ho-MS) is crucial for effective radioembolization therapy.
• Existing methods may face challenges in environments with varying R2 values.
• Simultaneous measurement of relaxation parameters is needed for precise Ho-MS concentration assessment.

Purpose of the Study:

• To introduce and validate a novel method, S0 estimation of the free induction decay combined with a single spin echo measurement (SOFIDSE).
• To enable simultaneous quantification of R2*, R2, and R2' for determining local Ho-MS concentration.
• To assess the utility of SOFIDSE in radioembolization applications.

Main Methods:

• SOFIDSE estimates R2* and signal magnitude at time 0 (S0) from a free induction decay multigradient echo readout.
• R2 is subsequently calculated using S0 and a single spin echo measurement.
• R2' is derived from R2* and R2; the method was validated against shifted spin echo (SSE) and dual spin echo measurements.

Main Results:

• SOFIDSE demonstrated a slight overestimation of R2 values compared to SSE, irrespective of Ho-MS concentration.
• R2' values derived from SOFIDSE and SSE showed excellent agreement (correlation coefficient = 1).
• Ho-MS-induced R2' values measured by SOFIDSE were independent of the surrounding tissue's R2 value.

Conclusions:

• SOFIDSE provides a robust method for quantifying Ho-MS concentrations.
• The technique is effective in media with spatially or temporally varying R2 values.
• SOFIDSE enables accurate Ho-MS quantification in a single acquisition, simplifying clinical application.