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The Feasibility of Quantifying MRI Contrast Agent in Pulsatile Flowing Blood Using DCE-MRI

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M Gwilliam

M N Gwilliam*, D J Collins , M O Leach, M R Orton , Institute of Cancer Research, London, UK


SU-D-18C-4 Sunday 2:05PM - 3:00PM Room: 18C

Purpose: To assess the feasibility of accurately quantifying the concentration of MRI contrast agent (CA) in pulsatile flowing blood by measuring its T₁, as is common for the purposes of obtaining a patient-specific arterial input function (AIF). Dynamic contrast enhanced (DCE) -MRI and pharmacokinetic (PK) modelling is widely used to produce measures of vascular function but accurate measurement of the AIF undermines their accuracy. A proposed solution is to measure the T₁ of blood in a large vessel using the Fram double flip angle method during the passage of a bolus of CA. This work expands on previous work by assessing pulsatile flow and the changes in T₁ seen with a CA bolus.

Methods: A phantom was developed which used a physiological pump to pass fluid of a known T₁ (812ms) through the centre of a head coil of a clinical 1.5T MRI scanner. Measurements were made using high temporal resolution sequences suitable for DCE-MRI and were used to validate a virtual phantom that simulated the expected errors due to pulsatile flow and bolus of CA concentration changes typically found in patients.

Results: : Measured and virtual results showed similar trends, although there were differences that may be attributed to the virtual phantom not accurately simulating the spin history of the fluid before entering the imaging volume. The relationship between T₁ measurement and flow speed was non-linear. T₁ measurement is compromised by new spins flowing into the imaging volume, not being subject to enough excitations to have reached steady-state. The virtual phantom demonstrated a range of recorded T₁ for various simulated T₁ / flow rates.

Conclusion: T₁ measurement of flowing blood using standard DCE-MRI sequences is very challenging. Measurement error is non-linear with relation to instantaneous flow speed. Optimising sequence parameters and lowering baseline T₁ of blood should be considered.

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