QASPER (Quantitative Arterial Spin Labelling Perfusion Reference) is a calibration and quality assurance standard for MRI perfusion measurements using Arterial Spin Labelling (ASL). It simulates the process of delivery of arterial blood to an organ in a controlled and reproducible manner.
Why use QASPER?
- To ensure consistency of your ASL acquisition over time.
- To help with the development of new ASL pulse sequences.
- To compare the values from ASL sequences across scanners
Are you using ASL to track disease progression? Do you wonder if quantitative ASL values vary because of hardware or physiology?
How does QASPER work?
QASPER is a complete, easy-to-use phantom for Arterial Spin Labelling. It mimics the delivery of blood to the capillary bed using a porous polyethylene plastic substrate that has pore sizes comparable to the capillaries (approximately 10um), which is fed by 60 arteriole scale tubes arranged in a ring. This results in an approximately toroidal-shaped region of perfusion signal. Unlike a volunteer, the rate of delivery of perfusate (the water-based liquid that circulates the QASPER phantom) is consistent every time, therefore the QASPER phantom is a stable reference that can be used to assess system variability for ASL perfusion MRI measurements.
At the heart of the QASPER phantom is an MRI compatible pump that delivers liquid at a known flow rate to a simulated capillary bed. During operation, fluid is pumped around a closed system that is simply placed on the patient couch of an MRI scanner; it is not necessary to put tubing through the waveguides or to empty and re-fill the system at each use. The phantom continuously reports via wireless connection to a computer application its real-time operating state such as flow rate, temperature, battery drain etc, and can also be controlled by the user, for example to set the flow rate set point to a specified value. The computer application provides an intuitive graphical user interface for visualisation and control of the phantom, providing complete control and assurance during image acquisition that the phantom is operating as intended. Furthermore, data acquired of each phantom session can be saved for later comparison and combined analysis with the imaging data.
The flow path within QASPER comprises of three compartments. The first simulates the feeding arteries and arterioles that supply blood to an organ. Vessel geometry and flow velocities within this region match those found in the human body. Compartment two uses a porous polymer substrate to simulate the microvascular, incoherent flow observed at the capillary bed. The third compartment represents the remainder of the cardiovascular system; venous return from the organ to the heart where it is pumped back. A deliberately long, labyrinthine flow path ensures that none of the labelled bolus is recirculated before the label decays and ensures fully developed equilibrium magnetisation.
- The same system flow rate is maintained at all times, to within 3% of the desired value.
- Benchmark ASL perfusion measurements across ASL measurement techniques and MRI systems.
- Internal flow meter is calibrated with traceability to internationally recognised standards.
- The phantom connects wirelessly to phantom control software, providing real time control, monitoring and recording of the flow rate and temperature.
- The exact flow rate and temperature during an MR acquisition can be determined, and cross-referenced for Quality Assurance validation.
- Compare measurements with ground truth reference data (WIP).
- Use as part of an ASL Quality Control procedure.
- A Oliver-Taylor et al., "A multi-site round robin assessment of ASL using a perfusion phantom". In: Proceeding of ISMRM 2019. 2653. 2019. Abstract (PDF). D-Poster (PDF).
- A Oliver-Taylor et al., “A Calibrated Perfusion Phantom for Quality Assurance of Quantitative Arterial Spin Labelling”. In: Proceedings of ISMRM 2017. 0681. 2017. Abstract (PDF). Presentation (PDF). Link to ISMRM Talk (login required)