Are you using ASL to track disease progression? Do you wonder if quantitative ASL values vary because of hardware or physiology?
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.