Design of a dynamic calibration phantom to be used to calculate the temporal resolution of a tomographic imaging device

Abstract

What follows is an account of the design and development of a calibration device for determining the temporal resolution of a tomographic imaging device. Current practice for characterizing the dynamic response of a tomographic imaging device, such as a Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) machine, uses image acquisition time as a surrogate for temporal resolution. At present, no standard method for characterizing the temporal resolution of a tomographic imaging device exists. Analogous to the spatial modulation transfer function used for characterizing spatial resolution, the concept of temporal Modulation Transfer Function (t-MTF) can be used to enable characterization of temporal resolution. A scanner's t-MTF represents the percent amplitude modulation in the image as a function of the input frequency. The calibration device uses slotted disks mounted to planetary gear sets' rotating ring gears. The sun gears are driven by a common shaft, thus allowing for about two decades of input frequencies to be obtained using a single motor and driveshaft. Preliminary results show a monotonic decline in the temporal modulation transfer as the input signal frequency is increased. As was hypothesized, there is more modulation at lower frequency and less modulation at higher frequency. Analogous to the definition of spatial resolution, one can define the frequency for which there is 10% temporal modulation transfer as the temporal resolution of a scanner.