Speaker
Ms
Leticia Ortega Maynez
(School of Chemical Engineering and Analytical Science at the University of Manchester)
Description
The very high resolution quad-HIDAC PET scanner has four detector banks each with
four planar high density avalanche chambers, forming 16 modules in total. The
scanner has a large field of view (FOV) of 170 mm x 170 mm x 280 mm able to do
whole body rodent imaging. It has many important applications, just one example
being dynamic neuroreceptor imaging in mice. However, detector normalisation is
crucial, meaning that degrading factors introduced by the scanner’s geometry and
detector efficiencies must be corrected. To see the effects on a reconstructed
image, a list-mode data set from a 18F uniformly filled cylindrical phantom (3cm in
diameter and 5cm in length) was reconstructed, which revealed problems in the
central transverse slices and a square shape due to the gaps between the planar
detectors.
In order to estimate the detector efficiencies a specific method for the quad-HIDAC
scanner is proposed. The approach creates four matrices, each representing a bank
of panel converters, such that each matrix element represents several stacked
detector elements. The method fits a 2nd order polynomial to each row of each of
these matrices in order to reduce noise, thus obtaining a better efficiency
distribution for each detector bank. In order to validate the method a Monte Carlo
simulation was developed. Different detector efficiency distribution models were
tested and events from a point source using these detection efficiencies were
simulated and recorded within a list-mode data file. The objective is recover the
efficiencies using only the coincidence events collected. The simulation shows that
the proposed method gives a good approximation for each model tested.
The efficiencies ei-ej, joining each line of response (LOR), were included within
an expectation maximisation (EM) reconstruction algorithm, which also includes a
scanner geometry normalisation. Various reconstruction approaches were tested to
see the difference between corrected images and uncorrected ones. The results show
a notably improved homogeneity in the reconstructed images across the transaxial,
coronal and sagittal views and an appreciable correction for the gaps between
detectors banks. The reconstructed images were corrected without using scatter or
attenuation corrections, which are relatively minor for this size of phantom.
Author
Ms
Leticia Ortega Maynez
(School of Chemical Engineering and Analytical Science at the University of Manchester)
Co-authors
Dr
David Hastings
(North Western Medical Physics, Christie Hospital)
Dr
J. Andrew Reader
(School of Chemical Engineering and Analytical Science at the University of Manchester)
Dr
Peter Julyan
(North Western Medical Physics, Christie Hospital)
