Object and detector scatter-function dependence on energy and position in high resolution PET

Abstract

We have shown in previous works that distinct non-stationary analytical scatter kernels can be extracted from line source measurements and used to independently subtract object scatter and subtract or restore detector scatter in high resolution PET. In this work, the dependence of the scatter components on energy threshold and source position I was investigated. Line source measurements were acquired in multispectral mode using the Sherbrooke PET simulator. Scatter parameters were extracted from data summed in energy windows with a lower threshold varying from 129 keV to 516 keV in steps of 42 keV, and a fixed upper threshold of 644 keV. Decreasing the lower threshold from 344 keV to 129 keV increases the trues by only 25%. but increases object scatter by 136% and almost triples detector scatter. A gain in efficiency by a factor of 2 or more would result from recovering the latter by restoration in the broad window. The intensity and shape of the scatter functions for both object and detector are shown to have a significant dependence on energy and position. This dependence needs to be taken into accwnt in the design of kernels for accurate scatter correction over a broad energy range.

Simultaneous Attenuation and Scatter Corrections in Small Animal PET Imaging

“…For phantoms, we have tested the method on 22 Na line source of effective diameter 0.85 mm, and on a 4 hot spots phantom made of a plexiglas cylinder of 11 cm diameter. The hot spots were made of 4 small bottles of diameter 25 mm equally filled with 18 FDG radiotracer, with one centered in the FOV and the other three were equally located at 8 mm from the centered bottle.…”

“…We have also studied the rats measured with 18 FDG in tumors and with 13 N-ammonia in the heart. The data were acquired with an energy threshold of 350 keV [22] and reconstructed with the maximum likelihood algorithm with 10 iterations [27]. For the simplicity of the application of the method, we considered the images of rats as made only of tissue.…”

“…Setting a high lower-energy threshold is to reduce the detection of scattered photons. In our previous works [22]- [23], we have demonstrated primary photons detected at lower energies and characterized primaries and scatter as a function of energy.…”

Performance evaluation and correction for scatter and attenuation on the LabPET4™ positron emission tomography system

“…Finally, photon scatter originating from within the object, gantry and detectors will produce a spatial blurring o f counts throughout an image. Again various methods for obtaining correction for this phenomenon has been explored in much detail [13][14][15][16][17][18][19][20][21][22][23] and will be addressed in Chapter 5.…”

“…Another group o f scatter correction algorithms rely on energy window manipulations to obtain information about the scatter distribution. One of these methods used a dual energy window [16] and an extension of this method was utilized to perform a multi-energy window scatter distribution estimate [22]. Grootoonk et al [16] assigned coincidence events to two energy windows occurring over the photopeak (380-850 keV) and over the Compton regime (200-380 keV).…”