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Advances in Radiotherapy
& Nuclear Medicine PET and Compton Camera CZT based system

A

B

Figure 10. Normalized activity profiles of Figure 7 with Gaussian fits after 800 iterations of MLEM. (A) Top row, normalized activity profiles in the x, y, and
z directions of positron emission tomography MLEM. (B) Bottom row, normalized activity profiles in the x, y, and z directions of Compton camera MLEM.
Abbreviation: MLEM: Maximum likelihood expectation maximization.

The computed FWHM values are summarized in Table 2. Summary of full width at half‑maximum results
Table 2, and the computed FWTM values are summarized from normalized activity profiles
in Table 3. The computed FWHM values in the x and z Iteration FWHM (mm)
directions of the PET reconstruction (3.701 – 4.025 mm)
show little to no improvement with iteration number and 20 800 3500
are a consequence of the positron range blur. However, x y z x y z x y z
the computed FWHM of CC reconstruction with 51 keV Profile
of energy blur in the x (1.669 mm) and z directions PET 4.052 6.286 4.008 3.821 2.728 3.704 3.826 2.379 3.701
(1.650 mm) show that under ideal conditions, the energy CC 1.386 2.165 1.368 3.536 7.533 3.418 1.669 3.509 1.650
resolution of CZT crystals allows for correction of positron Abbreviations: CC: Compton camera; FWHM: Full width at
range effects in the x and z directions. half-maximum; PET: Positron emission tomography.
4. Discussion subset of COR-LOR coincidences, such as those referenced

The results from the GATE simulation demonstrate an in Figure 3, is used to supplement PET reconstruction
increase in sensitivity for the detection of the Compton of the superset of LORs, then this would be seen as an
kinematics of high-energy prompt-gammas that enter increase in overall system sensitivity.
the CZT crystals. This enhancement can be attributed to Moreover, CC reconstruction using our dual-panel
the high Compton scattering cross section of CZT and system demonstrates the capability to estimate source
the 4 cm edge-on detector thickness, which allows for the locations free of positron-range artifacts in the xz plane
subsequent photoelectric detection of Compton scattered parallel to the detector faces. Although the number of
gammas originating from prompt gammas. This permits iterations of MLEM needed to provide 1 mm FWHM
our dual-panel CZT system to gather COR projection data, measurements in the x and z directions significantly
which is used for CC image reconstruction free of positron increases when taking CZT energy resolution (5%)
range effects. The results of this study do not directly lead into account, this provides promising results that CC
to an increased PET sensitivity for this system; however, in information retained by the system can be leveraged to
potential joint PET-CC reconstruction algorithms, if the provide improved CC-informed PET reconstruction.

Volume 2 Issue 2 (2024) 9 doi: 10.36922/arnm.3330