Takahashi Akihiko, Himuro Kazuhiko, Baba Shingo, Yamashita Yasuo, Sasaki Masayuki
Division of Medical Quantum Science, Department of Health Sciences, Kyushu University, Fukuoka, Japan.
Division of Radiology, Department of Medical Technology, Kyushu University Hospital, Fukuoka, Japan.
Asia Ocean J Nucl Med Biol. 2018 Winter;6(1):24-31. doi: 10.22038/aojnmb.2017.9673.
Yttrium-90 (Y) is a beta particle nuclide used in targeted radionuclide therapy which is available to both single-photon emission computed tomography (SPECT) and time-of-flight (TOF) positron emission tomography (PET) imaging. The purpose of this study was to assess the image quality of PET and Bremsstrahlung SPECT by simulating PET and SPECT images of Y using Monte Carlo simulation codes under the same conditions and to compare them.
In-house Monte Carlo codes, MCEP-PET and MCEP-SPECT, were employed to simulate images. The phantom was a torso-shaped phantom containing six hot spheres of various sizes. The background concentrations of Y were set to 50, 100, 150, and 200 kBq/mL, and the concentrations of the hot spheres were 10, 20, and 40 times of those of the background concentrations. The acquisition time was set to 30 min, and the simulated sinogram data were reconstructed using the ordered subset expectation maximization method. The contrast recovery coefficient (CRC) and contrast-to-noise ratio (CNR) were employed to evaluate the image qualities.
The CRC values of SPECT images were less than 40%, while those of PET images were more than 40% when the hot sphere was larger than 20 mm in diameter. The CNR values of PET images of hot spheres of diameter smaller than 20 mm were larger than those of SPECT images. The CNR values mostly exceeded 4, which is a criterion to evaluate the discernibility of hot areas. In the case of SPECT, hot spheres of diameter smaller than 20 mm were not discernable. On the contrary, the CNR values of PET images decreased to the level of SPECT, in the case of low concentration.
In almost all the cases examined in this investigation, the quantitative indexes of TOF-PET Y images were better than those of Bremsstrahlung SPECT images. However, the superiority of PET image became critical in the case of low activity concentrations.
钇-90（Y）是一种用于靶向放射性核素治疗的β粒子核素，可用于单光子发射计算机断层扫描（SPECT）和飞行时间（TOF）正电子发射断层扫描（PET）成像。本研究的目的是通过使用蒙特卡罗模拟代码在相同条件下模拟Y的PET和SPECT图像来评估PET和轫致辐射SPECT的图像质量，并对它们进行比较。
使用内部蒙特卡罗代码MCEP-PET和MCEP-SPECT来模拟图像。体模是一个躯干形状的体模，包含六个不同大小的热球。Y的背景浓度设置为50、100、150和200 kBq/mL，热球的浓度为背景浓度的10、20和40倍。采集时间设置为30分钟，使用有序子集期望最大化方法重建模拟的正弦图数据。采用对比恢复系数（CRC）和对比度噪声比（CNR）来评估图像质量。
当热球直径大于20 mm时，SPECT图像的CRC值小于40%，而PET图像的CRC值大于40%。直径小于20 mm的热球的PET图像的CNR值大于SPECT图像的CNR值。CNR值大多超过4，这是评估热区可分辨性的一个标准。在SPECT的情况下，直径小于20 mm的热球不可分辨。相反，在低浓度情况下，PET图像的CNR值降至SPECT的水平。
在本研究中检查的几乎所有情况下，TOF-PET Y图像的定量指标均优于轫致辐射SPECT图像。然而，在低活度浓度情况下，PET图像的优势变得至关重要。
