TY - JOUR
T1 - Assessment of the image quality of virtual monochromatic spectral computed tomography images
T2 - a phantom study considering object contrast, radiation dose, and frequency characteristics
AU - Masuda, Shota
AU - Sugisawa, Koichi
AU - Minamishima, Kazuya
AU - Yamazaki, Akihisa
AU - Jinzaki, Masahiro
N1 - Funding Information:
We would like to express our gratitude to Mr. Toshio Watanabe, general manager of the Office of Radiological Technology of our hospital, for his assistance with this study.
Publisher Copyright:
© 2021, Japanese Society of Radiological Technology and Japan Society of Medical Physics.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
PY - 2021/3
Y1 - 2021/3
N2 - Fast kilovoltage (kVp)-switching technology cannot obtain conventional 120 kVp images; thus, 70 keV virtual monochromatic spectral computed tomography (CT) images (VMSI) are generally used. The contrast-to-noise ratio (CNR) is used to evaluate the image quality of VMSI; however, CNR does not include frequency characteristics. The present study aimed to investigate the evaluation methods of VMSI considering frequency characteristics by comparing the image quality of 70 keV VMSI with that of conventional 120 kVp images. The evaluated object contrasts were 70 and 300 Hounsfield units (HU). Scans used two radiation dose levels: low (LD) and standard (SD). The volume CT dose index of LD and SD was 4.8- and 12 mGy, respectively. Images were reconstructed by filtered back projection, evaluating CNR, noise power spectrum (NPS), task transfer function (TTF), and system performance (SP) function calculated as TTF2/ NPS. The total NPS values (spatial frequency range: 0.2 ~ 0.4 mm−1) of 70 keV VMSI were higher than those of 120 kVp images. The spatial frequency TTF values that reached 10% (f10%) of the 70 keV VMSI changed based on object contrast. For the low-contrast condition, a lower f10% was observed with 70 keV VMSI. The CNR of 70 keV VMSI was comparable to that of 120 kVp images in low- and high-contrast conditions. However, for 70 keV VMSI, SP of low-contrast was low, and SP of high-contrast was high, compared with those of 120 kVp images. This study suggested that only CNR was not sufficient to evaluate the image quality of VMSI; thus, evaluation methods considering frequency characteristics should be used.
AB - Fast kilovoltage (kVp)-switching technology cannot obtain conventional 120 kVp images; thus, 70 keV virtual monochromatic spectral computed tomography (CT) images (VMSI) are generally used. The contrast-to-noise ratio (CNR) is used to evaluate the image quality of VMSI; however, CNR does not include frequency characteristics. The present study aimed to investigate the evaluation methods of VMSI considering frequency characteristics by comparing the image quality of 70 keV VMSI with that of conventional 120 kVp images. The evaluated object contrasts were 70 and 300 Hounsfield units (HU). Scans used two radiation dose levels: low (LD) and standard (SD). The volume CT dose index of LD and SD was 4.8- and 12 mGy, respectively. Images were reconstructed by filtered back projection, evaluating CNR, noise power spectrum (NPS), task transfer function (TTF), and system performance (SP) function calculated as TTF2/ NPS. The total NPS values (spatial frequency range: 0.2 ~ 0.4 mm−1) of 70 keV VMSI were higher than those of 120 kVp images. The spatial frequency TTF values that reached 10% (f10%) of the 70 keV VMSI changed based on object contrast. For the low-contrast condition, a lower f10% was observed with 70 keV VMSI. The CNR of 70 keV VMSI was comparable to that of 120 kVp images in low- and high-contrast conditions. However, for 70 keV VMSI, SP of low-contrast was low, and SP of high-contrast was high, compared with those of 120 kVp images. This study suggested that only CNR was not sufficient to evaluate the image quality of VMSI; thus, evaluation methods considering frequency characteristics should be used.
KW - Computed tomography
KW - Dual-energy computed tomography
KW - Fast kilovoltage switching
KW - Task-based image quality
KW - Virtual monochromatic spectral computed tomography images
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U2 - 10.1007/s12194-020-00597-w
DO - 10.1007/s12194-020-00597-w
M3 - Article
C2 - 33400064
AN - SCOPUS:85099001016
VL - 14
SP - 41
EP - 49
JO - Radiological Physics and Technology
JF - Radiological Physics and Technology
SN - 1865-0333
IS - 1
ER -