[Window width as a dosage-relevant factor in high-contrast structures in CT].
OBJECTIVE
To establish the relationship between window width and dose to be applied in low-dose high-resolution (HR) computed tomography (CT).


METHODS
Low-dose HR CT-scans of the petrous bone displayed with different window values were analyzed for identification of osseous details. For two homogeneous phantoms, standard deviation of CT-numbers were measured in order to calculate the fraction of pixels not displayed within the correct grey level.


RESULTS
The broadest window used (4000 HU) allowed the best distinction of osseous structures. Standard deviation of CT-numbers in the phantoms varied between 28.5 and 43.2 (mean = 33.6) HU. Thus, only 26.6% of all pixels are displayed in the correct grey level for a 1000 HU-window, but 82.3% for a 4000 HU-window.


CONCLUSIONS
When using low doses and HR-reconstruction algorithms, large window widths allow for an optimal assessment of high-contrast structures. Under these conditions, even high standard deviations of the CT-numbers will not compromise image evaluation. Due to the restricted number of grey-levels that can be distinguished by the human eye, image noise is compressed into a smaller number of discernable grey-levels. Because of the inverse square root function between dose to be applied and window width used (derived in the article), an even minor enlargement of window permits considerable reductions of patient exposure while the discernable image noise remains constant.
Husstedt
H
H
Abteilung Neuroradiologie, Medizinische Hochschule Hannover.
Prokop
M
M
Becker
H
H
D016477:Artifacts; D006801:Humans; D010579:Petrous Bone / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data
Fensterweite als dosisrelevanter Faktor bei Hochkontraststrukturen in der CT.