| Objective: To compare the image quality under different doses conditions andto evaluate the effect of low-dose scanning of ankle articulation and wristarticulation on the representation of normal structure and on the image quality underthe condition of applying256-slices spiral CT scanning with different tube currentand tube voltage and, then to explore the feasibility and clinical significance of256-slices low-dose spiral CT scanning of temporal bone.Methods: The data of106(130wrist and ankle) patients who were received CTexamination in a certain hospital from Sep,2012to Sep,2013were collected andthe people with abnormal bone density (alcoholics, Large quantity application ofglucocorticoid in3months, post menopausal women, with a history of diabetesmellitus,≥70year-old human) were excluded. The patients were divided into theexperiment group and the control group just used conventional dose, being scannedby Phillips256slice intelligent CT (iCT) imagery system. The same scanningcoefficients were applied because the thickness and density of the bone structure ofankle/wrist and the structure of soft tissue were similar: SFOV was250mm,collimation was1.4mm, matrix was768×768, conventional dose condition was120kV/240mAs（control group）, low-dose condition groups were100kV/100mAs,100kV/80mAs,100kV/60mAs and80kV/60mAs (experimental groups). Dose wasmeasured by the CTDIvoland DLP description (have measured and corrected by CTwater phantom) of PHILIPS256CT iCT spiral CT windows. Third partyworkstation was IntelliSpace Portal V4.0.1. With the reconstruction of the acquiredimages, he standard deviation (SD) of CT in the regions of interest at the same levelwas used as the objective score; by double-blind review from two experts of radiology, evaluation of images under all kinds of the scanning doses was assubjective score. The score was analyzed with statistical method.Results: In the80kV/60mAs group, the objective score was2.65±0.53, noisewas43.83±7.17, the satisfaction on the image was poor, so the group was given upafter10images capture were performed. When scanning dose conditions were120kV/240mAs,100kV/100mAs,100kV/80mAs,100kV/60mAs,80kV/60mAs,DLP was235.74±17.34,43.94±6.33,40.88±4.17,26.48±3.41,18.19±1.72,respecitively; subjective score was3.97±0.16,3.58±0.51,3.29±0.46,3.06±0.27,2.65±0.53, respectively; objective score (noise) was7.76±1.68,10.18±3.97,23.03±4.17,34.88±6.27,43.83±7.17, respectively. There were significantdifference in the subjective and objective score between all the experimental groupsand the control group, and among all the experimental groups（P<0.05）. Comparedwith the images in the control group, the subjective score was decreased slightlyabout the bone, soft tissue, artifacts and noise, three-dimensional reconstruction andso on in the images in the experimental groups with the dose condition of100kV/100mAs,100kV/80mAs,100kV/60mAs, however, the mean objective score wasabove3; SD of objective score increased.Conclusion: Compared with the image from conventional dose volume(120kV/240mAs), when the scanning condition decreased to80kV/60mAs, and thedose of patient decreased to18.19±1.72Gy·cm, subjective score of image qualitywas2.65±0.53, which was insufficient to meet the needs of diagnosis. Whenscanning condition decreased to100kV/60mAs, the dose of patient decreased from235.74±17.34mGy·cm to26.48±3.41mGy·cm，subjective score was3.06±0.27, theCT3D image quality tended to be in sound level, the portion of superior qualityimage decreased, but with low dose volume, the axial images and3D images couldrepresent the anatomical relation better, and correctly represent the specialinformation of ankle joint and wrist joint jury, which could meet the clinical demandand protect the patient. |
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