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Vpliv nepravilnega centriranja objekta na dozo in šum pri računalniški tomografiji abdomna
ID Hribar, Teja (Author), ID Vončina, Katja (Author), ID Starc, Tina (Mentor) More about this mentor... This link opens in a new window, ID Mišič, Jure (Co-mentor)

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MD5: FDC6E27E731A700BE360900416B675F3
PID: 20.500.12556/rul/ec88ade0-8be3-40e2-929d-cc2731e057e0

Abstract
Uvod: Na delovanje AEC sistema pri računalniški tomografiji močno učinkuje postavitev pacienta v izocenter CT gantirja. Nepravilno centriranje v vertikalni smeri povzroči spremenjeno velikost objekta slikanja na topogramu, kar se odraža v nepravilnem delovanju AEC sistema in posledično v nepravilni izbiri ekspozicijskih parametrov, spremenjeni dozni obremenitvi na objekt slikanja in spremembi kvalitete slike. Namen: Namen raziskovalnega dela je ugotoviti posledice v dozni obremenitvi in kvaliteti slike, ki jih za sabo pusti nepravilna nastavitev objekta slikanja v vertikalni smeri. Metode dela: Meritve so potekale na Kliničnem inštitutu za radiologijo v Univerzitetnem kliničnem centru Ljubljana na 64-reznem računalniškem tomografu Siemens Somatom definition. Meritve smo opravljali s fantomom celotnega trupa z oznako PBU 60, kjer smo uporabili v naprej določen protokol za slikanje zgornjega abdomna. Položaj fantoma v vertikalni smeri je variiral od 4,95 cm nad izocentrom do 15 cm pod izocentrom s premiki po 1 cm. Za merjenje posledic nepravilnega centriranja smo uporabili monitorsko-komercialni program za merjenje CTDIVOL vrednosti in program ImageJ za merjenje standardnega odklona HU vrednosti na štirih izbranih anatomskih mestih na enaki rezini pri vsakem premiku mize. Izvedba statistične analize je potekala v programu SPSS 21.0., s pomočjo linearne regresije in korelacije. Rezultati: Rezultati so pokazali linearno povezavo med velikostjo premera fantoma na topogramu in spremenjenim položajem fantoma v vertikalni smeri. CTDIVOL vrednosti so se pri odmiku mize 5 cm nad izocentrom povečale za 10% in zmanjšale za 10% pri premiku mize za 15 cm pod izocenter. Pri zvišanju CTDIVOL vrednosti, se je količina šuma na sliki zmanjšala in obratno, pri znižanju CTDIVOL vrednosti, se je količina šuma povečala. Razprava in sklep: Na podlagi statističnih izračunov smo dokazali, da se ob postavitvi objekta nad izocentrom velikost objekta na topogramu poveča, dozna obremenitev naraste, kvaliteta slike pa se temu primerno izboljša, zato slika vsebuje manj šuma. Ob postavitvi objekta nižje od izocentra se velikost objekta na topogramu zmanjša, dozna obremenitev pade, količina šuma na sliki pa se poveča.

Language:Slovenian
Keywords:CT abdomna, nepravilno centriranje, kvaliteta slike, CTDIVOL
Work type:Bachelor thesis/paper (mb11)
Organization:ZF - University College of Health Studies
Year:2017
PID:20.500.12556/RUL-94565 This link opens in a new window
COBISS.SI-ID:5339755 This link opens in a new window
Publication date in RUL:05.09.2017
Views:1311
Downloads:542
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Secondary language

Language:English
Title:Effects of mis-centering on dose and noise at computed tomography of the abdomen
Abstract:
Introduction: Positioning of the patient at CT has high influence on the proper operation of AEC system at computed tomography. Off-centering in vertical line cause a change in the size of the object on localizer, which have an effect on AEC system and leads to incorrect exposition and deviation in patient dose and image quality. Purpose: Our purpose is to determine the impact of vertical mis-centering on dose exposure of the object and image quality. Methods: Measurements were taken with the 64-MDCT CT scanner Siemens Somatom definition at the Institute of Radiology in University Medical Centre Ljubljana. For scanning we used whole body phantom labelled PBU 60 and a clinical protocol for upper abdomen CT. Phantom positions varried from 4,95 cm above the isocenter to 15 cm below in 1 cm steps. We used commercial radiation dose-monitoring software for analyzing and recording CTDIVOL data and program ImageJ for measure the standard deviation of Housfield units on four different anatomical places on the same picture, every 1 cm step. All the statistics analyses were performed in the SPSS 21.0. programme. Results: The results have shown a linear relation between the size of the object on localizer and vertical mis-centering of the phantom. The range of CTDIVOL values were for 10% higher at 5 cm above the isocenter and 10 % lower at 15 cm below the isocenter. If CTDIVOL value increase, the standard deviation of Housfield units decrease and opposite if CTDIVOL value decrease, the standard deviation of Housfield units on the picture increase. Discussion and conclusion: With the statistic analyses we proven that the central plate with the phantom placed above the isocenter leads to the increase of diameter of the phantom on the localizer and the radiation dose and decrease of the amount of the noise on the reconstructive image. If the central plate with the phantom is placed below the isocenter the diameter of the phantom and the radiation dose diminish, but the amount of the noise on the picture rises.

Keywords:abdomen CT, mis-centring, image quality, CTDIVOL

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