Vpliv različnih postavitev lokalizacijskih posnetkov na določanje avtomatske modulacije toka v računalniški tomografiji : magistrsko delo

Plečko, Christian (author), Mekiš, Nejc (mentor), Viltužnik, Rebeka (comentor), Fošnarič, Miha (reviewer)

Uvod: Računalniška tomografija (CT) se začne s topogramom, ki sistemu ATCM zagotavlja vhodne podatke za prilagoditev tokovnih sunkov. Izbira postavitve topograma, anteriorno-posteriorni (AP), posteriorno-anteriorni (PA) in lateralni (LAT) ali njunih kombinacij, neposredno vpliva na oceno velikosti pacienta in posledično na sevalno dozo. Namen: Ugotoviti, kako različne postavitve lokalizacijskih posnetkov vplivajo na parametre avtomatske modulacije toka in sevalno dozo pri CT slikanju prsnih organov. Metode dela: Meritve so bile izvedene na fantomu PBU60 na CT Siemens Somatom Drive na Kliničnem inštitutu za radiologijo UKC Ljubljana. Opravljenih je bilo 50 meritev (n=10 na vsako kombinacijo) pri petih postavitvah: AP, PA, LAT, AP+LAT in PA+LAT. Zabeležili smo vrednosti CTDIvol, DLP ter efektivnih tokovnih sunkov (mAs). Za statistično analizo smo uporabili Kruskal-Wallisov test, Wilcoxonov test za odvisne vzorce ter Pearsonov korelacijski koeficient (IBM SPSS V29). Rezultati: Najnižje vrednosti CTDIvol so bile izmerjene pri kombinaciji AP+LAT (1,81 ± 0,07 mGy), najvišje pa pri samostojnem PA topogramu (2,43 ± 0,04 mGy). Razlika med AP+LAT in PA+LAT je znašala 15,42 % pri CTDIvol (p < 0,001) in 17,29 % pri DLP (p < 0,001). Pričakovane vrednosti CTDIvol in DLP so bile pri vseh kombinacijah statistično značilno višje od izmerjenih vrednosti (p < 0,005), kar odraža zasnovano predvidevanje sistema CARE Dose 4D. Pearsonov koeficient je potrdil visoko pozitivno korelacijo med efektivnimi mAs ter CTDIvol in DLP. Vrednosti SNR so se gibale med 1,73 ± 0,22 (PA) in 2,15 ± 0,21 (LAT), vrednosti CNR pa med 83,91 ± 17,86 (AP+LAT) in 102,48 ± 12,62 (LAT). Kljub statistično značilnim razlikam v doznih parametrih med posameznimi kombinacijami topogramov razlike v SNR in CNR med večino parov niso dosegle statistične značilnosti – pri primerjavi AP+LAT in PA+LAT sta bili vrednosti SNR (p = 1,000) in CNR (p = 0,269) primerljivi. Razprava in zaključek: PA topogram zaradi geometrijske povečave projekcije sistematično preceni efektivni premer telesa in poveča tokovne sunke brez izboljšanja kakovosti slike. Kombinacija AP+LAT zagotavlja algoritmu ATCM pravilno oceno eliptične geometrije telesa in dosega najnižjo sevalno dozo. Optimizacija postavitve topograma je enostaven ukrep, ki ga radiološki inženir lahko uveljavi brez sprememb protokola ali dodatne opreme.

• Language: Slovenian
• Keywords: magistrska dela, radiološka tehnologija, računalniška tomografija, lokalizacijski posnetek, topogram, avtomatska modulacija toka, CTDIvol in DLP
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: ZF - Faculty of Health Sciences
• Place of publishing: Ljubljana
• Publisher: [C. Plečko]
• Year: 2026
• Number of pages: 57 str., [2] str. pril.
• PID: 20.500.12556/RUL-184630
• UDC: 616-07
• COBISS.SI-ID: 284888067
• Publication date in RUL: 11.07.2026

Secondary language

• Language: English
• Title: The effect of different localizer radiographs positioning on automatic tube current modulation in computed tomography : master thesis

Abstract

Introduction: Computed tomography (CT) begins with a topogram, which provides the automatic tube current modulation (ATCM) system with input data for adjusting tube current. The choice of localizer positioning, anteroposterior (AP), posteroanterior (PA), lateral (LAT), or their combinations, influences the ATCM algorithm's estimation of patient size and consequently affects the radiation dose. Purpose: To determine how different localizer positionings and combinations affect ATCM parameters and radiation dose in chest CT imaging. Methods: Measurements were performed on a PBU60 phantom using a Siemens Somatom Drive CT at Institute of radiology, UMC Ljubljana. A total of 50 acquisitions were performed (n = 10 per combination) across five configurations: AP, PA, LAT, AP+LAT and PA+LAT. CTDIvol and DLP and effective tube current (mAs) were recorded. Statistical analysis was performed using the Kruskal-Wallis test, Wilcoxon test and Pearson correlation coefficient (IBM SPSS V29). Results: The lowest CTDIvol values were measured with the AP+LAT combination (1,81 ± 0,07 mGy), while the highest were recorded with the PA localizer (2,43 ± 0,04 mGy). The difference between AP+LAT and PA+LAT was 15,42 % for CTDIvol (p < 0,001) and 17,29 % for DLP (p < 0,001). Expected CTDIvol and DLP values were statistically significantly higher than actual measured values across all configurations (p < 0,005), reflecting the predictive design of the CARE Dose 4D system. Pearson correlation confirmed a strong positive relationship between effective mAs and both CTDIvol and DLP. SNR values ranged from 1,73 ± 0,22 (PA) to 2,15 ± 0,21 (LAT), and CNR values ranged from 83,91 ± 17,86 (AP+LAT) to 102,48 ± 12,62 (LAT). Despite statistically significant differences in dose parameters across localizer combinations, SNR and CNR differences between most pairs were mostly non-significant. The comparison of AP+LAT and PA+LAT yielded comparable SNR (p = 1,000) and CNR (p = 0,269) values. Discussion and conclusion: The PA localizer overestimates the effective patient diameter due to geometric magnification of the projection, increasing tube current without improving image quality. The AP+LAT combination provides the ATCM algorithm with a more accurate estimate of the elliptical body geometry and achieves the lowest radiation dose. Optimising localizer positioning is a simple measure radiographers can implement without modifying protocols or requiring additional equipment.

• Keywords: master's theses, radiologic technology, computed tomography, localizer radiograph, topogram, automatic tube current modulation, CTDIvol and DLP