CT Thorax lavdose - En sammenligning av et organdosemodulerings program X-CARE og vismut beskyttelse
DOI:
https://doi.org/10.7577/radopen.1996Keywords:
Radiografi, CT thorax, bildekvalitet, organdosemodulering, Vismut beskyttelse, SNR, CNRAbstract
Innledning
Computertomografi (CT) er en hyppig utført undersøkelse i Norge. Både mammae og thyroidea er strålefølsomme organer som eksponeres ved en CT thorax undersøkelse. For å få ned inngangsdosen (ESD) til slike strålefølsomme organer kan man enten benytte seg av en organspesifikk adaptiv dose reduksjons protokoll (X-CARE) eller isteden legge vismut beskyttelse over de strålefølsomme organene ved CT-undersøkelsen. I denne studien sammenligner vi huddosen (ESD) over mamma, samt bildekvalitet, ved bruk av disse to metodene ved en CT thorax lavdose undersøkelse?
Material og metode
30 spiral skanninger, hvorav ti standard lavdose, ti med vismut beskyttelse og ti med X-CARE, ble utført på et Alderson fantom, kombinert med Care Dose 4D, på en Siemens SOMATOM Definition Edge 128 CT maskin. ESD ble målt, CTDIvol og Dose-lengde-produkt (DLP) ble hentet ut fra doserapporten. Den objektive bildekvaliteten ble analysert, og vurdert ved hjelp av tre Region Of Interest (ROI), plassert hhv i luft, i lungeparenkymet og i pleura parietale. Signal til støyforhold (SNR) og kontrast til støyforhold (CNR) ble regnet ut ifra ROI verdiene.
Resultater
ESD til mamma viste dosereduksjon sammenlignet med en standard CT thorax lavdose; hhv 16,5 % dosereduksjon ved bruk av vismut beskyttelse, og 0,44 % ved X-CARE. Det var ingen forskjell i CTDIvol og DLP ved standard lavdose skanningen eller skanningen med vismut beskyttelse. Skanningen med X-CARE ga en økning i CTDIvol og DLP på omtrent 12 %. SNR og CNR i lungeparenkymet og pleura parietale var høyest ved standard lavdose undersøkelsen. Bildestøyen økte 48 % ved vismut og 26,4 % ved X-CARE.
Konklusjon
ESD ble markant redusert ved CT thorax lavdose undersøkelsen med vismut beskyttelse, men ga samtidig en markant økning i bildestøyen. X-CARE reduserte ESD minimalt sammenlignet med standard lavdose skanningen, men ga økt bildestøy. Den mest effektive måten å oppnå en optimal lavdose undersøkelse på, er ved å utføre en standard CT thorax lavdose protokoll.
Abstract
Introduction
Computed tomography (CT) is a frequent examination conducted in Norway. Mammae and thyroid gland are both dose sensitive body organs, which are being exposed during a thoracic CT examination. Therefore, an optimization of protocols is necessary and X-CARE (organ-based tube current modulation) or bismuth protection may be applied during a CT examination. Will the two methods give a difference in the entrance surface dose (ESD) to mamma and the image quality of a low-dose thoracic CT examination?
Materials and methods
Thirty spiral CT scans of which ten was standard low-dose, ten with bismuth shielding and ten with X-CARE was performed on an Alderson phantom, combined with CARE Dose 4D and carried out on a Siemens SOMATOM Definition Edge 128. Measures as ESD, CTDIvol and Dose-length-product (DLP) were obtained from the dose report. The image quality was analysed objectively and assessed using three Region of Interest (ROI), placed in air, lung parenchyma and parietal pleura. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were calculated from the ROI results.
Results
ESD to the mammary gland demonstrated a dose reduction compared to a standard thoracic CT low dose. Respectively; 16.5 % dose reduction with bismuth shielding and 0.44 % with X-CARE. There was no difference in CTDIvol and DLP between the standard low-dose scans and the scans with bismuth shielding. The CT scans with X-CARE gave an increase in CTDIvol and DLP by approximately 12 %. SNR and CNR in the lung parenchyma and parietal pleura were highest during the standard low-dose scans. Bismuth shielding increased the noise with 48 % and X-CARE with 26,4 %.
Conclusion
ESD was significantly reduced during the CT thoracic low-dose examination using bismuth shielding, however notably the bismut increased the image noise. X-CARE reduced the ESD minimally compared to the CT low-dose scans, and it also increased the image noise. The most efficient way to achieve an optimal thoracic CT examination is to use a standard low-dose protoco
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