MultiDetector-row Computed Tomography (MDCT) or MultiSlice Computed Tomography (MSCT) has undergone remarkable progress since its first introduction at the end of the 1990s. Given that CT examinations are generally recognized as a relatively high-dose procedure, concern has been expressed at the associated increase in doses. The International Committee on Radiation Protection (ICRP) noted in their report No.87 that absorbed doses in tissues from CT are among the highest observed in diagnostic radiology (i.e. 10–100 mGy). Therefore, the purpose of this thesis is to calculate the dosimetric quantities for brain, chest, and abdomen-pelvis examinations that were carried out using Philips Brilliance 16 and Brilliance 64 CT Scanners of the University General Hospital “Attikon”, as well as to perform their intercomparison. For brain examinations, axial technique was utilized. However, for chest and abdomen-pelvis examinations, spiral technique was applied. The effect of overranging (or overscanning) is connected with spiral mode and its contribution to patient dose is really important in case of MSCT scanners. Therefore, the contribution of the overrange effect for body examinations carried out was calculated. In the framework of this thesis, the contribution of overrange to the effective dose received by patients submitted to the forementioned examinations is calculated. Additionally, dose measurements were carried out in order to estimate the radiation burden to the eye lenses and the thyroid during the typical brain examination, both when eye lenses are inside and outside the irradiation field. / Οι Υπολογιστικοί Τομογράφοι (ΥΤ) πολλαπλών τομών έχουν σημειώσει μεγάλη πρόοδο από την κλινική εφαρμογή τους στις αρχές του 1990. Λαμβάνοντας υπ’ όψιν ότι οι εξετάσεις ΥΤ συνεπάγονται υψηλή ακτινική επιβάρυνση του ασθενή, η μελέτη τους έχει συγκεντρώσει το ερευνητικό ενδιαφέρον της επιστημονικής κοινότητας. Η Διεθνής Επιτροπή Ακτινοπροστασίας (ICRP) επισημαίνει στην αναφορά Νο 87 ότι η απορροφούμενη δόση στους ιστούς από εξετάσεις ΥΤ είναι από τις υψηλότερες στη διαγνωστική ακτινολογία (10-100 mGy). Συνεπώς, σκοπός της παρούσας διπλωματικής εργασίας είναι ο υπολογισμός των δοσιμετρικών μεγεθών για τις συνήθεις εξετάσεις εγκεφάλου, θώρακος και άνω-κάτω κοιλίας, οι οποίες πραγματοποιούνται με τους ΥΤ πολλαπλών τομών Brilliance 16 και Βrilliance 64 της Philips στο Π.Γ.Ν “ΑΤΤΙΚΟΝ ”,καθώς επίσης και η σύγκριση των αντίστοιχων δόσεων μεταξύ των συγκεκριμένων ΥΤ. Οι ασθενείς που υποβάλλονται σε εξετάσεις θώρακος και άνω-κάτω κοιλίας που πραγματοποιούνται με ελικοειδή τεχνική λαμβάνουν επιπλέον δόση (overscan) που οφείλεται στην τεχνική αυτή. Η συνεισφορά του “overscan” είναι ιδιαίτερα σημαντική στους ΥΤ πολλαπλών τομών, οπότε επιπλέον στόχος αυτής της διπλωματικής είναι ο υπολογισμός της. Τέλος, πραγματοποιήθηκαν μετρήσεις της δόσης του θυρεοειδή και των φακών των οφθαλμών κατά την υποβολή ασθενών στη συνήθη εξέταση εγκεφάλου, τόσο στην περίπτωση παρουσίας των οφθαλμών εντός όσο και εκτός πεδίου ακτινοβόλησης.

Vainikinių arterijų tyrimas daugiapjūviu kompiuteriniu tomografu (DKT) į klinikinę praktiką įdiegtas nesenai. Tai neinvazyvus tyrimo metodas, kurį galima atlikti ir ambulatoriniams pacientams. Tačiau greta savo privulumų, jis turi ir trūkumų – dėl nuolatinio vainikinių arterijų judėjimo širdies ciklo metu gali atsirasti liekamųjų judesio artefaktų atkuriant vaizdus. Jų tikimybė priklauso ne tik nuo aparato, kuriuo atliekamas tyrimas, techninių charakteristikų, bet ir nuo širdies veiklos ypatumų. Yra atlikta nemažai tyrimų, įvertinančių vainikinių arterijų vaizdų kokybės priklausomybę nuo širdies susitraukimų dažnio, jo variabilumo, kitų faktorių. Kairiosios Hiso pluošto kojytės blokados, sąlygojančios nesinchronišką skilvelių susitraukimą ir atsipalaidavimą, įtaka vaizdų kokybei tyrinėta mažai. Šiame tyrime buvo palyginta vaizdų kokybė tarp pacientų, kuriems nustatyta visiška kairiosios Hiso pluošto kojytės blokada ir nėra laidžiosios sistemos sutrikimų, grupių. Analizuota vainikinių arterijų įvertinimo visuose širdies ciklo rekonstrukciniuose intervaluose įtaka vaizdų kokybės vidurkiui. Nustatyta, kokia yra DKT tyrimo diagnostinė vertė identifikuojant hemodinamiškai reikšmingas vainikinių arterijų stenozes. Kadangi DKT tyrimas susijęs su jonizuojančia spinduliuote, įvertinti rentgeno vamzdžio srovės stiprumo moduliavimo ypatumai. Taip pat nustatyta širdies susitraukimų dažnio, jo variabilumo įtaka vaizdų kokybei, esant visiškai kairiosios Hiso pluošto kojytės blokadai. / Multislice computed tomography (MSCT) coronary angiography is one of the latest usage area of the computed tomography technology. It s a non-invasive diagnostic tool, wich can be performed in ambulant patients. MSCT coronary angiography beside it's advantages has some drawbacks. The main drawbacks are lower spatial resolution and residual motion artifacts in MSCT images. Therefore quality of coronary images and diagnostic value of MSCT angiography differs, depending on patient's clinical characteristics, especially on heart contraction features during scanning. Asynchronic contraction and relaxation of the right and left ventricles, caused of bundle branch block can also influence image quality of MSCT coronary angiography. To date, there are only few studies, conducted to analyse diagnostic performance of MSCT coronary angiography in patients with left bundle branch block. Although influence of heart rate, heart rate variability and the other factors (for example, age, sex, body mass index) on MSCT image quality are quite well investigated. Thus, the present study were designed to investigate the influence of complete left bundle branch block on image quality of MSCT coronary angiography more detail in comparison with control patients group without electrical conduction disturbances, reveal the diagnostic value of MSCT angiography to identify hemodinamicaly significant coronary stenosis.

<p>Kompjuterizovana tomografija (CT) je jedan od najznačajnijh dijagnostičkih modaliteta, čija upotreba raste iz decenije u deceniju. U ukupnom broju radiolo&scaron;kih pregleda CT je zastupljena sa 5-10%, ali je njen doprinos ukupnoj dozi za populaciju veći od 50%. Osnovni pokazatelji kvaliteta slike i doza, kao i prateći radijacioni rizik zavise od primenjene radiografske tehnike odnosno CT pregleda. U smislu&nbsp; dobre radiolo&scaron;ke prakse i u skladu sa osnovnim principima za&scaron;tite od zračenja, poželjna je primena najniže moguće doze za pacijenta uz održavanje kvaliteta slike i dijagnostičke informacije. Cilj istraživanja jeste definisanje optimalnog protokola pregleda vi&scaron;eslojnom CT za dijagnozu pojedinih regija tela, kao i da se utvrde doze i radijacioni rizik za pacijente pre i nakon optimizacije protokola. Analizom je obuhvaćeno ukupno 437 pacijenata, koji su podeljeni u grupe prema regijama tela koje su snimane: I&ndash;nekontrastni CT glave, II-CT glave sa i.v. kontrastom, III-CT grudnog ko&scaron;a, IV-CT abdomena i karlice i V-CT angio (CT angiografija aortoilijačnog segmenta i donjih ekstremiteta). Studija je izvedena u 2 faze: u I fazi je kori&scaron;ćen standardni protokol za regiju tela koja se snimala, a u II fazi CT pregledi su izvedeni po modifikovanom protokolu (promenom parametra vrednosti mAs), uz minimalne zahteve u pogledu kvaliteta slike.Na osnovu dozimetrijskih&nbsp; pokazatelja procenjena je efektivna doza i radijacioni rizik za pacijente u obe faze. U studiji su kori&scaron;ćene smernice iz Vodiča EUR 16262&nbsp; EN, u kojima su definisani parametri za procenu kvaliteta slike da bi se analizirali različiti anatomski preseci određenih regija tela koji su se snimali. Kvalitet slike za svakog pacijenta je ocenjen pomoću trostepene skale vizualizacije za svaki parametar anatomske regije: 0-detalji su vidljivi, 1-detalji se prikazuju, 2-detalji se jasno prikazuju. Kori&scaron;ćena je subjektivna metoda gde su dva iskusna radiologa vr&scaron;ili interpretaciju slike. Konačna ocena kvaliteta slike svakog pregleda odgovara zbiru svih parametara procenjenih po trostepenoj skali&nbsp; vizualizacije. Zatim je za potrebe izračunavanja veličine FOM (figure of merit) izračunata vrednost indeksa ocene kvaliteta slike (zbir svih&nbsp; ocena parametra/brojem parametara). Vrednost FOM je izračunata kao količnik indeksa ocene kvaliteta slike i efektivne doza po pacijentu. Prosečna vrednost FOM za svaku grupu ispitanika nam je poslužila kao relativni pokazatelj za upoređivanje između neoptimizovane i optimizovane grupe ispitanika za isti tip pregleda. Poređenjem vrednosti efektivne doze u prvoj i drugoj fazi istraživanja kvantifikovano je smanjenje radijacionog opterećenja za pacijente nakon optimizacije protokola. Rezultati su pokazali da je optimalnim izborom protokola u&nbsp;&nbsp; smislu parametara ekspozicije (smanjenjem vrednosti mAs) moguće značajno smanjiti dozu zračenja kod pregleda glave za 7,5%, kod pregleda glave sa angiografijom za 7%, kod pregleda grudnog ko&scaron;a za 40%, kod pregleda abdomena i karlice za 25%. Grupa CT angio&nbsp; nije mogla da bude optimizovana, jer aparat nije prihvatao promenu kvaliteta slike kod zadatih parametara optimizacije. Primenom standardnih protokola postiže se kvalitet slike bolji nego &scaron;to je neophodno, a samim tim i veća doza zračenja nego &scaron;to je potrebno. Optimalnim izborom protokola u smislu parametara ekspozicije moguće je značajno smanjiti dozu zračenja, uz održavanje kvaliteta slike koji je dovoljan za adekvatnu radiolo&scaron;ku interpretaciju slike.</p> / <p>Computed&nbsp; tomography (CT) is one of the most significant diagnostic methods whose application has been increasing from decade to decade.&nbsp; Among the total number of radiological examinations CT accounts for 5-10%, however, its contribution in the whole dosage for the population is greater than 50%. Main indicator of the quality of images and dosages as well as the accompanying irradiation risk depend on applied radiographic technique that is CT examination. In the sense of good radiological practice and in accordance with basic principles of protection from irradiation, the application of the lowest possible dosage for a patient together with preserving the quality of image and diagnostic information are mostly welcomed. The goal of the research is to define the optimum examination protocol by multislice CT in diagnostics of certain body regions as well as to determine dosages and irradiation risk for patients both before and after protocol optimization. The analysis has included 437 patients divided into groups according to body regions which have been scanned: I-unenhanced head CT, II contrast enhanced head CT, III&ndash;chest CT, IV&ndash;abdomen and pelvis CT and&nbsp; V&ndash;angio CT (CT angiography of aortoiliac segment and lower extremities). The study has been conducted in 2 phases: in the first phase standard protocol for the scanned body region has been applied, and in the second phase CT examinations have been carried out according to the modified&nbsp; protocol&nbsp; (by change of parameters of values mAs)&nbsp; with minimum&nbsp; requirements&nbsp; regarding&nbsp; the&nbsp; image&nbsp; quality. On&nbsp; the&nbsp; basis&nbsp; of&nbsp; dosimetric&nbsp; indicators&nbsp; the&nbsp; efficient&nbsp; dosage&nbsp; and&nbsp; irradiation&nbsp; risk&nbsp; for&nbsp; the patients in both phases have been assessed. In the study the guidelines form the Guide EUR&nbsp; 16262&nbsp; EN&nbsp; have&nbsp; been&nbsp; observed&nbsp; where&nbsp; parameters for&nbsp; the&nbsp; assessment&nbsp; of&nbsp; image quality&nbsp; have&nbsp; been&nbsp; defined&nbsp; in&nbsp; order&nbsp; to&nbsp; analyze&nbsp; different&nbsp; anatomic&nbsp; cross sections of certain body&nbsp; regions.&nbsp; Image quality&nbsp; for&nbsp; each&nbsp; patient&nbsp; was&nbsp; assessed&nbsp; by&nbsp; three-level visualization&nbsp; scale&nbsp; for&nbsp; each&nbsp; parameter&nbsp; of&nbsp; anatomic&nbsp; region:&nbsp; 0&ndash;details&nbsp; are&nbsp; visible, 1&ndash;details are&nbsp; presented,&nbsp; 2&ndash;details are clearly&nbsp; presented.&nbsp; A&nbsp; subjective&nbsp; method&nbsp; was applied&nbsp; where&nbsp; two&nbsp; experienced&nbsp; radiologists performed&nbsp; the&nbsp; image interpretation. Final assessment&nbsp; of&nbsp; image quality&nbsp; of&nbsp; every&nbsp; examination corresponds&nbsp; to&nbsp; the&nbsp; sum&nbsp; of&nbsp; all parameters&nbsp; according&nbsp; to&nbsp; three-level&nbsp; visualization&nbsp; scale. Further,&nbsp; for&nbsp; the&nbsp; need&nbsp; of calculation of the size of FOM (figure of merit) the value of the index of assessment of the&nbsp; image&nbsp; quality&nbsp; (sum of all assessments of parameters/number of&nbsp; parameters) has been&nbsp; calculated.&nbsp; The&nbsp; value of&nbsp; FOM&nbsp; has&nbsp; been&nbsp; calculated as a quotient&nbsp; of&nbsp; the&nbsp; image quality assessment index and effective dosage per patient.&nbsp; The average value of FOM for&nbsp; every&nbsp; group&nbsp; of&nbsp; patients&nbsp; has&nbsp; offered us a&nbsp; relative&nbsp; indicator for&nbsp; comparison of&nbsp; non-optimum&nbsp; and optimum group of&nbsp; patients&nbsp; for&nbsp; the&nbsp; same&nbsp; type&nbsp; of&nbsp; examinations.&nbsp; By comparison of values of effective dosage in the first and second phase of the research a decrease in irradiation load for patients after protocol optimization was quantified. The results have&nbsp; shown&nbsp; that&nbsp; by&nbsp; optimum&nbsp; protocol&nbsp; selection&nbsp; in&nbsp; the&nbsp; sense&nbsp; of&nbsp; exposition parameters (by&nbsp; reduction of&nbsp; values of&nbsp; mAs) it is&nbsp; possible to reduce significantly&nbsp; the irradiation dosage at&nbsp; unenhanced head CT examination for 7,5%, at contrast enhanced head CT examination for 7%, at chest CT examination for 40%, at abdomen&nbsp; and pelvis CT examination for 25%. The group CT angio could not be optimized since the device&nbsp; did&nbsp; not&nbsp; accept&nbsp; the&nbsp; change in image quality at set&nbsp; optimization parameters. By application&nbsp; of&nbsp; standard&nbsp; protocols the image quality&nbsp; better&nbsp; than required&nbsp; was&nbsp; achieved and along with this, a higher irradiation dosage occurred than required. By selection of protocol in the sense&nbsp; of&nbsp; exposition parameters it is possible to reduce irradiation dosage significantly along with preserving image quality which is&nbsp; sufficient for adequate radiological image interpretation.</p>