Unit:
Κατεύθυνση Ιατρική Φυσική-ΑκτινοφυσικήLibrary of the School of Health Sciences
Supervisors info:
Κωνσταντίνος Περισυνάκης, Αναπληρωτής Καθηγητής, Τμήμα Ιατρικής, Πανεπιστήμιο Κρήτης
Ιωάννης Δαμηλάκης, Καθηγητής, Τμήμα Ιατρικής, Πανεπιστήμιο Κρήτης
Θωμάς Μαρής, Αναπληρωτής Καθηγητής, Τμήμα Ιατρικής, Πανεπιστήμιο Κρήτης
Original Title:
Μελέτη του συστήματος αυτόματου ελέγχου έκθεσης ενός μοντέρνου συστήματος Υπολογιστικής Τομογραφίας. Πως το μήκος της εντοπιστικής σάρωσης επιδρά στην καμπύλη διαμόρφωσης ρεύματος κατά μήκος μιας εξέτασης.
Translated title:
Automatic Exposure Control system of a modern CT scanner: How the lenght of Scanned Projection Radiographs affects current modulation
Summary:
With their vast technological improvement, Computed Tomography (CT) scanners have been able to form an integral part of medical imaging. The increment of radiation dose of the total population, as a result of their increasing use, demands limitation, in a way - of course - such that there is no significant impact on the overall quality of the examination.
Automatic exposure control (AEC) systems are at the center of this effort who can achieve dose reduction up to 68%. The operation of those systems will be studied in this master's thesis.
As confirmed by the statistical study we conducted, the operator of a CT scanner, with the ultimate purpose of limiting the radiation dose which will be received by the subject, they reduce the length of Scanned Projection Radiographs (SPRs) which are a vital parameter for the proper functioning of AEC systems.
In this study we focus on the length of the SPRs in order to study how it affects current modulation curves.
In first step, a preliminary study was conducted in order to better understand the way SmartmA (GE Healthcare, Milwaukee, Wisconsin) works.
Specifically, we examined the noise distribution through an image set, using both SmartmA and AutomA systems as well as the effect of the Noise Index on the noise quantity of the final images. We also attempt to understand the way SmartmA utilizes SPRs to define the current modulation curve. Finally, in the preliminary measurements, we studied the distribution of radiation absorbance for 5 anthropomorphic PMMA phantoms that represent the average individual in different ages.
The core of this study contains the scanning of those phantoms in chest area proportional to a lung examination. By maintaining a constant Image Volume (I.V.), we gradually change the length of the SPRs, recording each time the mA tables provided by the system.
The evaluation of the results confirmed that the limitation of the SPRs may deprive valuable information from SmartmA. This would leads to an inability to a proper current modulation by increasing the values usually observed at the same I.V. between 5% and 32.6%.
This increase is particulary important because of the presence of radiation-sensitive organs , the so called Organs At Risk (OARs), that may be near the I.V. and even more so when seen in the younger population.
Main subject category:
Health Sciences
Keywords:
Computed Tomography, CT, Automatic Exposure Control, AEC, Automatic Tube Current Modulation, ATCM, Scanned Projection Radiographs, SPR, Scout, Scouts, Length, Scanned Projection Radiographs length, Scout lenght, SmartmA, Smart mA, AutomA, Auto mA, Revolution GSI, General Electric, mA tables, Image Volume, IV, Primary Exposed Volume, PEV, Primary Exposed Body Volume, PEBV, Overscanning, z-overscanning
