30 Questions
What is the purpose of the CTDI phantom?
To give an average dose for a single axial slice
What is the length of the CTDI phantom?
15 cm
What is the advantage of using a calibrated 100-mm-long pencil ion chamber?
It is used to find the dose profile
What is the shape of the CT profile?
Bell-shaped
What is CTDI100?
The integral dose recorded by the chamber over its entire 100 mm length
What two factors contribute to the CT profile being bell-shaped?
Finite size of the focal spot and Compton scatter
What is the purpose of weighting the average of ion chamber readings in CTDI measurements?
To derive a more representative value of CTDI
What is the term 'pitch' related to in a real clinical helical scan?
The distance of the table movement for one x-ray rotation
What is the limitation of CTDIvol in representing the overall risk of a CT scan?
It does not account for the exposure of the entire patient anatomy
What is the purpose of calculating the dose-length product (DLP) in CT scans?
To better represent the overall risk of a real clinical study
How is the effective dose (ED) typically calculated from the dose-length product (DLP) in CT scans?
By multiplying DLP by a constant factor
What is the typical range of effective doses for a chest CT examination?
5-7 mSv
What is one way to reduce exposure of the female breast during a CT scan?
Control the kVp
Who is typically responsible for the entire QA program and remediation actions in a CT facility?
The chief physicist
What is the purpose of the CTDI phantom in CT quality assurance?
To measure the dose of radiation
What is the frequency of re-accreditation required by the American College of Radiology for CT facilities?
Every three years
What is the primary focus of the accreditation program set up by the American College of Radiology for CT?
The individual CT at a facility
What type of personnel are responsible for undertaking semi-annual and annual QA activities in a CT facility?
Medical physicists
What is the purpose of submitting a set of clinical images of various types?
To demonstrate the quality assurance protocols used routinely at the facility
What is the primary function of the ACR CT phantom?
To assess the average HU value for pure water and other parameters
What is the pass/fail criterion for the adult head protocol using the small CTDI phantom?
80 mGy
What is the purpose of the contrast-detail test device?
To measure the low-contrast resolution of the CT scanner
What is the minimum high-contrast resolution required for the CT scanner?
0.4 lp/mm
Why is the determination of doses central in CT?
Because it is crucial for patient safety and image quality
What is the main contributor of collective dose to the patient population?
CT
What is required to obtain a usable image in CT?
Sufficient irradiation of the image receptor
What does CTDI represent in a CT machine?
A patient-independent measure of machine output
Why is the reduction of CT doses important in imaging?
To decrease patient exposure to radiation
What is the current gold standard for CT QA guidelines?
ACR CT Accreditation Program
What is the goal of developing improved technologies and re-examining protocols in CT imaging?
To obtain clinically adequate images with lower exposure levels
This quiz covers the concept of CTDI (Computed Tomography Dose Index) and how it relates to effective dose in CT scans, including the calculation of dose-length product and conversion factors.
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