CTDI and Effective Dose in CT Scans

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What is the purpose of the CTDI phantom?

To give an average dose for a single axial slice (correct)

To transform DLP into effective dose

To convert the dose profile into a numerical value

To measure the X-ray output of a CT machine

What is the length of the CTDI phantom?

25 cm

20 cm

15 cm (correct)

10 cm

What is the advantage of using a calibrated 100-mm-long pencil ion chamber?

It is used to find the dose profile (correct)

It is used to measure the X-ray output of a CT machine

It provides a more accurate dose profile

It is used to transform DLP into effective dose

What is the shape of the CT profile?

Bell-shaped Signup and view all the answers

What is CTDI100?

The integral dose recorded by the chamber over its entire 100 mm length Signup and view all the answers

What two factors contribute to the CT profile being bell-shaped?

Finite size of the focal spot and Compton scatter Signup and view all the answers

What is the purpose of weighting the average of ion chamber readings in CTDI measurements?

To derive a more representative value of CTDI Signup and view all the answers

What is the term 'pitch' related to in a real clinical helical scan?

The distance of the table movement for one x-ray rotation Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

How is the effective dose (ED) typically calculated from the dose-length product (DLP) in CT scans?

By multiplying DLP by a constant factor Signup and view all the answers

What is the typical range of effective doses for a chest CT examination?

5-7 mSv Signup and view all the answers

What is one way to reduce exposure of the female breast during a CT scan?

Control the kVp Signup and view all the answers

Who is typically responsible for the entire QA program and remediation actions in a CT facility?

The chief physicist Signup and view all the answers

What is the purpose of the CTDI phantom in CT quality assurance?

To measure the dose of radiation Signup and view all the answers

What is the frequency of re-accreditation required by the American College of Radiology for CT facilities?

Every three years Signup and view all the answers

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 Signup and view all the answers

What type of personnel are responsible for undertaking semi-annual and annual QA activities in a CT facility?

Medical physicists Signup and view all the answers

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 Signup and view all the answers

What is the primary function of the ACR CT phantom?

To assess the average HU value for pure water and other parameters Signup and view all the answers

What is the pass/fail criterion for the adult head protocol using the small CTDI phantom?

80 mGy Signup and view all the answers

What is the purpose of the contrast-detail test device?

To measure the low-contrast resolution of the CT scanner Signup and view all the answers

What is the minimum high-contrast resolution required for the CT scanner?

0.4 lp/mm Signup and view all the answers

Why is the determination of doses central in CT?

Because it is crucial for patient safety and image quality Signup and view all the answers

What is the main contributor of collective dose to the patient population?

CT Signup and view all the answers

What is required to obtain a usable image in CT?

Sufficient irradiation of the image receptor Signup and view all the answers

What does CTDI represent in a CT machine?

A patient-independent measure of machine output Signup and view all the answers

Why is the reduction of CT doses important in imaging?

To decrease patient exposure to radiation Signup and view all the answers

What is the current gold standard for CT QA guidelines?

ACR CT Accreditation Program Signup and view all the answers

What is the goal of developing improved technologies and re-examining protocols in CT imaging?

To obtain clinically adequate images with lower exposure levels Signup and view all the answers