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Thyroid shields versus z-axis automatic tube current modulation for dose reduction at neck CT.

David A Leswick¹, Megan M Hunt, Steven T Webster

¹Department of Medical Imaging, Royal University Hospital, University of Saskatchewan, Saskatoon, SK, Canada. david.leswick@saskatoonhealthregion.ca

|September 11, 2008

Summary

Z-axis automatic tube current modulation (ATCM) significantly reduces thyroid radiation dose during neck CT scans. While shields offer some benefit, ATCM is more effective for dose reduction, though it can increase image noise.

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X-ray Dose Reduction through Adaptive Exposure in Fluoroscopic Imaging

X-ray Dose Reduction through Adaptive Exposure in Fluoroscopic Imaging

Published on: September 11, 2011

Area of Science:

Radiology
Medical Imaging
Radiation Physics

Background:

Neck CT scans involve radiation exposure to the thyroid gland.
Minimizing radiation dose is crucial for patient safety, especially in diagnostic imaging.
Thyroid shields and advanced CT techniques are explored for dose reduction.

Purpose of the Study:

To evaluate the efficacy of in-plane bismuth thyroid shields and z-axis automatic tube current modulation (ATCM) in reducing radiation dose to the thyroid during neck CT.
To assess the impact of these techniques on image noise in the thyroid and surrounding tissues.

Main Methods:

A phantom study was conducted using a female phantom and an eight-section CT scanner.
Radiation dose was measured using thermoluminescent dosimetry (TLD) chips in the thyroid, bone marrow, and soft tissues.
Scans were performed with fixed tube current and z-axis ATCM, both with and without thyroid shields.

Main Results:

Z-axis ATCM alone reduced thyroid dose by 78% (to 17.0 mGy), while shields reduced it by 42% (to 44.7 mGy).
The combination of shields and ATCM achieved an 83%-85% dose reduction (11.9-12.9 mGy).
ATCM reduced overall scan dose-length product by 60%, but shield use significantly increased thyroid image noise.

Conclusions:

Z-axis ATCM is a highly effective method for reducing thyroid radiation dose in neck CT.
Combining shields with ATCM offers marginal additional dose reduction but at the cost of increased image noise.
The findings suggest ATCM as a primary strategy for thyroid dose optimization in neck CT examinations.