A tin filter's dose reduction effect revisited: Using the detectability index in low-dose computed tomography for the chest

Akira Hasegawa; Katsuhiro Ichikawa; Yusuke Morioka; Hiroki Kawashima

doi:10.1016/j.ejmp.2022.05.006

A tin filter's dose reduction effect revisited: Using the detectability index in low-dose computed tomography for the chest

Phys Med. 2022 Jul:99:61-67. doi: 10.1016/j.ejmp.2022.05.006. Epub 2022 May 25.

Authors

Akira Hasegawa¹, Katsuhiro Ichikawa², Yusuke Morioka³, Hiroki Kawashima⁴

Affiliations

¹ Department of Radiological Technology, Faculty of Medical Technology, Niigata University of Health and Welfare, 1398 Shimami-cho, Kita-ku, Niigata-shi, Niigata 950-3198, Japan; Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: akira-hasegawa@nuhw.ac.jp.
² Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: ichikawa@mhs.mp.kanazawa-u.ac.jp.
³ Graduate School of Medical Science, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan; Department of Radiology, Toyama Prefectural Central Hospital, 2-2-78, Nishinagae, Toyama-shi, Toyama 930-8550, Japan. Electronic address: equitess1869@hotmail.co.jp.
⁴ Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: kawa3@med.kanazawa-u.ac.jp.

PMID: 35623206
DOI: 10.1016/j.ejmp.2022.05.006

Abstract

Purpose: To reevaluate a tin filter's (TF) dose reduction effect in computed tomography (CT) using a combination of an anthropomorphic chest phantom and a rod-shaped phantom.

Methods and materials: A third-generation dual-source CT system equipped with a built-in TF was employed. A chest phantom was scanned under low-dose conditions of 0.2 to 1.0 mGy with the TF at 100 kV (TF100kV) and without it at 100 kV and 120 kV (NF100kV and NF120kV). To eliminate effects other than that of the TF, only filtered back projection (FBP) was used for image reconstruction. On the images of the rod phantom placed inside the lung field, the CT number and the spatial resolution using the modulation transfer function (MTF) were measured. Using these indices plus the noise power spectrum (NPS) that was also measured, the detectability index based on the non-prewhitening model observer (d'_NPW) was calculated.

Results: The CT numbers and MTFs were almost identical across the three conditions. The area under the NPS curve was decreased by 13-17% with the TF compared with non-TF conditions. NPS increases at low frequencies of < 0.06 mm^-1 observed in NF120kV and NF100kV were eliminated by TF100kV. The potential dose reduction by the TF, estimated using the d'_NPW values, turned out to be 22 to 25%.

Conclusion: Based on the analysis of the FBP images of a chest phantom, the dose reduction attributable only to the TF was estimated at 22-25%, notably lower than those reported in previous studies.

Keywords: Chest computed tomography; Detectability index; Radiation dose; Tin filter.

MeSH terms

Algorithms
Drug Tapering*
Phantoms, Imaging
Radiation Dosage
Radiographic Image Interpretation, Computer-Assisted / methods
Tin*
Tomography, X-Ray Computed / methods

Substances

Tin