SU‐D‐103‐06: Bismuth Shield Usage in MDCT Thoracic Scans: Organ Dose Vs. Image Quality

N. Januzis, G. Nguyen, L. Hurwitz, D. Frush, J. Hoang, C. Lowry, T. Yoshizumi

Research output: Contribution to journalArticle

Abstract

Purpose: To study Bismuth (Bi) shielding for the breast, organ dose and image quality were compared under the following conditions: (1) tube current modulation (TCM), (2) TCM with a Bi shield placed after topogram, and (3) manually reduced tube current (RTC) with no Bi. Methods: All measurements were performed with a 64‐slice scanner at 120 kVp. Organ dose was measured with MOSFETs using an adult male anthropomorphic phantom with supine breast attachments. The reference exposure and reduced exposure (with 4‐ply Bi shield) was measured with an ion chamber located at the level of the breast. The mA was reduced by normalizing the reference mA to the ratio of the reduced exposure to the reference exposure. Image quality was measured using a high contrast insert placed in the lung. Regions of Interest (ROIs) were drawn in thoracic organs to measure signal‐to‐noise ratio (SNR), percent contrast (%Contrast), noise, and HU values. Results: Organ doses (mGy) for the three scans (TCM, TCM with Bi, and RTC) were 11.1, 6.89, and 6.04 to the breast; 8.83, 8.01, and 7.62 to the lung; and 8.20, 7.36 and 8.40 to the heart, respectively. HU increase was greatest in the TCM with Bi scan for organs closest to the shield. The SNRs were 37.6, 34.1, and 43.3 and the %Contrast values were 349.2, 326.3, and 354.3 with TCM, TCM with Bi, and RTC, respectively. Conclusion: For thoracic CT, this RTC method provides a dose reduction to the breast similar to that of the TCM with Bi. Decrease in SNR and %Contrast in the TCM with Bi scan was expected due to decrease in photons reaching the detectors and beam hardening from the shield, respectively. Increased SNR in RTC scan was due to the increased mA compared to TCM scan at the level of measurement. U.S. NRC Health Physics Fellowship Grant No. NRC‐HQ‐12‐G‐38‐0022.

Original languageEnglish (US)
Number of pages1
JournalMedical physics
Volume40
Issue number6
DOIs
StatePublished - Jun 2013
Externally publishedYes

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Bismuth
Thorax
Breast
Health Physics
Lung
Photons
Noise
Ions

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

SU‐D‐103‐06 : Bismuth Shield Usage in MDCT Thoracic Scans: Organ Dose Vs. Image Quality. / Januzis, N.; Nguyen, G.; Hurwitz, L.; Frush, D.; Hoang, J.; Lowry, C.; Yoshizumi, T.

In: Medical physics, Vol. 40, No. 6, 06.2013.

Research output: Contribution to journalArticle

Januzis, N. ; Nguyen, G. ; Hurwitz, L. ; Frush, D. ; Hoang, J. ; Lowry, C. ; Yoshizumi, T. / SU‐D‐103‐06 : Bismuth Shield Usage in MDCT Thoracic Scans: Organ Dose Vs. Image Quality. In: Medical physics. 2013 ; Vol. 40, No. 6.
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title = "SU‐D‐103‐06: Bismuth Shield Usage in MDCT Thoracic Scans: Organ Dose Vs. Image Quality",
abstract = "Purpose: To study Bismuth (Bi) shielding for the breast, organ dose and image quality were compared under the following conditions: (1) tube current modulation (TCM), (2) TCM with a Bi shield placed after topogram, and (3) manually reduced tube current (RTC) with no Bi. Methods: All measurements were performed with a 64‐slice scanner at 120 kVp. Organ dose was measured with MOSFETs using an adult male anthropomorphic phantom with supine breast attachments. The reference exposure and reduced exposure (with 4‐ply Bi shield) was measured with an ion chamber located at the level of the breast. The mA was reduced by normalizing the reference mA to the ratio of the reduced exposure to the reference exposure. Image quality was measured using a high contrast insert placed in the lung. Regions of Interest (ROIs) were drawn in thoracic organs to measure signal‐to‐noise ratio (SNR), percent contrast ({\%}Contrast), noise, and HU values. Results: Organ doses (mGy) for the three scans (TCM, TCM with Bi, and RTC) were 11.1, 6.89, and 6.04 to the breast; 8.83, 8.01, and 7.62 to the lung; and 8.20, 7.36 and 8.40 to the heart, respectively. HU increase was greatest in the TCM with Bi scan for organs closest to the shield. The SNRs were 37.6, 34.1, and 43.3 and the {\%}Contrast values were 349.2, 326.3, and 354.3 with TCM, TCM with Bi, and RTC, respectively. Conclusion: For thoracic CT, this RTC method provides a dose reduction to the breast similar to that of the TCM with Bi. Decrease in SNR and {\%}Contrast in the TCM with Bi scan was expected due to decrease in photons reaching the detectors and beam hardening from the shield, respectively. Increased SNR in RTC scan was due to the increased mA compared to TCM scan at the level of measurement. U.S. NRC Health Physics Fellowship Grant No. NRC‐HQ‐12‐G‐38‐0022.",
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T2 - Bismuth Shield Usage in MDCT Thoracic Scans: Organ Dose Vs. Image Quality

AU - Januzis, N.

AU - Nguyen, G.

AU - Hurwitz, L.

AU - Frush, D.

AU - Hoang, J.

AU - Lowry, C.

AU - Yoshizumi, T.

PY - 2013/6

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N2 - Purpose: To study Bismuth (Bi) shielding for the breast, organ dose and image quality were compared under the following conditions: (1) tube current modulation (TCM), (2) TCM with a Bi shield placed after topogram, and (3) manually reduced tube current (RTC) with no Bi. Methods: All measurements were performed with a 64‐slice scanner at 120 kVp. Organ dose was measured with MOSFETs using an adult male anthropomorphic phantom with supine breast attachments. The reference exposure and reduced exposure (with 4‐ply Bi shield) was measured with an ion chamber located at the level of the breast. The mA was reduced by normalizing the reference mA to the ratio of the reduced exposure to the reference exposure. Image quality was measured using a high contrast insert placed in the lung. Regions of Interest (ROIs) were drawn in thoracic organs to measure signal‐to‐noise ratio (SNR), percent contrast (%Contrast), noise, and HU values. Results: Organ doses (mGy) for the three scans (TCM, TCM with Bi, and RTC) were 11.1, 6.89, and 6.04 to the breast; 8.83, 8.01, and 7.62 to the lung; and 8.20, 7.36 and 8.40 to the heart, respectively. HU increase was greatest in the TCM with Bi scan for organs closest to the shield. The SNRs were 37.6, 34.1, and 43.3 and the %Contrast values were 349.2, 326.3, and 354.3 with TCM, TCM with Bi, and RTC, respectively. Conclusion: For thoracic CT, this RTC method provides a dose reduction to the breast similar to that of the TCM with Bi. Decrease in SNR and %Contrast in the TCM with Bi scan was expected due to decrease in photons reaching the detectors and beam hardening from the shield, respectively. Increased SNR in RTC scan was due to the increased mA compared to TCM scan at the level of measurement. U.S. NRC Health Physics Fellowship Grant No. NRC‐HQ‐12‐G‐38‐0022.

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