Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry

Ioannis Sechopoulos, Kristina Bliznakova, Xulei Qin, Baowei Fei, Steve Si Jia Feng

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patients last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breasts volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patients last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27 higher than that estimated using the true heterogeneous glandular tissue distribution (Wilcoxon Signed Rank Test p 0.00046). For dedicated breast CT, the overestimation of normalized glandular dose was, on average, 8 (49 kVp spectrum, p 0.00045) and 4 (80 kVp spectrum, p 0.000089). Only two cases in mammography and two cases in dedicated breast CT with a tube voltage of 49 kVp resulted in lower dose estimates for the homogeneous tissue approximation compared to the heterogeneous tissue distribution. Conclusions: The normalized glandular dose based on the homogeneous tissue mixture approximation results in a significant overestimation of dose to the imaged breast. This overestimation impacts the use of dose estimates in absolute terms, such as for risk estimates, and may impact some comparative studies, such as when modalities or techniques with different x-ray energies are used. The error introduced by the homogeneous tissue mixture approximation in higher energy x-ray modalities, such as dedicated breast CT, although statistically significant, may not be of clinical concern. Further work is required to better characterize this overestimation and potentially develop new metrics or correction factors to better estimate the true glandular dose to breasts undergoing imaging with ionizing radiation.

Original languageEnglish (US)
Pages (from-to)5050-5059
Number of pages10
JournalMedical physics
Volume39
Issue number8
DOIs
StatePublished - Aug 2012
Externally publishedYes

Fingerprint

Breast
Mammography
X-Rays
Tissue Distribution
Adipose Tissue
Nonparametric Statistics
Ionizing Radiation

Keywords

  • breast CT
  • dose
  • mammography
  • Monte Carlo
  • x-ray

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry. / Sechopoulos, Ioannis; Bliznakova, Kristina; Qin, Xulei; Fei, Baowei; Feng, Steve Si Jia.

In: Medical physics, Vol. 39, No. 8, 08.2012, p. 5050-5059.

Research output: Contribution to journalArticle

Sechopoulos, Ioannis ; Bliznakova, Kristina ; Qin, Xulei ; Fei, Baowei ; Feng, Steve Si Jia. / Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry. In: Medical physics. 2012 ; Vol. 39, No. 8. pp. 5050-5059.
@article{f935f7fc75c44b62a0f35b6cf315c58d,
title = "Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry",
abstract = "Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patients last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breasts volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patients last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27 higher than that estimated using the true heterogeneous glandular tissue distribution (Wilcoxon Signed Rank Test p 0.00046). For dedicated breast CT, the overestimation of normalized glandular dose was, on average, 8 (49 kVp spectrum, p 0.00045) and 4 (80 kVp spectrum, p 0.000089). Only two cases in mammography and two cases in dedicated breast CT with a tube voltage of 49 kVp resulted in lower dose estimates for the homogeneous tissue approximation compared to the heterogeneous tissue distribution. Conclusions: The normalized glandular dose based on the homogeneous tissue mixture approximation results in a significant overestimation of dose to the imaged breast. This overestimation impacts the use of dose estimates in absolute terms, such as for risk estimates, and may impact some comparative studies, such as when modalities or techniques with different x-ray energies are used. The error introduced by the homogeneous tissue mixture approximation in higher energy x-ray modalities, such as dedicated breast CT, although statistically significant, may not be of clinical concern. Further work is required to better characterize this overestimation and potentially develop new metrics or correction factors to better estimate the true glandular dose to breasts undergoing imaging with ionizing radiation.",
keywords = "breast CT, dose, mammography, Monte Carlo, x-ray",
author = "Ioannis Sechopoulos and Kristina Bliznakova and Xulei Qin and Baowei Fei and Feng, {Steve Si Jia}",
year = "2012",
month = "8",
doi = "10.1118/1.4737025",
language = "English (US)",
volume = "39",
pages = "5050--5059",
journal = "Medical Physics",
issn = "0094-2405",
publisher = "AAPM - American Association of Physicists in Medicine",
number = "8",

}

TY - JOUR

T1 - Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry

AU - Sechopoulos, Ioannis

AU - Bliznakova, Kristina

AU - Qin, Xulei

AU - Fei, Baowei

AU - Feng, Steve Si Jia

PY - 2012/8

Y1 - 2012/8

N2 - Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patients last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breasts volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patients last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27 higher than that estimated using the true heterogeneous glandular tissue distribution (Wilcoxon Signed Rank Test p 0.00046). For dedicated breast CT, the overestimation of normalized glandular dose was, on average, 8 (49 kVp spectrum, p 0.00045) and 4 (80 kVp spectrum, p 0.000089). Only two cases in mammography and two cases in dedicated breast CT with a tube voltage of 49 kVp resulted in lower dose estimates for the homogeneous tissue approximation compared to the heterogeneous tissue distribution. Conclusions: The normalized glandular dose based on the homogeneous tissue mixture approximation results in a significant overestimation of dose to the imaged breast. This overestimation impacts the use of dose estimates in absolute terms, such as for risk estimates, and may impact some comparative studies, such as when modalities or techniques with different x-ray energies are used. The error introduced by the homogeneous tissue mixture approximation in higher energy x-ray modalities, such as dedicated breast CT, although statistically significant, may not be of clinical concern. Further work is required to better characterize this overestimation and potentially develop new metrics or correction factors to better estimate the true glandular dose to breasts undergoing imaging with ionizing radiation.

AB - Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patients last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breasts volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patients last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27 higher than that estimated using the true heterogeneous glandular tissue distribution (Wilcoxon Signed Rank Test p 0.00046). For dedicated breast CT, the overestimation of normalized glandular dose was, on average, 8 (49 kVp spectrum, p 0.00045) and 4 (80 kVp spectrum, p 0.000089). Only two cases in mammography and two cases in dedicated breast CT with a tube voltage of 49 kVp resulted in lower dose estimates for the homogeneous tissue approximation compared to the heterogeneous tissue distribution. Conclusions: The normalized glandular dose based on the homogeneous tissue mixture approximation results in a significant overestimation of dose to the imaged breast. This overestimation impacts the use of dose estimates in absolute terms, such as for risk estimates, and may impact some comparative studies, such as when modalities or techniques with different x-ray energies are used. The error introduced by the homogeneous tissue mixture approximation in higher energy x-ray modalities, such as dedicated breast CT, although statistically significant, may not be of clinical concern. Further work is required to better characterize this overestimation and potentially develop new metrics or correction factors to better estimate the true glandular dose to breasts undergoing imaging with ionizing radiation.

KW - breast CT

KW - dose

KW - mammography

KW - Monte Carlo

KW - x-ray

UR - http://www.scopus.com/inward/record.url?scp=84864651612&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84864651612&partnerID=8YFLogxK

U2 - 10.1118/1.4737025

DO - 10.1118/1.4737025

M3 - Article

C2 - 22894430

AN - SCOPUS:84864651612

VL - 39

SP - 5050

EP - 5059

JO - Medical Physics

JF - Medical Physics

SN - 0094-2405

IS - 8

ER -