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Liquid tissue surrogates for X‐ray and CT phantom studies
Author(s) -
FitzGerald Paul F.,
Colborn Robert E.,
Edic Peter M.,
Lambert Jack W.,
Bonitatibus Peter J.,
Yeh Benjamin M.
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12617
Subject(s) - hounsfield scale , adipose tissue , attenuation , imaging phantom , nuclear medicine , effective atomic number , materials science , biomedical engineering , chemistry , medicine , physics , computed tomography , radiology , optics , biochemistry
Purpose To develop a simple method for producing liquid‐tissue‐surrogate ( LTS ) materials that accurately represent human soft tissues in terms of density and X‐ray attenuation coefficient. Methods and materials We evaluated hypothetical mixtures of water, glycerol, butanol, methanol, sodium chloride, and potassium nitrate; these mixtures were intended to emulate human adipose, blood, brain, kidney, liver, muscle, pancreas, and skin. We compared the hypothetical densities, effective atomic numbers (Z eff ), and calculated discrete‐energy CT attenuation [Hounsfield Units ( HU )] of the proposed materials with those of human tissue elemental composition as specified in International Commission on Radiation Units ( ICRU ) Report 46. We then physically produced the proposed LTS materials for adipose, liver, and pancreas tissue, and we measured the polyenergetic CT attenuation (also expressed as HU ) of these materials within a 32 cm phantom using a 64‐slice clinical CT scanner at 80  kV p, 100  kV p, 120  kV p, and 140  kV p. Results The predicted densities, Z eff , and calculated discrete‐energy CT attenuation of our proposed formulations generally agreed with those of ICRU within < 1% or < 10 HU . For example, the densities of our hypothetical materials agreed precisely with ICRU 's reported values and were 0.95 g/ mL for adipose tissue, 1.04 g/ mL for pancreatic tissue, and 1.06 g/ mL for liver tissue; the discrete‐energy CT attenuation at 60 keV of our hypothetical materials (and ICRU ‐specified compositions) were −107  HU (−113  HU ) for adipose #3, −89  HU (−90  HU ) for adipose #2, 56  HU (55  HU ) for liver tissue, and 31  HU (31  HU ) for pancreatic tissue. The densities of our physically produced materials (compared to ICRU ‐specified compositions) were 0.947 g/ mL (0.0%) for adipose #2, 1.061 g/ mL (+2.0%) for pancreatic tissue, and 1.074 g/ mL (+1.3%) for liver tissue. The empirical polyenergetic CT attenuation measurements of our LTS materials (and the discrete‐energy HU of the ICRU compositions at the mean energy of each spectrum) at 80  kV p were −104  HU (−113  HU ) for adipose #3, −87  HU (−90  HU ) for adipose #2, 59  HU (55  HU ) for liver tissue, and 33  HU (31  HU ) for pancreatic tissue; at 120  kV p, these were −83  HU (−83  HU ) for adipose #3, −68  HU (−63  HU ) for adipose #2, 55  HU (52  HU ) for liver tissue, and 35  HU (33  HU ) for pancreatic tissue. Conclusion Our method for formulating tissue surrogates allowed straightforward production of solutions with CT attenuation that closely matched the target tissues' expected CT attenuation values and trends with kV p. The LTS s' inexpensive and widely available constituent chemicals, combined with their liquid state, should enable rapid production and versatile use among different phantom and experiment types. Further study is warranted, such as the inclusion of contrast agents. These liquid tissue surrogates may potentially accelerate development and testing of advanced CT imaging techniques and technologies.

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