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Acoustic radiation force contrast in MRI: Detection of calcifications in tissue‐mimicking phantoms
Author(s) -
Mende Jessica,
Wild Judith,
Ulucay Deniz,
Radicke Marcus,
Kofahl AnnaLisa,
Weber Bernd,
Krieg Robert,
Maier Karl
Publication year - 2010
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 - 10.1118/1.3512806
Subject(s) - imaging phantom , mammography , calcification , materials science , displacement (psychology) , nuclear medicine , ultrasound , magnetic resonance imaging , medical imaging , nuclear magnetic resonance , biomedical engineering , breast cancer , medicine , radiology , physics , cancer , psychology , psychotherapist
Purpose: Mammography is a widely used tool for the screening of breast cancer, and calcifications are a common finding in most mammograms. The location, size, number, morphology, and distribution of calcifications are an important information to differentiate a benign lesion from probably malignant pathologies. Calcifications are not detectable with a standard dynamic contrast enhanced breast MRI. The authors present a novel method for the detection and imaging of calcifications in breast tissue without ionizing radiation or contrast agents. Methods: Measurements of localized tissue displacement in phantoms due to applied acoustic radiation force were performed. This displacement was imaged with a displacement sensitive spin‐echo MRI sequence. Pieces of eggshell that represent calcifications were embedded in tissue‐mimicking agarose phantoms. The sizes of the calcifications were 0.8 × 0.8 × 0.4 , 1.5 × 1.5 × 0.4 , and 2 × 3 × 0.4mm 3 . The calcifications were scanned with ultrasound (U.S.) at 2.5 MHz and intensities up toI s p t a = 7.18 W / cm 2 . The U.S. beam was moved inside the phantom by a computer‐controlled three‐dimensional hydraulic positioning system. The U.S. beam was scanned over the two smaller calcifications with the displacement sensitivity of the MRI sequence parallel to the U.S. beam path. Grayscale coded maps of the displacement scans are presented. For the 0.8 × 0.8 × 0.4mm 3calcification, the U.S. intensities were varied. Finite element simulations were performed to verify if the experiments complied with theory. Results: The authors found that the displacement caused by the U.S. is increased at the position of the calcification. The area of increased displacement is at least twice as large as the calcification itself. The simulations show this increase in displacement and area at the position of the calcification. When changing the displacement sensitivity direction to perpendicular to the U.S. beam, a crossed black and white four‐leaf clover is visible at the position of the calcification. Conclusions: The U.S. is scattered and reflected by the calcifications. This leads to the increased displacement which is transmitted to the surrounding material because of the elastic coupling between the calcification and the agarose material. Due to the high differences in acoustic impedance and elastic properties between the surrounding tissue and the calcification, even the detection of pieces smaller than the resolution of the MRI scanner is possible. The acoustic radiation force contrast in MR phase‐difference images offers a positive signal for calcifications from a smooth background in phantoms. This method offers a possibility of differentiating qualitatively and quantitatively hard calcifications from stiffer inclusions such as tumors.