Cone Beam Breast CT with a High Resolution Flat Panel Detector- Improvement of Calcification Visibility
Y Shen*, Y Zhong, C Lai, T Wang, C Shaw, UT MD Anderson Cancer Center, Houston, TXTU-E-217BCD-6 Tuesday 2:00:00 PM - 3:50:00 PM Room: 217BCD
To investigate the advantage of a high resolution flat panel detector for improving the visibility of microcalcifications (MCs) in cone beam breast CT
A paraffin cylinder was used to simulate a 100% adipose breast. Calcium carbonate grains, ranging from 125 - 140 µm to 224 - 250 µm in size, were used to simulate the MCs. Groups of 25 same size MCs were embedded at the phantom center. The phantom was scanned with a bench-top CBCT system at various exposure levels. A 75µm pitch flat panel detector (Dexela 2923, Perkin Elmer) with 500µm thick CsI scintillator plate was used as the high resolution detector. A 194 µm pitch detector (Paxscan 4030CB, Varian Medical Systems) was used for reference. 300 projection images were acquired over 360º and reconstructed. The images were reviewed by 6 readers. The MC visibility was quantified as the fraction of visible MCs and averaged for comparison. The visibility was plotted as a function of the estimated dose level for various MC sizes and detectors. The MTFs and DQEs were measured and compared.
For imaging small (200 µm and smaller) MCs, the visibility achieved with the 75µm pitch detector was found to be significantly higher than those achieved with the 194µm pitch detector. For imaging larger MCs, there was little advantage in using the 75µm pitch detector. Using the 75µm pitch detector, MCs as small as 180 µm could be imaged to achieve a visibility of 78% with an isocenter tissue dose of ~20 mGys versus 62% achieved with the 194 µm pitch detector at the same dose level.
It was found that a high pitch flat panel detector had the advantages of extending its imaging capability to higher frequencies thus helping improve the visibility when used to image small MCs.