Program Information
Measured Hounsfield Units in Lung Nodules Varies with CT Reconstruction Filters and Slice Thickness
Y Zhang1*, K Little2 , A Sanchez1 , I Reiser1 , J Chung1 , H MacMahon1 , Z Lu1 , (1) Department of Radiology, The University of Chicago, Chicago, IL (2) Department of Radiology, Ohio State University, Columbus, OH
Presentations
TU-RPM-GePD-IT-1 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Imaging ePoster Theater
Purpose: Hounsfield units (HU) are routinely measured in chest CT studies to characterize lung nodules. However, substantial variations in HU can be caused by reconstruction filters and slice thicknesses. It is important to identify these sources of HU variations to maximize precision and accuracy of HU measurements.
Methods: 11 mm-diameter spheres of acrylic and LDPE were placed in a cylindrical phantom, and scanned at 80, 100, 120, and 140 kVp using GE, Philips and Siemens scanners. The images were reconstructed using ten reconstruction filters. A circular and annular ROI were drawn to measure HU of the entire cross-section and the edge of the sphere, respectively. A Lungman phantom with spherical nodules of four diameters, 3mm, 5mm, 8mm and 10mm was scanned and reconstructed with slice thicknesses of 1mm, 3mm and 5mm by Siemens scanner.
Results: The HU values for acrylic increased with increasing kVps, and varied with reconstruction filters. For GE, the variation was most pronounced with the lung filter where edge enhancement was involved in the reconstruction. HU with the lung filter increased by 47.5 compared to the standard filter using the entire ROI. For the annular ROI that only encompassed the edge, HU with the lung filter increased by 162 compared to the standard filter. The HU measured from Philips and Siemens systems followed a similar trend. From the Lungman scan, the slice thickness setting affected measured HU due to partial volume effect. The effect was more pronounced when the slice thickness was more than 50% of the nodule size.
Conclusion: Reconstruction filters alter the measured HU of target objects, especially the lung filter. The accuracy of measured HU also depends on slice thickness, especially for small nodules. It is crucial for radiologists to be aware of the sources of HU variations to measure HU accurately and consistently.
Funding Support, Disclosures, and Conflict of Interest: Yue Zhang is partially supported by RSNA/AAPM Imaging Physics Residency Program Grant.
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