Body size and tube voltage dependent corrections for Hounsfield Unit in medical X-ray computed tomography: theory and experiments

Abstract

The purpose of this work is to present a body size and tube voltage dependent correction scheme for the Hounsfield Unit, HU, in medical X-ray Computed Tomography imaging. Boltzmann photon transport equation was employed to study X-ray interaction with bulk water in CT imaging. Experimentally measured X-ray output in body of phantoms and attenuation cross sections of water were employed in the derivation of beam intensity in X-ray imaging. A Somatom Emotion CT scanner from Siemens and electron density phantoms from CIRS were employed to acquire CT images of different body sizes and different tissue materials located at different depths from body’s surface. Tube voltage and depth dependent effective attenuation of bulk water was found from theoretical analysis in agreement with measured size-specific correction factors for CTDIvol under different tube voltages. A size and tube voltage dependent correction scheme for the Hounsfield Unit is established. For the same tissue material, body size has much larger impact on the CT number variations than that of depth from the body surface in phantom measurements. Good results were achieved by applying the established correction scheme on the experimentally measured CT number variations under different tube voltages and body sizes.

Internal calibration for opportunistic computed tomography muscle density analysis

“…Notably, ex vivo bovine and swine tissue samples were scanned instead of human participants, which may have different tissue densities that influenced the internal calibration derived muscle density values. These samples do not account for differences in patient anatomy (i.e., patient size) which have been noted to impact resulting HU values [45–47]. However, the internal calibration approach utilized here should be less dependent on patient characteristics as reference values are taken from the patient themselves, which should account for patient-specific alterations in x-ray attenuation.…”

Impacts of Phantom Off-Center Positioning on CT Numbers and Dose Index CTDIv: An Evaluation of Two CT Scanners from GE

“…Contrasting the off-center variation characteristics of the approximately constant CT numbers and dose index CTDIv of the APEX scanner to the linearly increased CT numbers and CTDIv of the HD750 scanner led to the conclusion that the linearly enlarged sizes of SPR images without off-center corrections caused the linear increase of the CT numbers and CTDIv. It suggests that the body size and tube voltage dependent correction scheme [21] should be able to correct for the variations of CT numbers caused by the increased body sizes…”

“…A Revolution APEX and a Discovery HD750 CT scanner of General Electric (GE) were used to acquire images of an electron density phantom (model 062M, 27 cm × 33 cm) of computerized imaging reference systems (CIRS), Inc. (Norfolk, VA, USA) and an anthropomorphic phantom (model PBU-60, 165 cm in length and 50 kg in weight) of Kyoto Kagaku Co. (Kyoto, Japan), respectively. All tissue insert holes within the electron density phantom were filled with water balloons to mimic an abdomen section of human body [21]. Both phantom images were acquired under automatic tube current modulation (ATCM) mode using default noise index and under body (abdomen) bowtie filters.…”

Tracing the Inside of Pigs Non-Invasively: Recent Developments

“…though Zheng et al [27] suggested using body size and body depth, as well as tube-voltage dependent correction factors for the calculation of the "correct" HU in order to account for Rayleigh scattering of water.…”