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Accuracy of Material Decomposition Calculations by Gemstone Spectral Imaging

A Scott

A Scott*, Y Zhou, J Allahverdian, Cedars-Sinai Medical Center, Los Angeles, CA

SU-C-134-4 Sunday 1:00PM - 1:55PM Room: 134

Purpose: To measure energy-specific CT number and effective Z accuracy for a variety of simulated tissues and to measure iodine concentration accuracy, using Gemstone Spectral Imaging (GSI).

Methods:We used a GE CT 750HD scanner and CIRS electron density phantom; the phantom is solid water with inserts simulating lung, bone, and soft tissues and has a syringe insert for iodine solutions. We used the GE GSI-49 protocol to scan and the GSI Viewer software to calculate effective Z, iodine concentration, and CT number between 40 and 140 keV. CIRS provided the mass density, true effective Z, and elemental composition of each phantom material and true CT numbers at matching energies were calculated using XCOM.

Results:The deviations between measured and calculated CT numbers varied from -610 HU (dense bone at 40 keV) to almost 0 HU (liver at 100 keV). For most materials the greatest divergence occurred at 40 keV and decreased with increasing energy to a stable error at 80 or 90 keV. The dense bone and lung had the greatest deviation, which did not stabilize until 130 or 140 keV. The calculated effective Z was accurate for trabecular bone and muscle, but with errors of approximately 10% for dense bone, breast, liver, and adipose tissue (GSI cannot measure Z for lung). Iodine concentrations were accurate within 10% for 38 mgI/cc and lower concentrations.

Conclusion:Our results show large inaccuracies in CT number for dense bone and lessened accuracy for most materials at energies less than 80 keV, but the RMS error is reduced by a factor of 2 - 4 when using 80+ keV data only. The effective Z of each material was within approximately 10%. Iodine concentration accuracy was within 10% for the lower concentrations. Altogether, clinical applications requiring 1-5% accuracy may not be feasible.

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