CT Contrast Media: Impact of Scanner Parameters On Enhancement and Detectability
Z E Labby1*, W F Sensakovic2-4, K J Labby5, J Turian6, (1) The University of Chicago, Chicago, IL, (2) Florida Hospital, Orlando, FL, (3) Florida State University, Tallahassee, FL, (4) University of Central Florida, Orlando, FL, (5) Northwestern University, Evanston, IL, (6) Rush University Medical Center, Chicago, ILSU-C-134-5 Sunday 1:00PM - 1:55PM Room: 134
Purpose: Uptake of iodine-based CT contrast media (CM) results in an increase in Hounsfield Unit (HU) value, allowing for improved detectability in CT. Further, because the increase in HU is proportional to CM concentration, quantitative measurement of HU enhancement can aid diagnosis and can determine hemodynamic properties of tissues (i.e., perfusion CT). Imaging protocol parameters (e.g., reconstruction kernel) can alter the HU-CM relationship, potentially confounding quantitation of contrast uptake. This phantom study measures the HU-CM relationship and determines the impact of imaging protocol parameters.
Methods: A solid water phantom was imaged with a Philips Big Bore CT Scanner. Eighteen custom cylinders with CM concentrations ranging from 0-50 mg of iodine/mL were placed in the phantom. Tube voltages of 90, 120, and 140kVp, current-time products of 100 and 400mAs, and reconstruction kernels of UB (smooth) and D (hi-res bone enhancing) were studied. A linear fit to the HU-CM data was calculated to evaluate HU enhancement. Contrast-to-noise ratio (CNR) was calculated to evaluate detectability.
Results: A linear relationship existed between HU and CM for all acquisitions (R-squared > 0.99). HU-CM linear slope ranged from 16 to 34 HU/mg-I/mL. A tube voltage of 140kVp increased the slope by 81% when compared to 90kVp, whereas 120kVp increased the slope by 20%. Kernel D produced a 10-15% increase in slope. For a 400mAs acquisition, CNR was optimized using 120kVp and the UB kernel, but CNR was optimized for 100mAs using 90kVp with the UB kernel.
Conclusion: HU enhancement is linear with concentration; however, the slope is strongly impacted by reconstruction kernel and tube voltage. Knowledge of CT scanning parameter impact on contrast media signal enhancement and detectability can guide optimization of CT protocols and improve interpretation of quantitative CT data.
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