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Enhancing diagnostic confidence in iso-attenuating structures

Abstract
Philips CT Clinical Science Philips Healthcare • USA

Purpose of the study

This study evaluated the imaging performance of various dual energy CT technologies: Spectral detector, dual-source and rapid-kVp-switching. Researchers from the Technical University of Munich, University Hospital of Cologne and Massachusetts General Hospital measured the accuracy of Iodine quantification, accuracy of Hounsfield Units (HU) of virtual monoenergetic images and image noise while varying patient size and radiation dose. This summary focuses on the iodine density accuracy evaluation for different DECT technologies. IQon Spectral CT demonstrated an average error of less than 0.2 mg/ml, the smallest across the DECT technologies evaluated.

The following is a summary of the study “Dual energy CT: a phantom comparison of different platforms for abdominal imaging,” published in European Radiology, February 2018.

Overview

Evaluation of iodinated contrast enhancement in lesions is commonly used in routine CT diagnosis to differentiate between pathologies. Diagnosis based on conventional attenuation values (HU) may not be sufficient in iso-attenuating structures, despite varying iodine uptake. In addition, HU-based diagnosis may suffer from conventional CT scanning accuracy limitations which arise from HU dependencies on patient size and x-ray beam characteristics, such as different kVps. Iodine density maps provided by spectral CT have the potential to overcome HU inaccuracies and inconsistencies, assisting radiologists achieve diagnostic confidence.

With the Philips IQon Spectral CT scanner, iodine density maps [mg/ml] are available, prospectively and retrospectively for every 120-140 kVp scan, alongside other spectral results and a true conventional reconstruction. These maps are generated from perfectly matched low and high energy CT sinograms which undergo projection based material decomposition into material-specific quantification image maps. Iodine density maps can be used for characterization and differentiation of hyper/hypo- enhancing tissue.

In the study, a semi-anthropomorphic abdomen phantom containing seven known iodine density rods (0.5, 0.75, 1.0, 2.0, 5.0, 10.0 and 15.0 mg/ml) was scanned on three different DECT systems with different fat-simulating extension rings to mimic small, medium and large patient sizes. Iodine density was evaluated for each of the rods and patient sizes at three different dose levels of 10 mGy, 20 mGy and 30 mGy. For each of the technologies, circular ROIs were placed on the different rods and an RMS (root-mean square) calculation for the deviation between the observed and true iodine density values was used to measure overall iodine concentration accuracy (filled bars in figure below). In addition, a mean signed deviation from the true iodine values was used to identify and quantify any biases in the overall Iodine quantification (hatched bars in figure below). Both RMS and mean signed deviations are performed across the different iodine densities.

Results

For all patient sizes and dose levels, the Philips IQon Spectral CT demonstrated accurate HU values for soft tissue-like materials over the complete energy range. For the adipose-like material, the quantified RMS deviations of IQon Spectral CT were between 1.7 HU and 5.0 HU. For rapid-kVp-switching and dual-source RMS deviations ranged between 4.7 HU to 10.1 HU and 2.9 HU to 4.4 HU respectively. For the liver-like material, the quantified RMS deviations of IQon Spectral CT were between 2.3 HU and 5.3 HU. For rapid-kVp-switching and dual-source, RMS deviations were ranged between 6.0 HU to 17.1 HU and 2.2 HU to 8.3 HU respectively.

Conclusion

The Philips IQon Spectral CT demonstrates reliable iodine quantification across patient sizes, radiation dose levels and iodine concentration levels.


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Apr 16, 2018

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Abstract
IntelliSpace Portal, IQon Spectral CT
abdomen, Body, dose, Dual Energy, iodine density, MonoE, phantom, prospective, retrospective, spectral CT
 

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