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Reduction of contrast media by using low monoE

Philips CT Clinical Science Philips Healthcare • USA

Takeshi Nakaura, MD PhD

Assistant Professor

Department of Diagnostic Radiology

Faculty of Life Science

Kumamoto University

1-1-1 Honjo, Chuo-ku

Kumamoto, 860-8556 Japan


The use of the smallest diagnostically appropriate amount of contrast media (CM) is desirable for patients with chronic kidney disease (CKD). Low tube voltage (kVp) scans combined with iterative reconstruction (IR) algorithms are well established techniques for CM dose reduction as well as radiation dose reduction. On the other hand, the low mono-energy (monoE) image with tube based dual energy CT (DECT) has been seldom used as a means of this purpose because the image noise of this method was extremely high compared to conventional scans.


The IQon Spectral CT manufactured by Philips Healthcare has been installed since 19th December 2016, in our department of radiology. We are performing an average of 40 patients per day and performing the low contrast dose protocol for patients with CKD. The aim of this presentation is to share with you our preliminary experience of the IQon CT for the contrast dose reduction.


Comparison with conventional low kVp scan and other DECT systems

Use of low tube voltages such as 80 kVp results in higher CT attenuation than 120 kVp due to the photo-electric effect, because the x-ray output energy at these low voltages is closer to the iodine k edge of 33 keV. The decrease in the x-ray tube voltage decreases the amount of penetrating radiation, resulting in increased image noise, especially in large patients. Recently, this weak point can be compensated by the high tube current setting or the iterative reconstruction.


DECT provides the reconstruction of virtual monoE images based on the two different energy projection datasets. The low kilo-electron volt (keV) images can offer the high iodine contrast, and several investigators have reported the usefulness of the low keV images generated from tube-based DECT systems (dual-source or rapid kV switching system) for iodine load reduction in CTA. However, many reports suggested that the monoE images generated by tube-based DECT systems could not maintain the image quality in extremely low keV setting. The image noise of two kVp image sets was reduced by averaging at middle keV setting; however, it was amplified at extremely low keV or high keV setting.


Thanks to its perfectly simultaneous acquisition of the 2 energy attenuations, dual-layer Spectral CT allows for using both a unique “anti-correlated statistical reconstruction algorithm” and iterative reconstruction techniques for spectral reconstruction of the raw data1,2. Therefore, decreased image noise is expected in virtual monoenergetic images relative to the noise in other dual-energy techniques images.


Low keV image for contrast dose reduction

Our preliminary experience suggests that low-keV monoE images are well suited for the low contrast dose examination compared to conventional low kVp images. First, the low keV monoE images allows the retrospective optimization of the image contrast for each examination and each organ of interest after the image acquisitions is completed. Second, the beam-hardening effects are minimized on virtual monoenergetic images.



  1. Kalender WA, Klotz E, Kostaridou L. An algorithm for noise suppression in dual energy CT material density images. IEEE Trans Med Imaging. 1988; 7(3):218-24.
  2. Kevin M. Brown1 SZc, and Gilad Shechter. Impact of spectral separation in dual-energy CT with anti-correlated statistical reconstruction. The 13th International Meeting on Fully Three Dimensional Image Reconstruction in Radiology and Nuclear Medicine. 2015:491-4.


Figure 1a Figure 1b
Figure 1a
Figure 1b

Low monoE image (55 keV) with 50% contrast material dose can offer the almost same enhancement to the conventional scan.



Figure 2a Figure 2b
Figure 2a
Figure 2b
Figure 2c
Figure 2c
Pulmonary thrombosis with low contrast dose scan - 1 mL/sec 60 cc (300 mgI/mL).

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Nov 7, 2017

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IntelliSpace Portal, IQon Spectral CT
13th MDCT Users Meeting abstracts, aorta, Body, chest, contrast, Effective Z, image quality, kidney/renal, MonoE, pulmonary imaging, retrospective, Vascular

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