Improvements to image quality using hybrid and model-based iterative reconstructions: a phantom study

Abstract

Background

The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose.

Purpose

To investigate how image quality depends on reconstruction method and to discuss patient dose reduction resulting from the use of hybrid and model-based iterative reconstruction.

Material and Methods

An image quality phantom (Catphan® 600) and an anthropomorphic torso phantom were examined on a Philips Brilliance iCT. The image quality was evaluated in terms of CT numbers, noise, noise power spectra (NPS), contrast-to-noise ratio (CNR), low-contrast resolution, and spatial resolution for different scan parameters and dose levels. The images were reconstructed using filtered back projection (FBP) and different settings of hybrid (iDose⁴) and model-based (IMR) iterative reconstruction methods.

Results

iDose⁴ decreased the noise by 15–45% compared with FBP depending on the level of iDose⁴. The IMR reduced the noise even further, by 60–75% compared to FBP. The results are independent of dose. The NPS showed changes in the noise distribution for different reconstruction methods. The low-contrast resolution and CNR were improved with iDose⁴, and the improvement was even greater with IMR.

Conclusion

There is great potential to reduce noise and thereby improve image quality by using hybrid or, in particular, model-based iterative reconstruction methods, or to lower radiation dose and maintain image quality.

Keywords

Computed tomography (CT)iterative reconstruction image quality noise dose reduction

Get full access to this article

View all access options for this article.

References

Almén A, Richter S, Leitz W. Swedish Radiation Protection Authority report 2008:03: Number of radiological examinations in Sweden; 2008 (in Swedish).

Leitz W, Almén A. Swedish Radiation Protection Authority report 2010:14: Patient radiation doses from X-ray examinations in Sweden - Development 2005–2008; 2010 (in Swedish).

European Commission. Medical radiation exposure of the European population. Radiation Protection No 180. 2014.

Kalender

Buchenau

Deak

. Technical approaches to the optimisation of CT. Phys Med 2008; 24: 71–79.

Deeder

Khawaja

Singh

. Computed tomography (CT) of the chest at less than 1 mSv: An ongoing prospective clinical trial of chest CT at submillisievert radiation doses with iterative model image reconstruction and iDose4 technique. J Comput Assist Tomogr 2014; 38: 613–619.

Hou

Liu

. Comparisons of image quality and radiation dose between iterative reconstruction and filtered back projection reconstruction algorithms in 256-MDCT coronary angiography. Am J Roentgenol 2012; 199: 588–594.

Kalra

Woisetschlager

Dahlström

. Radiation dose reduction with Sinogram Affirmed Iterative Reconstruction technique for abdominal computed tomography. J Comput Assist Tomogr 2012; 36: 339–346.

Katsura

Matsuda

Akahane

. Model-based iterative reconstruction technique for radiation dose reduction in chest CT: comparison with the adaptive statistical iterative reconstruction technique. Eur Radiol 2012; 22: 1613–1623.

Katsura

Sato

Akahane

. Comparison of pure and hybrid iterative reconstruction techniques with conventional filtered back projection: Image quality assessment in the cervicothoracic region. Eur J Radiol 2013; 82: 356–360.

10.

Pontana

Duhamel

Pagniez

. Chest computed tomography using iterative reconstruction vs filtered back projection (Part 2): image quality of low-dose CT examinations in 80 patients. Eur Radiol 2011; 21: 636–643.

11.

Ren

Dewan

. Comparison of adaptive statistical iterative and filtered back projection reconstruction techniques in brain CT. Eur J Radiol 2012; 81: 2597–2601.

12.

Yamada

Jinzaki

Hosokawa

. Dose reduction in chest CT: comparison of the adaptive iterative dose reduction 3D, adaptive iterative dose reduction, and filtered back projection reconstruction techniques. Eur J Radiol 2012; 81: 4185–4195.

13.

Yasaka

Katsura

Akahane

. Model-based iterative reconstruction for reduction of radiation dose in abdominopelvic CT: comparison to adaptive statistical iterative reconstruction. Springerplus 2013; 7: 209–209.

14.

Beister

Kolditz

Kalender

. Iterative reconstruction methods in X-ray CT. Phys Med 2012; 28: 94–108.

15.

Willemink

de Jong

Leiner

. Iterative reconstruction techniques for computed tomography part 1: technical principles. Eur Radiol 2013; 23: 1623–1631.

16.

Swedish Radiation Safety Authority. SSMFS 2008:20 The Swedish Radiation Safety Authority's Regulations and general advice on diagnostic standard doses and reference levels, 2008 (in Swedish).

17.

Scibelli A. Philips Healthcare Whitepaper. iDose⁴ iterative reconstruction technique. Available at: http://www.healthcare.philips.com/pwc_hc/main/shared/assets/documents/ct/idose_white_paper_452296267841.pdf (accessed 8 October 2015).

18.

Mehta

Thompson

Morton

. Iterative model reconstruction: simultaneously lowered computed tomography radiation dose and improved image quality. Med Phys Int 2013; 2: 147–155.

19.

The International Commission on Radiation Units and Measurements. Noise assessment in CT. In: ICRU Report 87. Radiation dose and image-quality assessment in computed tomography. Journal of the ICRU Vol 12 No 1. Oxford: Oxford University Press, 2012:121–134.

20.

Börjesson

Håkansson

Båth

. A software tool for increased efficiency in observer performance studies in radiology. Radiat Prot Dosimetry 2005; 114: 45–52.

21.

Kyoto Kagaku co. LTD, PH-4 CT Torso Phantom CTU41. Available at: https://www.kyotokagaku.com/products/detail03/pdf/ph-4_catalog.pdf (accessed 10 October 2015).

22.

Aurumskjöld M-L, Ydström K, Tingberg A, et al. Model-based iterative reconstruction enables the evaluation of thin-slice computed tomography images without degrading image quality or increasing radiation dose. Radiat Prot Dosimetry 2015 Nov 20 Epub ahead of print.

23.

Olsson M-L, Norrgren K. An investigation of the iterative reconstruction method iDose⁴ on a Philips CT Brilliance 64 using a Catphan 600 phantom. Proc SPIE 8313, Medical Imaging 2012: Physics of Medical Imaging, 831348.

24.

Olsson M-L, Norrgren K, Söderberg M. Improvement of CT image quality with iterative reconstruction iDose⁴. Conference paper ECR 2014: C-0387.