European Radiology

, Volume 29, Issue 12, pp 6550–6558 | Cite as

Liver CT perfusion: which is the relevant delay that reduces radiation dose and maintains diagnostic accuracy?

  • Alessandro Bevilacqua
  • Silvia Malavasi
  • Valérie VilgrainEmail author
Computed Tomography



High radiation dose during CT perfusion (CTp) studies contributes to prevent CTp application in daily clinical practice. This work evaluates the consequences of scan delay on perfusion parameters and provides guidelines to help reducing the radiation dose by choosing the most appropriate delay.


Fifty-nine patients (34 men, 25 women; mean age 68 ± 12) with colorectal cancer, without underlying liver disease, underwent liver CTp, with the acquisition starting simultaneously with iodinated contrast agent injection. Blood flow (BF) and hepatic perfusion index (HPI) were computed on the acquired examinations and compared with those of the same examinations when a variable scan delay (τ) is introduced. Dose length product, CT dose index, and effective dose were also computed on original and delayed examinations.


Altogether, three groups of delays (τ ≤ 4 s, 5 s ≤ τ ≤ 9 s, τ ≥ 10 s) were identified, yielding increasing radiation dose saving (RDS) (RDS ≤ 9.5%, 11.9% ≤ RDS ≤ 21.4%, RDS ≥ 23.8%) and decreasing perfusion accuracy (high (τ ≤ 4 s), medium (5 s ≤ τ ≤ 9 s), low (τ ≥ 10 s)). In particular, single-input and arterial BF and HPI were more insensitive to delay as regards the absolute variations (only 1 ml/min/100 g and 1%, respectively, for τ ≤ 9 s), than portal and total BF.


Using delays lower than 4 s does not change perfusion accuracy and conveys unnecessary dose to patients. Conversely, starting the acquisition 9 s after contrast agent injection yields a RDS of about 21%, with no significant losses in perfusion accuracy.

Key Points

• Scan delays lower than 4 s do not alter perfusion accuracy and deliver an unnecessary radiation dose to patients.

• Radiation dose delivered to patients can be reduced by 21.4% by introducing a 9-s scan delay, while keeping accurate perfusion values.

• Using scan delays higher than 10 s, some perfusion parameters (portal and total BF) were inaccurate.


Contrast media Colorectal neoplasms Liver diseases Radiation dosage Tomography, X-ray computed 



Arterial blood flow


Cohort-oriented absolute differences


Patient-oriented absolute differences


Blood flow


Volumetric CT dose index


CT perfusion


Dose length product


Examination acquired


Delayed examination


Effective dose


Hepatic perfusion index


Integer number for statistical differences


Portal blood flow


Cohort-oriented percentage differences


Patient-oriented percentage differences


Perfusion unit


Radiation dose saved


Total blood flow


Time concentration curves



This study has received funding by a grant from the Programme Hospitalier de Recherche Clinique - PHRC 2007 no. AOM07228, France, and sponsored by Assistance-Publique Hôpitaux de Paris (APHP).

Compliance with ethical standards


The scientific guarantor of this publication is Prof. Valérie Vilgrain.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

Alessandro Bevilacqua, MS, PhD, kindly provided statistical advice for this manuscript and is one of the authors of this manuscript.

Informed consent

Written informed consent was waived by the Institutional Review Board.

Ethical approval

Institutional Review Board approval was obtained.


• Retrospective

• Diagnostic or prognostic study

• Performed at one institution

Supplementary material

330_2019_6259_MOESM1_ESM.docx (27 kb)
ESM 1 (DOCX 27 kb)


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Copyright information

© European Society of Radiology 2019

Authors and Affiliations

  • Alessandro Bevilacqua
    • 1
    • 2
  • Silvia Malavasi
    • 2
    • 3
  • Valérie Vilgrain
    • 4
    • 5
    Email author
  1. 1.DISI (Department of Computer Science and Engineering)University of BolognaBolognaItaly
  2. 2.ARCES (Advanced Research Center on Electronic Systems)University of BolognaBolognaItaly
  3. 3.CIG (Interdepartmental Centre “L. Galvani” for integrated studies of Bioinformatics, Biophysics and Biocomplexity)University of BolognaBolognaItaly
  4. 4.Department of Radiology, Assistance-Publique Hôpitaux de Paris, APHP, HUPNVSHôpital BeaujonClichyFrance
  5. 5.Sorbonne Paris Cité, INSERM CRIUniversité Paris DiderotParisFrance

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