Page 225 - Hospital Authority Convention 2018

Service Enhancement Presentations

F8.4 Young HA Investigators Session 14:30 Room 421

Reduction of Radiation and Intravenous Contrast Doses in Triphasic Contrast Computed Tomography
Abdominal Aortogram
Mo CKM, Cheng JHM, Lee ASL, Lam KM, Leung BST, Chu CY, Tam CW, Kan WK
Department of Radiology, Pamela Youde Nethersole Eastern Hospital, Hong Kong HOSPITAL AUTHORITY CONVENTION 2018

Introduction
Prolonged nature of imaging surveillance by Computed Tomography abdominal aortogram (CTAA) with triphasic protocols
impose substantial radiation exposure and contrast doses to post-EVAR patients, who are at higher risk for renal impairment.

Objectives
To reduce both radiation and intravenous contrast doses of CTAA via implementation of new imaging protocol, while
maintaining comparable diagnostic quality.

Methodology
A three-phase project from 1 April 2015 to 30 September 2017 was conducted, including consecutive patients who
underwent triphasic CTAA in our department. In the second and third phases, urgent examinations were excluded. To
benchmark baseline radiation doses, data from first phase (1 April 2015 – 31 December 2015) were retrospectively analysed.
A new low-contrast low-kV protocol was implemented in second phase (1 March 2016 – 30 November 2016), in which tube
voltage was reduced from 120kV to 100kV, and intravenous contrast (Omnipaque 350mg/ml) was reduced from 80ml to 60ml.
Further refinement of protocol was performed in the third phase (1 January 2017 – 30 September 2017), tube current was
adjusted to a low-dose protocol (SureExp 3D® Low Dose) in plain and arterial phases, and remained unchanged in delayed
phase (SureExp 3D® Standard). Patient demographics and radiation doses in terms of dose-length products (DLPs, mGycm)
of each case were collected. To ensure comparable diagnostic confidence, both quantitative and qualitative image quality
assessment were performed. Quantitative parameters included aortic enhancement, contrast attenuation gradient, image
noise and contrast-to-noise ratio. For qualitative parameters, visual assessment analysis was performed by two radiologists
based on grading scale (noise 1-3, artefact 1-3, diagnostic quality 1-5).

Results
Mean DLP from baseline assessment of 55 patients (mean 78.5 years) was 2102.5mGycm. In second phase, all 35 patients
(mean 79.5 years) received 25% reduction in contrast volume. Mean DLP was 1866.3mGycm, equivalent to 11.2% reduction.
For image quality, all quantitative and qualitative parameters showed no significant differences. In third phase, 35 patients
(mean 76.4 years) were included. Mean DLP was further reduced to 1721.0mGycm, equivalent to further reduction by 7.8%
and overall reduction by 18.1%. Mild increase image noise in arterial phase from 12.8HU to 16.7HU was noted. However, there
was no significant difference in qualitative image noise assessment, as well as other quantitative and qualitative parameters
of image quality. Tuesday, 8 May 2018

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