Implementation of Size-Dependent Local Diagnostic Reference Levels for CT Angiography

Hub Boere; Nienke G Eijsvoogel; Anna M Sailer; Joachim E Wildberger; Michiel W de Haan; Marco Das; Cecile R L P N Jeukens

doi:10.2214/AJR.17.18566

Implementation of Size-Dependent Local Diagnostic Reference Levels for CT Angiography

AJR Am J Roentgenol. 2018 May;210(5):W226-W233. doi: 10.2214/AJR.17.18566. Epub 2018 Mar 23.

Authors

Hub Boere¹, Nienke G Eijsvoogel^{1

2}, Anna M Sailer^{1

3}, Joachim E Wildberger^{1

2}, Michiel W de Haan¹, Marco Das^{1

4}, Cecile R L P N Jeukens¹

Affiliations

¹ 1 Department of Radiology and Nuclear Medicine, Maastricht University Medical Center, P. Debyelaan 25, 6229 HX, Maastricht, The Netherlands.
² 2 CARIM, School for Cardiovascular Diseases, Maastricht University Medical Center, Maastricht, The Netherlands.
³ 3 Department of Radiology, Stanford University School of Medicine, Stanford, CA.
⁴ 4 Klinik für Diagnostische und Interventionelle Radiologie, Duisburg, Germany.

PMID: 29570369
DOI: 10.2214/AJR.17.18566

Abstract

Objective: Diagnostic reference levels (DRLs) are established for standard-sized patients; however, patient dose in CT depends on patient size. The purpose of this study was to introduce a method for setting size-dependent local diagnostic reference levels (LDRLs) and to evaluate these LDRLs in comparison with size-independent LDRLs and with respect to image quality.

Materials and methods: One hundred eighty-four aortic CT angiography (CTA) examinations performed on either a second-generation or third-generation dual-source CT scanner were included; we refer to the second-generation dual-source CT scanner as "CT1" and the third-generation dual-source CT scanner as "CT2." The volume CT dose index (CTDI_vol) and patient diameter (i.e., the water-equivalent diameter) were retrieved by dose-monitoring software. Size-dependent DRLs based on a linear regression of the CTDI_vol versus patient size were set by scanner type. Size-independent DRLs were set by the 5th and 95th percentiles of the CTDI_vol values. Objective image quality was assessed using the signal-to-noise ratio (SNR), and subjective image quality was assessed using a 4-point Likert scale.

Results: The CTDI_vol depended on patient size and scanner type (R² = 0.72 and 0.78, respectively; slope = 0.05 and 0.02 mGy/mm; p < 0.001). Of the outliers identified by size-independent DRLs, 30% (CT1) and 67% (CT2) were adequately dosed when considering patient size. Alternatively, 30% (CT1) and 70% (CT2) of the outliers found with size-dependent DRLs were not identified using size-independent DRLs. A negative correlation was found between SNR and CTDI_vol (R² = 0.36 for CT1 and 0.45 for CT2). However, all outliers had a subjective image quality score of sufficient or better.

Conclusion: We introduce a method for setting size-dependent LDRLs in CTA. Size-dependent LDRLs are relevant for assessing the appropriateness of the radiation dose for an individual patient on a specific CT scanner.

Keywords: CT angiography; image quality; local diagnostic reference levels; radiation dose; size-dependent diagnostic reference levels; volume CT dose index (CTDIvol).

MeSH terms

Aortic Diseases / diagnostic imaging*
Artifacts
Body Size*
Computed Tomography Angiography / instrumentation
Computed Tomography Angiography / standards*
Contrast Media
Humans
Iohexol / analogs & derivatives
Radiation Dosage*
Reference Values
Signal-To-Noise Ratio
Software

Substances

Contrast Media
Iohexol
iopromide