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Impact of a Reduced Tube Voltage on CT Angiography and Radiation Dose

Results of the PROTECTION I Study

Bernhard Bischoff, MD^_*, Franziska Hein, MD^_*, Tanja Meyer, MD^_*, Martin Hadamitzky, MD^_*, Stefan Martinoff, MD, Albert Schömig, MD^_*, Jörg Hausleiter, MD^_*,_*

^_* Klinik für Herz- und Kreislauferkrankungen, Deutsches Herzzentrum München, Klinik an der TU München, Munich, Germany
Institut für Radiologie und Nuklearmedizin, Deutsches Herzzentrum München, Klinik an der TU München, Munich, Germany

^_* Reprint requests and correspondence: Dr. Jörg Hausleiter, Deutsches Herzzentrum, Lazarettstrasse 36, 80636 München, Germany (Email: hausleiter{at}dhm.mhn.de).

Objectives: The aim of this study was to determine the impact of a reduced 100-kV tube voltage on image quality and radiation exposure in a pre-defined subgroup analysis of the international, multicenter radiation dose survey PROTECTION I (Prospective Multicenter Study on RadiaTion Dose Estimates Of Cardiac CT AngIOgraphy I) study.

Background: Cardiac computed tomography angiography (CCTA) has become a frequently used diagnostic tool in clinical practice. Despite continually improving CT technology, there remain concerns regarding the associated radiation exposure. A reduced tube voltage of 100 kV has been proposed as an effective means for dose reduction in nonobese patients.

Methods: The study assessed the relevant radiation dose parameters as well as quantitative and qualitative diagnostic image quality data in a subgroup of 321 patients (100 kV: 82 patients; 120 kV: 239 patients), who were scanned at study sites that applied a 100-kV tube voltage in at least 1 patient. Diagnostic image quality was assessed by an experienced CCTA investigator with a 4-point score (1: nondiagnostic to 4: excellent image quality). Effective radiation dose was estimated from the dose-length-product of each CCTA study.

Results: The use of the 100-kV scan protocol was associated with 53% reduction in CCTA median radiation dose estimates, when compared with the conventional 120-kV scan protocol (p < 0.001). Although image noise significantly increased by 26.3% with 100 kV, signal- as well as contrast-to-noise ratios also increased by 7.9% (p = 0.254) and 10.8% (p = 0.027), respectively. Reduction of tube voltage did not impair diagnostic image quality (median diagnostic score: 3.5 [3.25 to 3.75] vs. 3.5 [3.0 to 3.75] for 100 kV vs. 120 kV; p = 0.22).

Conclusions: In this nonrandomized PROTECTION I dose survey, reducing the CCTA tube voltage to 100 kV in nonobese patients is associated with a significant reduction in radiation exposure while maintaining diagnostic image quality. Thus, the 100-kV scan technique should be considered for CCTA dose reduction in adequately selected patients.

Key Words: computed tomography • coronary artery disease • tube voltage

Abbreviations and Acronyms   BMI = body mass index   CCTA = cardiac computed tomography angiography   CT = computed tomography   DLP = dose-length-product   ECG = electrocardiography

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