Radiologists can dramatically lower cardiac CT radiation dose in some patients
(4 Apr 2008: VIDYYA MEDICAL NEWS SERVICE) -- Radiologists can now lower the radiation dose delivered by cardiac CT angiography by 39% in adult patients weighing 185 pounds or less, according to a study performed at the University of Erlangen in Erlangen, Germany.
The study included one hundred patients, weighing 185 pounds or less, who underwent cardiac CT angiography either using a tube voltage of 120 kV or 100 kV. Results showed that the effective radiation dose for patients scanned with 120 kV ranged from 8.8 to 16.9 mSv; the effective radiation dose for patients scanned with 100 kV ranged from 4.9 to 11.9 mSv. “At the same time, the overall image quality was preserved. Image quality scores using 120 kV were 2.7 plus/minus 0.5; scores using 100 kV were 2.6 plus/minus 0.4,” said Tobias Pflederer, MD, lead author of the study.
“Coronary CT angiography has tremendously high accuracy for detecting and ruling out coronary artery stenosis. It is expected that indications for coronary CT angiography will grow in the future,” he said.
“The standard coronary CT angiography protocol uses the higher tube voltage value of 120 kV however our study shows that 100 kV can be used instead. It is important to keep the radiation dose as low as possible, especially in younger and female patients,” said Dr. Pflederer.
Image Quality in a Low Radiation Exposure Protocol for Retrospectively ECG-Gated Coronary CT Angiography
Tobias Pflederer1, Larissa Rudofsky1, Dieter Ropers1, Sven Bachmann1, Mohamed Marwan1, Werner G. Daniel1 and Stephan Achenbach1
1 All authors: Department of Internal Medicine 2 (Cardiology), University of Erlangen, Ulmenweg 18, D-91054 Erlangen, Germany.
OBJECTIVE. The purpose of our study was to systematically compare the image quality of dual-source CT coronary angiography using 100 kV instead of 120 kV.
SUBJECTS AND METHODS. One hundred patients with a body weight 85 kg were included. A dual-source CT scanner was used (330-milliseconds rotation, 0.6-mm collimation, 56 ± 7 mL of IV contrast agent at 5 mL/s). Each patient was randomized either to scanning protocol group 1 (120 kV and 330 mAs) or protocol group 2 (100 kV and 330 mAs). ECG pulsing was used for all patients. Data sets were assessed by two independent observers for image quality, signal-to-noise ratio, and contrast-to-noise-ratio. Effective dose was determined based on dose–length product.
RESULTS. There were no significant differences in body weight or heart rate between the two groups (70 ± 10 kg and 57 ± 8 bpm [beats per minute] vs 70 ± 9 kg and 59 ± 8 bpm). Use of 100 kV led to significant reduction of radiation exposure (group 1: 12.7 ± 1.7 mSv; volume CT dose index [CTDIvol], 47.8 ± 6.1 mGy and group 2: 7.8 ± 2.0 mSv; CTDIvol, 28.6 ± 6.3 mGy; p < 0.001). Interobserver agreement in assessing image quality ( = 0.71) was close. Mean patient-based image quality scores were not significantly different (group 1, 2.7 ± 0.5 and group 2, 2.6 ± 0.4; p = 0.75). Also, vessel-based scores showed no significant differences. Beyond the level of significance, group 1 and group 2 showed one and two nonassessable patients and two and three nonassessable vessels, respectively. Mean intraluminal attenuation, contrast enhancement, and image noise were significantly higher for 100 kV, whereas signal-to-noise and contrast-to-noise-ratios were not different between the two scanning protocols.
CONCLUSION. The use of lower tube voltage leads to significant reduction in radiation exposure in noninvasive coronary CT angiography. Image quality in nonobese patients is not negatively influenced.
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