Date Published: January 24, 2019
Publisher: Public Library of Science
Author(s): Hyun Kyung Lim, Hong Il Ha, Hye Jeon Hwang, Kwanseop Lee, Yuchen Qiu.
Objective of this study was to evaluate the effectiveness of the iterative reconstruction of high-pitch dual-source chest CT (IR-HP-CT) scanned with low radiation exposure compared with low dose chest CT (LDCT).
This study was approved by the institutional review board. Thirty healthy adult volunteers (mean age 44 years) were enrolled in this study. All volunteers underwent both IR-HP-CT and LDCT. IR-HP-CT was scanned with 120 kVp tube voltage, 30 mAs tube current and pitch 3.2 and reconstructed with sinogram affirmed iterative reconstruction. LDCT was scanned with 120 kVp tube voltage, 40 mAs tube current and pitch 0.8 and reconstructed with B50 filtered back projection. Image noise, and signal to noise ratio (SNR) of the infraspinatus muscle, subcutaneous fat and lung parenchyma were calculated. Cardiac motion artifact, overall image quality and artifacts was rated by two blinded readers using 4-point scale. The dose-length product (DLP) (mGy∙cm) were obtained from each CT dosimetry table. Scan length was calculated from the DLP results. The DLP parameter was a metric of radiation output, not of patient dose. Size-specific dose estimation (SSDE, mGy) was calculated using the sum of the anteroposterior and lateral dimensions and effective radiation dose (ED, mSv) were calculated using CT dosimetry index.
Approximately, mean 40% of SSDE (2.1 ± 0.2 mGy vs. 3.5 ± 0.3 mGy) and 34% of ED (1.0 ± 0.1 mSv vs. 1.5 ± 0.1 mSv) was reduced in IR-HP-CT compared to LDCT (P < 0.0001). Image noise was reduced in the IR-HP-CT (16.8 ± 2.8 vs. 19.8 ± 3.4, P = 0.0001). SNR of lung and aorta of IR-HP-CT showed better results compared with that of LDCT (22.2 ± 5.9 vs. 33.0 ± 7.8, 1.9 ± 0.4 vs 1.1 ± 0.3, P < 0.0001). The score of cardiac pulsation artifacts were significantly reduced on IR-HP-CT (3.8 ± 0.4, 95% confidence interval, 3.7‒4.0) compared with LDCT (1.6 ± 0.6, 95% confidence interval, 1.3‒1.8) (P < 0.0001). SNR of muscle and fat, beam hardening artifact and overall subjective image quality of the mediastinum, lung and chest wall were comparable on both scans (P ≥ 0.05). IR-HP-CT with 120 kVp and 30 mAs tube setting in addition to an iterative reconstruction reduced cardiac motion artifact and radiation exposure while representing similar image quality compared with LDCT.
Low-dose chest computed tomography (LDCT) is widely used to screen for lung cancer; the utility thereof became clear during the National Lung Screening Trial . However, repeated CT scans are inevitably associated with increased radiation doses, although the mean radiation dose per scan is only approximately 1.5 mSv [2, 3]. As low-level radiation-related carcinogenesis is stochastic in nature, the radiation exposure associated with screening CT has become of concern, despite the utility of CT for lung cancer evaluation [2, 4]. Lung tissue status is assessable by CT using reduced radiation doses; the consistency of air within the lungs and the pulmonary parenchyma differ significantly. Many studies seeking to reduce the LDCT radiation dose even further are available [5–8]. The approaches include reductions in tube current and voltage, automatic tube current modulation, and the use of new hardware such as selective in-plane shielding [9–11]. Current efforts are focused principally on the development of image reconstruction algorithms. Iterative reconstruction (IR) has been employed to reduce LDCT image noise, the incidence of artifacts, and false-negative findings, especially in low-current settings. In addition, IR allows for substantial radiation dose savings and improves image quality [5, 7, 8, 12, 13].
Various techniques are used to reduce the CT radiation dose and improve image quality. Recent studies have focused on reducing the tube voltage or current or on the use of IR algorithms. Voltage and current reductions directly reduce the radiation dose; some preliminary reports on less than 1 mSv LDCT have been available. However, such reductions inevitably increase noise and compromise diagnostic confidence. IR can reduce image noise [26–28].