ABSTRACT
OBJECTIVE: To describe the quantitative image quality and histogram-based evaluation of an iterative reconstruction (IR) algorithm in chest computed tomography (CT) scans at low-to-ultralow CT radiation dose levels. MATERIALS AND METHODS: In an adult anthropomorphic phantom, chest CT scans were performed with 128-section dual-source CT at 70, 80, 100, 120, and 140 kVp, and the reference (3.4 mGy in volume CT Dose Index [CTDIvol]), 30%-, 60%-, and 90%-reduced radiation dose levels (2.4, 1.4, and 0.3 mGy). The CT images were reconstructed by using filtered back projection (FBP) algorithms and IR algorithm with strengths 1, 3, and 5. Image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were statistically compared between different dose levels, tube voltages, and reconstruction algorithms. Moreover, histograms of subtraction images before and after standardization in x- and y-axes were visually compared. RESULTS: Compared with FBP images, IR images with strengths 1, 3, and 5 demonstrated image noise reduction up to 49.1%, SNR increase up to 100.7%, and CNR increase up to 67.3%. Noteworthy image quality degradations on IR images including a 184.9% increase in image noise, 63.0% decrease in SNR, and 51.3% decrease in CNR, and were shown between 60% and 90% reduced levels of radiation dose (p < 0.0001). Subtraction histograms between FBP and IR images showed progressively increased dispersion with increased IR strength and increased dose reduction. After standardization, the histograms appeared deviated and ragged between FBP images and IR images with strength 3 or 5, but almost normally-distributed between FBP images and IR images with strength 1. CONCLUSION: The IR algorithm may be used to save radiation doses without substantial image quality degradation in chest CT scanning of the adult anthropomorphic phantom, down to approximately 1.4 mGy in CTDIvol (60% reduced dose).
Subject(s)
Adult , Humans , Cone-Beam Computed Tomography , Noise , Signal-To-Noise Ratio , Thorax , Tomography, X-Ray ComputedABSTRACT
PURPOSE: The purpose of this study was to assess the added value of screening low-dose computed tomography of the chest (LDCT) covering the abdomen in evaluating abdominal solid organs to the screening abdominal ultrasonography (US). MATERIALS AND METHODS: We prospectively enrolled a consecutive series of 393 physical check-up patients, who underwent screening abdominal US and LDCT of the chest from January to February, 2008. LDCT covered the lungs, liver, pancreas, gallbladder, spleen, and both kidneys. The 1st screening abdominal US were performed without information from the LDCT, and then abdominal images covered by LDCT were immediately evaluated. Then a 2nd US session was done with additional information from LDCT and US examination was focused to the findings of LDCT. Perpatient and per-lesion analyses were performed. RESULTS: In per-patient analysis, additional focal lesions were found in 20 patients (5.1%) for liver and 9 patients (2.3%) for kidneys in the 2nd US sessions. In per-lesion analysis, 154 and 73 focal lesions were found in liver and kidneys, respectively, in the 1st US sessions. On the 2nd US session, 186 and 86 lesions were found in liver and kidneys, respectively. 20.8% and 17.8% of focal lesions were additionally found on 2nd US session in liver and kidneys, respectively. Most (62.5%) of the additional lesions detected in liver were located in segment 7 and 8, the hepatic dome. CONCLUSION: Previewing LDCT of the chest and abdominal solid organs before performing screening abdominal US can enhance the diagnostic performance of US in physical check-up patients.