The Optimal Energy Level of Virtual Monochromatic Images From Spectral CT for Reducing Beam-Hardening Artifacts Due to Contrast Media in the Thorax.

OBJECTIVE: The purpose of this study is to determine the optimal energy level of virtual monochromatic images from spectral CT compared with conventional polychromatic images for reducing beam-hardening artifacts caused by contrast media in the thorax. MATERIALS AND METHODS: A total of 101 consecutive patients who underwent chest CT with contrast enhancement were retrospectively included in this study. The same contrast media and injection protocols were applied to the whole study population. Virtual monochromatic image datasets ranging from 70 to 200 keV and conventional polychromatic images were obtained. Readers' subjective image quality scores were recorded for conventional polychromatic and virtual monochromatic images obtained at 70, 100, 130, and 200 keV. Image noise, CT attenuation difference, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were also obtained in each algorithm. Comparisons of parameters between algorithms were performed. RESULTS: The best subjective image quality score and significantly lower image noise were observed for 130-keV virtual monochromatic images compared with conventional polychromatic images (all p < 0.001). Also, CT attenuation differences were significantly lower for both 100- and 130-keV virtual monochromatic images than for conventional polychromatic images (all p < 0.001). Meanwhile, the lowest differences in CT attenuation were observed for 100-keV virtual monochromatic images compared with conventional polychromatic images. However, there were no significant differences in CT attenuation between 100- and 130-keV virtual monochromatic images. SNR was similar between 130-keV virtual monochromatic images and conventional polychromatic images, although both SNR and CNR decreased as the energy level increased. CONCLUSION: Virtual monochromatic imaging reduced beam-hardening artifacts and improved image quality, and optimal evaluation of chest CT was best achieved at 100 and 130 keV.

Spontaneously healed asymptomatic pulmonary tuberculosis: prevalence of airflow obstruction, and correlation between high-resolution CT findings and pulmonary function tests.

RATIONALE AND OBJECTIVES: We investigated the relationships between spontaneously healed asymptomatic pulmonary tuberculosis (SHAPTB), airflow obstruction (AFO), and high-resolution computed tomography (HRCT) findings. MATERIALS AND METHODS: We selected 82 participants with SHAPTB diagnosed by interferon-γ release assay and 8044 with normal chest radiographs (CXR). We applied a CT scoring system for the extent of tuberculous sequelae to correlate the HRCT findings with pulmonary function test. We compared the AFO prevalence between subjects with and without SHAPTB. RESULTS: The subjects with SHAPTB diagnosed by interferon-γ release assay had a significantly higher prevalence of AFO (13.4% [11/82]) than those with normal CXR (7.4% [595/8044]). The important HRCT findings that correlated with AFO were the number of lung segments with TB sequelae and the CT score for emphysema. CONCLUSION: The subjects with SHAPTB had a higher AFO prevalence than those with normal CXR, and the important HRCT findings correlated with AFO were the extent of tuberculous sequelae and emphysema.

Updated National Diagnostic Reference Levels and Achievable Doses for CT Protocols: A National Survey of Korean Hospitals.

Background: In 2021, the Korean government proposed a new CT diagnostic reference level. This study performed a nationwide survey and developed new DRLs and AD for 13 common CT examinations. We compared other countries' DRLs for CT examinations. Methods: This study investigated the CTDIvol and DLP of the 12 types of CT protocols for adults and brain CT protocol for pediatrics. A total of 7829 CT examinations were performed using 225 scanners. We defined the DRLs values in the distribution of radiation exposure levels to determine the nationwide patient dose and distribution status of the dose. Results: This study showed that the new Korean national CT DRLs are slightly higher or similar to those of previous surveys and are similar or lower than those of other countries. In some protocols, although the DLP value increased, the CTDIvol decreased; therefore, it can be concluded that the patient's dose in CT examinations was well managed. Conclusions: The new CT DRLs were slightly higher than or similar to that of the previous survey and were evaluated to be similar or lower than CT DRLs of other countries. These DRLs will be used for radiation optimization and effective dose calculation for an individual.

The development of a diagnostic reference level on patient dose for CT examination in Korea.

The purpose of this research is to develop a diagnostic reference level for computed tomography (CT) suitable for Korean medical purposes. The direction of CT application and details on patient dose were investigated by survey, and the dose measurement is targeted in general hospitals registered with the Korean Hospital Association. The dose measurement was done with head and body phantom, and an accurate dosimeter was utilised in medical institutions that participated in the survey. The survey and dose measurements on the patient dose showed that the 75th percentiles in the distribution of weighted CT dose index (CTDIw) were 50.5 and 45.4 mGy for the head and 14.4 and 25.30 mGy for the body portions, respectively. Based on these research data, the target patient doses that are believed to be achievable for CT examination in Korean circumstances are about 48 +/- 4 mGy in the head and 20 +/- 8 mGy in the body.

Patient dose measurements in diagnostic radiology procedures in Korea.

This study is the first nationwide investigation aimed at estimating the patient dose for radiographic examinations in Korea including gastrointestinal studies, computed tomography and mammography. The survey data from 161 hospitals and the dose data from 32 hospitals were analysed. The third quartile entrance surface dose, dose area product (DAP), weighted CT dose index (CTDIw) and mean glandular dose (MGD) were reported. All the estimated doses were less than the stated International Atomic Energy Agency (IAEA) reference levels for radiographic examinations. However, DAPs for the fluoroscopic examinations had higher dose values than the IAEA reference levels. In addition, the CTDIw and MGD were lower than the IAEA reference levels.

Radiation dose reduction from low-kilovoltage liver computed tomography using multidetector row computed tomography.

The primary goal of this study was to ascertain the reduction in radiation dose when conducting low-kilovoltage liver computed tomography (CT) examinations using multidetector row CT (MDCT). Fifty patients under follow-up who were diagnosed with liver cancer were examined using a 16-slice MDCT scanner and volume CT dose index (CTDI(vol)) measured according to the methods of examination, which were based on a three-phase CT scan conducted in the previous year and a four-phase CT scan was done a year later. Scanning parameters were 120 kVp-140 mA s, 120 kVp-120 mA s and 80 kVp-280 mA s. The CTDI(vol) was decreased to ∼47% at 80 kVp -280 mA s. The results indicate that low-kilovoltage liver CT is a useful means of reducing radiation doses.

The development of a diagnostic reference level on patient dose for head computed tomographyangiography examinations in Korea.

The primary goal of this study was to analyse the state of patient doses in the field for head computed tomography angiography (HCTA) examinations in the Republic of Korea. All survey data, including CT application and patient dose details, were obtained from the general hospitals registered in the Korean Hospital Association. The systematic analysis of patient dose data would allow target value to be established for the weighted CT dose index (CTDIw), volume-weighted CTDI (CTDIvol) and a dose-length product (DLP), which might be used to set diagnostic reference levels. The survey on patients' dose showed that the 75th percentiles in the distribution of CTDIw, CTDIvol and DLP were 34.09, 26.7 and 1816 mGy for the HCTA examinations, respectively.

The development of a guidance level for patient dose for CT examinations in Korea.

The primary goal of this study was to analyse the state of patient doses in the field of computed tomography (CT) examinations in the Republic of Korea. All survey data including the CT applications and patient dose details were obtained from general hospitals registered in the Korean Hospital Association. The systematic analysis of the patient dose survey gives target values of the weighted computed tomography dose index (CTDI(w)) and the dose-length product (DLP). The targeted CTDI(w) values were 69, 69, 31, 19, 44, 25, 24, 20, 2, 19 and 19 mGy for the brain non-contrast enhancement (BNCE), brain contrast enhancement (BCE), neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. The targeted DLP values were 1056, 2112, 762, 1234, 1338, 2794, 2742, 2378, 2836, 1844 and 1939 mGy cm for the BNCE, BCE, neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. Comparing with the EUR recommendation, especially in the DLP, the adjustment of the total scan phase frequency and the shortening of the scan phase in each scan phase are needed to reduce the patients radiation exposure to international standards.