Impact of pixel value truncation on image quality of low dose chest CT.

PURPOSE: In some noisy low dose CT lung cancer screening images, we noticed that the CT density values of air were increased and the visibility of emphysema was distinctly decreased. By examining histograms of these images, we found that the CT density values were truncated at -1024 HU. The purpose of this study was to investigate the effect of pixel value truncation on the visibility of emphysema using mathematical models. METHODS AND MATERIALS: Assuming CT noise follows a normal distribution, we derived the relationship between the mean CT density value and the standard deviation (SD) when the pixel values below -1024 HU are truncated and replaced by -1024 HU. To validate our mathematical model, 20 untruncated phantom CT images were truncated by simulation, and the mean CT density values and SD of air in the images were measured and compared with the theoretical values. In addition, the mean CT density values and SD of air were measured in 100 cases of real clinical images obtained by GE, Siemens, and Philips scanners, respectively, and the agreement with the theoretical values was examined. Next, the contrast-to-noise ratio (CNR) between air (-1000 HU) and lung parenchyma (-850 HU) was derived from the mathematical model in the presence and absence of truncation as a measure of the visibility of emphysema. In addition, the radiation dose ratios required to obtain the same CNR in the case with and without truncation were also calculated. RESULTS: The mathematical model revealed that when the pixel values are truncated, the mean CT density values are proportional to the noise magnitude when the magnitude exceeds a certain level. The mean CT density values and SD measured in the images with pixel values truncated by simulation and in the real clinical images acquired by GE and Philips scanners agreed well with the theoretical values from our mathematical model. In the Siemens images, the measured and theoretical values agreed well when a portion of the truncated values were replaced by random values instead of simply replacing by -1024 HU. The CNR of air and lung parenchyma was lowered by truncating CT density values compared to that of no truncation. Furthermore, it was found that higher radiation dose was required to obtain the same CNR with truncation as without. As an example, when the noise SD was 60 HU, the radiation dose required for the GE and Philips truncation method was about 1.2 times higher than that without truncation, and that for the Siemens truncation method was about 1.4 times higher. CONCLUSIONS: It was demonstrated mathematically that pixel value truncation causes a brightening of the mean CT density value and decreases the CNR of emphysema. Our results indicate that it is advisable to turn off truncation at -1024 HU, especially when scanning at low and ultra-low radiation doses in the thorax.

Reductions in High-End Imaging Utilization With Radiology Review and Consultation.

Following the uptake of value-based purchasing in concert with health care reform in the United States, providers, insurers, and patients are looking for ways to reduce excessive, dangerous, and/or inappropriate high-end imaging utilization (HEIU). Inappropriate HEIU is associated with patient safety risks due to unnecessary exposure to radiation, misappropriation of scarce equipment resources and staff, complications to clinical care, and needless, excessive costs for the patient, hospital, and payer. This paper presents a cost-effective radiology-initiated improvement program piloted in the Christiana Hospital Coordinated Care Network. The pilot demonstrated the effectiveness of regulating high-end imaging orders through radiologists' review of requests of the order as part of the consult process. Over the 2014-2015 fiscal year, 2,177 high-end imaging orders were reviewed by 26 radiologists for approval, rejection, or recommendation of an alternate examination. Of the orders, 86.7% (1887) were approved, 4.0% (87) were rejected, and 9.3% (203) received recommendation for an alternate examination. Based on improved patient safety, cost savings, and appropriate resource use, these findings suggest that radiologists' review can effectively reduce excessive HEIU. This method, with an appropriate algorithm to assist with handling a larger volume of orders, would be ideal to implement systemwide to manage HEIU cost efficiency, simultaneously providing radiologists with more control in their area of expertise and positively impacting quality, safety, and value-based purchasing goals.

Osteoprotegerin is a Better Serum Biomarker of Coronary Artery Calcification than Osteocalcin in Type 2 Diabetes.

OBJECTIVE: Coronary artery calcification (CAC) is a prominent feature of atherosclerosis and is associated with cardiovascular events. In vitro studies have suggested that osteoprotegerin (OPG) and osteocalcin (OC) exert anticalcification potential in the vessel wall. The objective of this study was to investigate the association of CAC and serum bone biomarkers in persons with type 2 diabetes. METHODS: We examined 50 individuals with type 2 diabetes. CAC imaging was performed by multidetector computed tomography. CAC scores ≥10, expressed in Agatston units, were considered abnormal. OC, undercarboxylated OC (ucOC), and OPG levels were determined by enzyme-linked immunosorbent assay. RESULTS: Abnormal CAC scores were found for 64% of the study cohort. OPG levels were significantly elevated (5.5 ± 2.0 pmol/L vs. 4.2 ± 1.7 pmol/L; P = .026) for those with abnormal CAC scores. No univariate differences were found for OC or ucOC. Logistic regression analyses revealed that an increase in serum OPG level was significantly associated with an increase in CAC score (odds ratio, 3.324; 95% confidence interval, 1.321 to 8.359; P = .011). Longer duration of diabetes was a significant covariate (P = .026), whereas nonsignificant covariates in the final model were age, gender, systolic blood pressure, body mass index, insulin resistance determined by the homeostasis model assessment for insulin resistance, leptin, adiponectin, and glycemic control. The Nagelkerke R2 for the model was 0.66. Neither OC nor ucOC were significantly associated with elevated CAC scores. CONCLUSION: Our results suggest that OPG is a more useful serum biomarker than OC or ucOC for identifying those at increased risk of arterial calcification in type 2 diabetes.