Influence of rib structure on detection of subtle lung nodules

PURPOSE: To access the influence of anatomic noise on the detectability of subtle lung nodules depicted on chest radiographs. MATERIAL AND METHODS: From normal chest radiography images, 132 square regions were extracted, of which the centers were on the upper margin of a rib, the inside of a rib, the lower margin of a rib, and the central region between two adjoining ribs. Simulated nodules were digitally superimposed at the centers of these extracted square images. Twelve radiologists viewed 50 soft-copy images consisting of these 792 processed images, including the noise-added images. The observer's confidence level for the square images containing single nodules was used as an index of observer performance. RESULTS: Results indicated statistically reliable effects of the relationship between rib structures and nodule positions on the detection performance (P < 0.001). The nodule detectability on the images with a center located between two adjoining ribs was significantly the best, whereas it was significantly the worst on the noise-added images with a center located between two adjoining ribs. CONCLUSION: The rib structures overlying a subtle lung nodule on chest X-ray images have a detrimental effect on nodule detection performance as anatomic noise, regardless of the nodule location on ribs.     

Pulmonary nodule size evaluation with chest tomosynthesis and CT: a phantom study

Objective:

We compared digital tomosynthesis (TOMO) and chest CT in terms of assessing the sizes of nodules located in zones where evaluation by simple radiography is limited.

Methods:

A total of 48 images comprising phantom nodules of four sizes in six different locations were used. Nodule size measurement errors for measurements using TOMO and CT images compared with the actual size from each observer were calculated. The inter- and intraobserver repeatability of the measured values and the agreement between the two techniques were assessed using the method described by Bland and Altman.

Results:

The mean measurement errors for all of the nodules and four observers were −0.84 mm [standard deviation (SD), 0.60 mm] on TOMO and −0.18 mm (SD, 0.71 mm) on CT images. The mean measurement errors for the different observers ranged from −1.11 to −0.55 mm for TOMO and from −0.39 to 0.08 mm for CT. Assessing the agreement between nodule size measurements using TOMO and CT resulted in mean measurement errors of −0.65 mm, with a 95% limit of agreement of −2.53 to 1.22 mm for comparison of TOMO with CT.

Conclusion:

Our results suggest that nodule sizes obtained using TOMO and chest CT are comparable, even for nodules located in areas where the size measurement is limited on simple radiography.

Advances in knowledge:

TOMO and CT can be used interchangeably, even for nodules located in a blind area on simple radiography.Solitary lung nodule detection has increased owing to the widespread use of CT imaging. Nevertheless, the most commonly used routine examination for lung nodules continues to be chest radiography, because it uses low radiation doses, is economical and is easy to use. Because chest radiographic images are two-dimensional projections of three-dimensional structures, early lung cancer detection on chest radiographs is often challenging. The projection of pulmonary vessels, bones and part of the mediastinum on lung fields often partially or completely obscures the pulmonary nodules, resulting in failure by the radiologist to detect lung nodules.^1,2Digital tomosynthesis (TOMO) has recently been applied to chest imaging for the detection of subtle nodules on simple radiography, with promising results.^3,4 It has been introduced as a modality with the potential to provide images similar to CT but at a comparably reduced cost and radiation exposure.⁴ James et al⁵ reported that 74% of lung nodules ≥4 mm in diameter that can be identified on CT can also be detected using TOMO. Vikgren et al⁶ also reported that 92% of nodules ≥4 mm in diameter are detectable using TOMO. In 2012, Johnsson et al⁷ compared the ability of TOMO and CT to detect nodule size in 20 patients and found that both methods could be used interchangeably for these measurements. This result calls for caution, however, because the limit of agreement (LOA) between the modalities is wider than for the intraobserver variability of each modality.Based on these studies, we hypothesized that TOMO is comparable to CT imaging for the detection of nodules located in areas where size measurement is limited using simple chest radiography because of overlapping structures. The purpose of this study was to assess the size determination of nodules located in these zones by TOMO and chest CT.     

Assessing the use of digital radiography and a real-time interactive pulmonary nodule analysis system for large population lung cancer screening

Rationale and objectives

To assess the use of chest digital radiograph (DR) assisted with a real-time interactive pulmonary nodule analysis system in large population lung cancer screening.

Materials and methods

346 DR/CR patient studies with corresponding CT images were selected from 12,500 patients screened for lung cancer from year 2007 to 2009. Two expert chest radiologists established CT-confirmed Gold Standard of nodules on DR/CR images with consensus. These cases were read by eight other chest radiologists (participating radiologists) first without using a real-time interactive pulmonary nodule analysis system and then re-read using the system. Performances of participating radiologists and the computer system were analyzed.

Results

The computer system achieved similar performance on DR and CR images, with a detection rate of 76% and an average FPs of 2.0 per image. Before and after using the computer-aided detection system, the nodule detection sensitivities of the participating radiologists were 62.3% and 77.3% respectively, and the A_z values increased from 0.794 to 0.831. Statistical analysis demonstrated statically significant improvement for the participating radiologists after using the computer analysis system with a P-value 0.05.

Conclusion

The computer system could help radiologists identify more lesions, especially small ones that are more likely to be overlooked on chest DR/CR images, and could help reduce inter-observer diagnostic variations, while its FPs were easy to recognize and dismiss. It is suggested that DR/CR assisted by the real-time interactive pulmonary nodule analysis system may be an effective means to screen large populations for lung cancer.     

Detectability of simulated pulmonary nodules on chest radiographs: Comparison between irradiation side sampling indirect flat-panel detector and computed radiography

Objective

To compare the detectability of simulated pulmonary nodules on chest radiographs between an irradiation side sampling indirect flat-panel detector (ISS-FPD) and computed radiography (CR).

Materials and methods

This study was an observer performance study. Simulated pulmonary nodules of 8 mm in diameter were superimposed on an anthropomorphic chest phantom. Chest radiographs were acquired under 2 exposure levels (4 and 3.2 mAs) with the ISS-FPD and the CR. Six thoracic radiologists evaluated all 40 images (10 patterns × 2 different exposure doses × 2 different systems) for the presence or absence of a lesion over each of 12 defined areas on a 3-megapixel monochrome liquid-crystal display. Receiver operating characteristic (ROC) curves were obtained for observation in predefined 480 areas. A jackknife method was used for statistical analysis. Differences with a P value of <0.05 were considered significant.

Results

The analysis of the observer detection of simulated pulmonary nodules showed larger areas under the ROC curve (AUC) by the ISS-FPD than by the CR. There was a statistically significant difference between the two systems at 3.2 mAs (P = 0.0330).

Conclusion

The ISS-FPD was superior to the CR for the detection of simulated pulmonary nodules at 3.2 mAs.     

Usefulness of computerized method for lung nodule detection on digital chest radiographs using similar subtraction images from different patients

Purpose

The purpose of this study is to evaluate the usefulness of a novel computerized method to select automatically the similar chest radiograph for image subtraction in the patients who have no previous chest radiographs and to assist the radiologists’ interpretation by presenting the “similar subtraction image” from different patients.

Materials and methods

Institutional review board approval was obtained, and the requirement for informed patient consent was waived. A large database of approximately 15,000 normal chest radiographs was used for searching similar images of different patients. One hundred images of candidates were selected according to two clinical parameters and similarity of the lung field in the target image. We used the correlation value of chest region in the 100 images for searching the most similar image. The similar subtraction images were obtained by subtracting the similar image selected from the target image. Thirty cases with lung nodules and 30 cases without lung nodules were used for an observer performance test. Four attending radiologists and four radiology residents participated in this observer performance test.

Results

The AUC for all radiologists increased significantly from 0.925 to 0.974 with the CAD (P = .004). When the computer output images were available, the average AUC for the residents was more improved (0.960 vs. 0.890) than for the attending radiologists (0.987 vs. 0.960).

Conclusion

The novel computerized method for lung nodule detection using similar subtraction images from different patients would be useful to detect lung nodules on digital chest radiographs, especially for less experienced readers.     

Influence of radiation dose and iterative reconstruction algorithms for measurement accuracy and reproducibility of pulmonary nodule volumetry: A phantom study

Purpose

To evaluate the influence of radiation dose settings and reconstruction algorithms on the measurement accuracy and reproducibility of semi-automated pulmonary nodule volumetry.

Materials and methods

CT scans were performed on a chest phantom containing various nodules (10 and 12 mm; +100, −630 and −800 HU) at 120 kVp with tube current–time settings of 10, 20, 50, and 100 mAs. Each CT was reconstructed using filtered back projection (FBP), iDose⁴ and iterative model reconstruction (IMR). Semi-automated volumetry was performed by two radiologists using commercial volumetry software for nodules at each CT dataset. Noise, contrast-to-noise ratio and signal-to-noise ratio of CT images were also obtained. The absolute percentage measurement errors and differences were then calculated for volume and mass. The influence of radiation dose and reconstruction algorithm on measurement accuracy, reproducibility and objective image quality metrics was analyzed using generalized estimating equations.

Results

Measurement accuracy and reproducibility of nodule volume and mass were not significantly associated with CT radiation dose settings or reconstruction algorithms (p > 0.05). Objective image quality metrics of CT images were superior in IMR than in FBP or iDose⁴ at all radiation dose settings (p < 0.05).

Conclusion

Semi-automated nodule volumetry can be applied to low- or ultralow-dose chest CT with usage of a novel iterative reconstruction algorithm without losing measurement accuracy and reproducibility.     

Standard versus inverted digital luminescence radiography in detecting pulmonary nodules: A ROC analysis

Objective

Observer performance tests were conducted to compare the effect of presenting digital luminescence radiography (DLR) monitor images in positive mode (“bones black”) or negative mode (“bones white”) in the detectability of subtle lung nodules.

Methods

Five radiologists independently reviewed digital radiographs of 55 patients with either (a) a single, small (6–12 mm), non- calcified peripheral nodule confirmed by chest CT (n = 47) or (b) normal finding (n = 8) confirmed by chest CT, respectively. Mean size of pulmonary nodules was 8.3 mm (range 6–12 mm, median 7 mm). Radiographs were displayed either in standard mode (bones white) or inverse intensity (bones black). A total of 550 observations resulted. For the evaluation ROC analysis was performed using a specialized computer algorithm.

Results

The standard presentation mode showed a sensitivity of 61.7% and a specificity of 72.5%, the inverse presentation mode a sensitivity of 68.1% and a specificity of 75.0%. ROC- analysis showed that the difference between the standard mode (Az- value 0.694) and the inverse mode (Az- value 0.810) was significant in favour of the inverse presentation mode (p = 0.001). This finding was especially observed in more experienced radiologist (Az- values 0.716 vs. 0.909, P < 0.001).

Conclusion

Our study demonstrates a significant advantage of the inverse mode in the detection of small pulmonary nodules compared with the commonly used negative mode when interpreted by more experienced radiologists.

Advance in knowledge

Inverse intensity images (“bones black”) may have some advantages in the detection of small pulmonary nodules in experienced readers when presented on a stand-alone display.     

Role of the chest radiography,spirometry, and high resolution computed tomography in the early diagnosis of the emphysema

Purpose

This study was performed to evaluate the role of the chest radiography pulmonary function tests, and HRCT in the early diagnosis of the emphysema.

Materials and methods

The study included 50 patients who had emphysema. Average age varies between 40 and 60 years. All patients were subjected to full history, clinical examination, laboratory investigations, cardiac investigations, chest radiography, pulmonary function tests and HRCT.

Results

I found high sensitivity of the HRCT in the early diagnosis of emphysema if compared with sensitivity of the chest radiography and pulmonary function tests.

Conclusions

HRCT has much greater sensitivity than chest radiography in early diagnosing of emphysema. HRCT is also capable of differentiating between the various types of emphysema and assessing its severity. The presence of emphysema can be suspected on chest radiography but this is not a sensitive technique for diagnosis. Also the chest radiography is not a very good indicator for the severity of disease. In addition a precise characterization of the emphysema by HRCT is desirable for adequate therapy and monitoring as well as preoperative assessment of the patient before surgical treatment of emphysema. Compared to spirometry, HRCT shows regional assessment of compartments involved (airways, parenchyma and vasculature). Moreover spirometry has no definite sensitivity.     

Frequency and significance of pulmonary nodules on thin-section CT in patients with extrapulmonary malignant neoplasms

Purpose

To determine the frequency and significance of pulmonary nodules detected on thin-section CT in patients with extrapulmonary malignant neoplasms.

Materials and methods

The institutional review board approved this study. This study retrospectively evaluated 308 patients with extrapulmonary carcinomas or sarcomas and had undergone thin-section chest CT (2 mm slice thickness) for staging. Three radiologists identified non-calcified nodules and evaluated the size, the growth and the distance from the nearest pleural surface. The characteristics of the nodules were defined based on the results of either a diagnostic biopsy or nodule growth.

Results

One or more non-calcified pulmonary nodules were detected in 75% of the patients (233/308). One hundred and thirty-seven of these patients had nodules that met the criteria of either benign or malignant nodules. Nodules smaller than 10 mm were more likely to be benign, whereas those 10 mm or greater were more likely to be malignant (22/26, 85%; P < .0001). Most nodules less than 10 mm from the pleura were benign (91%), whereas approximately half of the nodules 10 mm or more away from the pleura were malignant (20/43, 47%; P < .0001). Patients with melanoma, sarcoma, or testicular carcinoma were more likely to have malignant nodules. A multivariable analysis demonstrated the nodule size (P < .0001) and distance from the pleura were predictive of malignancy.

Conclusion

The nodule detection rate on thin-section CT in patients with extrapulmonary malignancy is high. Most of the nodules smaller than 10 mm or less than 10 mm from the pleura are benign.     

The diagnostic performance of chest ultrasonography in the up-to-date work-up of the critical care setting

Background

Management of patients in the critical care setting is crucial. The availability, the absence of ionizing radiation and the non invasive nature of chest ultrasonography (US) have currently increased its use in the up-to-date work-up of various pleuropulmonary abnormalities in the critical care setting.

Objective

To evaluate the sensitivity, specificity and diagnostic accuracy of chest US for various pleuropulmonary abnormalities in intensive care unit (ICU) patients.

Materials and methods

Ninety consecutive patients admitted in chest ICU with respiratory distress were assessed clinically and by chest radiography (CXR). They were suspected to have a provisional diagnosis of any of the following pathological entities: pneumonic consolidation, bronchogenic carcinoma, metastatic pulmonary nodules, pleural effusion, pneumothorax, hydropneumothorax and mesothelioma. These patients were scheduled for chest computed tomography (CT) and prospectively reviewed using chest US. The results of chest US were compared with these of chest CT for each encountered pathological entity using chest CT as the diagnostic standard of reference to subsequently calculate the sensitivity, specificity and diagnostic accuracy of chest US.

Results

The sensitivity, specificity and diagnostic accuracy of chest US were 100%, 96% and 97% for pneumonic consolidation, 71%, 100% and 98% for bronchogenic carcinoma and 92%, 100% and 99% for pneumothorax respectively. The sensitivity, specificity and diagnostic accuracy of 100% for the rest of the included pathological entities were obtained.

Conclusion

Chest ultrasonography has a considerable diagnostic performance for various pleuropulmonary pathological conditions that may be encountered in the ICU patients making it as an adjunct tool in the up-to-date work-up of the ICU setting.     

Grey-scale inversion improves detection of lung nodules

Objective

The current study aims to establish whether detection of solitary pulmonary nodules can be improved by inverting the grey scale of posteroanterior (PA) chests.

Methods

30 PA chest images were presented on 2 occasions to 16 senior radiologists on either primary or secondary class displays in the standard or inverted mode. 15 images within each group contained a single nodule positioned in a range of anatomical sites. A receiver operating characteristic (ROC) methodology was used to explore differences between the presentation modes.

Results

Improved ROC scores were evident with inverted (Az 0.77) compared with standard (Az 0.73) (p=0.02) images; however, this difference was seen only with the primary displays. The benefits seen are most likely owing to increased nodule luminance with the inverted images, particularly when using primary displays.

Conclusion

This study demonstrates that the inverted image can offer advantages in lung nodule detection over the standard presentation mode when images are viewed on high-specification viewing systems. The study has demonstrated that there is an improvement in the detectability of lung nodules on an inverted image with a primary display monitor that is not evident with secondary displays. This is likely to be the result of increased nodule luminance on primary displays when images are presented in the inverted mode.In radiology there is an increasing use of digital display technology, which has had an enormous impact on medical image presentation [1-3]. This is no longer limited to CT or MRI, but is equally relevant to projectional radiography in which digital images are acquired using computed radiography, direct and indirect digital radiography and scanning technologies [3].In digital imaging systems raw image data are normally processed using look-up tables and other algorithms so that, when the image is first presented, it requires minimum reader time or effort to change contrast or brightness details. Nonetheless, further image processing techniques are often applied by the observer with the aim of increasing the diagnostic value of an image [4,5], and one such feature, which is available with almost all image workstations, is inversion of the grey scale of an image. Even though inversion algorithms have been available for as long as digital images, the diagnostic advantages of the inverted mode over the standard mode remain unclear.Previous work examining the efficacy of image inversion has focused on either dental or chest radiology. The dental research demonstrated higher levels of accuracy when measuring endodontic wires inserted into extracted pre-molars for the inverted compared with the standard mode [6]; no differences in periodontal bone loss measurements between inverted and unprocessed images [7]; and low diagnostic agreement between standard and inverted panoramic images for the detection of mental foramen and mandibular canal [8]. The chest studies showed that inversion mode is commonly used by intensive care unit clinicians to view the end point of line and tube placements but was inconclusive regarding detection sensitivity [9]; no advantage in inversion mode for nodule detection of pulmonary nodules, but the effect of familiarity with standard image and observer experience needs to be accounted for [10]; and better detection in the inverted mode than in the standard mode using film–screen systems assessed by residents-in-training [11]. Although these previous studies suggest that inverting the images may offer certain advantages in specific situations, further studies involving expert thoracic radiologists and a better understanding of the mechanisms for potential improvement with inversion are required.The current study focused on inversion of chest images and used a receiver operating characteristic (ROC) methodology to investigate the detectability of a solitary pulmonary nodule. Two classes of monitor displays were considered and images were assessed by expert chest radiologists.     

Detection and construction of chest wall on breast magnetic resonance images

Purpose

The purpose of this study is to propose a method for detection and construction of chest wall for breast magnetic resonance images.

Methods

A volume of breast MR slices are firstly acquired and utilized to detect initial points of chest wall. To calibrate the chest wall curve, the points along the curve is set with reference to its neighboring points. Through the calibration method, a curve of chest wall can be detected from a volume of breast magnetic resonance (MR) slices. Such a curve can be applied for segmentation of breast region in a volume of MR images.

Results

The experimental results reveal that the minimal RMSE was measured from the setting two polynomial functions and the points from the vertical position ≤320. If all edge points are used to simulate the curve, two circle functions can reach the minimal RMSE.

Conclusion

The experimental results verify that chest wall for breast density estimation can be better simulated by two circle functions, which simulate right and left chest walls respectively. Furthermore, such a simulation curve is suggested to utilize partial edge points under the given vertical position.     

Can real-time ultrasound elastography using the color score and strain ratio differentiate between benign and malignant solitary thyroid nodules?

Background

Solitary thyroid nodule may represent a multitude of thyroid disorders; therefore, detection of whether these nodules are benign or malignant is crucial for patient’s triage.

Objective

To evaluate the diagnostic performance of the latest generation of real-time ultrasound elastography (USE) in differentiation between benign and malignant solitary thyroid nodules.

Materials and methods

Thirty consecutive patients who were referred for surgical treatment were prospectively examined by real-time USE. Tissue stiffness on real-time USE was determined with light compression using the standard elastography color scoring system according to Rago criteria ranging from 1 (low stiffness over the entire nodule) to 5 (high stiffness over the entire nodule and surrounding tissue). The strain ratio (normal tissue to lesion strain ratio) was calculated. The histopathological examination of these resected nodules was used as the diagnostic standard of reference.

Results

Scores of 1 and 2 with Rago criteria were highly significant seen in benign nodules, whereas, scores of 4 and 5 with Rago criteria were highly significant seen in malignant nodules (p < 0.001) with a sensitivity, specificity and diagnostic accuracy of 78.6%, 78.9% and 78.8% respectively. Additionally, the best strain ratio cut-off value for discrimination between benign and malignant nodules by using receiver operating characteristic analysis was 2.20 (area under the curve of 0.861; p value <0.001) with a consequential sensitivity, specificity and diagnostic accuracy of 85.7%, 90.5% and 88.6% respectively.

Conclusion

Both the color score and the strain ratio are higher in malignant solitary thyroid nodules than those in benign ones. Consequently, real-time USE can be used for the differentiation of benign and malignant solitary thyroid nodules. Eventually, this reduces the number of superfluous surgical procedures on benign thyroid nodules.     

Limited value of shape, margin and CT density in the discrimination between benign and malignant screen detected solid pulmonary nodules of the NELSON trial

Purpose

To evaluate prospectively the value of size, shape, margin and density in discriminating between benign and malignant CT screen detected solid non-calcified pulmonary nodules.

Material and methods

This study was institutional review board approved. For this study 405 participants of the NELSON lung cancer screening trial with 469 indeterminate or potentially malignant solid pulmonary nodules (>50 mm³) were selected. The nodules were classified based on size, shape (round, polygonal, irregular) and margin (smooth, lobulated, spiculated). Mean nodule density and nodule volume were automatically generated by software. Analyses were performed by univariate and multivariate logistic regression. Results were presented as likelihood ratios (LR) with 95% confidence intervals (CI). Receiver operating characteristic analysis was performed for mean density as predictor for lung cancer.

Results

Of the 469 nodules, 387 (83%) were between 50 and 500 mm³, 82 (17%) >500 mm³, 59 (13%) malignant, 410 (87%) benign. The median size of the nodules was 103 mm³ (range 50–5486 mm³). In multivariate analysis lobulated nodules had LR of 11 compared to smooth; spiculated nodules a LR of 7 compared to smooth; irregular nodules a LR of 6 compared to round and polygonal; volume a LR of 3. The mean nodule CT density did not predict the presence of lung cancer (AUC 0.37, 95% CI 0.32–0.43).

Conclusion

In solid non-calcified nodules larger than 50 mm³, size and to a lesser extent a lobulated or spiculated margin and irregular shape increased the likelihood that a nodule was malignant. Nodule density had no discriminative power.     

The value of bedside Lung Ultrasonography in diagnosis of neonatal pneumonia

Purpose

The aim of this prospective study was to assess lung ultrasonography as an alternative to bedside radiography for the diagnosis of neonatal pneumonia.

Patients & methods

The study was performed on 75 neonates admitted during the period from October 2011 to October 2012 in the NICU of Cairo University Pediatric Hospital presenting with clinical picture of pneumonia. Chest X-rays and lung US were done.

Results

Chest X-ray findings denoting lung infections were present in 64 cases (85.3%), and the remaining 11 cases (14.6%) had a free chest X-ray. Ultrasonography revealed pneumonic patches in 68 patients (90.6%), 7 (9.3%) had free US scans. US and chest X-rays detected pneumonic patches in 64 cases (85.3%), US detected pneumonic patches in 18 cases (24%) with chest X-rays having signs of chest infections other than pneumonic patches and in 4 cases (5.3%) with clear chest X-rays.

Conclusion

Bedside lung ultrasonography is highly sensitive, specific, and reproducible for ruling out underlying pneumonic process as well as in early detection and follow up of possible complications and can be considered an attractive alternative to bedside chest radiography and thoracic computed tomography with minimal radiation exposure.     

Abnormalities of fetal rib number and associated fetal anomalies using three dimensional ultrasonography

Aim

To determine incidence of abnormal number of fetal ribs and its association with other fetal anomalies using 3D ultrasonography.

Materials and methods

A prospective study conducted on 188 singleton pregnant women searching for fetal anomalies including the incidence of abnormal number of fetal ribs and other anomalies. Static 3D volumes with volume contrast imaging using spine map were used. Rendered images were displayed and the ribs were counted.

Results

173 fetuses (92%) were having normal number of ribs. Fifteen fetuses (8%) were found to have abnormal number of ribs; ten fetuses (5.3%) had 11 ribs. On the other hand five fetuses (2.7%) had supernumerary 13 ribs. Eight fetuses (4.2%) were having abnormal number of ribs with no associated anomalies (isolated abnormal number). Seven fetuses (3.7%) in this study had associated anomalies.

Conclusion

Abnormal number of fetal ribs more to be an isolated finding (4.3%) but it may also be seen with other anomalies (3.7% in this study). 3DUS is useful for scanning the fetal ribs in the mid trimester of the pregnancy for early detection of associated genetic aberrations.     

Fractal-feature distance analysis of radiographic image

RATIONALE AND OBJECTIVES: We have conducted a fractal analysis of low-dose digital chest phantom radiographs and evaluated the relationship between the fractal-feature distance and the tube current-exposure time product. MATERIALS AND METHODS: Chest phantom radiographs were obtained at various mAs values (0.5-4.0 mAs) and 140 kVp with a computed radiography system, and the reference images were acquired at 13 mAs. The lung field images were converted to binary images after processing them using the rolling-ball technique; a fractal analysis was conducted using the box-counting method for these binary images. The fractal-feature distances between the low-dose and reference images were calculated using the fractal dimension and the complexity. RESULTS: For all binary images of lung fields, the relationship between the length of the square boxes and the number of boxes needed to cover the positive pixels of the binary image was linear on a log-log scale (r > or = 0.99). For mAs > or = 3.0, the fractal-feature distances were almost constant, whereas for mAs < or = 2.5, they increased depending on the reduction in mAs values. CONCLUSION: We have shown that a binary image of the lung field obtained from a chest phantom radiograph can be analyzed by the box-counting method and that its fractal-feature distance grows as the radiation dose declines.     

Diagnostic utility of real-time ultrasound elastography for prediction of malignancy in solid thyroid nodules

Aim of the work

To study the diagnostic utility of real-time ultrasound elastography (USE) in predicting malignancy in thyroid nodules.

Materials and methods

Forty-five patients with solitary solid thyroid nodules were included in this study. The thyroid nodules were examined by B-mode ultrasound, color flow Doppler ultrasound, and real-time ultrasound elastography (USE). The final diagnosis was obtained from histopathological findings. Tissue stiffness on USE was scored from 1 (low stiffness over the entire nodule) to 6 (high stiffness over the entire nodule and surrounding tissue).

Results

Twenty-eight (62.2%) patients had a final diagnosis of malignancy based on histopathological evidence of malignant thyroid nodules, while 17 (37.8%) were diagnosed as benign nodules. Anteroposterior/transverse (AP/T) diameter more than 1 cm, ill-defined margins and spot micro calcifications were the most predictive conventional ultrasound patterns of malignancy. Elasticity score of 4–6 was highly predictive of malignancy (P < 0.0001), with a sensitivity of 89.3%, a specificity of 88.2% and an accuracy of 88.9%.

Conclusion

Ultrasound elastography is an accurate non invasive tool for evaluating thyroid nodules. It has more appropriate value in the differential diagnosis of thyroid malignancy and enhances the diagnostic assurance of ultrasonographers.     

Hypovascular hepatic nodule showing hypointensity in the hepatobiliary phase of gadoxetic acid-enhanced MRI in patients with chronic liver disease: prediction of malignant transformation

Purpose

To investigate the predictive factors of malignant transformation of hypovascular hepatic nodule showing hypointensity in the hepatobiliary phase images of gadoxetic acid-enhanced MRI (HHN).

Materials and Methods

The clinical data and imaging findings of dynamic contrast-enhanced computed tomography (DCE-CT) and gadoxetic acid-enhanced MRI for a total of 103 HHNs in 24 patients with chronic liver disease were retrospectively investigated. After the results of follow-up examinations were investigated, HHNs were categorized into the three groups for each comparison: (1) nodules with enlargement and/or vascularization and others, (2) nodules with only enlargement and others, (3) nodules with only vascularization and others. Enlargement and/or vascularization during the follow-up period were defined as malignant transformation of HHN. The frequency of each clinical datum and imaging finding in each group was compared to identify the predictive factors for malignant transformation in HHN.

Results

Multivariate analysis showed that a nodule size of 9 mm or more on the initial gadoxetic acid-enhanced MRI was a significant predictive factor for the enlargement and/or vascularization of HHN (P < 0.05). On the other hand, the hypoattenuation on the delayed phase imaging of the initial DCE-CT was a significant predictive factor for the enlargement or vascularization of HHN (P < 0.05).

Conclusion

A nodule size of 9 mm or more on the initial gadoxetic acid-enhanced MRI and hypoattenuation on the delayed phase imaging of initial DCE-CT would be helpful for predicting the outcome of HHN in patients with a risk of hepatocellular carcinoma.     

Dose reduction in chest CT: Comparison of the adaptive iterative dose reduction 3D,adaptive iterative dose reduction,and filtered back projection reconstruction techniques

Objectives

To assess the effectiveness of adaptive iterative dose reduction (AIDR) and AIDR 3D in improving the image quality in low-dose chest CT (LDCT).

Materials and methods

Fifty patients underwent standard-dose chest CT (SDCT) and LDCT simultaneously, performed under automatic exposure control with noise index of 19 and 38 (for a 2-mm slice thickness), respectively. The SDCT images were reconstructed with filtered back projection (SDCT-FBP images), and the LDCT images with FBP, AIDR and AIDR 3D (LDCT-FBP, LDCT-AIDR and LDCT-AIDR 3D images, respectively). On all the 200 lung and 200 mediastinal image series, objective image noise and signal-to-noise ratio (SNR) were measured in several regions, and two blinded radiologists independently assessed the subjective image quality. Wilcoxon's signed rank sum test with Bonferroni's correction was used for the statistical analyses.

Results

The mean dose reduction in LDCT was 64.2% as compared with the dose in SDCT. LDCT-AIDR 3D images showed significantly reduced objective noise and significantly increased SNR in all regions as compared to the SDCT-FBP, LDCT-FBP and LDCT-AIDR images (all, P ≤ 0.003). In all assessments of the image quality, LDCT-AIDR 3D images were superior to LDCT-AIDR and LDCT-FBP images. The overall diagnostic acceptability of both the lung and mediastinal LDCT-AIDR 3D images was comparable to that of the lung and mediastinal SDCT-FBP images.

Conclusions

AIDR 3D is superior to AIDR. Intra-individual comparisons between SDCT and LDCT suggest that AIDR 3D allows a 64.2% reduction of the radiation dose as compared to SDCT, by substantially reducing the objective image noise and increasing the SNR, while maintaining the overall diagnostic acceptability.